Clay Minerals Effects for Metal Reclamation from Leached Solution

*Murugesan Manikkampatti Palanisamy, Akilamudhan Palaniappan, Venkata Ratnam Myneni, Kannan Kandasamy, Minar Mohamed Lebbai and Padmapriya Veerappan*

## **Abstract**

The recent advancements in technology play a pivotal role in mankind's life and have a significant stint in the generation of E-waste. The present investigation focuses on the recovery of heavy metals from Printed Circuit boards (PCBs) by applying two efficient techniques viz., leaching and adsorption. A combination of leaching and adsorption is a novel and productive approach to recovering heavy metals from like PCBs. After the phases of chemical leaching, the solution was recovered through adsorption and is eco-friendly. The process is carried out to increase the separation rate, reduce the time spent and reach the limits of incineration and pyrolysis methods. Adsorption provides the recovery of heavy metals with respect to the required adsorbent since it is a surface phenomenon. The optimum condition of process variables was found through response surface methodology (RSM). The maximum recovery of copper ions (97.33%) was obtained at the optimum operating conditions such as adsorbent size of 0.04 mm, adsorbent dosage of 3.5 gm L−1 and the temperature of 80°C with 0.845 desirability. This investigation was found to be an eco-friendly way to recover copper ions and does not cause any environmental issues.

**Keywords:** E-waste, leached solution, bentonite clay, EDXs, aqua regia, response surface methodology

## **1. Introduction**

Electronic waste or e-waste is designated as the discarded electrical or electronic devices which are intended for reuse, recycle, resale, or disposal. Technological innovation, market expansion, economic growth and the short life of electrical and electronic equipment (EEE) have led to significant growth in waste of EEE (WEEE). PCBs are the main component of this equipment which generally contains 40% of metals, 30% of ceramics and 30% of plastics [1–3]. The metallic composition consists primarily of 10–30% of copper (Cu) and other metals such as Tin (Sn), Zinc (Zn), Lead (Pb), Nickel (Ni), Iron (Fe), Silver (Ag), Cadmium (Cd), Gold (Au), etc. depending on sources of printed circuit boards

(PCB) [4]. Informal processing of e-waste in developing countries can lead to adverse effects on human health and environmental pollution. In 2016, 44.7 million metric tons of e-waste were produced worldwide [5, 6]. If the e-waste was directly disposed of by filling the soil without removing metal ions from PCBs, the pollution of land and water supplies would result. These metals adopt mediums such as dust, air, water and soil to meet the human framework. Exposure to metals such as Pb and Cd affects reproductive health, development, mental instability and damage to human DNA [7–9]. Health symptoms like headache, dizziness, irritation in the eye, nose, mouth, etc. are caused by exposure to Cu which is present in landfills [10, 11]. The methods that can be used to recover metals from PCBs are essentially physical/mechanical and chemical separations. Several studies on the feasibility of metal recovery from PCBs have been investigated in the last decade. Hydrometallurgical procedures, such as leaching, are very intentional in these studies. Several leaching reagents demonstrate major improvements in metal recovery. When treated with different acidic media, HNO3, HCl and H2SO4, PCBs were cut to extract Cu2+ ions, the recovery percentage of Cu2+ was 97.5 percent, 65 percent and 76.5 percent respectively [12].

A novel ultrasonically assisted treatment process assisted in the reduction, recovery and higher separation from homogeneous heavy metals waste. The studies showed the complete recovery of copper and iron from PCB waste sludge by converting them into separated copper sulfate and ferric chloride solutions. The process has a high separation and recovery efficiency to extract metals. The results indicate that a metal recovery facility treating PCB waste sludge containing 3.14–4.85% copper and 3.71–4.23% iron achieved a copper recovery efficiency of 95.2–97.5% and iron recovery efficiency of 97.1–98.5%. However, because they were fully used in chemical leaching reagents, this process had some limitations in terms of waste emission and effects [13].

Many more studies were performed and reported the various operating conditions on the recovery of heavy metals such as Ag, Au, Ni, and copper found in PCBs. About 80% of the precious metals in the PCB are contained in the particle size ranges from 3.33 mm to 0.43 mm. Column leaching outcome shows that the gold dissolution rate is higher than those of the silver and copper during the first 10 days of the process. From the day 11 there is a reduction in the gold and silver recovery rate due to the copper oxide and copper hydroxide layers on the material surface. The cyanidation of PCBs provides the recovery rates such as 47.9% of Au, 51.6% of Ag, 48.1% of Ni and 77.2% of Cu in a column leaching using NaCN reagent whereas, the activated carbon adsorption process provides 97.3% of Au, 99.3% of Ag, 98.2% of Ni, and 80.7% of Cu [14]. Other useful metals remain as traces in the leaching solution. The deposition of extracted metals possesses different dendritic growth with respect to leaching reagent used. The copper recovered by leaching of PCBs with H2SO4 solution presented a fine dendritic structure with branches of about 80−100 μm [15, 16]. Significant recovery rates of copper through chemical leaching was reported in our previous researches [13, 14]. The hydrometallurgical method is a great concern to reseachers because it has low consumption of reagents, energy, less environmental pollution. The study deals with the extraction of copper ions Cu2+ from PCBs by two stage leaching technology [17] under various conditions of particle size, time, pulp density and temperature of the PCBs and find the optimum value for the maximum recovery of metals in both as well as experimental and predicted value through response surface methodology (RSM).

Researchers employed heavy metals retrieving methods such as electro wining, electro refining, cementation and the ion exchange techniques. These methods have some defects causing release of secondary pollutants, etc. So for this study, adsorption technique with natural adsorbents was introduced. Heavy metals have been

#### *Clay Minerals Effects for Metal Reclamation from Leached Solution DOI: http://dx.doi.org/10.5772/intechopen.98368*

acknowledged as potential health and environmentally hazardous materials. Many studies have been shown that these metals are toxic even at low concentrations. The presence of these toxic metals can cause in turn accumulative poisoning, destroy liver cancer, and brain damage when found above the tolerance level. Two locally available adsorbents namely bentonite clay and roasted date pits were collected. The date pits were roasted in an oven at 130°C for 4 hr. and ground in a mill to obtain powder for experimentation. The two adsorbents were analysedby surface area analyzer. The adsorbents are a mixture of heavy metal ions such as copper, cobalt, zinc, lead, arsenic, cadmium and chromium in the industrial waste water. The heavy metal concentration levels in the industrial waste water were above the permissible concentration levels. In addition the minimum removal efficiency of metal ions by adsorption using bentonite clay and the roasted date pits was 97% [18]**.** 15 g granules of the mobile PCB sample were leached in the 250 ml solution using 500 ml glass beaker which contained the pre determined amount of the ammonium thiosulfate and copper sulfate at various pH values. All leaching experiments were carried out at an agitation speed of 250 rpm and temperature. After 8 hrs leaching the solution was removed and was filtered by the Whitman 40 filter paper to separate the residual PCBs from the solution. The residue was then dried in the vacuum oven for 2 hr. at 130°C to remove all the moisture from the sample and the samples were weighed and the weight of the residue was calculated. In case PCB granules 56.7% gold could be leached under the optimized conditions viz., ammonium thiosulfate 0.1 M, stirring speed 250 rpm and at room temperature in 8 hr. time duration. In case of complete PCB unit the maximum gold leaching was 78.8% at thiosulfate 0.1 M, copper sulfate 40 mm, Ph 10–10.5, stirring speed 250 rpm at room temperature in 8 hr. time duration [19].

The residual mercury is to be treated and deposited in a geological repository with a clay barrier between the waste and the rock. In reality, hazardous chemical waste is for the most part deposited at the surface under drained conditions, while long-lived and high level nuclear waste in most programmes is intended to be deposited in geological formations below the ground water level. For sodium based bentonites, two modes of swelling exist: crystalline and osmotic. Crystalline swelling takes place only during the addition of low fractions of water. While osmotic swelling can take place for much larger additions. In the present work, the feasibility of applying nuclear long-lived waste disposal concepts to chemical hazardous substances is being tested. The elements needed for at least a simple safety analysis are identified and described in the present paper and will be tested experimentally and theoretically. In addition to mobility tests, the experiment included demonstration of a technique for compacting a mixture of spent batteries and bentonite clay. From the experiment, the sufficient extraction of chemicals was taken [20].

Based on previous researchers copper recovering techniques from various wastes and to overcome the drawbacks, the researchers opt for a new method such as adsorption by bentonite clay. Clays and clay minerals are of great importance due to the unique properties including hardness, durability, strong plasticity and plasticitythat make them ideal for industrial applications [21, 22]. Due to their complex shapes, clays have limited particle sizes and highly specific surface areas. They have been recognized as one of the most suitable low-cost adsorbents and standard components in a variety of industrial applications. Bentonite is an aluminum phyllosilicate adsorbent derived from montmorillonite. It is a sedimentary rock composed primarily of clays with a typical 2:1 layer structure and high concentrations of Na+ , Ca2+, and K+ ions found between the layers. Acid treatment on clay minerals has additional mineralogical and mineralogical impacts on a mineralogical system [23]. Due to its cation capacity, greater surface area and adsorption capacity for

various organic and inorganic ions, acid-activated bentonite has been a traditional commodity for removing metal ions. In this present study, Copper recovery from PCB leached solution with treated bentonite clay has been studies thoroughly and the experimental results are optimized through RSM.

## **2. Materials and methods**

## **2.1 Sample collection and preparation**

The waste PCBs are obtained from e-waste disposal units in India. For experimental use, 500 g scraps of PCBs are broken into 15–20 cm particles and shredded using pliers and four blade cutting shredder into small pieces around 50 x 50 mm to 30 x 30 mm [12, 17, 24]. Metals and non-metals need to be separated [15, 16]. This separation is not as simple due to the difference in the physical characteristics of metals and non-metals. Hence, different separation methods, such as pneumatic separation, magnetic separation, filtering, eddy current separation, electrostatic separation, etc., are used to enrich metals and non-metals [12, 17].

The crushed PCBs obtained from the crusher are then pulverized and further exposed for milling operation for better size reduction using a ball mill and particles of different mesh sizes are analyzed. The weight fraction of crushed PCBs obtained from the lower screens of jaw crushers with a capacity of 80 kg hr.−1 and a clearance of 10 mm is much lower, making better ion recovery impossible. Thus, it is subjected to 5 mm clearance in the same jaw crusher, yielding samples weighing 65, 53, 48, and 36 grams for sieves with mesh sizes of 0.3, 0.18, 0.05 mm, and pan, respectively, when screened using a rotary sieve shaker at a speed of 60 rpm with a power of 0.25 HP and a single phase 80 volt supply. As the reduction in size increases the rate of recovery of metal ions [8], the resulting crushed samples are processed into powder form using a pulverizer with a disk diameter of 175 mm operated by a 3-phase motor at 1400 rpm in a 225–445 V supply. The resulting powder samples are screened under different mesh sizes and the weight fraction of the bottom products (Sieves from 52 B.S.S. to pan) is increased but not adequate for the anticipated recovery. The pulverized PCB powder is milled in a ball mill having a ball weight of 500 grams at a speed of 60–120 rpm with a mill diameter of 200 mm driven by a 0.25 HP 3 phase motor which results in a size reduction and the highest weight fraction is obtained at lowest sieves. The weight fractions obtained at each sieve are collected separately and subjected to leaching (**Figure 1**).

## **2.2 Chemical leaching experimentation with aqua regia**

## *2.2.1 Aqua regia preparation*

The metal recovery from PCBs is carried by two stages of leaching media (first stage HCl and HNO3 and second stage HCl and H2SO4). It is prepared by mixing HCl and HNO3 in a 3:1 ratio under specified conditions of temperature, time and surrounding conditions. In previous studies (**Table 1**) with aqua regia as a leaching reagent, Copper was extracted from PCBs with a high recovery rate [15, 16, 19, 21, 22].

Aqua regia preparation involves mixing of strong acids. The two concentrated acids were mixed in 3:1 ratio (HCl:HNO3), Concentrated HCl (35%) and HNO3 (65%). The solutions should be keptaway from organic contaminants, because it leads to vigorous or violent reaction and low temperature should be maintained.

