BIO-STABILIZATION OF ARSENIC IN SOLID WASTES OBTAINED BY LIME TREATMENT OF BIOLEACHING LIQUORS

The feasibility of biological stabilization of arsenic-containing bioleach liquors was evaluated at laboratory scale. The principle of the proposed process is to oxidize the As(III) present in the liquor using As(III)-oxidizing bacteria, in order to obtain a final solid residue containing mainly the more stable As(V) form. An As(III)-oxidizing consortium named CAsO1, selected by BRGM, was used to perform experiments with real liquors from bioleaching of gold-bearing concentrates. In a first experiment, it was decided to increase the pH of the liquor and incubate the resulting solids with CAsO1. Ca(OH)2 was used to increase pH. Two pH values were chosen: pH 4 and pH 7. Significant differences were observed between inoculated and not inoculated systems at pH 4, but not at pH 7. The more stable solids were obtained at pH 4 in the inoculated systems and the As(III) concentration in the solids was 40 % lower in the inoculated than in the not inoculated systems. At pH 7, the solids phases of inoculated and not inoculated systems were not significantly different. In a second experiment, bacteria were injected directly in the reactor used for lime treatment, during the course of iron precipitation. This biological treatment allowed to decrease the As(III)/As(V) ratio in the resulting solids by 70%. 1