Ionic Liquid-based Electrowinning for Refining of Rare Earth Oxides/Salts
Rare earth (RE) elements are used in a variety of energy and defense critical technologies, including permanent magnets and rechargeable batteries, but the vast majority of the extraction of the oxides and the subsequent refining to convert the oxide to metal is done overseas. Coal and coal-based resources represent a significant potential domestic source of REs. Current RE refinement technologies use high temperatures and highly reactive and toxic chemicals. The development of new techniques and processes to refine rare earth oxides and salts to rare earth metals would enable domestic production of RE elements and provide a high value product for which the U.S. is currently dependent on other nations (particularly China) for its supply. TDA is used computational techniques to design or select ionic liquids (IL) that can solvate individual rare earth cations from their oxide and salt forms. The solvated rare earth cations were next reduced to metals using an electrowinning process, directly plating out pure metals from these ionic liquids. In Phase I we applied our computation methods to a wide range of ionic liquids to identify those that have both a wide electrochemical stability window and which can effectively solvate the RE cations. We demonstrated both the solvation process step and the subsequent electrowinning processes step on a lab scale, and explored basic process parameters such as temperature, plating current density and plating time. We found process conditions at room temperature that resulted in efficient neodymium plating at 5 mA/cm2 of electrode. Further, the ionic liquid remained stable and the cation was unchanged even after a full 24 hours of use in the plating bath. This indicates that we will be able to reuse the ionic liquid many times in this batch process. An engineering analysis was performed to identify the energy and capital requirements for a pilot plant. A 1 metric ton per moth pilot plant has a total CAPEX of $412,413, and OPEX of $2,012,670 and produces $2,648,592 worth of neodymium metal per year. This assumes a batch process with 66% time online. The OPEX% of product value is 76% and the payback period based on the CAPEX and OPEX is less than one year. The energy consumption is 1.5 kWh/kg heodymum metal produced, and the process should be easily reduced in Phase II, where our goal is to lower the energy requirement to 0.77kWh/kg REM, or lower. This will be accomplished by optimizing the time and temperature of the dissolution step (as the main source of power requirement is overcoming the thermal losses of heating the stirred tank reactor used in this first step). In contrast, the conventional high temperature motle salt process requires up to 10 kWh/kg REM, thus our new process is far more energy efficient. Currently the molten salt process requires 7 times the energy of our unoptimized process, and we expect after optimizing the temperature and duration of the first process step in Phase II that we can increase our advantage to 14-21 times better than the motlen salt process. Our commercialization strategy is to license both the ionic liquid formula and rare earth refining process. Our end customers would be REE producers (mining companies and recyclers), while our primary customer will be suppliers of chemicals and equipment to the REE refining industry. TDA will develop and validate the technology in Phase II. We have the capability to produce moderate quantities of ionic liquid in-house (enough to see the process through its pilot demonstration and initial commercial use), and would then move to toll production. When we need large scale (multi-ton) quantities we will license compositions and synthesis processes to to a chemical company who produces and sells ionic liquids.
- Research Organization:
- TDA Research, Inc.
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- SC0021884
- OSTI ID:
- 1970362
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- TDA_R_2101_035_PhI_F_R; TDA_R_2101_035_PhI_R
- Country of Publication:
- United States
- Language:
- English
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