Case study: Öko-Institut’s study on permanent magnets used in industry in Baden-Württemberg

Today’s blog is on a study conducted last year by Öko-Institut, dealing with permanent magnets used in industry in Baden-Württemberg – one of the federal states in Germany. The project was funded by the Ministry of the Environment, Climate Protection and the Energy Sector of Baden- Württemberg.

bawuekarte

Source: Flickr /Creative Commons

Industrial applications of permanent magnets include motors, generators, and applications related to attractive magnetic forces, i.e. magnetic separators in sorting plants, but also to remove metal contamination e.g. during food production and many other industries, and for lifting. The poor availability of data on these types of magnet applications was the motivation for the study. Baden-Württemberg was chosen for the case study since a relatively high percentage of the German manufacturing industry is based there. Permanent magnet use in motors and generators is most important in terms of volumes. Furthermore, their dysprosium content is higher than that of magnets used for attraction purposes. To be more specific, synchronous servomotors are the most important application of permanent magnets in industry. These motors are more energy efficient than their predecessors (three-phase asynchronous motors). Their use has been accelerated by an EU directive on efficiency standards for new electric motors.

In order to investigate the use of permanent magnets in industry in Baden-Württemberg, a bottom-up analysis was conducted, based on a company survey and supported by industry associations. This approach proved to be difficult due to a general lack of knowledge on permanent magnet use in most of the companies surveyed. This is not overly surprising since the magnets are mainly components part of larger equipment and not purchased as stand-alone items. In absence of relevant or rather, sufficiently detailed production statistics, expert interviews were conducted with producers of magnets and motors using permanent magnets as well as industry association representatives. The interviews provided a good understanding of the use and stock distribution of permanent magnets in industry in Germany. The numbers were then extrapolated for Baden-Württemberg. Furthermore, historic and future production data was collected in these interviews, which also allowed an estimation of the future magnet recycling potential.

 

diagramm

Source: Öko-Institut, calculations based on information from expert interviews

As shown in the figure above – data here refers to the whole of Germany and motors from industrial applications expected to reach the end of lives – the projected increase in the use of synchronous servomotors and the subsequent accumulation of permanent magnets in use over time means an increase in recycling potential for permanent magnets from industrial applications. However, the actual recycling potential is compromised by the common exports of industrial machinery for reuse abroad – effectively an extension of in-use lifetimes.

recycling electric motors

Recycling of electric motors in Nanjing, China.

The introduction of a recycling system is complicated by the lack of a collection, sorting and disassembly system, meaning that a reliable feedstock supply is not yet available. In light of the expected increase in recycling potentials, the authors recommend the establishment of those systems by 2030, ideally on a European level in order to enable the collection of sufficiently large quantities. In addition, a mandatory labelling system indicating the presence and types of permanent magnets in industrial machinery is recommended.

References

Buchert, M., Manhart, A., Sutter, J., 2013. Untersuchung zu Seltenen Erden: Permanentmagnete im industriellen Einsatz in Baden-Württemberg: Öko-Institut e. V., Freiburg, 54 pp. Accessed 16 December 2014.

EU, 2012. Commission Communication in the framework of the implementation of the Commission Regulation (EC) No 640/2009 implementing Directive 2005/32/EC of the European Parliament and of the Council with regard to ecodesign requirements for electric motors, 2 pp. http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:C:2012:394:0020:0021:EN:PDF. Accessed 24 April 2015.

Kuenl, G., 2013. Deutschland politisch: (map listed under creative commons license). https://www.flickr.com/photos/83518068@N02/10067129533/in/photolist-gkAESR.

Stougard. Wikimedia Commons, License: CC-BY-SA-3.0, www.creative-commons.org.

 

MINING RARE EARTHS FROM THE OCEAN FLOOR

Dear reader!

In one of previous EREAN blogs you could read about the idea of space mining of lanthanides. By now it seems like science fiction while deep-sea mining is much closer to be brought to real practice.

The interest in extreme forms of mining is explained by the recent dramatic rises in the price of many metals (e.g. lanthanides), driven by depletion of conventional land-based sources and by large increases in demand outstripping available supply [1].

The particular interest in deep-sea mining is based on recently discovered tremendous amounts of metal deposits on the ocean floor. These deposits exist in different forms (e.g. crusts, polymetallic nodules, muds etc.) and contain valuable metals such as Mn, Ni, Cu as well as rare earths [2,3].

