Study On Risk Assessment And Remediation Technology Of A Chromium Contaminated Site In Qinghai Province

Soil is the resource that human beings depend on.The problem of heavy metal pollution in the process of industrialization in our country is becoming more and more serious,and heavy metal chromium is paid more and more attention due to the "three factors".In this paper,we focus on the health risks of the site and the applicability of chemical reduction stabilization techniques to chromium-contaminated site restoration projects for a chromium pollution site in Qinghai Province,from the site of environmental survey,health risk assessment to the soil repair laboratory test and site pilot risk control process.Through the calculation and experiment,the main conclusions are as follows:There are serious chromium pollution of the soil in a chromium contaminated site and the chromium slag field.The chromium pollution in the chemical plant is mainly concentrated in the calcining workshop,the leaching workshop and the original chrome slag field,the pollution area is about 12,000 m2.Chromium contamination has a smaller lateral diffusion range,with longitudinal diffusion and pollution depth to groundwater level.The distribution of chromium in the slag field is not uniform,the total chromium concentration in the soil is 5781 mg/kg.There is a serious chromium pollution in the groundwater of this plant,and its flow direction is west to north.The pollution source is mainly located in the leaching workshop and the surrounding area,and the pollution halo divergence direction is related to the groundwater flow direction.Trivalent chromium and hexavalent chromium as a concern pollutant to the health risk assessment of Haibei Chemical Plant.The results showed that the risk of carcinogenicity of hexavalent chromium in the surface soil was more than 10-6 and reached the order of 10-4,with passways as oral intake soil,skin contact with soil and inhale soil particles,and the total carcinogenic risk was 10-3,the risk level is higher.Hexavalent chromium non-carcinogenic hazards index also exceeded the acceptable value of 1 in each exposure route,with a total non-carcinogenic hazards index was 10.58 at a higher risk level.The non-carcinogenic hazards index of trivalent chromium in the surface soil are far less than 1 with passways as oral intake soil and skin contact with soil,the level of harm within the acceptable range,but in the inhale soil particles,non-carcinogenic hazards index is up to 7.03,the harm level is higher..Based on the health risk of the site,the target value for the trivalent chromium and hexavalent chromium is calculated.The target of soil remediation was 11.8 mg/kg for carcinogenic risk,106.3 mg/kg for non-carcinogenic hazards index,and 74.5 mg/kg for leaching risk of hexavalent chromium.The site is industrial land.It is suggested that the surface of the site should be hardened and the surface of the soil is blocked.Mainly to consider the risk of leaching,repair target value of hexavalent chromium is 50mg/kg.Through the laboratory small test and site pilot,to determine the chemical reduction stabilization techniques can better repair the soil of hexavalent chromium pollution site,repair effective time faster,and does not produce secondary pollution.The remediation agent was ferrous sulfate and calcium hydroxide,and FeSO4 reduced Cr(VI)to Cr(III)in the soil,and then formed hydroxide precipitate fixed in the soil,the addition was 8%.Ca(OH)2 as a pH neutralizer,to provide a stable environment for the restoration of the soil,the addition was 1.5%.The content of hexavalent chromium and its leaching toxicity in the soil after repaired were far less than those specified in the relevant standard.