Research On The Heavy Metal Pollution And Remediation Technology Of The Soil In Phosphate Tailings Area

The soil pollution is usually ignored even though soil is the relying basis forexistence and development of mankind. Currently, the type and quantity of heavymetals in tailings which penetrate into soil environment have increased gradually as thespeed and scale of mineral resources development continuously extend. The soil in thevicinity of the tailings is polluted and affected most seriously, which has threatened thesurvival of mankind. Hence, many governments and scholars have paid more and moreattention to the environmental hazards and the related repair methods of the heavymetals contaminated soil. In this paper the samples from Haikou and Jinning wereselected and researched to represent the heavy metal contamination in the entire miningarea and the nearby. The basic characteristics of the tailing samples, migration andleaching mechanism of heavy metals and remediation methods were studied andresearched, which provide reference and a new way for the remediation of other typesof soils.In this paper, physical and chemical characteristics of sample, such as moisturecontent, pH value, composition and structure, etc., were strictly and carefully tested byXRD, XRF, Atomic fluorescence spectrometry, microwave digestion, and some otherchemical detection methods. The samples, which were detected to be acidic and havesparse structure contain Zn, Cu, Pb, As, Cr, Cd and some other heavy metals. Thesecharacteristics of the samples are conducive to the migration and transformation ofheavy metals.The total content, speciation, morphology and quantitative analysis of the heavymetals in the samples were studied during the process of the experiements. The contentof zinc, cadmium and arsenic were found to be larger than the listed soil backgroundvalues in Yunnan. The available speciation proportion of Cd was highest compared withother harmful elements, followed by the ranking of Zn, which improved the feasibilityof the release and migration to some extent. The leaching toxicity value of Zn and Aswere more than that of the cited standards, which could pose a significant threat to thesurrounding environment. The value of the Cd did not exceed the standardized one, butthe potential risk can not be ignored. In order to intuitively reflect the pollution degreeof heavy metal elements, the single factor index evaluation method and Nemerowcomprehensive pollution index method were choosed to calculate the related indexes. The pollution caused by Zn, Cd and As were found to be quite serious which must begiven adequate attention.The bacteria was used to repair the contaminated soil samples and check thefeasibility of the bioremediation. The remediation test was functioned by the commonbacterium in the leaching of heavy metals, bacteria A.f. The microbes were carefullyseparated and enriched before the domestication experiment. Passivation film formedfast in the process of the experiment. So the scanning electron microscopy was used tovalidate the existence of the passivation membrane and the leaching toxicity test for thebioremediated samples was also conducted compared to the test result of the originalones. It was proved that passivation membrane can reduce the leaching of heavy metalsfrom soil samples and reduce toxicity hazard to the environment. The microbialremediation of heavy metal contaminated phosphorus tailing soil was feasible. However,this bioremediation method has its own shortcomings in view of the environmentaleffect.In order to avoid secondary pollution, the electrokinetic removal method, theso-called microbial-electrokinetic combination remediation method was designed toremove and recycle the dissolved heavy metal ions and iron ion in solution. In thispaper, the A.f bacteria domesticated pulp density was enlarged to20%and thecultivation cycle was shortened to7days, which could increase the treatment capacityof the contaminated soil at per unit time. After the test, the residue speciation proportionof soil samples have been elevated, the environment activity been reduced, and thevalue of the environment leaching toxicity also dropped to below that in basic standards.The removal rate of heavy metal was introduced to visually display hyphenatedtechnology in the effect on removal of heavy metals. It is concluded that the averageremoval rate of Zn in the soil are66.00%,31.93%and72.30%respectively based on thecalculation of three repairing methods, bioremediation, and microbial-electrokineticremediation. The average removal rate of Cd are65.29%,41.56%and65.29%, and9.63%,10.32%and25.15%separately for As. The microbial-electrokineticcombination remediation method is proved to be more suitable for the remediation ofthe contaminated soil samples than the other two methods according to the averageremove rate of heavy metals.