The extraction of nitric acid and thorium nitrate by tri-n-octylphosphine oxide in cyclohexane

Abstract

The distribution of nitric acid and thorium(IV) nitrate between aqueous solutions and solutions of tri-n-octylphosphine oxide in cylcohexane has been examined as a function of temperature and various extraction variables at constant aqueous ionic strength. Up to a maximum concentration of 0·4 M, the distribution behaviour of nitric acid was found to be consistent with first power dependency on the organic reagent concentration. In the case of acidic thorium nitrate solutions, provided the concentration of both thorium(IV) and hydrogen ion are maintained below 0·01 M, the extraction of the metal as Th(NO 3) 4·3TOPO is indicated. At higher concentrations the formation of organic adducts containing both the metal nitrate and nitric acid takes place. The temperature dependency of the extraction is very small in the case of the acid extraction and too slight in the case of thorium nitrate to be observed by the analytical methods used. During the course of these studies the solubility and density of saturated tri-n-octylphosphine oxide solutions in cyclohexane in the temperature range of 6·5–35°C was also measured.