Beryllium Separation

Nearly a century after Wohler and Bussy liberated beryllium, Alfred Stock and Hans Goldschmidt devised the first commercial process, in which a mixture of the fluorides of beryllium and barium is electrolyzed. The molten beryllium separates out at the water-cooled iron cathode (24). 

Separates iron, beryllium and aluminum as follows The nearly neutral HCl solution is precipitated by cold KOH and digested in excess until the separated Fe-(OH)s has a clear brown color. The fluid is then diluted with water and boiled fifteen minutes. All beryllium separates out carrying some iron. Aluminum is determined in filtrate. Beryllium precipitate is ignited, dissolved and retreated to remove iron. 

Inclusion compounds of the Cg aromatic compounds with tris((9-phenylenedioxy)cyclotriphosphazene have been used to separate the individual isomers (43—47). The Schardinger dextrins, such as alpha-cyclodextrin, beta-dextrin, and gamma-dextrin are used for clathration alpha-dextrin is particularly useful for recovering PX from a Cg aromatic mixture (48,49). PyromeUitic dianhydride (50) and beryllium oxybenzoate (51) also form complexes, and procedures for separations were developed. 

Other fluorinated derivatives of acetylacetone are trifluoroacetylacetone (CF3COCH2COCH3) and hexafluoroacetylacetone (CF3COCH2COCF3), which form stable volatile chelates with aluminium, beryllium, chromium(III) and a number of other metal ions. These reagents have consequently been used for the solvent extraction of such metal ions, with subsequent separation and analysis by gas chromatography [see Section 9.2(2)]. 

The number of reported applications to analytical determinations at the trace level appear to be few, probably the best known being the determination of beryllium in various samples. The method generally involves the formation of the volatile beryllium trifluoroacetylacetonate chelate, its solvent extraction into benzene with subsequent separation and analysis by gas chromatography..61... 

Discussion. Some of the details of this method have already been given in Section 11.11(C), This procedure separates aluminium from beryllium, the alkaline earths, magnesium, and phosphate. For the gravimetric determination a 2 per cent or 5 per cent solution of oxine in 2M acetic add may be used 1 mL of the latter solution is suffident to predpitate 3 mg of aluminium. For practice in this determination, use about 0.40 g, accurately weighed, of aluminium ammonium sulphate. Dissolve it in 100 mL of water, heat to 70-80 °C, add the appropriate volume of the oxine reagent, and (if a precipitate has not already formed) slowly introduce 2M ammonium acetate solution until a precipitate just appears, heat to boiling, and then add 25 mL of 2M ammonium acetate solution dropwise and with constant stirring (to ensure complete predpitation). 

Beryllium is sometimes precipitated together with aluminium hydroxide, which it resembles in many respects. Separation from aluminium (and also from iron) may be effected by means of oxine. An acetic (ethanoic) acid solution containing ammonium acetate is used the aluminium and iron are precipitated as oxinates, and the beryllium in the filtrate is then precipitated with ammonia solution. Phosphate must be absent in the initial precipitation of beryllium and aluminium hydroxides. 

Although the formula for beryllium chloride is BeCl2, the compound exists in chains in the solid state. The bonding is covalent, and the environment around each Be is essentially tetrahedral with each Cl bridging between two Be atoms separated by 263 pm. 

The structure of dimethylberyllium is similar to that of trimethylaluminum except for the fact that the beryllium compound forms chains, whereas the aluminum compound forms dimers. Dimethylberyllium has the structure shown in Figure 12.3. The bridges involve an orbital on the methyl groups overlapping an orbital (probably best regarded as sp3) on the beryllium atoms to give two-electron three-center bonds. Note, however, that the bond angle Be-C-Be is unusually small. Because beryllium is a Lewis acid, the polymeric [Be(CH3)2] is separated when a Lewis base is added and adducts form. For example, with phosphine the reaction is... 

Other methods reported for the determination of beryllium include UV-visible spectrophotometry [80,81,83], gas chromatography (GC) [82], flame atomic absorption spectrometry (AAS) [84-88] and graphite furnace (GF) AAS [89-96]. The ligand acetylacetone (acac) reacts with beryllium to form a beryllium-acac complex, and has been extensively used as an extracting reagent of beryllium. Indeed, the solvent extraction of beryllium as the acety-lacetonate complex in the presence of EDTA has been used as a pretreatment method prior to atomic absorption spectrometry [85-87]. Less than 1 p,g of beryllium can be separated from milligram levels of iron, aluminium, chromium, zinc, copper, manganese, silver, selenium, and uranium by this method. See also Sect. 5.74.9. 

Copaux-Kawecki An improved version of the Copaux process for extracting beryllium from beryl, which permits recovery of the fluorine. Addition of ferric sulfate to the dilute sodium fluoride solution remaining after the separation of the beryllium hydroxide precipitates sodium tetrafluoroferrate, which is then used in place of sodium fluorosilicate. 

For the elucidation of chemical reaction mechanisms, in-situ NMR spectroscopy is an established technique. For investigations at high pressure either sample tubes from sapphire [3] or metallic reactors [4] permitting high pressures and elevated temperatures are used. The latter represent autoclaves, typically machined from copper-beryllium or titanium-aluminum alloys. An earlier version thereof employs separate torus-shaped coils that are imbedded into these reactors permitting in-situ probing of the reactions within their interior. However, in this case certain drawbacks of this concept limit the filling factor of such NMR probes consequently, their sensitivity is relatively low, and so is their resolution. As a superior alternative, the metallic reactor itself may function as the resonator of the NMR probe, in which case no additional coils are required. In this way gas/liquid reactions or reactions within supercritical fluids can be studied... 

For in situ x-ray diffraction measurements, the basic construction of an electrochemical cell is a cell-type enclosure of an airtight stainless steel body. A beryllium window, which has a good x-ray transmission profile, is fixed on an opening in the cell. The cathode material can be deposited directly on the beryllium window, itself acting as a positive-electrode contact. A glass fiber separator soaked in liquid electrolyte is then positioned in contact with the cathode followed by a metal anode (3). A number of variations and improvements have been introduced to protect the beryllium window, which is subject to corrosion when the high-voltage cathode is in direct contact with it. 

Metallic beryllium is produced by reduction of beryllium halide with sodium, potassium or magnesium. Commercially, it is obtained primarily from its ore, beryl. Beryllium oxide is separated from silica and alumina in ore by melting the ore, quenching the solid solution, and solubilizing in sulfuric acid at high temperatures and pressure. Silica and alumina are removed by pH adjustment. Beryllium is converted to its hydroxide. Alternatively, beryl is roasted with complex fluoride. The products are dissolved in water and then pH is adjusted to produce beryllium hydroxide. 

Insoluble silica residues are removed by filtration. The solution now contains beryllium, iron, yttrium, and the rare earths. The solution is treated with oxalic acid to precipitate yttrium and the rare earths. The precipitate is calcined at 800°C to form rare earth oxides. The oxide mixture is dissolved in an acid from which yttrium and the rare earths are separated by the ion-exchange as above. Caustic fusion may be carried out instead of acid digestion to open the ore. Under this condition sihca converts to sodium sihcate and is leached with water. The insoluble residue containing rare earths and yttrium is dissolved in an acid. The acid solution is fed to an ion exchange system for separating thuhum from other rare earths. 

---