The Transformation Of Heavy Metalspeciation Distribution In Washing Treatment For Contaminated Riversediment

Heavy metals in sediment exsit in different fraction and speciation. The mobility and toxicity of the heavy metal are not only related to its total concentration, but also depends on the distribution of the metals. Washing can remove heavy metals from the the city rev ier contaminated sedment. At the same time, it could be change the speciation of the metals. It aimed at controlling the mobitlity of the heavy metal in which the sediment is washed by different washing agents. The experiments have been conducted to study the changes of the metal frction before and after the sediment washing and estimate the mobility risk. More experiments have been carried out to seek the reason that washing agents alter the distribution of metals. The stability of metals in washed sedimen t have been checked out according to the different disposal. At last, both the removal ability and security of the washed sediment were taken into accout to choose appropriate washing agents in application.It indicated that kinds of washing agents had different influence on the metal speciation. The acid had an evident effect on the metal spciciatin. And the propotions of the Cu, Zn and Pb were increased. The potential mobility of acid washed sediment would improve or not obviously reduced. The chelates di dn’t have evident influence on the whole metal distributions while the weaker speciation is partly removed which still account for large propotion. The chloride salts containing acid was less effective to remove metal contaminant and change the metal distribution. The oxidizing agents could make the propotion of acid extraction rised. And the potential mobility of oxide washed sediment would improved or not obviously reduced.Further study on the reason how washing agents alter the distribution of metals shows that HCl extract metals mainly through destroy the paticle strcture while it could make the stronger fractions transform to the weaker. EDTA is capable of promoting the removal of metals by means of chelation of the target metals from the particles. In the process, the weaker bound is easily removed and there is no evident sign that the stronger transform to the weaker bound. Hydrogen peroxide works mainy because of the faintly acid solution, decresing the absorbility of the particles and oxdixing the p art of the oxidizing substances which containing metals.In order to study the mobility of metals in washed sediment, experiment was carried out according to the different disposal, such as marine disposal. It indicated that the mobility of metals in trea ted sediment had increased in different degree. The acid washed sediment leached much more than the untreated one, And Zn obviously leched more in the EDTA washed sediment than untreated. The hydrogen peroxide makes Zn to be less unstable.