Study On Solidification/Stabilization For Remediation Of Chromate Contaminated Soil

Chromium Salts is used widely in the national economy.It is an important basic raw material for the chemical industry,Light industry and advanced alloy materials.At home and abroad,the important problem which faced by the Chromate production is pollution of chromium slag.Since 1958,our country started producing chromium Salts,it has produced 3.8 million tons of chromium salts and also has brought 9.85 million tons of chromium residue.There are only more than 2 million tons slag had got treatment and comprehensive utilization.Affected by precipitation,dust,02 and CO2,huge quantities of Cr(VI)are leaking out of the stockpiling untreated chromium slag,and then contaminate the surrounding soil and groundwater,which cause serious pollution to the environment and great threat to human health.Solidification/stabilization is a more mature disposal technology of solid waste,Through mixed soil and adhesive,contaminants in soil are converted into low toxicity and insoluble material,and then captured or fixed in the mineral lattice.Pollutants are isolated with the surrounding environment.The mobility and biological availability are reduced.Thereby the risk of contamination is reduced.Degree and regularity of chromium contamination soil in the typical chromium slag pollution sites were investigated.It revealed that the pollution regularity accorded well with particles non-point source diffusion model.Chromium species were mainly in residual form.The sampling sites were evaluated by using potential ecological risk index method,results showed that 25 out of 29 sampling sites could be classified as slightly ecological pollution,while 3 of them could be classified as moderately polluted,only one of them was severely polluted.The sampling sites were evaluated by using geo-accumulation index method,results exhibited that the Igeo of 29 sampling sites were totally greater than 5,the minimum was 7.95 and the maximum is 13.17,all of them belonged to severe pollution.According to the solidification and stabilization experiments,iron vitriol(FeSO4·7H2O)was the best for solidification and stabilization of chromium in the three of FeSO4·7H2O,Na2SO3 and Na2S·9H2O,the solidification and stabilization rate of total chromium and hexavalent chromium were more than 99%,which meet the leaching standards.The best molar ratio and mass ratio were 3 and 2,the minimum liquid to solid ratio was 0.5,and the best reaction interval time was 0 h.The solidification and stabilization rate of total chromium and hexavalent chromium were more than 99%after 60 days of solidification and stabilization when the content of chromium was 4000 mg/kg in soil.The real chromium contamination soil was treated by iron vitriol and calcium hydroxide,results showed that the content of hexavalent chromium of leaching solution in slightly polluted sampling sites decreased to 0.040 mg/L from 0.315 mg/L,and the solidification and stabilization rate was 87.47%.Hexavalent chromium concentration of leaching solution in severely polluted sampling sites decreased to 0.004 mg/L from 313.947 mg/L,and the solidification and stabilization rate was close to 100%.