The main practical applications of electrolysis are: 1. Extraction of Metals 2. Refining of Metals 3. Production of Chemicals 4. Electroplating 5. Electro-Typing 6. Electro-Forming 7. Electro-Cleaning.
Application # 1. Extraction of Metals:
There are two methods of extraction of metal on the basis of physical states of the ore. In the first method the ore is treated with a strong acid to obtain a salt and solution of such salt is electrolysed to liberate the metal. In the second process the ore is in a molten state and it is electrolysed in a furnace.
(i) Extraction of Zinc:
The zinc ore is treated with sulphuric acid. The zinc sulphate solution which is obtained as a result of it is then electrolyted. In the electrolytic tank, the cathodes are of aluminium and the anodes are of lead. The current density is kept 1000 A/m2 and zinc is deposited on cathode. The energy consumption is about 3000 to 5000 KWH per tonne.
ADVERTISEMENTS:
(ii) Extraction of Aluminium:
The ores of aluminium are bauxite and cryolite. These are treated chemically and reduced to aluminium oxide and then dissolved in fused cryolite and electrolysed in a furnace. Aluminium deposits at the cathode and settles down at the bottom. To keep the electrolyte in a fused state the temperature of the furnace is about 1000°C. The current of about 4000 ampere is needed to complete the process and energy consumed is about 20,000 to 25,000 kWH per tonne.
Application # 2. Refining of Metals:
The main advantages of extraction of a metal by electrolytic processes are that the purity of product obtained is 98 to 99%. Further refining is done by electrolysis. The anode is made of the extracted metal. Pure metal is deposited at the cathode. The electrolyte is made of the metal solution e.g. for copper, it is copper sulphate and for nickel, it is nickel chloride. Energy consumption in copper refining by electrolytic process is 150 to 300 kWH/tonne of refined copper.
The following table gives the information on refining of metals:
Application # 3. Production of Chemicals:
Many chemicals such as caustic soda (NaOH) chlorine gas etc. are manufactured by electrolysis on large scale. Potassium permaganate hydrogen and oxygen etc. are also produced by electrolysis on a large scale.
Application # 4. Electroplating:
This is the process of covering the articles made up of cheap metals by a thin covering of precious metal such as iron with nickel chromium, silver or gold with one or more of the following aim of view:
i. Protection of metals against corrosion.
ADVERTISEMENTS:
ii. Giving shiny appearance to articles.
iii. Giving reflecting properties to reflectors.
iv. Replacing work-out material.
Application # 5. Electro-Typing:
This is a process by which type wood cuts etc. are reproduced in copper by a process of electro-plating. In this process a mould is first made of the type in wax, then it is coated with black lead to give it metallic surface and then it is subjected to the process of electro-deposition. Thus, a film of copper is formed on the prepared surface.
Application # 6. Electro-Forming:
ADVERTISEMENTS:
This is another application of electro-deposition. Reproduction of objects by electro-deposition on some sort of mould or form is known as electro-forming.
In the reproduction of coins, molles, engraving etc. a mould is first made by impressing the object, say, in wax. The surface of the wax, which bears exact impressions of the object, is coated by powdered graphite in order to make it conducting. The mould is then dipped in an electro-forming cell as a cathode. After obtaining coating of desired thickness, the article and the wax core, is melted out of the metal shell.
Application # 7. Electro-Cleaning:
The article to be cleaned of oil and grease is made the cathode and the iron tank or vat filled with an electrolyte solution of the electrolyte and heavy current is passed through the solution. Caustic soda and hydrogen are produced at cathode which removes the grease from the surface of the article. The process is called cathodic cleaning and is applicable to zinc and aluminium. For anodic cleaning, article is made anode.