The data shown in the phase diagram for arsenopynte over the course of biooxidation (Fig. 1) suggest that at the values of pH and Eh typical of deep biooxidation, arsenopyrite is thermodynami- unstable and transforms into compounds with the highest of the element. The polysulfide mechanism of arsenopyrite oxidation under these conditions is not probable. However, the thermodynamic probability of oxidation is realized to the degree determined by the kinetic conditions. Investigation of the biooxidation mechanism requires the study of the phase composition of the mineral surface under different conditions of oxidation and com- parison with the data obtained from the thermodynamic analysis. The phase composition of the surface of arsenopyrite was deter mined using X-ray phase analysis. Three samples were analyzed: the original arsenopyrite section, the arsenopyrite section after oxidation with Fe ions obtained by the dissolution of Fez(so4)3 .9H20, and the arsenopyrite section obtained after biooxidation in the presence of Fe3+ ions resulting from the microbial oxidation of Fe2 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 ofarse- nopyrite with Fe3+ ions resulted in the formation of goethite and hydrogoethite (FeooH, Fe00H 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 (Gorelik et al. 1970). After the biooxidation of arsenopyrite, the xRDpattern changed sig nificantly compared with the original one. Although goethite (approxi- mately 30%) was still present on the surface, the content of elemental sulfur was significantly higher (up to 50x) 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
The data shown in the phase diagram for arsenopynte over the course of biooxidation (Fig. 1) suggest that at the values of pH and Eh typical of deep biooxidation, arsenopyrite is thermodynami- unstable and transforms into compounds with the highest of the element. The polysulfide mechanism of arsenopyrite oxidation under these conditions is not probable. However, the thermodynamic probability of oxidation is realized to the degree determined by the kinetic conditions. Investigation of the biooxidation mechanism requires the study of the phase composition of the mineral surface under different conditions of oxidation and com- parison with the data obtained from the thermodynamic analysis. The phase composition of the surface of arsenopyrite was deter mined using X-ray phase analysis. Three samples were analyzed: the original arsenopyrite section, the arsenopyrite section after oxidation with Fe ions obtained by the dissolution of Fez(so4)3 .9H20, and the arsenopyrite section obtained after biooxidation in the presence of Fe3+ ions resulting from the microbial oxidation of Fe2 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 ofarse- nopyrite with Fe3+ ions resulted in the formation of goethite and hydrogoethite (FeooH, Fe00H 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 (Gorelik et al. 1970). After the biooxidation of arsenopyrite, the xRDpattern changed sig nificantly compared with the original one. Although goethite (approxi- mately 30%) was still present on the surface, the content of elemental sulfur was significantly higher (up to 50x) 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
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