Mobility And Adsorption Of Cr(Ⅲ) And Cr(Ⅲ)-Organic Acid In Soils

Cr (Ⅵ) is harmful to environment and human. Research shows that Cr(Ⅲ) can be converted to Cr (Ⅵ). So the study of adsorption and mobility of Cr(Ⅲ) in soils is important for understanding of Cr (Ⅵ) environmental behavior. It is well known that plant roots and microorganisms exude organic acids which are likely complexed with soluble Cr(Ⅲ). Cr(Ⅲ)-organic acids will change the adsorption and mobility of Cr(Ⅲ) in soils. In order to find out the potential problem of the contamination of Cr(Ⅲ)-organic acid, here this study investigated the absorption and mobility of Cr(Ⅲ)-organic acid synthesized in laboratory in soils under approximate environmental conditions in a laboratory setting.In chapter Ⅰ At pH4.0,6.5,9.0and different water soil ratios, adsorption of soluble Cr(Ⅲ) and chelated forms of Cr(Ⅲ), such as Cr(Ⅲ)-EDTA and Cr(Ⅲ)-citrate by black soil, yellow-brown soil and red soil were investigated in batch systems to predict the adsorption discrepancy between Cr(Ⅲ) and Cr(Ⅲ)-organic acid. Results indicate that Cr(Ⅲ) is very strong to be bound to soil, while Cr(Ⅲ)-organic acid has no or a little interaction with soil. However, Cr(Ⅲ)-organic acid can remain in soil to some extent, such as Cr(Ⅲ)-citrate, it is relatively strong absorbed. The adsorption amounts of Cr(Ⅲ) and Cr(Ⅲ)-organic acid complexes were greatly consistent with the distribution species depending on pH. Generally speaking, higher pH is beneficial to sorption of Cr(Ⅲ) in soils and Cr(Ⅲ)-organic acid in red soil, but weakens adsorption of Cr(Ⅲ)-organic acid in black soil and yellow-brown soil. Organic matters in soils influence the absorption of Cr(Ⅲ) and Cr(Ⅲ)-organic acid significantly.In chapter Ⅱ At25℃and pH4.0,6.5and9.0, the mobility of Cr(Ⅲ) and Cr(Ⅲ)-EDTA/citrate were investigated in batch reaction systems to predict the effect of low molecular organic acids after complexed with Cr(Ⅲ) on the mobility of Cr(Ⅲ). Results indicate that bad mobility for soluble Cr(Ⅲ) and good mobility for Cr(Ⅲ)-EDTA/citrate. Nevertheless the diversity of oranic ligands and soil properties, Cr(Ⅲ)-organic acid exhibits different mobility, such as the mobility of Cr(Ⅲ)-citrate is not better than Cr(Ⅲ)-EDTA. Higher pH is beneficial to mobility of Cr(Ⅲ)-citrate in black soil and yellow-brown soil and goes against the mobility of Cr(Ⅲ)-citrate in red soil.