METHOD OF PRODUCING COMPOUND FERTILISERS Russian patent published in 2011 - IPC C05G1/06 

FIELD: chemistry.

SUBSTANCE: invention can be used in agriculture to produce sulphur-containing NPK compound fertilisers. The method involves neutralisation of phosphoric and sulphuric acid in three steps, addition of potassium chloride, granulation and drying the product. The phosphoric acid used is wet-process phosphoric acid which contains 33-40% P₂O₅ and 1.2-2.0% magnesium compounds in terms of MgO. At the first neutralisation step, phosphoric acid is mixed with absorption effluent until density of the mixture becomes equal to 1.36 - 1.44 g/cm³ and then neutralised to obtain a reaction mass with molar ratio NH₃/H₃PO₄ equal to 0.3-0.5. At the second step, the reaction mass and sulphuric acid are neutralised with ammonia in a tubular reactor to obtain pulp with molar ratio NH₃/H₃PO₄ equal to 0.8-0.9 or 1.3-1.4. Sulphuric acid is added in amount of 0.7-2.4 t of monohydrate per 1 t of P₂O₅. At the third step, the pulp undergoes after-ammoniation in a granulator-ammoniator to molar ratio NH₃/H₃PO₄ equal to 1.0-1.7. Further, if necessary, a nitrogen-containing component is added, where the said component used can be carbamide or ammonium nitrate in dry form in amount of 2-11% of the weight of the end product, and then granulated.

EFFECT: method enables to obtain sulphur-containing NPK compound fertilisers of different brands with improved physical properties with high efficiency of the process.

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