Reaction mechanism for the formation of ammonium jarosite

The composition of ammonium jarosite precipitated over different times, temperatures and initial pH have been determined. The mole ratio of ferric and sulfate species in the precipitates is initially higher than stoichiometric but reaches an equilibrium ratio of 3:2 after several hours. Thermogravimetric analyses (TG) and differential thermal analyses (DTA) were conducted to examine the weight losses in ammonium jarosite during its decomposition. Based on the experimental results, possible reaction mechanisms for the formation of ammonium jarosite are proposed and the possible multiple pathways by which jarosite precipitation could occur are discussed. A preliminary thermodynamic study on the iron–sulfate–water system support the proposed reaction mechanism.