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

FIELD: agriculture. SUBSTANCE: method comprises decomposition of apatite concentrate with nitric acid, recovery of calcium nitrate by neutralization, decomposition of low-grade phosphate stock with preneutralized solution containing nitric and phosphoric acids, additional ammoniation of the resulting suspension, evaporation of neutralized suspension, mixing of evaporated pulp with ammonium nitrate melt and potassium salt granulation and drying of final product. In this case, preammoniation of solution containing nitric and phosphoric acids is carried out to pH of 0.6-1.2, and decomposition of low-grade phosphate stock is carried out in two stages: preneutralized solution is fed to first stage in amount required to attain L:S ratio of 0.8-1.2:1 in pulp, and remaining portion of preneutralized solution is added in second stage, and boron-containing compounds are added to mixture in amount of 0.13-0.25% of boron in final product, boron- containing compounds being boric acid or borate ore. The resulting fertilizer contains P₂O₅ in water-soluble and nitrate-soluble forms, has improved physico-mechanical properties and uses cheap phosphate stock. EFFECT: more efficient preparation method. 2 cl, 3 ex