Sulfuric Acid and Ammonium Sulfate Leaching of Alumina from Lampang Clay
The rapid development of the global alumina industry has led to a considerable increase in the production alumina and processing of alumina from non-bauxitic sources. Lampang clays comprise various minerals that contain about 22.70 wt% of extractable alumina. Local clay was ground, activated by calcination and treated with sulfuric acid to extract alumina. In the activation step, the effects of temperature and time on the extraction of alumina and iron were investigated. The leaching experiments were performed on clay samples with particle sizes less than 200 mesh. The samples were calcined at different temperatures, ranging from 450°C to 1050°C, and for different periods, ranging from 30 to 150 min. The optimum conditions for the extraction of alumina from Lampang clay include grinding the clay to pass through a 200 mesh sieve, calcining the ground clay at 750°C for 30 min, extracting the alumina from the calcined clay by leaching with 3M sulfuric acid, and using an acid to clay ratio of 80 wt% at 100°C for 120 min. An aluminum dissolution efficiency of 95.1 % was achieved under the conditions that resulted in the maximum dissolution efficiency of iron (26.6 %).