*Clay Minerals Effects for Metal Reclamation from Leached Solution DOI: http://dx.doi.org/10.5772/intechopen.98368*

#### **Figure 1.**

*Schematic diagram of primary raw PCBs; in to stepwise size reduction under the various mechanical operations (jaw crusher, roll crusher, thermal heater and pulverized mills produced small sizes between 4 and 0.05 mm).*


#### **Table 1.**

*Recovery data of copper with different leaching agents.*

#### *2.2.2 Experimentation with various parameters on copper recovery*

All the experiments were conducted in a conical flask with a temperature controlled shaker. Primary analysis was conducted by applying specific conditions to obtain a standard recovery rate. 20 g of PCB samples are allowed to mix with 0.5 liters of leaching media at 80°C and shaken in a mechanical shaker at a shaking speed of 120 rpm for 3 hours. At the end of this contact time, the shaker is stopped and solutions in the conical flask are filtered using filter paper. After complete filtration and metal composition retained is determined. The leaching rate depends on various parameters such as shaking intensity, size, contact time, pulp density and temperature. Different values for the recovery rate and the composition of heavy metals are obtained by varying these parameters. The samples are then tested and time results are analyzed over the recovery rate. The leached copper was reclaimed with the help of bentonite clay.

## **2.3 Copper ion reclaimation by adsorption**

Adsorption operation is extensively applicable in chemical operations for the reclamation of copper ions from the leached solution. Some other techniques have been used in previous studies, like precipitation, cementation process, liquid membrane techniques and ion exchange process. These methods have their specific advantages and disadvantages. Some of the methods are:


To overcome all these downsides, a new technique has to be developed for the separation of copper ions (Cu2+) from the leached solution. The stability of adsorption operation compared to other separation operations is the major reason for the recent renovation for selective separation and recovery of copper ions from the leached solution. Therefore, a suitable technique has to be selected so that the highest rate of copper recovery can be achieved. Cu2+ ions are recovered more effectively with these A-Bent adsorbent.

## *2.3.1 Physical activation method*

250 grams of both adsorbents were taken in the thermal crucible and were dried for about 5 hr. for thermal activation at 900°C. The samples obtained are from 1 μm to 5 μm. The higher specific surface area is obtained due to the removal of unwanted gaseous molecules from the Non-Activated Adsorbents (NAA). The activated adsorbents are shown in **Figure 2a,b**.

**Figure 2.**

*(a) The schematic diagram for bentonite clay thermal activation at 600°C. (b) Chemical activation by used concentrated HCl and HNO3.*

## *2.3.2 Chemical activation method*

The chemical activation involves the chemical reaction of the precursor with the activating agent at temperature 600°C. Initially, the Bentonite clay is washed with tap water and undergoes solar drying until the complete moisture content is removed. Once the moisture is completely removed from the adsorbent again, it will be washed with tap water and again dried under sunlight. The materials were mixed with a Nitric acid solution (85 percent of purity) at a ratio of 1:2 by mass (materials: HNO3 solution) and they are stirred well for 2 h and then conveyed to a stainless steel plate which is placed in a muffle furnace and heated at 550°C for 2 h. By natural cooling, the temperature is brought down to room temperature. Then, the adsorbent samples (C-A Bent) were crushed to less than 1 μm size and all the adsorbent samples were weighted and washed with 0.1 mol L−1 HCl to remove the surface ash.

Then, the adsorbent samples were washed with de-ionized water to remove the HCl and dried for 24 h at 150°C. After drying, both samples were ground and sieved. Chemically activated samples of both adsorbents are found favorable surface properties like C-A Bent have the maximum specific surface area 817 m2 g−1, less than 0.5 μm sizes and Pore volume is 0.1 cm3 g−1. Then, the adsorbent samples of C-A PSC have the specific surface area of 1026 m2 g−1, pore volume 0.37cm3 g−1 and pore size 0.5 μm. The prepared samples were tested with the help of the Scanning Electron Microscope (SEM-FEI-Quanta FEG 200F) which is shown in **Figure 3a,b**.

## *2.3.3 Adsorbent characterization and studies*

The feed to adsorption is copper solution recovered by leaching. Adsorption of copper ions on Bent was carried out in a batch system in both activated and NA-Adsorbents. 2 gram of adsorbent was added to 20 ml of the leached solution in a conical flask. The mixture was to be shaken at 200 rpm for 5 h at 80°C. After complete adsorption is done, the samples were filtered and copper concentration was analyzed by using EDXs which is used for the analysis of the elemental characterization of a sample in conjunction with SEM. The energy of the beam current is typically in the range of 100Na, Schottky emitter ranges between(−200v to 30 kV), magnifications range 12X−105X, and resolution of 2 Nanometer (Gold Nano-particles suspended on carbon substrate). Then, the adsorption efficiency of an adsorbent (Bent) was determined by the following Eq. (1).

#### **Figure 3.** *(a) The SEM images of bentonite clay thermal activation at 600°C. (b) Chemical activation by used concentrated HCl and HNO3.*


**Table 2.**

*Levels of different process variables in coded and un-coded form chemical leaching % of copper ions (box-Benhken method).*

$$\text{Removal Efficiency} \left( \% \right) = \left( \text{C}\_o - \text{C}\_e \right) / \text{C}\_o \times 100 \tag{1}$$

Co is the initial concentration of metal ions from leached samples. Ce is the metal ions concentration after adsorption operation [27].

## **2.4 Response surface methodology (RSM)**

Studies were conducted in order to obtain the optimum valves of various parametersfrom the recovery of copper ions from leached solution by Response surface methodology. The influence of various parameters (Size of adsorbent, adsorbent dosage and temperature) were studied for copper ions recovery. In this analysis, input parameters were taken into account aretemperature, adsorbent dosage and temperature. Based on the ideal experimental conditions for the shaking intensity and dimensions of the metals optimum recovery percentage the leaching variable input parameters were calculated (**Table 2**).

## **3. Results and discussion**

## **3.1 Sample analysis of PCBs (sizes and metal elements)**

The graphical representation of the size analysis reveals that, subject to size decrease sequence, the fraction of sample generated on the screens with larger mesh sizes has decreased. The total weight collected in the sieves is, however, maintained similar roughly with marginal loss. The sample collected at the ball mill is much less than 0.05 mm from the analytical data of each procedure. Numerous experiments have used a shredded sample dimension less than 0.5 mm, contributing to an elevated copper recovery rate [25]. Present findings consist of 0.05 mm of the sample held above the pan for the liquidation used particle scale. EDXs have been used to analyze the copper concentrations of preliminary samples. To ensure uniformity and to obtain results of copper by EDXs, samples were randomly mixed (**Figure 4**) and the final composition of metals by weight % (Cu 3.15%, Sn 42.4%, Zn 1.16%, Pb 27.81% and others metals 25.48%).

## **3.2 Maximum copper recovery of leaching by optimization study**

Experiments carried out based on RSM results. In addition to that ANOVA, response surface plots, quadratic model equation and CCD were analyzed for experimental conditions. Hence, the results obtained for Optimum removal of Cu 95.33%, with a desirability of 0.761 were obtained at Time 5 hours, Temperature 90.01°C, pulp density 25 g L−1.

*Clay Minerals Effects for Metal Reclamation from Leached Solution DOI: http://dx.doi.org/10.5772/intechopen.98368*

#### **Figure 4.** *Presents of copper ions from PCBs sample by EDXS.*

The optimum values were found under the studied parameters at which the maximum recovery is obtained. Therefore, The experiments done above optimized three parameters with two experimental parameters (80 rpm of speed and 0.05 mm particle size). Therefore, the optimized gives 20 grams of the sample treated with 0.5 liter of aqua regia at this optimum condition, metal compositions present in to the PCBs by after leaching (Cu 0.09 weight percentage) are shown in EDXs results (**Figure 5**). The results obtained at optimum condition shows that the recovered rate of copper is 97.06%.

## **3.3 Adsorption studies for copper recovery from leached solution**

Adsorption studies are explained for the recovery of coppers from leached solution with the help of Bentonite clay as an adsorbent. Hence, all the adsorption results for recovery concerning various parameters are evaluated and studied as

**Figure 5.** *EDXs spectrum analysisfor copper ions removal after leaching treatment of (PCBs).*

explained based on previous research [28] and compared; we get the optimum condition to obtain maximum recovery of metals. The optimum condition is the value of concentration, size, temperature and time at which the maximum recovery is obtained. The optimum conditions are 4 g of adsorbent dosage, 0.05 μm particle size of adsorbent, 80°C of temperature and 4 hours of contacting time. Under these conditions, chemically activated bentonite clay gives maximum adsorption rate when compare to other adsorbents. Therefore, the present study was experimented to recover the copper ion (Cu2+) from the leached solution with the use of optimal parameters and constructive results obtained in chemically activated adsorbents.

The results show (**Figure 6**) that at optimum condition, the recovery is 97% of Copper. This is the most favorable condition to obtain the maximum recovery of copper ions which was found initially 3.119 weight percentage of copper and after copper present in adsorbent 3 weight percent therefore copper were recoverd 97.33%. The optimal values are tested the specified parameters by response surface methodology.

## **3.4 Optimization parameters by design of experiments (DOE)**

Optimize and evaluate individual process variables for better recovery rates by analyzing operating parameters and reducing the number of tests. The CCD (Central Composite Design) for Cu, adsorption was calculated with optimized operating parameters and RSM maximum copper recovery. The CCD results shown in **Table 3** experimental and predicted copper adsorption were analyzed.

## *3.4.1 RSM for copper reclaimation from leached solution*

Statistical modeling methods were used to evaluate the multiple regression of the experiments designed to determine the multivariable equation (**Table 3**). RSM concept data plots collected in the final regression equation in terms of coded recovery variables for Cu recovery. The final equation in terms of the coded factors equation discussed Eq. (2). The equation in terms of coded factors can be used to make predictions about the response for given levels of each factor. By default, the high levels of the factors are coded as +1 and the low levels are coded as −1. The

**Figure 6.** *EDXs images in metal compositions for after adsorption.*


#### *Clay Minerals Effects for Metal Reclamation from Leached Solution DOI: http://dx.doi.org/10.5772/intechopen.98368*

**Table 3.**

*Experimental and predicted results from CCD with optimal parameters for copper adsorption.*

#### **Figure 7.**

*RSM plots and interactions between the the temperarure, adsorbent dosage and size of adsorbent by Cu recovery.*

coded equation is useful for identifying the relative impact of the factors by comparing the factor coefficients.

$$\begin{array}{l} \text{@of Cu} = +96.33 + 0.7688 \times A + 0.7388 \times B + 1.10 \times C \\ \quad - 0.4750 \times A \times B + 1.03 \times A \times C - 0.287 \times B \times C \\ \quad + 1.09 \times A^2 - 3.96 \times B^2 - 3.86 \times C^2 \end{array} \tag{2}$$

The response of each parameter was Predicted within the limits through the model in function of coded factor. Here, the maximum and minimum coded factor termed as +1 and −1. The response surface were visualized in three dimensional plots that exhibit two factors functions while keeping the other factors constant. The predicted design plots, shows the above red zones were found at 97.33% of Cu and above yellow zones confirms 93% of Cu, and above blue colors confirms 88.95% of Cu. It shown in **Figure 7** and contour plots for copper recovery (**Figure 8**).

#### **Figure 8.**

*Contour plots and interactions between the temperarure, adsorbent dosage and size of adsorbent by Cu recovery.*

## *Clay Minerals Effects for Metal Reclamation from Leached Solution DOI: http://dx.doi.org/10.5772/intechopen.98368*

## *3.4.2 Evaluation of the model*

P-values less than 0.0500 indicate model terms are significant. In this case A, B, C, AC, A2 , B2 , C2 are significant model terms. Analysis of variance correspond to experimental results were presented in **Table 4**. The Model F-value of Cu 34.28 implies the model is significant. There is only a 0.01% chance that an F-value this large could occur due to noise. Also, the acceptable and reasonable value of lack of fit with F-value of Cu 0.9321, with probability (>0.05) indicates the suitability of the method for good presentation of experimental data. Implied that the model was accurate. Also, the acceptable and reasonable value of lack of fit with F-value of Cu 0.02322, with probability (>0.05) indicates the suitability of the method for good presentation of experimental data.

