Extraction kinetics of niobium by tertiary amine N235 using Lewis cell

• The extraction rate is controlled by a chemical reaction at the interface.
• The mass flux equation of niobium extraction was obtained.
• The rate determining step of forward extraction was obtained.
• Ea, Δ‡H°, Δ‡S° and Δ‡G° were obtained.

The kinetics of the forward extraction of NbO(C2O4)33 − by N235 was investigated using a Lewis cell. Different parameters such as the niobium concentration, oxalic acid concentration, hydrogen ion concentration, and R3N concentration, as well as extracting temperature were studied separately to examine their effect on the extraction rate of NbO(C2O4)33 −, and a rate equation was deduced based on the analysis. The experimental results demonstrate that the rate of NbO(C2O4)33 − extraction is controlled by a chemical reaction at the interface rather than in the bulk phase. Further analysis suggests that the NbO(C2O4)33 − extraction rate is first order with respect to hydrogen ion concentration, niobium concentration, and R3N concentration, and zero order with respect to oxalic acid concentration. The mechanism of NbO(C2O4)33 − extraction is controlled by the slow distribution of the R3NH+ at the interface to form NbO(C2O4)3⋅R3NH2 − between the liquid phase and the interface.