Study On Chemical Stabilization Remediation Of Mercury-contaminated Soil

In view of the objective straits of the serious dangers for human health and ecological environment caused by mercury-contaminated soils,and the urgent demand of the treatment and remediation for contaminated soils posed by Soil Pollution Prevention and Control Action Plan,studies on remediation of mercury-contaminated soils have increasingly become a hot issue in the field of environmental science,and this study therefore has a prospective but profoundly realistic significance.Based on reviewing the profiles about soil mercury contamination and its progress on remediation researches,the study on chemical stabilization remediation of mercury-contaminated soil using FeS and CaSx as stabilizers,was performed from the aspects of stabilization parameters optimization,stabilization effect evaluation and stabilization mechanism research in this paper.The main results are as follows:(1)The optimal conditions for FeS stabilization are as follows:S/Hg molar ration was 2.0,soil particle size was 20 mesh,stabilization pH was 5.0 and stabilization time was 5.0 d.Under the above conditions,the stabilization efficiency of Hg in the soil reached 99.78%(2)The optimal conditions for CaSx stabilization are as follows:CaSx addition dosage was 10%of soil mass,soil particle size was 60 mesh,stabilization pH was 10.0 and stabilization time was 5,0 d.Under the above conditions,the stabilization efficiency of Hg in the soil reached 99.91%(3)Interfering ion Cl-had a significant but complicated influence on the stabilization effect of FeS.However,the concentration of Hg in soil leachate after the stabilization by FeS was still lower than the limit of 0.10 mg/L in GB 5085.3-2007,and the lowest stabilization efficiency of Hg was 98.16%.In the meanwhile,the influence caused by Cl' on the stabilization effect of CaSx was strongly correlated with the concentration of Cl" in the soil,namely,the influence increased when the Cl/Hg molar ration increased(4)After the stabilization remediation by FeS and CaSx,the leaching rate of Hg in the soil decreased from 13.571%to 0.032%,0.013%,respectively.The Hg concentration in the leachate decreased from 33.819 mg/L to 0.075 mg/L,0.029 mg/L,respectively,which were significantly lower than the limit of 0.10 mg/L in GB 5085.3-2007,indicating that the soil after the stabilization remediation no longer had the toxic leaching characteristics.(5)After the stabilization remediation by FeS and CaSx,the contents of exchangeable Hg,carbonates bound Hg,Fe-Mn oxides bound Hg,organic bound Hg and residual Hg in the soil varied from 51.26%,20.26%,16.20%,7.53%,4.75%to 1.16%,5.11%16.29%,7.63%,69.81%and 0.40%,8.94%,13.16%,6.19%,71.31%,respectively.The content of residual Hg in the soil after the stabilization remediation significantly increased,and the stabilization index increased from 0.110 to 0.363,0.365,respectively,indicating that the harm or potential impact of Hg in soil on the environment was weakened.(6)The XRD analysis showed that the main stabilization products by FeS and CaSx were HgS,Fe1-xS and HgS,elemental sulfur,respectively,which demonstrated that the main mechanism of stabilization Hg was formation of HgS precipitation.The SEM images showed that the soil surface after the stabilization remediation changed rough compared with that before the stabilization remediation,which perhaps was caused by the pH changes that the stabilization pH was more corrosive than that of the natural soil.