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Selective Extraction of Rare Earth Elements from Permanent Magnet Scraps with Membrane Solvent Extraction Daejin Kim, Lawrence E. Powell, Laetitia H. Delmau, Eric S. Peterson, Jim Herchenroeder, and Ramesh R. Bhave Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b01306 • Publication Date (Web): 24 Jun 2015 Downloaded from http://pubs.acs.org on July 5, 2015

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Environmental Science & Technology

Selective Extraction of Rare Earth Elements from Permanent Magnet Scraps with Membrane Solvent Extraction

1 2 3 4 5

Daejin Kim, Lawrence E. Powell, Lætitia H. Delmau1, Eric S. Peterson2, Jim Herchenroeder3, Ramesh R. Bhave*

6 7

Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA

8

1

9 10

Nuclear Materials Processing Group, Oak Ridge National Laboratory, Oak Ridge, TN, USA 2

Center for Advanced Energy Studies, Idaho National Laboratory, Idaho Falls, ID, USA 3

Molycorp Magnequench, Greenwood Village, CO, USA

11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

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ABSTRACT

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The rare earth elements (REEs) such as neodymium, praseodymium, and dysprosium were

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successfully recovered from commercial NdFeB magnets and industrial scrap magnets via

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membrane assisted solvent extraction (MSX). A hollow fiber membrane system was evaluated to

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extract REEs in a single step with the feed and strip solutions circulating continuously through

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the MSX system. The effects of several experimental variables on REE extraction such as flow

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rate, concentration of REEs in the feed solution, membrane configuration, and composition of

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acids were investigated with the MSX system. A multi-membrane module configuration with

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REEs dissolved in aqueous nitric acid solutions showed high selectivity for REE extraction with

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no co-extraction of non-REEs, whereas the use of aqueous hydrochloric acid solution resulted in

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co-extraction of non-REEs due to the formation of chloroanions of non-REEs. The REE oxides

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were recovered from the strip solution through precipitation, drying, and annealing steps. The

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resulting REE oxides were characterized with XRD, SEM-EDX, and ICP-OES, demonstrating

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that the membrane assisted solvent extraction is capable of selectively recovering pure REEs

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from the industrial scrap magnets.

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Table of Contents (TOC)/Abstract Art

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INTRODUCTION

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The world today has hugely benefited from the application of rare earth elements (REEs) to

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most high-tech devices such as cell phones, rechargeable batteries, computers, TV, and

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fluorescent lighting.1-3 These REEs are the 15 lanthanides in the periodic table along with

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scandium and yttrium. Over 90% of REEs worldwide are currently being produced in China

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which until very recently had restricted REE exports. The rising REE demand in high-tech

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devices over the past two decades resulted in skyrocketing prices of REEs in just a few years.4-7

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This motivated the US Department of Energy to launch the Critical Materials Institute in 2013 in

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order to tackle the REE supply challenge, focusing on three different areas such as diversifying

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REE supplies, developing REE substitutes, and recycling REE wastes.8 Among those

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approaches, this study focuses on the recovery and recycling of end-of-life REE products. When

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compared to REE mining processes, recycling of REEs from post-consumer products provides

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significant environmental benefits with regard to air emissions, groundwater contamination, soil

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acidification, eutrophication, and climate change.2

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The recoverable REEs from end-of-life products are 1) neodymium (Nd), dysprosium (Dy),

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and praseodymium (Pr) from NdFeB permanent magnets used in automobiles, mobile phones,

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hard disk drives, computers, tablets, electric motors, and hybrid electric vehicles, 2) europium

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(Eu), terbium (Tb), and yttrium (Y) from phosphors in fluorescent lamps, LEDs, LCD

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backlights, and plasma screens, and 3) lanthanum (La), cerium (Ce), Nd, and Pr from nickel

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metal hydride batteries in rechargeable batteries, and hybrid electric vehicle batteries.9 Even

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though there are a variety of end-of-life products available for REE recovery, the actual REE

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recovery is currently estimated to be less than 1% due to low efficiencies and limitations in



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recycling processes.10 Therefore, it is pivotal to develop and improve the effective REE recycling

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process in order to widen the reuse of REE-containing end-of-life products.

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Even though commercial REE recycling is presently very limited, the REEs can be recovered

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through several processing technologies such as hydrometallurgy, pyrometallurgy, and gas-phase

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extraction. Hydrometallurgy uses strong acid to dissolve REE-containing end-of-life products

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and then uses basic solutions to selectively precipitate the REEs of interest. This process includes

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solvent extraction, leaching, and precipitation. However, this process requires high chemical

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usage and suffers from generation of large amounts of chemical waste and low selectivity due to

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co-extraction of non-REEs.9 The pyrometallurgical process utilizes high temperatures to

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chemically convert feed materials into the valuable REEs. This process requires fewer

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processing steps than the hydrometallurgical route, but it requires larger energy input and

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generates larger amounts of solid waste.9,11 The REE recovery by gas phase extraction route is

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based on volatility differences, involving chlorination and carbochlorination, but corrosive

