小分子有机酸对紫色土中Pb的活化机理研究

The Mechanism of Low-Molecular-Weight Organic Acids on Lead Desorption in Purple Soils

以紫色土为研究对象,分别用强酸和小分子有机酸盐模拟柠檬酸、酒石酸、乙酸中质子和酸根离子,研究典型小分子有机酸对紫色土中铅(Pb2+)的活化作用,探讨其对紫色土中Pb2+的活化动力学。结果表明:乙酸对Pb2+的活化以质子作用为主,240min内的快反应阶段达到最大解吸量的76.05%,能快速解吸静电吸附态Pb2+;酒石酸则表现出较强的络合配位作用,其钠盐对紫色土中Pb2+的活化能力大于酒石酸自身;柠檬酸在借助滴定模拟的方法时,无法判断质子与酸根的作用大小,在动力学中使用双指数动力学模型得出,慢反应占总反应的比例最高达48.39%,由于较高的络合稳定常数与较多的有机配体,能够破坏更多化学键而与Pb2+形成多齿多核状络合物,释放专性结合位点的Pb2+。

Hydrochloric acid,citrate,tartrate and acetate were used to simulate the protons-function and ligand-function of low-molecular-weight organic acids（LMWOAs）for mobilizing lead（Pb^2＋）in purple soils.A desorption kinetic study was used to study the desorption effects of Pb^2＋ by typical LMWOAs in different concentrations.The results indicated that：Proton-function was the main mechanism for Pb^2＋ desorption by acetic acids,and the desorption capacity of fast reaction stage（0～240min）reached 76.05%of maximum desorption capacity.The Pb^2＋ bonds through electrostatic interaction were mobilized rapidly in this stage.Tartaric acid showed a strong complex function,the desorption capacity of tartrate was higher than tartaric acid.The quantitative analysis of proton-function and ligand-function by citric acid were unclear in simulation,so kinetics study was used to citric acids desorption process further,and the double exponential kinetics equation fitted well for citric acids（r ranges from 0.949 to 0.985,P〈0.01）.The proportion of slow reaction stage（after 240min）was up to 48.39%,and more chemical bonds between Pb^2＋ and ligands could be destroyed by complexation.Pb^2＋ in specific binding sites were released by the forming process of multi-dentate or multinuclear complexes.