Rational Technology for Separation of Rare-Earth Elements of the Yttrium Group

The features of the extraction technology for the separation of rare-earth elements (REEs) of the yttrium group are considered with regard to the sharp reduction in the price of individual oxides. The price reduction has the same nature as the low prices of lanthanum and cerium oxides and is associated with a predominant increase in the consumption of praseodymium and neodymium and a slow increase in the consumption of other REEs, with the exception of terbium and dysprosium. Since all REEs are extracted from rare-earth concentrates, less in demand ones are stored or sold at very low prices. Elements such as samarium, europium, gadolinium, and dysprosium are used in high-tech instruments and devices. In this case, it is possible to allow the operation of low-profit production, but technological solutions must certainly be built taking into account the minimum costs and be the most economically effective. The authors propose a technology for separating elements of the yttrium group including the stages of isolation of yttrium 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). In the last operation, concentrates of the yttrium group REEs are isolated simultaneously. The process is carried out in the mode of complete internal irrigation using a 30 vol % solution of bis(2,4,4-trimethylpentyl)-phosphinic acid as an extractant. First, all cells of the cascade are filled with the initial solution. Separation zones are formed in the cells of the cascade with the accumulation of terbium–dysprosium, holmium–erbium, and thulium–ytterbium–lutetium concentrates. After the accumulation of products, the solution of concentrates is drained from the cells and the process starts again. If there is a need for any element of the yttrium group, the corresponding binary or ternary concentrate is separated to isolate the required element.