Preparation
NdCl3 is produced from minerals monazite and bastnäsite. The synthesis is complex because of the low abundance of neodymium in the Earth's crust (38 mg/kg) and because of difficulty of separating neodymium from other lanthanides. The process is however easier for neodymium than for other lanthanides because of its relatively high content in the mineral - up to 16% by weight, which is the third highest after cerium and lanthanum. Many synthesis varieties exist and one can be simplified as follows:
The crushed mineral is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths. The acidic filtrates are partially neutralized with sodium hydroxide to pH 3-4. Thorium precipitates out of solution as hydroxide and is removed. After that the solution is treated with ammonium oxalate to convert rare earths in to their insoluble oxalates. The oxalates are converted to oxides by annealing. The oxides are dissolved in nitric acid that excludes the main components, cerium, whose oxide is insoluble in HNO3. Neodymium oxide is separated from other rare-earth oxides by ion exchange. In this process, rare-earth ions are adsorbed onto suitable resin by ion exchange with hydrogen, ammonium or cupric ions present in the resin. The rare earth ions are then selectively washed out by suitable complexing agent, such as ammonium citrate or nitrilotracetate.
This process normally yields Nd2O3; the oxide is difficult to directly convert to elemental neodymium, which is often the goal of the whole technological procedure. Therefore the oxide is treated with hydrochloric acid or ammonium chloride to produce the less stable NdCl3:
- Nd2O3 + 6 NH4Cl → 2 NdCl3 + 3 H2O + 6 NH3
The thus produced NdCl3 quickly absorbs water and converts to NdCl3·6H2O hydrate, which is stable for storage, and can be converted back into NdCl3 when necessary. Simple rapid heating of the hydrate is not practical for that purpose because it causes hydrolysis with consequent production of Nd2O3. Therefore anhydrous NdCl3 is prepared by dehydration of the hydrate either by slowly heating to 400 °C with 4-6 equivalents of ammonium chloride under high vacuum, or by heating with an excess of thionyl chloride for several hours. The NdCl3 can alternatively be prepared by reacting neodymium metal with hydrogen chloride or chlorine, though this method is not economical due to the relatively high price of the metal and is used for research purposes only. After preparation, it is usually purified by high temperature sublimation under high vacuum.
Read more about this topic: Neodymium(III) Chloride
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