Oxidation-reduction process for enhancing the color of and stabilizing wet process phosphoric acid

  • US 4,808,391 A
  • Filed: 05/01/1987
  • Issued: 02/28/1989
  • Est. Priority Date: 05/01/1987
  • Status: Expired due to Term
First Claim
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1. A process for preparing color-enhanced and stabilized wet-process phosphoric acid comprising the steps of:

  • providing a quantity of black-colored wet-process phosphoric acid which has a P2 O5 concentration of from about 58-72%, and contains incidental carbonaceous and metallic impurities therein;

    subjecting said quantity of phosphoric acid to an initial oxidation step in order to produce a decarbonized, oxidized acid, said initial oxidation step including the steps of heating the acid to a temperature of from about 400 to 525°

    F., agitating the acid, and adding an oxidizing agent to the acid,said initial oxidation step being carried out until the acid changes color from black and when diluted 1;

    100 by weight with deionized water exhibits an EMF of greater than about 700 mv, as compared with a standard solution of 0.01M potassium dichromate having an EMF of 600 mv;

    thereafter subjecting the initially oxidized acid to a secondary reduction step for reducing the dark-colored oxidized metal complexes in the acid and producing a stabilized green color in the acid,said secondary reduction step being carried out until the acid again changes color and when diluted 1;

    100 by weight with deionized water exhibits an EMF of less than about 700 mv, as compared with said standard solution.

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