GB1238188A - - Google Patents

Abstract

1,238,188. Ammonium phosphates and nitrate; calcium carbonate. ENTREPRISE MINIERE ET CHIMIQUE EX OFFICE NATIONAL INDUSTRIEL DE L'AZOTE. 1 July, 1968 [17 Aug., 1967], No. 31313/68. Heading C1A. Mono- and/or di-ammonium phosphates are obtained from ores containing phosphate and calcium ions by attacking the ore with nitric acid, extracting the reaction mixture with a polar organic solvent or solvents, purifying the organic solvent layer, ammoniating the purified extract to form a precipitate of mono- and/or diammonium phosphate, a light phase containing solvent and a heavy aqueous phase, decanting the light phase and recycling it to the extraction step, separating the ammonium phosphate precipitate, washing this precipitate, recycling the wash waters and part of the heavy aqueous phase to the purification step, and cycling the aqueous solution from the purification step to the extraction step. The organic solvent may be a branched or straight chain aliphatic alcohol containing 4 to 6 carbon atoms, e.g. OXO alcohols. As shown, phosphate rock and nitric acid are introduced into 3. The resulting solution is fed to zone 4, where it is cooled, giving tetra-hydrated calcium nitrate crystals which are washed in 5 and returned to 3. The mother liquor is fed to liquid-liquid extraction zone 8, where it is contacted with the polar organic solvent. The raw extract is fed to a second extraction battery, where it is contacted with recycled ammonium nitrate solution from 18. The purified extract is led to neutralization zone 13, reacted with ammonia gas, preferably so as to maintain pH 3.5, and the light phase (solvent, some water, traces of monoammonium phosphate) recycled in lines 15 and 9 to extraction battery 8. A crystal slurry is recovered from the base of 13, fed to 18, where the crystals are separated and washed, giving the ammonium phosphate in line 20. The wash water, together with some mother liquor, is recycled to 11. The aqueous phase leaving zone 11 is led to zone 8, and the raffinate leaving 8 is fed, together with the rest of mother liquor from 18 into distillation column 31, where organic solvent is removed from the top, passed through condenser 32, and recycled to 8. The raffinate, freed of organic solvent, is collected at the bottom of the column, and fed to zone 34, together with calcium nitrate tetrahydrate from 5, and treated with ammonia and carbon dioxide gases. The reaction mixture is filtered at 38, so removing calcium carbonate, and leaving concentrated ammonium nitrate solution.