[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.
College of Life Science, Northwest Science and Technology University of Agriculture and Forestry, Yangling 712100, China. yatiyang@hotmail.com
Yati
Y
Yang
Xudong
X
Wang
Yiping
Y
Zhang
Aihua
A
Qu
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