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Sintered Neodymium Iron Boron Waste and Recycled Magnets

Sintered neodymium iron boron (NdFeB) permanent magnets have excellent properties and are widely used in automotive, home appliance, wind power, and consumer electronics. They are currently the most important permanent magnet material on the market. In recent years, with the rapid development of the electronics and information industry, wind power, and new energy vehicles, the demand for NdFeB magnets continues to grow, and the annual production of sintered NdFeB magnets has also gradually increased.

Sintered NdFeB permanent magnet

A large amount of production waste is generated during the production process of sintered NdFeB magnets. At the same time, more and more discarded electromechanical equipment containing NdFeB magnets leads to a large amount of NdFeB waste. The rare earth element content accounts for more than 30% in NdFeB materials. Rare earth resources are non-renewable. Using economical and effective methods to recover valuable substances from NdFeB waste can create certain economic value, save resources, and reduce environmental pollution.

Generation of Sintered NdFeB Waste

From raw material pretreatment to final product inspection, each process in the production of sintered NdFeB magnets inevitably generates waste or defective products. The waste generated during the production process can reach about 25%-30% of the total raw material weight.

Generation of NdFeB Scrap

Due to differences in process techniques, shape specifications, etc. among different companies, the loss rate in machining processes varies, resulting in slightly different overall loss rates. However, it is an indisputable fact that the material loss rate in the production process of NdFeB magnets is very high, and machining losses and unqualified surface treatment account for most of the waste generated in the entire NdFeB production process.

Recovery Methods for Sintered NdFeB Waste

The recovery of NdFeB waste is usually carried out in two directions: first, separating and extracting various elements in the NdFeB waste, especially rare earth elements, to prepare oxides or other compounds with a certain purity as raw materials for different fields; second, using waste to prepare NdFeB magnets or other products with certain functions, such as preparing recycled sintered magnets, absorbing materials, etc.

1.Element Extraction from Waste
The extraction of elements from waste can be divided into wet recovery and dry recovery. Wet methods include hydrochloric acid leaching, double salt precipitation, etc. Dry methods include oxidation, chlorination or molten metal extraction. Compared to wet recovery, dry recovery is more environmentally friendly. Waste powders and slurries with higher oxidation levels generally use elemental separation and extraction methods for recovery. (Molten metal extraction in dry recovery requires waste with lower oxidation levels.)

2.Preparation of NdFeB using Waste
The waste-to-magnet recovery method has the advantages of being direct and efficient. For waste with low oxidation levels, it can be used to prepare recycled NdFeB permanent magnets. This makes full use of the complete grain boundary structure characteristics of NdFeB waste, without having to go through dissolution, separation and other purification processes again. They only need a little processing and can be used to prepare magnets.

National Standard for Recycled Sintered NdFeB – GB/T 34490-2017

1.Raw Material Selection
The recycled sintered NdFeB permanent magnets are prepared from two types of NdFeB scrap: a) plate, block and other shaped sintered NdFeB waste generated during production; b) various scraped plate, block and other shaped sintered NdFeB waste with plating layers from discarded magnetic devices. The main component of the recycled sintered NdFeB permanent magnet material used should be sintered NdFeB and have magnetizability.

2.Raw Material Classification
By sampling and testing the total rare earth and heavy rare earth (dysprosium and terbium) content of the scrap sintered NdFeB, the scrap materials are classified into the following five categories. Scrap sintered NdFeB materials with rare earth content less than 28.5% are not suitable for manufacturing recycled magnets.

3.Material Recycling
After prescribed processing, the scrap sintered NdFeB is made into recycled sintered NdFeB magnets. The recycling process includes raw material pretreatment, raw material crushing, raw material inspection, performance recovery, etc.

Experiments show that after adding 2% PrNd, the coercivity of the magnet recovered to 102% of the primary product, the remanence and energy product reached 95% and 90% of the primary product respectively, and the squareness decreased. Adding terbium by grain boundary diffusion can significantly improve the coercivity of the magnet.

4.Requirements for Materials
The total rare earth content of the recycled sintered NdFeB permanent magnet material should ≥30.0%. The main magnetic properties at room temperature (20°C) should meet the following requirements. If there are special requirements, the supplier and purchaser can negotiate separately.
Basic Magnetic Properties
The magnetic property requirements for recycled sintered NdFeB are basically the same as those for sintered NdFeB. The main difference is that there are no high-grade products for recycled sintered NdFeB.

Auxiliary Magnetic Properties
Affected by factors such as raw materials, some auxiliary magnetic property requirements for recycled sintered NdFeB can be slightly lower than those for sintered NdFeB, such as remanence, temperature coefficient of intrinsic coercivity, hardness, flexural strength, etc.

The requirements for size and geometrical tolerances are exactly the same between the national standard for recycled sintered NdFeB and sintered NdFeB.