Sulfuric acid leaching of South African chromite. Part 2: optimization of leaching conditions

The effects of temperature, duration, sulfuric acid concentration and oxidant on the leaching of South African chromite were investigated in this work. It was found that the extraction yield of chromium increased with temperature, limited by a chromium-rich sulfate precipitating from the solution when the temperature became too high, resulting in the decline of chromium recovery. The spinet phase of the ore shrank while the extraction yield of chromium increased with the duration of the leaching, leveling out after 60 min. A porous amorphous silica phase was obtained as the metal elements leached and the spinet phase flaked, creating a resistance for the dissolution of the inner spinet phase. The results also showed that the sulfuric acid concentration and oxidant have a marked influence on the extraction yield of chromium and on the leaching reaction rate, and the best results were obtained for 80%-wt sulfuric add and an oxidant/chromite (mass) ratio oxidant above 1/10. The extraction yield of chromium was improved by the employment of agitation, and 1800 rad s(-1) was the reasonable speed. (C) 2014 Elsevier B.V. All rights reserved.