**6. Advances in adsorption of heavy metals between natural zeolites with different chemical formulas**

The following figure shows the main formulas of the unit cell of the main natural zeolites used in the world. It is observed that all these structural characteristics have an incidence or directly influence the adsorption of contaminants. But it is observed that the ion exchange capacity is related in a special way to the number of exchangeable cations of the first parenthesis (LINDEA, NATROLITE, ANALCIMA, LAUMONTITE).

### **6.1 Physicochemical characteristic of the main zeolites**

**Figure 4** shows the physical and specific characteristics of most zeolites, especially the ionic exchange capacity for those zeolites that have a single exchangeable base, which would be in accordance with the present work in which the study is presented. where greater adsorption of heavy metals was obtained with a zeolite that did not have interchangeable bases, but rather a binary compound (O Mg).

Observing that **Figure 5** of natural zeolites had a different adsorption activity, a characterization was carried out by means of X-Ray Diffraction (XRD).

It is observed that **Figure 5** under the same adsorption conditions as **Figure 6**, but with different chemical formulas in its unit cell, have a different adsorption capacity, favorable for **Figure 5**. It is also observed that depending on the chemical formula it is possible that the spatial configuration or shape of the unit cell has changes that favor adsorption.

In this work, a sample with the compound formula (O Mg) corresponding to **Figure 5** and another sample in which the chemical formula has interchangeable bases (K, Na, Mg) which corresponds to **Figure 6**.

In the **Figure 5** (Sample 14-0078), shows a chemical structure with an amorphous material that corresponds to 86%, this indicates that this sample space does not behave as a crystalline structure, on the other hand, unlike the chemical structure of other zeolites, the cations in the first bracket of sample X is a compound: MgO, in the other zeolites it is a cation, in this sense, it is considered that this structure favors the adsorption process due to the presence of oxygen as well as the large space amorphous (86%). In addition, this property of this sample (**Figure 5**), allows to have a longer rupture time and saturation time with respect to sample 2 (**Figure 6**).

In the **Figure 6** (Sample 14-0079), Meets the standard of a chemical structure of zeolites, that is, it follows a crystalline model; the amorphous space is only 3.3%. and its exchangeable cations that corresponding to the first bracket is not a compound, and the other natural zeolites behave like this. It is suggested that this is the reason for the decrease in its adsorption process when compared to **Figure 5.**

### *Advances in the Adsorption Capacity, Rupture Time and Saturation Curve of Natural Zeolites DOI: http://dx.doi.org/10.5772/intechopen.110008*



### **Figure 4.**

*FONT: F. Morante. Zeolitas naturales del Ecuador: Geología, Caracterización y Aplicaciones. ESPOL. 2014 ISBN:978-9978-310-90-8.*

### **7. Fixed bed concentration models**

According to Morante, F., [13], Hartini et al. [33], Erdem [34] in the fixed bed concentration models, the concentrations in the fluid phase and the solid phase vary with time and the position of the bed, the greatest mass transfer takes place near the inlet. of the bed, where the fluid comes into contact with the adsorbent. If the solid initially has no adsorbate, the concentration in the fluid decreases exponentially with distance to almost zero before reaching the far end of the bed. After a few minutes, the solid near the inlet is nearly saturated, and most of the mass transfer takes place away from the inlet. The concentration gradient assumes an S shape.

**Figure 7** represents the physical process of a fixed bed concentration model based on natural zeolites or also called molecular sieves. Using fixed-bed concentration models with zeolites (ZNAA), that is, natural zeolites activated in an acid medium,

**Figure 5.** *FONT: C. Montaño 2022.*

with granulometries of 0.25 mm–1 mm, solutions with known concentrations (0.032 N of ZnSO4 H2O) are prepared and the fractions are collected in 100 ml volumetric flasks that are analyzed by atomic absorption to determine the concentration in ppm of cation Zn2+, the analysis finished when the concentration of the Zn2+ cation in the zeolite column effluent is close to or similar to the initial concentration of the Zn2+ cation. The columns have the same conditions (sample mass in grams g of zeolites, height in cm, volume in cm<sup>3</sup> , diameter in cm, density in g/cm<sup>3</sup> , flow rate in cm3 /h, and To ).

**Figure 7** also shows the operation of the liquid phase on the solid phase, the liquid phase is represented by the solution of 0.01 N Zn SO4. The solution passes through the zeolite column, the dark shading represents the adsorption of the Zn2 + cation, as it moves downward, initially the concentration in the effluent is zero (C 1), until the adsorption zone reaches the base of the column, then the breaking point (C2) is reached. The rupture time is established when the concentration of the Zn2+ cation in the effluent reaches 5% of the initial concentration (C0), from the rupture time the concentration of the Zn2+ cation grows rapidly (C3) until reaching the initial concentration (C 0), at this moment the zeolite column is totally saturated (C 4)

At the beginning of the test in these columns with time both in the liquid phase as well as in the solid phase and its limits are considered between C/C0 (concentration ratio corresponding to the fluid and the feed) is from 0.95 to 0.05.

*Advances in the Adsorption Capacity, Rupture Time and Saturation Curve of Natural Zeolites DOI: http://dx.doi.org/10.5772/intechopen.110008*

**Figure 6.** *FONT: C. Montaño 2022.*

**Figure 7.** *Font : C. Montaño, autor.*

### **8. Rupture curve/rupture time**

Breakdown curve and breakup time are understood as the concentration curve or amount of the cation to be adsorbed in a certain time for the fluid or solution that comes out through the natural zeolite columns that act as adsorbent material.

