Experimental Study On Heavy Metals Adsorption Or Release From Sediments Of East Dongting Lake

In this paper,selecting East Dongting Lake sediments as the research object, analyzed the characteristics of heavy metal pollution and the adsorption-release rule of heavy metals in the sediments.The research results could provided scientific basis for pollution controlling and governance. The main contents and results were as follows:(1) Through determing the content of heavy metals in sediments and pore water on six sampling points, learned that the worst of ecological harm was Cd, its content exceeded soil national standard GradeⅢand the pollution in delta import from Xiangjiang river was the most serious; the content of Cu was within the soil national standards Grade II (besides Miluo River section); the content of Pb was within the soil national standards Grade I; the content of Zn was out of the soil national standards Grade III (besides Yue Yang town).(2) The state of Cd was priority to residual, ion exchange and carbonate combination patterns were higher levels; Cu was mainly organic and Fe-Mn oxidesiron, the residual ratio was larger; Pb was mainly Fe-Mn oxidesiron, also residual was in large proportion; Zn was mainly residual and organic.(3) Sediments were assessed by Geo-accumulation Index Method,the result showed that the order of the four heavy metals pollution lever was delta import from Xiangjiang river> Yueyang City> miluo river> Xinqiang river> Bianshan> YueYang town. The ecological risk index assessment showed that pollution of Bianshan was the slightest. Heavy metal content in porewater exceeded the limit of surface water standard levelⅤmore than tens times.(4) In elemental adsorption and competition absorption, adsorptions of heavy metal with temperature, pH, and ionic strength were similar. Temperature conditions on the influence of heavy metals adsorpted to sediments of East Dongting Lake were relatively minor. When 25℃,the adsorption was according with the Langmiur adsorption isotherm model and Freundlich adsorption isotherm model in elemental adsorption;in competition adsorption the adsorption was according with Langmiur adsorption isotherm model. The pH on the adsorption quantity of changes had a major influence. With the pH increasing, adsorption of metal ions had obviously increased. In elemental adsorption, the order of adsorption quantity of four kinds of metal ions was Pb²⁺>Cu²⁺>Zn²⁺>Cd²⁺; in competition adsorption was Cu ²⁺>Pb ²⁺>Cd ²⁺>Zn ²⁺. In elemental adsorption, along with the ionic strength increasing, the adsorption capacity of Zn²⁺ had the greatest change, followed by Cd²⁺,Pb²⁺,Cu²⁺. Metal ions in the adsorption quantity competition adsorption decreased, and trend was consistent with elemental adsorption.For a variety of reasons, the heavy metal adsorption in competition adsorption was reduced.(5) Release kinetics of heavy metals from sediments in Yueyang city section of east dongting lake was accord with Elovich dynamic model. Four kinds of heavy metals in acidic environment were releasing faster, as pH rising, release rate increased slowly gradually until the equilibrium trends. The order affected by temperature to four kinds of metal ions was Pb²⁺>Cd²⁺>Cu²⁺>Zn²⁺. Along with the increase of ionic strength, four kinds of metal release quantity increased. From the ionic strength for 0.01 mol/L to 0.1 mol/L, the order of adsorption quantity of four kinds of metal ions was Cd ²⁺>Cu²⁺>Zn²⁺>Pb²⁺.