Eduardo CesarA sample of metallic didymium developed at IPTEduardo Cesar
An important step was taken to allow Brazil to produce supermagnets in the future. The development of technology to produce didymium — a mixture of two metals and the precursor of alloys for magnets with a higher magnetic flux density — opens the way for the manufacture of this product, not yet made in Brazil. Didymium consists of two rare earth elements, praseodymium (Pr) and neodymium (Nd), from the lanthanide group. The high-power magnets are used, for example, in electric vehicle motors and power generators in wind turbines. The news announced in February 2016 is the result of a partnership between the Institute for Technological Research (IPT), the Companhia Brasileira de Metalurgia e Mineração (CBMM) and the Brazilian Agency for Industrial Research and Innovation (Embrapii), linked to the Ministry of Science, Technology and Innovation (MCTI).
In the project begun in 2014, the group of IPT researchers from the Metallurgical Processes Laboratory, led by metallurgical engineer João Batista Ferreira Neto, developed technology to transform didymium oxide, a coffee-colored power, into ingots of pure metal. “We developed the reduction stage, which means transforming the oxide into metal by removing the oxygen. In order to do this, we assembled reactors that operate at 1,200 degrees Celsius (°C) and produce bars of metallic didymium. In a subsequent stage — for which we also intend to develop technology — this material will be used to produce a metallic alloy of didymium, iron and boron for later manufacture of the supermagnet,” explains Ferreira Neto. The project to develop metallic didymium cost R$9 million, with R$3 million from the CBMM, R$3 million from Embrapii, and IPT’s contribution consisting of equipment, infrastructure and the salaries of seven researchers.
Magnetic field
In order to produce a magnet, one must first obtain the didymium-iron-boron alloy in power form and align the particles using a magnetic field applied during compacting, followed by sintering (solidifying the material) and heat treatment. Magnets made in Brazil are composed of barium- or strontium-based ferrite, present, for example, in small refrigerator magnets. Magnets containing neodymium, iron and boron have a magnetic field at least three times stronger than those made of ferrite.
The magnet market is growing apace. In 2010, sales totaled $2 billion worldwide. They are expected to reach $5 billion by 2020, and $10 billion by 2030, principally due to the increase in the importance of wind power. The demand for didymium or neodymium magnets ranges from 600 kilograms (kg) to 1 metric ton per megawatt (MW) of installed capacity just for wind generators. One MW can supply power for about 200 residences, on average. The forecast is that another 10 gigawatts (GW) of wind power will be installed between 2016 and 2019, just in Brazil.
Eduardo CesarDidymium oxide produced by CBMM in Araxá (MG)Eduardo Cesar
Currently, the magnets used in Brazilian industry are imported, although the country has the second largest reserve of rare earth elements in the world, behind only China. China leads world production of magnets and has the technology to both extract and purify rare earth elements and produce strong magnets. “There is little information on the separation of rare earth elements and the production of metallic alloys for magnets outside of China,” says Ferreira Neto.
The most powerful commercial magnets used in the world are made of neodymium or didymium. At CBMM’s mines in Araxá, Minas Gerais State, the production of rare earth elements begins with their separation out of monazite, a mineral found in the tailings of niobium mining, among other geological sites. Neodymium and praseodymium always appear together in the same mineral.
CBMM sells all niobium products used by industry, such as the ferroniobium used in the steel industry, pure metallic niobium, and special oxides of this material. Brazil is the largest producer in the world. Niobium is added to steel in an average proportion of 500 grams per metric ton. This small amount of steel increases its mechanical resistance without affecting its malleability. Thus you can use less steel in the final application, for example, by using thinner, lighter steel plates. Niobium is also used in aircraft engine combustion chambers, among other applications. “We do not sell the raw material, but rather transform niobium in accordance with the client’s needs. We export 96% of the 65,000 metric tons of niobium produced annually, with 22% to 25% going to China,” says CBMM president and metallurgical engineer Tadeu Carneiro.
“We developed the technology to separate monazite [which contains rare earth elements] from tailings. In the first separation phase we obtain double sulfate containing the 17 rare earth elements, all of which have industrial use; the problem is to obtain them in an economical way,” he explains. It is also difficult to separate neodymium and praseodymium; this is why the company uses didymium oxide. “We built a semi-industrial unit to produce double sulfate, with a capacity of 3,000 metrics tons a year,” explains Carneiro. CBMM also built a pilot plant to separate four rare earth compounds from double sulfate using solvent extraction technology. This allows it to obtain cerium, lanthanum, and didymium oxides, plus the other rare earth elements. The concentration of didymium represents 15% to 20% of the total amount of rare earth elements in monazite.
“R$80 million was spent on this separation line,” says Carneiro. The company is controlled by the Moreira Salles group, which holds 70%. The remaining 30% belongs to consortia of Chinese, Japanese and Korean companies. “We hope to be able to produce a didymium-iron-boron alloy,” says Carneiro. “Later, we will surely need to join forces with companies in the sector that produce alloys and magnets. We are investing in knowledge, but when it comes time to sell, we will need other partners.”
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