Waste and recycled neodymium iron boron magnetic steel
The production of sintered neodymium iron boron inevitably generates waste or scrap in every process from raw material pretreatment to final product testing. The waste generated during the production process can reach about 25% -30% of the total weight of the raw materials.
Due to differences in process techniques, shape specifications, and other aspects among different enterprises, the loss rate in the machining process varies, ultimately resulting in different overall loss rates. However, it is an undeniable fact that the material loss rate in the neodymium iron boron production process is high, and the machining loss and surface treatment of non-conforming products are the units that generate the most waste in the entire neodymium iron boron production process. The recycling method of sintered neodymium iron boron waste is usually divided into two directions: one is to separate and extract various elements, especially rare earth elements, from neodymium iron boron waste, prepare oxides or other compounds with certain purity, and use them as raw materials in different fields; The second is to use waste materials to prepare neodymium iron boron magnets or other products with certain functions, such as preparing regenerated sintered magnets, absorbing materials, etc. The extraction of waste elements can be divided into two types: wet recovery and dry recovery. Wet methods include hydrochloric acid dissolution method, double salt precipitation method, etc., while dry methods include oxidation method, chlorination method, or molten metal extraction method. Compared to wet recycling, dry recycling is more environmentally friendly. Mud materials, powders, and other highly oxidized neodymium iron boron waste materials are generally sampled and extracted using the method of separating and extracting these elements for recovery. The extraction method of molten metal in dry recycling requires waste with a low degree of oxidation. The method of using waste to prepare neodymium iron boron permanent magnets has the advantages of being direct and efficient. For block shaped waste with low oxidation degree, it can be used to prepare regenerated neodymium iron boron permanent magnets. This can fully utilize the complete grain boundary structure of neodymium iron boron block waste, without the need for further purification processes such as dissolution and separation. With slight treatment, it can be used to prepare magnets. The national standard GB/T 34490-2017 for regenerated sintered neodymium iron boron includes two types of waste neodymium iron boron used in the preparation of regenerated sintered neodymium iron boron permanent magnet materials: one is the sheet-like and block shaped sintered neodymium iron boron waste generated during the production process; The other type is sintered neodymium iron boron waste with plated sheets, blocks, and other shapes dismantled from various scrapped magnetic devices after use. The main component of the waste sintered neodymium iron boron permanent magnet material used should be sintered neodymium iron boron and have rechargeable magnetism. Sampling and testing of the total rare earth content and heavy rare earth (dysprosium, terbium) content of waste sintered neodymium iron boron materials, and classifying the waste materials into the following five categories based on the test results. Waste sintered neodymium iron boron materials with rare earth content less than 28.5% are not suitable for manufacturing recycled magnets.
3 Material Recycling
Waste sintered neodymium iron boron is processed according to the prescribed process to produce regenerated sintered neodymium iron boron. The regeneration process includes raw material pretreatment, raw material crushing, raw material inspection, performance regeneration, etc.
The total rare earth content of the regenerated sintered neodymium iron boron permanent magnet material should be ≥ 30.0%, and the main magnetic properties at room temperature (20 ℃) should meet the following requirements. If the demand side has special requirements, the supply and demand sides can negotiate separately. The national requirements for the magnetic properties of regenerated sintered neodymium iron boron are basically the same as those of sintered neodymium iron boron, with the main difference being that the regenerated sintered neodymium iron boron grades do not have high-grade products.
The auxiliary magnetic properties are affected by factors such as raw materials. The national standard requires that some auxiliary magnetic properties of regenerated sintered neodymium iron boron be slightly lower than those of sintered neodymium iron boron, such as remanence and intrinsic coercivity temperature coefficient, hardness, bending strength, etc.