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aluminum chloride and hydrogen chloride gas generated from this process pose serious

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environmental and safety hazards.12,13

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Membrane assisted solvent extraction (MSX) can provide another alternative to recover

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REEs, eliminating the disadvantages of traditional equilibrium-based solvent extraction

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processes such as loading, flooding, and third phase formation.14,15 In the continuous operation

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mode, separation in MSX is enhanced under non-equilibrium conditions due to the maintenance

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of high driving forces over extended periods of time compared to equilibrium limited

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conventional solvent extraction. While the solvent extraction process carries out extraction and

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stripping in two separate steps, MSX combines both processes in a single step, circulating the

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feed and strip solutions continuously without dispersion of different phases.16,17 Utilizing hollow 4 ACS Paragon Plus Environment

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fiber membrane modules in the MSX system provides high contact surface area per unit volume

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to achieve a high REE extraction rate. In the MSX system, an organic phase consisting of

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extractant and organic solvent is immobilized in the pores of hollow fiber membranes, and the

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aqueous feed and strip solutions flow through the lumen and shell side of hollow fiber modules,

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respectively, as shown in Figure S1 (Supporting Information). The organic solvent is immiscible

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with very low solubility in aqueous solution which minimizes extractant and solvent losses.

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Acidic extractants are widely used in current industrial practice, but they suffer from

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relatively low REE selectivity due to simultaneous co-extraction of other cations such as Fe, Cu,

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and Ni.18,19 On the contrary, neutral extractants such as tetraoctyl diglycol amide (TODGA) and

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trialkyl phosphine oxides (Cyanex 923) have shown the capability of selectively extracting

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several lanthanides and actinides such as cerium, europium, uranium and cesium.20-22 Therefore,

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we have utilized neutral extractants, TODGA and Cyanex 923 in this work. They were evaluated

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to selectively extract REEs from permanent magnets in the presence of non-REEs such as Fe, B

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and other transition metals (Cu, Ni) used in the outer coating. The distribution coefficient (D) is

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the ratio of REE concentration in the organic phase to that in the aqueous phase at equilibrium. D

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values of neodymium extracted by TODGA and Cyanex 923 were first measured to determine

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their relative efficiencies prior to incorporating them in the membrane supports. The effects of

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the concentration and flow rate of the feed solution, membrane configuration and acid

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composition on REE extraction were then systematically investigated using commercial NdFeB

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magnets. The MSX system was also utilized to extract REEs from industrial scrap magnets. The

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REEs in the scrap magnets were recovered from the strip solution in the MSX system by

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precipitating, filtration, drying, and annealing steps. The resulting REE oxides were



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characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and

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inductively coupled plasma-optical emission spectroscopy (ICP-OES).

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EXPERIMENTAL

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The distribution coefficient of neodymium was determined by mixing organic phase with the

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REE-containing aqueous solution for 2 hours, followed by separating aqueous phase from

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organic phase. The organic phase is composed of extractants (TODGA (Marshallton Research)

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or Cyanex 923 (CYTEC Industries Inc.)), tri-butyl phosphate (TBP, Stauffer Chemical

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Company) as another extractant, and IsoparTM L (Isoparaffin, ExxonMobil Chemical) as solvent.

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The aqueous phase was prepared by dissolving permanent magnets, neodymium(Nd)-iron(Fe)-

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boron(B) magnets (K&J Magnetics, Grade D42) in 1-6 M HNO3 and 3-6M HCl. The

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concentration of REEs in the organic phase was back-calculated from the REE concentration in

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the aqueous phase measured by ICP-OES (IRIS Intrepid II XSP, Thermo Electron Corporation).

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Hydrophobic membranes are desirable for the extraction of REEs because hydrophobicity

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prevents wetting of the membrane by aqueous feed solution and also prevents the displacement

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of organic phase immobilized in the pores into the strip solution. For this reason, hydrophobic

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polypropylene membrane modules (MicroModule®, Membrana, area: 100 cm2, ID: 0.25 mm,

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number of hollow fibers: 700) were used as membrane supports. The REE sources for the feed

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solution were chosen from three different NdFeB magnets; commercial NdFeB magnets from 1)

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K&J Magnetics (Grade D42) and industrial scrap magnets from 2) Molycorp Magnequench

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(Harrodsburg, KY) and 3) Daido Electronics Co. Ltd (Japan). The composition of the magnets is

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shown in Table S1 (Supporting Information). These magnets were dissolved in concentrated

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nitric acid or hydrochloric acid for 24 hours.


