NdFeB magnetic material, due to its excellent magnetic properties and is called "magnetic king", is widely used in many fields. In the production of NdFeB magnets will produce about NdFeB scrap 20% of the weight of raw materials, including turning blocks and oil waste and so on. NdFeB scrap contains about 30% of rare earth elements  (which contains about 90% of neodymium, the balance of terbium, dysprosium, etc.). China is a big producer of NdFeB materials, accounting for 80% of the global output. In 2005, China produced 32,200 tons of NdFeB, resulting in more than 7000 tons of NdFeB scrap, the current annual output of NdFeB to more than 20% growth rate is expected to China's production of NdFeB will be More than 100,000 tons, will produce about 20,000 tons of NdFeB scrap. In order to save resources, reduce industrial waste at the same time, protect the environment, the comprehensive utilization of NdFeB waste resources is necessary. And will have significant social benefits and considerable economic benefits.
1 NdFeB waste recycling process
1.1 hydrochloric acid excellent solution [2-4] The principle of the hydrochloric acid excellent solution method is to strictly control the acid decomposition process conditions, so that the waste of rare earth in hydrochloric acid solution preferentially dissolved. Excellent solution method from the oxidation roasting, decomposition and impurity removal, separation and precipitation, precipitation burning 4 parts.
(1) Oxidative roasting: This step is the key of the optimal solution method, which converts rare earth into oxide and iron into Fe2O3 to facilitate the next acid decomposition.
(2) Decomposition and impurity removal: adding a small amount of water into the reactor, adding hydrochloric acid and materials in portions, controlling the rare earth concentration and pH, and prioritizing the rare earths to separate and extract the rare earths; using the P50 to separate the rare earth elements from the chlorinated rare earth solution, Get a single rare earth chloride; Lake burning: the extraction solution into the sedimentation tank, ammonium oxalate precipitating agent was added to give rare earth oxalate or rare earth carbonate precipitation, the rare earth oxide was obtained. 1.2 whole solution method
1.2 The whole solution method is to use hydrochloric acid as a solvent, the scrap of rare earth elements and iron are all dissolved in an ionic state, and then through iron removal, extraction and separation process to obtain rare earth oxides. The whole solution by the dissolution of the dissolution, removal of iron, extraction and separation, precipitation, burning and other four parts.
(1) leaching and dissolving: the neodymium iron boron scrap sieved directly with concentrated hydrochloric acid dissolved at room temperature, rare earth and iron into ion form, the use of hydrogen peroxide oxidation of Fe2 + to Fe3 +;
(2) Iron removal: the use of N503 extraction of iron;
(3) Extraction and separation: the solution after iron removal uses P507 to extract and separate the rare earth elements to obtain a single rare earth chloride;
(4) Precipitation to obtain a rare earth oxide.
1.3 sulfate double salt method
Sulfate - double salt method is the use of sulfuric acid as a solvent to dissolve NdFeB waste, and then the solution at a certain temperature and Na2SO4 reaction to generate ammonium sulfate double salt precipitation, the double sulfate precipitation add oxalic acid solution to generate rare earth oxalate Precipitation, obtained by burning rare earth oxide.
2 development trend
At present, the main NdFeB waste recycling hydrometallurgical process. Hydrochloric acid dissolution - extraction process, easy to achieve large-scale production, but oxalic acid or ammonium bicarbonate precipitation washing wastewater pollution, and the use of ammonia as a saponifier, the concentration of ammonia nitrogen in wastewater is high, resulting in water pollution. The use of sulfuric acid - double salt precipitation process, it is difficult to achieve large-scale production, and dissolved all dissolved Fe into ferrous sulfate, resulting in the recovery of rare earth elements of iron waste, but also cause water pollution. From the economic and environmental protection point of view, the use of hydrochloric acid solution method better than other processes. The method can reduce the amount of acid used, acid slag can be directly sold as iron ore concentrate to the steel plant or to the cement plant as an iron correction element for the production of cement; in the extraction and separation of caustic soda or lime water instead of ammonia as a saponifier, Can effectively reduce ammonia nitrogen in wastewater.
Neodymium iron boron permanent magnet material, whether it is the scale of demand, or the growth rate of demand, are quite amazing. Although China is a rare earth power whose industrial reserves account for more than 70% of the world's total reserves, rare earths are non-renewable resources and produce a large amount of wastes during deep processing of mining and new materials, resulting in environmental pollution and waste of resources. Neodymium oxide, neodymium oxide, terbium oxide, dysprosium oxide, cobalt oxide and other precious products can be obtained from NdFeB scrap. Recycling of industrial waste, in line with the national development of circular economy industrial policy.
Article from NdFeB Industry Network