Study Of Separation Of Pyrite And Arsenopyrite By Bioflotation And Its Mechanism

Arsenic is a pro-sulphur element, so usually it's associated with sulfide minerals, and it's one of the main impurity elements of non-ferrous metal smelting. In addition, arsenic is very harmful to the environment and human health. Therefore it's quite necessary to lower arsenic content of sulfide ores. Usually arsenic is present in the form of arsenopyrite. Because crystal structure and surface properties of them are very similar, it is very difficult to separate arsenopyrite from pyrite. Among the separations of various metal sulfide mineral and arsenopyrite, that of pyrite and arsenopyrite is considered to be the representative one, which will provide valuable help to separate arsenic from other sulfide minerals. So the study on separation of pyrite and arsenopyrite has great theoretical and practical significance.The financial support of this paper has been provided under the research program "Separation of polymetallic sulfide ore containing arsenic from Huajing Mining Co., Ltd., Tongling". The representative pyrite and arsenopyrite were choosen to be the research object, and the separation of them was researched by bioflotation, achieving the desired results. Then, to understand the mechanism of separation of pyrite and arsenopyrite, the influence made by bacterial on the oxidation of minerals surface was analyzed. And the analysis was done by the electrochemical behavior and the scanning electron microscope of the minerals surface, through electrochemical and morphology, respectively. The main results are as follows:1. Through the tests of basic conditions of flotation of pyrite and arsenopyrite, it's found that, the separation of the two minerals can be assisted by the addition of copper sulfate and the change of slurry pH, bacterial concentration and the time of bacteria reacting with minerals.2. When the minerals were conditioned together, the recovery of pyrite increased, while that of arsenopyrite declined. Thus, the selectivity was improved, and the separation pyrite and arsenopyrite by bioflotation is feasible.3. When the mixed mineral interacting with 5.0×10′cells/mL bacterial cells for 5 min and further conditioning with 6 mg/L copper sulfate and 9.5 mg/L isopropyl xanthate, the recovery of pyrite in the floated fraction was 86.40%, while that of arsenopyrite was. 22.10%.4. Electrochemical studies show that, during the oxidation of pyrite and arsenopyrite, elemental sulfur which is favorable for flotation has been produced. Compared with pyrite, the peroxidation potential of the surface of arsenopyrite surface is relatively low. AsO43- generated for peroxidation easily forms arsenate with Fe3+ on the arsenopyrite surface. The arsenate is similar with scorodite in structure, which is hydrophilic and negative for flotation. The corrosion potential of pyrite is higher than that of arsenopyrite, so they will form a galvanic cell. The oxidation of pyrite is suppressed, whereas that of arsenopyrite is accelerated. These can explain the phenomenon mentioned in 2.5. Surface morphology observations show that, the bacteria cells can adsorb on both pyrite and arsenopyrite. The corrosion of cells on pyrite is selective, but that of cells on arsenopyrite is uniform. During the same long time, the corrosion of bacteria cells on arsenopyrite is more intense than that of cells on pyrite. These also could explain the results of the flotation of mixed mineral.