Which methods are usually employed for purifying the following metals: (i) Nickel (ii) Germanium

Which methods are usually employed for purifying the following metals:
(i) Nickel
(ii) Germanium


2 Answers

Sunil Kumar FP
askIITians Faculty 183 Points
8 years ago
1. Nickel
Purification of nickel oxides to obtain the purest metal is performed via the Mond process, which increases the nickel concentrate to greater than 99.99% purity. This process was patented by L. Mond and has been in industrial use since before the beginning of the 20th century. In the process, nickel is reacted with carbon monoxide at around 40–80 °C to form nickel carbonyl in the presence of a sulfur catalyst. Iron gives iron pentacarbonyl too, but this reaction is slow. If necessary, it may be separated by distillation. Dicobalt octacarbonyl is also formed in this process, but it decomposes to tetracobalt dodecacarbonyl at the reaction temperature to give a non-volatile solid.
Nickel is re-obtained from the nickel carbonyl by one of two processes. It may be passed through a large chamber at high temperatures in which tens of thousands of nickel spheres, called pellets, are constantly stirred. It then decomposes depositing pure nickel onto the nickel spheres. Alternatively, the nickel carbonyl may be decomposed in a smaller chamber at 230 °C to create fine nickel powder. The resultant carbon monoxide is re-circulated and reused through the process. The highly pure nickel produced by this process is known as "carbonyl nickel".

2. Germanium
Ores are treated with strong HCl and the GeCl4 repeatedly distilled to purify. It is then hydrolysed to GeO2 which is reduced by hydrogen to powdered Ge which is then melted at 1100C and cast into ingots.
askIITians Faculty 164 Points
8 years ago
Refinind of Ni by Mond’d Process
This process has three steps:

1. Nickel oxide is reacted with Syngas at 200C to remove oxygen, leaving impure nickel. Impurities include iron and cobalt.NiO (s) + H2(g) → Ni (s) + H2O (g)
2. The impure nickel is reacted with excess carbon monoxide at 5060C to form the gas nickel carbonyl, leaving the impurities as solids.Ni (s) + 4 CO (g) → Ni(CO)4(g)3. The mixture of excess carbon monoxide and nickel carbonyl is heated to 220250C. On heating, nickel tetracarbonyl decomposes to give nickel:Ni(CO)4(g) → Ni (s) + 4 CO (g)

Refining of Germanium is done by zone refining
Meals of very high purity can be obtained by this method by removing an impurity, which shows difference in solubility of the liquid and solid states of the metal. A circular heater is fitted around a rod of impure metal and is slowly moved down the rod. At the heated zone, the rod metls and as the heater passes on, pure metal crystallizes while impurities pass into the adjacent molten part. In this way, the impurities are swept over one end of the rod, which is finally discarded. The heater may have to be moved from one end to the other more than once. Ge, Si and ga used as semiconductors are refined in this manner; gallium-arsenide and indium-antimonide are also zone refined

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