Recovery of REEs from immiscible silicate-phosphate slags/molten ash with focus on recycling of LFP
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School of Chemical Engineering |
Master's thesis
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en
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99
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The global demand for rare earth elements (REEs) is rapidly increasing due to their essential role in green technologies such as solar panels, electric vehicles, and wind energy. As a result, the number of end-of-life (EOL) products containing REEs is also increasing, leading to more REE-containing waste being generated annually. At the same time, the global supply of REEs is largely controlled by China, which creates supply risk for other regions, including the European Union. For this reason, REEs have been added to the list of critical raw materials (CRMs) in the EU. In addition to supply challenges, the production of REEs is also affected by the so-called balance problem, which leads to the overproduction of some REEs and underproduction of others. Recycling of REEs is considered one possible solution to reduce both the supply risk and the balance problem. In this study, the recovery of REEs from incinerator bottom ash (IBA) was investigated through high-temperature treatment. The use of lithium iron phosphate (LFP) and calcium pyrophosphate (Ca₂P₂O₇) as phosphorus sources was studied to promote the formation of immiscible silicate and phosphate liquid phases, enabling the selective partitioning of REEs into the phosphate phase. Another purpose of using LFP was to investigate the potential for selective recovery of lithium (Li) under the applied conditions. A series of experiments was conducted in a vertical tube furnace at 1150 °C and 1200 °C under controlled oxygen partial pressures of 10⁻⁷, 10⁻⁹, and 10⁻¹¹ atm, each with a holding time of 48 hours. The samples were analysed using scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDS), electron probe microanalyser (EPMA), and laser ablation inductively coupled plasma - mass spectrometry (LA-ICP-MS). According to the results, the samples with LFP as the phosphorus source, treated at 1200 °C and at low oxygen partial pressures of 10⁻⁹, and 10⁻¹¹ atm, showed clear formation of two immiscible liquid phases (silicate and phosphate) without the presence of solid phases. Both of the studied REEs (La and Nd) were strongly enriched in the phosphate phase, indicating effective selective partitioning. However, lithium was almost equally distributed between both phases, meaning that its recovery was not possible under the given conditions. While the process successfully concentrates REEs into the phosphate phase, an additional step will be required to recover them from the phosphate for practical use.Description
Supervisor
Lindberg, DanielThesis advisor
Klemettinen, LassiJeon, Junmo