Survey of recycled rare earths metallurgical processing

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1 Survey of recycled rare earths metallurgical processing C. D. Anderson, C. G. Anderson* and P. R. Taylor Rare earths have become critical for our energy and materials driven society. While primary production must ramp up to fill growing demands, the recycle of these strategic elements must also be initiated. This paper will outline the potentials of and metallurgical technologies employed for Rare earths recycle from various secondary sources. Les éléments de terres rares jouent maintenant un rôle critique dans notre société axée sur l énergie et les matériaux. Alors qu on doit accroître la production primaire pour satisfaire la demande grandissante, on doit également initier le recyclage de ces éléments stratégiques. Cet article souligne les types de technologie métallurgique utilisés ainsi que leur potentiel pour le recyclage des éléments de terres rares à partir de diverses sources secondaires. Keywords: Rare earths, Lanthanides, Recycling, Extractive metallurgy, Magnets, Catalysts, Batteries This paper is part of a special issue on Advances in Rare Earths: From Mine to Materials Introduction When investigating the recovery of rare earths from secondary sources it is necessary to understand the nature of the sources to be processed. As of 2009, the USGS reports the distribution of rare earths by end use, in decreasing order, was: chemical catalysts 22%, metallurgical applications and alloys 21%, petroleum refining catalysts 14%, automotive catalytic converters 13%, glass polishing and ceramics 9%, rare earth phosphors for computer monitors, lighting, televisions 8%, permanent magnets 7%, electronics 3%, and others 3%. 1 Additionally, it is reported that the amount of recycling was quite small and consisted primarily of rare earth magnet scrap, although with the sharp increase in the price of rare earths, and the potential shortage in supply, focus in this area is continually growing. Thus, the opportunities, whether realistic or not, are extremely vast in the recycling of rare earth containing materials. The following subsections will present methods proposed for the recycling of rare earths based on the feed material type. Recycling of rare earth magnets Currently, investigations are ongoing in the area of recycling production scrap and end-of-life materials in the rare earth magnet industry. The following techniques Kroll Institute for Extractive Metallurgy, George S. Ansell Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, CO 80401, USA *Corresponding author, cganders@mines.edu illustrate potential methods for the recovery of rare earths from secondary RE magnet sources. Recycling of rare earth magnet sludge by selective chlorination During the production of neodymium magnets, a byproduct of production is the so called magnetic sludge. This byproduct contains high amounts of neodymium, thus a process for the recovery of Nd has been proposed. In this process the Nd present is selectively chlorinated/distilled by the addition FeCl 2 via the following reactions 2Nd (in sludge) z3fecl 2 <3Fez2NdCl 3 (1) 1=2Nd 2 O 3 z1 : 5FeCl 2 z : 5C<1 : 5CO (g) zndcl 3 zfe 0 (2) The process involves placing the magnetic sludge, iron chloride, and activated carbon in graphite crucibles and heating the samples to K in an inert argon atmosphere. Condensate products were collected at the top of the furnace in collectors. Experimental results show that 96% of the neodymium and 94% of the dysprosium present in the sludge were extracted into the chloride phase, producing a mixture of 99?2% pure mixture of neodymium and dysprosium tri-chlorides. 2 Figure 1 illustrates this process. Recycling of neodymium magnets using molten magnesium A process for the direct extraction and recovery of neodymium from RE magnetic scraps using liquid magnesium as the extractant was investigated. Magnesium has been ß 2013 Canadian Institute of Mining, Metallurgy and Petroleum Published by Maney on behalf of the Institute Received 11 December 2012; accepted 20 May 2013 DOI / Y Canadian Metallurgical Quarterly 2013 VOL 52 NO 3 249

1 Vacuum distillation of rare earth chlorides 2 selected as an ideal extracting agent for this process due to its strong affinity for Nd, ability to form a low viscosity liquid alloy, low interaction