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Using the commercial NdFeB magnets, the membrane assisted solvent extraction was carried

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out with 2 L feed solution containing approximately 1000 and 2000 ppm Nd and the strip

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solution of 0.23 or 0.5 L. The molar concenstration of HNO3 in the feed solution was 6 M and

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the strip solution was 0.2 M HNO3. The pores of hollow fibers in the membrane modules were

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filled with organic phase consisting of the TODGA, IsoparTM L, and TBP in the ratio of 3:4:3,

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respectively. The shell side of hollow fibers was supplied with the aqueous strip solution, and the

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lumen side of the hollow fibers was fed with the feed solution containing REEs. Both the feed

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and strip solutions were simultaneously circulated throughout the MSX system with peristaltic

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pumps. The feed solution was thoroughly mixed with a mixer (Talboys, TROEMNER, LLC) to

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maintain uniform concentration. The pressure on the feed side was maintained at 15 psig and the

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strip side was kept at atmospheric pressure. The flow rate of the feed solution varied from 35 to

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105 mL/min to investigate the effect of flow rate on REE recovery. For ICP analysis, ~5 mL

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samples were collected from both feed and strip solutions over the duration of the experiment.

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The effect of membrane configuration on REE extraction was studied by connecting 8-

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membrane modules in series and parallel (Figure S2, Supporting Information). Experiments with

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3 and 6 M hydrochloric acid were also conducted to study the effect of acid composition on REE

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extraction. 0.2M HCl solution was used as the strip on shell side of the module.

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Upon the optimization of experimental conditions with the commercial NdFeB magnets, the

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two industrial scrap magnets procured from Molycorp Magnequench and Daido Electronics were

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utilized to recover REEs with the MSX system. The extracted REEs in the strip solution from

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those scrap magnets were precipitated out with oxalic acid, followed by filtration, drying at room

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temperature, and annealing at 750 oC for 2 hours. The resulting REE oxides were characterized

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by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX, HITACHI S-4800). 7 ACS Paragon Plus Environment


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The recovered REEs were re-dissolved in nitric acids to evaluate the purity of REE oxides with

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ICP-OES (IRIS Intrepid II XSP, Thermo Electron Corporation).

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RESULTS AND DISCUSSION

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The critical requirement in the extraction of REEs with the MSX system is the incorporation

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of a selective extractant in organic phase by impregnation in the pores of hollow fiber support.

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We have evaluated two different neutral extractants, TODGA and Cyanex 923. These were first

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evaluated to determine the distribution coefficient of neodymium at various acid concentrations.

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Although the distribution coefficient is a function of temperature, pH, metal ion concentration,

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extractant and solvent concentration, the effect of molar acid concentration on the distribution

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coefficient was only considered in this study.23 Figure 1 shows distribution coefficients of

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neodymium from NdFeB magnets (D42) obtained with TODGA and Cyanex 923 in aqueous

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HNO3 and HCl solutions. As shown in Figure 1, distribution coefficient of Nd extracted by

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TODGA was substantially greater than that obtained with Cyanex 923 at several different

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representative acid concentrations. High D values with TODGA can be attributed to strong

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oxygen donor atoms in TODGA, whereas low D values on Cyanex 923 are likely due to the low

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adsorption ability of Cyanex 923 for the REEs.24,25 This result confirms that TODGA is more

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suitable than Cyanex 923 for extraction of REEs from NdFeB magnets. Thus, TODGA was

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chosen as the preferred extractant in the MSX system to extract REEs from the permanent

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magnets in this research.

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There are several process variables that can have an effect on REE recovery in the MSX

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system, such as REE concentration, molar concentration of acid, and membrane area. These

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variables were investigated in a prior study.26 The molar concentration of HNO3 in the feed and


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strip was chosen as 6M and 0.2M, respectively. This was based on favorable values of

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distribution coefficient at high acid concentration. The 8-membrane module system was used to

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extract REEs. Another experimental variable that can impact REE extraction is the feed flow

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rate. The flow rate of the feed side in the 8-membrane modules was varied from 35 to 105

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mL/min, while keeping all other experimental conditions constant. Figure S3 (Supporting

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Information) shows the effect of flow rate of the feed solution on REE recovery in the MSX

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system. As can be seen in Figure S3, the ratio of REE concentration in the strip to the feed only

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slightly decreased as the feed flow rate increased, suggesting that the extraction rate is not

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significantly impacted by the feed flow rate. Therefore, a feed flow rate of 35 mL/min was

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selected in the MSX system for the rest of this study.

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The 8-membrane modules were connected in parallel to enable the feed solution to be evenly

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distributed into each membrane module, as shown in the schematic of Figure S2 (a) (Supporting

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Information). Figure 2 shows the elemental composition of (a) the feed (commercial NdFeB

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magnets (K&J Magnetics, Grade D42)) and (b) the strip solutions while operating the 8-

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membrane module system for 55 hours. The molar concentration of nitric acid in the feed and the

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strip was 6M and 0.2M, respectively. At around 24 hours from the start, Nd concentration in the

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strip was about 900 ppm and then decreased slowly as operating time increased, whereas Pr

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concentration kept increasing over 55 hours. As shown in Figure 2 (c), the Nd concentration ratio

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in the strip to the feed was > 1.0 after a run time of 20 hours, and the concentration of Pr in the

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strip increased up to 95% of the initial Pr concentration in the feed. Figure 2 (d) shows extraction

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rates of Nd and Pr while running the 8-membrane module system. In both cases, the REE

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extraction rates rapidly declined at the beginning of the run even at high REE concentration,

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indicating that REE extraction may be significantly limited by the amount of extractants 9 ACS Paragon Plus Environment


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available in the pores of hollow fibers. Typically, MSX system does not experience any fouling

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issue often caused by the accumulation of particulate matter. However, in order to maintain the

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desired concentration of extractants in the membrane pores, the organic phase might need to be

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supplemented periodically to achieve long term stability (>1000 hours). The expected frequency

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of replenishing extractants would be once every couple of months.

