Process for the preparation of chromic acid

Details Process for the preparation of chromic acid Process for the preparation of chromic acid

C - Chemistry, Metallurgy

25

B

23/233, 204/63,

C25B 1/22 (2006.01) C01G 37/033 (2006.01) C25C 1/10 (2006.01)

Patent

CA 2032369

Process for the preparation of chromic acid A B S T R A C T A process for the production of chromic acid, comprising a) dissolving ferrochrome in sulphuric acid, optionally with the addition of catholyte and/or anolyte overflow from the electrolysis, b) removing undissolved constituents by filtration, c) adding a reducing agent in a quantity more than equivalent to the quantity of iron(III) and chromium(IV) in the solution, d) precipitating chromium(III) hydroxide by raising the pH to about 4-6 by the addition of a base while maintaining the reducing conditions in the solution, e) separating the precipitated chromium hydroxide while maintaining the reducing conditions, Le A 27 320 f) working up the aqueous solution containing iron by oxidation; precipitating iron(III) hydroxide or iron(III) oxide and optionally isolating the sulphate in the solution as sodium sulphate, ammonium sulphate or calcium sulphate, g) dissolving the separated chromium hydroxide in chromic acid and optionally sulphuric acid in such a manner that either a single solution in chromic acid is produced or two solutions are produced, one in chromic acid and another in sulphuric acid, h) separating the solution(s) from undissolved constituents and i) employing the solution of chromium hydroxide in chromic acid as anolyte in the electrolytic production of chromic acid in an electrolytic cell divided by a membrane, and either using the same solution as catholyte in the above mentioned electrolytic cell divided by a membrane or using the solution of chromium Le A 27 320 hydroxide in sulphuric acid as catholyte in the above mentioned electrolytic cell divided by a membrane, hydrogen and/or metallic chromium being deposited electrolytically at the cathode and/or chromium(II) ions being produced electrolyti- cally. Le A 27 320

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