Sodium hydroxide treatment monazite

The chemical treatment used depends upon the composition of the mineral. The sodium hydroxide treatment of monazite. Figure 8, is preferably used since it has the advantage of removing phosphates more readily than the sulfuric acid procedure. 

Gadolinium is produced from both its ores, monazite and bastnasite. After the initial steps of crushing and beneficiation, rare earths in the form of oxides are attacked by sulfuric or hydrochloric acid. Insoluble rare earth oxides are converted into soluble sulfates or chlorides. When produced from monazite sand, the mixture of sand and sulfuric acid is initially heated at 150°C in cast iron vessels. Exothermic reaction sustains the temperature at about 200 to 250°C. The reaction mixture is cooled and treated with cold water to dissolve rare earth sulfates. The solution is then treated with sodium pyrophosphate to precipitate thorium. Cerium is removed next. Treatment with caustic soda solution fohowed by air drying converts the metal to cerium(lV) hydroxide. Treatment with hydrochloric or nitric acid sol-... 

Monazite concentrate is processed either with sulfuric acid, like bastnasite, to produce a mixture of sulfates but the usual process is an alkaline treatment. The alkali process is preferred since it removes the phosphates more readily [9]. Whichever method is chosen the radioactive thorium must be completely removed. After benefication the monazite concentrate is finely ground and reacted with a hot concentrated sodium hydroxide at 140° to 150°C. Insoluble hydroxides of the rare-earths and thorium are formed while trisodium phosphate and excess sodium hydroxide remain in solution. The next step is hydrochloric acid attack on the solids portion. The thorium remains insoluble and a crude thorium hydroxide can be filtered off Trace contaminants that do carry through into solution, such as uranium and lead, as well as some thorium, are removed by coprecipitation with barium sulphate in a deactivation step. The cerium-containing product will be a rare-earth chloride differing only marginally in the proportions of the various rare- earths present, to the analogous rare-earth chloride produced from bastnasite. 

A common procedure begins with a treatment of monazite sand with 50-70% sodium hydroxide at 1,400°C to convert thorium oxide to hydroxide. The filtered hydroxide is then dissolved in hydrochloric acid and the pH adjusted to 5-6 to precipitate thorium but not the main fraction of the rare earth elements. After dissolution of the hydroxide in nitric add, thorium is extracted with methyl isobutyl ketone (MIBK) or TBP in kerosene. Thorium is then stripped from the solvent using an alkali solution. 

Strong base such as NaOH (sodium hydroxide) is an often preferred alternative in the case of monazites and xeno-times because the phosphate is removed more efficiently than by the H2SO4 treatment. 

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