Effects of Organic Acids and Phosphate on Lead Release from Two Contaminated Soils

Soil culture and chemical extraction were used to study the effect of different low molecular weight organic acids and phosphate on lead release in two exogenous contaminated soils. The result showed that the amount of soluble lead of red soil and brown soil increased with the increase of concentration of organic acids. When the concentration of the tested organic acids was no less than 1 mmol·L-1, the amount of lead released by three organic acids at the same concentration was citric acidacetic acidoxalic acid. While the concentration of organic acids was no more than 0.5 mmol·L-1, the amount of soluble lead was oxalic acidcitric acidacetic acid. After a mix of 2 g·kg-1 P, contami- nated red soil and 50 mmol·kg-1 organic acids in three different orders, soluble lead leaching rates of red soil dealt with citric acid were 66% (organic acid first), 58%(phosphate and organic acid added simultaneously), and 70%(P first), respectively; while in terms of oxalic acid and acetic acid were 90% , 89% , 94% and 10% , 8% , 10% . In brown soil, these results were 106.46%, 104.43%, 105.19%(citric acid); 43%, 48%, 58%(oxalic acid); 38%, 42%, 55%(acetic acid). Therefore, the lowest soluble lead leaching rates in red soil was lower than that in brown soil under the tested conditions.