Phosphate acid sludges formed in the production of wet process phosphoric acids are converted to potassium polyphosphates by reaction with a potassium salt at elevated temperatures. Sodium salts may be introduced to reduce the fusion temperature and magnesium compounds with an increase in fusion temperature; the reaction system will also accept a variety of micronutrients. The potassium polyphosphate product formed has a high degree of citrate solubility establishing its excellent utility as a fertilizer.
