Studies On Moderate Thermophile(S.thermosulfidooxidans) Leaching Chalcopyrite

Moderate thermophilic bacteria is concurrently autotrophic bacteria, able to withstand higher temperatures and has a strong cell wall. Comparing to mesophilic bacteria and thermophilic archaea its biological properties is unparalleled.The bacteria used in this paper are S.thermosulfidooxidans and A.ferrooxidans. The effect of many factors, such as temperature, pH, the concentration of copper ion, on the bacteria growth and the oxidation activity of ferrous ion and surphur were investigated. And then the differences of chalcopyrite bioleaching by S.thermosulfidooxidans and A.ferrooxidan were studied, meanwhing the interaction of factors which have an effect on the bioleaching of chalcopyrite was investigated. Then flask leaching and column leaching tests of sulphide copper ore were carried out in order to study the superiority of S.thermosulfidooxidans. Finally the dissolution machanism of chalcopyrite was studied by electrochemical methods, SEM, X-Ray diffraction.The bacteria growth and oxidation activity of ferrous ion and surphur were investigated. It was indicated that the bacteria grew best and its oxidation activities of ferrous ion and surphur were highest when the particle size was-0.038mm, the temperature was 50℃and the pH value was 1.6, otherwise bacterial growth and oxidation activity were intensively inhibited. The research also showed that The tolerance of S.thermosulfidooxidans to copper ion reached to 2g/L much higher than that of A.ferrooxidans, which will help S.thermosulfidooxidans adapt to high concentration leaching of sulphide copper ore.The dissolution behavior of chalcopyrite was determined by the crystal structure. The semiconductor electrochemical investigation demonstrated that chalcopyrite was oxidized by the transfer of holes between semiconductor and solution surface in initial, and the electron transfer in succession. In presence of bacteria, the corrosion current was higher than that in bacteria being absent, and the dissolution rate of chalcopyrite tend to increase with the increase of holes number and transport velocity.The decomposition process of chalcopyrite was analyzed using Eh-pH diagram of CuFeS2-H2O system. It showed that intermediate, CusFeS4, CuS, Cu2S, accrue and the transformation of CuFeS2→CuS→Cu2+ or CuFeS2→Cu5FeS4→Cu2S→CuS→Cu2+ may exist in chalcopyrite decomposition process. Preferential dissolution of Fe2+ than Cu2+ was demonstrated. In actual leaching systems, there might be the presence of sulfur and Fe3+ might exist primarily in the form of precipitation of iron hydroxide.The bioleaching of chalcopyrite were conducted to research the leaching behaviors of chalcopyrite. It indicated that S.thermosulfidooxidans with stong adaptability had better performance on the leaching of chalcopyrite than A.ferrooxidans. For 30 days of bioleaching the copper extraction yield by S.thermosulfidooxidans was 92.53% much higher than that by A.ferrooxidans which was just 52.36%. It was made clear that copper dissolution was affected by the particle size, pulp density, pH value and inoculum size. The bioleaching rates of chalcopyrite reached the highest with the particle size of-0.038mm, pulp density of 2%, pH value of 1.6, inoculum size of 5%.The bioleaching of sulphide copper ore were carried out in flask and column to study the superiority of S.thermosulfidooxidans. It showed that copper extraction rate increased rapidly in prior period of bioleaching, however it slowed gradually in later period because of jarosite and(or) suphur precipitating on the ore surface. The copper extraction yield in flask reached 92.53% for 30 days of bioleaching, and that in column was 55.27% for 70 days of bioleaching. The low potential which ranging from 400mV to 430mV was also found in the bioleaching processChalcopyrite surface SEM graph of before and after leaching shows that when in sterile, chemical oxidation of chalcopyrite occurred in lattice defects or cracks, however the surface of chalcopyrite has been severe corrosion with inoculum.It was showed that not only bacterial direct effect but also bacterial indirect effect occured in the bioleaching of chalcopyrite by S.thermosulfidooxidans, the bacteria feeded on chalcopyrite, and the potential kept low. It has been indicated by previous research results that chalcopyrite will be converted into chalcocite, covelline at low potential, due to electron transfer or the reduction of Fe2+, therefore, maintaining a low potential in leaching system will benefit bacterial leaching of chalcopyrite.The data of residues'SEM graphs and X-Ray diffraction patterns showed that chalcopyrite surface was corrupted by both S.thermosulfidooxidans and A.ferrooxidans and a layer formed on it. The layer leached by S.thermosulfidooxidans were jarasite and sulphur, but the layer leached by A.ferrooxidans was just sulphur.