C - Chemistry – Metallurgy – 25 – B
Patent
C - Chemistry, Metallurgy
25
B
362/56, 204/62.5
C25B 1/14 (2006.01) C01B 11/14 (2006.01) C01G 37/02 (2006.01) C25B 1/26 (2006.01) C25B 15/08 (2006.01)
Patent
CA 1124676
ABSTRACT OF THE DISCLOSURE Chromates are removed from aqueous alkali metal chlorate solutions by either of two processes. In the first process, a water-soluble sulfide such as NaHS is added to the chromate-containing chlorate solution, at a temperature of about 40-60°C and at a pH of 7-8, in an amount ranging from 70-200% (and preferably, 100%) of the stoichio- metric value required to react with the chromate; and then a water-soluble ferrous salt (preferably FeSO4) is added in an amount of from 30-100% (preferably about 57%) of the stoi- chiometric amount required; and the pH of the solution is adjusted so that the final pH is in the range of about 1.8 to about 3Ø The soluble sulfide is converted to elemental sulfur and the chromated is converted to an insoluble, tri- valent Cr-containing material, which is subsequently removed from the solution. The low pH of the filtered liquor renders it particularly suitable for use in a chlorine dioxide generator. In the second process, The pH of the chromate- containing chlorate solution is first adjusted to a value within the range of 7-11, and preferably to about 11, and the solution is heated to a temperature of 40-60°C. An "iron mud" is prepared by reacting a ferrous salt, e.g., FeSO4, with sodium hydroxide in ? molar ?proportions of 1 part ferrous salt to 1.5-1.8 parts of NaOH, the amount of ferrous salt employed being from about 3 to about 5 times the stoichiometric amount required to reduce the chromate present in the solution. Then the "iron mud" is added slowly to the chlorate solution with vigorous agitation, and the pH is controlled to a value within the range of 10-12. The insoluble trivalent chromium-containing material so formed is subsequently removed from the solution. This invention is effective in removing chromates from alkali metal chlorate solutions having a NaC1O3 con- centration in the range of 600-750 gpl, at which concen- tration previous processed for the removal of chromates are largely ineffective.
293442
Atkinson Jennifer G.
Kindl Bruno
Gowling Lafleur Henderson Llp
Huron Chemicals Limited
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