Remediation Of Heavy Metals Zn,Cr And Cd In Soil By Bioleaching

With the rapid development of society and the frequent activities of human beings,a large amount of heavy metals such as chromium and cadmium have been discharged into the soil,which lead to heavy metal contaminated show and are harmful to human health.Heavy metal contaminated soil is one of the most serious environmental problems in China.At present,kinds of treatment methods have been used to remediate heavy metal contaminated soil,including electrokinetic chemical remediation technology,chemical extraction technology and phytoremediation technology.Although these technologies have some achievements in practical application,they also have some shortcomings.Electrokinetic chemical remediation technology can destroy soil ecology to a certain extent,chemical extraction technology can cause secondary pollution problems,and phytoremediation technology treatment will need more time for remediation.Bioremediation technology has the advantages of low cost,fast remediation and no secondary pollution,so it is one of the most ideal remediation methods for soil pollution.In this paper,bioleaching technology was used to remediate heavy metal contaminated farm Land and abandoned industrial sites soil.The effects of heavy metal concentration,sulfur powder addition,Thiobacillus inoculation,temperature and shaking speed on remediation were systematically studied,results showed that:（1）When inoculum amount of Thiobacillus was 7.5%,sulfur powder addition was4000 mg·kg^-1,and rotation speed of incubator was 150 r·min^-1 at 30℃,the soil pH reached the lowest value of 4.2,the leaching rate of Cr⁶⁺attained the maximum of 60%after 15 days of incubation in the soil with Cr⁶⁺concentration of 1150 mg kg^-1 and Zn²⁺concentration of 500 mg·kg^-1,while the leaching rate of Zn²⁺reached the maximum of70%in the soil with Cr⁶⁺concentration of 550 mg·kg^-1 and Zn²⁺concentration of 300mg·kg^-1.（2）The addition of sulfur powder has an important effect on remediation of Cr⁶⁺and Zn²⁺contaminated soil,the leaching rate of Zn²⁺increased with the increase of sulfur powder concentration varying from 1600-4000 mg·kg^-1.While the leaching rate of Cr⁶⁺was similar as the addition sulfur powder was in the range of 2400-4000 mg·kg^-1.（3）In Cr⁶⁺and Zn²⁺contaminated soil,the increase of Thiobacillus inoculum amount can promote the leaching rate of Zn²⁺,but the leaching rate decreased significantly during later stage of inoculation,while the leaching rate of Cr⁶⁺increased with the increase of Thiobacillus inoculation amount and became steady in the later stage of inoculation.（4）In Cr⁶⁺and Zn²⁺contaminated soil,the leaching rate of Cr⁶⁺and Zn²⁺could be significantly increased and the remediation could be enhanced by increasing the rotation speed of inoculation within a certain range.However,the leaching rate of Cr⁶⁺and Zn²⁺would decrease and the remediation would be inhibited if the temperature was too high or too low.（5）Bioleaching has limited effect on the remediation of abandoned cadmium industrial sites.When the concentration of Cd²⁺was in the range of 450-950 mg·kg^-1,the leaching rate increases with the increase of Cd²⁺concentration,and the maximum leaching rate is 35%,while the minimum leaching rate was 10%.