## 3 Results and Discussion
### Leaching Tests
#### 3.2.2 pH dependence Leaching Behavior  
The immobilization of metals in the geopolymeric matrix has been evaluated through the EN 12457-2 compliance test, comparing the leaching results with the limits of the EU landfill regulation, as well as through the availability test. However, these tests are not  
Figure 3: Concentrations (mg/kg) of contaminants in the leachate after the availability and equilibrium/compliance leaching tests of the geopolymers with EAFD at 75 \({}^{\circ}\)C and 225 \({}^{\circ}\)C.  
sufficient to describe the wide range of conditions in which the developed material can be used [30]. With the pH-dependent leaching test, the behavior of the immobilized elements of a waste is studied in very different pH situations (between 2 and 12). Given that, the mobilization of some metals can change even by orders of magnitude in just one pH unit, it is important to perform this characterization of the material [47]. The concentrations of each of the leached elements are shown in Figures 4 and 5 with different dosages of EAFD as a function of the pH, and the curing temperature of the geopolymer. The elements can be grouped according to their behavior with the pH in two groups. The first of the groups is formed by Cd, Cr, Pb, Zn, Ba, Cu, Sb, and Ni (Figures 4 and 5). These elements leach at acid-neutral pH for a certain pH value are hardly mobilized, a behavior that is independent of the dosage of waste and the curing temperature of the geopolymer. For geopolymers without EAFD, leachate concentrations are much lower than when the waste is introduced. In some cases, there is a pH range where the concentrations present a minimum. Although the behavior of the elements is similar in different matrices, that range in which the pH is minimal can vary substantially depending on the sorption phases and the complexation reactions that occur with the components of the matrix [55]. In this material, the minimum in the concentrations of Cr is between pH 5-6, for Pb and Cu is 6-7 and for Zn, Cd, and Ni is between 8-9, behaviors similar to those found in [16; 23; 56]. Ba though leached more at acidic pH does not present a minimum at any pH as occurs with the rest of the elements mentioned above. The reference sample without EAFD is the one with the highest concentrations of Ba present in the leachate, decreasing when introducing EAFD, but without significant variations in the quantity introduced. For As, Mo, and Se, the behavior is contrary to that described for the previous group of elements (Figure 5), presenting the highest concentrations in leachate at basic pH. Increasing the concentration of EAFD in the geopolymer causes that the leaching increase at basic pH. For Mo at pH between 5.5 and 6, it begins to increase its presence in the leachate but it is not until pH 7 when the influence of the concentration of EAFD begins to appear until pH 12, an influence that is minimized by increasing the curing temperature at 225 C.  
Se present slight variations of concentrations in the leachate, being at pH 6 when it undergoes a slight increase and from pH 7 to pH 12 when the influence of the concentration of EAFD becomes evident, the higher concentration the presence of Se in the leachate. As have a pH range, from 3 to 8 for As, in which their concentration in the leachate is very low, close to 0, and for pH values outside that range reach leachate concentrations of up to 15 mg/kg. The dosage of EAFD in the geopolymers does not have a significant effect on the leaching of this element, because as seen above, arsenic comes mainly from clay. In the case of these elements, As, Se, and Mo, the natural pH of the material in the equilibrium test, around 12, coincides with the range of the greatest leaching, for that reason they are the elements that are closest to or exceed the leaching limits for non-hazardous waste landfill [51; 52].