A hydrometallurgical method of energy saving type for separation of rare earth elements from rare earth polishing powder wastes with middle fraction of ceria

Efficient Self-cleaning and antibacterial ceramics with active sites fully exposed obtained from rare earth waste

The utilization of rare earth polishing powder waste (RPW) to prepare antibacterial ceramics can effectively avoid problems of pollution in the recycling process and waste of rare earth resources. Herein, a novel RPW-based antibacterial ceramics was developed, which possesses the core-shell structure with ceramics as the cores and the CeO2/BiOCl as the superficial coating. The antibacterial ceramics display notable antibacterial activity, and the inactivation rates of 3.3 log under visible light irradiation in 30 min and 2.4 log under darkness in 1 h were achieved, and the zone of inhibition values was found to be 16.6 mm for E.coil. The hardness of antibacterial ceramics was measured to be 897 (±38) HV, higher than commercial porcelain's hardness (600 HV). The antibacterial mechanism was verified by the Ce ion release, reactive species, and fluorescence-based live/dead cells. This study presents a novel antibacterial ceramic structure and green economic reuse method of rare earth waste.

Challenges and opportunities for sustainable valorization of rare earth metals from anthropogenic waste

Progressively and projected integration of rare earth metals (REMs) in modern technologies, especially in the clean energy, consumer electronics, aerospace, automotive, and defense sectors, place REMs as critical raw materials in the supply chain and strategic metal from the fourth industrial revolution perspective. Current REM production from the primary mineral resources in the supply chain versus industrial demand is at a bottleneck. Alternatively, REM-bearing anthropogenic wastes are pertinent and potent to addressing the critical supply chain bottleneck. Although secondary REM resources are prudent to address the critical supply chain bottleneck, the absence of effective and efficient technologies to recover these REMs from anthropogenic waste imposes challenges and provides opportunities. Hence, this review analyses and discusses the significance of anthropogenic wastes for REM recovery, the status of recycling technologies for sustainable valorization of REMs, challenges, and opportunities. The current review covers the potential quantitative REM wealth locked in various anthropogenic waste like (i) spent rare earth permanent magnets, (ii) spent batteries, (iii) spent tri-band REM phosphors, (iv) bauxite industry residue red mud, (v) blast furnace slag and (v) coal mines, and coal byproducts and status of valorization technologies for circularizing the REMs. In industrial waste like red mud, steelmaking slag, blast furnace slag, and coal fly ash typically 109,000, 2000, 39,000, and 354,000 tons of REM get scrapped, respectively, in a conservative estimation. In the years 2020 and 2021, respectively, 240,000 and 280,000 tons of REM were produced by mine production in contrast to 504,000 tons of REM that were scrapped with REM-bearing industrial waste. This review revealed that total REM currently getting scrapped with anthropogenic waste versus projected REM demand for the years 2022, 2023, 2024, and 2025 could be standing at 2.66, 2.51, 2.37, and 2.23, respectively. Our investigation revealed that efficient recovery of REMs from anthropogenic waste is significant and promising but associated with challenges like lack of industrial-scale valorization process, lack of a clear strategy, road map, policy, effort, funding, and diversified research.

Recovery of Cerium Oxide Abrasive from an Abrasive–Glass Polishing Waste through Alkaline Roasting Followed by Water Leaching

Abrasive–glass polishing waste is generated from the polishing process of glass components by using cerium oxide abrasive, which contains the cerium oxide abrasive and the polished glass. This study attempted to recover the cerium oxide abrasive from the abrasive–glass polishing waste through removing the polished glass by alkaline roasting using sodium hydroxide (NaOH) followed by water leaching. The experimental results indicated that the polished glass in the abrasive–glass polishing waste could be fully removed under the optimal alkaline roasting and water leaching conditions of roasting temperature of 450 °C, mass ratio of polishing waste to NaOH of 1:1, roasting time of 30 min, leaching pH of 3, leaching temperature of 25 °C, and liquid–solid ratio of 25 mL/g. The characteristics including elemental composition, particle size distribution, mineralogical phases, and morphology of the recovered cerium oxide abrasive obtained under the optimal conditions were similar to those of the original unused one, which was suitable to be reused for polishing again.

