Monazite, xenotime, bastnaesite, and mixed composite ores are mainly processed for their rare earth elements. However, these minerals also contain radioactive components such as uranium (U) and thorium (Th), which are co-extracted with rare earth elements during hydrometallurgical ore processing. The enrichment of both nuclides (Th and U) presents strategic and economic opportunities for nuclear energy generation and eases disposal issues of radioactive waste. The industrial recovery of these nuclear fuels makes use of solvent extraction techniques by means of traditional diluents, including kerosene, toluene, and other petroleum-based compounds, leading to loss of solvent and environmental issues. As a result, the sustainability of the overall process appears to some extent compromised or reduced. The need rises, therefore, to identify and develop new high-extraction-efficient, chemically stable, and recyclable compounds for the recovery of U and Th. This study assesses the extraction efficiency of eco-friendly phase combinations (extractant-diluent) against traditional ones.
A synthetic solution was made to simulate real rare earth leachate nature. The solution was prepared in sulfate media (H2SO4) by dissolution of the lanthanide series (Z=57-70), Th and U salts. While the gangue matrix was represented by calcium (Ca), magnesium (Mg), and iron (Fe) salts. Varying process parameters, including acidity level (0.5-3M), solvent type (Isopar-L, HVO100), and extractant-diluent concentration (ratio) (0.05-2M) were evaluated at constant contact time (30 minutes). The effect of the assessed parameters was evaluated by metal quantification using mass spectrometric analysis (ICP-MS).
The results revealed that all assessed parameters had an impact on metallic transfer or process efficiency. The selectivity (separation factor) toward Th and U was observed to be inversely proportional to the acid concentration. In this sense, the lowest acid concentration (0.5 M H₂SO₄) significantly enhanced the extraction of heavy elements, Including Actinides (Th and U). Similarly, low combination ratio (extractant/diluent) displayed the highest selectivity towards radioactive nuclides and preference on light (Z57-62) and heavy (Z63-70) rare earth elements. Lastly, the diluent type exposed that biobased (HVO100) media could be used as a substitute to IsoparL since it possessed higher efficiency at all acidity levels and lower combination (extractant/diluent) ratios, leading to a greener process. Preference. These findings promote cleaner, cost-efficient nuclear fuel recovery, with the potential for scaling up, optimizing solvent recovery, and integrating the plant to inform future work on sustainable REE processing.