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Figures S4 (a) and (b) (Supporting Information) show the elemental concentration of NdFeB

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magnets in the feed and strip solutions when the feed concentration was doubled from ~1000

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ppm to ~2000 ppm Nd, while maintaining all other conditions as shown in Figure 2. It can be

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seen from Figure S4 (b) that Nd, Dy and Pr were selectively recovered with no co-extraction of

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non-REEs such as Fe and B. The other non-REEs such as Cu and Ni used in the outer coating of

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the magnets were also undetectable by ICP-OES. This high selectivity of REEs over non-REEs

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could be attributed to the non-equilibrium separation process of membrane assisted solvent

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extraction. In this case, REEs are continuously extracted at high driving forces without

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approaching equilibrium where co-extraction can occur. However, as shown in Figure S4 (c)

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(Supporting Information), the recovery of Nd and Pr with higher concentration of feed solution

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(~2000 ppm Nd) decreased by about 50%, indicating that REE extraction through the membrane

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is not limited by concentration gradient, but by the amount of available extractants in the hollow

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fiber pores. Figure S5 (Supporting Information) shows the extraction results while running the 8-

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membrane module system for 96 hours with increased strip volume (0.5 L). All other conditions

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were identical to those reported for Figure S4. The behavior of the Nd, Pr, Dy recovery over time

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with the higher strip volume was very similar to that of REEs with the strip volume of 0.23 L

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(see Figure S4, Supporting Information). A small increase in the extraction rate was observed


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with the higher strip volume in Figure S5 (d) compared to the lower strip volume (0.23 L) in

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Figure S4 (d).

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In order to evaluate the influence of membrane module configuration on REE extraction, the

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8-membrane modules were connected in series as shown in Figure S2 (b). All other extraction

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conditions were identical to those reported in Figure S5. Figures 3 (a) and (b) show the

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concentration of NdFeB magnet elements in the (a) feed and (b) strip solutions while running the

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8-module system in series for 96 hours. The ratio of REE concentrations in the strip to the feed

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solution and REE extraction rates with the 8-modules in series configuration are shown in

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Figures 3 (c) and (d). The Nd and Pr recoveries with the 8-membrane modules connected in

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series were about 20% higher than that with the 8- modules in parallel. In addition, the extraction

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rate for the first 24 hours run time was almost double to that observed for the 8-modules

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connected in parallel. These results confirm that the membrane configuration in series shows

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better REE extraction performance than the configuration where modules are connected in

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parallel.

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The use of hydrochloric acid instead of nitric acid for REE extraction was evaluated in the

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MSX system as it is generally the preferred acid in many traditional precipitation and extraction

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technologies for REE recovery. Figures 4 (a) and (b) show the elemental concentration in the

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feed and strip solutions while operating the 8-membrane module system connected in series with

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6M HCl in the feed and 0.2M HCl in the strip. Figures 4 (c) and (d) show the ratio of REE

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concentration in the strip to the feed and REE extraction rate, respectively. As shown in Figure 4

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(b) and (c), significant amounts of Fe and B were co-extracted with REEs into the strip solution.

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The ratio of Fe concentration in the strip to the feed in 48 hours was about 1.6 which is much

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higher than that of Nd and Pr in Figure 4 (c). The co-extraction of REEs could be attributed to 11 ACS Paragon Plus Environment


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the formation of tetrachloroanions of non-REEs in the presence of HCl as described below.27

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This mechanism is not applicable as nitrate anions are not formed that can be coextracted when

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nitric acid is used for REE extraction.

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2Fe + 6HCl → 2FeCl + 3H TODGA + FeCl + HCl ↔ TODGA · H · FeCl

+ 3Cl ↔ [(TODGA) 3TODGA · H · FeCl

Nd] (FeCl ) + 3HCl + Nd

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Figures S6 (a) and (b) (Supporting Information) show the elemental concentration in the feed

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and strip when 3M HCl was used in the feed solution with the 8-membrane modules to extract

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REEs from permanent Nd-based magnets. As shown in Figures S6 (b) and (c) (Supporting

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Information), even though the ratio of Nd and Pr in the strip to the feed was significantly higher

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compared to that with 6 M HCl in the feed, the co-extraction of Fe was still observed resulting in

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high concentration of Fe in the strip, unlike when HNO3 was used in the aqueous solutions. As

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can be seen from these results, although HCl is widely used in current industrial practice, it

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would be more desirable to use HNO3 in the MSX system to recover high purity REEs from the

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Nd-based magnets, based on the results obtained in this study. However, utilizing ionic liquids,

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such as trihexyl(tetradecyl)phosphonium chloride, which has shown high distribution ratio for

