Using ionic liquids for the separation of rare earths

Dear reader,

We are happy to share with you our first publication in Green¬†Chemistry:¬†“Extraction and separation of neodymium and dysprosium from used NdFeB magnets: an application of ionic liquids in solvent extraction towards the recycling of magnets”¬†by¬†Sof√≠a¬†Ria√Īo¬†and¬†Koen Binnemans

Green

In this paper, we present a process for the extraction and separation of neodymium and dysprosium from used NdFeB magnets, using ionic liquids in solvent extraction as an application towards the recycling of magnets.

We have developed a procedure for the efficient extraction and separation of rare earths and other valuable elements from used NdFeB permanent magnets. First, we prepared an iron-free leachate from an used magnet using nitric acid. Afterwards, we separated the cobalt through a liquid-liquid extraction process using¬†the ionic liquid trihexyl(tetradecyl)phosphonium nitrate as an organic phase. Neodymium and Dysprosium were separated using¬†ethylenediaminetetraacetic acid (EDTA) as a selective complexing agent during liquid‚Äďliquid extraction with the same ionic liquid. Once the metals were separated they were precipitated with oxalic acid and then calcined in order to obtain their respective oxides, which are the starting materials for the production of new magnets.¬†Nd2O3, Dy2O3¬†and CoO were obtained with purities of 99.6%, 99.8% and 99.8%, respectively. Besides this, recycling of the employed ionic liquid for reuse in rare earths separation was also demonstrated.

Kitchen Chemistry: removing neodymium from NdFeB magnets

Post  written by TOM VANDER HOOGERSTRAETE 
(@TomVanderh1)

You probably know that a lot of people are collecting stamps, coins, stones, cards, DVDs, etc. But some of them are also collecting the elements of the periodic table. For neodymium, the most interesting and best available source is a NdFeB magnet. (
http://www.versuchschemie.de/topic,9178,-Neodym%28III%29-sulfat+aus+Festplattenmagneten.html and http://www.sciencemadness.org/talk/viewthread.php?tid=14145)

As kitchen chemist do not have the equipment and facilities of universities of companies, the techniques and steps required for isolating neodymium from the magnet need to be very simple, cheap and straightforward. Moreover, the chemicals should be non-toxic, have small hazards, and need to be available in simple drugstores. In this blog, I will give some very simple methods to remove and isolate (‚Äúpure‚ÄĚ) neodymium from NdFeB magnets.

First of all, it is very difficult to obtain ‚Äúpure‚ÄĚ neodymium metal because of the low redox potential of this element (E¬į = -2.3 V) and the low free energy of formation of the oxide compounds.1 Under ambient conditions, in the presence of oxygen or water, it is even impossible. Moreover, nowadays NdFeB magnets contain a lot of different (non-) metallic additives (http://erean.eu/wordpress/additives-in-ndfeb-magnets/) all behaving differently in a chemical separation process. NdFeB magnets can contain several other rare-earths elements such as praseodymium, dysprosium or terbium. The separation of neodymium from these metals can only be performed by solvent extraction.2 It is also ‚Äúpossible‚ÄĚ to separate the rare earths by fractional crystallization but even more steps than solvent extraction processes are required to obtain ‚Äúpure‚ÄĚ rare-earths.3 The best available NdFeB magnets are those present in hard disk drives. And luckily, these magnets contain no heavy (and expensive) rare-earths such as terbium or dysprosium because hard disk drives are working at relative low temperatures.4 However, neodymium can be substituted by significant amounts of praseodymium because this hardly changes the magnetic properties of the permanent magnets. As the price of Pr is slightly higher than the price of Nd, substitution of Nd by Pr is mainly done for economical reasons: the production costs for a high purity separation of these two neighboring rare-earth elements can be decreased, and substitutions by Pr could avoid price fluctuation by overproduction related to the so called Balance Problem.5 If your final precipitate is lavender of color, than neodymium is probably quite pure. If you obtain a much darker oxide precipitate, than you probably obtained a mixture of neodymium (lavender) and praseodymium oxide (black)

So, let us assume that we would like to obtain a high pure neodymium (hydr)oxide powder from a HDD drive containing mainly praseodymium as impurity. First, the magnets need to be removed from the HDD drive from a computer (check youtube, e.g. https://www.youtube.com/watch?v=YKzPt18aE_0). Secondly, the magnets need to be removed from the brackets (https://www.youtube.com/watch?v=GQhSy-Kz5DM). The magnet can be (partly) demagnetized by heating above 200 ¬įC in an oven. The magnet coating can be removed with a file or sandpaper. The magnet is very brittle and, if necessary, it can be broken in smaller particles by using a hammer. HCl, H2SO4, H2O2, NaOH, NH4OH, ethanol and oxalic acid are chemicals available in a drugstore (or on internet?) which can be used for a hydrometallurgic rare-earth removal process.

