Multi-criteria evaluation of the extraction methods of rare earth elements from aqueous streams

This study aims to evaluate the extraction methods of rare earth elements (REEs) from aqueous solution streams using the analytic hierarchy process (AHP) method. However, their extraction from aqueous solutions is challenging due to their low concentration and complex chemical properties. The AHP method is a multi-criteria decision-making tool that allows for the prioritization of different criteria based on their relative importance. In this study, eight extraction methods were evaluated based on three criteria: economic justification, technical justification, and environmental justification. The eight methods included adsorption, biosorption, chemical precipitation, electrocoagulation, ion flotation, ion exchange, membrane filtration, and solvent extraction. The results showed that flotation was the most efficient method for REE extraction, with a score of 0.176, followed by adsorption, with a score of 0.149. Biosorption and solvent extraction had lower scores of 0.147 and 0.136, respectively. Besides, another AHP was conducted to prioritize the three surfactant categories used in the ion flotation process based on seven criteria: capacity, cost, efficiency, recovery duration, repeatability, scalability, and selectivity. The three surfactant categories included bio-based, chemo-based, and nano-based surfactants. The results indicate that nano-surfactants were the most suitable surfactants for REE extraction by ion flotation with a score of 0.465, followed by chemo-surfactants with a score of 0.390. Overall, this study provides valuable insights into evaluating different REE extraction methods using the AHP methodology. The findings can help researchers and industry professionals decide on selecting appropriate REE extraction methods based on their specific needs and priorities.