2 fashion. Results show that metallic Nd of 98% purity was directly recovered using this process. Additionally, the extracting agent, Mg, is able to be reused for further extraction of Nd from magnetic scrap. 3 An example of this process is illustrated in Fig Vacuum distillation of rare earth chlorides 2 selected as an ideal extracting agent for this process due to its strong affinity for Nd, ability to form a low viscosity liquid alloy, low interaction with iron, high vapour pressure above 800uC, and melting point of 649uC. In the process, Nd magnet scraps were pulverized to below 2 mm and placed in an iron crucible. This crucible was suspended over a tantalum crucible containing Mg. The reaction vessel was then sealed shut by TIG welding, and heated in an electric furnace to a temperature range of K. Owing to the high vapour pressure of magnesium (0?59 atm at 1300 K) the Mg in the bottom crucible evaporates and condenses in the top vessel. The Nd present in the scrap is then transferred to the liquid magnesium and drains to the bottom vessel via slots in the bottom of the crucible. Neodymium has a low vapour pressure (10 26 at 1300 K) and is thus concentrated in the bottom crucible, while the Mg is continually evaporated and condensed in a cyclical Recycling of Nd Fe B scrap using acidic dissolution and precipitation A process for the utilisation of sulphuric acid leaching and recovery of neodymium from Nd Fe B magnet scrap was investigated. Results showed that extraction of Nd reached almost 100% without the aid of heating or agitation, using an acid to scrap ratio of 2 at a molarity of 2. After dissolution, the aqueous Nd was precipitated as either an Nd double salt prior to fluorination or directly fluorinated using hydrofluoric acid. Results showed that recoveries exceeding 99% were possible using this method. Additionally, aqueous iron present was removed via the precipitation of jarosite. 4 An example of the proposed flowsheet is shown in Fig. 3. Recycling of Nd Fe B/Sm Co alloy magnets by way of roast/leach/solvent extraction process A process involving the oxidative roasting, hydrochloric acid leaching, and solvent extraction process has been investigated. In this process, the Nd Fe B compound and Sm Co alloy were ground to 100% passing 200 US mesh, each sample was then roasted at 700uC for 8 h prior to lixiviation. Leaching results showed that Nd and Sm increased with increasing HCl concentration and increased residence time, and extraction rates of 97% (Nd) and 94% (Sm) were achieved. The pregnant solution was then sent to solvent extraction where Sm was extracted using EHPNA/TOPO extractant, and Nd was extracted using EHPNA. At a ph of 2 these extraction rates exceeded 95% extraction. 5 An example 2 Proposed process flowsheet for Nd extraction using liquid Mg Canadian Metallurgical Quarterly 2013 VOL 52 NO 3

3 Proposed USBM process flowsheet 4 of the proposed flowsheet for this process is shown in Fig. 4. Recycling of luminescent lighting materials Multistep method for recycling of rare earths from lamps A method (US patent application no.

3 3 Proposed USBM process flowsheet 4 of the proposed flowsheet for this process is shown in Fig. 4. Recycling of luminescent lighting materials Multistep method for recycling of rare earths from lamps A method (US patent application no ) has been proposed for the recovery of rare earth elements such as terbium, europium, and yttrium from spent fluorescent lamps. There is approximately 10% by weight, calculated as oxide, of these elements in this material. This process involves dismantling the lamps by a proprietary mechanical method, selectively dissolving the contained rare earth elements, and precipitating them as compounds suitable for further processing. The individual process steps are: mechanical separation of coarse parts, separation of the halophosphates, extraction of RE fluorescent materials readily dissolved in hydrochloric acid (Y 2 O 3, Eu 2 O 3 ), extraction of RE fluorescent materials insoluble in acids (Re Phosphates), digestion of the remaining components containing RE (RE aluminates), and final treatment. 6 These techniques are illustrated in Fig. 5. Recovery of europium and yttrium metal from spent fluorescent lamps Powder coating on the inner surface of fluorescent glass tubes containing 1?62% europium oxide, 1?65% yttrium oxide, 34?48% calcium sulphate, 61?52% calcium orthophosphate, and 0?65% other impurity metals was subject to a pressure leaching/solvent extraction process for the recovery of Eu and Y. After breaking the tubes in 30% aqueous acetone, to avoid Hg emissions, the contained powder was collected. This material was subjected to pressure leaching for 8 h at a temperature 125uC, using a 4 molar sulphuric/nitric mixture, and operating pressure of 5 MPa. These operating parameters allowed for the dissolution of 96?4%Y and 92?85% of the Eu in the powder. After leaching, the sulphate solution is converted to thiocyanate and is sent for solvent extraction using a trimethylbenzyl ammonium chloride extractant. The extraction step yielded 99%Y and 97%Eu extraction, at solvent to organic ratios of 2. The loaded phase is then stripped using N-tributylphosphate in 1M nitric acid, which produces nitrate salts of Eu and Y. The europium nitrate is separated from the yttrium nitrate by dissolution in ethyl alcohol. After separation of the nitrates, both are ready for thermal hydrogen reduction and production of both europium and yttrium metal. 7 An example of the proposed process is shown in Fig. 6. Treatment of exhaust fluorescent lamps to recover yttrium The development of an integrated process for the recovery of mercury and Y contained within fluorescent lamp phosphor powder has been investigated. To optimise the recovery of yttrium a full factorial experimental design was implemented to determine the factors which significantly influence the extraction and yttrium. Three different lixiviants, nitric, hydrochloric, and sulphuric acid were tested. Owing to the formation of NOX during the use of nitric acid, its use was discontinued. The highest amounts of yttrium extraction were 90 and 85% when using hydrochloric and sulphuric acid. In addition, sulphuric acid showed advantageous due to the reduction of soluble Ca, Pb and Ba. Precipitation experiments performed on synthetic solutions using oxalic acid to produce yttrium oxalate, showed that a 99% pure yttrium oxalate product is possible. 8 A flowsheet for the proposed process is shown in Fig. 7. Canadian Metallurgical Quarterly 2013 VOL 52 NO 3 251

