Figure 3

(A) Decomposition curves and (B) model for chemical control. The alkaline decomposition curves show an induction period, where the K and S percentages appear at negligible levels; during that period active points are formed until a reaction front is established. Afterwards, a progressive conversion period appears, where the K and S concentrations progressively increase until reaching stabilization, which indicates the reaction has concluded. The spherical particle model with decreasing core and chemical control was used to determine the rate experimental constant. This kinetic model has been applied to jarosites that do not contain arsenic, and it has been proved that it best describes the alkaline decomposition process [14–18].