Intensifying the extraction of rare earth elements by a mini-channel counter-current extractor

Developing new extraction processes is essential for the effective separation of rare earths. Liquid-liquid countercurrent extraction of rare earth elements was conducted in innovatively developed mini-channel extractors with a diameter of 4 - 6 mm. 30 % saponified P507/sulfonated kerosene was used as extractant to form monodispersed droplets and flowed upward in the vertical mini-channel by buoyancy. LaCl3 solution (La2O3 + HCl solution) was used as the continuous phase and flowed downward by gravity. The influence of the superficial velocity of organic phase, superficial velocity of aqueous phase, the diameter and length of mini-channel on the extraction yield, volumetric mass transfer coefficient and theoretical stages were studied. The volumetric mass transfer coefficients were in the range of 0.07 x 10-3 - 5.46 x 10-3 s- 1. It is much higher than that in co-current mini-channel and traditional extractors. An empirical correlation of volumetric mass transfer coefficients was established with a prediction error of +/- 20 %. The strong relative movement of two phases and the maximal driving force of mass transfer give the counter-current mini-channel extractor an excellent mass transfer performance. When the mini-channel length was greater than 250 mm, the number of extraction stages was larger than one. The research results provide guidance for the design of novel extractors and the improvement of rare earth elements extraction.