REE(III) recovery from spent NiMH batteries as REE double sulfates and their simultaneous hydrolysis and wet-oxidation

Efficient recovery of REEs present in the battery waste is a modern problem that has proven to be difficult to solve in an efficient manner. The raw material investigated in the current study is mixed alkaline rare earth element (REE) double sulfate (DS) precipitate, originating from the sulfuric acid leachate of nickel-metal hydride battery (NiMH) waste. Typically, REE can be precipitated as a mixture of REE double sulfates, however the real challenge is the separation of REEs from each other's into pure fraction. The study elucidates the process by which the DS are transformed into hydroxides with simultaneous in-situ conversion of Ce(III) to Ce(IV) by air. Air flow rate (0-1 L/h), temperature (30-60 °C), liquid-solid ratio (L/S, 12.5-100 g/L), 3REE/NaOH mol ratio (1-1.6) and time (60-240 min) were varied in the study of oxidation and double sulfate conversion. Best oxidation achieved was 93% along near-complete dissociation of double sulfate matrix (52767 ppm Na reduced to 48 ppm Na). After parameter optimization, a larger batch was produced to conduct selective dissolution of REE(III) into HNO₃ media, leaving concentrated impure Ce(OH)₄ as the end product.

Valorization of waste NiMH battery through recovery of critical rare earth metal: A simple recycling process for the circular economy

The process flowsheet consists of three main circuits, i.e., metal extraction by acid leaching, critical rare earth metal (REM) recovery from leach liquor and pure Co/Ni recovery by solvent extraction. Quantitative metal extraction using 1 M H₂SO₄, pulp density of 25 g/L at 90 °C from waste NiMH battery was achieved. From leach liquor using 10 M NaOH, at pH 1.8, more than 99% REM was precipitated out and isolated through calcination at 600 °C. Undesired metals like Mn, Al, Zn, and Fe were scrubbed out from the leach liquor using 0. 7 M D2EPHA at the equilibrium pH of 2.30. From the scrubbed raffinate Co and Ni was separated using 0.5 M Cyanex 272 at pH 4.70 through solvent extraction. At pH 4.70 Co was completely extracted from solution leaving Ni in solution, which can be recovered completely. From Co loaded Cyanex 272, the Co was stripped by 1 M H₂SO₄ and regenerated Cyanex 272 can be reused and close the loop. Similarly, the undesired metal loaded D2EPHA can be regenerated and reused and close the loop. As the process is close-loop process recovers critical REMs, Co, and Ni, the valorization process efficiently addresses the circular economy and recycling challenges associated with waste NiMH battery.

Characterization and Feasibility Studies on Complete Recovery of Rare Earths from Glass Polishing Waste

One of the main applications of ceria (CeO2) is its use in glass polishing. About 16,000 tonnes of rare earth oxides, which is about 10% of total rare earth production, are used for polishing applications. The waste generated in glass polishing contains rare earths, along with other impurities. In this study, two different glass polishing waste samples were characterized and two different processes were proposed for the complete recovery of rare earths from polishing waste, i.e., an acid-based process and an alkali-based process. The polishing waste samples were characterized with inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-gravimetric analysis (TGA) and particle size analysis. Chemical analysis showed that sample A (CeO2-rich waste from plate glass polishing) contained a high amount of impurities compared to sample B (CeO2-rich waste from mirror polishing). XRD analysis showed that sample B contained CeO2, LaO0.65F1.7 and LaPO4 compounds, whereas sample A contained CaCO3 in addition to rare earth compounds. SEM-EDX analysis showed the presence of alumino-silicates in sample A. Leaching experiments were carried out at 75 °C at different acid concentrations for the recovery of rare earths from polishing waste samples. The leaching results showed that it is difficult to dissolve rare earths completely in acid solutions due to the presence of fluorides and phosphates. Hence, undissolved rare earths in the leach residue were further recovered by an alkali treatment with NaOH. In another approach, polishing waste samples were directly treated with NaOH at 500 °C. After alkali treatment followed by water leaching, rare earths can be completely dissolved during acid leaching. Rare earths from polishing waste can be recovered completely by both the acid-based process and the alkali-based process.

Recovery of Cerium from Glass Polishing Waste: A Critical Review

Ceria is the main component in glass polishing powders due to its special physico-chemical properties. Glass polishing powder loses its polishing ability gradually during usage due to the accumulation of other compounds on the polishing powder or due to changes in the particle size distribution. The recovery of cerium from the glass polishing waste results in the efficient utilization of natural resources. This paper reviews processes for the recovery of rare earths from polishing waste. Glass polishing powder waste can be reused via physical, physico-chemical or chemical processes by removing silica and/or alumina. The removal of silica and/or alumina only improves the life span up to some extent. Therefore, removal of other elements by chemical processes is required to recover a cerium or cerium-rich product. However, cerium leaching from the polishing waste is challenging due to the difficulties associated with the dissolution of ceria. Therefore, high acid concentrations, high temperatures or costly reducing agents are required for cerium dissolution. After leaching, cerium can be extracted from the leach solution by solvent extraction or selective precipitation. The product can be used either in glass polishing again or other high value added applications.