Application of silica-based sorbents to extraction of rare earth elements from loparite processing products

Abstract

Apatite and loparite are the main sources of rare earth elements (REE) in Russia. Loparite is a complex titanate and niobate containing up to 30% wt. of REE oxides predominantly of the cerium group. Extraction processing methods are used at the stages of group separation and separation of REE concentrates. Tributyl phosphate (TBP) is a widely used extracting agent for these purposes. Extraction technologies have a number of disadvantages, in particular, a large number of separation stages because of low separation coefficients of individual REE combined with difficulties in separating liquid phases. The use of TBP-containing sorbents allows to eliminate the latter disadvantage. Both organic polymers and inorganic compounds may be used as sorbent carriers; among inorganic ones, silica is widely used, and it was selected for this study. The purpose of this work was to study the effect of variations of the proposed methods for synthesis of silica and modified TBP based sorbents on their ability to extract REE from the solutions of loparite concentrate processing. The article briefly describes a procedure for sorbent samples synthesis. Tetraethoxysilane, tributyl phosphate, stannic chloride and nanotubes have been used as starting reagents for the synthesis. A number of physicochemical properties have been determined for the synthesized samples (pore volume and their average diameter, surface area and morphology, acid-base properties of the surface), and thermogravimetric analysis has been performed. The sorption properties of the samples have been tested by the example of REE extraction from process solutions of loparite working up. The separation coefficients of Sm/La pairs up to 3.7, Pr/Nd up to 1.8 were obtained; therefore, the studied samples may be potentially used for samarium isolation from the REE combination, as well as for Pr -Nd pair separation.