小分子有机酸对恒电荷土壤胶体Pb^(2+)吸附-解吸的影响

Effect of low molecular weight organic acids on Pb^(2+) adsorption and desorption by constant charge soil colloids

供试土壤胶体对Pb2 + 吸附及吸附态Pb2 + 的解吸等温线均符合Freundlich和Langmuir等温式 .吸附常数Ka 值大小为土娄土 >黄绵土 >黑垆土 >黄褐土 ,其大小次序与表面总电荷密度σ0 大小一致 ,表明了各土壤胶体对Pb2 + 吸附强度的大小 .在小分子有机酸作用下 ,吸附量降低 ,吸附亲和力增加 ,柠檬酸的影响大于草酸的影响 ;解吸后残留Pb2 + 吸附常数Kd 值的大小基本为土娄土 >黄褐土 >黑垆土 >黄绵土 ,反映了解吸残留Pb2 + 吸附强度的大小 ,与各土壤胶体有机质和游离氧化铁含量有关 .在NaNO3 和草酸溶液中 ,吸附 解吸等温线相距较远 ,吸附 解吸之间存在着滞后性 ;在柠檬酸作用下 ,吸附 解吸等温线基本接近 ,二者之间具有一定的可逆性 .

The isothermal curves of Pb 2+ adsorption-desorption by soil colloids followed Freundlich and Langmuir equation. The adsorption constant K a 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 σ 0, an indicator of the strength of Pb 2+ adsorption by each soil colloid. Low molecular- weight organic acids (LMWOAs) made Pb 2+ 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 Pb 2+ 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 Pb 2+ after desorption, and was related to the contents of organic matter and free ferric oxide. The isothermal curves of Pb 2+ desorption from soil colloids were obvious higher than those of Pb 2+ adsorption. In NaNO 3 and oxalic acid background solution, the isothermal curves of Pb 2+ adsorption were far away from those of Pb 2+ desorption, showing that the hysteretic degree between adsorption and desorption was very large. The isothermal curves of Pb 2+ desorption from soil colloids were closed to those of Pb 2+ adsorption in citric acid background solution, which showed that the Pb adsorption and desorption was reversible.