Towards the Circular Economy of Rare Earth Elements: Lanthanum Leaching from Spent FCC Catalyst by Acids

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.

Analysis of Lanthanum and Cobalt Leaching Aimed at Effective Recycling Strategies of Solid Oxide Cells

Lanthanum and cobalt are Critical Raw Materials and components of Solid Oxide Cells—SOCs electrodes. This review analyses lanthanum and cobalt leaching from waste materials (e-waste, batteries, spent catalysts), aiming to provide a starting point for SOC recycling, not yet investigated. The literature was surveyed with a specific interest for leaching, the first phase of hydrometallurgy recycling. Most references (86%) were published after 2012, with an interest higher (85%) for cobalt. Inorganic acids were the prevailing (>80%) leaching agents, particularly for lanthanum, while leaching processes using organic acids mostly involved cobalt. The experimental conditions adopted more diluted organic acids (median 0.55 M for lanthanum and 1.4 M for cobalt) compared to inorganic acids (median value 2 M for both metals). Organic acids required a higher solid to liquid ratio (200 g/L), compared to inorganic ones (100 g/L) to solubilize lanthanum, while the opposite happened for cobalt (20 vs. 50 g/L). The process temperature didn’t change considerably with the solvent (45–75 °C for lanthanum, and 75–88 °C for cobalt). The contact time was higher for lanthanum than for cobalt (median 3–4 h vs. 75–85 min). Specific recycling processes are crucial to support SOCs value chain in Europe, and this review can help define the existing challenges and future perspectives.

Extraction of Lanthanum Oxide from Different Spent Fluid Catalytic Cracking Catalysts by Nitric Acid Leaching and Cyanex 923 Solvent Extraction Methods

A laboratory-scale procedure was developed to obtain lanthanum oxide from spent fluid catalytic cracking catalyst, commonly used in the heavy crude oil cracking process. Two different solids, consisting mainly of silica, alumina, and a certain amount of rare earth elements, were leached under several conditions to recover the rare earths. Nitric acid leaching lead to the highest recovery of lanthanum, reaching a recovery percentage greater than 95% when a 1.5 M concentration was used. Subsequently, liquid phases were subjected to a liquid–liquid extraction process using Cyanex 923 diluted in Solvesso 100, and the lanthanum was quantitatively extracted. Lanthanum was also quantitatively stripped using oxalic acid to obtain the corresponding lanthanum oxalates, as revealed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Fourier transform infrared (FTIR) techniques. After thermal treatment at 1200 °C for 2 h, these solids yielded lanthanum oxide.