Electrorefining: Principle, Process and Exam-Oriented Notes

 Electrorefining: Principle, Process and Exam-Oriented Notes

By Home Academy

Electrorefining is an important electrolytic process used in metallurgy to obtain metals in a highly pure form. It is widely used for the purification of metals such as copper, silver, gold, nickel, zinc and lead. From an examination point of view, electrorefining is frequently asked in chemistry, metallurgy, and general science sections of SSC, JKSSB, JE, and other competitive exams.

Electrorefining is defined as the process of purification of an impure metal by using electrolysis. In this method, the impure metal acts as the anode, a thin sheet of pure metal acts as the cathode, and a soluble salt of the metal is used as the electrolyte. When electric current is passed through the electrolytic cell, the metal dissolves from the anode and gets deposited in a pure form on the cathode.

The principle of electrorefining is based on the fact that during electrolysis, only the metal ions of the desired metal are discharged at the cathode, while impurities either remain in solution or settle at the bottom of the cell as anode mud. Less reactive impurities do not dissolve, whereas more reactive impurities remain in the electrolyte.

In the electrorefining process of copper, impure copper is used as the anode, a thin sheet of pure copper is used as the cathode, and acidified copper sulphate solution is used as the electrolyte. When current is passed, copper atoms from the anode lose electrons and form Cu²⁺ ions, which move towards the cathode and gain electrons to form pure copper metal. Precious metals like gold and silver present as impurities fall down as anode mud.

Electrorefining helps in achieving very high purity levels, often up to 99.99 per cent. This makes the metal suitable for electrical and electronic applications where high conductivity is required. The method is economical for large-scale purification and allows recovery of valuable by-products from anode mud.

Some important advantages of electrorefining include high purity of metal, recovery of precious metals, and controlled deposition at the cathode. However, it requires continuous electrical energy and is mainly suitable for metals that can form soluble salts.

From an exam perspective, it is important to remember that in electrorefining, the anode is impure, the cathode is pure, and the electrolyte is a soluble salt of the same metal. Anode mud contains insoluble impurities such as gold, silver, platinum and silica, depending on the metal being refined.

Electrorefining should not be confused with electroplating. In electroplating, a thin layer of metal is deposited on an object for protection or decoration, whereas electrorefining is specifically used for purification of metals.

In competitive exams, common questions are asked on the principle, components of the electrolytic cell, role of anode mud, and examples of metals refined by this method. Understanding the copper electrorefining process is especially important, as it is the most frequently asked example.

In conclusion, electrorefining is a crucial metallurgical process that plays a vital role in producing high-purity metals for industrial use. Its clear mechanism, practical importance, and frequent appearance in exams make it a must-study topic for all science and engineering aspirants.

1. Electrorefining is mainly used for the
   A. Extraction of metals from ores
   B. Concentration of ores
   C. Purification of metals
   D. Alloying of metals
   Correct Answer: C

2. In electrorefining, the impure metal is used as the
   A. Cathode
   B. Electrolyte
   C. Anode
   D. Salt bridge
   Correct Answer: C

3. Which of the following acts as the cathode in electrorefining?
   A. Impure metal
   B. Graphite rod
   C. Thin sheet of pure metal
   D. Metal oxide
   Correct Answer: C

4. The electrolyte used in electrorefining is generally
   A. Molten metal
   B. Insoluble salt of the metal
   C. Soluble salt of the same metal
   D. Distilled water
   Correct Answer: C

5. During electrorefining of copper, the electrolyte used is
   A. Copper nitrate solution
   B. Acidified copper sulphate solution
   C. Molten copper sulphate
   D. Sodium sulphate solution
   Correct Answer: B

6. In electrorefining, less reactive impurities generally
   A. Deposit on the cathode
   B. Remain dissolved in electrolyte
   C. Form anode mud
   D. Evaporate
   Correct Answer: C

7. Which of the following metals is commonly purified by electrorefining?
   A. Sodium
   B. Potassium
   C. Copper
   D. Calcium
   Correct Answer: C

8. Anode mud obtained during electrorefining of copper mainly contains
   A. Iron and zinc
   B. Aluminium and magnesium
   C. Gold and silver
   D. Sodium and potassium
   Correct Answer: C

9. The purity of metal obtained by electrorefining can be as high as
   A. 90%
   B. 95%
   C. 98%
   D. 99.99%
   Correct Answer: D

10. Electrorefining differs from electroplating because electrorefining is used for
    A. Decorative coating
    B. Corrosion protection
    C. Increasing thickness of metal
    D. Purification of metals
    Correct Answer: D