有机酸对珠江三角洲水稻土镉解吸行为的影响

Effect of Organic Acids on Cadmium Desorption from Paddy Soil of the Pearl River Delta in China

用批平衡实验方法，研究了3种有机酸及其两两混合酸在一系列pH值梯度下（pH3～7）对珠江三角洲沉积型水稻土镉（Cd）解吸的影响．结果表明，只有柠檬酸及含柠檬酸的混合酸在较低酸度区（pH〉5）可以显著促进Cd的解吸，这一效应与浓度成正相关，而苹果酸、草酸及二者的混合酸在所试验酸度范围均促进了Cd吸附，特别是草酸，促进作用随浓度的升高而增强．在较低pH区（pH〈5），苹果酸最有利于Cd解吸，在高pH区（pH≥5），柠檬酸最有利于Cd解吸，草酸的Cd解吸能力最低．混合有机酸交互作用不显著，对Cd解吸的影响约等于各个单独酸的作用之和，但在一些酸度条件下，可存在颉颃作用．

Cadmium is one of the most serious contaminants in cuhivated lands in China. Its behavior can be affected by minor organic acids in soil. Batch equilibrium experiments were conducted to study the effects of three organic acids and their mixed solutions on Cd desorption from paddy soil of the Pearl River Delta in China at a serial medial pH values from 3 to 7. Results showed that only citric acid and the mixed solutions containing it could significantly increase the desorption of Cd from the soil at pH higher than 5.0. The higher the concentration of citric acid, the more the desorbed Cd. Malic acid and oxalic acid and their mixed solutions all increased the adsorption of Cd from soil. Among the three acids, oxalic acid desorbed least Cd, malic acid most at low pH and citric acid most at high pH. Mixing organic acids did not increase or decrease Cd desorption in comparison with single acid alone. Cd desorption was contributed mainly to the individual acids, little to the interaction among the acids. Fig 3, Tab 2, Ref 22