Study On Heavy Metal Pollution And Stabilization Of Sediment In East Dongting Lake

East Dongting Lake area exsited many industrial and mining enterprises and suffer serious heavy metal pollution.Heavy metals in the water are deposited in the sediment by various ways.After several decades of accumulation,the concentration of heavy metals Cu,Pb,Zn and Cd in the sediments of the Dongting Lake has been exceeded.When the environmental conditions change,the sediment in the heavy metals can be re-released,absorbed by aquatic organisms,and then through the food chain into the human body,seriously endangering aquatic life and human health.Therefore,immobilize heavy metal polluted sediment in east Dongting lake is immediately.The method of fixed/stabilizing is a kind of traditional method of restoring heavy metal contaminated sediment.It has the advantages of low cost,short restoration period,good remediation effect and easy operation.It is a very effective method for sediment pollution control.However,the choice of stabilizer must take into account its origin,price,efficiency and potential toxicity.Zeolite molecular sieves are widely available and inexpensive,and because of their strong exchange of metal ions and their porous structure is very likely to plays an important role in the remediation of heavy metal polluted sediment in Dongting Lake.In this study,we first evaluated the pollution status of heavy metals Cu,Pb,Zn and Cd in the sediments of Dongting Lake by using the Geo-accumulation index and Potential ecological risk index.Then,the stabilization effect of three kinds of stabilizer of limestone,manganese dioxide and natural zeolite on heavy metals Cu,Pb,Zn and Cd was studied by BCR sequential extaction.Finally,three kinds of natural zeolite with different size(0-0.5mm,0.5mm-1mm,1mm-2mm)were modified and screened with three modifiers(HC1,NaOH and NaCl)to get the best condition for removal of heavy metals,then the effect of heavy metal Cu,Pb,Zn and Cd on sediments was studied by selected zeoliteThe results show that:1,the concentration of heavy metals Cu,Pb,Zn and Cd in the sediment of Dongting Lake exceed the average of soil and sediment standards.The pollution degree of Zn,Cu and Pb in the sediment is between the unpolluted and the moderate polluted,and the Cd is in the serious pollution.Zn,Cu and Pb have low potential risk to the lake ecosystem,but the potential ecological risk index index of Cd is high,which leads to the overall risk of four metals in the lake sediments.2,limestone can effectively stabilize the sediments in the Cu and Zn,but it has enhancedthe sediment of Cd and Pb mobility.Manganese dioxide can reduce the extractable concentration of Cd and Pb in the sediment.Natural zeolite has no obvious effect on the stability of heavy metals in sediments,and its role is not as good as limestone and manganese dioxide.3,modified by NaCl,the diameter of 0.5-1mm between the natural zeolite has the highest cation exchange value and the strongest metal adsorption capacity.The modified zeolite has different stabilizing effects on the four kinds of heavy metals in the sediments of Dongting Lake.The modified zeolite has the best effect on the remadiation of Cd,reduces the exchangeable concentration of Cd,and increases the recoverable concentration of Cd and the residual concentration.The modified zeolite can also stabilize the heavy metals Cu,Zn and Pb in the sediment by reducing the exchangeable concentrations of Cu,Zn and Pb,and then increasing the concentration of another more stable metal form.