Intensified Nd extraction in small channels for NdFeB magnet recycling

Neodymium (Nd) was continuously extracted from aqueous solutions by trioctylphosphine oxide (TOPO) dissolved in the ionic liquid 1-Butyl-3-methylimidazolium Bis (trifluoromethanesulfonyl)imide ([C4mim][Tf2N]) in small channel contactors. Kinetic studies confirmed a 1:6 Nd:TOPO extraction mechanism at high initial Nd concentrations of 0.005 and 0.01 M in a 0.001 M nitric acid aqueous phase. The continuous flow extractions were carried out in channels with 0.5 and 1 mm diameter and the effects of mixture velocity and residence time on the extraction efficiency and the mass transfer coefficient were investigated. At equal phase mixture velocities, the flow pattern studies highlighted a plug flow regime at mixture velocities of 0.01 to 0.05 m/s for both channels, resulting in interfacial areas of up to 4900 m2/m3 in the 0.5 mm channel and 2500 m2/m3 in the 1 mm channel. After 37.5 s residence time, extraction efficiencies of 80 % were found in the 0.5 mm channel at a KL alpha of 0.09 s-1 and 70 % at 0.04 s-1 in the 1 mm channel. The same extraction efficiencies were achieved in 1-2 h in the batch systems.

Automated summary

Neodymium (Nd) was continuously extracted from aqueous solutions using trioctylphosphine oxide (TOPO) dissolved in the ionic liquid 1-Butyl-3-methylimidazolium Bis (trifluoromethanesulfonyl)imide ([C4mim][Tf2N]) in small channel contactors. The study confirmed a 1:6 Nd:TOPO extraction mechanism at high initial Nd concentrations in a nitric acid aqueous phase. The effects of mixture velocity and residence time on the extraction efficiency and mass transfer coefficient were investigated.