CHARACTERISTICS OF WATER-SOLUBLE FULVIC ACID-COPPER AND FULVIC ACID-IRON COMPLEXES

Abstract

Water-soluble fulvic acid [FA]-C and FA-Fe complexes were prepared with FA:metal ratios of 1:0.5 and 1:1, at pH 4 and 6. After the complexes were freeze-dried, they were characterized by chemical, spectroscopic (IR, ESR and Mossbauer), X-ray, and thermal (differential thermal analysis) methods. The major FA functional groups involved with metal complexing were COOH and phenolic OH groups. ESR data showed that substantial portions of the metals in the complexes formed inner sphere complexes with the FA. The Cu in all complexes was divalent, whereas the Fe was trivalent. From X-ray diffraction patterns, it appeared that metals brought FA molecules closer together by bridging adjacent FA molecules. The thermal stability of FA decreased as it complexed with metals. Apparently, the complexing of Cu and Fe exerted strains on the structure of the FA, therby lowering its resistance to thermal decomposition. At least protions of the Cu and Fe are strongly complexed by the FA.