Abstract: A process for producing ammonium phosphate that is substantially free of arsenic which comprises:(a) reacting crude phosphoric acid containing dissolved arsenic having a +5 valence state with ammonia and arsenic-reducing agent in sufficient proportions to form an ammonium phosphate solution and to reduce the arsenic from the +5 valence state;(b) forming ammonium phosphate crystals from said solution, leaving a mother liquor that contains substantially all of said arsenic; and(c) recovering said ammonium phosphate crystals that are substantially free of arsenic from said mother liquor.

Abstract: Diluted sulfuric acid used in the production of wet process phosphoric acid is obtained by the admixing of gypsum-containing waste water with concentrated sulfuric acid and subsequently cooling in a liquid-to-liquid heat exchanger. By maintaining the concentration of the diluted acid at from about 65 to 80% H.sub.2 SO.sub.4, harmful formation of scale in the heat exchanger is prevented. The process permits the recovery of P.sub.2 O.sub.5 values from gypsum-containing waste waters and does not require expensive dilution tanks or flash coolers.