4 4 Pyrometallurgy/hydrometallurgy flowsheet for Nd/Sm extraction 5 Recycling of rare earth batteries Hydrometallurgical recovery of rare earth from NiMH batteries using sulphuric acid leaching A process for the hydrometallurgical recovery of rare earths from spent nickel metal hydride (NiMH) batteries has been investigated. In this process, the battery type AB 5 and AB 2 were cut in half longitudinally and the positive and negative electrodes were mechanically crushed prior to leaching. A 2M sulphuric acid solution, solid to liquid ratio of 1 : 10, and a temperature of 20uC was used for dissolution of the contained rare earth elements. After lixiviation, caustic soda is added to raise the ph and selectively precipitate the rare earth elements as double sulphates, i.e. [NaRE(SO 4 ) 2 6H 2 O]. Experimental results show that from 1 tonne of spent battery material about 37?5 kgof rare earths (as metal) can be recovered at a grade of approximately 80%. 9 Additionally, research has shown that leaching in 2M sulphuric acid is an efficient method for the dissolution of rare earth elements. 10 They have also shown that this process is independent of temperature and the addition of hydrogen peroxide as an oxidising agent. Experimental results show that it is possible to separate aqueous Cd, Co, and Ni from the leach liquor using solvent extraction techniques. Recycling from various sources Recovery of rare earths and yttrium from red mud by selective leaching A method for the recovery of lanthanide and yttrium from red mud, a byproduct of the aluminium industry, 252 Canadian Metallurgical Quarterly 2013 VOL 52 NO 3

5 Method for recovery of rare earths from fluorescent lamps 6 has been investigated. The bauxite deposits of Central Greece used in this work have a total rare earth concentration of up to 1%.

5 5 Method for recovery of rare earths from fluorescent lamps 6 has been investigated. The bauxite deposits of Central Greece used in this work have a total rare earth concentration of up to 1%. Experimental results show that dilute (0?5M) nitric acid was the lixiviant which allowed for the highest selective recoveries of the lanthanides, especially yttrium. Leaching conditions for this work were T525uC, t524 h, and a solid to liquid ratio of 1 : 50. In addition to higher yttrium recoveries, the use of nitric acid facilitates the proposed solvent extraction step better than HCl due to larger distribution coefficients obtained. Recoveries obtained were approximately 90% for Y, 70% for (Dy, Er, Yb), 50% for (Nd, Sm, Eu, Gd), and 30% for (La, Ce, Pr). Figure 8 illustrates the dissolution of the contained elements as a function of time. 11 Recovery of rare earths from scrap metal alloys A process for the recovery of rare earths from alloy scrap containing rare earths has been patented. 12 In this process, the rare earth containing material is leached in a sulphuric acid solution (2M) to dissolve the contained RE elements. After dissolution, a hydroxide such as NaOH, KOH, or NH 4 OH is added to precipitate the double salt of the RE and the alkali element [Nd 2 (SO 4 ) 3.Na 2 SO 4 ] or an ammonium compound. After precipitation, this salt is converted to a rare earth salt amenable for use in thermite or other metallothermic reduction processes. Hydrofluoric acid may be used as the fluorinating agent to form a rare earth fluoride. Additionally, aqueous iron can be precipitated out of solution as jarosite as well as boron via a zinc borate precipitation. A flowsheet of the proposed process is shown in Fig. 9. Recycling of catalysts Although catalysts make up a significant percentage of rare earth end use, there is very little data available on the recovery of REE from any of these secondary sources. Interestingly enough, the USGS reports that all platinum rhenium catalysts used in the petroleum industry were recycled in 2010 (Ref. 13) although nothing is mentioned about the recovery REE from catalysts. Therefore, the ability to adequately collect REE containing catalysts exists, although the technology for an economical recovery method may not, yet. Potential areas of research The previous sections have illustrated the current methods utilised for the recycling of rare earths. Owing to the current boom of the rare earth industry, research has been largely focused in the fields of exploration, mineral extraction, mineral and chemical processing, and recycling. Thus, potential areas of research in this industry are continually growing. The following sections will illustrate some of these areas. Chemical processing After concentrating the REE, in the form of the REO concentrate, chemical processing is used to form a Canadian Metallurgical Quarterly 2013 VOL 52 NO 3 253