As presented in **Table 5**, the model presents the high R<sup>2</sup> value of Cu0.9778 indicates that there was a good agreement between the experimental and predicted


### **Table 4.**

*ANOVA table for model to predict % of leaching of copper.*


#### **Table 5.**

*Quality of the quadratic model for the adsorption of copper.*

**Figure 9.** *Comparison plot between the experimental and predicted data.*

**Figure 10.** *Desirability plot for recovery of copper from leached solution.*

**Figure 11.** *EDXs spectrum analysis for metal ions obtained for after adsorption.*

results. Also, the predicted R2 value Cu 0.9353was which were in reasonable agreement with the adjusted R2 value of Cu 0.9493. Adeq Precision measures the signal to noise ratio. A ratio greater than 4 is desirable. Your ratio of Cu 18.125 indicates an adequate signal. This model can be used to navigate the design space. Predicted value were Showed (**Figure 9**) of the responses from model was in agreement with observed values over the selected range of independent variables with reasonable higher values of coefficient of determination (R<sup>2</sup> ).

## *3.4.3 Desirability plot for recovery of copper from leached solution*

The desirability profile for the removal percentage of copper versus the variables is shown in **Figure 10**. The desirability varies from 0.0 to 1.0 corresponds to approaching from undesirable to the very desirable condition. Optimum removal of Cu 97.33%, has been obtained with the desirability of 0.845 which was obtained at adsorbent dosage 2 gm L−1, size of adsorbent 0.4 mm temperature 90°C.

Therefore, this design has been analyzed for experimental and predicted valves of metal separations' of chemical leaching, the values of desirability rate was found in the range of prediction is 0.845. Since the optimum values are predicted then optimal parameters are used to run the copper recovery process.

## **3.5 Maximum copper recovery by optimization study**

Experiments carried out based on RSM results. In addition to that ANOVA, response surface plots, quadratic model equation and CCD were analyzed for experimental conditions. Hence, the results obtained for Optimum removal of Cu 97.33%, with a desirability of 0.845 were obtained at adsorbent dosage 2 gm L−1, size of adsorbent 0.4 mm temperature 90°C.

The optimum values were found under the studied parameters at which the maximum recovery is obtained. Therefore, The experiments done above optimized three parameters with two experimental parameters (size of adsorbent 0.4 mm temperature 90°C). Therefore, the optimized gives 2 grams of the sample treated with 0.5 liter of leched solution at this optimum condition, metal compositions present in to the PCBs by after leaching (Cu 0.09 Weight percent) are shown in SEM with EDXs results (**Figure 11**). The results obtained at optimum condition shows that the recovery of copper are 97.06% of copper.

## **4. Conclusions and outlook**

In summary, copper in waste PCBs were leached into corresponding reagents during the two-stage chemical leaching. The effectiveness of two-stage chemical leaching media (HCl and HNO3, H2SO4 and HCl) was employed for the separation of copper ions during the treatment of PCBs is evaluated. The results of this study, C-A Bent adsorbents assist in the 97% of effective copper separation for Chemical leached solution Therefore, the Study concluded that, copper ions are recovered effectively from leached solutions by using adsorption techniques under optimum conditions in the presence of C-A Bent adsorbent. These types of metal leaching operations are promoted in order to reduce the environmental problems caused by these kinds of heavy metals. The analysis demonstrates the dependency of the recovery rates. Optimum removal of Cu 97.33% with a desirability of 0.845 was achieved at adsorbent dosage 2 gm L−1, Size of adsorbent 0.4 mm temperature 90°C. Hence this form of heavy metal leaching and adsorption reclamation process is proposed with a view to reducing environmental impacts (caused by heavy metals). It was concluded that the combination of aqua regia leaching and bent adsorption is an effective and economic way for the recovery of copper from leached solution.

According to studies, modifying the surface of the clay increases the rate of adsorption, but this raises the total cost and results in the introduction of additional chemicals into the atmosphere. As a result, attempts will be taken in the future to resolve these issues. Only a few field trials have been performed, and more systematic studies are needed to decide the best conditions for using clay minerals as adsorbents.

## **Acknowledgements**

This study was carried out with utilization of the laboratory facilities in Erode Sengunthar Engineering College and Kongu Engineering College. The corresponding author would like acknowledge and thank to his parents and brother P. Selvarasu, PG Assist Zoology, Govt Higher Secondary school, Vellore for their kind support.

## **Nomenclature**


*Clay Minerals Effects for Metal Reclamation from Leached Solution DOI: http://dx.doi.org/10.5772/intechopen.98368*

## **Highlights**


## **Author details**

Murugesan Manikkampatti Palanisamy1 \*, Akilamudhan Palaniappan2 , Venkata Ratnam Myneni3 , Kannan Kandasamy4 , Minar Mohamed Lebbai<sup>2</sup> and Padmapriya Veerappan<sup>5</sup>

1 Centre for Education, Council of Scientific and Industrial Research–Central Electro Chemical Research Institute (CSIR–CECRI), Karaikudi, Tamil Nadu, India

2 Department of Chemical Engineering, Erode Sengunthar Engineering College, Erode, Tamil Nadu, India

3 Department of Chemical Engineering, Mettu University, Mettu, Ethiopia

4 Department of Chemical Engineering, Kongu Engineering College, Erode, Tamil Nadu, India

5 Department of Applied Electronics, Erode Sengunthar Engineering College, Erode, Tamil Nadu, India

\*Address all correspondence to: engineermurugesh@gmail.com

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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[11] Masavetas, I, Moutsatsou, A, Nikolaou, E, Spanou, S, Zoikis-Karathanasis, A and Pavlatou, EA 2009, 'Production of copper powder from printed circuit boards by Electrodeposition', Global NEST Journal, vol. 11, no. 2, pp. 241-247.

[12] Xie, F, Cai, T, Ma, Y, Li, H, Li, C, Huang, Z and Yuan, G 2009, 'Recovery of Cu and Fe from printed circuit board waste sludge by ultrasound: Evaluation of industrial application', journal of cleaner production, Elsevier Ltd, vol. 17, no. 16, pp. 1494-1498.

[13] Montero, R, Guevara, A and De La Torre, E 2012, 'Recovery of gold, Silver, Copper and Niobium from Printed Circuit Boards Using Leaching Column Technique', Journal of Earth Science and Engineering, vol. 2. pp. 590-595.

[14] Vijayaram, R and Chandramohan, K 2013, 'Chemical Engineering and Process Technology Studies on Metal (Cu and Sn) Extraction from the Discarded Printed Circuit Board by Using Inorganic Acids as Solvents', vol. 4, no. 2, pp. 2-4.

[15] Vijayaram, R, Nesakumar, D and Chandramohan, K 2013, 'Copper

*Clay Minerals Effects for Metal Reclamation from Leached Solution DOI: http://dx.doi.org/10.5772/intechopen.98368*

extraction from the discarded printed circuit board by leaching.', Research Journal of Engineering Sciences, vol. 2, no. 1, pp. 11-14.

[16] Murugesan Manikkampatty Palanisamy and Kannan Kandasamy 2020, "Comparative studies on Bentonite clay and peanut shell carbon recovering heavy metals from printed circuit boards" Journal of Ceramic Processing Research. vol. 21, pp. 75-85.

[17] Saad, A 2010, 'Removal of heavy metals from industrial wastewater by adsorption using local Bentonite clay and roasted date pits in Saudi Arabia', Trends in Applied Sciences Research, vol. 5, pp. 138-145.

[18] Tripathi, A., Kumar, M., Sau, D. C., Agrawal, A., and Chakravarty, S. (2012). "Leaching of gold from the waste Mobile phone printed circuit boards (PCBs) with ammonium Thiosulphate, Int. J. Metallurgical Engg. 1 (2012) 17-21.

[19] Sjöblom, R, Bjurström, H and Pusch, R 2003, 'Feasibility of compacted bentonite barriers in geological disposal of mercury-containing waste', Applied Clay Science, vol. 23, pp. 187-193.

[20] Gu, S., Kang, X., Wang, L., Lichtfouse, E., Wang, C., 2019. "Clay mineral adsorbents for heavy metal removal from wastewater: A review". Environ. Chem. Lett. 17, 629-654.

[21] Ahmadi, A., Foroutan, R., Esmaeili, H., Tamjidi, S., 2020. "The role of bentonite clay and bentonite clay @ MnFe2O4 composite and their physicochemical properties on the removal of Cr (III) and Cr (VI) from aqueous media". Environ. Sci. Pollut. Res. 27 (2020) pp. 14044-14057.

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[23] Yazici, EY and Deveci, H 2013, 'Extraction of metals from waste printed circuit boards (WPCBs) in H2SO4-CuSO4-NaCl solutions', Hydrometallurgy, vol. 139, pp. 30-38.

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[25] Abdennebi, N, Bagane, M and Chtara, C 2013, 'Removal of copper from phosphoric acid by adsorption on Tunisian Bentonite', Journal of Chemical Engineering Process Technology, vol. 4, pp. 166-170.

[26] N. Abdennebi, M. Bagane, C. Chtara, Removal of copper from phosphoric acid by adsorption on Tunisian Bentonite. J Chem Eng Process Technol. 4 (2013) 166-170.

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[28] Ping, Z, Zeyun, F, Jie, L, Qiang, L, Guangren, Q and Ming, Z 2009, 'Enhancement of leaching copper by electro-oxidation from metal powders of waste printed circuit board', Journal of Hazardous Materials, vol. 166, pp. 746-750.

## **Chapter 7**

## Towards the Use of Yellow Clay in Fired Bricks

*Maryam Achik, Boutaina Moumni, Hayat Benmoussa, Abdellah Oulmekki, Abdelhamid Touache, Gil Gonzalez Álvaro, Francisco Guitián Rivera, Antonia Infantes-Molina, Dolores Eliche-Quesada and Olga Kizinievic*

## **Abstract**

This chapter deals with the study of the possibility of using yellow clay - which was only used in pottery so far- in the civil engineering field as building materials, especially in the field of fired bricks. With the aim to improve the technological properties of yellow clay based bricks, two wastes were used as secondary raw materials. The first one is a mineral waste - pyrrhotite ash - this waste was neither characterized nor valued before by any other author. While the second waste is an organic waste - cedar sawdust - which is from the artisanal sector. Clay bricks containing yellow clay and different content of wastes were prepared and tested to evaluate their technological properties: water absorption, bulk density, porosity and mechanical strength… The test results indicate that the addition of wastes to clay bricks improves their technological properties and highlights the possibility of wastes reuse in a safe and sustainable way.

**Keywords:** clay, bricks, mineral waste, organic waste, mechanical strength, clay bricks, waste, pyrrhotite ash, recycling

## **1. Introduction**

Recently, the study of the reuse of industrial solid waste in the fields of construction materials (fired bricks, tiles, etc.), pavement materials and concrete has received considerable attention across the world. The recovery of wastes is used to develop environmentally friendly technologies, to reduce negative impact on the environment and landfill waste in large storage and disposal areas, and to reduce production costs for new products. However, the recovery of wastes depends on their chemical composition, their microstructure and their physical and hydrodynamic properties. For example, industrial waste containing iron oxide, silicon oxide, aluminum oxide - in the form of major oxides with various contents - such as fly ash (with major oxides: SiO2, Al2O3, Fe2O3), pyrite ash (major oxide: Fe2O3), red mud (major oxides: Fe2O3, TiO2, Al2O3, SiO2), as well as biomass ash, were studied and reused in various fields. There are many applications for these wastes:


On the other hand, the reuse of wastes in the field of terracotta is not the only reason to conduct research on the addition of certain solid residues in a clay matrix, even though it was the ultimate goal of this research. Other reasons can be taken into consideration. In fact, waste can:


Therefore, the reuse of wastes as additives in the ceramics sector has more reason to be than recycling. So, various research has focused on improving the performance of clay bricks. Some authors have studied the effect of wastes on manufacturing processes - and more specifically the firing process - and others have estimated the amount of waste that can be added to meet masonry standards. It consists of the evaluation of the technological properties of bricks versus the nature of the waste and the rate of its incorporation into the clay matrix.

The literature shows that the addition of waste glass improves the compressive strength, water absorption and porosity rates of bricks. Also, this waste increases the shrinkage of bricks [10, 11].

The addition of other additives such as sawdust and marble residue resulted in bricks with good compressive strength, especially for 15–20 wt.% of marble powder content [12]. The water absorption of these bricks was very high to be used in the field of civil engineering [13].

Another example of organic waste concerns the addition of biomass ash such as sugar cane bagasse and rice husk ash to clay bricks. These wastes reduce mechanical strength and increase the ability of bricks to absorb water [7, 8]. These two types of bricks have interesting thermal insulation properties and are also lighter which is an advantage in terms of transportation and use in the areas affected by the earthquake [8, 14].

