Behavior of toxic elements in the thermal decomposition of industrial sodium jarosite: a kinetic analysis

In this study, an analysis of the behavior at high temperatures of toxic metals (As, Pb, and Cd) present in industrial sodium jarosite was carried out. The chemical and structural characterization of industrial sodium jarosite was carried out. Different mineral species associated with jarosite were found, such as franklinite (13.7%), analcime (12.1), orthoclase (4.4%) and other minority phases (1.4%), which are present from processes prior to the precipitation of jarosite industry. The amount of toxic elements such as arsenic, lead and cadmium was quantified, and their behavior was studied at high temperatures from 100 °C to 1000 °C, in addition, a kinetic of thermal decomposition of industrial jarosite study was carried out and the apparent activation energy of each of the mass losses was determined. The first loss of mass has an apparent activation energy of 22.32 kJ mol⁻¹, the second loss of 42.23 kJ mol⁻¹, and the third of 46.31 kJ mol⁻¹, losing a total of 36.10% of the total compound, and within the rest of mass (63.9%) as hematite and other toxic metals such as arsenic, lead, cadmium are found, which at 1000 °C are kept within the compound. The analysis carried out by DSC shows that there are 4 endothermic reactions and a very slight exothermic reaction. Endothermic reactions are due to the loss of water at low temperatures and the loss of sulfur at high temperatures, so the exothermic reaction is attributed to the oxidation of the metals present in jarosite. The results were corroborated by XPS, XRF, AAS, and XRD, where residues were analyzed after calcination at different temperatures and where it is shown that at 1000 °C such elements are present within the compound, so the building materials despite being subjected to sintering at high temperatures, retain these toxic elements.