Rare-earth chlorides

Re OPe . The final step in the chemical processing of rare earths depends on the intended use of the product. Rare-earth chlorides, usually electrolytically reduced to the metallic form for use in metallurgy, are obtained by crystallisation of aqueous chloride solutions. Rare-earth fluorides, used for electrolytic or metaHothermic reduction, are obtained by precipitation with hydrofluoric acid. Rare-earth oxides are obtained by firing hydroxides, carbonates or oxalates, first precipitated from the aqueous solution, at 900°C. 

An alternative process for opening bastnasite is used ia Chiaa high temperature roastiag with sulfuric acid followed by an aqueous leach produces a solution containing the Ln elements. Ln is then precipitated by addition of sodium chloride as a mixed sulfate. Controlled precipitation of hydroxide can remove impurities and the Ln content is eventually taken up ia HCl. The initial cerium-containing product, oace the heavy metals Sm and beyond have been removed, is a light lanthanide (La, Ce, Pr, and Nd) rare-earth chloride. 

Production of Cerium Derivatives. Moderately pure (90—95%) cerium compounds can be made from rare-earth chloride through oxidation with, for example, hypochlorite to produce an iasoluble cerium hydrate. The other lanthanides remain ia solutioa. The hydrate, oa calciaatioa, coaverts to Ce02. 

A rare-earth chloride, mischmetal FCC catalysts kon metallurgy principal component... 

The cerium concentrate derived from bastnasite is an excellent polish base, and the oxide derived direcdy from the natural ratio rare-earth chloride, as long as the cerium oxide content is near or above 50 wt %, provides an adequate glass poHsh. The polishing activity of the latter is better than the Ce02 Ln0 ratio suggests. Materials prepared prior to any Ln purification steps are sources for the lowest cost poHshes available used to treat TV face plates, mirrors, and the like. For precision optical polishing the higher purity materials are preferred. 

In a similar manner, treatment of anhydrous rare-earth chlorides with 3 equivalents of lithium 1,3-di-ferf-butylacetamidinate (prepared in situ from di-ferf-butylcarbodiimide and methyllithium) in THF at room temperature afforded LnlMeCfNBuOils (Ln = Y, La, Ce, Nd, Eu, Er, Lu) in 57-72% isolated yields. X-ray crystal structures of these complexes demonstrated monomeric formulations with distorted octahedral geometry about the lanthanide(III) ions (Figure 20, Ln = La). The new complexes are thermally stable at >300°C, and sublime... 

The presumed nonintercalation of a given compound may, however, be due to the fact that appropriate experimental conditions for intercalation have not yet been found. Thus, some of the rare-earth chlorides originally considered not to intercalate Cll, V5), do, in fact, do so in the presence of a complexing agent S21). In addition, the role of chlorine in compound formation has been the subject of controversy. Whereas Croft (Cl) considered the presence of an excess of chlorine to be nonessential, it has since been shown to be a sine qua non for compound formation (D3, RIO, H13, Rll, S22, B17, H25). Moreover, contrary to earlier assumptions (RIO), chlorine does not act as a catalyst, but is incorporated into the graphite to a greater or lesser extent Rll, D3). In cases where the presence of chlorine is apparently not required... 

Water vapor is produced in the reaction, but the hydrolysis of the rare earth chloride formed is prevented by using excess ammonium chloride. After the reaction, the remaining ammonium chloride is removed completely by heating in vacuum at 300-320 °C. 

Rare-earth chlorides, 74 643 Rare-earth elements (REEs)... 

Enthalpies of solution of anhydrous rare-earth chlorides in nonhy-droxylic solvents are also scant. What values exist are collected together in Table XII (178, 183, 218, 220-222), which includes alcohol and water values for ease of comparison. The values in this table are direct calorimetric measurements, performed on anhydrous trichlorides. The value for gadolinium trichloride in dimethylformamide is... 

The metallothermic reduction of the oxides by La produces the metals Sm, Eu, Tm, Yb, all having high vapour pressures. The reaction goes to completion due to the removal of the rare earths by volatilization from the reaction chamber (lanthanum has a low vapour pressure). The remaining rare earth metals (Sc, La, Ce, Pr, Nd, Y, Gd, Tb, Dy, Ho, Er, Lu) can be obtained by quantitative conversion of the oxides in fluorides, followed by reduction with Ca. The metallothermic reduction of the anhydrous rare earth chlorides could be also used to obtain La, Ce, Pr and Nd. The molten electrolysis can be applied to obtain only the first four lanthanide metals, La, Ce, Pr and Nd, because of the high reactivity of the materials that limits the operating temperatures to 1100°C or lower. 

Aluminum chloride has extensive commercial applications. It is used primarily in the electrolytic production of aluminum. Another major use involves its catalytic applications in many organic reactions, including Friedel-Crafts alkylation, polymerization, isomerization, hydrocracking, oxidation, decarboxylation, and dehydrogenation. It is also used in the production of rare earth chlorides, electroplating of aluminum and in many metal finishing and metallurgical operations. 