The performance of clay-based bricks containing various amounts of rice husk ash or wood ash was also evaluated. The study has shown that bricks containing up to 10 wt.% of the rice husk ash and those containing 30 wt.% of the wood ash respect the standard requirements of clay masonry units [15]. Other work on the same waste has shown that 20 wt.% of the wood ash can be added to the ceramic

## *Towards the Use of Yellow Clay in Fired Bricks DOI: http://dx.doi.org/10.5772/intechopen.99009*

matrix as a natural, economical and environmentally friendly pigment, thus allowing the lightening of bricks [16]. Another study has shown that adding sawdust to clay bricks improves porosity and results in lightweight bricks [17].

Among the ash waste category, there is another industrial waste, rich in hematite Fe2O3, which is the pyrrhotite ash. Few studies were carried out for this waste to explore areas of its recovery in industry [18–22]. It was generated between 1964 and 1982 [1] by the sulfuric acid manufacturing process from the combustion of pyrrhotite ore extracted from the Kettara mine in Marrakech (Morocco). Pyrrhotite ash is currently stored in large quantities in a large open space in the southwest of Morocco.

The present work is a contribution to evaluate the effect of the addition of two types of wastes on the technological properties of fired bricks-based yellow clay. This clay, whose main components are silica, calcium carbonate and kaolinite, was only used in pottery so far. The two wastes used are the pyrrhotite ash, which is a mineral waste, and the cedar sawdust, which is an organic waste from the artisanal sector.

## **2. Method and materials**

The approach followed throughout this study is presented in **Figure 1**. The chemical, physical, mineralogical, environmental, thermal and mechanical characterization were carried out. Many analytical techniques were used, namely: X-ray diffraction (XRD), X-ray fluorescence (FRX), Fourier transform infrared (IR) spectroscopy, reservoir, Inductively Coupled Plasma Spectrometry (ICP),

**Figure 1.**

*Global methodologies used to carry out this study.*

Thermogravimetric Analysis (TGA), Differential Thermal Analysis (DTA), Hydrogen potential (pH), Scanning Electron Microscopy (SEM), distribution particle size, bulk density, apparent porosity, shrinkage, weight loss, water absorption, three-point flexural strength and compressive strength.

Three raw materials were used, namely:


The characterization of the raw materials concerns the identification of:


The **Figure 2** shows the steps of making bricks and the characterization of the fired bricks with different contents of pyrrhotite ash and sawdust.


*Towards the Use of Yellow Clay in Fired Bricks DOI: http://dx.doi.org/10.5772/intechopen.99009*

**Figure 2.** *The procedure adopted to carry out this work from the raw materials to the final bricks.*


## **3. In-depth study of the clay matrix**

## **3.1 Summary of the chemical and physical properties of the yellow clay**

The **Figure 3** shows the percentages of metal oxides obtained by XRF analysis. The **Table 1** shows the physicochemical characteristics of the clay with the main remarks drawn from this analysis.

The X-ray fluorescence analysis of yellow clay (**Figure 3**) shows the presence of several chemical elements [22]. According to the literature [23–25] this clay seems to be a calcareous clay which can be used in the production of low refractory building bricks.

As shown in **Table 2**, analysis by infrared spectroscopy of the clay reveals the presence of characteristic bands of silica, calcium carbonate and kaolinite. These results were confirmed by the X-ray analyzes which show the presence of crystalline phases of silica, calcite and kaolinite [22].

#### **Figure 3.**

*X-ray fluorescence of clay raw.*


#### **Table 1.**

*The main chemical properties of yellow clay.*


#### **Table 2.**

*The main characteristics of yellow clay.*

## **3.2 Thermal study of clay bricks**

The chemical analysis of the clay highlights the possibility of using it to develop terracotta bricks. Given that this clay has never been used as a clay bricks, and in order to understand its behavior at different temperatures to establish a firing program, a thermal study was realized.

## *3.2.1 Thermal expansion test*

This measurement was studied by the DIL 402 Expedis dilatometer with a heating rate of 3°C/min. The test was carried out on bricks made of clay with percentages of pyrrhotite ash: 0 wt.%, 30 wt.% and 60 wt.%. The expansion curves obtained are shown in **Figure 4**.

L0: Length of the brick before thermal expansion;

L: Length of the brick during thermal expansion;

dL / L0: the thermal expansion factor.

From the results of the thermal expansion illustrated in **Figure 4**, and DTA / TGA detailed in a previous publication [22], two aspects are noted:

*Towards the Use of Yellow Clay in Fired Bricks DOI: http://dx.doi.org/10.5772/intechopen.99009*

#### **Figure 4.**

*Expansion curves for clay-based bricks with different pyrrhotite ash content: (a) 0 wt.%; (b) 30 wt.% and (c) 60 wt.%.*


In this case, thermal expansion analysis (**Figure 4**) shows that all samples expand continuously without any deformation detected up to 750°C.

#### *3.2.2 Brick heat treatment program*

Based on the DTA/TGA analysis [22] and the dilatometry test, four temperature ranges can be identified. These areas are illustrated in **Table 3**. The identification of

*Figure 5. Brick expansion profiles for bricks with 0, 30 and 60 wt.% pyrrhotite ash.*


#### **Table 3.**

*Justification of the adopted firing program.*

these areas allowed to establish the most suitable heat treatment program for firing bricks made from yellow clay and pyrrhotite ash. This firing program highlights the treatment temperature as a function of time as well as the heating rate. **Figure 6** shows the established program.

After studying the possibility of making terracotta bricks-based on yellow clay from Fez, new elements are sought to be used as additives in order to improve the technological properties of bricks. Pyrrhotite ash was chosen to this end. It is a mineral waste that was studied and valorized for the first time in our previous work [19, 21]. The physicochemical characterization of the pyrrhotite ash showed that it is a mineral waste rich in hematite, silica and alumina. It is also weakly hygroscopic and exhibits a low loss on ignition (3.4%) with a density around of 4.33 g/cm3 .

Morphological analysis by the scanning microscope shows that the pyrrhotite ash particles have a spherical shape with a relatively smooth surface. Obviously, the particles having a spherical shape and a smooth surface retain a small quantity of water, which confers to the pyrrhotite ash a weakly hygroscopic character.

The particle size of the pyrrhotite ash is continuous and contains grain fractions having a diameter between 1 μm and 125 μm. It is well known that mixing different fractions generally led to a compact material because the relatively small particles can get lodged in the interstices between the larger ones. So the material

*Towards the Use of Yellow Clay in Fired Bricks DOI: http://dx.doi.org/10.5772/intechopen.99009*

**Figure 6.** *Clay firing program.*

**Figure 7.** *Leaching test in a tank or tank with renewal of the lixiviant.*

fills the volume more compactly [19]. Another work dedicated to the study of the behavior of pyrrhotite ash towards the environment has been published [21]. The main steps (**Figure 7**) and results (**Figure 8**) of this environmental study are shown below.

The test protocol is taken from the Dutch Standard NEN 7345 adapted to the Moroccan hydrological context. (MBMD: Modified Building Materials Decree) [1]. It is a Standard used to highlight the polluting potential of the fly ash recovered in construction materials.

Test protocol and conditions are the following:


**Figure 8.** *The cumulative results of the heavy metals studied.*

The leachates obtained were filtered using a 0.45 μm membrane filter, and after measuring the pH, they were acidified to pH 0.9–1.1 with a concentrated HNO3 solution. After determining the concentration of heavy metals (Cr, Zn, Cd, Pb and Cu) using an Inductively Coupled Plasma Spectrometry, the εi (Σmg / m2 ) value was calculated and compared with limits U1 and U2 to identify the category of this waste. The **Figure 8** shows that all cumulative of the heavy metals studied are below the limit U1 [26–28], so the pyrrhotite ash can be classified as waste that can be reused in construction materials.

## **4. Elaboration of yellow clay-based bricks**

Currently, the unique application of the yellow clay is the pottery. So, this study aims to valorize the yellow clay differently. The feasibility to elaborate bricks for construction based on the yellow clay was more detailed in an article previously published [22].

## **4.1 The effect of adding a mineral waste: case of pyrrhotite ash**

The study of bricks treated at 1000°C shows that substituting up to 30 wt.% natural clay with pyrrhotite ash has a positive effect on the technological properties of bricks.

A notable variation of all these properties was observed namely: shrinkage, weight loss, porosity, bulk density, water absorption capacity and mechanical strength. **Table 4** summarizes the results obtained for the brick containing 0 wt.%, 20 wt.%, 30 wt.% and 40 wt.% ash as well as the requirements of certain standards for building bricks available in the literature*.*

In order to better respond to the imperatives of the sustainable development that requires the respect of the environment and the rational use of resources and energy, it was deemed necessary to further study the manufacture of bricks-based clay and ash by seeking to optimize the manufacturing conditions using minimum of energy. For this reason, the evaluation of the technological properties of bricks containing ash was also made for bricks fired at 900°C. The **Table 5** summarizes results of this study.

At 900°C, the brick containing 20 wt.% of pyrrhotite ash exhibits the best flexural strength (28.69 MPa). Since it reveals a low porosity, it was decided to improve

### *Towards the Use of Yellow Clay in Fired Bricks DOI: http://dx.doi.org/10.5772/intechopen.99009*


#### **Table 4.**

*Summary of the clay bricks study with 0, 20, 30 and 40 wt.% content of pyrrhotite ash fired at 1000°C.*


#### **Table 5.**

*Summary of the clay bricks study with 20 wt.% and 30 wt.% content of pyrrhotite ash fired at 900°C.*


**Table 6.**

*The technological properties of the best formulation of clay-ash-sawdust bricks fired at 900 and 1000°C.*

this formula (20 wt.% of pyrrhotite ash – 80 wt.% of yellow clay), by adding an organic element which evaporates during firing, leaving pores which will lighten the brick thus produced. For this purpose, cedar sawdust was chosen to be added to yellow clay bricks incorporating 20 wt. % of pyrrhotite ash.

### **4.2 The effect of adding an organic waste: case of cedar sawdust**

**Table 6** shows that bricks containing 20 wt.% of pyrrhotite ash, 80 wt.% of clay and 5 wt.% of sawdust of the total mass has characteristics corresponding to the requirements of international standards for terracotta bricks, whether fired at 900°C or 1000°C. However, those fired at 900°C are more resistant to compression with a value of 11.82 MPa against 10.78 MPa for those fired at 1000°C.

## **5. Discussion**

The technological evaluation of bricks containing pyrrhotite ash was mainly carried out by measuring shrinkage, weight loss, bulk density, porosity, dilatometery and mechanical strength.

About bricks containing yellow clay and pyrrhotite ash, the results (**Table 4**) shows that the addition of the mineral waste increases the bulk density and flexural strength. However, the addition of up to 30 wt.% of waste enhances the flexural strength. This property decreases when 40 wt% of waste is added. Bricks containing pyrrhotite ash up to 30 wt.% exhibits a good bulk density with an increase of the flexural strength. Such a behavior was attributed in our previous work [22] to:


The maximum of flexural strength is obtained for the brick containing 30 wt.% of waste. The flexural strength decreases for bricks containing more than 30 wt.% of waste. This behavior was attributed in our previous work [20] to the firing temperature that should be higher than 1000°C, as well as the complex mineralogical transformations, occurring during the firing and cooling process, that depend on the content of Fe2O3 and fluxing oxides.

The evolution of porosity is in accordance with the water absorption values but is not in accordance with the bulk density and flexural strength values especially for the percentage of 40 wt.%. This behavior was explained in our previous work [22] by the fact that the increase of the waste content causes the coalescence of pores which leads to generating regions of weakness, which, in turn, weakened the mechanical properties of the bricks when the content of pyrrhotite ash is higher than 30 wt.%.

The bricks with 20 wt.% of pyrrhotite ash and 80 wt.% of clay - fired at 900°C - have the best mechanical properties with a flexural strength of the order of 28.69 MPa (**Table 5**). Knowing that the bricks intended for construction must have a mechanical strength which exceeds 7 MPa [29]. However, this type of bricks have a shrinkage of 11% (which exceeds the limit <8%) [30], a weight loss near the limit 14.75% (<15%) [31] and also a porosity around the lower limit 19.6% (> 20%), which makes the bricks with 20 wt.% of pyrrhotite ash and 80 wt.% of clay dense and heavy. In order to improve all these properties, another element has been added to bricks containing 20 wt.% of pyrrhotite ash. This element should promote the formation of pores, which will reduce the bulk density of the bricks and obviously make them lighter. To remain around the concept of recycling waste to protect and serve the environment, the element chosen is an organic waste which is cedar sawdust from the artisanal sector in the city of Fez.