The best separations are based on difference in water solubility of metal double sulphates (fractional precipitation process).6-9 After dissolving the metal in H2SO4, neodymium is precipitated as double salt (Nd2(SO4)3‚ąô(NH4)2SO4‚ąô6H2O, Nd2(SO4)2‚ąôNa2SO4‚ąô6H2O or NaNd(SO4)2‚ąôxH2O) by the addition of NH4OH or NaOH whereas other elements such as boron, iron, cobalt and copper remain in solution. The precipitation process is depending on the pH and has an optimum between a pH of 1.5 and 2 (so pH paper strips can be useful here). The double salt can be converted to a hydroxide by the addition of an excess of base.7 Another interesting separation possibility is based on the difference in solubility product of the metal sulphate salts. By reducing the volume of the aqueous phase, neodymium will precipitate first and the transition metals will remain in solution (fractional crystallization process).10 An improved separation can be achieved by introducing ethanol into the system.10 Moreover, the solubility of neodymium sulphate decreases whereas the solubility of iron, copper, aluminium and cobalt sulphate increases with increasing temperature. Therefore, the crystallization process needs to be performed at high temperatures.

A separation process from chloride media is less straightforward and neodymium will be obtained in a lower purity. First, iron(II), produced during the dissolution process, needs to be oxidized towards iron(III) by using H2O2. Afterwards, the pH needs to be increased above 2. In this way, iron(III) precipitates as iron (hydr)oxide. Due to the complex iron (hydr)oxide chemistry and the formation of difference species at different pH values, the iron precipitate is often very difficult to remove by filtration. Afterwards, copper can be removed by the addition of NH4OH, in which the rare-earths will precipitate as hydroxides and copper remains in solution as amine complex. However, the separation of neodymium cobalt is not possible. Aluminium can be removed from neodymium by increasing the pH above 12.5 in which aluminium becomes soluble (Al(OH)4- complex). If ether is available in your kitchen, you can also try to extract the iron into the ether phase at high HCl concentrations leaving neodymium behind in the aqueous phase.

Another possibility to separate neodymium from iron can be achieved by the addition of oxalic acid to a mixture of Fe(II) and Nd(III).11 Afterwards, the addition of oxalic acid will lead to the precipitation of neodymium oxalate salt whereas the iron(II) oxalate salt is slightly water soluble, especially at lower pH values. No separation between neodymium and for instance cobalt or copper is achieved and the process is only possible from chloride media as H2SO4 and HNO3 will also convert iron(II) into iron(III). It is also important to avoid oxidation of iron(II) towards iron(III) by air. Otherwise, iron(III) will coprecipitate with neodymium as oxalate salt. The conversion of iron(II) in iron(III) by oxygen can be minimized by avoiding contact with air of keeping the pH low.

What about boron? Boron is not that reactive to acid, and it could be that it is only partly dissolving during acid treatment. Dissolved boron will precipitate at higher pH values. Therefore, boron can be removed from the rare-earths by precipitation process with oxalic acid at low pH values.9,11,12

Good luck and work safely

 

(1)    D. Kennedy, Rare Earth Metallurgy, An industrial viewpoint, Summer School on Rare Earth Technology from 18/08/2014 to 21/08/2014 in Leuven, 2014.

(2)    A. Leveque, Extraction and Separation of Rare Earths, Summer School on Rare Earth Technology from 18/08/2014 to 21/08/2014 in Leuven, 2014.

(3)    C. James, a new method for the separation of the yttrium earths, Journal of the American Chemical Society, 1907, 29, 495-499.

(4)    K. Binnemans, P. T. Jones, B. Blanpain, T. Van Gerven, Y. Yang, A. Walton, and M. Buchert, Recycling of Rare Earths: a Critical Review, Journal of Cleaner Production, 2013, 51, 1-22.

(5)    K. Binnemans, P. T. Jones, K. Acker, B. Blanpain, B. Mishra, and D. Apelian, Rare-Earth Economics: The Balance Problem, JOM, 2013, 65, 846-848.

(6)    J. W. Lyman and G. R. Palmer, US5129945 A, 1992.

(7)    H. Koshimura, In Report of Tokyo Metropolitan Industrial Technology Center, 113-118, 1987.

(8)    Y. Wei, N. Sato, and M. Nanjo, Solubility of samarium sulfate and neodymium sulfate in sulfate solutions. Fundamental study on the recycling of rare earth magnet materials, MMIJ, 1989, 105, 965-970.

