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Rare earth elements (REEs) are critical to our modern world. Recycling REEs from used products could help with potential supply issues. Extracting REEs from chloride media with tetrabutyl diglycolamide (TBDGA) in carbon dioxide could help recycle REEs with less waste than traditional solvents. Carbon dioxide as a solvent is inexpensive, inert, and...
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Context 1
... mole percent of 1-octanol ranged from 0.5 to 3 mol%. The TBDGA concentration and the flow rate of the 1-octanol TBDGA solution for each mole percent studied are shown in Table 1. ...Context 2
... pressure was kept constant at 34.1 MPa. The mole percent 1-octanol was 2%, and the 2% 1-octanol and TBDGA solution conditions are shown in Table 1. The temperature tested were 2, 23, 40, and 50 • C. ...Context 3
... temperature was kept constant at 23 • C, and the percent mole 1-octanol was 2%. The conditions of the TBDGA in 1-octanol solution are shown in Table 1. Pressures tested were 13.8, 20.7, 24.1, 27.6, and 34.5 MPa. ...Context 4
... TBDGA-Eu complex appeared to preferentially partition to the 1-octanol phase in the cell versus the CO 2(l) phase. Table 1. ...Similar publications
Recycling rare-earth elements (REEs) from Nd-Fe-B magnet waste is an important step towards building a sustainable REE supply chain. In this study, two different processes were systematically investigated and compared. In the leaching stage, the effect of increasing H2SO4 or HCl concentrations were studied and it was determined that, although both...
Citations
... Molten salt electrolysis, spanning both thermal and electrochemical methods, has been widely applied for the separation and extraction of REEs [22]. Compared to aqueous solutions, high-temperature molten salts offer superior media for electrochemical processing of REEs, owing to their heightened chemical stability, conductivity, reaction rates, broad applicable temperature range, and negligible vapor pressures. ...
Recent advances in electrochemical methods show promise for more sustainable recycling of rare earth elements (REEs) from end-of-life NdFeB permanent magnets. Demand for NdFeB magnets is rapidly growing for clean energy applications, motivating recycling efforts to diversify REE supplies. Core electrochemical steps involve selective dissolution of REE-rich phases at the anode and reduction of REE ions at the cathode. Pretreatment including demagnetization, mechanical size reduction, and leaching help liberate and concentrate the REEs. Thermal demagnetization and mechanical crushing make the magnets brittle and improve leachant penetration. Acid leaching dissolves REEs but co-dissolves iron. To facilitate high-temperature recovery of REEs, molten salt electrolytes such as chlorides are utilized, whereas ionic liquids enable recovery under milder conditions, albeit with a caveat of potential decomposition during the process. Aqueous solutions have been most thoroughly investigated for versatility and affordability. Fluoride-based molten salt electrolytes effectively dissolve RREs and provide stable environments for high-temperature electrodeposition, enhancing the efficiency and sustainability of rare earth element recovery. Additional purification is needed to isolate high purity REE oxides and metals, using techniques like solvent extraction, selective precipitation, and electroseparation. Key factors for optimal electrochemical recycling are maximizing selectivity for REEs, minimizing energy use and waste generation, and simplifying integration. While technical challenges remain, recent advances demonstrate electrochemical technologies can improve the sustainability of recycling critical REEs from permanent magnets.
... Leaching of rare earths has been explored with other solvent media, including supercritical fluids. 46,47 Rare-earth salts and oxides are only sparingly soluble in supercritical fluids; however, the addition of novel adducts, such as tri-n-butyl phosphate-nitric acid (TBP-HNO 3 ), to supercritical carbon dioxide or tetrabutyl diglycolamide in 1-octanol modified carbon dioxide can dramatically improve solubility. Extraction of REE from NdFeB magnets and lighting phosphor material using these systems has been reported. ...
... Extraction of REE from NdFeB magnets and lighting phosphor material using these systems has been reported. 46 Again, formal published LCA or TEA is not available for this approach. ...
Rare-earth element (REE) demand is expected to increase by a factor of up to 7 by 2040. Recycling avoids the significant hurdles associated with opening new mines, but collection and disassembly of REE-containing devices are barriers. Absolute and relative abundances of REEs and co-occurring constituents differ significantly in secondary compared to primary sources, presenting challenges and opportunities. REE concentrations are typically low, but manufactured devices include only the desired REE, avoiding the “REE balance problem” that besets natural ores. Fewer REEs need to be separated, as compared to separation of the entire lanthanide series. Co-recovery of precious (e.g., Au, Ag, Pt) or base metals (e.g., Cu, Sn, Zn) from e-wastes can offset recycling costs. Some examples of recently developed approaches for REE extraction and separation are presented here, with an emphasis on methods offering environmental benefits such as lower toxic chemical usage and reduced energy costs.
Graphical abstract
... The initial enrichment process takes an advantage of a gravitational method, using devices such as a jig, a spiral separator, a cone concentrator, a concentration table or a hydrocyclone. The obtained concentrate undergoes further processes, such as: flotation, leaching, magnetic-electrostatic separation or the use of concentrated acid solution and extraction with concentrated sodium hydroxide [4,6,15,17,20,21,23]. The final stage of the work aimed at recovering or obtaining the feed with a significant concentration of rare earth elements (from the selected material with prospective sufficient REE content) in the gravitational beneficiation process. ...
The aim of the article is to present the results of laboratory analyses determining the content of rare earth elements (REE) in hard coal type 31.1. Coal was extracted directly from the mining excavation located in the Upper Silesian Coal Basin. Mass spectrometry tests with ionization in inductively coupled plasma (ICP-MS), were aimed at the quantitative analysis of the share of REE in coal, taking into account the economic aspects of recovery of these elements. Fine ground hard coal samples and ashes obtained after coal burning were assessed for the rare earth elements concentration. Results of the rare earth elements concentration (lanthanum and cerium) in hard coal are similar in the values obtained in previous tests. The current analyses present higher concentration of europium or neodymium. The article also contains the concept of possible future research work, consisting in the recovery of rare earth elements using, among others, a classifying hydrocyclone.