Adding sawdust to the bricks has the effect of reducing their weight so that the brick becomes light. The addition of organic waste results in light bricks or porous bricks. The bricks become more porous [20% -55%] and meet European standards [15, 30] and the compressive strength remains above 7 MPa.

Experience has shown that bricks with a sawdust content of up to 5 wt.% of the mixture consisting of 20 wt.% of pyrrhotite ash and 80 wt.% of clay treated at 900° C, exhibits compressive strength of the order of 11.82 MPa, a porosity of 50.14% and a bulk density of 1.8 g/cm3 , and thus meet European standards for building bricks.

## **6. Conclusions and outlook**

The main objective of this study has been satisfactorily achieved. Yellow clay used in pottery field so far was valorized in a field in high demand around the world, that of the building bricks. By adding mineral and organic wastes, pyrrhotite ash and sawdust, the technological properties of yellow clay based bricks were improved.

This study has demonstrated the feasibility of using by-products (pyrrhotite ash and sawdust) as a partial clay substitute in fired clay products. Waste's content affected all technological fired brick properties significantly. Based on the results of the physical-mechanical properties evaluations of the end products and the environmental evaluation industrial waste is recommended as a raw material (pyrrhotite ash and sawdust) in the manufacture of fired clay products. Use of this waste could have practical implications as a means of recycling and for achieving costs savings in brick production, as fewer raw clay materials would be required. Most importantly, the added value of this study is the reuse of two wastes at a time in a brick with good technological performance that should be economically and environmentally beneficial.

On the other hand, this study made it possible to determine the optimal formulation and favorable conditions for the production of bricks based on yellow clay and wastes. With the view to make it exploitable, it is necessary to apply it on an industrial scale to verify the reproducibility of the results obtained in the laboratory. Even to build a prototype (typical house) in order to study the durability of the bricks in real conditions while following the parameters influenced by the properties of the bricks, namely the climate and the air quality inside the typical house.

Finally, this work opens the way to lead the reflection in order to expand the range of products where it will be possible to valorize the yellow clay and develop other materials used in the fields of buildings and civil engineering.

## **Acknowledgements**

This work would not have been possible without collaboration with universities at international level. Note that the majority of the experimental part was carried out in Spain and the rest between Morocco and Lithuania.

Institute of Ceramics of Galicia, the University of Santiago, Compostela, Spain;

Department of Inorganic, Crystallographic and Mineralogical Chemistry of the Faculty of Sciences of the University of Malaga in Spain;

Department of Environmental Chemistry and Materials Engineering of the University of Jaén in Spain;

Composite Materials Laboratory at the Building Materials Institute of Vilnius Gediminas Technical University in Lithuania;

## **Author details**

Maryam Achik1 , Boutaina Moumni1 , Hayat Benmoussa1 \*, Abdellah Oulmekki1 , Abdelhamid Touache2 , Gil Gonzalez Álvaro3 , Francisco Guitián Rivera3 , Antonia Infantes-Molina4 , Dolores Eliche-Quesada<sup>5</sup> and Olga Kizinievic6

1 Laboratory of Processes, Materials and Environment, Faculty of Sciences and Techniques, Sidi Mohamed Ben Abdellah University, Fez, Morocco

2 Laboratory of Mechanical Engineering, Faculty of Science and Techniques, Sidi Mohamed Ben Abdellah University, Fez, Morocco

3 Galician Institute of Ceramics, University of Santiago de Compostela, Spain

4 Department of Inorganic Chemistry, Crystallography and Mineralogy, Faculty of Sciences, University of Malaga, Spain

5 Department of Chemical Environmental, and Materials Engineering, Advanced Polytechnic School of Jaén, University of Jaén, Spain

6 Institute of Building Materials, Vilnius Gediminas Technical University, Vilnius, Lithuania

\*Address all correspondence to: hayat.benmoussa@usmba.ac.ma

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Towards the Use of Yellow Clay in Fired Bricks DOI: http://dx.doi.org/10.5772/intechopen.99009*

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[21] M Achik, A Oulmekki, M Ijjaali, H Benmoussa, O. Kizinievic, environmental study and valorization of an ashy waste: Case of pyrrhotite ash, IOP Conf Series. 606 (2019). https://doi. org/10.1088/1757-899X/660/1/012075.

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[24] S. Abbas, M.A. Saleem, S.M.S. Kazmi, M.J. Munir, Production of sustainable clay bricks using waste fly ash: Mechanical and durability properties, Journal of Building Engineering. 14 (2017) 7-14. https://doi. org/10.1016/j.jobe.2017.09.008.

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of MSW incineration residues from facilities with different air pollution control systems. Durability of matrices versus carbonation. Waste Management. Volume 21, Issue 4, July 2001, Pages 313-323. https://doi.org/10.1016/ S0956-053X(00)00082-9

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## **Chapter 8**

## Fire Resistant Geopolymers Based on Several Clays Mixtures

*Ameni Gharzouni, Clément Alizé and Sylvie Rossignol*

## **Abstract**

This chapter aims to highlight the effect of clay mixture mineral composition and alkali concentration of potassium alkaline solutions on the thermal behavior of geopolymer materials. For this, three mixtures composed of kaolin (pure, impure kaolin or mixture of both), calcium carbonate, sand and potassium feldspar and three potassium alkaline silicate solutions with different concentrations were used (5, 6 and 7 mol.L−1). At first, the effect of rotary calcination parameters at 750°C such as the dwell time (30, 60, 120 and 180 min) and weight powder (100, 400 and 500 g) was investigated. It was demonstrated that the kaolin dehydroxylation is quasi complete (> 90%) and do not significantly depend on the dwell time and powder weight. Whereas the carbonate decomposition degree increases with the increase of dwell time and the decrease of powder weight but still not complete (<80%). These differences influence the feasibility of consolidated materials. Indeed, a flash setting occurs for samples based mixtures with high calcium carbonate decomposition degree (> 50%) and low wettability values (500 μL/g) for the three used alkaline solutions. The thermal behavior at 1000°C depends on the chemical composition of the aluminosilicate source and the concentration of alkaline solution. A conservation of the compressive strength at 43 MPa after thermal treatment at 1000°C of geopolymers based on mixture of pure and impure kaolin and a low potassium concentration solution (5 mol.L−1) was evidenced.

**Keywords:** geopolymers, kaolin, rotary oven, thermal properties, compressive strength

## **1. Introduction**

Thermal resistance is an essential property for different applications. Inorganic refractory materials are generally used. However, the preparation of these materials requires high-temperature solid state reactions [1]. As an alternative, geopolymer materials, synthetized at low temperature (less than 100°C), are known to have good thermal stability. The term geopolymer was introduced by Davidovits [2] to design amorphous three-dimensional materials resulting from the activation of an aluminosilicate source by an alkaline solution [3]. They are generally synthesized from metakaolin [4, 5] or other more abundant and low-cost clays or industrial coproducts [6, 7]. The thermal stability of metakaolin based geopolymers is due to the densification resulting from viscous sintering and pore network collapse [8]. The effect of calcium on the thermal behavior was also highlighted [9]. It was proven that the addition of low amount of calcium increases the densification temperature and improves the mechanical strength after thermal treatment. Dupuy et al. [10],

have shown that geopolymers based on argillite (mainly composed of interlayered illite/smectite and 22% of calcite) exhibit a good thermal resistance that depends on the argillite calcination process. Indeed, a higher resistance is obtained for furnacecalcined argillite compared to flash calcined one due to the complete dehydroxylation of clay minerals and decomposition of carbonates. Tognonvi et al., [11] have also shown that the addition of argillite improved significantly the thermomechanical properties of kaolin-based geopolymers due to the in-situ formation of wollastonite, leucite and zeolite-type phases. Rashad and Zeedan [12] found that for fly ash based materials, the concentration of the activator had a significant effect on and residual strength after heating. As the concentration of the activator increases, the initial strength compressive strength increases. However, as the concentration of the activator increases, the residual compressive strength after firing decreases. Barbosa et al. [13], have also evidenced the crystallization of feldspar, kalsilite and leucite at 1000°C in potassium based gopolymers. Consequently, the mineralogy and thermal treatment of the used aluminosilicate is an important parameter controlling the thermal behavior of geopolymers. Raw clays contains naturally clay minerals, carbonate and feldspar. Calcium carbonate decomposes between 600 and 800°C into free lime and carbon dioxide. However, depending on the relative humidity, the produced CaO can react with H2O to form Ca(OH)2 [14]. The carbonate thermal decomposition depends on different parameters such as the nature and crystalline structure, the sample weight, the particle size, the purge gas… [15]. Furthermore, the calcination process can also influence the carbonate decomposition. For example, it was demonstrated that the limestone calcination in a pilotscale rotary kiln calcination depends essentially on heat transfer and feed rate, whereas rotational speed and inclination angle are less important [16]. The calcination process have also an important role on the chemical, physical and structural properties of clays. San Nicolas et al. [17] have undertaken a comparative study between rotary and flash calcinations of kaolin and have shown that the method of thermal treatment influences the physical properties of resulting metakaolins and therefore and their reactivity for geopolymer synthesis. That is why it is necessary to understand the effect of mixture of kaolin, calcite and feldspar. The interaction between kaolinite and calcite upon thermal treatment was also studied [18, 19]. It was evidenced that calcite decomposition was influenced by the ratio of kaolinite to calcite, the CO2 flow rate, the mixing, the heating rate and the volatiles during the dehydroxylation of kaolinite.

To understand the thermal behavior of geopolymer based on clays, it is necessary to understand the role played by each constituent of the clay. Thus, fundamental research on clay mixtures should be undertaken. The objective of this study is to exacerbate the effect of rotary furnace on the physical and chemical properties of clay mixtures and on the thermal behavior at 1000°C of the resulting geopolymers.

## **2. Effect of rotary furnace on clay mixtures properties**

Three clay mixtures, named F1, F2 and F3, were studied as detailed in **Table 1**. They are composed of 40 wt. % of kaolin (pure and/or impure kaolin), 15% of calcium carbonate, 35% of sand and 10% of potassium feldspar. The difference between the two kaolins is the purity. In fact, impure kaolin has a Si/Al molar ratio of 1.44 and contains mo quartz, calcite and hematite. However, the pure metakaolin has a Si/Al molar ratio equal to 1. The mixtures were thermally treated at 750°C in a laboratory-scale rotary furnace (HTR 11/150 + 301 controller, Carbolite Gero) with different parameters. The dwell time was varied at 30, 60, 120 and 180 min. Furthermore, for the same dwell time of 60 min, the powder weight was


*Fire Resistant Geopolymers Based on Several Clays Mixtures DOI: http://dx.doi.org/10.5772/intechopen.98566*

**Table 1.**

*Nomenclature and the weight percentage of each constituent of the mixtures.*

varied at 100, 400 and 500 g. The effect of these parameters on the calcined powder was investigated.

#### **2.1 Dehydroxylation and carbonate decomposition degree**

Thermal analysis (DTA-TGA) were performed on raw and calcined mixtures. An example of the obtained curves for raw F1 mixture is plotted in **Figure 1**. Three endothermic pics accompanied with three weight losses are observed in the temperature ranges 30–200°C, 400–600°C and 600–800°C. The first one is attributed to the release of adsorbed and free water [20]. The second weight loss between 400 and 600°C corresponds to the dehydroxylation of kaolin [21]. The weight loss, between 600 and 800°C, is due to the decomposition of calcium carbonate [22]. The comparison between the raw and calcined mixtures permits to calculate the kaolin dehydroxylation degree or the calcium carbonate degree (A) as Eq. (1)

$$\mathbf{A} = \mathbf{1} - \frac{m\mathbf{2}}{m\mathbf{1}} \times \mathbf{100} \tag{1}$$

where, m2 is the mass fraction of the residual hydroxyl groups or CO2 in the calcined mixture and m1 is the mass fraction of the hydroxyl groups or CO2 in the raw mixture.

In order to understand the effect of dwell time and powder weight, the kaolin dehydroxylation degree and the carbonate decomposition rate were plotted in function of the dwell time in **Figure 2A**. No significant change of the dehydroxylation degree can be observed in function of the dwell time (**Figure 2A.a**). Regardless of the mixture, the dehydroxylation degree varies between 92 and 99% revealing a quasi-complete dehydroxylation of kaolin. However, lower values of carbonate decomposition degree and varying in function of the dwell time are noticed (**Figure 2A.b**). In general, the decomposition degree increases with the increase of the dwell time. For F1 mixture, the decomposition degree increases from 32 to 49% at 30 and 180 min, respectively. F2 mixture shows the highest decomposition degree of 80% after 180 min. F3 mixture exhibits similar results as F1 mixture with a decomposition degree of 50% after 180 min.

