Study On Remediation Effect Of Different Stabilizers With Mercury Contaminated Soil

Hg is a toxic heavy metal what is widely used in industrial production due to its special physical and chemical properties.The anthropogenic activities lead to soil contamination with varying degrees of mercury.Due to the limited self-pu rification ability of soil for mercury contamination,the corresponding soil remediation technology emerged.In this paper,using the chemical stabilization remediation technology to treat mercury contamination soil was aimed at converting the form of mercury with high biological activity into the form of mercury with low biological activity through stabilizers,as to reduce the toxicity and mobility of Hg and enable the contaminated soil to be reused.Ca(OH)2,KH2PO4,bentonite,diatomite and NazS were selected as stabilizers to repair mercury-contaminated soil.Through the study on the remediation effect with different stable time and different content of each stabilizers to mercury-contaminated soil,the optimal stabilization time of each stabilizer was determined and the optimal content of each stabilizers was screened,in order to screen out suitable stabilizers and experimental conditions for pot experiment.In the pot experiment,Commelina communis was used as the indicator plant.Through analyzing The distribution of Hg content in various organs of C communis combined with soil pH,mercury bioavailability levels in soil and the BCR extraction state of Hg,the remediation effect of single stabilizer and composite stabilizers on Hg contaminated soil was comprehensively evaluated to screen the stabilizer combination with the best remediation effect.The study on the remediation effect with different stable time or different content of each stabilizers to mercury contaminated soil is revealed:(1)The addition of Ca(OH)2 or bentonite would significantly change the pH in soil and make it strongly alkaline.The pH in soil changed from nearly neutral to slightly acidic with the application of KH2PO4.Na2S or diatomite had no significant effect on soil pH.(2)The optimal stabilization time of Ca(OH)2,Na2S and bentonite was 14 d,and the optimal stabilization time of diatomite was 21 d,while KH2PO4 did not play a role in the restoration within the stabilization time.(3)Among the five stabilizers,Ca(OH)2,Na2S and diatomite had better remediation,with the increase of each stabilizer content,the decrease of mercury bioavailability levels in soil was 96.2%-99.9%,86.69%-90.36%,and 85.53%-94.47%,respectively.The reduction rate was over 85%and the repair effect was obvious.Among them,the best content of Ca(OH)2 was 20 g/kg,the best content of diatomite was 20 g/kg,and the best content of Na2S was S:Hg=5.In the pot experiment,Ca(OH)2,diatomite and Na2S were used as stabilizers,and C communis was used to as indicator plant,and the remediation effects of single stabilizers and compound stabilizers on rapairing mercury contaminated were evaluated by combining the changes of relevant indexes in soil.The following conclusions was obtained:(I)Planting C communis or not had no significant effect on soil pH of each treatment group.In the treatment group with Ca(OH)2,the soil pH was relatively high,so the dosage should be paid attention to when using lime materials as stabilizer,because the soil pH was too high,which was not conducive to the growth of plants.(2)In the treatment group with Hg and without any stabilizer,the mercury bioavailability levels in soil with C.communis was significantly lower than that in the group without C communis.Indicating that the C communis can absorb bioavailable Hg in the soil through the roots during its growth,thus achieving the biological migration of Hg.Except for the G treatment group,other expernmental treatment groups can reduce the bioavailability of Hg in soil.The content of bioavailability Hg in each treatment group from high to low is:G>S>C>G+S>C+G>C+S>C+G+S.The results showed that the remediation effect of composite stabilizer was better than that of single stabilizer,among which Ca(OH)2,Na2S and diatomite combined(C+G+S treatment group)had the best repair effect.(3)The content of Hg in the roots,stems and leaves of C communis was showed from high to low as follows:root>stem>leaf.The mercury content in all organs of C communis in the composite stabilizer was lower than that in the single stabilizer treatment group,among which Ca(OH)2,Na2S and diatomite combined(C+G+S treatment group)had the lowest content.In summary,combined with the changes of Hg content in various organs of C communis,soil pH value and the speciation of Hg in soil,the comprehensive analysis shows that,among the single stabilizer,Ca(OH)2 had the best remediation effect,followed by Na2S.Among the composite stabilizer,combination of Ca(OH)2,Na2S and diatomite had the best remediation effect.