Obtaining granular NPK fertilizers from single superphosphate and urea
A laboratory study was conducted to elaborate methods for obtaining granular NPK fertilizers from mixtures of single superphosphate (SSP) with urea and potassium salts. Samples of products of various grades containing 32–39% fertilizer nutrients and some micronutrients (B, Cu, Co, Mo, Mn) were obtained and their characteristics determined. Instead of cured SSP the usage of a fresh den product was recommended to reduce environmental pollution. The best results were obtained by drying den superphosphate and neutralizing it with limestone before mixing it with other components. Granulation of mixtures should be carried out by the thermic method at 80–95°C, on account of the liquid phase from melting urea. The hardness of the granules obtained by this method, when stored in a dry room, remained satisfactory for 3 months.