Effects Of Organic Acids On Heavy Metal Speciation In Soil Of Qingdao

Selecting yellow brown soil in Qingdao as study object, this paper studied the transformation of the heavy metal speciation of Cd and Pb in soil after added external heavy metals by using chemical extraction method, and also studied the effects of single and combined organic acids (malic acid and citric acid) on chemical speciation of Cd and Pb in heavy metal contaminated soil, with the purpose of providing theoretical basis for organic acids remediation and finding practical methods to enhance phytoremediation of heavy metal contaminated soil. Main conclusions of the study are as follows:1. Residual fraction is the most component of Cd and Pb in original soil, respectively, accounting for 45.83% and 63.39%. After external heavy metal entered soil, exchangeable Cd and Fe-Mn oxide-bound Pb became the majority. Each form concentration increased with the concentration of external heavy metal added, but residual fraction is the lowest with a decreasing trend.2. For different pollution levels of soil CdⅠ-CdⅣ, different concentration of malic acid and citric acid addition can effectively activate Cd in the soil. After external Cd entered, with higher concentration of organic acids added, citric acid can make percentage content of exchangeable Cd significantly increased, and basically reached the peak under the concentration of 10mmol/kg. Malic acid can make the percentage content of carbonates Cd significantly increased. By comparison, the Cd mobilization effect of citric acid is more obvious than malic acid.3. For different pollution levels of soil PbⅠ-PbⅣ, different concentration of malic acid and citric acid addition can effectively activate Pb in the soil also. After external Pb entered, with higher concentration of organic acids added, citric acid make percentage content of exchangeable and carbonates Pb significantly increased, and reached the peak under the concentration of 20mmol/kg. Malic acid make the percentage content of exchangeable Pb first increased then kept on. As a result, the Pb mobilization effect of citric acid is more obvious than malic acid.4. The two kinds of organic acids combined addition can significantly improve Cd and Pb mobilization effect compared with single addition. With higher concentration rate of organic acids added, mobilization effect of Cd first increased then kept on, mobilization effect of Pb gradually increased. It is basic anastomotic with single addition experiment.5. Primary analysis of effects of organic acids on heavy metal chemical speciation indicated that malic acid and citric acid combined addition can effectively activate Cd and Pb. It provides practical methods to enhance phytoremediation of heavy metal contaminated soil and it is easy to spread and has wide application prospect.