Research on the design of extractant/diluent and equipments for the separation and purification of heavy metals.

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The extraction of hydrochloric acid by tri-n-octylmethylammonium chloride was investigated as a basis for the study of the metal extraction from this acid solution, employing diluents with differing solvating characteristics to the extractant, such as benzene, xylene, chloroform and 2-ethylhexyl alcohol. Extraction equilibrium formulations were established for each diluent system. These are reasonably interpreted by the solvation effect of each diluent employed.The extraction of metals such as cobalt and vanadium was studied employing benzene to weakly solvate the extractant. In benzene, the extractant was found in the study of the acid extraction to need stabilizing molecules to surround itself. An extraction scheme is presented, which assumes that the extraction of metals occurs via reaction with the monochloride acid-complex of the extractant, i.e., via the replacement of water and acid in the extractant hydration sphere by metal ion. The data obtained were successfully analysed according to this scheme.The solvating effect diluent such as chloroform and 2-ethylhexyl alcohol causes a decrease in the requirement for water and acid as stabilizing molecules for the extractant and thus prevents water and acid from taking part in the mechanism of metal extraction. This effect simplifies the mechanism of metal extraction. The principal effect is, however, to reduce the extraction performance of the extractant due to stabilization with the diluent. Actually, the extractant is stabilized by forming a bisolvate with alcohol molecules.Continuous flow extraction was successfully operated, using one stage mixer-settler and employing xylene as a diluent, under the conditions of mean residence time of solutions of about 5 min in the mixer and about 10 min in the settler. The extraction equilibrium in the mixer and complete phase separation in the settler have been met satisfactorily.