**3. Materials and methods**

The fly ash used in this study originated from a coal thermo power station located in southern Brazil that operates with pulverized Brazilian coal. Ashes and synthetic zeolites produced by hydrothermal treatment were previously characterized chemically and mineralogically and subsequently used in sorption experiments. These experiments were performed with synthetic solutions of sulphate salts of Pb (II), Cu(II), Zn(II), and Mn(II) prepared with analytical grade reagents in deionized water.

### **3.1. Zeolite preparation**

288 Ion Exchange Technologies

formation of a monolayer on the solid surface [27] .

implies a highly porous structure.

from different solid sorbents [28] .

**2.6. Sorption isotherms** 

and solution [26] .

The sorption phenomena are classified into two types: physical sorption and chemisorption. In physical sorption occurring weak interactions like Van der Waals, featuring a reversible process . By not having any sort of change in the nature of the species involved, the physical sorption is a non-specific, and can occur for different adsorbates [26] .In the chemical sorption or chemisorption, the chemical species involved are altered, as there is an effective exchange of electrons between the solid and the adsorbed molecule, resulting in the

If the sorption of one or more ionic species is accompanied by simultaneous desorption of an equivalent amount of ionic species, this process is regarded as ion exchange. The shapes of sorption usually encountered in environmental studies are the physical sorption, chemical sorption and ion exchange [2] .Being essentially a phenomenon of sorption surface, that has an sorption capacity of sorbent significant, must have large surface area, which

The sorbent materials, in turn, are natural substances or synthetic crystalline structure whose inner surface of the pores is accessible by a selective combination between the solid

The sorption isotherms are the main way of studying the capacity to remove toxic metals

To obtain the sorption isotherms is the first step for quantitative evaluation of the sorption mechanisms. The data obtained from the isotherms can be used to project and define the operating conditions of industrial equipment that are based on the principle of sorption [1].

Isotherms relates the concentration of the adsorbate fluid phase and solid phase at a certain temperature and are represented in graphic form, presenting in various ways that reflect the behavior of the mechanism of sorption. In general, the isotherms convex represent usually the solid microporous sorbent. The more complex shapes may be associated with multilayer

We can cite as examples, the isotherms of Henry, Langmuir, Freundlich, BET and Radke-Prausnitz. The Langmuir and Freundlich isotherms are the most commonly used to demonstrate the balance of removing a metal ion sorption, and are the most used models to

To provide us with data on the mechanisms of sorption isotherms can be linearized and

The fly ash used in this study originated from a coal thermo power station located in southern Brazil that operates with pulverized Brazilian coal. Ashes and synthetic zeolites

sorption or the varying sizes of pores of the sorbent material.

describe the mechanisms of sorption on zeolites [29].

applied to mathematical models.

**3. Materials and methods** 

The coal fly ash was submitted to hydrothermal treatment at different temperatures, reaction times, NaOH concentrations, solid/ liquid ratios (S/L) and aluminum/silicon (Al/Si) ratios as shown in Table 1. A Plackett–Burmann experimental design (25-2 fractional factorial design) was used in order to identify the most important variables in a preliminary analysis [30]. The tests were performed in duplicate. The molar ratio Al/Si was modified by adding analytical grade Al2O3 in the reaction media.

The hydrothermal treatment was carried out in a 450 ml reactor PARR-4562, made of Nickel-200 equipped with a turbine impeller and stirred constantly at 300 rpm. The reaction products were filtered and washed with water to remove the excess of sodium hydroxide.

The mineralogical characterization of the zeolites as well as of the ashes was carried out by X-ray diffraction (XRD) in a Bruker – AXS D5005 powder diffractometer with Goebel mirror and CoKa (35 kV/40 mA) radiation.


**Table 1.** Experimental conditions of the hydrothermal experiments

### **3.2. Preliminary evaluation of the response variable**

The zeolites as well as the coal fly ash were washed up to pH 9 and subsequently dried at 60oC for 24 h before the sorption experiments. The sorption capacity was determined by contacting, 50 ml of Mn and Cu solutions (100 mg/l) with 0.5 g of zeolites in plastic bottles. The solution pH of each test was chosen conveniently, between 4 and 5 to avoid cation precipitation.

The bottles were shaken for 2 h at 180 rpm in a KS501 IKA shaker and the solids were filtered with Whatman filter paper. The concentrations of metal ions of all tests were determined in a Varian Atomic Absorption Spectrometer - model Spectra 50B.

The sorption capacity was defined as a percentage and calculated by the equation (1):

$$\text{Sorption capacity (\%)} = \text{((C.-}C\_c) \text{)} \times 100\tag{1}$$

Ci and Ce are respectively initial and final concentrations of the metal ion in solution.

## **3.3. Sorption experiments**

The sorption experiments for the heavy metals, Cu2+, Pb2+, Zn2+, and Mn2+ with synthesized zeolite were carried out using the shaking device and methodology described previously in Section 3.2. A concentration range from 100 to 3000 mg/l was used for each cation. Only the zeolitic material from test 8 (Table 1) was used as sorbent.

The obtained data were plotted and adjusted with isotherm sorption models to analyze the cations sorption onto the sorbents.

### **3.4. Investigation of temperature effect – Thermodynamic study**

Samples of 30 g ash were mixed with 150 ml of a 3 mol/L NaOH solution. This mixture was reacted in an autoclave Parr - 4562, made of nickel alloy 200, equipped with a turbine impeller for 2 hours and 350 rpm agitation and temperatures of 50, 100, 150, 200 and 250 ° C. The product formed after cooling was filtered, washed with 2 liters of distilled water and dried at 60 ° C for 24 hours.
