Applications of Electrolysis Electroplating Electroforming Electrorefining

Applications of Electrolysis

Electrolytic Refining of Metals

Electrolytic refining extracts impurities from crude metals. In this process, a block of crude metal is the anode, a diluted salt of the metal is the electrolyte, and pure metal plates are the cathode.

Electrolytic Refining of Copper

For understanding the process of electrolytic refining of metals, we will discuss about an example of electrolytic refining of copper. Copper extracted from its ore, known as blister copper, is 98 to 99 % pure but it can easily be made up to 99.95% pure for electrical application by the process of electrorefining.

In electrolysis, impure copper serves as the anode (positive electrode), copper sulfate acidified with sulfuric acid as the electrolyte, and pure copper plates coated with graphite as the cathode (negative electrode).
Copper sulfate splits into positive copper ions (Cu^{+ +}) and negative sulfate ions (SO₄ ^{− −}). The copper ions move to the negative electrode (cathode), take electrons, and become copper atoms deposited on the cathode’s graphite surface.

The sulfate ions (SO₄ ^{− −}) move to the positive electrode (anode), gain electrons, and form radical SO₄. Since radical SO₄ cannot exist alone, it reacts with the copper anode to form CuSO₄. CuSO₄ then dissolves, splitting into copper ions (Cu^{+ +}) and sulfate ions (SO₄ ^{− −}). The copper ions move to the cathode, gain electrons, and deposit as copper atoms on the cathode’s graphite surface. This transfers copper from the impure anode to the cathode.

The metallic impurities of anode are also merged with SO₄, forming metallic sulfate and dissolve in the electrolyte solution. The impurities like silver and gold, which are not effected by sulfuric acid-copper sulfate solution, will settle down as the anode sludge or mud. At a regular interval of electrolytic refining of copper, the deposited copper is stripped out from the cathode and anode & is replaced by a new block of crude copper.
NB :- In the process of electrolytic refining of metals or simply electro refining, the cathode is coated by graphite so that the chemical deposited, can be easily stripped off. This is one of the very common applications of electrolysis.

Electroplating

The process of electroplating is theoretically same as electrorefining – only difference is that, in place of graphite coated cathode we have to place an object on which the electroplating has to be done. Let’s take an example of brass key which is to be copper-platted by using copper electroplating.

Copper Electroplating

We have already stated that copper sulfate splits into positive copper ion (Cu^{+ +}) and negative sulfate ion (SO₄ ^{− −}) in its solution. For copper electroplating, we use copper sulfate solution as electrolyte, pure copper as anode and an object (a brass key) as cathode. The pure copper rod is connected with positive terminal and the brass key is connected with negative terminal of a battery. While these copper rod and key are immersed into copper-sulfate solution, the copper rod will behave as anode and the key will behave as cathode. As the cathode or the brass key is connected with negative terminal of battery, it will attract the positive cations or Cu^{+ +} ions and on reaching of Cu^{+ +} ions on the surface of the brass key, they will receive electrons from it, become neutral copper atom and are about to be deposited on the surface of the brass key as uniform layer. The sulfate or SO₄ ^{− −} ions move to the anode and extract copper from it into the solution as mentioned in the process of electro-refining. For proper and uniform copper plating, the object (here it is brass key) is being rotated slowly into the solution.

Electroforming

Electroforming is the reproduction of objects by depositing metal onto a mold. First, an impression of the object is taken on wax or similar material. The wax mold is coated with graphite to make it conductive. The mold is then dipped into the electrolyte solution as the cathode. During electrolysis, the metal deposits on the graphite-coated surface. Once a layer of desired thickness is obtained, the article is removed and the wax is melted, leaving a metal shell. Electroforming is commonly used to reproduce gramophone record discs. The original recording is made on a wax record, which is then coated with gold powder to make it conductive. The mold is dipped into a blue vitriol electrolyte with a copper anode, creating a master plate used to stamp many shellac discs.

Video Presentation of Basic Principle of Electrolysis