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NdFeB Waste Utilization Process Summary

NdFeB Waste Utilization Process Summary

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he excellent magnetic properties of NdFeB magnetic materials are used in various fields, and a large amount of waste residue is generated in the production process of NdFeB magnetic materials.

  The excellent magnetic properties of NdFeB magnetic materials are used in various fields, and a large amount of waste residue is generated in the production process of NdFeB magnetic materials. In order to save resources, avoid waste of rare earth resources, reduce industrial waste, and protect the environment, it is necessary to make resource utilization of NdFeB waste.

  NdFeB magnetic materials, known as "Magnetic King" due to their excellent magnetic properties, are widely used in many fields. In the production process of NdFeB magnets, NdFeB waste, which is about 20% by weight of the raw material, is generated, including turning blocks and oil-impregnated waste. The NdFeB waste contains about 30% of rare earth elements [1] (containing about 90% of barium, and the rest are barium, strontium, etc.). China is a major producer of NdFeB materials, accounting for 80% of global production. In 2005, China produced 35,200 tons of NdFeB, resulting in more than 7,000 tons of NdFeB waste. At present, the annual production of NdFeB is increasing at a rate of more than 20%. It is estimated that the production of NdFeB in China will be 2010. More than 100,000 tons will produce about 20,000 tons of NdFeB waste. In order to save resources, reduce industrial waste and protect the environment, it is necessary to comprehensively utilize NdFeB waste resources. And it will produce significant social benefits and considerable economic benefits.

  1 NdFeB waste recycling process

  1.1 hydrochloric acid solution method [2-4]

  The principle of the hydrochloric acid solution method is to strictly control the acid decomposition process conditions, so that the rare earth in the waste material is preferentially dissolved in the hydrochloric acid solution. The excellent solution method consists of four parts: oxidative roasting, sub-dissociation, extraction separation, and precipitation burning.

  (1) Oxidation roasting: this step is the key to the excellent dissolution method, converting rare earth into oxide and converting iron into Fe2O3 to facilitate the next acid decomposition;

  (2) Separation of impurities: a small amount of water is added to the reactor, hydrochloric acid and materials are added in portions to control the concentration of rare earth and pH, and the rare earth is preferentially extracted and separated: the rare earth element is separated by P50 after removing the rare earth chloride solution. Obtaining a single rare earth element chloride; precipitating and burning: the extraction separation liquid is driven into a precipitation tank, and an ammonium oxalate precipitating agent is added to obtain rare earth oxalate or rare earth carbonate precipitated and fired to obtain a rare earth oxide.

  1.2 Total Dissolution Method [5]

  The total solution method uses hydrochloric acid as a solvent to dissolve all the rare earth elements and iron in the waste into an ionic state, and then obtains a rare earth oxide by a process such as iron removal, extraction and separation. The total dissolution method consists of four parts: leaching and dissolving, iron removal, extraction separation, and precipitation burning.

  (1) Leaching and dissolving: the NdFeB waste is sieved and directly dissolved in concentrated hydrochloric acid at room temperature, and the rare earth and iron are converted into an ion form, and the Fe2+ is oxidized to Fe3+ using hydrogen peroxide;

  (2) Iron removal: extraction of iron by N503;

  (3) Extraction and separation: the solution after de-ironing is extracted by P507 to separate rare earth elements to obtain a single rare earth chloride;

  (4) Precipitation burning to obtain a rare earth oxide.

  1.3 Sulfuric acid double salt method [1,6,7]

  The sulfuric acid-multi-salt method dissolves the NdFeB waste by using sulfuric acid as a solvent, then reacts the solution with Na2SO4 at a certain temperature to form ammonium sulfate double salt precipitates, and precipitates the double salt of sulfuric acid into the oxalic acid solution to form rare earth oxalate. Precipitation, after ignition, obtain rare earth oxide.

  2 Development trends

  At present, the recovery of NdFeB waste is mainly carried out by hydrometallurgical process. The hydrochloric acid dissolution-extraction process is easy to achieve large-scale production, but the oxalic acid or ammonium bicarbonate precipitation washing wastewater is highly polluted, and the ammonia water is used as a saponifying agent, so that the ammonia nitrogen concentration in the wastewater is high, causing water pollution. It is difficult to achieve large-scale production by using the sulfuric acid-double salt precipitation process, and all of Fe is converted into ferrous sulfate during dissolution, which causes waste of iron element and causes water pollution. From the perspective of economy and environmental protection, the use of hydrochloric acid soluble solution is better than other processes. The method can reduce the amount of acid used, and the acid slag can be directly sold as an iron concentrate to a steel plant or to a cement plant as an iron correction element for producing cement; in the extraction and separation, caustic soda or lime water is used as a saponifier instead of ammonia water. It can effectively reduce ammonia nitrogen in wastewater.

  NdFeB permanent magnet materials are quite amazing both in terms of the scale of demand and the growth rate of demand. Although China is a large rare earth country, its industrial reserves account for more than 70% of the world's total reserves, but rare earths are non-renewable resources, and generate a large amount of waste in the deep processing of mining and new materials, causing environmental pollution and waste of resources. Valuable products such as cerium oxide, cerium oxide, cerium oxide and cobalt oxide can be obtained from the NdFeB waste. The recycling of industrial waste is in line with the industrial policy of the country to develop a circular economy.