Monazite caustic soda digestion process

Fig. 1.4. Caustic soda digestion process for recovery of rare earths from monazite [2],...

Monazite. The commercial digestion process for monazite uses caustic soda. The phosphate content of the ore is recovered as marketable trisodium phosphate and the rare earths as RE hydroxide (10). The usual industrial practice is to attack finely ground monazite using a 50% sodium hydroxide solution at 150°C or a 70% sodium hydroxide solution at 180°C. The resultant mixed rare-earth and thorium hydroxide cake is dissolved in hydrochloric or nitric acid, then processed to remove thorium and other nonrare-earth elements, and processed to recover the individual rare earths (see... 

The use of various techniques discussed so far is well illustrated by the processing steps adopted in the economic recovery of rare earths from monazite in India [25]. The first step in the processing of monazite is digestion with caustic soda and this is schematically shown in Fig. 1.11. The main reaction that takes place during digestion may be written as ... 

A commercial digestion process is currently in use for the extraction of REE, including yttrium from monazite. The process is based on the application of caustic soda, and one of the products is REE hydroxide. The rare earths are leached from bastnaesite with hydrochloric acid (or sulfuric acid), followed by calcination at >600°C they are then treated with 16 M nitric acid (Kirk-Othmer 1999). Yttrium is produced as pure silver metal, both on the laboratory and industrial scale, by molten salt electrolysis and metallothermic reduction of the fluoride, oxide, or chloride with calcium following an enrichment process, after separation by fractionated crystallization, ion exchange... 

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