Acidity, Quotient Values and Metal Retention Power of Humic Acids of Varying Molecular Weights

Humic acids were separated into different molecular weight fractions by Sephadex gel filtration. Paper chromatographically separated fractions of humic acids were also obtained. Some high molecular weight humic acids were extracted from soils. The lowest molecular weight fractions have the highest total acidity and highest quotient values. There is a direct relationship between molecular weight and metal holding capacity. The lowest molecular weight fraction has the maximum metal fixing capacity. Metal adsorbed follows the order: Cu⁺² > Fe⁺² > Mn⁺². All the acidic functional groups of humic acids do not participate in the complex formation as a result of which there are some residual acidities of the organo-metallk complexes.