汞污染砂质土壤萃取修复技术研究

On the extract-compensation technology of the mercury-contaminated soils

分别采用HAc、NH_4Ac和Na_2S_2O_3种萃取剂萃取污染土壤中汞,研究了萃取剂对汞的萃取效果和萃取条件对萃取率的影响,并分析了用Na_2S_2O_3溶液萃取前后土壤中汞的形态变化。结果表明,Na_2S_O_3溶液对汞的萃取效果最好。适宜萃取条件为:Na_2S_2O_3浓度O.01mol/L,土液比(即土样质量(g):萃取剂体积(mL))1:6,萃取时间6 h。当土壤中汞的质量比为124.35 mg/kg时,萃取率为82.03%。经Na_2S_2O_3溶液萃取后,土壤中可交换态和酸溶态汞基本完全去除,土壤中汞的生物有效性显著降低。萃取后土样的浸出毒性检测符合《危险废物鉴别标准浸出毒性鉴别》(GB 5085.3—2007)中要求的无害化堆放标准。

This paper is aimed to present our experimental results for such solutions as HAc, NH4Ac and Na2S2O3 to be used to extract mercury residues in the polluted soil and the extraction effects and efficiency under different extraction conditions, while analyzing the content variations of mercury form in the polluted soils before and after Na2S2O3 solution extraction. In proceeding with our study, we have conducted leaching toxicity testing experiments with the polluted soil extracted by means of Na2S2O3 solution under the optimal extraction conditions. The results of our experiments indicate that the extraction efficiency of HAc and NH4Ac solution on the mercury residues tends to be very low, whereas that of Na2S2O3 solution proves to be higher. The optimal extraction conditions for Na2S2O3 solution were： the optimal concentration—0.01 mol/L; the ratio of soil to solution—1∶6, and extraction time—6 h. In addition, when the concentration of mercury in the polluted soil is 124.35 mg/kg, the extraction efficiency should be 82.03%. We can also find that before being extracted by Na2S2O3 solution, the bioavailability of mercury in polluted soil is very high, with mercury mainly existing in an exchangeable form, hydrochloric acid solution form, rarely existing in nitric acid solution form, humic acid fraction form, organic matter bound form, sulfide form and residual form, their mass ratios usually accounted for 63.64 mg/kg, 36.35 mg/kg, 4.62 mg/kg, 8.36 mg/kg, 3.64 mg/kg, 8.36 mg/kg, and 0.34 mg/kg, respectively. When extracted by Na2S2O3 solution under the optimal extraction condition, the bioavailability of mercury would be significantly reduced and the exchangeable form, hydrochloric acid solution form and nitric acid solution form of mercury expected to be almost totally removed, though the other four forms of mercury would be slightly diminished, with their mass ratios being 0.49 mg/kg, 4.64 mg/kg, 1.36 mg/kg, 5.80 mg/kg, 1.25 mg/kg, 5.51 mg/kg, 0.22 mg/kg, respectively. When extracted by Na2S2O3 solution under the optimal extraction condition, it would be possible for the polluted soil to be relieved from the mercury in according with the standard of harmless pile of Identification Standards for Hazardous Waste—Identification for Extraction Toxicity（GB 5085.3—2007）.