Study On The Derivation Method Of Remediation Target Values For Antimony/Arsenic In Contaminated Soil Of Antimony Mining Areas

There are abundant productions of antimony mines in China and severe pollution in antimony mining areas,which requires risk control and remediation of the soil in antimony mining areas.At present,the only relevant standard for soil remediation target values(RTVs)in China is the "Guidelines for the Development of Target Values for Soil Pollution Remediation of Construction Land(Trial)".Although the standard mentions the derivation of RTVs for protecting human health,groundwater,surface water,and other ecological environment,the current calculation method for soil RTVs is only for the protection of human health and groundwater,not including surface water.In addition,the remediation goal of the standards is to reduce the total amount of pollutants,but in fact,only a small portion of the total amount is truly harmful to sensitive objectives.The existing soil remediation technologies,such as solidification and stabilization,are based on the principle of reducing the availability of pollutants.Therefore,if based on the total amount,it is impossible to determine whether the remediation goals have been achieved.In response to the above issues,this study takes two typical antimony mining contaminated sites as case studies.First,by investigating the main pollution characteristics of the two case sites in the antimony mining area,key parameters of the site,potential future uses,and sensitive objectives are collected,and conceptual site models are established.Second,this study derived RTVs for leachable and bio-accessible Sb/As in soil based on different protection objectives.Finally,this study proposes a general method for deriving the target values for Sb/As remediation in soil from antimony mining areas.The main conclusions are as follows:(1)The pollution in the surface soil of the antimony mining area is mainly Sb,accompanied by As.The average total amount is higher than the intervention value of China,and the distribution is extremely uneven.The leachability of Sb in surface soil is higher than that of As,and Sb may be more easily transported in the environment than As.The bio-accessible concentration of Sb in the background soil is greater than that in the contaminated site soil,and the simulated concentration of gastric fluid is higher than that of enteric fluid.The bio-accessible concentration of As in contaminated site soil is much higher than that in background soil,and the higher value between enteric and gastric simulation results varies depending on the site.The total concentration of Sb in polluted sites decreases with depth and gradually approaches the background value.Sb in the surface soil may continue to migrate downwards in a leachable state,and the total amount and leaching concentration of As in the polluted site decrease with depth and gradually approach the background value.The residue and humic acid binding forms of Sb/As are mainly present in the rhizosphere soil of plants in the antimony mining area.(2)In order to protect human health,the bio-accessible concentration of Sb/As in soil is proposed as the remediation target.Based on the recommended exposure and toxicity parameters,the soil RTVs of Sb and As for protect human health are67.35mg/kg and 6.09 mg/kg,respectively.In order to protect groundwater,the leachable concentration of Sb/As in soil is proposed as the remediation target.The calculation results show that the soil RTVs of Sb and As for protecting groundwater in the Qinglong case are 0.35 mg/kg and 1.77 mg/kg,respectively.The soil RTVs of Sb and As for groundwater protection in Xihe case site are 0.18 mg/kg and 0.36 mg/kg,respectively.A simplified model for deriving the soil RTVs was proposed for rivers and lakes(or reservoirs)surrounding polluted sites,with soil leachable concentration as the remediation target.The RTVs for Sb and As in the Qinglong case site are 1.56 mg/kg and 15.6 mg/kg,respectively.(3)Based on the remediation target values of this study,screening values and intervention values of China,the scope and depth of soil remediation were divided,and the soil remediation volume was calculated.The results show that for Sb,the total soil remediation volume based on the RTVs in this study is greater than that based on screening and intervention values of China.For As,the total soil remediation volume based on the RTVs in this study is less than that based on the screening value but greater than based on the intervention value.Overall,although the RTVs in this study did not reduce remediation costs,compared to the standards of China,the protection objectives considered are more comprehensive.In addition,the remediation goals based on leachable and bio-accessible concentration in this study can be achieved through remediation techniques such as solidification and stabilization.Based on the total amount,Sb and As need to be removed from the soil.The remediation method is too complex,and the remediation cost may also be greatly increased.(4)A general method and process for deriving the RTVs of Sb/As remediation in soil of antimony mining areas have been established: 1)constructing a conceptual model of the site;2)Polluted area investigation to obtain key site parameters;3)Based on the model and parameters,calculate the theoretical values of soil RTVs based on different protection objectives;4)Considering the pollution situation and background values,determine the final RTVs.5)Divide the scope of remediation and calculate the required total soil remediation volume.