Membrane assisted solvent extraction for rare earth element recovery
Systems and methods for the recovery of rare earth elements are provided. The systems and methods generally include membrane assisted solvent extraction using permeable hollow fibers having an immobilized organic phase within the pores of the hollow fibers. The permeable hollow fibers are generally in contact with an acidic aqueous feed on one side thereof and a strip solution on another side thereof. The systems and methods generally include the simultaneous extraction and stripping of rare earth elements as a continuous recovery process that is well suited for post-consumer products, end-of-life products, and other recovery sources of rare earth elements.
1. A method for the recovery of rare earth elements, the method comprising:
providing a plurality of hollow fibers including a lumen side spaced apart from a shell side to define a membrane therebetween, the membrane including a plurality of pores dispersed therein;
wetting the plurality of pores of the membrane for each of the plurality of hollow fibers by impregnating the plurality of pores with an immobilized organic phase;
directing a continuous flow of an aqueous feed solution including a rare earth element along one of the lumen side or the shell side of the plurality of hollow fibers, wherein impregnating the plurality of pores is performed prior to the step of directing a continuous flow of an aqueous feed solution; and
directing a continuous flow of a strip solution along the other of the lumen side or the shell side of the plurality of hollow fibers;
wherein the organic phase includes an extractant, isoparaffin, and an organic solvent, and wherein rare earth elements are extracted from the feed solution and stripped from the organic phase in a continuous process, such that the concentration of the rare earth elements in the organic phase decreases across a thickness of the hollow fibers.
2. The method according to claim 1 further including adding an extractant to the feed solution to maintain a desired concentration of the extractant in the organic phase.
3. The method according to claim 1 wherein the extractant is tetraoctyl diglycol amide, trialkyl phosphine oxide, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, carbamoyl phosphoryl oxides, or sec-octylphenoxy acetic acid.
4. The method according to claim 1 wherein the organic solvent includes tributyl phosphate, xylene, hexane, octanol, or kerosene.
5. The method according to claim 1 wherein the organic phase includes tetraoctyl diglycol amide and tributyl phosphate.
6. The method according to claim 1 wherein the plurality of hollow fibers are formed from a hydrophobic material.
7. The method according to claim 1 wherein the feed solution includes a pressure differential with respect to the strip solution.
8. The method according to claim 1 wherein the plurality of hollow fibers define a mean inner diameter of between 0.1 mm and 1.0 mm inclusive.
9. The method according to claim 1 wherein the plurality of hollow fibers define a mean outer diameter of between 0.1 mm and 1.0 mm inclusive.
10. The method according to claim 1 wherein the plurality of hollow fibers define a mean pore size of the plurality of pores of less than 0.1 microns.
11. The method according to claim 1 wherein the feed solution includes a higher molar concentration of an acid than the strip solution to define a chemical potential gradient between the feed solution and the strip solution.