Oxidation-reduction process for enhancing the color of and stabilizing wet process phosphoric acid
DCFirst Claim
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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Abstract
A two-stage oxidation/reduction process for preparing commercially valuable, color enhanced and stabilized low viscosity wet process phosphoric acid is provided which yields improved acid that can be concentrated to superphosphoric acid and/or converted to high quality liquid fertilizer by reaction with ammonia, all without reversion to black color or excessive sludge formation in the fertilizer. The preferred process involves initially oxidizing a starting black acid having a 58-72% P2 O5 concentration by addition of an oxidizing agent such as NH4 NO3 with heating and agitation until the oxidized acid exhibits an EMF of greater than about 700 mv as compared with a 600 mv standard; the oxidized acid is then subjected to a reduction step to lower the valence of metallic impurities, by aging and/or adding reducing agents such as ferrous iron compounds to the acid. The reduction is carried out until the EMF of the product is less than 700 mv relative to the standard and a stabilized green color is produced in the acid. The final acid product may be concentrated if in the form of orthophosphoric acid, or cooled and directly reacted with ammonia if the product is SPA.
15 Citations
22 Claims
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1. A process for preparing color-enhanced and stabilized wet-process phosphoric acid comprising the steps of:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A process for treating black colored wet-process phosphoric acid comprising the steps of:
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providing a quantity of the black wet-process phosphoric acid having a P2 O5 concentration of from about 58-72%, and incidental carbonaceous and metallic impurities therein; subjecting said quantity of phosphoric acid to an 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 oxidation step being carried out until the acid changes color from black and assumes a dark greenish-brown to purple color and the acid 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. - View Dependent Claims (21, 22)
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Specification