Characteristics of product layer and effects of sulfur-bearing ions on pyrite leaching in sodium aluminate solutions

Abstract

During the utilization of high-sulfur bauxite by the Bayer process, the pyrite will react with sodium aluminate solution and generate various sulfur-bearing ions, however, the effect of these ions on pyrite leaching is seldom studied. This work clarifies the reaction mechanism of pyrite in various sulfur-bearing sodium aluminate solutions by characterizing electrochemistry and the product layers. The results show that the sulfur leaching efficiency are 48.0, 56.2, 23.1, 90.6 and 58.3 % in sulfur-free, S2-, S2O32-, SO32- and SO42--bearing sodium aluminate solutions at 260 °C for 40 min, respectively. With the disproportionation of S2O32- and accumulation of products, a dense sulfur-rich layer formed on the surface of pyrite retards the diffusion of sulfur into solution. However, the presence of SO32- can catalyze the transformation of pyrite into hematite plates, forming a loose layer which accelerates the diffusion of S2- and S2O32- into solution. In the presence of S2- and SO42-, the formation of easily removed products from surface slightly promote the reaction between pyrite and sodium aluminate solution.