Recovery of phosphates from elemental phosphorus bearing wastes

A process for converting aqueous elemental phosphorus-containing materials into orthophosphate containing intermediate products suitable for subsequent reaction with ammonia to produce nitrogen and phosphorus-containing fertilizer products, which process comprises the steps of:

• (a) introducing into reactor means predetermined quantities of nitric acid, sulfuric acid, and aqueous elemental phosphorus-containing residue, said aqueous elemental phosphorus-containing residue containing from about 2 to about 20 percent by weight elemental phosphorus;
• said nitric acid ranging from about 40 to about 70 weight percent concentration and of quantity to provide from about 5 to about 150 percent excess nitric acid relative to the stoichiometry of the chemical equation:
• 20HNO.sub.3 +3P.sub.4 +8H.sub.2 O.fwdarw.12H.sub.3 PO.sub.4 +20NO;
• said sulfuric acid ranging from about 93 percent to about 98 percent by weight and of quantity, relative to the proportion of said nitric acid, to provide weight ratios, H.sub.2 SO.sub.4 :HNO.sub.3 ranging from about 1 to about 3;
• (b) maintaining the temperature in said reactor means at about the boiling point of the material maintained therein, for a period of time sufficient to oxidize substantial amounts of the elemental phosphorus values thereof;
• (c) adding gaseous oxidizing media to said reactor means in quantity sufficient to convert substantial amounts of the nitric oxide formed in step (b), supra, to nitrogen dioxide;
• (d) removing from said reactor means said nitrogen dioxide and introducing same and water into scrubber means;
• (e) removing from said scrubber means in step (d), supra, the resulting dilute nitric acid;
• and
• (f) recovering from said reactor means as intermediate product the resulting oxidized liquid from step (b), supra;
• said process being characterized by the fact that the elemental phosphorus content of the oxidized intermediate product in step (b), supra, is less than about 2 ppm and the orthophosphate portion of the total phosphorus content thereof is greater than about 90 percent.