Purification and Thermochemical Conversion of Ammonium Sulphate: A Pathway to Sustainable Waste Recycling

Ammonium sulphate produced as a by-product of the coke-chemical process at JSC “QARMET” (Kazakhstan) contains impurities such as tarry substances and pyridine-based sulphates. These impurities cause adverse effects, including strong odour, caking, and atypical appearance, while pyridine sulphates also increase acidity (pH < 5). This study investigates the purification of substandard ammonium sulphate to expand its potential applications. Mechanisms for producing complex fertilisers from the purified product were examined. The results provide a fundamental theoretical and technological basis for developing new production lines for chemical products, including compound fertilisers. Thermochemical interactions between potassium carbonate and molten ammonium bisulphate were studied. It was found that at equimolar ratios of 2 NH₄HSO₄ to K₂CO₃, ammonium potassium sulphate (NH₄KSO₄) forms in the temperature range of (157-260) °C; above 260 °C, potassium sulphate and ammonium sulphate are produced, with concurrent pyrolysis of ammonium sulphate to ammonium bisulphate and ammonia. Upon cooling, various double bisulphates form, depending on the ratio of potassium sulphate to ammonium bisulphate.