Beneficiation of alunite by pyro- and hydrometallurgical treatment of alunite-K2CO3 mixtures

High-temperature roasting of alunite in the presence of K2CO3 gives rise to a reaction that results in up to an 80% recovery of its potassium content as K2SO4 by leaching of the roasted mixture. K2SO4 is also generated from t he reaction between the added K2CO3 and the SO3 driven off during roasting of the alunite. This limits the environmental and corrosive problems involv ed in the thermal treatment of this mineral. A solid residue containing mai nly aluminum oxide is also obtained. This could be used as raw material for the production of aluminum as the use of K2CO3 does nor introduce differen t cations than are in the are. A statistical study was performed on the fac tors assumed to affect the recovery of potassium, namely, roasting temperat ure, K2CO3- alunite stoichiometric ratio and leaching temperature.