Department of Agricultural Chemistry and Soil Science, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal, 741252.
Present addres: 1Directorate of Research, Bidhan Chandra Krishi Viswavidyalaya, Kalyani, Nadia, West Bengal, 741235.
The natural humic and fulvic acids and the synthetic humic acids, characterized in respect of their important physico-chemical properties, as discussed in part 1 of this paper, were employed to study the complexation equilibria between chromium (Cr) and the humic/fulvic acid samples by having recourse to the ion-exchange equilibrium method. The stability constants (log K) of the resulting Cr-humic acid complexes exhibited wide variations, while the corresponding log K values for the Cr-fulvic acid complexes had less variation. The relationships between the given log K values and the relevant physico-chemical properties of the present humic/fulvic acids were ascertained by examining the simple correlation coefficients and the appropriate step-up multiple regression equations. It was found that the log K values depended more on the molecular weight of the given humic/fulvic acids and their time to attain stable higher pH during pH-metric titration. Thus, the hydrophobic moieties of the given humic/fulvic acids appeared to exert stronger influence in imparting the given stability to the resulting Cr-humic/fulvic complexes, as compared to the acidic functional groups of these humic/fulvic acids.
Humic substances, humic acid, fulvic acid, chromium, chromium-humic complexes, stability constant
