腐殖酸—金属离子反应动力学特征与稳态指标的探讨  

KINETICS OF METAL ION REACTIONS WITH HUMIC ACIDS AND INDEX FOR STEADY-STATE

作　　者：魏世强[1] 李光林[1] sterberg R 王定勇[1] 

机构地区：[1]西南农业大学资源与环境学院,重庆400716 [2]Department of Chemistry,Swedish University of Agricultural Sciences,Uppsala,sesweden75007

出　　处：《土壤学报》2003年第4期554-561,共8页Acta Pedologica Sinica

基　　金：国家自然科学基金项目 (4 0 0 710 49);教育部留学回国人员启动基金项目资助

摘　　要：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。Kinetics of humic acids interactions with proton and calcium ions were studied u sing modified potentiometric titration Solutions of 1 and 2 g L -1 humic acids i n 0 1 mol L -1 NaClO 4 or KCl were titrated with 0 1 mol L -1 HClO 4 or HCl from pH 7 5 to about 2 6 at 24 ℃ under carefully controlled anaerobic conditions Th e reaction kinetics were well described by a traditional relaxation equation Y=Y 0 EX P( -t/τ ) In each titration point occurred an initial fast relaxation of re dox p otential ( E R) and glass electrode potential ( E G), followed by furthe r slow relax ation and/or oscillations of E R And eventually, the reaction reached a s teady s tate, indicating the non-equilibrium nature of humic acid solution system The a nalyses of time-resolved data of E G for the stepwise addition of calcium ions to humic acid solutions revealed that the overall reaction rates were diffusion-c o ntrolled rather than reaction-controlled After relaxation down to a steady st at e E R showed a linear pH dependence with an almost constant slope of 45 3 ±1 mV/p H unit despite the differences of humic acid concentrations and supporting elect rolytes, which then could be applied as an index of the arrival at a steady stat e of the humic acid interactions with metal ions The characteristics of proton reactions with humic acids were studied using the suggested index, and well repr oducible results were obtained Four types of binding sites HA,H 2A,H 3A an d HA 2 with accordingly apparent pK-values of 5 79～5 82, 3 77～3 84, 1 64～1 7 1 and 2 75～2 79 were found existing in the studied humic acids

关 键 词：腐殖酸-金属离子 反应动力学 特征特性 稳态指标 地球 生态环境 天然有机物 

分 类 号：S153.1[农业科学—土壤学] X131[农业科学—农业基础科学]