Several other processes also are apphed for the commercial production of europium. In general, all processes are based upon the initial steps involving opening the mineral (bastnasite or monazite) with sulfuric acid or sodium hydroxide, often followed by roasting and solubihzation. In one such process after separation of cerium, the soluble rare earth chloride mixture in HCl solution is pH adjusted and treated with bis(2-ethylhexyl)phosphate to obtain europium sesquioxide, EuaOs. 

In the electrolytic process, a fused mixture of anhydrous rare earth chlorides (obtained above) and sodium or potassium chloride is electrolyzed in an electrolytic cell at 800 to 900°C using graphite rods as the anode. The cell is constructed of iron, carbon or refractory hnings. Molten metal settles to the bottom and is removed periodically. 

In the 22 years between 1908 and 1930 about 1 100 - 1 400 tons of flints were produced as the most inportant rare earth product. This required the consumption of about 1 300 - 1 800 tons of rare earth oxides in the form of rare earth chloride. 

Ammino-derivatives of Rare Earth Salts—Derivatives of Neodymium Chloride and Samarium Chloride—Pyridine Derivatives of Rare Earth Chlorides. 

A study was made by Freeman and co-workers (93) of the effect of deuterium on the luminescence decay times of solvated rare earth chlorides. Hutchison and Mangum (94) and Robinson (95) had previously shown that there is a substantial increase in the mean triplet-state lifetimes of aromatic organic compounds when the hydrogen is replaced by deuterium. Robinson... 

It is interesting to note that the emission spectra of the terbium chlorides solvated with H20 and D20 show no discernible differences. Since the rare-earth chlorides solvated with D20 are isostructural with the chlorides solvated with H20 and since the emission spectra are essentially identical, Freeman et al believe that the variations in lifetime are not brought about by changes in the radiative-transition probabilities, but are a consequence only of changes in radiationless quenching efficiencies. They speculate that the decreased efficiency upon substitution of D20 for H20 must be related to the large changes in vibrational frequencies associated with substitution of the H atoms by the D atoms. 

The rare earth chlorides can be separated through sublimation but a very high temperature and good vacuum are required. Recently [46] Eu2+ has been obtained pure by the distillation of its halides using the fact that Eu2+-halides are less volatile than the halides of trivalent rare earths. Sm, Eu and Yb oxides can be reduced to the divalent state by carbon and volatilized selectively from a mixture with other rare earth oxides [47]. 

Table 26. M—N stretching vibrations (cmr1) in rare earth chloride complexes of 2,2 -dipyridyl and 1,10-phenanthroline [369]...

Borohydride.—By reacting anhydrous rare earth chlorides with lithium borohydride (LiBIL) in THF, their chloroborohydrides (eq. 21) can be isolated [264—266]. In the case of europium no borohydride was... 

Until 1964, monazite, a thorium-rare-earth phosphate, REPO4TI13 (P04)4, was the main source for the rare-earth elements. Australia, India, Brazil. Malaysia, and the United Slates are active sources. India and Brazil supply a mixed rare-earth chloride compound after thorium is removed chemically from monazite. Bastnasite, a rare-earth fluocarbonate mineral REFCO3. is a primary source for light rare earths. From 1965 to about 1985. an open-pit resource at Mountain Pass, California, has furnished about two-thirds of world requirements for rare-earth oxides. In the early... 

Mischmetal is produced commercially by electrolysis, The usual starting ingredient is the dehydrated rare earth chloride produced from monazite or bastnasite. The mixed rare earth chloride is fused in an iron, graphite, or ceramic crucible with the aid of electrolyte mixtures made up of potassium, barium, sodium, or calcium chlorides. Carbon anodes are immersed in the molten salt. As direct current flows through the cell, molten mischmetal huilcls up in the bottom of the crucible. This method is also used to prepare lanthanum and cerium metals. 

Osmotic coefficients for KC1 and CaCh were obtained from Appendix 4 of G. N. Lewis, M. Randall, K. S. Pitzer, and L. Brewer, Thermodynamics, Second Edition, McGraw-Hill Book Company, New York, 1961. Values for LaCl3 were obtained from F. H. Spedding, H. O. Weber, V. W. Saeger, H. H. Petheram, J. A. Rard, and A. Habenschuss, Isopiestic Determination of the Activity Coefficients of Some Aqueous Rare Earth Electrolyte Solutions at 25 °C 1. The Rare Earth Chlorides , J. Chem. Eng. Data, 21, 341-360 (1976). 

Manipulation. A concentrated solution of the anhydrous rare earth chloride J in ethyl alcohol (20 to 30 g. chloroform per 100 ml. absolute ethanol) is electrolyzed using a 110-volt direct current with the cell in series with a variable resistance. The current density should not exceed 0.05 to Fig. i.—Ceil for 0.1 amp. per square centimeter in order to eaXamargam8.rare Prevent dispersion of the mercury. The solution is electrolyzed for 15 to 40 hours. Under these conditions, a liquid to pasty amalgam is obtained containing 1 to 3 per cent of rare earth metal by weight. Results of typical runs are given in the accompanying table. 

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