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iron over REEs in HCl, may be an option to post-treat the HCl based strip solution to recover

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pure REEs.28

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Upon the optimization of the MSX system performance with commercial NdFeB magnets,

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the REE recovery from industrial scrap magnets with membrane assisted solvent extraction was

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investigated. The end-of-life scrap magnets were procured from Molycorp Magnequench, which

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contains about 30 wt.% REEs (see Table S1). Figure 5 (a) shows the elemental concentration of 12 ACS Paragon Plus Environment

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the Magnequench scrap magnet dissolved in 6M HNO3. The elemental concentrations in the strip

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solution and the ratio of REEs in the strip to the feed while operating the 8-membrane module

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system are shown in Figures 5 (b) and (c), respectively. The results show that only REEs such as

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Nd, Pr, and Dy were selectively extracted from the scrap magnets into the strip solution with the

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MSX system, without any co-extraction of non-REEs such as Fe and B. Figure S7 (Supporting

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Information) shows the REE extraction results obtained with the industrial scrap magnets

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procured from Daido Electronics. As shown in Figures S7 (b) and (c), only REEs were

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selectively recovered from Daido Electronics scrap magnets with the MSX system, and there was

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no co-extraction of non-REEs in the strip solution over the 120 hour run. These results clearly

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demonstrate that membrane assisted solvent extraction is capable of selectively recovering REEs

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from industrial scrap magnets.

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The REEs extracted into the strip solution from the scrap magnets were then precipitated

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with oxalic acid, followed by filtration, drying, and annealing steps. Figure S8 (Supporting

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Information) shows the XRD patterns of resulting REE oxides recovered from the scrap magnets

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procured from Molycorp Magnequench. The majority of peaks shown in the XRD analysis

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correspond to the peaks for REE oxides such as Nd2O3 (JCPDS 21-0579) and PrO1.83 (JCPDS

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06-0329), indicating that REE oxides were successfully recovered from industrial scrap magnets

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via the MSX system. The purity of recovered REEs was examined by SEM-EDX analysis, as

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shown in Figure 6. There is no indication of the presence of iron in the recovered REE oxides

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based on the EDX analysis. In addition, when the recovered REE oxides were analyzed by the

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ICP-OES after being re-dissolved in the nitric acid solution, only REEs such as Nd, Pr, and Dy

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were detected with non-detectable concentration of non-REEs in the sample. The XRD patterns

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for recovered REE oxides from Daido scrap magnets are shown in Figure S9 (Supporting 13 ACS Paragon Plus Environment


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Information) and their SEM-EDX analysis are presented in Figure S10 (Supporting Information).

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Figures S9 and S10 also demonstrate that nearly pure REEs were successfully recovered from

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different scrap magnets with the MSX system. These results confirm that the membrane assisted

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solvent extraction technology is capable of selectively extracting REEs from industrial scrap

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magnets. This is the first comprehensive research showing the successful demonstration of

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applying membrane assisted solvent extraction to REE recovery from Nd-based scrap magnets.

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In comparison, the traditional approaches of utilizing precipitation result in low recovery and

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the recovered REE may contain significant levels of non-REEs such as Fe and Co.29,30 It is also

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difficult to dispose of hazardous wastes. The use of equilibrium-limited solvent extraction would

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require a large number of stages to produce highly pure REEs suitable for reuse. The significant

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possibility for solvent and extractant losses due to solubility in highly acidic solutions may also

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hinder its application for REE recycling and reuse. The recovery of REEs in highly pure form is

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essential to potentially enable its direct use in REE recycling. There would be a huge cost

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advantage if the REE oxides are recovered in nearly pure form as it would eliminate the need for

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further purification and processing prior to reuse. Thus, the application of membrane assisted

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solvent extraction to the REE recovery from the scrap magnets would result in a more

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environmentally friendly and cost-effective process compared to the conventional routes such as

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precipitation and solvent extraction.

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ASSOCIATED CONTENT

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309

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Supporting Information: Table S1, Figure S1, S2, S3, S4, S5, S6, S7, S8, S9, S10. AUTHOR INFORMATION Corresponding author: *E-mail: [email protected], Tel: (865)574-6025 14 ACS Paragon Plus Environment

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ACKNOWLEDGEMENTS

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This research/work is supported by the Critical Materials Institute, an Energy Innovation Hub

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funded by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy,

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Advanced Manufacturing Office. The authors would like to thank Dr. Huseyin Ucar at ORNL for

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his assistance in XRD analysis.

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REFERENCES

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(1) Critical Materials Strategy, U.S. Department of Energy, DOE/PI-0009, December 2011.

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(2) Schüler, D.; Buchert, M.; Liu, R.; Dittrich, S.; Merz, C. Study on rare earths and their

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recycling. Final Report for The Greens/EFA Group in the European Parliament; Öko-Institut

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e.V.; www.oeko.de/oekodoc/1112/2011-003-en.pdf, 2011.

