Amalgams rare earth

An alternative to solve the diffusion problem is to use very fine Ln powders. The finest powders are prepared chemically by decomposing a relatively unstable Ln compound whose second component evaporates easily. Appropriate compounds are the amalgams and the hydrides. Rare earth amalgams are synthesized by heating metal turnings with mercury at 320°C in a sealed pyrex... 

The monazite sand is heated with sulfuric acid at about 120 to 170°C. An exothermic reaction ensues raising the temperature to above 200°C. Samarium and other rare earths are converted to their water-soluble sulfates. The residue is extracted with water and the solution is treated with sodium pyrophosphate to precipitate thorium. After removing thorium, the solution is treated with sodium sulfate to precipitate rare earths as their double sulfates, that is, rare earth sulfates-sodium sulfate. The double sulfates are heated with sodium hydroxide to convert them into rare earth hydroxides. The hydroxides are treated with hydrochloric or nitric acid to solubihze all rare earths except cerium. The insoluble cerium(IV) hydroxide is filtered. Lanthanum and other rare earths are then separated by fractional crystallization after converting them to double salts with ammonium or magnesium nitrate. The samarium—europium fraction is converted to acetates and reduced with sodium amalgam to low valence states. The reduced metals are extracted with dilute acid. As mentioned above, this fractional crystallization process is very tedious, time-consuming, and currently rare earths are separated by relatively easier methods based on ion exchange and solvent extraction. 

Various processes separate rare earths from other metal salts. These processes also separate rare earths into specific subgroups. The methods are based on fractional precipitation, selective extraction by nonaqueous solvents, or selective ion exchange. Separation of individual rare earths is the most important step in recovery. Separation may be achieved by ion exchange and solvent extraction techniques. Also, ytterbium may be separated from a mixture of heavy rare earths by reduction with sodium amalgam. In this method, a buffered acidic solution of trivalent heavy rare earths is treated with molten sodium mercury alloy. Ybs+ is reduced and dissolved in the molten alloy. The alloy is treated with hydrochloric acid, after which ytterbium is extracted into the solution. The metal is precipitated as oxalate from solution. 

The use of lithium amalgam electrodes allows better control of electrode potential than the potassium amalgam electrode. Separations of Sm from Gd, Eu from Sm, Sm from Eu and of Yb from heavy rare earths have been successfully carried out by Onstott [135—137]. 

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. 

Concentration of Amalgams. Rare earth metal amalgams may be concentrated with respect to their rare metal content by removal of mercury through distillation under reduced pressure. An all-glass distilling apparatus should be used for this purpose, since cork or rubber stoppers will not withstand the temperature required to eliminate much of the mercury. The apparatus depicted in Fig. 2 has been found satisfactory for this purpose. 

As the mercury is removed, the liquid or pasty amalgam changes gradually to a grayish-black, powdery mass containing approximately 15 per cent of rare earth metal by... 

These concentrated amalgams are very pyrophoric and on contact with air or moisture take fire or glow. By heating to temperatures around 1000°C. in a vacuum furnace the remainder of the mercury may be removed to give the rare earth metals in very pure form.26,20... 

Acetic acid-acetic anhydride, 85 Alkali azides, 79 Alkaline earth azides, 79 Alumino-oxalates, 36 Amalgams, 5 concentration of, 17 preparation of, 6 rare earth metal, 15 Ammonium nitrourethane, 69 Ammonium perrhenate, 177 Antimony oxyiodide, 105 Antimony triiodide, 104 Aquopentammino cobalti bromide, 187, 188... 

Rare earth chlorides, anhydrous, 28 Rare earth metals, 18 amalgams, concentration of, 17 Rhenium, metallic, 175 by reduction of ammonium per-rhenate, 177... 

Cement, laboratory, 1 189 Cerite, extraction of, 2 44 Cerium, phosphor containing strontium sulfide and, 3 23 separation of, from rare earth mixtures, 2 43, 47, 48 test for, 2 50 Cerium amalgam, 1 15 Cerium-group earths, separation of, from yttrium earths by doublesulfate method, 2 44, 46 Cerium (III) magnesium nitrate, 2Ce(N03)s-3Mg(N03)2-24H,0, separation of praseodymium from lanthanum by, 2 57 Cerium(III) nitrate, 2 51 Cerium (IV) nitrate, basic, 2 49 Cesium, cesium azide for preparation of, 1 79... 

The classical chemical methods to separate lanthanoids were based upon the redox behavior of Ce, Sm, Eu, and Yb , Other classical methods (fractional crystallization) are essentially physical processes. Cerium is oxidized to the 4-I- state and separated from the 3+ rare earths by solvent extraction, iodate precipitation, or selective hydrolysis or precipitation of basic Ce(IV) compounds in weakly acidic solution. Europium is reduced and maintained in H2O as Eu " by Zn amalgam and precipitated as EUSO4. Sm and Yb are extracted from H2O by reduction into dilute Na or Li amalgam. 

---