低分子有机酸/盐对复合污染土壤中Cd、Pb有效性的影响

Effects of Low Molecular-weight Organic Acids/Salts on Availability of Cadmium and Lead in Mixed Metal-polluted Soils

模拟森林凋落物淋洗液中草酸/盐和柠檬酸/盐浓度范围,研究了不同浓度草酸/盐和柠檬酸/盐溶液对复合污染土壤中镉(Cd)、铅(Pb)有效性的影响及机制。结果表明:草酸/盐、柠檬酸/盐均促进腐殖质层(A1)和淀积层(B)土壤中Cd、Pb的活化释放,以浓度5.0mmol·L-1时释放效果最显著,且对Pb的释放效应强于Cd。低分子有机酸盐对Cd、Pb的释放效率强于同浓度的相应有机酸,即草酸/盐强于草酸、柠檬酸/盐强于柠檬酸,低分子有机酸/盐类物质促进重金属释放的主要机理在于有机酸阴离子反应。同浓度草酸/盐和柠檬酸/盐对Cd、Pb有效性的影响,表现为柠檬酸/盐强于草酸/盐,即柠檬酸强于草酸,柠檬酸/盐强于草酸/盐,这与2种低分子有机酸的化学结构、离解常数及其和重金属形成络合物的稳定性大小有关。几种浸提剂对A1层土壤Cd、Pb的活化释放效应明显高于B层。

A series of batch experiments were conducted to study the effects of low molecular-weight organic acids/salts on availability of cadmium and lead in mixed metal-polluted soils by simulating concentrations of oxalic and citric acids in forest litter leachates. Result showed that oxalic acid/oxalate and citric acid/citrate encouraged Cd and Pb release in A1 and B horizons,of which 5. 0 mmol/L concentration had the best capacity,and the release capacities of Pb were higher than those of Cd. Oxalate and citrate solutions both had much higher soil Cd/Pb-release efficiency than oxalic acid and citric acid solutions at the same concentration,therefore,the mechanisms for oxalic acid/oxalate and citric acid/citrate to promote the release of soil Cd and Pb consists in the reactions of oxalic and citric acids anions. The effects of citric acid/citrate on the availability of Cd and Pb are more obvious than those of oxalic acid/oxalate at the same concentration,i. e. citrateoxalate, citricoxalic,which is related with chemical structure,dissociation constant,and complexation capacities of the extractants. The release capacities of Cd and Pb by the extractants of A1 horizon soil are higher than those of B horizon.