Recovery of Rare Earth Metals By Electrodeposition from Ionic Liquids

Rare earth elements have become increasingly important to modern life as they are used in nickel-hydride batteries in current hybrid vehicles, as phosphors in fluorescent and LED lighting, and magnets used in computer hard disks and various automotive subsystems.¹ In recent years the prices of the many of these elements have increased drastically due to reduced exports.² Developing recycling methods for these elements is becoming a necessity for meeting future demands. Electrodeposition is a low-cost technique that could prove exceedingly useful to recover these elements from various sources. Traditional aqueous electrolytes are unsuitable for the electrodeposition of rare earth elements because they lie outside the electrochemical window of stability. This requires alternative electrolytes. Ionic liquids have received considerable attention as alternative electrolytes for electrodeposition due to several of their interesting chemical and physical properties. The large electrochemical windows of ionic liquids allow for the electrodeposition of electropositive elements, such as rare earth metals. In addition, the low volatility and high thermal stability of these solvents allows higher temperatures to be used in electrochemical processes.

Recently, our group has used ionic liquids to electrodeposit various elements and compounds, including Ge, Se, GeS_x, and MoS_x.^3,4,5 This was done by finding and synthesizing appropriate elemental precursors and ionic liquids for electrochemical deposition. This same strategy has been employed for the electrodeposition on rare earth metals. A number of precursors have been synthesized and investigated for electrodeposition. The effect of temperature on the electrodeposition was investigated. In addition, several ionic liquids were employed to investigate the effect of the cation and anion on the deposits.

References

1.) Van Gosen, B.S.; Verplanck, P.L.; Long, K.R.; Gambogi, J.; Seal II, R.R. The Rare-Earth Elements – Vital to Modern Technologies and Lifestyles. United States Geological Survey, USGS Mineral Resources Program. Reston, VA. November 2014.

2.) Rare Earth Elements: A Review of Production, Processing, Recycling, and Associated Environmental Issues. Environmental Protection Agency, National Risk Management Research Laboratory. Cincinnati, OH. December 2012.

3.) Murugesan, S.; Kearns, P.; Stevenson, K.J. Langmuir. 2012, 28(13), 5513-5517.

4.) Murugesan, S.; Akkineni, A.; Chou, B.P.; Glaz, M.S.; Vanden Bout, D.A.; Stevenson, K.J. ACS Nano. 2013, 7(9), 8199-8205.

5.) Redman, D.W.; Murugesan, S.; Stevenson, K.J. Langmuir. 2014, 30, 418-425.