METHOD OF PREPARING COMPLEX FERTILIZERS Russian patent published in 2001 - IPC

FIELD: complex treatment of phosphate ores by nitric acid method. SUBSTANCE: method comprises decomposing phosphorite stock with nitric acid, recovering calcium nitrate by crystallization, neutralizing nitrogen-phosphate extract with ammonia, vaporization, mixing with ammonium nitrate melt and potassium salt, granulation and drying of final product; nitric acid treatment of stick is carried out in two stages; 60-90% of nitric acid based on stoichiometric amount are fed per CaO to first stage, and process is carried out at temperatures from 30 to 40 C for 15-60 min to pH of 0.03-0.25 of pulp; 30-60% of nitric acid based on stoichiometric amount are fed to second stage. EFFECT: reduced foaming, lower evolution of nitrogen oxides, increased content of nutrients and greater fraction of aqueous P₂O₅ is product. 3 ex, 1 tbl