| Tailings are a kind of solid waste, which are remained by crushing and flotation of mineral. At present, China’s stock of tailings has reached 80 billion tons, And the number is still growing, Long time storage of tailings brought a series of environmental pollution problems, such as contaminations of soil and water. Contanimation of tailings has become one of important issues facing during the sustainable development of our country and the world. This paper took Pb-Zn tailings A and its surrounding soil of Xinjiang Yili Kazak Autonomous Prefecture as the research object, To determine the contents of Cu, Pb, Zn, Cd, Ni, Cr in Pb-Zn tailings and soils by using electric heating plate and microwave digestion ICP-OES method. Speciation extraction of heavy metals from samples by using modified BCR method. leaching experiments of heavy metals in Pb-Zn tailings were carried out by using TCLP leaching method. environmental risks of heavy metals were evaluated, and discussed the influences of leaching of heavy metals in Pb-Zn tailings, which were carried out under the conditions of different pH values, salinities of leaching agents and tailings samples in different size,In this paper,Influencial factors analization of heavy metals were carried out for tailings A and tailings B.The main research results of this paper are as follows:Main research conclusions of Pb-Zn tailings:(1) Contents of heavy metals:The content of heavy metals is a layer distribution. Contents of Pb, Cd, Cu, Ni in the lower tailings samples were larger than those in the surface tailings, and contents of Zn and Cr in surface tailings were larger than those in the lower tailings in some samples.(2)Speciation distributions of heavy metals:Different heavy metals showed different speciation, migration and transformation capacities, Heavy metals in acid extractable/exchangeable and reducible fractions were easier to be leached, which becomes the threat to the environment.Zn, Cd, Cu, Cr in Pb-Zn tailings were mainly existed in residual fraction, migration and transformation capacity of which were low, Pb mainly existed in acid extractable/exchangeable fraction, migration and transformation ability of which was higher. heavy metals in the lower tailings were more stable than those in the surface tailings, The proportion of Pb, Zn, Cd in acid extractable/exchangeable fraction in surface tailings were higher than those in the lower tailings, and Cd, Zn and Pb in surface tailings were more easily to be released.(3)Leaching characteristicsof heavy metals: leaching rates of heavy metals in Pb-Zn tailings were different, and heavy metals in the surface tailings were more easily to be released. Leaching rates order of heavy metals in surface tailings was Pb>Cd>Zn>Cu>Cr, Leaching rates order of heavy metals in lower tailings was Pb>Cd>Cu>Zn>Cr, Pb in tailings was the easiest one to be leached, and Cr was the most difficult one to be leached. leaching concentrations of heavy metals in lower tailings were larger than those in surface tailings. leaching rates of Zn, Cd, Cu in surface tailings were larger than those in lower tailings, leaching rate of Pb was little difference compared to leaching rates of Cr. Leaching concentrations of Zn, Pb, Cd exceeded standards, but Cu and Cr didn’t.(4)Leaching influencial factors of heavy metals: heavy metals in Pb-Zn tailings showed different leaching patterns under different environmental impact factors. Heavy metals in tailings were more easier to leach in the acidic environment. With the pH values of extraction reagent changed, leaching concentrations of Pb, Zn, Cu changed larger, leachig rates of Ni and Cr changed smoothly. leaching concentrations of heavy metals in tailings varies with the change of the salinities, In tailings A, the leaching concentration of Cr decreased with the increase of salinity, leaching concentrations of Zn and Pb increased with the increase of salinity, and the effect of salinity change on the Ni and Cu leaching was not obvious. In tailings B, the leaching concentration of Zn decreased with the increase of salinity, leaching concentrations of Pb and Cu increased with the increase of salinity, and the effect of salinity change on the Cr and Ni leaching was not obvious.acidic leaching reagent with NaCl, was good for reducing leaching toxicity of heavy metals in Pb-Zn tailings. For Cr and Ni, salinity and pH values of leaching reagent were higher, the toxicity was lower. For Cu and Pb, salinity of leaching reagent was lower, pH value was higher, toxicity was lower. For Zn, In tailings A, pH value of leaching reagent was higher, salinity was lower, toxicity was lower, In tailings B, pH value and salinity of leaching reagent were higher, toxicity was lower. The effect of particle size change on the leaching of heavy metals was also different, Particle sizes change of Pb-Zn tailings samples had little effect on leaching concentrations of Cr, Ni, Cu, leaching rates of Zn and Pb increased with the decrease of particle sizes.Main research conclusions of soils around Pb-Zn tailings reservoir:(1) Contents of heavy metals:Heavy metals in the surface and profile soil existed different degrees of pollution, and Pb was the most polluted. contents of heavy metals were larger than regional background values, except Ni, Cr of pollution profiles. Content of Pb was two times larger than regional background. contents of heavy metals in the pollution profiles were vertically uniform, pollution had spreaded to 1 m.(2) Speciation distributions of heavy metals: heavy metals were all mainly existed in the fraction of residue, compared with surface soils, heavy metals in the middle and lower soils of pollution profiles were more stable.(3) Ecological environment risk assessment of heavy metals:The risks of heavy metals to the environment are different, Pb showed much more serious environmental risk. Zn,Ni,Cu,Cr existed low risk in the surface or profile soils, Pb existed medium risk in some sites, It is necessary to keep an eye on environmental risk of Pb.Thus, On the basis of this study, It provided basic data and scientific basis for the risk assessment and remediation of heavy metals pollution, and also provided references for the environmental management of tailings reservoir. |
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