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

Roasting alunite, KAl3(SO4)2(OH)6, with K2CO3 leads to the formation of K2SO4, thus reducing the amount of pollutant SO3. When a mixture of K2CO3 and alunite with a stoichiometric ratio of 1:5 was roasted at 900 degrees C and the residue leached at 100 degrees C, 80% of the K2SO4 formed was recovered. Roasting temperature, rather than stoichiometric ratio or leaching temperature, was the most important factor affecting potassium recovery. X-ray analysis revealed that the residue from leaching contained up to 80% Al2O3, plus unleached K and the Si present in the ore. A preliminary thermal study showed that the amount of SO3 driven off was limited largely by the reaction with K2CO3. The process would allow the treatment of alunite-polluted kaolin ores without the evolution of SO3, to give a residue suitable for use in the ceramics industry.
Roasting alunite, KAl3(SO4)2(OH)6, with K2CO3 leads to the formation of K2SO4, thus reducing the amount of pollutant SO3. When a mixture of K2CO3 and alunite with a stoichiometric ratio of 1:5 was roasted at 900 degrees C and the residue leached at 100 degrees C, 80% of the K2SO4 formed was recovered. Roasting temperature, rather than stoichiometric ratio or leaching temperature, was the most important factor affecting potassium recovery. X-ray analysis revealed that the residue from leaching contained up to 80% Al2O3, plus unleached K and the Si present in the ore. A preliminary thermal study showed that the amount of SO3 driven off was limited largely by the reaction with K2CO3. The process would allow the treatment of alunite-polluted kaolin ores without the evolution of SO3, to give a residue suitable for use in the ceramics industry.