Obtaining Metals

Refined metals, as traded on the open market, vary considerably in composition. However, there are strict specifications for certain impurity elements for a number of metals. The degree of purity of common industrial metals obtained from modem metallurgical practices is shown in Table 2 (3). 

The metal obtained by this process contains less iron and oxygen than that from the chrome alum electrolyte. The gas content is 0.02 wt % O, 0.0025 wt % N, and 0.009 wt % H. If desired, the hydrogen content can be lowered still further by a dehydrogenation treatment. 

Purification. The metal obtained from both electrolytic processes contains considerable oxygen, which is beheved to cause brittieness at room temperature. For most purposes the metal as plated is satisfactory. However, if ductile metal is desired, the oxygen can be removed by hydrogen reduction, the iodide process, calcium refining, or melting ia a vacuum ia the presence of a small amount of carbon. 

In the calcium refining process, the chromium reacts with calcium vapor at about 1000°C ia a titanium-lined bomb, which is first evacuated and then heated to the proper temperature. A pressure of about 2.7 Pa (20 p.m Hg) is maintained during heating until the calcium vapor reaches the cold end of the bomb and condenses. This allows the calcium vapor to pass up through the chromium metal where it reacts with the oxygen. Metal obtained by this process contains 0.027 wt % oxygen, 0.0018 wt % nitrogen, 0.008 wt % carbon, 0.012 wt % sulfur, and 0.015 wt % iron. 

The anode residues must be chemically processed to recover the plutonium remaining in the residues. This may amount to about 10% of the feed mass if delta alloy is the feed metal. Either aqueous or pyrochemical processes may be used for anode recovery. One pyrochemical process used for recovery utilizes oxidation of the plutonium with zinc chloride to form plutonium chloride salt, followed by calcium reduction of the PUCI3 contained in the salt phase to produce pure plutonium metal (the impurities follow the zinc metal obtained from the oxidation reaction and are discarded to waste). Impurities more stable than calcium chloride remain in the salt phase and are also... 

Figure 20-20 shows in schematic fashion some of the alternative paths leading from ores to pure metals. These paths include four general processes of which the essential chemical process is reduction to yield the neutral metal. First is separation. Generally, a metal ore obtained from a mine contains a particular compound of some desired metal mixed with various other materials. The mineral must be separated from these other contaminants. Separation often is followed by conversion, in which the mineral is treated chemically to convert it into a form that can be easily reduced. The third step is reduction. After a suitable compound has been obtained, it is reduced to free metal by chemical reaction with a reducing agent or by electrolysis. The metal obtained by reduction often contains small amounts of impurities, so the final step is refining to purify the metal. 

The use of adatoms of foreign metals obtained by imderpotential deposition on the platinum surface is another convenient method for investigating the effect of a promoter on the electrocatalytic properties of platinum. However, the effect of adatoms in this case has been shown to be not as effective for electrooxidation of methanol as for the oxidation of other organic molecules such as formic acid adatoms of tin, however, showed a positive effect on the rate of methanol oxidation. ... 

Solid metals obtained upon solidification of the molten metal exhibit grain structure. They consist of fine crystallites randomly oriented in space. The size of the individual crystallites (grains) is between 10 m (fine-grained structure) and 10 m (coarse-grained structure). The crystal stracture of the individual grains as a rule is not ideal. It contains various types of defects vacant sites, interstitial atoms or ions, and dislocations (lattice shearing or bending). Microcracks sometimes evolve in the zones between crystallites. 

There are little data available. The only piece of information consists in rhodium being obtained by the reduction of its derivatives by hydrogen. The metal obtained occludes large quantities of hydrogen. If it is desorbed from hot rhodium, it combusts in air. Thus, the treatment has to be carried out in inert gas. Rhodium is inert, not even fluorine reacts with it. It occludes oxygen, but only reacts slowly when it is hot. It reacts with halogens at very high temperatures. 

Fig. 7.25 Mossbauer absorption spectra of Zn metal obtained at 4.2 K and at two different pressures. The source is Ga/Cu (from [75])...

In practice, the production of vanadium by aluminothermic reduction is also governed by some other considerations. The reduction has to be carried out under an inert atmosphere (helium or argon) to avoid nitrogen pick-up from the air by vanadium metal. The composition of the oxide-aluminum charge has to be so chosen that the thermit (metal obtained by aluminothermic reduction) contains between 11 and 19% aluminum. This is necessary for the subsequent refining step in the vanadium metal production flowsheet. Pure vanadium pentoxide and pure aluminum are used as the starting materials, and the reduction is conducted in a closed steel bomb as shown in Figure 4.17 (C). 

Reduction of the fluoride Generally, Ca with RF3 is heated up to 1450°C in a Ta crucible. After cooling, the slag and the reduced metal are easily separated. The metal obtained contains Ca, some fluoride and Ta, which can be removed by vacuum melting (for La, Ce, Pr, Nd) or by vacuum melting plus distillation (Gd, Tb, Dy, Ho, Er, Lu, Sc, Y). Especially pure Ca must be used, such as triple-distilled Ca further re-distilled under low He pressure and handled in He-filled glove boxes. 

Whether the reuse of the metals obtained from incineration as a preservative, or some form of permanent immobilization is preferable requires careful thought. Low-temperature pyrolysis has been suggested as an alternative to incineration, since this would be expected to lead to lower losses of metals (Helsen elal., 1998). 

Elemental composition Pd 86.93%. O 13.07%. The oxide may be identified by x-ray diffraction. The oxide readily can be reduced with hydrogen and the water formed can be measured by gravitmetry or other wet methods. Also, palladium metal obtained from reduction of the oxide may be digested in aqua... 

Heap (dump) acid leaching of copper sulfide ores is possible with the aid of microbial oxidation. Not all copper minerals are sulfidic, however— malachite, azurite, and chrysocolla are basic copper carbonates—and sulfuric acid heap leaching of low-grade copper carbonate ores can give solutions from which the Cu2+ ion can be separated by solvent extraction (Section 17.3) and copper metal obtained by electrowinning. 

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