Influence Factors Of Migration And Transformation Characters Of Cr(Ⅵ) In Soil And Risk Assessment

At present, heavy mental has coursed more and more pollution, and it is harmfulto our healthy and daily life. Chromium is one of the most dangerous heavy metals,chromium usually exists in the morphology of C（rⅥ）and C（rⅢ）in the environment.C（rⅥ）has more toxicity than C（rⅢ）and easily absorbed by us, it could be enrichedthrough the food chain and can not be broken down by microorganisms. It isrecognized as carcinogenic and mutagenic substances. Chromium is migrationcontaminants, it could course contamination to soil and groundwater. Therefore, it isnecessary to study the migration and conversion of chromium.We studied its influencing factors including pH, organic matter, inorganic ions,and lithology medium of the soil through dynamic column to see how it affectsmigration and transformation of Cr（Ⅵ），analysis the movement and transformationfeature of chromium in different conditions, partition coefficient was determined bystatic experiments in order to assess the contamination risk of chromium, after theexperiment，we take the soil in the column to analysis its forms, then calculate there-release risk. Specific experimental methods and results are as follows：（1）We get following conclusions though different influencing factors:①pH of soil has more effect to migration and transformation of Chromium.When the soil pH is neutral or alkaline, Cr（Ⅵ）migrates fastly, and concentration ofoutlet is high, reached2.60mg/L in100d, it is52%of the influent concentration,strong acid or alkali conditions are not conducive to the migration of Cr（Ⅵ）.②Theeffluent concentration of Cr（Ⅵ）presents a decreasing trend with the increase of soilorganic matter, When the organic matter reaches a certain value, effluentconcentration of Cr（Ⅵ）changed little. It illustrate that the presence of the organicmatter can inhibit the migration of Cr（VI）.③The presence of dihydrogen phosphatecan inhibit the adsorption of soil and accelerated organic matter on the reduction of Cr（Ⅵ）, The presence of sulfate can reduce the Effluent concentration of the Cr（Ⅵ） significantly, and we can’t detect Cr（Ⅵ）in a short time. In carbonate soil, Cr（Ⅵ）migrates easily, it proved that the presence of carbonate is conducive to the migrationand transformation of Cr（Ⅵ）.④In kaolin, the partition coefficient is bigger thanbentonite. so, the migration of Cr（Ⅵ）is slower in kaolin.（2） We determinate the partition coefficient of different soil though staticexperiments and assess their risks too, the result show that：①In different pH soil, thesize of the partition coefficient is: acid soil> lime soil> alkaline soil> salt soil, proofthat C（rⅥ）in saline soil migrate easiest, alkaline soil followed, lime soil and acid soilmigrate rather poor.②When the content of organic matter increased, the partitioncoefficient increased too，the migration risk of Cr（Ⅵ）reduced.③In differentinorganic ions soil, the size of the partition coefficient is: SO₄^2-> CO₃^2-> H₂PO₄^-, itproofs that: in the three soils, H₂PO₄^-migrate easiest, and SO₄^2-migrate poor.④Inlithology medium, partition coefficient in kaolin is bigger than bentonite, sochromium migrated slower in kaolin.（3） After the experiment，we take the soil in the column to analysis its forms,then calculate the re-release risk. The result show that:①In different pH soils, there-release risk is: lime soil> alkaline soil> salt soil>acid soil, so, when soil pHincreased，the risk of re-release increased，too.②The re-release risk increase whenthe content of organic matter increase.③In different inorganic ion soils, the order ofre-release is:SO₄^2-＞CO₃^2-＞H₂PO₄^-.④The soils of bentonite and kaolin, there-release risk of bentonite is more than kaolin，so, in the bentonite, C（rⅥ） is moreeasy to migrate, it’s more danger than kaolin to groundwater.