Extraction of Nickel

The nickel ore is extracted from mines. It is properly crushed and cleaned. The cleaned ore is concentrated by beneficiation. The concentrated ore is roasted in reverberatory furnace in presence of sufficient air supply. During the roasting process, sulphur and arsenic are removed. The nickel sulphide is converted to nickel oxide. The nickel oxide is reduced by passing of carbon monoxide through the nickel oxide concentrate. The nickel oxide is heated with coke and coal. The oxygen is removed by formation of carbon dioxide and carbon monoxide. Crude nickel is produced and removed from the furnace. The crude nickel has impurities like iron, cobalt and copper. The impurities are removed by electro refining. The electrolyte used for electro refining is mixture of nickel sulphate and nickel chloride. The presence of nickel chloride facilitates in the dissolution of crude nickel and permits higher current density. Impurities pass into the solution along with the nickel metal. The electrolyte cell is divided into two compartments by a porous diaphragm. In the anode side, air is pumped into the solution. Slowly, iron is oxidized and iron hydroxide is precipitated. The impurities of iron hydroxide are separated from the solution. The remaining electrolyte is treated with fluorine gas and nickel carbonate. Supply of oxygen is continued. Cobalt is slowly oxidized. During electrolysis, precipitation of cobalt hydroxide takes place. It is separated for further use. Till now some amount of copper remain as impurities. Nickel powder is added and electrolysis continues. Copper precipitates and is separated for further use.

Electrorefining of Nickel

Electro-refining of Nickel is carried out in the concrete cell. The cell is constructed in pairs with the center busbar acting as the distributing bar for the cathode in one tank and anode in the other. Anode used in this case is cast from metal that is produced by smelting reduction of nickel sulphide. Cathode is made either of Stainless Steel or Aluminium Sheet. The number of cathodes are less than the number of anodes. When current is passed, nickel dissolves at the anode end and deposited at the cathode end. Another method of extraction of nickel is by electrolysing the concentrated ore. The temperature of the electrolysis is around 55'C. The electrolyte is mixture of nickel chloride and nickel sulphate. The anode is of crude nickel and the cathode is aluminium. Nickel hydroxide is added to the electrolyte during electrolysis.

Electroplating of Nickel

Nickel coatings are widely used to protect anticks of steel. Nickel provides protection against water, alkalides, alkaline salt solutions and many organic chemicals. Steel equipments used in food processing industry is plated with nickel to protect the food product from roating and toxic contamination. Nickel is electroplated on motorparts and cycleparts. The various electrolyte baths commonly used are Walts solution, Allchloride solution, Bright Nickel Solution and Sulphamate Solution. The Walts solution uses nickel sulphate, nickel chloride and boric acid. When the steel equipment is dipped into the electroplating solution and direct current is passed into the solution, nickel particles are deposited on the surface of the steel equipment. Nickel is deposited on the steel which acts as a cathode and nickel rods are used as anode. The nickel sulphate solution helps in dissolution of nickel rods at the anode point. The nickel chloride helps in precipitation of nickel at the cathode end. In this method, the electroplating is dull white in color. It is strong, hard and thick.

It has a longer lifetime to get fine grain plating of nickel particle , nickel chloride with boric chloride is used. The rate of nickel plating is faster and the appearance of the nickel is pleasing. Bright nickel plating method is used for coating of nickel on decorative items. To improve the brightness and to increase the longevity, cobalt is added to the solution. Organic chemicals are added to the solution for further improvement of appearance of the nickel coating. The sulphamate solution is used for chemical plating. In this case, the equipment is immersed in the solution for certain period. Slowly nickel powders are mixed into the solution. After sometime, nickel particles are deposited on the surface of the equipment.