Continuous intensified liquid-liquid extraction of Neodymium using ionic liquids in small channels

The creation of sustainable supply streams of rare earth elements (REE) is of global significance. One approach to such aims is to recycle REE from secondary resource streams via solvent extraction. The objective of this thesis is to develop a novel solvent extraction processing route for the recycling of NdFeB magnet swarf. By applying small channel contactors and an ionic liquid (IL) solvent, experimental investigations pursue two research themes: (i) kinetics of IL Nd solvent extraction, and (ii) small channel operating parameters of IL Nd extraction. Experimental investigations into the kinetics of IL Nd extraction yielded new mechanisms of extraction at high extraction percentages and selectivity toward Nd. Subsequent application of small channels resulted in intensified mass transfer, significantly reducing the residence time required for extraction. These investigations however also highlighted a potential limitation of IL in small channels, with an increase in mixture velocity resulting in a plateau in extraction efficiency at 0.03 m/s. To investigate this particle image velocimetry (PIV) was applied to study the flow topology in an aqueous plug with increased mixture velocity. Studies highlighted diminished internal vortices regarding their geometry and vorticity in line with the extraction efficiency plateau. Studies went on to develop the extraction system into a multi-step extraction and stripping setup with in-line membrane separation investigating stripping kinetics and system hydrodynamics. Stripping was found to be kinetically limited and membrane separation was seen to significantly affect both the flow rate and hydrodynamics across the setup. The thesis provided new insights into Nd extraction by IL in small channels, defining new sets of operating parameters for optimised operation.