| Vanadium pentoxide reserves in Panzhihua mining area of Sichuan province account for about 62% of the national reserves of vanadium.It is known that the vanadium compounds are of moderate or high toxicity and the vanadium in the environment could enter into soils by a series of behaviors,such as transportation and transformation,which in turn affects human llife.Therefore,it is urgent to study on the spatial distribution of vanadium in the Panzhihua mining area and analyse its ecological and environmental effects.The development of bioremediation based on indigenous microorganisms in soil is of practical significance.The results from the analysis of soil samples collected from five different vanadium manufacturing locations in Panzhihua mining area showed that the contents of vanadium in all soil samples were significantly exceeded the soil vanadium background value(82.4 mg/kg)in China.Remarkably,the vanadium content of ordinary soil in smelting area reached up to 4793.6 mg/kg,which indicated that the surface soils of Panzhihua mining area were contaminated with varying degrees of vanadium.The results by the analysis of high-throughput sequencing technology showed that the genera such as Trichococcus,Zoogloea and Comamonas were relatively abundant in bacterial community,and Ascomycota with high abundance was the widespread fungus in all soil samples.Redundancy analysis showed that organic matter,available phosphorus and available sulfur were the main environmental factors that affected soil bacterial community,and the presence of vanadium promoted the changes of bacterial community structures.After 240 days of domestication,the main format of vanadium in ordinary soil samples was changed from residual fraction to acid-extractable,reducible and oxidized fractions with strong activity.The results of gene sequencing showed that the long-term cultivation with vanadium changed the community structures of bacteria and fungi in soils,and the community structures of bacteria converged to similar one,which mainly composed by Actinobacteria,Proteobacteria and Acidobacteria.Some of the bacteria and some fungi enriched in soils had shown the ability to reduce or tolerate heavy metals such as vanadium,such as Arthrobacter sp.had exhibited a superior Cr(VI)removal capability,and Aspergillus niger and Penicillium simplicissimum could recover vanadium from the converter slag.The efficiencies of vanadium(V)reduction(initial concentration: 75 mg/L)were higher than 60% after 3 days operation,indicating the potential ability of microorganism to repair vanadium contaminated soil.The chemical leaching technology was used as the pretrement method of vanadium contaminated soil,and nine kinds common eluent,such as hydrochloric acid,oxalic acid and EDTA,were selected.The leaching experiments were carried out in a single rinse,compound rinse and mixed dilution plus leaching.Results showed that oxalic acid(0.50 mol/L)was the most economical and practical single eluent,and the removal rate of vanadium in the smelting farmland soil was 26.0% after 12 hours of leaching.The removal efficiency of vanadium in acid extracted,reducible and oxidizable fractions was as high as 96.8%.The long-term acclimated indigenous microorganism removed exceeded 90% of the total vanadium in the oxalic acid eluent after 12 h operation,which resulted in the removal of vanadium from soils and the recovery of tetravalent vanadium through spontaneous precipitated.This study has promoted the understanding about the status of environmental pollution and ecological effects of vanadium,and developed a cost-effective means of ex-site remediation for vanadium-contaminated soils,which provides a new idea for the effective repair of such contaminated sites. |
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