Consequently, the kaolin dehydroxylation is quasi-complete whatever the dwell time. However, depending on the mixture, the carbonate decomposition is partial and increases for longer dwell time. This result reveals than more energy is needed for calcium carbonate decomposition.

Similarly, the kaolin dehydroxylation degree and the calcium carbonate decomposition degree were plotted in function of the powder weight in **Figure 2B**. The

**Figure 1.** *Thermal curves ( ) weight loss and ( ) heat flow of raw F1 mixture.*

**Figure 2.**

*Evolution of (a, c) kaolin dehydroxylation and (b, d) carbonate decomposition degrees in function of the (A) dwell time and (B) powder mass for* ▪ *F1 • F2 and ▲ F3 calcined mixtures.*

*Fire Resistant Geopolymers Based on Several Clays Mixtures DOI: http://dx.doi.org/10.5772/intechopen.98566*

dehydroxylation degree values are very high, similar and varying between 91 and 99% (**Figure 2B.a**). A more significant difference can be observed in the carbonate decomposition degree. Indeed, it decreases with the increase of powder weight (**Figure 2B.b**). For F1 mixture, it decreases from 61 to 22% for 100 and 500 g, respectively. F2 and F3 mixtures show similar result with a decrease from 53 to 33% for 100 and 500 g, respectively. Consequently, the smaller powder weight, the higher decomposition degree. This result is in accordance with literature [23, 24].

Thus, the rotary thermal treatment parameters and more precisely the dwell time and the powder weight influence the calcium carbonate decomposition in kaolin and carbonate mixtures. Indeed, it increases with the increase of dwell time and the decrease of powder weight but remains not complete.

#### **2.2 Wettability value**

No significant differences were detected in the particle size of the different powders. Indeed, the median diameter is equal to 9, 60 and 60 μm for F1, F2 and F3 mixtures respectively, regardless if the used calcination parameters. So, a focus

**Figure 3.**

*Evolution of wettability values in function of the (A) dwell time and (B) powder mass for* ▪ *F1* • *F2 and ▲ F3 calcined mixtures.*

#### **Figure 4.**

*Protocol of geopolymer sample preparation.*

has been put on the wettability value which is an indicator of the aluminosilicate reactivity for geopolymer synthesis [5]. It corresponds to the volume of water that can be adsorbed by one gram of powder until saturation. In order to determine the calcination parameters effect, the wettability values were also plotted in function of the dwell time and the powder weight in **Figure 3**. At first the raw mixtures have different wettability values (533, 430 and 497 μL/g for F1, F2 and F3 mixtures respectively. Whatever the mixture, the wettability values increase with the increase of dwell time. The highest values are obtained for F1 mixture due to the higher purity of the used kaolin (740, 533 and 583 μL/g for F1, F2 and F3 mixtures, respectively). Less impact can be observed of the powder weight on the wettability values (**Figure 3B**). Quite similar values are observed whatever the mixture for the different powder weight. Thus, the wettability values are more sensitive to the dwell time and the chemical composition of the initial mixtures. Consequently, rotary calcination parameters induces differences in chemical composition and properties of the clay mixtures. This fact will induce different reactivity in alkaline media (**Figure 4**).

## **3. Thermal properties evaluation of geopolymer materials**

## **3.1 Feasibility of geopolymer materials**

Feasibility tests of consolidated materials were carried out for all the studied mixtures. Sample were prepared by mixing calcined mixtures with three potassium alkaline solution with different potassium activation solution with different concentration (5, 6 and 7 mol.L−1). The samples were cast in closed polysterene mold and kept at room temperature. Examples of the visual aspect of the different obtained samples are presented in **Figure 5**. Whatever the used solution, samples exhibit either flash setting (hardening after few seconds of mixing before total homogenization of the mixture) (**Figure 5A**) or a consolidated appearance and a reddich color due to the initial color of the used kaolin containing hematite [25] (**Figure 5B**). The flash setting seems to be only linked to the calcined mixtures and not to the used alkaline solution. That is why the feasibility of consolidated materials was plotted in function of the properties of the calcined mixtures i.e. the wettability value and the calcium carbonate decomposition degree in **Figure 6**. For F1 mixture, whatever the dwell time, the samples are feasible. This is due to low carbonate decomposition degree <49% and high wettability values (> 600 μL/g). For F2 mixture, for a dwell time exceeding 60 min, a flash setting is observed. It corresponds to high carbonate decomposition degree exceeding 40% and a wettability

#### **Figure 5.**

*Example of (A) flash consolidated sample (S1F2, dwell time = 180 min) and consolidated sample (S3F2, dwell time = 30 min) (B) before and (C) after thermal resistance at 1000°C.*

*Fire Resistant Geopolymers Based on Several Clays Mixtures DOI: http://dx.doi.org/10.5772/intechopen.98566*

**Figure 6.**

*Feasibility of consolidated materials in function of the wettability value and the calcium carbonate decomposition degree of the different calcined mixture for* ▪ *F1* • *F2 and ▲ F3 mixtures (grey: flash setting).*

value from 500 μL/g. Concerning F3 mixture, flash setting is obtained from a dwell time of 120 and 180 min corresponding to carbonate decomposition degree of 50% and a wettability values about 500 μL/g.

To sum up, flash setting occurred for mixtures with high calcium carbonate decomposition degree (>50%) and low wettability values about 500 μL/g. This result is in accordance with literature where flash setting was generally associated with high "CaO" content [26, 27].

#### **3.2 Thermo-mechanical properties**

In the following section, only the thermal behavior of the sample based on mixture with a dwell time of 30 min (no flash setting) with the different alkaline solutions was evaluated. Samples were heated at 1000°C during 1 hour in an oven. An example of the visual aspect of the thermally treated geopolymer is presented in **Figure 5**. C. It is shown a color lightening and no cracks. The samples were subjected to compression tests before and after thermal resistance at 1000°C. The obtained compressive strength values are given in **Table 2**. Before thermal treatment, the highest compressive strength values are obtained with K7 solution (from 47 to 54 MPa for K7F1 and K7F2, respectively). This fact can be explained by the higher reactivity of this solution due to its higher alkali concentration permitting to favor the geopolymer reaction and to reinforce the final structure [28]. After thermal treatment, with K6 and K7 solution, whatever the mixture, a decrease of the compressive strength is noticed especially with F1 mixture (based on pure kaolin) showing a drastic decrease from 30 to 3 MPa and from 46 to 20 MPa with F2 and F3 mixtures, respectively. With K5 solution, a decrease of compressive strength is obtained for F1 and F2 mixtures. However, the mechanical strength are conserved using F3 mixture (43 MPa). The reduction in strength is due to the dehydration of the geopolymer matrix creating internal stress, weakening the structure [29].


**Table 2.**

*Compressive strength value before and after thermal resistance at 1000°C.*

Consequently, the compressive strength are governed by the reactivity of the alkaline solution. However, after thermal treatment, the compressive strength depend on the chemical composition of the aluminosilicate source.

## **3.3 Structural investigation**

In order to explain the different mechanical behaviour and for more accurate information on the structural change of the samples after thermal treatment at 1000°C, XRD characterization was performed. Examples of XRD patterns for K7F1 (σafter 1000°C/σbefore 1000°C = 0.5), K7F2 (σafter 1000°C/σbefore 1000°C = 0.9) and K5F3 (σafter 1000°C/σbefore 1000°C = 1), before and after thermal resistance are presented in **Figure 7**. Before thermal treatment, similar phases are observed such as quartz, orthoclase and residual calcite. Impurities such as hematite are detected in F2 and F3 based samples and are due to the used kaolin. After thermal treatment, the patterns evidence the persistence of quartz and orthoclase and the formation of new crystalline phases such as leucite K(AlSi2O6) [30], kalsilite (KAlSiO4), potassium aluminium silicate (KAl(SiO4)) and wollastonite (CaSiO3) [31]. In fact, the amorphous phase crystallizes to form potassium aluminum silicate KAl(SiO4), kalsilite and leucite. Calcium reacts from silica of the amorphous phase to form wollastonite. These phases are refractory and are the origin of the thermal resistance of the samples [32, 33]. More leucite seems to be formed in detriment of kalsilite in K5F3 and K7F2 compared to K7F1 sample. This due to higher Si/Al ratio of this sample. Indeed, the formation of leucite is favored at higher Si/Al molar ratio [13]. This fact can explain the conservation of mechanical strength for this sample.

In summary, the thermal treatment at 1000°C leads to the formation of crystalline phases which depend on the initial chemical composition of the mixture. To correlate the thermal behaviour to the chemical composition, the compressive strength ratio (σafter 1000°C/σbefore 1000°C) was plotted in function of the molar ratio (nCa + nSi)/nK in **Figure 8**. It is demonstrated that the compressive strength ratio increases from 0.1 to 1 with the increase of the molar ratio (nCa + nSi)/nK from 1 to 1.6. Indeed, the increase of this molar ratio means the increase of the availability of calcium and silica able to form crystalline phases at high temperature. The decrease of the potassium concentration seems also to favor the thermal resistance. Consequently, the thermos-mechanical behavior is related to the structural changes after thermal treatment which is intimately linked with the initial chemical composition of the used precursors.

*Fire Resistant Geopolymers Based on Several Clays Mixtures DOI: http://dx.doi.org/10.5772/intechopen.98566*

**Figure 7.**

*XRD patterns of geopolymers (a, a') K7F1, (b, b') K7F2 and (c, c') K5F3, before (A) and after (B) thermal resistance at 1000°C (Q-quartz (01-070-3755), Ca-calcite (00-005-0586), A-anatase (00-021-1272), L-leucite (04-013-2099), Wo-wollastonite (00-043-1460), Ka-kalsilite (00-066-0070), Or-orthoclase (04-009-3610).*

#### **Figure 8.**

*Evolution of the compressive strength ratio (*σ *after thermal resistance/* σ *before thermal resistance) in function of the molar ratio (nCa+nSi)/nK for* ▪ *F1* • *F2 and ▲ F3 mixtures with K5 (empty), K6 (black) and K7 (grey).*

### **4. Conclusion**

The objective of this study is to evaluate the thermal behavior of geopolymer materials based on different clay mixtures and potassium alkaline solution with different concentrations. Three clay mixtures composed of 40 wt. % of kaolin (pure or impure kaolin or mixture of both), 15% of calcium carbonate, 35% of sand and 10% of potassium feldspar, were studied. At first, the effect calcination parameters at 750°C in a rotary furnace was investigated. Indeed, the effect of dwell time (30, 60, 120 and 180 min) and weight powder (100, 400 and 500 g) on the kaolin dehydroxylation and the calcium carbonate decomposition degrees. It was shown that the kaolin dehydroxylation is quasi complete (> 90%) and varies very slightly with the dwell time and powder weight. However, more significant changes are observed for the carbonate decomposition degree which it increases with the increase of dwell time and the decrease of powder weight but still not complete (from 50 to 80%) even after 180 min of dwell time at 750°C. Consolidated materials were prepared based on the different mixtures and alkaline solutions with different concentrations (5, 6 and 7 mol.L−1). A problem of flash setting has been encountered and was due to the properties of the calcined mixtures (high calcium carbonate decomposition degree (> 50%) and low wettability values about 500 μL/g) and not the used alkaline solution. The thermal behavior at 1000°C of the sample based on mixture with a dwell time of 30 min with the different alkaline solutions was evaluated. Before thermal treatment, the highest compressive strength were obtained for the highest alkali concentration of the used solution (54 MPa). However, after thermal treatment, the compressive strength depend on the chemical composition of the aluminosilicate source. A general decrease of the mechanical strength was observed a drastic decrease was obtained with mixture based on pure kaolin. A slight decrease for sample based on impure kaolin. A conservation of the compressive strength with mixture based on mixture of pure and impure kaolin. Formation of new crystalline refractory phases such as leucite, kalsilite, potassium aluminium silicate and wollastonite was evidenced. Thus, in order to obtain thermal resistant materials with conservation or increase of residual strength after 1000°C, it is recommended to use a low concentrated potassium alkaline solution and an aluminosilicate rich of calcium.

