Determination of organic phase complexes formed on extraction of iron(III) from aluminium nitrate solutions with versatic 10

The extraction of Fe(III) from concentrated aluminium nitrate solutions by Versatic 10 in Escaid 110 was studied, using an AKUFVE system for the determination of extraction isotherms at constant pH values. The extraction data were analysed initially by classical slope analysis but this was found to be inadequate due to the complexity of the organic phase speciation. A statistical technique was then used to evaluate the compositions of the organic phase complexes by finding the best fits to the extraction data. Equilibrium constants governing the extraction of these complexes were calculated. Independent measurements of the amount of Versatic acid bound in the organic iron complexes were made by quantitative infrared analysis of organic extracts. Agreement between the statistical and infrared results was good. Complexes of the general form (Fe(OH) 3− V n · sHV) x were found, where n varied from 1 to 2 and s from about 0.5 to 2.5, with both decreasing as the iron loading in the organic phase was increased. Values of 2 or 3 were generally found for x, indicating the predominance of dimers and trimers.