| The high-grade ore and easy to handle ore is declining, environmental protection requirements continue to improve, and demand for metals is increasing. The tailings contain a lot of rare metals and nonferrous metals, the stockpiling of tailings can cause serious pollution to the water and soil environment. Rational development and utilization of the tailings has important significance in the utilization of resources and prevention of heavy metal pollution. At present, it is effective to use the hydrometallurgical and pyrometallurgical processes to treat the metal tailings, but they have high energy consumption and cost, and it is easy to cause secondary pollution. However, bioleaching is relatively low cost, high safety, simple to operate, and environmentally friendly.Therefore, the research on bioleaching of sulfide tailings has great significance, which can provide a new way for the comprehensive utilization of tailings.In this paper, the bioleaching process of lead-zinc sulfide mine tailings was studied.The growth activity and kinetics of the Acidithiobacillus ferrooxidans (A.f) were studied.Then, the influence of different factors on the bioleaching lead-zinc sulfide tailings was studied. The optimum bioleaching conditions were determined, and the kinetics of bioleaching was deduced. At the same time, the bioleaching shaking flask experiment was verified by the scale-up experiment. Based on the optimum bioleaching conditions,the effects of heavy metals speciation, mineral phase and surface morphology during the bioleaching process were studied, and the extracellular polymeric substances (EPS)matrix plays a roles of bioleaching were studied. In the end, Pb in bioleaching tailings residue was recovered by brine leaching, and the metal in the leaching solution was recovered and removed by sodium sulfide precipitation.(1) The effect of the different initial pH, Cu2+ and Zn2+ concentration on the activity of the growth of A. f was investigated, and the bacterial growth curves, bacteria concentration, pH, Fe2+ and oxidation-reduction potential in the culture solution were obtained. When initial pH was too high (3.0) or low (1.0), the growth activity of bacteria was greatly inhibited. Only in pH 2.0, A. f can grow rapidly in a suitable growing environment. A. f is tolerant to Cu2+ and Zn2+ some extent. With the increase of Cu2+ and Zn2+, the inhibitory effect of the growth activity of A.f was also increased. When c(Cu2+)?0.5 g/L, little effect on the growth activity of A. f is brought to Cu2+. When c(Cu2+) is 1.0-2.0 g/L, the growth activity of A.f were obviously influenced by Cu2+ and appeared to delayed effects. When c(Cu2+) is over 3.5 g/L, the growth and activity of A. f are completely inhibited. When c(Zn2+)?20 g/L, little effect on the growth activity of A.f is brought to Zn2+. When c(Zn2+) is 30 g/L, the growth and activity of A. f were obviously influenced by Zn2+.Based on the model of Monod function, the growth kinetics equation of A. f at differelt Cu2+ and Zn2+ was built up. The correlation of kinetic curve is better,which showed that the kinetics equation could well describe the growth of A. f at different initial Cu2+ and Zn2+.(2) Study on the bioleaching of heavy metals in lead-zinc mine tailings at different initial pH and pulp density using A. f, and the transformation in the speciation of heavy metals, mineral phase and surface morphology during the bioleaching is helpful to understand the bioleaching process. The impact of different parameters was studied,including the effects of initial pH (1.5-3.0) and solid concentration (5-20%) for bioleaching. The optimum conditions of bioleaching were obtained (pH 2.0 and 5% pulp density). The results showed that the bioleaching strongly affected pH and the recovery efficiencies of heavy metals. With increasing initail pH and pulp density in the bioleaching, the pH value decrease rate and the bioleaching rate of heavy metals increased first and then decreased. 80.00% of Cu, 85.45% of Fe, 4.12% of Pb and 97.85% of Zn were recovered from mine tailings at the optimum condition of 50 g/L pulp density and initial pH 2.0. The analysis of BCR, XRD and SEM indicated that the bioleaching had a significant impact on changes in the speciation of heavy metals,mineral phase and surface morphology. In the bioleaching process, the transformation in the metal speciations, mineral phase and surface morphology were a gradual process over time. First, the mobile fractions of the heavy metals were bioleached, and then the stabile fractions of heavy metals were gradually bioleached. Sphalerite (ZnS) and pyrite(FeS2) decreased significantly during bioleaching, and a large number of two minerals were produced. Surface morphology presented an abundance of voids. More secondary minerals appeared around the deep alteration zones and voids.(3)The adsorption of A. f on the mineral surface and the mechanism of the EPS matrix were studied. According to the optimal conditions of bioleaching, the adsorption capacity of bacteria, the polysaccharide, protein and TOC in different EPS fractions were studied. With the increase of bioleaching time, the contents of TOC, polysaccharide,protein in TB-EPS and LB-EPS and the adsorption of bacteria changed with the different stages of bioleaching. Three dimensional fluorescence spectra showed that the composition of the TB-EPS fractions was constantly changing, and the bioleaching mainly occurred in the TB-EPS layer. During bioleaching, abundant humic substances were produced in EPS, humic substances and extracellular enzymes formed stable complexes. Meanwhile the humic substances could decrease the toxicity of metal ions by complexation. Large amounts of tryptophan protein are also produced in EPS. The trend of increase and decrease of humic substances and tryptophan protein was consistent.They may form complexes to promote bioleaching.(4)The process for leaching Pb from bioleached residue by brine leaching, and recovery and removal metal from leaching solution by sulfide precipitation were investigated. The leaching efficiency of Pb was directly proportional to NaCl concentration in brine leaching, which was inversely proportional to pulp density, and the effect of leaching time on the leaching rate of Pb is very slight. The dosage of sodium sulfide was proportional to the precipitation rate during the leaching process. More than 84% of the lead was extracted from the bioleaching residues at a 150 g/L sodium chloride concentration. Pb concentrate was quantitatively produced from the brine leaching solution by adding sodium sulfide as precipitant. Optimum conditions of Pb precipitation were found to be 0.6g/L Na2S, and the precipitation rate of Pb was 99.92%. |
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