小分子有机酸对六种典型土壤中镉吸附-解吸的影响

Effect of Low Molecular Weight Organic Acids on the Adsorption-Desorption of Cd in Six Types of Soil

研究了柠檬酸和苹果酸对重金属镉在6种农田土壤中吸附-解吸行为的影响,同时探讨了有机酸pH对重金属镉在土壤中吸附的影响。试验结果表明镉浓度较低时,柠檬酸和苹果酸对土壤吸附镉的影响较小;镉浓度较大时,两种有机酸对土壤吸附镉具有抑制作用,而且柠檬酸的抑制作用大于苹果酸。在有机酸作用下土壤对重金属镉的吸附强度大于无酸条件下的吸附强度。随着有机酸浓度的增加碱性土壤对重金属镉的吸附量逐渐减小,在碱性土壤中有机酸对镉的吸附具有抑制作用;酸性土壤中低浓度有机酸促进重金属镉的吸附,而高浓度又抑制镉的吸附,柠檬酸的抑制作用大于苹果酸。与对照(NaNO3体系)相比,柠檬酸和苹果酸对土壤吸附镉均表现为抑制作用。不论是在有酸体系或无酸体系中土壤对重金属镉的吸附量都随体系pH值的增加而增加。

Effects of citric acid an d malic acid on the adsorption-desorption of Cd from six farmland soils were studied. We also studied the effect of organic acid pH on Cd adsorption. The results showed that when the Cd concentration was low, the citric acid and malic acid had little effect on the adsorption of Cd; when the concentration was higher, two kinds of organic acid had inhibitory effects on the adsorption of Cd, and the inhibitory effect of citric acid was greater than malic acid. The adsorption strength of Cd in soils with acid condition was greater than the adsorption strength without acid. As the concentration of the organic acids increased, the Cd adsorption capacity was decreased gradually and the organic acids inhibited the Cd adsorption in the alkaline soils. The organic acids promoted the Cd adsorption with low concentrations but inhibited the Cd adsorption with high concentrations, and the inhibitory effect of citric acid was greater than malic acid. Compared with control （NaNO3 system）, the citric acid and malic acid showed inhibitory effects on Cd adsorption. No matter how with or without organic acid the capacity of Cd, the adsorption increased with the increasing pH.