Extraction Chromatographic Materials for Clean Hydrometallurgical Separation of Rare-Earth Elements Using Diglycolamide Extractants

Abstract

The uncertain supply of the rare-earth elements (REE) from conventional sources such as bastnaesite and monazite demands the search for alternative sources. Unconventional sources such as phosphate rock and mine tailings have REE contents at the level of only hundreds to a thousand parts per million, which challenges the conventional REE separation methods such as solvent extraction (SX) and ion exchange (IX). Alternatively, the potential of extraction chromatography (EXC) has been explored, as it combines the selectivity of SX and the convenience of column techniques of IX. Herein, we report a novel EXC material incorporating N,N′-dimethyl-N,N′-dioctyl-3-oxa-diglycolamide (DMDODGA) into a porous solid support because DMDODGA exhibits higher extraction efficiency for REE in SX than does conventional N,N,N′,N′-tetraoctyl-3oxa-diglycolamide (TODGA) and as also compared with similarly made conventional TODGA-based EXC material. The extraction of mixed REE by DMDODGA and TODGA resins was evaluated in H 2 SO 4 , HCl, and HNO 3 media as a function of acid concentration. The REE feed concentrations were adjusted to achieve stoichiometric REE concentration and excess REE concentration, conditions that reflect near or complete saturation of resin capacity. In general, extraction at the same acid concentration followed the order HNO 3 > HCl > H 2 SO 4 . The extraction strength of the DMDODGA resin is significantly higher than that of the TODGA resin in all three examined mineral acids, especially at lower H 2 SO 4 and HCl concentrations (0.01 and 0.1 M), making it a promising EXC material for hydrometallurgical extraction of REE.

Sustainable Recycling of Rare-Earth Elements from NdFeB Magnet Swarf: Techno-Economic and Environmental Perspectives

“…The existing literature on REE recovery from magnet swarf has primarily concentrated on lab-scale research, which is fraught with technological, economic, and environmental challenges. Most of these recycling processes incorporate either pyrometallurgical or hydrometallurgical methods for recovering REEs. − Pyrometallurgical processes consume a large amount of energy due to high-temperature requirements in converting feedstocks into REEs. For example, Hua et al immersed NdFeB magnet swarf into a molten pool of chloride salts at a temperature ranging from 600 to 1200 °C for 1 – 12 h to recover REEs in a chloride form .…”

Efficient Capture and Release of the Rare-Earth Element Neodymium in Aqueous Solution by Recyclable Covalent Organic Frameworks

“…To assess the effect of the COF architecture as a solid support for the DGA ligand, we compared the highest qe value of the Ugi-COF-DGA with the maximum adsorption capacities reported for other DGA-functionalized solid materials. [56][57][58][59][60][61][62][63][64][65] The newly developed Ugi-COF-DGA possesses the highest adsorption capacity among the best-reported DGA-modified supports (Figure 2f). Furthermore, it exhibits one of the highest reported qe values for Nd adsorption to date (Table S1).…”

The State of Critical and Strategic Metals Recovery and the Role of Nuclear Techniques in the Separation Technologies Development: Review

“…In general, REE recovery at the same concentration of the acids showed a trend of HNO 3 > HCl > H 2 SO 4 . In all three inorganic acids, the removal efficacy of the DMDODGA polymer was much stronger compared to the TODGA resin, particularly when using low concentrations of H 2 SO 4 and HCl (0.01 and 0.1 M), rendering it a prospective EXC substrate for the hydrometallurgical recovery of REE [157].…”

“…The possibility of extraction chromatography (EXC) for REEs has also been investigated since it merges the specificity of solvent extraction with the efficiency of ion exchange column procedures. In H 2 SO 4 , HCl, and HNO 3 solution, the extraction of mixed REEs by N, N -dimethyl-N, N -dioctyl-3-oxa-diglycolamide (DMDODGA) and traditional N, N, N , -tetraoctyl-3-oxa-diglycolamide (TODGA) resins were evaluated as a function of acidic concentration [157]. The adsorption of REEs' cations and kinetics were studied in 152/154 Eu at trace amounts of metal-to-ligand ratio (1:50) in HCl and HNO 3 to establish the highest weight distribution ratio values (D w ) achievable without loading implications.…”