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(3) Alonso, E.; Sherman, A. M.; Wallington, T. J.; Everson, M.P.; Field, F. R.; Roth, R.;

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Kirchain, R. E. Evaluation rare earth element availability: a case with revolutionary demand

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(4) Stone, R. As china’s rare earth R&D becomes ever more rarefied, others tremble. Science 2009, 325, 1336-1337. (5) Service, R. F. Nations move to head off shortages of rare earths. Science 2010, 327, 15961597. (6) Humphries, M. Rare earth elements: the global supply chain. Congressional Research Service Report for Congress, 2013; https://www.fas.org/sgp/crs/natsec/R41347.pdf. (7) Du, X.; Graedel, T. E. Global in-use stocks of the rare earth elements: a first estimate. Environ. Sci. Technol. 2011, 45, 4096-4101. (8) Cho, A. Hubs aim to reinvent DOE research culture. Science, 2013, 340, 914-918.



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(9) Binnemans, K.; Jones, P. T.; Blanpain, B.; Gerven, T. V.; Yang, Y.; Walton, A.; Buchert, M. Recycling of rare earths: a critical review. J. clean. Prod. 2013, 51, 1-22. (10)

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Huang, K.; Li, J.; Xu, Z. A novel process for recovering valuable metals from waste

nickel-cadmium batteries. Environ. Sci. Technol. 2009, 43, 8974-8978. (12)

Uda, T. Recovery of rare earths from magnet sludge by FeCl2. Mater. Trans. 2002, 43,

55-62. (13)

Itoh, M.; Miura, K.; Machida, K. Novel rare earth recovery process on Nd-Fe-B magnet

scrap by selective chlorination using NH4Cl. J. Alloys Compd. 2009, 477, 484-487. (14)

Lee, L. T. C.; Ho, W.-S.; Liu, K.-J. Membrane solvent extraction. US Patent, 1976,

3,956,112. (15)

Ho, W. S. W.; Poddar, T. K. New membrane technology for removal and recovery of

chromium from waste waters. 2001, Environ. Prog. 20 (1), 44-52. (16)

Yun, C. H.; Prasad, R.; Sirkar, K. K. Membrane solvent extraction removal of priority

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organic pollutants from aqueous waste streams. Ind. Eng. Chem. Res. 1992, 31 (7), 1709-

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1717.

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Gaikwad, A. G.; Chitra, K. R.; Surender, G. D.; Damodaran, A. D. Membrane solvent

extraction of some rare earth elements. Chem. Biochem. Eng. Q. 2003, 17 (3), 191-199. (18)

Lee, M.-S.; Lee, J.-Y.; Kim, J.-S.; Lee, G.-S. Solvent extraction of neodymium ions from

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Li, W.; Wang, X.; Meng, S.; Li, D.; Xiong, Y. Extraction and separation of yttrium from

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the rare earths with sec-octylphenoxy acetic acid in chloride media. Sep. Purif. Technol.

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2007, 54 (2), 164-169.

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Horwitz, E. P.; McAlister, D. R.; Thakkar, A. H. Synergistic enhancement of the

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extraction of trivalent lanthanides and actinides by tetra-(n-octyl)diglycolamide from

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chloride media. Solvent Extr. Ion Exc. 2008, 26 (1), 12-24.

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Shimojo, K.; Kurahashi, K.; Naganawa, H. Extraction behavior of lanthanides using a

diglycolamide derivative TODGA in ionic liquids. Dalton Trans. 2008, 37, 5083-5088. (22)

Larsson, K.; Ekberg, C.; Odegaard-Jensen, A. Using Cyanex 923 for selective extraction

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in a high concentration chloride medium on nickel metal hydride battery waste.

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Hydrometallurgy, 2012, 129, 35-42.

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Baker, R. W. Membrane technology and applications, 3rd ed.; John Wiley and Sons Ltd.:

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Lee, G. S.; Uchikoshi, M.; Mimura, K.; Isshiki, M. Distribution coefficients of La, Ce, Pr,

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Nd, and Sm on Cyanex 923-, D2EHPA-, and PC88A-impregnated resins. Sep. Purif.

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Sasaki, Y.; Tsubata, Y.; Kitatsuji, Y.; Sugo, Y.; Shirasu, N.; Morita, Y.; Kimura, T.

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Extraction behavior of metal ions by TODGA, DOODA, MIDOA, and NTAamide

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extractants from HNO3 to n-Dodecane. Solv. Extr. Ion. Exc. 2013, 31, 401-415.

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Membrane solvent extraction for the selective recovery of rare earth elements from

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neodymium-based permanent magnets. Separ. Sci. Technol. 2015, submitted.



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Nararro, R.; Gallardo, V.; Saucedo, I.; Guibal, E. Extraction of Fe(III) from hydrochloric

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separations relevant to rare-earth magnet recycling. Green Chem, 2013, 15, 919-927.

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Gerasimova, L. G.; Nikolaev, A. I.; Maslova, M. V.; Okhrimenko, R. F. Utilization of

waste containing rare-earth elements. Theor. Found. Chem. Eng.

