GB1109624A - Electrolytic purification of chromate liquors - Google Patents

Abstract

<PICT:1109624/C6-C7/1> A method of electrolytically reducing the halide ion concentration present in a chromate containing liqour comprises feeding said liquor to the anode compartment of an electrolytic cell having anode and cathode compartments separated by a diaphragm, feeding an electrolyte to said cathode compartment and effecting a discharge of halogen gas by electrolysis, the anode liquor withdrawn from the cell thus having a reduced halogen content. The chromate containing liquor may be formed by roasting chrome ore, lime and sodium carbonate at elevated temperature to produce a roasted mixture, leaching to produce a chromate containing liqour, which is then treated with CO2 or H2SO4 to produce a liquor containing sodium dichromate. A side feed of this liquor is then treated as above to reduce the halide content therein prior to re-joining the main feed which is concentrated and Na2Cr2O7.2H2O is crystallized therefrom. The pH of the liquor entering the cell is preferably below 7, e.g. between 5 and 6. The anode may be of platinized titanium and the cathode of steel. The diaphragm may be formed by a semi-permeable membrane, thus preventing passage of CrO3 ions into the cathode compartment, and the electrolyte used in said compartment may be NaOH. The cell comprising walls top and bottom members may be formed in two identical halves about a vertical plane, the membrane, 15, being located between the two cell halves, Figs. 4 and 5 (not shown).