GRANULATED FERTILIZER CONTAINING WATER SOLUBLE FORMS OF NITROGEN, MAGNESIUM AND SULPHUR, AND METHOD OF ITS PREPARATION

摘要

Granulated fertilizer, containing water soluble forms of nitrogen, magnesium and sulphur, contains 15 to 30 % by weight of nitrogen, 1 to 18 % by weight of sulphur, 2 to 10 % by weight of magnesium, expressed as magnesium oxide MgO, in the form of boussingaultite - (NH₄)₂SO₄.MgSO₄.6H₂O and binary salts ammonium nitrate - 2NH₄NO₃.(NH₄)₂SO₄ and 3NH₄NO₃.(NH₄)₂SO₄, wherein the content of boussingaultite in the fertilizer is 40 to 45 % by weight. Magnesite is treated with concentrated nitric acid containing 30 to 80 % of HNO₃ at a temperature of 60 °C to 130 °C, under formation of reaction mixture containing magnesium nitrate, calcium nitrate, or possibly, according to the content of metallic compounds in magnesite, nitrates of iron, manganese and further metallic elements, and the remainder of undecomposed magnesite, the reaction mixture is subseguently neutralized with an alkaline agent to pH of 3 to 7.5, the neutralized reaction mixture is subseguently left to react with ammonium sulphate at a temperature of 80 to 130 °C for 20 to 80 minutes under formation of a slurry of boussingaultite (NH₄)₂SO₄-MgSO₄.6H₂O, containing 10 to 30 % by weight of water, which slurry is mixed with dried recycle from the preceding production in the ratio of 1 :2 to 1 :10 and it is granulated under formation of wet granulate, from which, after removing free water, the final product is obtained.