Infrared spectroscopy of metal carboxylates: II. Analysis of Fe(III), Ni and Zn carboxylate solutions

Abstract

The metal carboxylate complexes present in the organic solutions used in the hydrolytic stripping process strongly affect the nature of the solid precipitated; in some cases, the product is a mixed oxide while in others, a mixture of single-metal oxides is obtained. Infrared (IR) spectroscopy is a useful tool for determining the speciation of metal loaded organic phases. In the previous work, relationships of the form [V-10]= αA ν M + βA ν D were obtained for the estimation of the free Versatic acid present in metal carboxylate solutions at given specific temperatures. In this work, infrared spectroscopy has been used for the speciation of single-metal Versatic 10™ solutions containing Fe(III), Zn and Ni at temperatures between 20 and 200 °C. It was found that iron and zinc predominantly form complexes with bidentate structures at all the concentration levels tested, while the nickel complexes contain bidentate ligands at low concentrations and both monodentate and bidentate ligands at high concentrations. The evidence found in this work supports the existence of a binuclear ferric Versatic complex, [Fe(OH)V 2] 2, with chelating Versatic groups forming an octahedron around each of the iron atoms. An oxo-centred structure, containing only bridging carboxylate groups, is proposed for the zinc Versatic complex, which is believed to be present in the organic medium as Zn 4O(V) 6.