... As reported in the literature, the ores were dissolved well in HCl or HNO 3 , but it was only attacked with concentrated H 2 SO 4 at high temperatures [10,12,13]. However, due to the complex metallurgy of lanthanides, there is no standard method for dissolution lanthanides-bearing ores [7,[15][16][17]. Leaching processes by such mineral acid lead to erosion of the processing facilities, co-separation of considerable proportions of other undesirable impurities and toxic waste streams. ...
In this study, the separation of lanthanides from phosphate ore using oxalic acid (C2H2O4), tartaric acid (C4H6O6), lactic acid (C3H6O3), sulfuric acid (H2SO4) and hydrochloric acid (HCl) was investigated. The ore was characterized before and after leaching processes by X-ray fluorescence (XRF), Scanning electron microscope (SEM), X-ray powder diffraction (XRD), and Fourier transform infrared (FTIR). The different parameters affect the leaching rate such as leaching time, acid concentration, liquid/solid ratios, temperature, and leaching kinetics were studied. The optimal leaching conditions were determined as 0.4 M C2H2O4, 2.5 M C4H6O6, 1.8 M C3H6O3, 2.0 M H2SO4, and 3.0 M HCl, with a liquid/solid (L/S) mass ratio of 6/1 C2H2O4, 8/1 for both C4H6O6 and C3H6O3, 5/1 for both H2SO4 and HCl at 30 °C, agitation rate ≈ 350 rpm and particle size ≈ 144.8 μm. Under these optimum conditions, the recovery percentage (%R) was 42.8% (for C2H2O4), 93.2% (for C4H6O6), 89.1% (for C3H6O3), 89.3% (for H2SO4), and 74.6% (for HCl). SEM and FTIR characterizations for the residue were investigated. Experimental data reveal that the leaching processes are fitted by chemical reaction models for C2H2O4 and C3H6O3, and by diffusion-reaction model for C4H6O6, H2SO4, and HCl. The activation energies for these models were estimated to be 43.3, 30.33, 45.8, 31.3, and 38.6 kJ/mol for C2H2O4, C4H6O6, C3H6O3, H2SO4, and HCl, respectively. All data were confirmed and explained by XRD, FTIR, and SEM studies.
With the reduction of available minerals, rare and precious metals recovered from waste are gradually becoming an effective alternative to the circular economy. Supercritical CO2 extraction is a novel, promising, and environmentally friendly method that can be used to address environmental issues brought by conventional metal extraction methods. This paper reports the role of rare and precious metals, reviews the pathways to recover valuable metals from “secondary resources”, discusses the key technical and environmental challenges of common approaches in the recovery of valuable metals by taking smelting soot as an example, and then highlights the potential of supercritical CO2 technology to extract valuable metals from solid waste. Furthermore, the research progresses of supercritical CO2 extraction technology are summarized, and the prospects for developing a green supercritical CO2 extraction technology are discussed from multiple perspectives, including process, device, influencing factors, mechanism, and application. By analyzing valuable metal extraction from solid waste and supercritical CO2 technology in detail, this paper provides useful theoretical support for effectively utilizing the resources in solid waste and developing potential resources in rare and precious metals.
Coal Fly Ash (CFA) is a promising technospheric resource of rare earth elements some of which are designated as critical metals in various countries due to their role in materials of contemporary significance, particularly in green energy technologies. The average REE content in CFA is about 0.05%. Due to the availability of huge volumes of CFA worldwide, focussed R&D efforts are being made to extract REEs from them along with various other valuable metals. It is the endeavour of all researchers involved to develop process schemes which are environmentally benign. Attaining such objective necessitates deeper understanding on the deportment of REEs in the feedstocks, possibility of pre-concentrating the valuables by physical beneficiation techniques and use of hydrometallurgical techniques which deploy bio-degradable or green solvents, enhancing the recyclability of reagents and conserving the process water. An important aspect in CFA utilization is to preserve the pozzolanic properties of CFA intact such that its bulk uses are not destroyed during the process of REE extraction. This chapter gives an overview on the developments in characterization of REEs in coal fly ash, strategies explored for their extraction and conceptual flowsheets developed on various feedstocks of CFA in different countries with added emphasis on Indian scenario.
The extraction of cerium from cotton substrate, as a matrix model, using supercritical CO2 modified with phosphorus extractant and co-solvent/water in wise proportions, has been investigated. Using a recently developed isobutyl amidophosphonate extractant, the aim of this study was to emphasize how besides the usually considered operating parameters (flow rate, pressure and temperature), the efficiency of supercritical CO2 extraction of cerium depends on the concentration of cerium nitrate deposits on the substrate (between 0.27 and 261 mg.gcotton⁻¹) and on the presence and composition of co-solvent/water mixture as well. The variations of the extraction efficiency with the nature of the Ce nitrate deposits (aggregates or homogenous layers) are explained by using a deposition model confirmed using SEM and coupled with SAXS data. Extraction is promoted when Ce nitrates deposits are in the form of segregated aggregates instead of homogeneous layers. Phase equilibrium data for CO2-ethanol-amidophosphonate and CO2-isopropanol-amidophosphonate ternary systems have been measured at 40 °C and 25 MPa to investigate the benefit of using a co-solvent. Extraction experiments show that adding a co-solvent and carefully adjusting the water concentration up to 30%wt are crucial to obtain high mass extraction yields, here up to 82%.
