The corresponding XRD patterns are shown in Fig. 2. The main phases identified from Fig. 2 are presented in Table 2. The results of the calculation demonstrated that arsenopyrite was in a stable state in the original sample, and the parameters of arsenopyrite's crystal lattice were completely identical to the standard values. Ferric leaching of arsenopyrite with Fe3+ ions resulted in the formation of goethite and hydrogoethite (FeooH, FeooH nH20) on its surface; their contents were 30-40% of those of the surface compounds. Rhombic elemental sulfur (up to 10%) was also present. These results agree with the phase diagram for arsenopyrite: goethite is most likely the product of the transition of ferric hydroxide to a more stable state resulting from the air-drying of the arsenopyrite section . After the bio oxidation of arsenopyrite, the xRD pattern changed significantly compared with the original one. Although goethite (approximately 30%) was still present on the surface, the content of elemental sulfur was significantly higher (up to 50%) than in the case of chemical oxidation. The crystal structure of this sulfur was markedly different from that of the rhombic modification. It could also be observed that the arsenopyrite surface was much more oxidized than that observed in the case of its oxidation with a solution of Fe2(so4)3.9H20 reagent