Metastable precipitation and ion-extractant transport in liquid-liquid separations of trivalent elements

• 成果类型: Article
• 署名作者: Sun, Pan; Lin, Xiao - Min; Berab, Mrinal K.; Lin, Binhua; Ying, Dongchen; Chang, Tieyan; Bu, Wei; Schlossman, Mark L.
• 署名单位: University of Illinois System; University of Illinois Chicago; University of Illinois Chicago Hospital; University of Chicago; United States Department of Energy (DOE); Argonne National Laboratory; University of Chicago
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-11883
• DOI: 10.1073/pnas.2315584121
• 发表日期: 2024-03-26
• 关键词: rare-earth-elements; solvent-extraction; 3rd-phase formation; water-interface; kinetics; ACID; zinc; adsorption

摘要

The extractant-assisted transport of metal ions from aqueous to organic environments by liquid-liquid extraction has been widely used to separate and recover critical elements on an industrial scale. While current efforts focus on designing better extractants and optimizing process conditions, the mechanism that underlies ionic transport remains poorly understood. Here, we report a nonequilibrium process in the bulk aqueous phase that influences interfacial ion transport: the formation of metastable ion-extractant precipitates away from the liquid-liquid interface, separated from it by a depletion region without precipitates. Although the precipitate is soluble in the organic phase, the depletion region separates the two and ions are sequestered in a long-lived metastable state. Since precipitation removes extractants from the aqueous phase, even extractants that are sparingly soluble in water will continue to be withdrawn from the organic phase to feed the aqueous precipitation process. Solute concentrations in both phases and the aqueous pH influence the temporal evolution of the process and ionic partitioning between the precipitate and organic phase. Aqueous ion-extractant precipitation during liquid-liquid extraction provides a reaction path that can influence the extraction kinetics, which plays an important role in designing advanced processes to separate rare earths and other minerals.