道南膜技术测定Ca(NO_3)_2溶液体系中汞的化学形态

Measuring mercury form in Ca(NO_3)_2 solutions using Donnan membrane technique

虽然道南膜技术(DMT)已经成功用于土壤/溶液中多种重金属自由态离子浓度的测定,但DMT技术测定Hg的形态尚未解决.采用DMT测定Ca(NO3)2溶液体系中Hg化学形态.实验结果表明,Hg在阳离子交换膜内的吸附除静电吸附外还存在结合力更强的化学吸附,Hg在阳离子交换膜内扩散成为Hg跨膜传输受阻的主要因素,限制道南膜技术用于Hg形态测定.Hg2+和Hg(OH)2都表现出在阳离子交换膜上的强烈吸附,供端(Donor)Hg损失达50%以上.缩短试验时间至8h以内,可在一定程度上降低Hg吸附.计算结果表明,由于大量的Hg滞留在阳离子交换膜内,在计算受端(Acceptor)Hg浓度时引入滞留系数补偿供端Hg的损失,较好地预测了Ca(NO3)2溶液体系中Hg的化学形态.

Although the Donnan membrane technique has been applied successfully to measure some free metal ions in the environmental system,it has never been used for identifying mercury form yet.The rate-limiting step of Hg transport from donor side to acceptor side was Hg diffusion in the membrane.Apart from electrostatic adsorption,there was strong chemical adsorption of Hg in the membrane which played an important role in restricting the applicability of DMT in Hg species measurement.The Hg loss in the donor side was more than 50% because of strong chemical adsorption on the cation exchange membrane.The chemical adsorption of Hg can be reduced by shortening the sampling time to 8 hours.When a retardation factor was introduced to account for the retardation of Hg in membrane,the chemical form of Hg in Ca（NO3）2 solution can be better predicted.