Granulation of finely crystalline ammonium sulphate using calcium oxide and sulphuric acid

Two types of finely crystalline ammonium sulphate (particle size distributions: white type 7% 2–3 mm, 45% 1–2 mm, 48% <1 mm; blue type 1% 2–3 mm, 8% 1–2 mm, 91% <1 mm) were granulated by adding calcium oxide and concentrated sulphuric acid using a rotating drum in the laboratory and pilot plant. The granules had satisfactory physical and chemical properties.The granules made in the pilot plant with 25 kg ammonium sulphate, 0.5 kg CaO, 1.26 litres of water and 0.9 to 1.125 litres of 98.5% H₂SO₄ had 80 to 97% of the granules within the size range of 1–3 mm, abrasion resistance of 0.4 to 0.8% <1 mm, crushing strength of 1.4 to 2.3 kg, critical relative humidity of 65–70%, pH 1.8 to 1.9 and N, S and Ca contents of 19, 24 and 1%. The quality of the granules when stored for 6 months alone or blended together with common fertilizers did not change.A glass house trial using barley demonstrated that the agronomic values of 4 prototype ammonium sulphate granules produced in the laboratory were similar to 3 standard granular ammonium sulphate fertilizers.The process of granulation which could easily be adopted in superphosphate manufacturing plants is recommended for plant scale testing.Provisional New Zealand Patent (No 236,025) applied for.