Hexavalent chromium removal from chlorate - by reduction with sulphide to the trivalent state

摘要

Hexavalent Cr is economically removed from concentrated aq alkali metal chlorate solns, esp. alkali-metal dichromates from chlorate solns made by electrolysis of salt solns. whereby cathodic alkali metal hydroxide reacts with anodic Cl2 and dichromate is added to inhibit the oxidation of the Fe cathode, by addn of 3(10-20) mole soluble sulphide, 3(10-13) mole Na2S or 12-13 mole Na2S2 per mole hexavalent Cr-cpd.. Reaction takes place at 40-80 (65) degrees C. The pH is then adjusted to 5 with H2SO4 until Cr(OH)3 ppts. This is pref. removed at pH 5-7. Hypochlorites are also removed in the process.