Rational technology for separation of yttrium-group rare-earth elements

Abstract

The paper studies the features of the extraction technology used to separate yttrium-group rare-earth elements taking into account sharply reducing prices for individual oxides. The latter, along with the low prices for lanthanum and cerium oxides, is associated with a predominant increase in the consumption of praseodymium and neodymium and a slow increase in the consumption of other rare-earth elements (REE), except for terbium and dysprosium. Since all REE are extracted from rare-earth concentrates, less marketable ones are stored or sold at extremely low prices. Elements such as samarium, europium, gadolinium, dysprosium are used in high-tech instruments and devices. At the same time, some low-profit production is possible, but process solutions must certainly be developed providing for minimum costs and be the most cost-effective. The authors propose a technology for separating yttrium-group elements including yttrium isolation stages in a single-stage mode by extraction with a mixture of three extractants (25 vol.% trialkylmethylammonium nitrate – 20 vol. % tributyl phosphate – 20 vol.% higher isomeric carboxylic acid) followed by separation of the triad of elements (samarium-europium-gadolinium) by extraction with organophosphoric acids: 30 vol.% solution of di-2-ethylhexylphosphoric acid or 30 vol.% solution of bis(2,4,4-trimethylpentyl)-phosphinic acid. At the last operation, yttrium-group REE concentrates are isolated simultaneously. The process is conducted in the conditions of complete internal irrigation with the 30 vol.% solution of bis(2,4,4-trimethylpentyl)-phosphinic acid used as an extractant. Initially, all the extraction cascade cells are filled with the initial solution. Separation zones are formed in the extraction cascade with the accumulation of terbium-dysprosium, holmium-erbium and thulium-ytterbium-lutetium concentrates in some cells. Once the products are accumulated, the concentrate solution is drained from cells, and the process starts again. If there is a need in some yttrium-group element, the corresponding binary or ternary concentrate is separated with the isolation of the element required.