Chromium-alum electrolysis

Finally, chromium metal can be obtained by electrowinning from chromium-rich liquors by two electrochemical processes chromium-alum electrolysis and chromic acid electrolysis. In chromium-alum electrolysis, the chromium-rich liquor is obtained by leaching high-carbon ferrochrome with recycled spent catholyte containing chromium alum [(NHJCr(S0J.12H30] and makeup sulfuric acid. It contains ammonium chromium alum. In chromic acid electrolysis, chromium trioxide is dissolved in deionized water acidified with sulfuric acid. The performance of each electrowinning process is presented in Table 4.85. 

Cowper-Coles found that a soln. of 100 parts of chrome-alum in 100 parts of water with 12 parts of barium sulphate does not yield a deposit of chromium metal on electrolysis. E. Placet found that when a soln. of chrome-alum and an alkali sulphate acidified with sulphuric acid, is electrolyzed, chromium is deposited at the cathode as a hard, bluish-white, lustrous metal, which, under certain conditions, crystallizes in groups resembling the branching of firs. Other metals and alloys— bronze, copper, iron, brass, etc.—may be plated with chromium, and a surface can be obtained to resemble oxidized silver. E. Placet and J. Bonnet have a number of patents on this subject. 

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