Bioleaching Remediation On The Soil At Pb/Zn Smelting Slag Site Using Penicillium Chrysogenum F1

Abstract:A large amount of slags rich in heavy metals had been produced during nonferrous smelting process. These smelting slags were directly piled and no recycling technology was used on them, thus the soil was polluted severely by heavy metals at Pb/Zn smelting slag site. Remediation on the heavy metal polluted soil is a focus in the world, especially in China. At present, chemical remediation and phytoremediation are often used to harness heavy metal polluted soil, but they own several shortcomings such as high cost, low efficiency and the possibility of secondary pollution. The characteristics of the heavy metal polluted soil, the strain's isolation and screening, and the technology and mechanism of bioleaching were studied in this paper. Some conclusions were drawn as follows:The characteristics of the soil at Pb/Zn smelting slag site were studied in this paper. It showed that the soil at Pb/Zn smelting slag site was severely polluted by heavy metals, the content of the heavy metals were as follows:1889.6mg·kg-1Pb,5682mg·kg-1Zn,48.4mg·kg-1Cd and1848.6mg·kg-1Cu, individually. According Chinese GB15618-1995, the content of Pb, Zn, Cd and Cu were5.4,18.94,80.7and18.5times as much as the secondary standard limit value. The heavy metals'spatial distribution pattern at the slag site was decreased with the increase of soil depth, and it was also decreased with the increase of the distance from the pollution sources.Based on the stress mechanism of microbes to survive in extreme environment, a fungi with the ability of heavy metal tolerance and producing organic acids was selected, it was identified as Penicillium chrysogenum (P. chrysogenum) using18S rDNA and ITS, and named as F1. P. chrysogenum F1can tolerate568mg·L-1Zn,188.9mg-L"1Pb,185mg·L-1Cu,4.8mg·L-1Cd and10.4mg-L"1Cr at the same time. The growth of P. chrysogenum F1was influenced by heavy metals and pH value. During the pH value range of5.0-9.0, P. chrysogenum F1grew normally. The growth of P. chrysogenum F1was fitted for SGompertz and Logistic model during the ratio range of0-1:13.3.A new method of two-step bioleaching was proposed. The optimization conditions of bioleaching using P. chrysogenum F1were as follows:the ratio soil to liquid of1:20, the temperature of28?, pH value of7.0,9·L-1glucose as carbon source and3g`L-1A as nitrogen source. Under the best condition, the removal percentage of Cd, Cu, Pb, Zn, Mn and Cr was74%,59%,24%,55%,57%and25%. The removal percentage by P. chrysogenum F1was better than by nitric acid, malic acid, humic acid and oxalic acid under the concentration of0.5%.The mechanism of bioleaching using P. chrysogenum F1was elaborated. The bioleaching remediation on heavy metal polluted soil at the slag site was the extraction of heavy metals by organic acids which produced by P. chrysogenum F1. During bioleaching process, glucose acid, pyruvic acid, citric acid, oxalic acid, malic acid and succinic acid were produced through the metabolism of glucose. After bioleaching process, there were many untouched extracellular polymeric substances and particles around the cell wall so that the heavy metal resistant mechanism of P. chrysogenum F1might be the interception of extracelluar polymeric substances.The regularity of the fractions'transformation of heavy metals was revealed. During bioleaching, all the fractions of Cd, Zn and Mn were extracted in ionic form, Fe-Mn oxide-bonded and organic fraction of Pb were transformed into residual fraction, Fe-Mn oxide-bonded of Cr was transformed into carbonate-bonded fraction, water-soluble fraction and ion-exchangeable fraction of Cu were transformed from Fe-Mn oxide-bonded.The regulation mechanism of glucose oxidase activity by heavy metal and pH value was found. For single metal, the inhibitory impact of Pb on extracellular glucose oxidase activity was the biggest than Cu, Cd, Mn and Cr, the activity of glucose oxidase was activated by Zn. The inhibitory impact of multi-metal was bigger than single metal. The activity of extracellular glucose oxidase was larger under acid condition than under neutral condition. P. chrysogenum F1selected from the soil at the slag site has the great potential for the remediation on heavy metal polluted soil.