388 389 390 391 392 393 394 395 396 397 398 399 400


Page 19 of 30


1200

(a)

Distribution Coef. of Nd


1200 1000 TODGA Cyanex 923

800 600 400 200 0

TODGA Cyanex 923

800 600 400 200 0

0

401

(b)

1000

1

2

3 4 5 HNO3 (M)

6

7

0

1

2

3 4 HCl (M)

5

6

7

402 403 404

Figure 1. Distribution coefficient of Nd from NdFeB magnets (D42) with TODGA and Cyanex 923 in (a) HNO3 and (b) HCl.

405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 19 ACS Paragon Plus Environment


1000 Elemental Conc. (ppm)

Elemental Conc. (ppm)

1000 800 600

(a)

400 200

800

0

600

(b)

400 200

20

40

0

60

20

REE extraction rate (g/cm2/h)

1.2 1.0 0.8 Nd 0.6

Pr

0.4

(c)

0.2 0.0 0

20

40

60

Time (h)

Time (h)

421 REE Conc. Ratio (Strip / Feed)

Nd Pr Fe B Dy

0

0

422

Page 20 of 30

40

60

6.E-05 Nd

5.E-05

Pr 4.E-05 3.E-05 2.E-05

(d)

9.E-06 -1.E-06 0

20

40

60

Time (h)

Time (h)

423 424 425 426

Figure 2. (a) The elemental concentration of NdFeB magnets in the (a) feed and (b) strip solutions while running the 8-module system in parallel, (c) the ratio of REEs in the strip to the feed and (d) REE extraction rate (feed: 6M HNO3, ~1000 ppm Nd, strip: 0.2M HNO3, 0.23 L)

427 428 429 430 431 432 433


Page 21 of 30


2500

2500

(b) Element Conc. (ppm)

Element Conc. (ppm)

(a) 2000 1500 1000 500 0 20

40 60 Time (h)

80

100

1500 1000 500

0

20

40 60 Time (h)

80

100

1.4E-04

3.0

(c)


REE Conc. Ratio (Strip / Feed)

434

Nd

2.5

Pr Dy

2.0 1.5 1.0 0.5

(d)

1.2E-04

Nd Pr

9.9E-05

Dy

7.9E-05 5.9E-05 3.9E-05 1.9E-05 -1.0E-06

0.0 0

436 437 438

Nd Pr Fe B Dy

0 0

435

2000

20

40 60 Time (h)

80

0

100

20

40 60 Time (h)

80

100

Figure 3. The elemental concentration of NdFeB magnets in the (a) feed and (b) strip solutions, and (c) the ratio of REEs in the strip to the feed and (d) REE extraction rate while running the 8module system in series for 96 hours (feed: 6M HNO3, 2L; strip: 0.2M HNO3, 0.5 L).

439 440 441 442 443 444 445 446 21 ACS Paragon Plus Environment


12000

(a)

6000



7000

5000 4000 3000 2000 1000 0 24

447

48 Time (h)

72

6000 4000 2000 0

24

48 Time (h)

72

96

1.E-03

(c)

1.6

Extraction rate (g/cm2/h)

Elemental Conc. Ratio (Strip/Feed)

Fe B Nd Pr

8000

96

2.0

Fe B Nd Pr

1.2 0.8 0.4 0.0 0

449 450 451

(b)

10000

0 0

448

Page 22 of 30

24

48 Time (h)

72

(d)

Fe Nd Pr B

8.E-04 6.E-04 4.E-04 2.E-04 0.E+00

96

0

24

48 Time (h)

72

96

Figure 4. The elemental concentration of NdFeB magnets in the (a) feed and (b) strip solutions, and (c) the ratio of REEs in the strip to the feed and (d) REE extraction rate while running the 8module system in series for 96 hours (feed: 6M HCl, 2L; strip: 0.2M HCl, 0.5 L).

452 453 454 455 456 457 458 459


Page 23 of 30


800

(a)

5000



6000

4000 3000 2000 1000 0

20

40 60 Time (h)

80

Nd Pr Fe B Dy

500 400 300 200 100

1.2 Nd

(c)

1.0

Pr

0.8

Dy

0.6 0.4 0.2 0.0 0

20

40 60 Time (h)

80

0

100


REE Conc. Ratio (Strip/Feed)

460

462 463 464 465

600

0

0

461

(b)

700

9.E-05 8.E-05 7.E-05 6.E-05 5.E-05 4.E-05 3.E-05 2.E-05 9.E-06 -1.E-06

40 60 Time (h)

80

(d)

0

100

20

20

100

Nd Pr Dy

40 60 Time (h)

80

100

Figure 5. The elemental concentration of scrap magnets (Molycorp Magnequench) in the (a) feed and (b) strip solutions, and (c) the ratio of REEs in the strip to the feed and (d) REE extraction rate while running the 8-module system in series for 100 hours (feed: 6M HNO3, 2L; strip: 0.2M HNO3, 0.5 L).

466 467 468 469 470 471 472



473 474 475

Figure 6. SEM-EDX analysis of REEs recovered from Magnequench scrap magnets by membrane assisted solvent extraction.

