Effect Of Sulfides On Stabilization And Volatilization Of Mercury In Purple Soil

With the final signing of the“Mercury Convention”of the Global Mercury Convention,which takes effect today,the issue of mercury pollution has increasingly attracted the attention of the international community.Among them,the anthropogenic sources of mercury are mainly industrial activities such as the mining and smelting of mercury ore,the selection of amalgamation of mercury,the smelting of zinc by the soil method,the production of alkali by the mercury method,and the burning of coal.The mercury pollution problem that has accumulated during the industrialization process has gradually emerged,and pollution incidents have become more frequent and pose a serious threat to the ecological environment and human health.As mercury has a relatively low vapor pressure and is mainly transported in the form of atmospheric mercury,local mercury contamination may cause global pollution.Mercury and its compounds have strong neurotoxicity and teratogenic effects and have a significant accumulation effect and genetic toxicity.They can enter the human body through the form of breathing,skin contact,and the food chain,causing great harm to human health.As a result of rapid economic development,Asia has become the largest mercury-emitting region,accounting for almost half of global mercury emissions.China is a major country in the production,use,and emission of mercury.There are many industries involved in mercury and the problem of soil mercury pollution is outstanding.How to select high-efficiency stabilizers and determine reasonable amounts for different levels of mercury pollution and different types of soil in China requires more comparative screening studies.In the selection of stabilizers,sulphides have received extensive attention.Sulfur ions or S²⁺ions generated in the soil can be combined with mercury in the soil to form a very insoluble,low toxicity,very stable compound of mercury sulphide?HgS?.thus alleviating soil mercury pollution.At the same time,the sustained stability and secondary environmental risks of contaminated soils after stabilization have not yet received sufficient attention.The sustainable stability of farmland soil stabilizers is an important basis for the safe production of crops,and the subsequent environmental risks?re-releasing,mercury volatilization into the atmosphere,etc.?of the stabilization treatment of industrial sites cannot be ignored.There is an urgent need to strengthen research on the stabilization and treatment of soil mercury pollution.In this paper,chemical stabilizing repair technology was used to select five different sulfide stabilizers?S,Na₂S,FeS,Na₂S₂O₃,and DTCR?dithiocarbamate??to stabilize mercury-contaminated soils and remove mercury from the soil.The compounds that become stable are permanently present in the soil.The goal is to reduce the mobility and toxicity of mercury in the soil.At the same time,the stability of mercury in soil after stabilization treatment and the change of mercury release flux from the soil to the atmosphere were investigated.The main findings are as follows:All the five kinds of stabilizers tested could significantly reduce the TCLP leaching toxicity of mercury in purple soil.The molar ratio of fixed S:Hg=1.Under different levels of mercury-contaminated soil,the order of relative stability was DTCR>Na₂S>Na₂S₂O₃>S>FeS.When the mercury pollution concentration is less than 150 mg·kg^-1,all five stabilizers can stabilize the soil mercury,but the time required to reach the stabilization standard is different,and Na₂S and DTCR can be realized in only 3 days.Soil mercury stabilization.Under different concentrations of mercury pollution,the treatment group with Na₂S and DTCR added could keep the mercury leaching concentration lower than the leaching standard(TCLP Hg<0.2 mg·L^-1)after 3 days of stabilization,and basically reached stable equilibrium and stabilized the efficiency.Both are above 98%.When the mercury pollution concentration was?150 mg·kg^-1,Na₂S and DTCR still maintained their high stabilizing ability,but the stabilization of the soil by element S and FeS could not meet the leaching standards.For soils where mercury contamination exceeds the standard three times or more does not meet the stabilization requirements,the use of two stabilizers,S and FeS,to stabilise high-concentration mercury contamination may require longer stabilization times or increase the amount of mercury.Different doses of stabilizers had different effects on reducing the TCLP leaching toxicity of mercury from purple soil.DTCR was used as a stabilizer and S:Hg=1.Stabilization treatment for 3 d reached the leaching standard.The optimal application rates of Na₂S and Na₂S₂O₃ are both S:Hg=5.During the application of Na₂S and Na₂S₂O₃stabilizers,the stabilizer S:Hg>20 will lead to redissolution of mercury sulfide,leading to a rise in mercury concentration in the leachate.Case.With S and FeS as stabilizers,when the S:Hg=5 and the stabilization time is 7 d,the stabilization of mercury in contaminated soil has reached the leaching standard.The increase of FeS dose can significantly increase the stabilization rate of purple soil.When these sulfides are selected as stabilizers to remedy soil mercury pollution,the appropriate amount of stabilizing agent and stabilization time should be determined according to the degree of soil mercury pollution.After the application of a series of sulfide stabilizers,the form of mercury in the purple soil was redistributed.With the extension of the stabilization time,the mercury in the exchanged mercury and carbonate in the soil decreased rapidly,and there was no obvious change trend in the iron-manganese oxidation mercury.The proportion of mercury in organic matter combined with residual mercury increased.Among the five forms of mercury,exchangeable mercury and carbonate-bound mercury are easier to leach out.The use of Na₂S or DTCR as a stabilizer can convert these two forms of mercury into a stable organic bound state,which is very effective.Decrease the leaching toxicity,so as to achieve the purpose of controlling soil mercury pollution.When Na₂S and Na₂S₂O₃ stabilizers are applied,excessive amounts lead to increased exchange mercury content in the soil.When S and FeS stabilizers were applied,the rate of morphological transformation in soil was slower,and increasing the amount of FeS stabilizer could effectively increase the morphological conversion rate of mercury.A multivariate stepwise regression method was used to conduct a regression analysis between the mercury TCLP mercury leaching concentrations of the soil and the five mercury species continuously extracted by the Tessier method.It was found that exchangeable mercury and carbonate bound mercury in the soil had a significant positive effect on mercury leaching concentrations in the soil.contribution.After applying a series of sulfide stabilizers,the pH value of the soil changed significantly.The greater the amount of several stabilizers,the more the pH decreased.Among them,DTCR had the least influence on the pH of mercury-contaminated soils,and Na₂S₂O₃ had the most significant effect on the pH of soils.The actual repair process requires reasonable control of the dosage.Through the long-term monitoring of stabilizers for mercury-contaminated soils,it was found that for the occurrence of a re-elevation of leaching concentrations,the five stabilizers have long-term stability.After application of a series of sulfide stabilizers,the mercury exchange flux at the soil/air interface in the soil decreased to varying degrees,and Na₂S and DTCR stabilizers significantly inhibited the mercury release flux from the soil.In order to stabilise soils with different concentrations of mercury contaminated with a fixed S:Hg molar ratio,the soil mercury releases were:S>FeS>Na₂S₂O₃>Na₂S>DTCR,and with the increase of mercury pollution in the soil,soil mercury The release flux also increases.When Na₂S and DTCR were applied to stabilise Hg-contaminated soil,the increase of stabilizing agent dose did not have much effect on the release of Hg from the soil to the atmosphere,while S and FeS stabilizers increased the stability of the amount of Hg/Hg at the interface.The exchange volume decreased significantly.When the amount of sulfide stabilizer was increased,the decreasing ranges of several sulfides were:S>FeS>Na₂S₂O₃>DTCR>Na₂S.