Manganese nodule

Fig. 1. Manganese nodule [4]

The comparison of the reserves for two largest land-based rare-earth element (REE) deposits, Bayan Obo (Obo) in China and Mountain Pass (MP) in the U.S. with the REEs in the Clarion-Clipperton ferromanganese nodule zone (CCZ) in the north-east Pacific and the prime ferromanganese crust zone (PCZ) in the central Pacific shows the following [2]. The land-based ore deposits are higher grade but lower tonnage ores: MP 0.48∙108 tonnes at 7% total REEs as oxides (TREO) and Obo 8.0∙108 tonnes at 6% TREO, compared to the CCZ (211∙108 tonnes at 0.07% TREO) and PCZ (75.3∙108 tonnes at 0.21% TREO). These grades and tonnages correspond to tonnes of contained TREO of 4.8∙107 Obo, 0.34∙107 MP; 1.6∙107 PCZ, and1.5∙107 CCZ [2].

Of even greater interest than these large tonnages of REEs is the percentage of the TREO that are heavy REEs (HREEs) because of their much greater economic value. The land-based deposits have less than 1% HREEs, whereas the CCZ deposits have a mean of 26% HREEs and the PCZ deposits have 18% HREEs [2].

polymetallic nodules on the seafloor

Fig. 2. Polymetallic nodules on the sea floor

So there appears to be no shortage of metal-rich resources available for mining throughout the world’s oceans. As a consequence, various governments and companies are now busy snapping up exploration and mining rights to vast tracts of the ocean floor in international waters, with these rights administered by a UN body called the International Seabed Authority (ISA) [1].

However mining of minerals at the depths of a few kilometers is still a technological challenge despite oil production on sea shelves is rapidly developing. Most likely the extraction process used to retrieve REEs from the seabed will be robotic.

Harvesting polymetallic nodules from the seafloor

Seabed mining remains politically and environmentally challenging. Environmental concerns which organizations such as The Ocean Foundation are concerned about include [5]:

• Physical disturbance and destruction of benthic habitat and seabed fauna. In addition to potential destruction of these organisms, they are in turn eaten by other marine life (which could have an impact on the upwards food chain).

• Subsurface noise affecting marine mammals and fish.

• Modification of the natural wave and current regime through removal or addition of substrate (potential coastal erosion both up and downstream).

• Risks associated with increased infrastructure, e.g. oil spills from vessels.

• At the Solwara 1 site (Papua New Guinea) a particular concern is that stocks of tuna could be contaminated by heavy metals and affect consumers eating such tuna.

In recognition that the full impact of deep seabed mining activities on the deep sea environment and marine ecosystem still remains unknown, the ISA regulations on prospecting and exploration specifically impose obligations on each contractor to monitor, evaluate and report to the ISA the environmental impacts of deep seabed mining.

References:

  1. http://www.rsc.org/chemistryworld/2013/05/mining-ocean-seafloor-asteroids-space-minerals
  2. J.R. Hein, K. Mizell, A. Koschinsky et al. Deep-ocean mineral deposits as a source of critical metals for high- and green-technology applications: comparison with land-based resources // Ore Geology Reviews, 51. 2013, p. 1-14.
  3.  Y. Kato, K. Fujinaga, K. Nakamura et al. Deep-sea mud in the Pacific Ocean as a potential resource for rare-earth elements // Nature Geoscience, 4. 2011, p. 535-539.
  4. http://www.popsci.com/scientists-find-unexpected-ore-deposit-middle-atlantic
  5. Rare earth elements. Deep sea mining and the law of the sea. Mayer Brown. 2014.

RARE EARTH ELEMENTS IN MAGNETOSTRICTIVE MATERIALS: TERFENOL-D

Detected first in early 1840s by James P. Joule, magnetostriction was identified as the change in the length of an iron sample when its magnetization changed. This first identified mode of magnetostriction was later named as the Joule effect and is currently the most common mechanism applied in magnetostrictive actuators. Expectedly, the inversed scenario in which a stress on such a material creates a change in its magnetization was defined as the Villari effect. This later effect, on the other hand, is commonly utilized in magnetostrictive sensors. The other two defined effects, namely the Wiedemann and the Matteuci, are also used in such devices including magnetoelastic torque sensors too [1]. Hence, similar to its different versions like piezoelectricity (electricity resulting from mechanical stress) or electrostriction (change in shape due to application of an electric field), magnetostriction is a property where a change in the dimension and/or shape is caused by magnetization process only in ferromagnetic materials such as iron, nickel and cobalt.