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Page 24 of 30

Page 25 of 30


1200

(a)



1200 1000 TODGA Cyanex 923

800 600 400 200 0

TODGA Cyanex 923

800 600 400 200 0

0

1

(b)

1000

1

2

3 4 5 HNO3 (M)

6

7

0

1

2

3 4 HCl (M)

5

6

7

2 3 4

Figure 1. Distribution coefficient of Nd from NdFeB magnets (D42) with TODGA and Cyanex 923 in (a) HNO3 and (b) HCl.

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1 ACS Paragon Plus Environment


1000 Elemental Conc. (ppm)


1000 800 600

(a)

400 200

800

0

600

(b)

400 200

20

40

0

60

20


1.2 1.0 0.8 Nd 0.6

Pr

0.4

(c)

0.2 0.0 0

20

40

60

Time (h)

Time (h)

21 REE Conc. Ratio (Strip / Feed)

Nd Pr Fe B Dy

0

0

22

Page 26 of 30

40

60

6.E-05 Nd

5.E-05

Pr 4.E-05 3.E-05 2.E-05

(d)

9.E-06 -1.E-06 0

20

40

60

Time (h)

Time (h)

23 24 25 26

Figure 2. (a) The elemental concentration of NdFeB magnets in the (a) feed and (b) strip solutions while running the 8-module system in parallel, (c) the ratio of REEs in the strip to the feed and (d) REE extraction rate (feed: 6M HNO3, ~1000 ppm Nd, strip: 0.2M HNO3, 0.23 L)

27 28 29 30 31 32 33 2 ACS Paragon Plus Environment

Page 27 of 30


2500

2500

(b) Element Conc. (ppm)

Element Conc. (ppm)

(a) 2000 1500 1000 500 0 20

40 60 Time (h)

80

100

1500 1000 500

0

20

40 60 Time (h)

80

100

1.4E-04

3.0

(c)


REE Conc. Ratio (Strip / Feed)

34

Nd

2.5

Pr Dy

2.0 1.5 1.0 0.5

(d)

1.2E-04

Nd Pr

9.9E-05

Dy

7.9E-05 5.9E-05 3.9E-05 1.9E-05 -1.0E-06

0.0 0

36 37 38

Nd Pr Fe B Dy

0 0

35

2000

20

40 60 Time (h)

80

0

100

20

40 60 Time (h)

80

100

Figure 3. The elemental concentration of NdFeB magnets in the (a) feed and (b) strip solutions, and (c) the ratio of REEs in the strip to the feed and (d) REE extraction rate while running the 8module system in series for 96 hours (feed: 6M HNO3, 2L; strip: 0.2M HNO3, 0.5 L).

39 40 41 42 43 44 45 46 3 ACS Paragon Plus Environment


12000

(a)

6000



7000

5000 4000 3000 2000 1000 0 24

47

48 Time (h)

72

6000 4000 2000 0

24

48 Time (h)

72

96

1.E-03 Extraction rate (g/cm2/h)

Elemental Conc. Ratio (Strip/Feed)

Fe B Nd Pr

8000

96

2.0

(c)

1.6

Fe B Nd Pr

1.2 0.8 0.4 0.0 0

49 50 51

(b)

10000

0 0

48

Page 28 of 30

24

48 Time (h)

72

(d)

Fe Nd Pr B

8.E-04 6.E-04 4.E-04 2.E-04 0.E+00

96

0

24

48 Time (h)

72

96

Figure 4. The elemental concentration of NdFeB magnets in the (a) feed and (b) strip solutions, and (c) the ratio of REEs in the strip to the feed and (d) REE extraction rate while running the 8module system in series for 96 hours (feed: 6M HCl, 2L; strip: 0.2M HCl, 0.5 L).

52 53 54 55 56 57 58 59


Page 29 of 30


800

(a)

5000



6000

4000 3000 2000 1000 0

20

40 60 Time (h)

80

Nd Pr Fe B Dy

500 400 300 200 100

1.2 Nd

(c)

1.0

Pr Dy

0.8 0.6 0.4 0.2 0.0 0

20

40 60 Time (h)

80

0

100


REE Conc. Ratio (Strip/Feed)

60

62 63 64 65

600

0

0

61

(b)

700

9.E-05 8.E-05 7.E-05 6.E-05 5.E-05 4.E-05 3.E-05 2.E-05 9.E-06 -1.E-06

40 60 Time (h)

80

(d)

0

100

20

20

100

Nd Pr Dy

40 60 Time (h)

80

100

Figure 5. The elemental concentration of scrap magnets (Molycorp Magnequench) in the (a) feed and (b) strip solutions, and (c) the ratio of REEs in the strip to the feed and (d) REE extraction rate while running the 8-module system in series for 100 hours (feed: 6M HNO3, 2L; strip: 0.2M HNO3, 0.5 L).

66 67 68 69 70 71 72



73 74 75

Figure 6. SEM-EDX analysis of REEs recovered from Magnequench scrap magnets by membrane assisted solvent extraction.

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