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A process for the preparation of nitrophosphate fertilizer by acidulation of phosphate rock by means of a mixture of HNO3 and NH4 HSO4, wherein the NH4 HSO4, serves for the acidulation as well as for the precipitation of the calcium present in the phosphate rock as CaSO4. 2H2 O. The latter is treated with a gas mixture containing NH3 and CO2, forming CaCO3 and (NH4)2 SO4. The (NH4)2 SO4 is thermally decomposed to form NH4 HSO4, which is recycled to the acidulation reaction. The acidulated phosphate rock solution is neutralized with NH3 to obtain the nitrophosphate fertilizer.