Study On Chemical Immobilization Of Lead Contaminated Soil In A Former Relocation Enterprise Site

Along with the aggravation of human activities and the expansion of city scale, increasing attentions have been paid to the influences of soil heavy metal pollutions on urban ecological environment and human health in the former relocation enterprise[0] site. This soil of former relocation enterprise[0] site in ChongQing is studied in the paper, and soil environment health risk of high-concentration Pb contamination site is assed by analyzing physicochemical characteristics and lead distribution characteristics of soil in site. Meanwhile, calcium carbonate, superphosphate, bentonite and zeolite are respectively added to high-concentration Pb contamination soil and then the soils are stabled for 60d, after that the chemical forms, toxicity leaching amount and leaching characteristics of lead in soil are studied, and the feasibility of chemical fixative to reduce Pb is analyzed. Following main conclusions are obtained:â‘ Soil characteristics analysis and environmental risk assessment in the former relocation enterprise[0] siteThe soil in the former relocation enterprise[0] site is seriously polluted by lead because of several years'operation of the enterprise.In addition to piling department of waste lead, lead content of other sampling points in the soil generally becomes lowered with increasing of the depth of sampling; for all the soil sampling points, Pb could continue to move downward because the mobility of Pb were greater than 0.45 at the ground layer (60~100cm). The form distribution of Pb showed the features of cohesion at soil cross-section. Because the soil is polluted by lead and is composed with sandy backfilled, lead morphological distrubtion did not showed good correlation with pH, organic carbon content, and total phosphorus content.The results of assessment using the action value of soil remediation showed that the value of Pi was greater than 1 for all sampling points, and the maximum reached to 78. The changes range of Pi value was fom7 to 61 [0]on the surface area (5~20cm), fom 6 to 76 on the heart layer (20~60cm), fom 3 to 78 on the end of soil (60~100cm). The sampling soil is seriously polluted by lead.As a result, it will effect the the living environment and urban ecological environment.â‘¡Chemical immobilization remediation research of lead containmination on soil site For contamined soil, the content of lead forms in order was residual form > organically bound form > Fe-Mn oxide bound form > acid extractable form. The residual state accounts for largest percentage, reaching to 60%; acid extractable form of Pb accounts for smallest percentage, reaching to 4%; the content of organically bound state and Fe-Mn oxide bound state is equivalent.Calcium carbonate, bentonite and zeolite are added to the high-concentrations Pb pollution oil, and the soil is stabled for 60 days. It is founded that pH is increased. acid extractable form concentrations of Pb significantly is decreased, while residual form concentration of Pb is increased overall, which manifested that all treatments had a fixing effect on Pb in soil. The treatment of the superphosphate had a best fixing effect, and possessed a greater potential to repair high-concentration Pb contaminated soil.â‘¢Soil chemical immobilization remediation enviromenatl assessmentCompared with control group which being added calcium carbonate, superphosphate, bentonite and zeolite to high-concentration Pb contamination soil and being stabled for 60d, toxicity leaching amount of other treatments significantly decreased.The decreasing range was respectively 67.46%, 89.24%, 79.88% and 80.90%, and the fixative capacity was respectively 1.33, 2.81, 1.58 and 1.60. The treatment of superphosphate had a best effect on reducing toxicity leaching amount of Pb in soil by compared to other treatments, and the capacity was also up to maximum.Simulating the acid rain circumstance using H2SO4and HNO3, then the repaired soil is leached.Researches showed that in conditions of leachating of pH4.5, compared with the control group,the pH and EC of nleachates from treatments of soil generally presented falling trends compared with control group. compared with control group, the Pb content of accumulated leachates from treatments significantly is decreased, and the decreasing range was respectively 76.88%, 98.32%, 90.85%, 72.25%. For all treatmens, the treatment ofsuperphosphate had a best effect on reducing leaching amount of Pb from soil. However, compared with the soil pre-leaching , soil pH is decreased,and the amount of acid extractable form of Pb dramatically enhanced, which means that the bioavailability and mobility of Pb is increased.The result could have serious negative impacts on the surrounding ecological environment.Compared with the treatment of distilled water, leachates from soil columns of each treatment had a certain influence on seed germination of mungbean, Mexican corn and alfalfa. Each treatment of leachates could delay time of seed germination and grow, lead to the poor growth. By compared with other treatments, leachate of control group without fixative has most influence on seed germination, while the leachate of superphosphate had an least influence.