Abstract
Recovery of rare earth elements (REEs) has become an attractive process owing to the high costs and limited availabilities of REEs. In addition, the recovery of REEs has become a necessity because of their high toxicity and negative environmental impacts. Conventional processes for the recovery of REEs from waste streams include chemical precipitation, coagulation, flocculation, flotation, ion exchange, adsorption, and electrochemical processes. These processes have various disadvantages such as high consumption of chemicals, high operational costs, and low purity of the extracted elements. Recently, membrane processes have been used for the recovery of REEs. Compared to conventional methods, membrane processes have higher selectivity for REEs and lower energy requirements; moreover, they offer the possibility of zero liquid discharge. Nevertheless, it is still important to evaluate the economic feasibility of using membrane techniques for the recovery of REEs. This review paper provides an overview of the application of membrane techniques for the recovery of REEs from waste streams. Rejection efficiency of several membrane processes and purity of the extracted REEs were analyzed. Economic feasibility of using membrane processes for the recovery of REEs was examined by comparing the capital and operational costs of the processes with the selling prices of REEs.
Highlights
Rare earth elements (REEs) are a set of seventeen elements, namely fifteen lanthanides and two d-transition metals (Sc and Y), with similar metallic characteristics (Dushyantha et al, 2020)
This review provides an overview of the application of membrane techniques for the recovery of REEs from waste streams
This review evaluates the techno-economic feasibility of using various membrane techniques for the recovery of REEs
Summary
Rare earth elements (REEs) are a set of seventeen elements, namely fifteen lanthanides and two d-transition metals (Sc and Y), with similar metallic characteristics (Dushyantha et al, 2020). Hydrometallurgy is a well-developed process for the extraction of REEs from REE-carrying substances such as natural ores and other sec ondary sources (Jha et al, 2016) It involves two stages: leaching and separation (Zhang et al, 2020). The recovery of REEs from waste streams or the aqueous solution obtained during hydrometallurgy is generally performed by several conventional techniques including pre cipitation, electrocoagulation, flotation, solvent extraction (SE), ion exchange, and adsorption (Heckley and Ibana, 2003; Pereao et al, 2018). Cyanex 272 extractant and a green solvent ionic liquid (1-octyl-3-methylimidazolium [OMIm]) were employed for the separation of REEs. Research related to the recovery of REEs from waste streams using various techniques has attracted extensive attention (Fig. 1).
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