Sulfate Removal from Alunitic Kaolin by Chemical Method

The removal of sulfate from alunitic kaolin by a chemical method, in which alunitic kaolin + potassium compound (KCl and KOH) was calcined at different temperatures and sulfate was extracted by distilled water, was studied in a batch reactor. The effects of calcination temperature, sample type, potassium compound amount, and sample preparation method on the sulfate removal were investigated. Sulfate removal yield varied with the selected parameters relative to the completion of the solid-phase reaction in which the sulfate in the alunitic kaolin was converted to soluble potassium sulfate. Maximum sulfate removal yield was obtained under the following working conditions: calcination temperature, 700 (degree)C; sample type, alunitic kaolin + KCl; potassium compound amount, 17.8% (15% more than the stoichiometric ratio); and solution phase method used for sample preparation. Maximum sulfate removal yield was 97%. By this way, the sulfate content of alunitic kaolin was decreased from 12.97% to below 1%.