## **Conflict of interest**

The authors declare no conflict of interest.

## **Author details**

Ameni Gharzouni, Clément Alizé and Sylvie Rossignol\* Institute of Research for Ceramics (IRCER, UMR CNRS 7315), Limoges Cedex, France

\*Address all correspondence to: sylvie.rossignol@unilim.fr

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Fire Resistant Geopolymers Based on Several Clays Mixtures DOI: http://dx.doi.org/10.5772/intechopen.98566*

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## **Chapter 9**

## Activated Clays and Their Potential in the Cement Industry

*Carlos Hernando Aramburo Varela, Luiz Felipe de Pinho, César Pedrajas Nieto-Márquez and Rafael Talero Morales*

## **Abstract**

The thermal activation of clays to produce highly reactive artificial pozzolans on a large scale is one of the most important technologies developed on an industrial scale to reduce CO2 emissions in cement manufacture. This technical document deals with the scientific basis for the thermal activation of clays to produce an extraordinarily high quality supplementary cementitious material (SCM) based on the contents of its hydraulic factors, reactive silica (SiO2 r–) and reactive alumina (Al2O3 r–). The production process and the optimization of its use in the new cements offers better performance, features and durability. Furthermore, its mixture with Portland cement is much more appropriate when carried out in a blending station after both components, activated clay and Portland cement, are ground separately and not jointly in a single mill.

**Keywords:** cement, activated clays, calcined clays, pozzolanic additions, low carbon

## **1. Introduction**

Currently, the cement industry is working on the search and use of new SCMs that allow the reduction of the clinker/cement factor in a significant way. The traditionally ones used are mainly blast furnace slags, natural pozzolans and fly ashes. In the case of the latter, and in view of the requirement to reduce "greenhouse-effect" gas emissions, the commitments acquired from COP21, and the forthcoming closure of coal-based electricity generation plants will greatly affect and seriously compromise their availability soon.

In the field of cements, mineral additions are understood to be natural or artificial inorganic materials or products that, added to Portland cement (PC) in certain quantities, improve its normal behavior, and may also sometimes provide some additional and specific positive quality or improve some of the characteristics of PC. As already mentioned before, the traditional mineral additions that are used in the cement and concrete industry, we can mention the pozzolanic additions (natural and artificial) and blast furnace slags, both which are known as active additions, in order to differentiate them of non-active or misnamed inert additions. The latter can be of limestone or siliceous origin and receive the common name of "filler", and none can be considered pozzolanic.

**Figure 1** shows the scarce availability of conventional SCMs in relation to the existence of limestone and clays. The availability of thermally activated clays on the

**Figure 1.** *Availability of MCSs worldwide. Their variability according to their composition.*

globe is quite large, giving the SCM the greatest potential in the cement industry, even more so given the future drastic reduction in the supply of fly ash.

The need to activate clays thermally for an industrial scale manufacturing arises also because of its very high pozzolanic reactivity and the high quality that it implies. In addition, the cement producer has the control over production capacity and quality. Here it is necessary to clarify the difference of terms like "calcined clay" and " activated clay". The first term, which is the most frequently used in publications, also includes the calcined clays of the ceramic and brick industry, which have very low pozzolanic activity. The second term, "activated clay" (AC), which is a clay with a much higher pozzolanic activity, therefore it will be the term used instead of "calcined clay" from now on.

The new technology to produce AC implies an industrial development that will bring greater sustainability in the cement industry bringing not only due to the considerable reduction of CO2 emission levels down to 70% compared to the Portland clinker manufacturing but also resulting in an important reduction in energy consumption.

## **2. Classification of pozzolanic additions by their chemical character**

Classifying and cataloging pozzolans according to their origin or by their total oxide content that is, according to their chemical composition [1, 2], is insufficient and not at all significant for the characterization of their reactivity. Therefore, R. Talero proposed a very different classification based on the results and conclusions of his research carried out with or without other authors [3–15], which is based on its chemical character resulting from its corresponding reactive silica content, SiO2 r–(%), and reactive alumina, Al2O3 r–(%) (Aluminum, Al, tetra- and/or penta-coordinated, which, in the case of the metakaolin is a metastable structure especially similar to the crystalline phase of the χ-alumina [16]). That is, under the same circumstances, capable of providing (depending on its amorphous or vitreous physical state and the average shape and size of its particles), every natural or artificial pozzolanic addition forming part of the cements and/or their derived products: concretes, mortars, pastes and prefabricated products.

Below are the chemical reactions (1)–(4) in which the hydraulic factors (reactive silica SiO2 r–, and reactive alumina Al2O3 r–) of the pozzolans are involved when they react chemically with the portlandite in an aqueous medium at room temperature, much faster with the portlandite of the PC fraction mixed:

$$\text{Ca}\text{SiO}\_2^{\text{-}-} + \text{CaO} + \text{H}\_2\text{O} = \text{C}?\\\text{S}?\\\text{H} + \text{Q} \tag{1}$$

$$\rm Al\_2O\_3^{\text{r-}} + CaO + H\_2O = \rm C\_3Al\_6, \rm C\_4Al\_{13}, \rm C\_4Al\_{19} + Q \tag{2}$$

$$\mathbf{C}\_4\mathbf{C}\_1\mathbf{H}\_{13} + \mathbf{H}\_2\mathbf{O} + \_{\text{gypuu}} = AFm + \mathbf{Q} \tag{3}$$

$$\rm{AFm} + \rm{H\_2O} + \_{\rm{gphum}} = \rm{AFt} + \rm{Q} \tag{4}$$

In this sense, it is very important to know the chemical character of pozzolans through the determination of the content of its hydraulic factors ((SiO2 r–(%) and Al2O3 r–(%)).

Depending on its chemical character, pozzolans will have a very different influence on all the properties, performance and behavior of the PC base materials; starting from its fresh state to the recently hardened and the completely hardened: rheological behavior of its fresh pastes [3], to the heat of hydration [4–6], the mechanical-resistant performance [7] and durability against attack of sulfates [8–11] and chlorides [12–15] and other natural aggressive chemical attacks (sea water - aggregate-alkali reactivity and carbonation) in which the particle shape and average size can influence its nature like in the case of siliceous pozzolans and the silicic ones on its chemical character such as in silica fume and diatoms above all.

### **3. The clays. Its thermal activation and pozzolanic properties**

The term "clay" refers to both a group of phyllosilicates and a granulometric division of the detritic rocks. This term also designates, in a not very precise way, a sediment or a rock constituted, in a great part, by minerals of the clay [17]. From a granulometric point of view, clay is any fraction smaller than 1/125 mm (≈ 4 μm) of a detritic rock, regardless of its composition. Although there is no precise size limit for clay minerals, most do not exceed 2 μm.

This crystalline structure is formed basically by two types of layers: tetrahedrons and octahedrons [18]. The tetrahedral layer has the group Si2O5 as basic unit, with

**Figure 2.**

*Structure of the clay minerals. A) Type 1:1 stratum. B) Type 2:1 stratum [18].*

the silicon in tetrahedral coordination and three oxygen of each tetrahedron shared with the adjacent ones forming a hexagonal structure (**Figure 2**). A part of the silicon atoms can be replaced by aluminum atoms and, occasionally, by Fe (III).

On the other hand, the octahedral layer has a cation, generally Al, Mg, Fe (II) or Fe (III), in octahedral coordination with oxygen or hydroxyl ions. The smallest tetrahedral structural unit of the octahedral layer consists of three octahedral and depending on the degree of occupation of the octahedral positions, the layers can be dioctahedral or trioctahedral. Dioctahedral minerals are those in which only two of the three octahedral of the structural unit have a cation in the center. When all the octahedral positions are taken, the minerals are called trioctahedral, and the cations occupying the octahedral positions are divalent (Mg, Fe (II)), while in the dioctahedral minerals the octahedral positions are occupied by trivalent cations (Al, Fe (III)).

The stacking of the layers and the substitutions of the ions determine different types of minerals in the clay. According to the layer stacking, they are divided in two big groups: those constituted by a tetrahedral layer and another octahedral layer, which share oxygen atoms (type 1:1) and those formed by two tetrahedral layers separated by an octahedral one (type 2:1).

Kaolinite, montmorillonite and illite clays, when undergoing adequate heating, can be activated as a result of a dihydroxylation process or loss of OH<sup>−</sup> groups from their crystalline network, through the following chemical reaction:

$$-OH^{-} + -OH^{-} \stackrel{\uparrow Q}{\rightarrow} H\_{2}O \uparrow + O^{2-} \tag{5}$$

The optimal temperature for this purpose usually ranges from 600–800°C, depending on the clay mineral composition itself. In synthesis, the clay thermal decomposition begins at 120°C with the loss of humidity (hygroscopic, colloidal and hydration water physically adsorbed, or absorbed in the material pores). As the process temperature increases, the hydroxyl groups begin to separate from the crystalline network (dihydroxylation stage). The increase in the vibration energy reaches a thermal agitation value adequate to enable the union with a nearby proton and form a water molecule that goes to the atmosphere to finally separate from the crystalline structure leaving it in an amorphous state that is not vitreous like that of fly ashes. At temperatures above 920° C, the AC becomes very unstable making the formation of spinel, pseudo-mullite or pre-mullite and even mullite possible [19]. **Figure 3** shows the thermal behavior of the most common clays [19]. The temperature values here given correspond to kaolinitic clays.

#### **Figure 3.**

*Thermal behavior of the most common clays and its consequences for their resulting final pozzolanicity at each temperature.*

*Activated Clays and Their Potential in the Cement Industry DOI: http://dx.doi.org/10.5772/intechopen.99461*

#### **Figure 4.**

*Increased pozzolanic properties of clay after thermal activation. Frattini test [20]. Results. Ages: 1, 2, 7 and 28 days.*

The thermal activation process of the clays produces an artificial pozzolan with an aluminic chemical character, according to R. Talero [3–15]. The chemically combined water of the clay released to the atmosphere acts on the coordination index of Al2O3 which was 6 [19]. After this thermal process, in optimum conditions (in coordination 4 or 5 [16]) it reacts chemically and very quickly with the portlandite of the liquid phase of the PC from the very first ages of its hydration. The physical state is amorphous and not vitreous like that of fly ash. On the other hand, the pozzolanic reaction of the latter, in the same circumstances and on an equal footing with everything else, is necessarily much slower.

Therefore, although kaolinitic clays have a higher content of Al2O3, a priori, it should not be a restriction as to which clay to use to produce an artificial pozzolan through thermal activation. Although finally and in any case, the suitability must be evaluated according to the content of SiO2 r– (%) and Al2O3 r– (%) in each mixture of clays that is possible to generate during its thermal activation process.

**Figure 4** shows the pozzolanic activity of a kaolinitic clay, determined by the EN 196–5 standard [20] before and after its optimal thermal activation.

### **4. Pyro process technology**

First, the clay must go through the drying, activation, and cooling processes. If the clay to be activated has a high content of iron (greater than 4%), it is important to ensure the change of color of the clay to gray during the thermal activation process to generate pozzolanic characteristics and thus promote its mixing with the PC.

The main parameters to obtain thermally AC and to guarantee its color change are the precise control of the adequate calcination temperature and the concentration of oxygen in the gases in the drying, activation, and cooling equipment.

The technology used for the combustion system of the drying and thermal activation processes allows operation with solid fuel, ensuring the stability of the flame even in a process with lower temperatures (less than 900°C).

**Figure 5.** *T-profiles of gases, material bed and refractory.*

The drying and thermal activation of the clays can be carried out by means of rotary kilns or with "flash technology". In the case of the use of rotary kilns, it is possible to reuse existing kilns in cement factories that are already out of service to adapt them, in any case, to their new condition of adequate heating of the clays for their activation.

**Figure 5** shows the temperature profiles of the gases, the material bed and the refractory lining of a mathematical model developed for the simulation of rotary kilns for the thermal activation of clays. In this case, the material fed into the kiln has already been dried at ≈ 250°C.

The flash technology is based on the dragging of small solid particles by a concurrent flow of hot gases to obtain high coefficients of heat and mass transfer in a more compact equipment. This technology can be used for the drying or activation process. In the case of applying a flash calciner, the process must be staged in several stages in a cyclone tower to ensure the proper residence time of the material in the temperature range of 750 to 850°C or "transit time", necessary for the activation to take place.

