The used sample was a solid plumbojarosite-argentian jarosite-hydronium jarosite solution. The stoichiometry of the alkaline decomposition and cyanide reaction in alkaline medium were studied. Alkaline decomposition shows an induction period, as well as a conversion period. Results on the reaction order and activation energy are consistent with the spherical particle model with decreasing core and chemical control. Six partial models and three global models were developed in order to describe its basic behavior. In every case the models were validated and tested for a plumbojarosite conversion of X = 0.75.