Potassium dihydrogen phosphate synthesis and the influence of bio-additives on NPK fertilizer production
摘要
Potassium dihydrogen phosphate (PDP) is widely used in science, industry, and agriculture because of its outstanding optical properties and high nutrient content. This study focused on the synthesis of PDP and the development of granular fertilizers with bio-additives. PDP was synthesized via a conversion reaction between KCl and NH4H2PO4 at a molar ratio of 0.7:0.3, at 40 °C for 2 h, producing a product with phosphorus and potassium concentrations close to pure KH2PO4. Granules were formed by using the synthesized PDP, dried lupin leaves, and calcium lignosulphonate as a binder, with up to 72.69% of granules in the commercial fraction (2–5 mm). Chemical analysis showed 4.0% N, 51.0% P2O5, 35.6% K2O, and granule strength of 22 N·granule−1. Thermal analysis (STA/DSC) confirmed granule stability up to 190 °C, indicating that the additives did not negatively affect thermal properties and that the granules are suitable for industrial drying and granulation conditions. SEM analysis showed irregular surface morphology and high moisture absorption, suggesting the need for protective coatings. The final fertilizer formula (5% calcium lignosulphonate, 2% lupin leaves, 21% moisture) yielded an NPK ratio of 4–51–36. Lupin leaves slightly increased nitrogen content but may be more effective in liquid fertilizers.