Nitric acid acidulation of phosphate rock and pyrolysis of acidulate to produce phosphatic and nitrogen fertilizers

Abstract

A modified method for producing a range of dicalcium phosphate containing phosphatic fertilizers and aqueous calcium nitrate is discussed. The process consists of reacting phosphate rock with nitric acid followed by pyrolysis of the resulting acidulate to produce dicalcium phosphate (CaHPO₄) and to liberate approximately one-half of the initially consumed nitric acid. Recycling of the liberated nitric acid allows production of available phosphate at approximately one-half the acid equivalents consumption normally utilized in wet-process acid production. The calcium nitrate by-product is separated from the phosphatic component of the pyrolyzate by dissolution in water followed by filtration. The initial HNO₃ : CaO acidulation ratio governs the available P₂O₅ content of the phosphatic fertilizer, which may be as high as 47%. The aqueous calcium nitrate stream may be processed to produce a variety of solid or fluid nitrogen fertilizer products. No “throwaway” by-products (other than possibly siliceous gangue) are produced. Estimates are given for raw materials needed and energy cost.