Introduction and Motivation
Throughout all stages of its life cycle, from its extraction from the earth, to its use in consumer products, neodymium and energy usage are closed tied. The mining of neodymium ores requires energy to run the machines, the separation of the ore requires water, heat, and plenty of power, and the magnetization of neodymium magnets requires incredibly powerful magnetic fields. However, neodymium as a material does not solely relate to energy consumption. Neodymium magnets are used in electric generators, like the kind required by wind turbines, to generate electricity from sources like water, wind, or steam. Other products made from neodymium, like speakers and laptops, encourage consumers to consume power, while others still, like the batteries found in hybrid and electric vehicles, help environmentally-minded consumers conserve power. By following the flow of neodymium from its extraction to its use or disposal, we can try to determine the overall impact that neodymium has on global energy consumption.
Extraction and Production
Hoping to better understand the energy implications of rare earth elements, a group of researchers from the Australian Commonwealth Scientific and Industrial Research Organization (CSIRO) conducted an extensive review of the mining, mineralogy, uses, sustainability, and environmental impact of rare earths. Unfortunately, the study derives many of its estimates from the process of mining and producing neodymium in Australia, since those figures were most accessible. However, when conducting their life cycle assessment, the authors attempted to use figures relating to China’s rare earth element production, since the country represents the overwhelming majority of neodymium supply. As a result, the authors occasionally had to make assumptions, use estimation, or work with whatever limited figures were available. Citing a case study by the Swiss Ecoinvent database, the authors assumed a rare earth oxide ore concentration of 6%. To analyze the energy impacts of extracting neodymium from this ore, the authors then determined the boundary of their assessment. This boundary included “the mining, concentration of REE oxides, and separation of neodymium oxide” and the process for energy estimation included “material and energy inputs, emissions and land use for the mining and concentration of bastnäsite ore with a rare earth oxide concentration of 6%”, by approximating infrastructure and land use as equal to that of iron ore mining. Finally, the energy assessment of neodymium’s production stage included roasting and cracking of the rare earth element concentrate with acid in a 500° C rotary kiln, and solvent extraction for the separation of rare earth oxides. Under these assumptions, the CSIRO study estimated the energy requirement of neodymium extraction and production to be 743 MJ/kg. Using the neodymium demand figures from my previous blog on neodymium flow results in the following yearly energy demands for neodymium extraction and production:
The scientific notation makes it difficult to appreciate the enormity of the results of these calculations. For comparison, consider that the third result, the projected energy requirement for the neodymium demand of 2050, equates to the energy stored in almost 50 megatons of TNT.
Manufacture and Processing
After neodymium metal is produced, it must be shaped into generic forms for the market. Unfortunately, it is very difficult to estimate the energy requirements of this process. However, we can use the energy requirements of rolling and coating steel to approximate the energy requirements of forming and coating neodymium. This step of the assessment is obviously less than ideal, but will have to suffice. According to the authors of Sustainable Materials: With Both Eyes Open, the global, yearly production of steel is 1040 Mt, the yearly energy cost to forming into stock products for market is 0.2 EJ, and the yearly energy cost to coat the steel with zinc is 0.6 EJ. This means steel requires .769 MJ/kg to form and coat. We’ll use this same figure for neodymium manufacture and processing, since neodymium magnets require a similar forming and coating process. After being shaped, however, neodymium magnets must be magnetized. This process involves subjecting the metal to extremely powerful magnetic fields. Estimating the energy cost of this process, thankfully, is rather simple. Accounting for losses due to heat, the energy required to magnetize a neodymium Nd-Fe-B magnet (the most common type) is approximately equal to twice the energy the magnet stores. The difficult part of this calculation is determining the energy stored in such a magnet. This can be accomplished by finding the area under the typical Nd-Fe-B magnet’s B-H curve, which is a graph of the magnet’s magnetic flux density (B) versus its auxiliary magnetic field (H).
Finding the area under the curve highlighted in red in the above neodymium B-H graph, and converting from meters cubed to kilograms by using the density of neodymium magnets yields a resulting 86.9 J/kg. Doubling this figure to account for heat loss, as mentioned before, results in an energy requirement of 173.8 J/kg to magnetize permanent neodymium magnets.
Interestingly enough, the 173.8 J/kg required to magnetize neodymium magnets is dwarfed by the .769 MJ/kg required to shape and coat the magnets, which is in turn dwarfed by the 743 MJ/kg required to mine, extract, and process the rare earth element itself. We’ll sum these three figures and round up a tad (to account for miscellaneous expenses) to arrive at an estimate of 745 MJ/kg required to create market-ready neodymium magnets.
