Observations on the dispersion and aggregation of clays by humic substances, I. Dispersive effects of humic acids

Abstract

Although humic substances are normally considered as aggregating agents in soil formation processes, we have shown that within a certain concentration range humic substances are also able to disperse soil particles. The dispersive effect was particularly evident at humic acid concentrations of around 40 mg l −1; at higher concentrations the action was less effective. At 40 mg l −1 humic acids were between 20 and 30% less effective than the commonly used hexametaphosphate at 0.4%. No significant differences were observed between the performance of humic acids at 40 mg l −1 and Calgon at 0.5%. When the performance of humic acid was compared with that of hexametaphosphate of equal strength (40 mg l −1), the former appeared approximately 140 times more effective for the dispersion of the fine clay fraction (< 0.6 μm) and approximately 1.2 times more efficient in the case the coarse clay fraction (0.6–2.0 μm).