LIGAND COMPETITION METHOD FOR DETERMINING STABILITY-CONSTANTS OF FULVIC-ACID IRON COMPLEXES

The stability constants for the complexes formed between iron species existing in ambient soil environments and fulvic acids (FA) extracted from organic wastes like sewage sludge, farm yard manure, poultry manu re and press mud (sugar industry waste) were determined in aqueous med ia of pH 5.0 and 8.5 at 25 +/- 1-degrees-C by a modified approach of t he ligand competition method. The method employed in the investigation consisted of a system containing known quantities of the citric acid and fulvic acid fraction of a range of molecular weight eluting simult aneously in a sephadex gel (G 25) column, competing for known amounts of iron species for complexation. The complexes of iron with the fulvi c acid fraction and the citric acid were separated by a sephadex gel ( G 25) chromatographic technique and the amount of iron complexed with two competing ligands were measured. The method was first tested by es timating stability constants for the formation of zinc-fulvic acid com plexed at pH 5.0 and 8.5. The values were found to be near those repor ted in literature by other known methods. The estimated values of log K for the formation of Fe complexes at pH 5.0 with FA for farmyard man ure (FYM), sludge, poultry manure and press mud were 12.025, 11.461, 1 3.955 and 13.815, respectively. Appreciable increase in the values of log K were found when the pH of the reaction was raised to 8.5.