Study On Application Of Bacterial Leaching In Iron-removal And Whitening Of Non-metallic Minerals

The application of biotechnology in mineral processing is the forefront research area in mining and metallurgical engineering in the 21st century, which includes the application of microbial oxidation leaching, microbial reduction leaching, metabolizing product leaching and microbial adsorption, etc. in the field of mineral processing.The microbial leaching of copper, uranium, gold, etc. has already been put into industrialized production. It is reported that over 25% of the copper is produced by microbial leaching in USA each year, and a lot of uranium ore companies are carrying out the same in Canada. In recent years, research and application of microbial leaching are under suitable development in our country. Microbial leaching technology has succeeded in application in Jiangxi Dexing Copper Mine.At present, the domestic and international research about the mineral biotechnology concentrates on the metallic ores mainly, and there is much less research in the fields of non-metallic ores. It is especially true that research about the microbial leaching of iron (Fe³⁺) in clay minerals appears very rare.This research adopts T. ferrooxidans as the bacterium source that has been collected and separated from the acid mine drainage of Jiangxi Dexing Copper Mine, and has been enriched through cultivation. The bacterium strains got vitality and relatively strong oxidizing leaching activity through taming. By this method, the relevant research focusing on removing the Fe²⁺ from kaolin system was carried out. Utilizing the pure cultivation method, the iron-reducing bacteria were obtained from the clay minerals (kaolin and mica ores). The relevant research focusing on removing Fe³⁺ from the clay minerals by these bacteria was carried out, in order to achieve the purpose of mineral purification and whitening.Studies have shown that T. ferrooxidans with high activity and uniform size can be obtained by dilution purification cultivation and enrichment cultivation. Factors such as temperature and pH value etc. have very great influence on the growth of the bactera. The purification cultivation experiments have shown that the bacteria grow best when the temperature is 30℃ and the pH value is 2.0. The taming cultivation experiments of T. ferrooxidans in the pyrite culture medium show that when pH is3.5⁴.0, the bacterial inoculating amount is 10%, temperature is 30°C, and the concentration of pyrite is 0.5%, the result of pyrite oxidation by T. ferrooxidans is the best.The experiments adopting T. ferrooxidans got by taming cultivation as leaching bacterium, and the contrastive tests between the shaking-bottle method and the recycling bio-reactor method were preformed under the same condition. The experiments show that the bacterial leaching result of kaolin by the recycling bio-reactor method is better than that by the shaking-bottle method. Through the investigation, the optimum conditions of treating kaolin of a Hubei mine have been obtained. The pH value is about 2.0, the bacterial inoculating amount is 40%, and the pulp concentration is 3%. The treatment results show that the iron-removal rate of kaolin reachs 77.4%, and the whiteness is from 72.8% up to 83.7%.Heterotrophic micpobes that can reduce Fe3+ in clay into Fe2+ can be obtained by the method of pure cultivation in artificial mineral mixture under constant temperature and anaerobic conditions. The experiments show that under the conditions of pure cultivation the activity of the heterotrophic microbes is in direct proportion to the amount of the sugar addition. The addition of hematite also has significant influence on the activity of the heterotrophic microbes. After treating the kaolin ore with the heterotrophic microbes for 30 d the rate of removal of Fe3+ in clay attained up to 0.60 mg/g clay. After treating the mica ore with the heterotrophic microbes for 15 d the rate of removal of Fe3+ in clay attained up to 66.4%. In addition, better results were achieved when treating the mica ore with the iron-reducing bacteria cultivated in the kaolin medium than that...