Post ¬†written by TOM VANDER HOOGERSTRAETE¬†
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.