Stability of some inorganic and organic complex compounds of zirconium and hafnium

Abstract

THE chemical properties of hafnium and zirconium are very similar. This explains the discovery of hafnium 133 years later than that of zirconium in spite of the fact that hafnium and zirconium are always present together. Despite the fact, that interest to the chemistry of zirconium and hafnium has increased during the last years, little is known about complex formation. There are only a few determinations of the composition and stability constants of zirconium compounds. Analogous data for hafnium are not available. Such a situation results first of all from the complexity of behaviour of these elements in solutions. Because of the high charge and small radius, zirconium and hafnium have a great tendency to undergo hydrolysis with the formation of polynuclear compounds. Investigation of the reactions involved in complex formation, which are competitive with the reactions of hydrolysis and formation of polynuclear compounds, is very complicated on account of the simultaneity of the several processes. New methods of investigation, namely, solvent extraction and ion exchange, make it possible to approach the investigation of complex formation by zirconium and hafnium with various substances in solutions in a more profound way. The present review sets forth the results of a number of our investigations of equilibrium reaction in the complexing of ions of Zt a+ and Hf 4+ with inorganic and organic addends. (1-6) The behaviour of these elements in sulphate, nitrate and chloride solutions was investigated. Oxalic acid and a number of carboxylic and hydroxycarboxylic acids were selected as organic complexing agents. To determine the compositions and stability constants of the complex compounds of zirconium and hafnium, we have used the method of ion exchange. EXPERIMENTAL