cerium oxide polishing powder production process
At present, the raw materials of ceric system rare-earth polishing powder are as follows:
(1) Cerium oxide (CeO2), obtained by separation of mixed rare earth salts (w(CeO2)=99%); ;
(2) rare earth hydroxide (cerium-rich) : mixed rare earth hydroxide (RE(OH)3), as the intermediate raw material (w(REO)=65%, w(CeO2)≥48%) after chemical treatment of rare earth concentrate (w(REO)≥50%);
(3) rare earth salts: mixed rare earth chloride (RECl3), less europium rare earth chloride extracted from mixed rare earth chloride (mainly containing La, Ce, Pr and Nd, w(REO)≥45%, w(CeO2)≥50%), including rare earth chloride, rare earth oxalate, rare earth carbonate, etc.
(4) Monobastnaesite: high-grade rare earth concentrate (w(REO)≥60%, w(CeO2)≥48%), including mixed rare earth concentrate from Baotou, Inner Mongolia, and bastnaesite concentrate from Weishan, Shandong and Mianning, Sichuan.
1. Solid phase reaction with rare earth concentrate or cerium enrichment as raw material
Direct preparation of polishing powder from ore can eliminate the complicated chemical extraction process and greatly reduce the production cost. Bastnaesite (rare earth concentrate with REO > 68%) is pulverized, graded, chemically treated, filtered, dried, calcined at 900℃ above, pulverized, graded and mixed to obtain bastnaesite polishing powder containing about 50% CeO2. Fluorine and silicon in the ore play an important role in ensuring the polishing effect of the product. This kind of rare earth polishing powder is produced by direct calcination with bastnaesite as raw material without synthesis intermediates, and the preparation process is simple. Although the production cost is greatly reduced, the grade of rare earth polishing powder obtained is not high.
2, with rare earth soluble salt as raw material calcination precipitation method
In the precipitation method, there can be a variety of ways, but also more suitable for the deployment of chemical components to improve the polishing performance, such as adding fluorosilicic acid for co-precipitation production of polishing powder, adding wolffonite polishing powder with high silicon content and so on. You can also control the technical conditions to achieve the purpose of controlling the granularity of products. For example, rare earth polishing powder is prepared with rare earth chloride as raw material, and the product can be obtained by chemical treatment, drying, calcination, grading and processing, such as adding precipitant to synthesize intermediates.
There are many methods to prepare polishing powder from rare earth chloride with different intermediates, such as basic salt method, oxalate method, carbonate method, hydroxide, sulphate double salt, etc.
(1) rare earth chloride solution dissolved in water, treated with alkali and oxidant to cerium hydroxide, and then treated with acid to cerium concentrate, adding precipitate to precipitate, after drying, calcination, grinding and grading, mixed to CeO2 80% to 90% cerium chloride polishing powder.
(2) Using rare earth chloride or cerium enrichment after separation as raw materials, the quality of rare earth polishing powder produced is good, but the production process is many, the cost is high. Generally, ammonium sulfate, oxalic acid, sodium carbonate or ammonium bicarbonate and ammonia water are used as precipitating agent. After calcination, grading, filtration, drying and other steps, the content of CeO2 is about 45%-55%. The optimal calcination temperature is 850 -- 950℃, and the calcination time is 2.5 -- 3h. However, the properties of the polishing powders prepared by different precipitating agents are different. The polishing powders prepared by ammonium sulfate as precipitating agent after alkalization and fluorosilicate fluoride have the best corrosion, while the polishing powders prepared by ammonium bicarbonate and ammonia as precipitating agent after boiling with water and fluorosilicate fluoride have the worst corrosion.
(3) RAre-earth fluorinated carbonate precipitation, washing, filtration, calcination and sieve ball grinding were obtained by using light rare-earth chloride as raw material and silfluoric acid and ammonium bicarbonate as precipitant. The product has fine particles, uniform, strong chemical activity, high polishing efficiency and wide application fields.
(4) Using rare earth carbonate mixture (Ce02 content of about 45%) as raw material to prepare high cerium polishing powder: The mixture of rare earth carbonate was calcined to produce rare earth oxide. CeO(oH)2 precipitation and trivalent rare earth solution were obtained by acid treatment. The high cerium polishing powder with Ce02 content of 98 -- 99% was obtained by washing CeO(OH)2 precipitation, drying and calcination, with surface area of 3-5 m2 / g and average particle size of 1.5 -- 2um. Compared with other polishing powder has excellent polishing ability, up to 320mg / 30m in.
