Aqueous two-phase systems for environmentally friendlier separation of rare earth elements and transition metals: Applications and new molecular insights

Author(s)

Neves, Heyder Pereira ; Silva, Lucas Andrade ; Prates, Leticia Maia ; Pereira, Alexandre Moni ; Miranda, Victoria Souza da Silva ; Correia, Julio Cesar Guedes ; Ferreira, Gabriel Max Dias ; Patino-Agudelo, Alvaro Javier ; Leao, Versiane Albis ; Mageste, Aparecida Barbosa

• Document type: Journal article
• Source: CHEMICAL ENGINEERING JOURNAL; v. 502, p. 14-pg., 2024-12-03.

Abstract

Aqueous two-phase systems (ATPSs) have been proposed as an alternative liquid-liquid extraction technique applicable for the separation of economically valuable metals. However, gaps in knowledge and the need for a deeper understanding of the mechanisms involved in metal extraction still hinder the widespread adoption of these systems. In this study, ATPSs formed by TX-100 and electrolytes were employed to separate La, Pr, and Nd from Al and Fe. Use of an ATPS composed of TX-100, NH4SCN, and water, at pH 2.00, with a phase ratio of 1:5, resulted in total extraction of Al and Fe, although there was also considerable co-extraction of REEs. When a phase ratio of 1:2 was used for an ATPS composed of TX-100, (NH4)2SO4, and water, with NH4SCN as extractant, at pH 1.00, it was possible to separate Fe from the other metals, with significantly lower co-extraction of REEs and Al (%ELa = 4.05 %, %EPr = 6.19 %, %ENd = 4.87 %, %EFe = 98.61 %, %EAl = 2.54 %). The results of density functional theory (DFT) calculations correlated well with the experimental metal extraction data, demonstrating that the characteristics and solvation of the complexes formed in the ATPS played a fundamental role in metal partitioning. Measurements of the physical properties of the ATPS phases revealed variations in viscosity and interfacial tension values, which could assist in developing applications on a larger scale. The findings demonstrated that ATPSs could be used to separate REEs from transition metals, with potential applications in the recovery of REEs present in secondary sources. (AU)

• FAPESP's process: 23/11091-9 - Thermodynamic modeling of the formation of giant micelles
• Grantee: Álvaro Javier Patiño Agudelo
• Support Opportunities: Scholarships in Brazil - Support Program for Fixating Young Doctors