来源：ACS Publications
Rare earth elements exhibit unique physicochemical properties that justify their broad technological applications and rising global demand. Concerns about supply risks and resource scarcity have intensified the search for alternative supply routes and secondary sources. In this study, rare earth elements were recovered from an acidic effluent generated during the hydrometallurgical processing of columbite. Citric acid was used as a complexing agent to promote metal differentiation, and its effects on selective precipitation and solvent extraction were evaluated. Complexation with citric acid at a Fe:cit ratio of 1:1.5 and at pH 3 produced a precipitate with a rare earth-to-Fe ratio ten times higher than that of the initial solution. Subsequent solvent extraction with 10% v/v D2EHPA in kerosene recovered 92% of the remaining rare earth elements, yielding a separation factor of 27. The proposed process generated two streams enriched in rare earth elements.