The experience in rotary kilns at an industrial level is extensive in Brazil with kilns of up to 1,100 Tm/day. And at the present time in Colombia with a kiln with a capacity of 1,500 Tm/day. Its operation is relatively simple and easy to understand by control room operators. Its operation control, in terms of adjusting the activation temperatures according to the quality control variables hour by hour, is relatively easy to handle, even though the short activation range in terms of temperature makes this control very demanding in order to obtain an AC of high pozzolanic activity. Therefore, it is important to say that the experience of thermal activation of clays with rotary kilns has already been several decades and there is not, nowadays, an industrial activation in "flash calciner" of such an important industrial size.

Finally, after having achieved the thermal activation of the clayey material, it is necessary to cool it. In this last stage and in the case of clays with a high Fe2O3 (%) content, it is also important to control the atmosphere to avoid that the material at high temperatures comes into contact with high air flows and thus avoid that the gray color obtained in the previous heating stages is maintained and not lost by the oxidation of the new thermally activated material. A technology that is perfectly suited to these two objectives (cooling the material and maintaining its gray color) is the rotary cooler**.**

## **5. Process control and verification variables**

One of the aspects that takes on an extraordinary importance in the process of thermal activation of clays, is how to assure the quality of these after having them thermally activated because there is still no analytical method or mechanical test that determines the pozzolanic activity in a direct and immediate way as soon as the AC has left the rotary kiln or the flash Calciner.

Therefore, the clay thermal activation must be determined in an indirect way to guarantee the highest possible content of Al2O3 r– (%) [21] and SiO2 r– (%) [22] after the process of thermal activation of the kiln by quick kiln adjustments in case it will be necessary. This will undoubtedly translate into a higher pozzolanic activity of the same [20], as mentioned above.

During this stage, and for the same reason, it is highly recommended to determine parameters such as Loss of Ignition (LOI), content of Kaolinite (%) before and after this calcination process and also its Pozzolanic Activity Index (PAI) after the calcination process. All these analyses must be correlated previously.

On this previous stage it is so important to determine the hydraulic factor contents of Al2O3 r– (%) [21] and SiO2 r– (%) [22] on the AC, in order to find the optimum temperature of every different clay available in the quarry.

In that sense, the activation temperature at which the highest contents of Al2O3 r– (%) [21] are obtained in the AC, will be the optimum temperature. Therefore, in this way it will also be possible to determine the upper and lower activation ranges, which indicate whether this optimal thermal activation temperature is exceeded to a certain extent, in such case, a recrystallization of the *amorphous* structure of the AC obtained will be produced, losing its activation level and, therefore, pozzolanic activity. And if, on the contrary, the temperature is very low, the needed dihydroxylation will not be achieved and its pozzolanic activity will be also very poor because it still has remains of raw clay without thermal activation. Either from kaolinite and/ or from illite and/or from montmorillonite or from a random mixture of all three or only two of them. This will undoubtedly result in a lower degree of replacement of Portland clinker in the cement to be designed, dosed and finally produced.

With all this information obtained through the analysis and verification tests that must necessarily be carried out at laboratory level, it is possible to clearly identify and determine the ranges in which these variables move according to the highest pozzolanic activity to be reached, since the mentioned analysis and tests must also be used in the quality control of AC at an industrial scale in the cement factory.

## **6. Inter-grinding**

The most common operation in the cement factories is the inter grinding in a single mill, of the Portland clinker, its setting regulator (natural gypsum stone) and the active and/or non-active mineral additions incorporated in each case, where the reduction in particle size occurs. For this reason, it is especially important to know the hardness indexes of the different materials to be grinded, their humidity, their proportions and granulometric feeding, in order to, with this information, design the load of grinding balls that each grinding chamber must carry, also according to the typology and physical quality of the cement to be produced.

The AC has a very high fineness. It could be said that 85% of its mass passes through the 1 mm mesh sieve, although, this value will depend on the type of clay, its mineralogical composition, and its quartz content. As an example, we can mention that the Bond hardness index for limestone can vary from 10 to 13 Kwh/Tm,

for an AC from 13 to 15 Kwh/Tm and for Portland clinker from 16 to 18 Kwh/Tm. The ranges may vary depending on the mineralogical composition, quartz content, origin, etc.

In some cases, the quartz content in the raw clayey material fed to the kiln can vary from 25 to 50%. This factor must be considered, therefore, in an inter-grinding. The AC has an intermediate hardness, although it is closer to that of limestone, having a very fine granulometric feeding so that it will be much easier to grind than limestone, leaving the first chamber of the mill quite empty. To obtain a performance of the same order of magnitude that the traditional cements, with security it will be possible to work with the specifications of a greater retained in the sieve N. ° 325, although its Blaine fineness will be also greater. As an example, for a "General Use", with a performance of ≈ 26 MPa at 28 days, it will be possible to work with a retention in screen No. 325 between 4 to 7% and a Blaine fineness between 4500 to 5500 cm2 /g.

In addition, quartz, although hard to grind, does not usually present a large size so that in this type of grinding it can play the role of "grinding admixture", also producing a cleaning effect of the balls and the lining of the mill, helping the grinding, thus being able to reduce or avoid the chemical admixture that improves the grinding itself. On the other hand, and due to the very low granulometry of the AC, the possibility of feeding it directly into the separator can also be studied. The physical aspects dealt with here make sense for replacement levels above 12%, but, however, with a low feed, its changes will not be much noticed. And as far as pozzolanic activity is concerned, this will become important with replacement levels above 8% depending on its Al2O3 r– (%) content.

As for the dosage of the cements with this pozzolan, the optimal relationship between all the components, Portland clinker, AC, other SCMs and gypsum, will depend on multiple factors. Therefore, each dosage must be studied and analyzed separately and exclusively, depending on the following premises or conditions: the mineralogical composition of Portland clinker, the reactivity of the AC produced (its contents of Al2O3 r– (%) and SiO2 r– (%)) and the optimum content of SO3, among others.

As an example, **Figure 6** shows the mechanical performances [23] obtained with two different types of PCs, with the same dosage of clinker, AC and limestone filler, and with the same grinding fineness, respectively. In this trial, two AC with different content of Al2O3 r– (%) and different proportion of gypsum added as setting regulator were used.

**Figure 6.**

*Performance obtained in the dosage of different cements according to the European normativity [23].*

Finally, it is also important to consider the very low granulometry of AC and its rheological behavior when it is so dry, in the transport systems, hoppers and dispensers because avalanches may occur in the hoppers and the control in the dosage may become somewhat difficult.

## **7. Separate grinding and blending stations**

Without a doubt the best grinding option to manufacture cements with several SCMs is separate grinding. From the point of view of particle grinding, the ideal is to grind materials of similar hardness because this ensures a more controlled and efficient grinding. In a inter grinding, the grinding is conducted by the harder material and this will define the retained in the sieve No. 325 and the Blaine fineness, therefore, the softer materials will be "over grinded" and these will affect the final particle size distribution of the product. Logically, the viability of this system will depend on the availability of equipment: two mills and their production capacities.

Separate grinding offers significant savings by eliminating the time required to prepare different products when changing from one product to another. These preparation times represent economical losses and inefficiencies when having to wait for the quality conditions of the new product in the mill to be able to make the changeover to the corresponding silo. An example of this is when changing from a product with a low clinker/cement factor to one with a higher clinker/cement factor. This cement with a higher production cost is "lost" when having to go to the silo with a lower specification.

On the other hand, separate grinding allows to gain in flexibility and grinding efficiencies by specializing the mills in a base product and not a type of cement. The different types of cement will be produced in the Blending Stations. The Control Room operator will be able to specialize his mill in a single "base product" and achieve better efficiencies, stability, and productivity in the grinding process by not having to make product changes and only adjusting improve production and quality.

Another great advantage in specializing the mills is that the room operators will not have to change mill settings and their operation will be easier to perform and carry out.

Separate grinding allows you to have two "intermediate products": the first one, a "base cement" and the second one, a "mix" containing the easiest materials to be ground. The base cement can be formed by the Portland clinker and setting regulator only and/or by some additional SCM, depending on the types of cement to be produced. The mix will be formed, instead, by the AC, the rest of the SCMs and the adequate amount of setting regulator according to its composition. The mixing percentages of each of the intermediate products will depend on the quality of their components and the qualities or types of cement to be produced.

The separate grinding of the mix allows a better control in terms of the Blaine fineness and the desired retained, being in this case of the AC, materials easier to grind than Portland clinker. Depending on the materials to be ground in this mix, a "coarser" grinding can be sought in terms of the retained in sieve No. 325, which could well be in a range between 10 to 15% and the Blaine fineness would be a resultant. This physical aspect will have great importance in the final fineness and in the conformation of the pore system in the final structure of the produced cement paste which will be, with all certainty, more compact than the one reached in the inter grinding. This will undoubtedly also result in greater mechanical resistance and durability of the cements to be produced in separate grinding with blending stations.

Finally, and as we have seen, separate grinding requires the assembly of blending stations, which are simple in their operation and design but at the same time, very demanding in terms of the Dosing systems to be used, therefore that is where the success of the latter lies. A blending station is equivalent to having a new high capacity and very high efficiency mill. Moreover, it does not need preparation times and only needs to introduce the corresponding mixture of the two intermediate products mentioned: the "base cement" and the "mix". The gain in terms of operation flexibility, dispatch logistics and customer service are unquestionable. For this technology it is essential to have a high-quality dosing and mixing equipment. Its capacity design will be determined by the dispatch and storage conditions.

## **8. Conclusions and outlook**


*Activated Clays and Their Potential in the Cement Industry DOI: http://dx.doi.org/10.5772/intechopen.99461*

## **Author details**

Carlos Hernando Aramburo Varela1 , Luiz Felipe de Pinho2 , César Pedrajas Nieto-Márquez3 \* and Rafael Talero Morales4

1 Carlos Aramburo Consultant, Cali, Colombia

2 Dynamis, Sao Paulo, Brazil

3 Cementos Argos, Medellín, Colombia

4 SACACH S.L, Madrid, Spain

\*Address all correspondence to: cpedrajas@argos.com.co

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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[12] Lannegrand R., Ramos G., Talero R. "Condition of knowledge about the Friedel's salt". Mater Construcc 51 (262), abr./may. / jun. 2001.

[13] Jones M.R., Macphee D.E., Chudek J.A., Hunter G., Lannegrand R., Talero R., Scrimeneour, S. N. "Studies using 27Al MAS RMN of AFm and AFt phases and the formation of Friedel's salt". Cem Concr Res, 33, p. 177- 182 (2003).

[14] Mejía R, Delvasto S, Talero R. "Chloride diffusion measured by a modified permeability test in normal and blended cements". Adv Cem Res, Vol. 15, n°3, p. 113-118 (2003).

[15] Talero R. "Synergic effect of Friedel's salt from pozzolan and from OPC co-precipitating in a chloride solution". Constr Build Mater, 33, p. 164-180 (2012).

[16] Trusilewicz L, Fernández-Martínez F, Rahhal V, *Activated Clays and Their Potential in the Cement Industry DOI: http://dx.doi.org/10.5772/intechopen.99461*

Talero R. "TEM and SAED Characterization of Metacaolin, Pozzolanic Activity". J Amer Ceram Soc, 95 (9), p. 2989-2996, 2012.

[17] Álvarez-Pérez A, Prada-Pérez JL. "Atlas de asociaciones minerales en lámina delgada". Vol. I Caps. 12 y 29: ASOCIACIONES MINERALES EN PROCESOS CERÁMICOS". Fundación Folch. Univ. de Barcelona – España. First Edition: UB 1997.

[18] Grim R.F. "Clay Mineralogy". Mc Graw-Hill, Nueva Tork, pp. 596, 1968.

[19] Grimshaw R.W. "The Chemistry and Physics of Clays and Allied Ceramic Materials", 4th Edition Revised, Ernes Benn Limited, London. 1971.

[20] UNE-EN 196-5:2006 Standard. "Methods of testing cement. Pozzolanicity test for pozzolanic cements". AENOR.

[21] UNE 80-225:2012 Standard: "Métodos de Ensayo de Cementos. Análisis Químico: Determinación del Dioxido de Silicio (SiO2) Reactivo en los Cementos, en las Puzolanas y en las Cenizas Volantes" AENOR.

[22] Talero, R. New method of wet chemical analysis to determine reactive alumina content in natural and artificial pozzolans. Priv. Communed. 2014.

[23] Norma UNE-EN 196-2: 2014. "Método de ensayo de cementos. Parte 2. Análisis químico de cementos". AENOR.

## **Chapter 10**
