Studies On Moderate Thermophile Intensifying Pentlandite Leaching

A moderately thermophilic acidophilic facultative chemoautotrophic bacterium, Sulfobacillus thermosulfidooxidans is strictly aerobic, optimum growth at 50癈0 Autotrophic growth occurs with ferrous iron and mineral sulfides as substrates. It grows heterotrophicly on yeast extract. It can oxidize elemental sulfur in the presence of yeast extract and easily grows in mixotrophic condition. It plays important role in metal sulfide ore leaching.In this paper, on the basis of determining growth curve of Sulfobacillus thermosulfidooxidans, with bacterial growth being expressed by the oxidation of ferrous iron, the effect of initial pH, bacterial inoculation amount and ferrous iron concentration on bacterial growth and ferrous iron oxidation was investigated. Experimental results showed that initial pH 1.6, inoculation amount 10% and ferrous iron concentration 50~100mM/l was suitable for bacterial growth and ferrous iron oxidation in mixotrophic conditions.Thermodynamic and electrochemistry analysis show that pentlandite nature is lively. It can be carried out simply acid dissolution. Single mineral leaching experiment confirmed that pentlandite spontaneously decomposed in acid medium but it leached slowly. After 8 days it only leached 12.48% of nickel. The existence of bacterium has strengthened pentlandite leaching course, under the condition of adding yeast extract leaching rate of nickel reached 63.67%, the leaching rate raised 55.63% comparing sterile control. In the course of leaching pentlandite with S.t, mineral pulp pH, bacterial inoculation amount, solid loading and dose of yeast extract is the major factor which influences nickel leaching rate. Since in bacterial leaching systemhaving plenty of NH4+, H+, K+, SO 4", as leaching course going on, ferric ion producedfrom pentlandite dissolving easily reacts with above-mentioned ion and forms jarosite which covers mineral surface and prevents leaching continue. X - ray diffraction analysis confirmed that in the course of bacterial leaching this kind of precipitate definitely generated. S.t is able to reduce ferric iron and grows in anaerobic media with ferric iron in the jarositic surface precipitate as a terminal electron accepter.When precipitate quantity is lost comparatively jarosite is decomposed by S.t and its effect on bacterial leaching is not significant. It was found that the jarosite was not completely removed thus it should reduce this kind of precipitate produce as far as possible in the course of bioleaching.Through designing experiment, mechanism of pentlandite leaching with S.t has been studied. Research showed that bacterial direct erosion, ferric chemical oxidation and acid leaching at the same time occured in the course of leaching pure pentlandite, in which bacterial direct mechanism was dominant while acid and ferric chemical leaching was not important. Bacterial SEM photograph confirmed that bacteria strongly attached to the mineral surface in the course of leaching and the attachment of bacteria to mineral had selectivity, bacteria mostly attached to crack and defect of mineral. The change of mineral surface showed that after pentlandite bioleaching it had been seriously eroded.Thermodynamic and electrochemistry analysis showed that galvanic interactions existed in mixed sulfides bioleaching. In experiment it was found that adding pyrite to bacterial leaching system accelerated pentlandite leaching. The observation of pentlandite - pyrite mixed mineral surface and X - ray diffraction analysis results demonstrated that pentlandite dissolved priorly while pyrite was protected as cathode in bioleaching.Using nickel concentrates, actual mineral bioleaching was carried out. Experimental results showed that Jinchuan nickel concentrate was easy to leach. Under sterile control, the leaching rate at pulp density 2%, 5% and 10% were 53.06%, 47% and 35.78% respectively. In the presence of bacteria leaching effect was accelerated. Adding yeast extract the leaching effect was improved further. For solid loading of 2% the bioleachin...