Research On Extract Remediation Technology Of Mercury Contaminated Soils

Mercury is the only liquid metal at room temperature, widely distributes in nature. Mercury and its compounds are widely used in chemical industry, metallurgy, electronics, instrumentation, medical, military and other fields. In the production, transportation, storage and waste disposal links, the serious unexpected environmental pollution accidents which are caused by the leakage or explosion of mercury and its compounds occurred at times, and comparing with the general environmental pollution incidents, the serious unexpected environmental pollution accidents caused by heavy metals have the characteristics of intensity pollution, rapidly spreading and difficultly repairing, in order to quickly solve the hazards problem of pollution accident, it is necessary to take effective rehabilitation measures.In this paper, the artificial mercury pollution soil sample 1 (silty clay) and soil sample 2 (silt) were studyed. Through carrying out the tests of selecting extraction medias, optimizing extraction conditions, analysising mercury species in soils before and after extracted and testing leaching toxicity of extracted soil, draw the following conclusions:(1)The mercury in tested soils could be effectively removed by Na2S2O3 solution.For soil sample 1, the best extractionconditions were :concentration 0.1mol·L-1, soil-liquid ratio 1:6, extraction time 12 h, when the concentration of mercury in contaminated soil was 107.86 mg/kg, the extraction efficiency was 65.32%. For soil sample 2, the best extractionconditions were:concentration 0.01mol·L-1, soil-liquid ratio 1:6, extraction time 6 h, when the concentration of mercury in contaminated soil was 124.35 mg/kg, the extraction efficiency was 82.03%.(2)Na2S2O3 solution could significantly remove the bioavailability form and the potential bioavailability form of mercury in two tested soils, and thereby greatly reduce the bioavailability of mercury in two tested soils. Before extraction, mercury of the two tested soils mainly existed in exchangeable form and hydrochloric acid solution form. The nitric acid solution form, humic acid fraction form, organic matter bound form, sulfided form, and residual form were all very low.After extraction, the exchangeable form, hydrochloric acid form and nitric acid solution form of mercury in two tested soil were significantly decreased, and they were almost completely removed; the other four forms of mercury slightly decreased(.3)The two tested soils which were extracted by Na2S2O3 solution turned into the general wastes, and accorded with the standard of harmless pile. By testing the leaching toxicity of soil sample 1 that was extracted under optimal extraction conditions, it was found that the concentration of Hg in leaching solution was 0.07~0.08 mg/L; By testing the leaching toxicity of soil sample 2 that was extracted under optimal extraction conditions, it was found that the concentration of Hg in leaching solution was 0.05~0.06mg/L; Both were below the mercury concentration limits(0.1mg/L)in the《Identification standard for hazardous wastes-identification for extraction toxicity》(GB5085.3-2007).(4)Soil sample 2 was extracted by Na2S2O3 solution (first extraction) and HCl solution (second extraction). The total extraction rate was 89.05%, which indicated that two extractions improved the extraction rate of mercury in soil sample 2.