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采用经改良的电位滴定法研究了腐殖酸与质子和钙离子反应的动力学特征 ,在恒温和连续通氩气保持严格无氧条件下 ,用标准酸将腐殖酸从中性滴定至pH2 6左右 ,在每一滴定点的反应动力学可分为快反应和慢反应两个阶段。各阶段体系的氧化还原电位 (ER)和玻璃电极电位 (EG)的变化可用松弛动力学方程Y =Y0 EXP(-t/τ)描述。在一定条件下 ,在慢反应阶段可观察到明显的震荡反应 ,表明腐殖酸体系为非平衡体系。腐殖酸与钙离子的反应是受扩散控制的慢反应过程。反应达到稳态后 ,ER 和EG 呈线形依托关系 ,其斜率ΔER/ΔpH(4 5 3± 1mV/pH)随腐殖酸和支持电解质不同变异甚小 ,可作为腐殖酸—金属离子反应的稳态指标。据此研究了腐殖酸的质子反应特征 ,获得了重现性很好的试验结果。表明供试腐殖酸存在HA、H2 A、H3A和HA2 四种类型配位基团 ,其表观解离常数 (pK)分别为 5 79～ 5 82、3 77～3 84、1 64～ 1 71和 2 75～ 2 79。
The kinetic characteristics of humic acid reaction with proton and calcium ion were studied by modified potentiometric titration. The titration of humic acid from neutral to pH2 6 The reaction kinetics at each titration point can be divided into two phases: fast response and slow response. The redox potential (ER) and glass electrode potential (EG) of each phase can be described by relaxation kinetic equation Y = Y0 EXP (-t / τ). Under certain conditions, a clear oscillatory reaction was observed during the slow reaction stage, indicating that the humic acid system is an unbalanced system. The reaction of humic acid with calcium ions is a slow reaction process controlled by diffusion. After the reaction reached steady state, ER and EG showed linear dependence, and the slope ΔER / ΔpH (453 ± 1mV / pH) with humic acid and supporting electrolytes varied very little and could be used as humic acid-metal ion reaction Steady-state indicator. Based on this, the proton reaction characteristics of humic acid were studied and good reproducibility test results were obtained. The results showed that HA, H2 A, H3A and HA2 exist in the tested humic acids and their apparent dissociation constants (pK) are from 5 79 to 5 82, 3 77 to 3 84 and 1 64 to 1 71 and 2 75-279.