酸度对胡敏酸与镉和锌离子络合反应的影响

用离子交换平衡法研究了不同pH下胡敏酸与锌、镉单独及复合存在下形成络合物的稳定性及配位数.结果表明：在Zn^2＋,Cd^2＋单独存在时,络合反应的稳定常数及配位数随着pH值的增大而增大;相同pH条件下,Zn^2＋和胡敏酸络合物的稳定常数及配位数大于Cd^2＋.在Zn^2＋,Cd^2＋复合存在时,pH的变化与胡敏酸络合金属离子的稳定常数及配位数没有明显依存关系;与单独存在时相比,在pH 3.5和pH7.0时,Zn^2＋,Cd^2＋和胡敏酸络合物的稳定常数和配位数都减小;而在pH 5.0时,Cd^2＋和胡敏酸络合物的稳定常数和配位数都增大,Zn^2＋和胡敏酸络合物的稳定常数和配位数都减小.

THE IMPACT OF ACIDITY ON THE COMPLEXATION REACTION OF HUMIC ACID WITH Cd2+ AND Zn2+

The stability and co-ordination number of the complex compounds of humic acid with Zn~(2+) and/or Cd~(2+) at different pH levels were determined with the cation-exchange equilibrium method. The stability and co-ordination number of the complex compounds increased with pH when Zn~(2+) or Cd~(2+) existed separately. With the same pH, the stability and co-ordination number of the complex compounds of humic acid with Zn~(2+) were higher than those with Cd~(2+). When Zn~(2+) and Cd~(2+) co-existed in the soil, no reciprocal relationship was observed between the stability and co-ordination number of the complex compounds and pH. As compared with the separately existing Zn~(2+) and Cd~(2+), the stability and co-ordination number of the complex compounds decreased at a pH of 3.5 or 7.0; at a pH of 5.0, the stability and co-ordination number of the complex compounds of Cd~(2+) increased and that of Zn~(2+) decreased.