土壤腐殖酸的质子解离平衡研究

Study on the Protonic Dissociation Equilibrium of Soil Humic Acid

本文用电位滴定法对提纯了的土壤胡敏酸ＨＡ、富啡酸ＦＡ 的质子解离平衡进行了研究，并根据离散模型和连续亲和谱模型对实验数据进行了分析，得知ＨＡ 和ＦＡ 均含有三类酸性基团，在离子强度为０．１ ｍ ｏｌ／Ｌ、温度２５℃的条件下，ｐＫａ１ 在ｐＨ＜ ３ 时已经解离，ｐＫａ２ 为４．５～５．５ 和４．５～５．０，ｐＫａ３ 为７．５～９．０ 和７．０～９．０。它们的解离度均随ｐＨ 值的升高而增加，这种变化正反映了腐殖酸酸性功能基的非均质性。用两种模型处理滴定数据所得的结果，在误差允许范围内是一致的。

The paper discusses the protonic dissociation equilibrium of pure soil humic acid and fulvic acid by the method of potentiometric titration.Discrete model and affinity spectrum model were employed to treat the experimental data. It was found that HA and FA contain three acidic groups,their apparent dissociation p K a were in the range of 2.0～3.0, 4.5～5.5, 7.5～9.0 and 2.0～3.0, 4.5～5.0, 8.0～9.0 respectively, in respect to 0.1 mol/L ionic strengths and temperature 25℃. Their dissociation degrees increased with pH and revealed the heterogeneous property of acidic function groups. The method is suitable to treat the data.