Magnetic scrap and regenerated sintered NdFeB permanent magnet
Sintered NdFeB permanent magnet materials have excellent performance and are widely used in automobiles, home appliances, wind power, consumer electronics and other fields. They are currently the most important type of permanent magnet materials on the market. In recent years, with the vigorous 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. In 2018, the output of NdFeB in my country has increased. Up to 157,000 tons.
In the production process of sintered NdFeB, a large amount of production waste will be produced. At the same time, more and more electromechanical equipment containing NdFeB magnets are beginning to be scrapped, and a large amount of NdFeB waste is also produced. The content of rare earth elements in NdFeB materials is more than 30%, and the rare earth resources are not renewable. The use of economical and effective methods to recycle the valuable substances in NdFeB waste can create certain economic value, save resources and reduce environmental pollution .
Production of sintered NdFeB waste
In the production of sintered NdFeB, from raw material pretreatment to final product inspection, waste or waste is inevitably generated in each process, and the waste generated during the production process can reach 25%-30% of the total weight of raw materials. As each company differs in process techniques, shape specifications, etc., the loss rate in the machining process is different, resulting in a different total loss rate. However, the material loss rate in the NdFeB production process is very high. Undoubted facts, and the loss of machining and unqualified products of surface treatment are the units that generate the most waste in the entire NdFeB production process.
Sintered NdFeB waste recycling method
The recycling of NdFeB materials is usually divided into two directions: one is to separate and extract various elements in NdFeB waste, especially rare earth elements, to prepare oxides or other compounds with certain purity, which are used as raw materials for different Field; the second is the use of waste materials to prepare neodymium iron boron magnets or other products with certain functions, such as the preparation of regenerated sintered magnets and wave-absorbing materials.
Extraction of waste elements
The extraction of waste elements can be divided into wet recycling and dry recycling. Wet methods include hydrochloric acid solution method, double salt precipitation method, etc., dry method includes oxidation method, chloride method or molten metal extraction method. Compared with wet recycling, dry recycling is more environmentally friendly. Slurry, powder and other highly oxidized NdFeB waste materials are generally recovered by the method of separation and extraction of such elements. (The molten metal extraction method in dry recycling requires lightly oxidized waste)
Preparation of NdFeB from waste
The recycling method for preparing NdFeB permanent magnets from waste has the advantages of directness and high efficiency. For the bulky waste with low oxidation degree, it can be used to prepare regenerated NdFeB permanent magnets, which can make full use of the characteristics of the complete grain boundary structure of the NdFeB bulk waste. It does not need to go through purification processes such as dissolution and separation. Add treatment can be used to prepare magnets.
National standard for regenerated sintered NdFeB (GB/T 34490-2017)
Raw material selection
The waste NdFeB used in the preparation of regenerated sintered NdFeB permanent magnet materials includes two types: one is the sheet and block sintered NdFeB waste generated during the production process; the other is the various types of magnetism scrapped after use Sintered NdFeB scraps with plated layers, blocks and other shapes disassembled from the device. The main component of the used waste sintered NdFeB permanent magnet material should be sintered NdFeB, which is magnetizable.
Classification of raw materials
Sampling and testing the total rare earth and heavy rare earth (dysprosium, terbium) content of waste sintered NdFeB, and dividing the waste materials into the following five categories according to the test results. Waste sintered NdFeB materials with rare earth content less than 28.5% are not suitable for manufacturing regenerated magnets.
Material regeneration
After the waste sintered NdFeB is treated in accordance with the prescribed process, it is made into regenerated sintered NdFeB. The regeneration process includes raw material pretreatment, raw material crushing, raw material inspection, performance regeneration, etc.
| Category | Total rare earth content% (mass fraction) | Dysprosium and terbium content% (mass fraction) |
| I | ≥28.5% | ≤1.0 |
| II | ≥28.5% | 0.5-2.0 |
| III | ≥28.5% | 1.5-3.0 |
| IV | ≥28.5% | 2.5-4.5 |
| V | ≥28.5% | >4.0 |
Experiments show that the coercivity, remanence and energy product of the magnet are restored and improved to a certain extent after adding rare earth alloy powder. Using the grain boundary diffusion method, adding dysprosium to the sintered waste NdFeB powder can significantly increase the coercivity of the magnet.
Material requirements
The total rare earth content of the regenerated sintered NdFeB permanent magnet material should be ≥30.0%.
Source: China Permanent Magnet Manufacturer – www.rizinia.com
