腐殖酸-锌络合物稳定性的研究

腐殖酸-金属络合物在土壤形成和植物营养等方面具有重要的作用。六十年代以来,这方面的研究日益增多。锌是植物所需的微量元素之一,在土壤中常以络合态存在。因此,以络合态存在的锌的数量及其稳定性对土壤的供锌能力将有较大的影响。不少研究者虽曾研究了腐殖酸一锌的稳定性^4,6,7,10],但所测得的稳定常数值差异甚大,有的可差几个甚至高达十个数量级。导致这种差异的原因很多,其中之一是各研究者所用的腐殖酸各人不同。一些研究者认为络合物的log K值因供试腐殖酸的腐殖化程度而异,另一些研究者认为log K值因腐殖酸分子大小不同而不同。本工作测定了不同来源的腐殖酸的某些性质及其与锌形成的络合物的稳定性,试图对它们之间的关系作一初步探讨。

STUDY ON THE STABILITY CONSTANTS OF ZINC-HUMIC ACID COMPLEXES

Stability constants of zinc-humic acid complexes separated from soils,compost,peat and weathered coals were determined by ion exchange equilibrium method.Humic substances studied varied markedly in average molecular weight,content of carboxyl and phenolic hydroxyl group,degree of dissociation of carboxyl group and aromaticity.The results showed that the stability constants of Zn-humic acid complexes varied with the different origins of the humic substances,with the highest logK of 7.85 for a weathered coal and the lowest value of 3.52 for the albic horizon of a albic brown forest soil.The log K was correlated significantly with the content of undissociated (Ar weakly dissociated) carboxyl group,but not with the content of total carbonyl group pr phenolic hydroxyl group,average molecular weight,or aromaticity of Mimic substances.