The rupture time tb is always less than t, and the amount of adsorbed cations at the rupture point is established by integrating the rupture curve at the time tb

### **Figure 8.**

*FONT: F. Morante. ZEOLITAS naturales del Ecuador: Geologìa, CaracterizaciònY Aplicaciones ESPOL 2014 ISBN:978-9978-310-90-8.*

The graph below shows how the adsorption breakup curve is formed and when it starts. The size of the curve is useful to determine the amount of adsorbed material.

**Figure 8** represents how the natural zeolites adsorb the heavy metal (Zn2+) over time until the saturation time, that is, when the natural zeolites do not have the capacity to adsorb more heavy metals. The rupture time tb is always less than t, and the amount of adsorbed cations at the rupture point is established by integrating the rupture curve at the time tb.

### **9. Experimental data**

### **9.1 Materials**

1.2 80 cm BURETTES

### 2.2 VOLUMETABLE FLAKS OF 100 ML

### 3.2 SAMPLES OF ZEOLITES (**Figure 9**)

In the adsorption test with fixed filters, the concentrations in the fluid phase and in the solid phase suffer variations over the time that the test lasts. As can be seen in **Table 3**, (**Figure 6**), which represents the zeolites with a chemical formula that have interchangeable bases (K, Mg, Na), had a rupture time of 1.4 h and a saturation time of 4 h in the adsorption process achieving a total Zn2+ adsorption of 161 Mg. Under the same conditions, (**Figure 5**), represents the zeolites where the chemical configuration is different and instead of interchangeable bases, they have a binary compound such as (O Mg), in the adsorption process it had a rupture time of 10 h and a saturation time of 14 h achieving a Zn2+ adsorption of 813 Mg (**Table 1**).

### **10. Results and discussion**

The results obtained in the test are:

*Advances in the Adsorption Capacity, Rupture Time and Saturation Curve of Natural Zeolites DOI: http://dx.doi.org/10.5772/intechopen.110008*

**Figure 9.** *FONT: C. Montaño 2022.*


**Table 1.**

*SAMPLE #1: Adsorption Column Data, Zeolite sample 1.*


With the data in SAMPLE # 1 and with the feed flow rate, the superficial velocity of the fluid (dissolution) is obtained, expressed in cm/h.

$$caudal \ cm \mathfrak{3}$$

$$\mathfrak{u}\_{\mathfrak{o}} \frac{h}{suction(cm\mathfrak{2})} \tag{3}$$

 $u\_o$   $76,40\,cm/h$ 

The feed rate of the cation (Zn2+) per cm2 of cross section, expressed in g/cm<sup>2</sup> /h, is obtained:

$$\mathbf{F\_A \xrightarrow[1000]{u \ast C}} \tag{4}$$

Where:

*<sup>u</sup>* <sup>¼</sup> *cm <sup>h</sup>* = Surface speed in centimeters per hour

**Co** Initial cation concentration, expressed in mg/cm<sup>3</sup>

$$\mathbf{F\_A0,763} \frac{\text{gZn}}{\text{cm}^3/\text{h}} \tag{5}$$

The breaking time of the ordinate C/CO 0.5 1.40 h.

The saturation time of the ordinate C/CO 1 10 h.

In such a way that the mass of Zn2+ adsorbed per gram of zeolite until saturation is.

$$FA \* . \int\_{0}^{\text{sat}} 1 - \frac{C}{C}$$

$$\mathbf{W\_{sat.}} \xrightarrow[d \times h]{0} \*d\tag{6}$$

From where:

**FA** Cation feed rate per cm2 of cross section in g/m2 h

**d** Zeolite density in g/cm<sup>3</sup>

**h** Height in cm of the filter bed

**ʃ(1- C/CO)ʅ \* dt.** Area bounded by the break curve and the ordinate C/CO 1, expressed in hours. The upper limit of integration is the saturation time **(tsat),** which corresponds to the ordinate of the curve where C/CO

$$\mathbf{W\_{sat.161}} \frac{\text{mgZn}}{\text{gzeolita}} \text{ is equal to 1} \tag{7}$$

To calculate the fraction of the unused bed, we have.

$$\mathbf{LUKh}^\* \left( \mathbf{1} - \frac{Wb}{Wsat} \right) \tag{8}$$

**h** length (height) of the filter bed, expressed in cm **Wb** adsorbed mass (Zn2+) per gram of zeolite to rupture time **Wsat** adsorber mass (Zn2+) per gram of zeolite at saturation point LUB **4,8 cm** (**Table 2**)

The results with the two samples of zeolites are as follows (**Table 3**):


**Table 2.**

*SAMPLE #2: Adsorption Column Data, Zeolite sample 1.*


**Table 3.**

*Final results of the adsorption process of the zeolite samples.*

*Advances in the Adsorption Capacity, Rupture Time and Saturation Curve of Natural Zeolites DOI: http://dx.doi.org/10.5772/intechopen.110008*

### **11. Discussion**

It is observed in this work that there is an influence that favors adsorption when natural zeolites have a chemical composition where there are no interchangeable bases (Na, K, Mg), if not, a binary compound (O Mg) and an upper amorphous space. at 80%. However, it is necessary to carry out other adsorption tests with other metals, especially those with a higher molecular weight than Zn2+, and also, it would be important to observe when there is more than one heavy metal in the solution or liquid phase.

The other scenario would be if the natural zeolites are enhanced with additives mentioned in this work: 1.1.4 (Significant advances with natural zeolites), these additives would surely improve the adsorption capacity of natural zeolites.