6 6 Flowsheet for recovery of metallic Eu and Y 7 product suitable for subsequent processing. A great deal of research has been performed in this field, but the potential exists for the implementation and optimisation of these techniques in both the primary and secondary sectors. Potential areas of research in this field include: (i) optimisation and/or innovations in leaching, separations and metal reduction techniques N minimisation of reagent consumption through techniques such as staged leaching, and the use of reagent regeneration techniques 254 Canadian Metallurgical Quarterly 2013 VOL 52 NO 3

7 7 Recovery of Y from fluorescent lights 8 N implementation of techniques used in other industries to improve REE extraction and recovery N development of new separations methods to purify rare earth oxides N development of new reduction methods to produce rare earth metals (ii) utilisation of primary processing techniques in the secondary industries to recover REE from: spent catalysts phosphors magnets N other potential sources of REE. Separation of rare earths Owing to the similar chemical behaviour of the rare earth elements, one of the most difficult areas in the industry is the separation of the REE after chemical processing. Originally, the tedious process of fractional precipitation and crystallization were used, with minimal success. Through focused research in the areas of solvent extraction and ion exchange, vast improvements in the separation of REE have been made, but further improvements are both possible and necessary. Potential areas of research in this field include: (i) ion exchange N use of selective exchange resins, including the potential for molecular recognition technology (MRT) resins N use of selective eluents in combination with selective elution technologies N implementation of continuous IX columns into existing flowsheets (ii) solvent extraction use of highly selective extractants N use of selective stripping agents 8 Concentration of lanthanides and yttrium versus leaching time (0?5M nitric, T525uC, S/L51 : 50) 11 Canadian Metallurgical Quarterly 2013 VOL 52 NO 3 255

8 for these critical elements, these technologies will mature in application and research will increase in key aspects such as separations. 9 Recovery of rare earths from alloy scraps 12 N optimisation of SX flowsheets and operational methodologies to ensure maximum extraction and stripping efficiency Conclusions This paper has outlined the technologies proposed for the recycling of Rare Earths. As global demand grows References 1. USGS: Mineral commodity summary: rare earths, ; 2011, Reston, VA, US Geological Survey. 2. T. Uda and M. Hirasawa: Rare earth separation and recycling process using rare earth chloride, metallurgical and materials processing: principles and technologies, Yazawa International Symposium, Vol.3, (ed. F. Kongoli et al.), Aqueous and electrochemical processing, 2003, T. Okabe, O. Takeda, K. Fukuda and Y. Umetsu: Scrap combination for recycling of valuable metals: direct extraction and recovery of neodymium metal from magnet scraps, Yazawa International Symposium, Vol.1, (ed. F. Kongoli et al.), Metall. Mater. Process.: Principles Technol., 2003, J. W. Lyman and G. R. Palmer: Recycling of NdFeB magnet scrap, (report of investigations), Salt Lake City, UT, Salt Lake City Research Center, Bureau of Mines, M. Niinae, K. Yamaguchi, Y. Nakahiro and T. Wakamatsu: Hydrometallurgical treatment of rare earth magnet scrap, Proc. XIX Int. Miner. Process. Congress on Physical & chemical processing, Vol. 2, Chapter 43, Chemical Processing, , R. Otto and A. Wojtalewicz-Kasprzak: US Patent no , Washington, DC, US Patent and Trademark Office, M. Rabah: Recyclables recovery of europium and ytrrium metals and some salts from spent fluorescent lamps, Waste Manag., 2008, 28, (2), I. Michelis, F. Francesco, E. Varelli and F. Veglio: Treatment of exhaust fluorescent lamps to recover yttrium, Waste Manag., 2011, 31, (12), L. Pietrelli, B. Bellomo, D. Fontana and M. Montereali: Rare earths recovery from NiMH spent batteries, Hydrometallurgy, 2002, 66, (1 3), L. Rodrigues and M. Mansur: Hydrometallurgical separation of rare earth elements, cobalt, and nickels from spent NiMH batteries, J. Power Sources, 2010, M. T. Ochsenkuhn-Petropoulou, M. Lyberopoulou, T. Ochsenkuhn and G. Parissakis: Recovery of lanthanides and yttrium from red mud by selective leaching, Anal. Chim. Acta, 1996, 319, (1 2), J. Lyman and G. Palmer: US patent no , Washington, D.C., US Patent and Trademark Office, USGS: Mineral commodity summary: rhenium, ; 2011, Reston, VA, US Geological Survey. 256 Canadian Metallurgical Quarterly 2013 VOL 52 NO 3

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