| More than 70% of Cu deposits in China are low grade and complex sulfide ores. The ore grades for various commodities show long-term declining trends over time. The exploitation of low grade chalcopyrite ore by traditional method was not economical. Bioleaching followed by solvent extraction (SX) and electrowinning (EW) operation has been used to extract Cu from secondary copper sulfides. However, when it was used to deal with primary copper sulfides such as chalcopyrite, the leaching rate was very low. Therefore, in order to make the bioleaching process completely successful, it needs to study the parameters that affect the microbial activity, which is critical to the bioleaching by accelerating the bioleaching process.Mechanistically based kinetic models are required for the design, optimization and control of bioleaching processes. The model of bioleaching includes direct leaching by the cells attached to the mineral surface (direct leaching mechanism), ferric leaching of sulfide minerals (indirect leaching mechanism) and leaching by both of these two mechanisms.Based on the above purpose, the main research in this work includes:1. Respirometry studies of bioleaching of low grade chalcopyrite ore using six acidophilic strainsRespirometry was used to study the growth and activity of six pure cultures of acidophilic bioleaching strains grown on a concentration series of low grade chalcopyrite ores under various pH and nutrient conditions. The oxygen consumption correlated with the amount of leached Cu during abiotic leaching of chalcopyrite, a linear correlation was found between oxygen consumption and Cu leached. The CO2 consumption rates were consistent with the cell growth rates. Therefore, it can be used as an indicator for microbial growth even with the very low grade chalcopyrite. The Sulfolobus metallicus, Acidithiobacillus ferrooxidans, Acidianus brierleyi and Leptospirillum ferriphilum were able to grow on a very low grade ore (equivalent to 0.1% Cu content). However, the two sulphur-oxidizing bacteria Acidithiobacillus caldus and Acidithiobacillus thiooxidans grew poorly on low grade ore. Growth rates of all strains, except for perhaps Sulfolobus metallicus at highest ore grades, displayed growth that was limited by substrate availability on this low grade ore.The decrease in solution pH from 3.0 to 1.0 enhanced both the cell growth and Cu dissolution. The addition of sulphur as an extra substrate resulted in slightly increased Cu extraction. Although the addition of ferrous sulphate facilitated Cu dissolution, the addition may complicate the downstream Cu recovery and may not economically feasible.2. Assess the factors that limit chalcopyrite bioleaching when using mixed bioleaching strainsThe effects of ore grade, pH, particle size and Fe2+ on chalcopyrite bioleaching using six strains under 28℃,37℃and 65℃have been investigated with an aid of Taguchi method and orthogonal arrays. The chalcopyrite bioleaching rate could be accelerated when the leaching temperature rose from 28℃to 65℃. The enhancement to leaching rate by temperature was more obviously at high temperature.The influence of the four tested experimental parameters on the Cu extraction became pronounced in the order of leaching solution pH< amounts of Fe2+ addition< chalcopyrite ore particle size< chalcopyrite ore grade.However, chalcopyrite ore particle size was the most significant effective factor on chalcopyrite bioleaching rate. The F-value was large than F0.10, which indicated that the small ore particle size could lead to high chalcopyrite leaching rate. 3. Competitive adsorption of binary mixture of Leptospirillum ferriphilum and Acidithiobacillus caldus onto pyriteThe competitive adsorption of binary mixtures of Leptospirillum ferriphilum LF-104 and Acidithiobacillus caldus MTH-04 onto pyrite surface was studied. The adsorption of pure L. ferriphilum and A. caldus, and their binary mixture onto pyrite were all in accordance with the Langmuir adsorption isotherm equation. The CAm value of the mixed culture was smaller than the sum of the combined CAm values of each species, the KA value of the binary mixture was also smaller than that of each single component, which indicated that these two bacteria had competitive adsorption sites on pyrite.Real-time quantitive PCR was used to quantify the relative amounts of L. ferriphilum and A caldus adsorbed onto the surfaces of pyrite when exposed to a mixture of these two microorganisms. The adsorption of L. ferriphilum was not affected by A. caldus. However, adsorption of A. caldus was greatly affected by the presence of L. ferriphilum. The percentages of adsorbed cells of L. ferriphilum were nearly the same for cells in the pure and binary mixture (44% and 45%, respectively), however the percentages of adsorbed A. caldus cells decreased significantly from 80% to 68% when changed from a pure culture to a culture mixed with L. ferriphilum. The decrease of absorbed cells of A. caldus (12%) indicated that some adsorption sites of A. caldus were the common or competitive adsorption sites, which were occupied preferentially by L. ferriphilum.Zeta potential measurement indicated that both bacteria were positively charged and the net electrical charge on L. ferriphilum surfaces was 3.7 times greater than the net electrical charge on A. caldus at pH 2.0. The FT-IR spectra showed the presence of CH, CH2, CH3, NH, NH2, NH3, COOH and CONH groups, which are common to any protein molecule. Zeta potential and FT-IR spectra revealed a greater amount of both positive charge and protein content on the surfaces of cells of L. ferriphilum when compared with cells of A. caldus. Besides, the greater KA value for L. ferriphilum when compared with A. caldus also revealed that the former had greater binding affinity for pyrite.4. Kinetic model for ferric leaching of sphalerite concentrate in the redox and Fe controlled reactorThe ferric leaching of zinc sulfide under controlled redox potentials (ORP) and Fe3+ concentrations was studied. An on-line monitoring system was constructed using the software programmed by Lab VIEW. A shrinking core model could be used to describe the dissolution kinetics of sphalerite concentrate in acidic ferric solution. The leaching rate constant kr was controlled by both the redox potential and the Fe3+ concentration, which indicated the present kinetic model needs improvement.Therefore, a new kinetic model for ferric leaching of zinc sulfide was proposed, the dissolution rate can be expressed by both the Fe3+/Fe2+ ratio and the Fe3+, all of the parameters in this model have been calculated by linear regression.5. Modeling and simulation of enargite bioleachingA mathematical model for enargite bioleaching at 70℃by Sulfolobus BC in shake-flasks has been constructed. The model included (1) the indirect leaching by Fe3+ and Fe3+ regeneration by suspended Sulfolobus, and (2) the direct leaching by the attached Sulfolobus.The model parameters were optimized using genetic algorithm (GA). Simulations of the ferric leaching and bioleaching processes were made using this model. The dynamic changes of concentrations of Cu2+, As3+, As5+, Fe3+ and/or Fe2+, as well as ferric-arsenate precipitation were accurately predicted.
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