Magnetostriction

In order to understand how the magnetostriction occurs, consider a ferromagnetic material as combination of several tiny permanent magnets (aka domains) where each domain is formed by many atoms. When such a material is not magnetized all the domains are randomly oriented within the material. However, when an external magnetic field is applied then these domains are aligned just like needle-like bi-polar magnets such that their axes are more or less parallel to one another. This re-orientation of all domains under applied magnetic field is only possible by rotation which causes internal strains within the material structure leading to the stretching (if there is + magnetostriction) or to the shrinkage (if there is – magnetostriction) along the applied field [2]. Actually, if you have ever been near to an electric power transformer you have already and perhaps unknowingly witnessed this effect: the annoying humming voice caused by the continuous distortion in the magnetostrictive core of the transformer [3]. Even in your electronics, you can hear this undesirable sound which is called coil noise caused by the same guy: magnetostriction. The magnetostrictive effect, hence the noise, increases with stronger applied field leading to stronger re-orientation of more and more domains and at some point all the domains throughout the material become orientated perfectly. At this point the material is said to reach the saturation point. In general, there are two modes of usage of magnetostrictive materials: (i) transferring magnetic energy into mechanical energy and (ii) transferring mechanical energy into magnetic energy [1]. The first mode is the basis for designing actuators for producing motion and/or force and for designing sensors to detect magnetic field states. A representative cross section for a typical actuator can be seen in the following figure. The other mode is used for sensing motion and/or force that is to design devices for inducing change in a material’s magnetic state and to design passive damping devices. Actuator Cross SectionThe effect of magnetostriction in base elements or simple alloys is actually small (volume change on order of 10-6 m/m) and can be neglected under normal operation conditions. The earlier applications of such materials (particularly nickel-based) right after the discovery of such property include telephone receivers, hydrophones, oscillators, torque-meters and scanning solars. It was not until 1970s for the magnetostriction to become “popular” area when “giant” magnetostrictive materials were first developed that had more than 10 times saturation strains than the earlier materials at room temperature. Until now, several alloys such as Fe-Al (Alfer), Fe-Ni (Permalloy), Co-Ni, Fe-Co, and Co-Fe-V (Permendur) and several ferrites (CoFe2O4 and NiFe2O4) have been developed offering significant improvements in magnetostrictive properties [4]. However, among alloys, the highest known magnetostriction is exhibited by Terfenol-D, (Ter for Terbium, Fe for Iron, NOL for Naval Ordnance Laboratory-the developer-, and D for Dysprosium). Terfenol-D, TbxDy1-xFe2 (x ~0.3), exhibits about 2,000 microstrains in a field of 2 kOe (160 kA/m) at room temperature and is the most commonly used engineering magnetostrictive material. Another very common magnetostrictive composite is the amorphous alloy Fe81Si3.5B13.5C2 with its trade name Metglas 2605SC. Favourable properties of this material are its high saturation-magnetostriction constant, λ, of about 20 microstrains and more, coupled with a low magnetic-anisotropy field strength, HA, of less than 1 kA/m (to reach magnetic saturation) [5].

Current applications for magnetostrictive devices include ultrasonic cleaners, high force linear motors, positioners for adaptive optics, active vibration or noise control systems, medical and industrial ultrasonic, pumps, and sonar. In addition, magnetostrictive linear motors, reaction mass actuators, and tuned vibration absorbers have been designed, while less obvious applications include high cycle accelerated fatigue test stands, mine detection, hearing aids, razor blade sharpeners, and seismic sources. Ultrasonic magnetostrictive transducers have been developed for surgical tools, underwater sonar, and chemical and material processing [1, 6]. It may not happen so frequently but in case you face such a life-threatening situation like MacGyver, it could also be quite handy to keep in mind this trick as in the following video (I know, who would put an antidote in such a case, right?).

References:

  1. http://www.public.iastate.edu/~terfenol/homepage.html
  2. http://www.sensorland.com/HowPage024.html
  3. http://www.freepatentsonline.com/2234968.html
  4. http://encyclopedia2.thefreedictionary.com/Magnetostrictive+Materials
  5. http://en.wikipedia.org/wiki/Terfenol-D
  6. Olabi, A. G., Grunwald, A., Design and application of magnetostrictive materials, Materials and Design, Volume 29, Issue 2, 2008, p. 469-483.