Concentration and Separation of Heavy Rare-Earth Metals at Stripping Stage

Olga Cheremisina,Alexander Fedorov,Daria Alferova,Vasiliy Sergeev

doi:10.3390/met9121317

Abstract

The separation and concentration processes of heavy rare-earth metals—yttrium, ytterbium, erbium, and dysprosium—during stripping from the organic phase based on di-2-ethylhexylphosphoric acid (D2EHPA, or DEHPA) solutions were investigated in this work. Optimal conditions providing high separation factors of rare-earth metals (REM) and their extraction degree to the aqueous phase were determined. The usage of sulfuric acid solutions with a concentration of 2–6 mol/L, depending on the type of extracted rare-earth element, was proposed as a stripping agent for rare-earth metals (REM), and the usage of oxalic acid solution was proposed as an iron stripping solution from the organic phase. To increase the REM stripping efficiency, the antagonistic effect of tributyl phosphate in the di-2-ethylhexylphosphoric acid-kerosene-tributyl phosphate system was considered. The possibility of increasing the capacity of the organic solvent by cleaning the organic phase from iron ions using oxalic acid solutions was revealed. The influence of temperature, aqueous and organic phase ratio, stirring rate, and re-extractant concentration on the distribution and separation factors of adjacent heavy rare-earth-metal (HREM) pairs during the re-extraction process were determined. A schematic diagram of the laboratory-tested separation process of heavy rare-earth metals into individual components with the obtaining of yttrium and ytterbium concentrates containing more than 99% of the target components was proposed.

Highlights

Apatite ore of the Khibiny deposit of the Murmansk region contains about 1% rare-earth metals (REM), with a predominant content of medium and heavy rare-earth groups
During the production of phosphate fertilizers by apatite treatment with sulfuric acid, a part of the REM is leached into wet-process phosphoric acid (WPA) [1]
Concentration, and refining of REM are due to the different strengths of the resulting complexes of rare-earth metals with di-2-ethylhexylphosphoric acid (D2EHPA)

Summary

Introduction

Apatite ore of the Khibiny deposit of the Murmansk region contains about 1% rare-earth metals (REM), with a predominant content of medium and heavy rare-earth groups. During the production of phosphate fertilizers by apatite treatment with sulfuric acid, a part of the REM is leached into wet-process phosphoric acid (WPA) [1]. This solution does not require any preliminary treatment (mixing, dissolving, and enrichment), which ensures its potential economic advantages [2]. Concentration, and refining of REM are due to the different strengths of the resulting complexes of rare-earth metals with di-2-ethylhexylphosphoric acid (D2EHPA). The larger the charge and the smaller the REM ion radius, the stronger the organic compound with rare-earth metals [3]

Objectives

Methods

Results

Conclusion