Transportation and Shipment
Since the life cycle of neodymium magnets does not end in the factory, neither will our assessment of the energy costs. After neodymium magnets are properly shaped, coated, and magnetized, they must be transported and shipped. While previous stages of this energy assessment have been difficult to accurately measure due to scale, uncertainty, estimation, or unavailability of data, transportation is probably the most concerning. Worst still, the transportation energy costs for neodymium, unlike the energy costs of coating the material, are very significant. Since both the CSIRO and the With Both Eyes Open studies are silent when it comes to such an estimation, we will attempt to use a figure provided by Dr. Jean-Paul Rodrigue and Dr. Theo Notteboom, authors of The Geography of Transport Systems. Drs. Rodrigue and Notteboom estimate that transportation “typically accounts for about 25% of all the energy consumption of an economy.” While this is a terribly imprecise and unscientific estimation, it would be a sin to neglect the energy costs of shipping such a widely used metal. Worse still, this figure does not take into account the additional material costs of packaging neodymium magnets. As mentioned in the previous blog on neodymium flow, the shipment of permanent rare earth magnets, due to their incredible strength, requires exorbitant amounts of packaging. Otherwise, the magnets could damage their shipping containers, shipping vehicles, one another, or the individuals handling them. For our purposes, the most significant impact of this packaging is that it reduces the amount of neodymium that can be transported in a given shipment. Keeping this in mind, we’ll adjust the 25% figure to 35% instead.
If transportation accounts for 35% of the energy costs of the neodymium industry, and the remaining 65% is the 745 MJ/kg we derived earlier, then neodymium extraction, production, manufacturing, processing, and shipment costs about 1146 MJ/kg.
Calculating the overall energy cost associated with the global demand of neodymium results in the above estimates. That third figure, the projected energy associated with neodymium from extraction to shipment in 2050, is now equivalent to almost 75 megatons of TNT. However, the impact of neodymium on energy consumption might not necessarily stop once the magnets are done being shipped. Certainly the abundance of consumer electronics like smartphones, laptops, headphones, and speakers, all of which require neodymium magnets, helps contribute to the amount of energy consumed by consumers globally. While we won’t attempt to estimate this contribution, since it is rooted in whether humans would have used that energy anyways, it is definitely worth considering.
Also worth considering is the positive impact that neodymium has on energy usage. Specifically, neodymium is used in generators. When neodymium magnets are rotated around a conductive metal, the magnetic field induces an electric current. As such, materials with strong magnetic properties, like neodymium, allow for incredibly useful means of converting the forces around us into energy. In fact, most forms of electricity generation, including hydro and wind, require strong magnets inside a generator. Even nuclear power and coal, which reside on opposite ends of the spectrum of CO2 emissions, revolve around the heating of water into steam, which in turn drives turbines comprised of rare earth elements like neodymium. Should neodymium been seen in a gentler light because it helps us generate energy from greener sources? Probably. Should neodymium as a material be penalized for helping the coal power industry? Probably not, but who’s to say? Adding further complexity to the issue, one must remember that the neodymium used to build those wind turbines and nuclear power plants required significant amounts of energy to process. According to the Bulletin of Atomic Sciences, a 2 megawatt wind turbine requires 800 pounds of neodymium. At 1146 MJ/kg, 800 pounds of neodymium costs 416 GJ. That very 2 MW wind turbine would have to operate for 2.4 days before it generates that much energy, meaning every wind turbine must spend its first 2.4 days of operation trying to offset the energy required to process its neodymium!
Issues and the Plan for the Future
In summary, using data where it is available and estimation where it is not, we can come to a rough approximation of the energy costs of neodymium production. However, as neodymium magnets enter the market, it becomes difficult to draw the lines and decide what results of neodymium usage should also be considered. A sudden halt in neodymium supply would result in a sharp drop in electronics production, which in turn would likely reduce the world’s energy usage. However, that halt would also cause a sharp drop in the production of turbines to be used in wind, hydro, and nuclear power generation. As such, the problem to be solved here is not “neodymium” itself, nor the amount of the material that is extracted and used. Instead, improving the environmental impacts associated with neodymium would require changing the way we use the material. Developing more efficient turbines and generators, with higher inductive coupling coefficients (for inducing electricity) and less friction, reducing the power draw of the electronic devices that use neodymium magnets, and improving the mining process of neodymium are all possibilities. As a environmentally minded citizen, lawmaker, or government leader, then, what should we do to improve the energy costs associated with this incredible material? Such a plan would require:
- Incentivizing the mining industry to develop less energy-intensive processes.
- Regulating the mining industry to ensure environmentally sound practices.
- Pushing for cleaner fuel for shipping options, by land, sea, and air.
- Encouraging technology makers to create low-power products.
- Funding research into more efficient generators, turbines, and magnet usage.
Unfortunately, the planks of this plan are large enough to prevent any citizen, or even lawmaker, from ensuring they occur. However, with sufficient pressure from globally and environmentally minded citizens, and with sufficient action from their representatives, progress could definitely be made.
Haque, Hughes, Lim, and Vernon. “Rare Earth Elements: Overview of Mining, Mineralogy, Uses, Sustainability and Environmental Impact.” Resources. MDPI. 2014.