Kinetics of Fe(II) oxygenation and the nature of hydolytic products as influenced by ligands

The rate of oxygenation of Fe(II) and the nature of the resulting hydrolytic products were studied in 0.01 M ferrous Perchlorate -NaOH system at pH 6.00 and 23.5°C in the presence of selected inorganic and organic ligands (ligand/Fe molar ratio = 0.1). The oxygenation followed first order kinetics. The presence of complexing ligands retarded the rate of oxygenation with the rate constant decreasing in the order, perchlorate>fluoride>nitrate>chloride>caibonate>sulfate>silicate>phosphate for the inorganic ligands, oxalate>acetate>tartrate>citrate for the organic ligands. In the absence of perturbing ligands, the hydrolytic product formed at pH 6.0 was predominantly goethite with small amounts of poorly crystalline lepidocrocite. Presence of chloride, nitrate and fluoride at the concentration studied had no significant effect on the nature of the hydrolytic products of oxygenation formed. Sulfate, carbonate, and oxalate promoted the formation of lepidocrocite at the expense of goethite, whereas acetate promoted the formation of goethite at the expense of lepidocrocite. Silicate, phosphate, and tartrate, with strong complexation with Fe perturbed the crystallization processes resulting in the formation of X-ray noncrystalline Fe oxides. No precipitate was observed in the presence of citrate.Krishnamurti G.S.R., Huang P.M. Kinetics of Fe(II) oxygenation and the nature of hydolytic products as influenced by ligands. In: Proceedings of the 9th international Clay Conference, Strasbourg, 1989. Vol I : Clay-organic interactions. Clay minerals in soils. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1990. pp. 195-204. (Sciences Géologiques. Mémoire, 85