OXIDATIVE DISSOLUTION OF ARSENOPYRITE BY MESOPHILIC AND MODERATELY THERMOPHILIC ACIDOPHILES

The purpose of this work was to determine solution- and solid-phase ch anges associated with the oxidative leaching of arsenopyrite (FeAsS) b y Thiobacillus ferrooxidans and a moderately thermoacidophilic mixed c ulture. Jarosite [KFe3(SO4)(2)(OH)(6)], elemental sulfur (S-0), and am orphous ferric arsenate were detected by X-ray diffraction as solid-ph ase products. The oxidation was not a strongly acid-producing reaction and was accompanied by a relatively low redox level. The X-ray diffra ction lines of jarosite increased considerably when ferrous sulfate wa s used as an additional substrate for T. ferrooxidans. A moderately th ermoacidophilic mixed culture oxidized arsenopyrite faster at 45 degre es C than did T. ferrooxidans at 22 degrees C, and the oxidation,vas a ccompanied by a nearly stoichiometric release of Fe and As. The redox potential was initially low but subsequently increased during arsenopy rite oxidation by the thermoacidophiles. Jarosite, S-0, and amorphous ferric arsenate were also formed under these conditions.