[Effect of low molecular weight organic acids on Pb2+ adsorption and desorption by constant charge soil colloids].
The isothermal curves of Pb2+ adsorption-desorption by soil colloids followed Freundlich and Langmuir equation. The adsorption constant Ka showed the trend of old manured loessal soil > yellow loessal soil > dark cultivated loessal soil > yellow cinamon soil, which was consistent with surface charge density sigma 0, an indicator of the strength of Pb2+ adsorption by each soil colloid. Low molecular-weight organic acids (LMWOAs) made Pb2+ adsorbed amount decreased and adsorption affinity increased, and the effect of citric acid was larger than that of oxalic acid. The constant Kd of residual Pb2+ adsorption after desorption showed the trend of old manured loessal soil > yellow cinamon soil > dark cultivated loessal soil > yellow loessal soil, which reflected the adsorption strength of residual Pb2+ after desorption, and was related to the contents of organic matter and free ferric oxide. The isothermal curves of Pb2+ desorption from soil colloids were obvious higher than those of Pb2+ adsorption. In NaNO3 and oxalic acid background solution, the isothermal curves of Pb2+ adsorption were far away from those of Pb2+ desorption, showing that the hysteretic degree between adsorption and desorption was very large. The isothermal curves of Pb2+ desorption from soil colloids were closed to those of Pb2+ adsorption in citric acid background solution, which showed that the Pb adsorption and desorption was reversible.
Yang
Yati
Y
College of Life Science, Northwest Science and Technology University of Agriculture and Forestry, Yangling 712100, China. yatiyang@hotmail.com
Wang
Xudong
X
Zhang
Yiping
Y
Qu
Aihua
A
D000327:Adsorption; D019343:Citric Acid / Q000494:pharmacology*; D003102:Colloids; D007854:Lead / Q000737:chemistry*; D008970:Molecular Weight; D019815:Oxalic Acid / Q000494:pharmacology*; D012987:Soil / Q000032:analysis*
D003102:Colloids; D012987:Soil; D019343:Citric Acid; D007854:Lead; D019815:Oxalic Acid