Technical Research On Leaching Heavy Metals From Copper Mine Tailings By Acidithiobacillus Ferrooxidans

The copper mine tailings containing heavy metals and toxic nonmetals would contaminate the soils and waters once these elements were released into environment, and then damaging the population health that will cause the environmental safety acc-ident. The bioleaching are widely used in metals extracting from low-grade ore as a gre-en technology, but the application on mine tailings is still in inchoate stage. This paper took advantage of the feature that the bioleaching could accelerate the release of toxic elements of mine tailings to harmlessly dispose the tailings for finding the applicable method of resolving the mine tailings environmental safety problem completely.This research was concerned with the bioleaching of copper mine tailings from a copper mine in Yunnan by Acidithiobacillus ferrooxidans. By characterization analysis of the tailings samples, isolation and purification of Acidithiobacillus ferrooxidans from an abandoned mine in Chongqing, shake flasks bioleaching tests at1%,5%and15%pulp density, the bioleaching tests in the self-made gas-solid-liquid internal recycle bio-reactor, the tests on effects of SDS, citric acid and oxalic acid on bioleaching of the copper mine tailings by ATCC23270, the following results were obtained:①The ave-rage diameter, median diameter, modal diameter and surface area of mine tailings were8.30μm,12.96μm,12.49μm and0.688m2/g separately. The main elemental composi-tion was that Si=250.35mg/g, Fe=141.9mg/g, Al=82.2mg/g, Ca=71.7mg/g, S=66.7mg/g, Cu=3.5mg/g, Mn=2.4mg/g, As=1.2mg/g and Cd=0.064mg/g. The main mineral composition of the mine tailings was consist of quartz and calciocopiapite, and the schematic of crystal structure about mine tailings was generated by VESTA.②The effect of bioleaching at1%pulp density was the best one among the3kind of pulp density and the sterile test, and the leaching rates of Fe and Cu were14.13%and18.96%separately.③The leaching tests by reactor showed that the leaching rate of1%pulp density bioleaching was the largest. The final leaching rates of Cu, Fe, Zn and Cd were19.14%,13.86%,76.28%and43.44%, but the bioleaching rate of As was less than sterile leaching, this is because that there was a lot of Fe3+in the solution resulting in the generation of FeAsO4sedimen.④The SDS had obvious inhibiting effect on bio-leaching. When the concentration of SDS was lOppm, the bacterial activity was suppressed completely. The citric acid and oxalic acid also suppressed the bacteria, but it couldn’t ignore that they were able to leaching the mine tailings as organic acid resulting in the better leaching rates.According to the results of above tests, it can be concluded that:①The contents of Fe and S were higher, and the Fe and S were just the important elements which were the sources of nutrition and energy. The metal atoms were wrapped up by the tetrahedral structure of quartz and complicated polyhedron structure of calciocopiapite that made the leaching of elements difficult.②In acid condition(pH<3.00), the Acidithiobacillus ferrooxidans accelerated the leaching of Fe and Cu.③The reactor maintained the optimum condition of bioleaching by controlling the aeration and generating the3phase internal recycle that made the final leaching rate not so far different from that of the sha-ke flasks tests.④The mechanism of SDS inhibition on bioleaching was that the SDS bond with the lipid and protein resulting in dissolving of cell wall and then the cell died. The citric acid and oxalic acid also inhibited the bacteria, but the chemical leaching eff-ect of organic acid made up for the weakness. They accelerated the dissolving of mine tailings by protonation on surface of tailings and chelation of metal ions. The mecha-nism of organic acid inhibition on bacteria was that the organic acid entered into cytop-lasm through cell wall and released the protons which destroyed the balance of pH. As a result, the cell function was damaged.⑤This paper set up a series of mathematical mo-dels by learning some sulfide mineral bioleaching models and improving them base on experimental condition and characteristic, and the model calculated results were in agr-eement with the experimental data.The final experimental results had almost reached the anticipated targets. The Aci-dithiobacillus ferrooxidans was able to leaching the metals and toxic nonmetal elements effectively that significantly reduced the environmental safety risk. It must be careful to choose the bioleaching technology on mine tailings which used the SDS as beneficia-tion reagent. The organic acid suppressed the bacteria, but the final leaching rates incr-easeed as the effect of acid leaching. The results of bioreactor were similar with that of shake flasks that demonstrated the leaching rate was stable with the reactingdose incr-easing, so the bioleaching of mine tailings will be applied in practice in the near future. This research enhanced the understanding of the mine tailings physical and chemical structure, and considered actual situation to affect the bioleaching, it’s important to resolve the environmental safety problem of copper mine tailings by bioleaching.