Study On The Reduction And Stabilization Of Chromium Contaminated Soils Treated By Compound Agent

With the rapid development of industry and agriculture,the types and quantities of chemical substances used continue to increase,exacerbating the pollution of heavy metals in the soil of China.Among them,chromium is a common type of heavy metal pollutants,mainly in the form of trivalent and hexavalent.Trivalent chromium is an indispensable trace nutrient element for humans and animals.On the contrary,hexavalent chromium is a toxic and dangerous substance It is easier to migrate in soil and pore water.People come into contact with chromium in the soil through oral,inhalation,skin contact,etc.Therefore,in order to reduce the impact of chromiumcontaminated soil on humans and organisms,it is urgently needed to be treated and evaluated.This study mainly uses chemical reduction repair technology and stabilized repair technology.Stabilized repair technology has already become a relatively mature repair technology.Compared with other repair technologies for treating chromiumcontaminated soil,chemical reduction technology is considered to have good repair effect and short time.,Cost and maneuverability is a kind of repair technology.This article mainly explores a compounding agent that can be applied to the project on a large scale through the four reducing agents of ferrous sulfate,sodium thiosulfate,sodium sulfide,and sodium dithionite.In order to prevent the reduced hexavalent chromium from oxidizing again,a phosphate stabilizer is added to quickly stabilize chromium in the soil.The main research content conclusions are as follows:(1)Studies on single / composite treatment of chromium-contaminated soils have shown that the use of ferrous sulfate and sodium thiosulfate to treat contaminated soil has a good remediation effect,of which the maximum stabilization efficiency of total chromium is 86.95% and 83.33%,respectively.The maximum stable efficiency of hexavalent chromium is 89.14% and 88.83%,and the maximum reduction efficiency of hexavalent chromium is 64.07% and 74.19%,respectively.The effective states of ferrous sulfate and sodium thiosulfate have decreased,respectively,from the original 27.4%.It decreased to 14.03% and 21.41%,and the residue state increased from 23.38% to 39.82% and 39.65% respectively.By analyzing the stability efficiency of total chromium and hexavalent chromium,the reduction efficiency of hexavalent chromium,and the form of chromium in the soil,it was determined The optimal compounding scheme of ferrous sulfate and sodium thiosulfate was formulated: the compounding ratio of ferrous sulfate and sodium thiosulfate was 4: 1;according to the "Standard for Pollution Control Value of Domestic Waste Landfill" 4.5mg of total chromium The maximum leaching concentration limit of L / L and 1.5 mg / L of hexavalent chromium was used as the evaluation index,and the addition amount of composite reduction was determined to be 7.5% to repair chromium pollution with a total chromium content of 11024 mg / kg and a hexavalent chromium content of 665.2 mg / kg.soil.(2)The experiments using sodium phosphate(TSP),sodium dihydrogen phosphate(MSP),and disodium hydrogen phosphate(DSP)in combination with reducing agents to treat chromium-contaminated soils have shown that the stability of sodium dihydrogen phosphate is the best;Among them,the stability efficiency of total chromium and hexavalent chromium of sodium dihydrogen phosphate reaches 98.98% and 99.63%;the effect of adding sodium dihydrogen phosphate on the reduction efficiency of hexavalent chromium is not obvious;in soil samples containing sodium dihydrogen phosphate,the soil The effective chromium in the medium was reduced from 10.17% to 5.82%.The unstable chromium in the soil was mainly transferred to the residue state,which increased the residue state from 19.32% to 26.01%.The dosage of sodium dihydrogen phosphate was determined to be 1.5%.The reduction efficiency of hexavalent chromium is 78.30%;the optimal compound for disposing of chromiumcontaminated soil is composed of a reducing agent 7.5% and a stabilizer 1.5%,ie 5: 1.(3)Pilot-scale research using compound agents.The pilot-scale experimental scheme is designed through a laboratory pilot test.The experimental scheme is determined to be a compounding of a reducing agent and a stabilizer with a compounding ratio of 5: 1.Plus,the agent is dissolved in water and applied to the contaminated soil in the form of a solution.The moisture content is about 20% and the curing time is 3 days.Due to the heterogeneity of the soil,a dosage of 2% is used for highly polluted soil.Compound agent,3% compound agent,for the sake of conservativeness,2% compound agent was added for low-contaminated soil and medium-contaminated soil;the test results of the pilot test showed that the collected soil samples used the "Solid waste leaching toxicity leaching method acetic acid buffer solution method"(HJ / T 300)for leaching toxicity assessment,and its leaching toxicity meets the entry requirements specified in the "Contamination Control Standards for Domestic Waste Landfill Sites"(GB 16889),that is,the leaching concentration of hexavalent chromium is <1.5mg / L and The total chromium leaching concentration was <4.5mg / L.In summary,it can be known that using a compounding ratio of reducing agent and stabilizing agent of 5: 1 has a better effect on the treatment of chromiumcontaminated soil,and reduces the harm of pollutant chromium to the environment.