SEPARATIONS OF YTTRIUM AND SOME RARE EARTHS BY LIQUID-LIQUID EXTRACTION

Abstract

The use of liquid-liquid extraction for the separation of some inorganic compounds was demonstrated. The yttrium-- rare earth concentrates were obtained from Fergusonite ore, Gadolinite ore, and a by-product from an ion-exchange resin separation process. In each case the mixture in terms of oxide was composed of from 50 to 60% yttrium and 5 to 15% heavy rare earths with the light rare earth fraction constituting the remaining material. Tributyl phosphate was generally employed for exracting nitric acid solutions of these concentrates. Single-stage exractions indicated that the relative exractability of certain rare earths from an aqueous system, 3.0 molar or greater in nitric acid, increases with atomic number. At lower nitric acid concentrations deviations from this trend were observed. The mass transfer values showed a minimum at a nitric acid concentration of about 6.0 molar. Yttrium extracts in the holmium region from a highly concentrated nitric acid system, in the dysprosium region from a 6 to 12 molar nitric acid system, in the gadolinium region from a 3.0 to 4.5 molar nitric acid system and with the lighter rare earths from very low nitric acid systems. A number of 20-stage countercurrent extractions were carried out employing nitric acid solutions ofmore » yttrium and rare earths as the aqueous feed phase and tributyl phosphate as the organic phase. When extracting their concentrated nitric acid solutions, the organic product generally contained yttrium and heavy rare earths while the aqueous product conteined the light rare earth fraction plus a small amount of yttrium and dysprosium. In one multistage exraction the organic product phase delivered 90 per cent of the total yttrium which gave an oxide that was 91 per cent pure. Extraction of a light rare earth fraction resulted in an enriched concentrate of praseodymium and samarium. Gadolinum and dysprosium were separated from yttrium to a considerable extent by extracting from a very low nitric acid solution. The extractions of these yttrium-rare earth concentrates showed the possibility of separating yttrium from any particular rare earth and of some individual rare earths. The liquid-liquid system presented indicated further the applicability of solvent extraction for separating inorganic compounds. Much of the information from this work is directly applicable to practical separation problems and therefore should be readily adaptable to specific laboratory and industrial scale operations. (auth)« less