A novel neutral-base coupling synergistic extraction system of Cyanex923 and primary amine N1923 for the recovery of cerium(IV) and fluorine from sulfuric acid medium

Abstract

Cyanex923 (A) and primary amine N1923 (B) mixture was developed as a novel neutral-base coupling extraction system for the recovery of cerium(IV) (Ce(IV)) and fluorine (F−) from sulfuric acid (H2SO4) medium. This system demonstrated excellent synergistic effects for both Ce(IV) and F− extraction. In Ce(IV) solution, the maximal synergistic coefficient (Rmax) for Ce(IV) was 2.93 at the Cyanex923 mole fraction (X) of 0.6. In Ce(IV)-F− solution, the presence of F− enhanced the synergistic extraction of Ce(IV) with the Rmax-Ce(IV) of 4.39 at XCyanex923 = 0.6, meanwhile the synergistic coefficient for F− (Rmax-F−) reached 4.33. The synergistic extraction mechanisms were systematically studied through multiple techniques including stoichiometry analysis, FT-IR and NMR characterizations. Equilibrium structures of extracted complexes were determined as Ce(SO4)2∙(A)1.5(B) and CeF(SO4)1.5∙(A)(B). Thermodynamic investigations revealed that the synergistic extraction processes were spontaneous. Specifically, the extraction process for Ce(IV) was endothermic and entropy driven, while the extraction process for Ce(IV)-F− was exothermic and enthalpy driven. The extracted Ce(IV) and F− can be almost stripped completely using HNO3 with additive H2O2, and CeF3 particles were obtained by reductive stripping from Ce(IV)-F− loaded organic phase as confirmed by XRD, SEM and DLS. The Cyanex923-N1923 system achieved comprehensive recovery of Ce(IV) and F− from the Bayan Obo mixed RE H2SO4 liquor and this excellent synergistic extraction performance suggests its high practical application potential.