Separation of Rare-Earth Elements Using Supported Liquid Membrane Extraction in Pilot Scale

Abstract

The use of supported liquid membrane extraction for recovery and separation of rare-earth elements (REEs) has been investigated. Experiments have been carried out using the different configurations: (1) standard hollow fiber supported liquid membrane operation (HFSLM), (2) renewal liquid membrane operation (HFRLM), and (3) emulsion pertraction technology (EPT). The experiments were performed in pilot scale using a hollow fiber module with a mass transfer surface area of 8 m2. Synthetic feed solution was used with compositions based on a process for recovery of REE from an apatite concentrate. The total concentration of REE in the feed was varied from 1 to 22 mM REE and the pH was varied in the range 1.5–3.2. Di(2-ethylhexyl) phosphoric acid (D2HEPA) diluted in kerosene, 10% (v/v), was used as the organic membrane solution, and 3 M HCl was used as stripping solution. In supported liquid membrane extraction, the extraction performance is governed by both the kinetics of REE transport through the membrane and by thermodynamics. The effect of feed composition on the selectivity and transport of REE through the liquid membrane have been investigated. The results show that the liquid membrane is more selective toward the heavy REE at lower pH values and higher REE concentration. HFRLM shows a higher transport rate than HFSLM, while the HFSLM configuration gives a higher selectivity toward individual REE. The membrane performance in HFSLM configuration rapidly decays with time, while in the HFRLM and EPT configurations, the performance is much more stable. Possible mechanisms for decaying membrane performance are discussed, and gel formation is identified as being of significant importance. Gel formation is observed at an organic loading above ∼46% for Nd, 38% for Y, 46% for Dy, and 65% for Er. The work performed in this study serves as an initial step to demonstrate that HFRLM and EPT can provide stable operation and be feasible options for processing of REE liquors. A process flow diagram for the recovery of the REE, present in the apatite concentrate, in three fractions is proposed based on the results from this study.

On membrane-based approaches for rare earths separation and extraction – Recent developments

“…Indeed, development of membrane separation of REEs witnessed a global contribution from LM techniques. Nevertheless, scale-up experiments were not satisfying mainly because of the problems with LM stability and efficiency while the efforts allow for a moderate optimism [144].…”

The Latest Achievements of Liquid Membranes for Rare Earth Elements Recovery from Aqueous Solutions—A Mini Review

“…They reported that under optimal experimental conditions, the Nd(III)/D 2 EHPA molar ratio was 1:3, which was consistent with the obtained results of computational calculations, and that the coordinated covalent bonds between Nd(III) and D 2 EHPA were formed through six oxygen atoms. The analysis of the reaction mechanism is important because, although in general, during the reaction with di-(2-ethylhexyl)phosphoric acid, each trivalent REE ion is extracted in a complex with six molecules of D 2 EHPA arranged as dimers; other stoichiometric ratios were also reported in different experimental conditions [33,34]. One of the important limitations associated with the use of D 2 EHPA/HFSLM-based separation methods is the stability/durability of the membranes.…”

Gravity-Driven Separation for Enrichment of Rare Earth Elements Using Lanthanide Binding Peptide-Immobilized Resin

“…A crucial step in manufacturing these devices involves utilizing highly pure REEs, often obtained through complex and nonsustainable processes. Current separation methods use liquid-phase strategies, including membrane separation techniques, electrodialysis, or acid leaching techniques. − However, these approaches involve high energy consumption, long processing times, environmental concerns related to the use of chemicals, potential generation of hazardous waste, and the need for complex equipment. Moreover, these methods may not universally apply to the entire palette of rare earth elements, leading to inefficiencies and limitations in achieving comprehensive separation.…”