Sintered NdFeB permanent magnet material has excellent performance and is widely used in automobiles, home appliances, wind power, consumer electronics, and other fields. It is the most important type of permanent magnet material currently on the market. In recent years, with the booming development of the electronic information industry, wind power, and new energy vehicles, the demand for NdFeB has increased, and the annual output of sintered NdFeB has gradually increased. During the production process of sintered NdFeB, a large amount of production waste is generated. At the same time, more electromechanical equipment containing NdFeB magnets is being scrapped, and a large amount of NdFeB waste is also generated. The content of rare earth elements in NdFeB materials accounts for more than 30%. Rare earth resources are non-renewable. Using economical and effective methods to recycle valuable substances in NdFeB waste can create certain economic value, save resources, and reduce environmental pollution.
Generation of Sintered NdFeB Waste:
In the production of sintered NdFeB, from raw material preprocessing to final product testing, every process inevitably produces waste or waste products. The waste generated during the production process can reach about 25%-30% of the total weight of the raw material.
Since each company has different process techniques, shape specifications, etc., the loss rate in the machining process is different, which ultimately results in a different total loss rate. However, the material loss rate in the NdFeB production process is very high. It is an undoubted fact that machining losses and defective surface treatment products are the units that generate the most waste in the entire NdFeB production process.
Recycling method of sintered NdFeB Waste:
The waste recycling of NdFeB materials is usually divided into two directions: one is to separate and extract various elements, especially rare earth elements, in the NdFeB waste to prepare oxides or other compounds with a certain purity, which can be used as raw materials for different applications. fields; the second is to use waste materials to prepare NdFeB magnets or other products with certain functions, such as preparing regenerated sintered magnets, absorbing materials, etc.
1 Extraction of waste elements
The extraction of waste elements can be divided into two types: wet recycling and dry recycling. Wet methods include hydrochloric acid dissolution method, double salt precipitation method, etc. Dry methods include oxidation, chlorination, or molten metal extraction methods. Compared with wet recycling, dry recycling is more environmentally friendly. NdFeB waste with a high degree of oxidation, such as slurry materials and powders, is generally recycled using the method of separation and extraction of such elements. (Molten metal extraction methods in dry recycling require lightly oxidized scrap).
2 Preparation of NdFeB from waste materials
The recycling method of using waste materials to prepare NdFeB permanent magnets has the advantage of being direct and efficient. For bulk waste with a low degree of oxidation, it can be used to prepare regenerated NdFeB permanent magnets, which can make full use of the complete grain boundary structure of NdFeB bulk waste without going through purification processes such as dissolution and separation. It can be used to prepare magnets after additional processing.
Regenerated sintered NdFeB
1 Raw material selection
The waste NdFeB used in the preparation of regenerated sintered NdFeB permanent magnet materials includes two categories: one is the flake and block sintered NdFeB waste generated during the production process; the other is various magnetic materials that are scrapped after use. Coated flakes, blocks, and other shapes of sintered NdFeB scraps disassembled from devices. The main component of the used waste sintered NdFeB permanent magnet material should be sintered NdFeB, and it should be magnetizable.
2 Raw material classification
Samples were taken to detect the total rare earth content and heavy rare earth (dysprosium, terbium) content of scrap sintered NdFeB, and the waste materials were classified into the following five categories based on the test results. Waste-sintered NdFeB materials with a rare earth content of less than 28.5% are not suitable for manufacturing recycled magnets.
3 Material recycling
After the waste sintered NdFeB is processed according to the prescribed process, regenerated sintered NdFeB is made. The regeneration process includes raw material pretreatment, raw material crushing, raw material inspection, performance regeneration, etc.
The manufacturing process of regenerated sintered gold iron boron.
Raw material pretreatment: batch the waste sintered nickel iron boron permanent magnet raw materials according to the batch production capacity; use physical or chemical methods to conduct appropriate surface treatment to remove coatings, oxidation rust, and other impurities.
Coarse crushing of raw materials: Use mechanical crushing, hydrogen crushing, or other methods to coarsely crush the pre-treated waste-sintered titanium iron boron materials and mix them evenly.
Raw material testing: Sampling and testing the total rare earth and dysprosium content of the scrap sintered nickel iron boron permanent magnet materials after coarse crushing according to batches, and classifying the waste materials based on the test results.
Performance regeneration: According to the detected total rare earth content and dysprosium content, add rare earth metal or alloy powder, adjust the total rare earth content of the magnet, etc., and strictly control the oxygen content and other magnesium content. The amount is enough to meet the requirements, and the regenerated sintered NdFeB material is made after mixing, fine crushing, molding, sintering, and heat treatment.