The chromium metal can be manufacture either by alumino thermic process or by electrochemical process . The metal produced by the former process are less pure and has limited application than that produced by the electrchemical. route .However, the electrochemical process is power intensive and therefore proper consideration should be given in selecting the location of the plant for adequte supply of power at less price.

PROCESS

Chromium metal is produced by the electrolysis of commercial grade chromic acid. The steps involved in the process are :

a)Preparation of the electrolytic bath solution -The chromic acid is mixed thoroughly with demineralised water in the mixing tank to form a uniform solution having concentration of 250 gm/litre. Proper protection should be taken since chromic acid is very much corrosive. Required amount of sulphuric acid is added to the solution so keep the sulphate ion concentration level at 2.5 gm/litre.

b)Electrolysis of Chromic acid Solution - The solution thus prepared is fed to the electrolytic cell. The cells are made of PVCwith FRP lining having Pb-Ag (99:1) alloy anodes and stainless steel cathode. The cathodes are treated separately before putting inside the cell for chromic acid electrolysis. The cell liquid temperature is maintained at around 39oC by circulating cell liquid through titanium heat exchanger. The cell voltage. cathode current density are maintained at the appropriated value.

After 24 hrs. of cell operation the cathodes are taken out of the cell, washed with the demineralised water. The deposits of chromium from the cathode are peeled off followed by treating with nitric acid to remove the adherent impurities, washing with water and finally drying. The dried chromium flakes are sold if required or it is ground in a stainless steel ball mill to desired particle size.