(9)    C. H. Lee, Y. J. Chen, C. H. Liao, S. Popuri, S. L. Tsai, and C. E. Hung, Selective Leaching Process for Neodymium Recovery from Scrap Nd-Fe-B Magnet, Metallurgical and Materials Transactions A, 2013, 44, 5825-5833.

(10)    N. Sato, y. Wei, M. Nanjo, and M. Tokuda, Recycling. Fundamental study on the recycling of rare earth magnet.(2nd Report). Recovery of Samarium and Neodymium from Rare Earth Magnet Scraps by Fractional Crystallization Method.: Fundamental study on the recycling of rare earth magnet, MMIJ, 1997, 113, 1082-1086.

(11)    T. Itakura, R. Sasai, and H. Itoh, Resource recovery from Nd-Fe-B sintered magnet by hydrothermal treatment, Journal of Alloys and Compounds, 2006, 408-412, 1382-1385.

(12)    J. Rabatho, W. Tongamp, Y. Takasaki, K. Haga, and A. Shibayama, Recovery of Nd and Dy from rare earth magnetic waste sludge by hydrometallurgical process, J Mater Cycles Waste Manag, 2013, 15, 171-178.

 

 

 

Rare earths – the vitamins of aircraft structural alloys

As the aircraft industry was evolving rapidly after the Second World War, light alloys with high strength at elevated temperatures became necessary for the design of high power engines that would help increase the flight speed.
Since the invention of duralumin (Al-Cu-Mg-Mn), the first alloy to become truly airborne, engineers and manufacturers never ceased study to obtain new, performant formulas for aircraft construction alloys.

¬† ¬†A Chinese report that summarizes the main applications of rare earth elements in ¬† ¬†the alloying of aircraft structural materials names them “the vitamins of aviation ¬† ¬†alloys”[1] suggesting that small additions of REEs in aircraft alloys are of vital ¬† ¬† ¬† ¬† ¬†importance just as small amounts of vitamins allow the human body to function ¬† ¬† ¬†properly.

REEs additions have highly beneficial effects on non-ferrous metal alloys like            aluminum, titanium and magnesium alloys which are now used in aircraft parts        construction.

The aircraft industry is interested in scandium, as it is similar to titanium having a high melting point corrosion resistance but it is significantly lighter. Scandium can be used in manufacturing reinforced aluminum alloys (scandium-reinforced aluminum). Not only are Al-Sc alloys suitably strong, they are also lighter and more corrosion resistant than other comparable aluminum alloys.

While most of the Al-Sc alloy used today is to be found in leisure and sporting goods (bicycle frames, baseball bats, golf clubs, hand guns, tent poles and lacrosse sticks) other environments for its use such as aircraft industry applications continue to be actively researched.
Scalmalloy¬ģ is Airbus Group‚Äôs second-generation aluminum-magnesium-scandium alloy (AlMgSc). It was developed for high and very high-strength extrusions, offering exceptionally high fatigue resistance and excellent weldability, being designed for use in components of transportation, defense, aerospace and leisure products.
AlMgSc exhibit an unique high-level of corrosion resistance, which allows the use without cladding (anticorrosion coating procedure) unlike the traditional aircraft aluminium alloys.

The addition of rare-earth metals (mainly neodymium, praseodymium and yttrium) into magnesium alloys induces alloy purification, improves the microstructure, and raises their tensile strenght at high temperatures. They increase fluidity and reduce the microporosity in cast alloys raising the casting quality and consequently bringing great advantages for production. Praseodymium is used as an alloying agent with magnesium to create high-strength alloys for aircraft engines while neodymium is found in the composition of QE22A magnesium based alloys which are widely used in the aerospace applications (aircraft gearboxes).

Similar improvements can be achieved when rare earths are added in titanium alloys which, though very expensive, are used where high strength is needed in load bearing applications such as landing gear and engine mounting brackets. [2], [3]

Rare earths play a major role in the development of high-end industries and the aircraft/airspace sectors make no exception as they benefit from the significant improvements that they brought in the performances of light-weight structural alloys.

[1] Z. Changzhong and L. Zhonghan, Rare-earth metals and their applications in aviation (1984); (http://www.dtic.mil/dtic/tr/fulltext/u2/a144410.pdf)

[2] L. L. Rokhlin, Magnesium alloys containing rare earth metals: structure and properties. CRC Press (2003), ISBN 0-415-28414-7;

[3] F. Habashi, Alloys: Preparation, Properties, Aplications, Wiley-VCH (1998), ISBN 3-527-29591-7;