Characteristics of soil humic acid dissociation and its complexation with copper
土壤胡敏酸的解离及其与Cu2+的络合特征

Potentiometric titration and CCM were performed the study on humic acid extracted from soils.Results showed that humic acid is a mixture of two monoprotic acids and it fits the electrostatic model in CCM at pH3-7 .The dissociation constants and Cu complexation constants were determined by the optimization procedure in the computer program FITEQL32.The dissociation constants p KpKHL1 is in the range of 3.50 to 4.89, p K HL2 6.17 to 8.38, pKHL1 / pKHL2 is below 105, which is consistant with the results of potentiometric titration curve. The Cu2+ complexation constant,is 1.346 for old manured loessal soil and 2.241 for dark cultivated loessal soil.A good optimization result is given by nonelectrostatic model.