Carbonate Conversion of Gypsum Using a Recirculating Ammonium Sulfate Solution

Abstract

Achieving a high degree of gypsum conversion is crucial to reducing environmental impact and enhancing the efficiency of industrial processes. This article presents a comprehensive investigation of the liquid-phase conversion of gypsum, using a 50% aqueous ammonium carbonate solution and incorporating a recycled ammonium sulfate solution. The study aims to enhance the conversion process's technological efficiency while improving the filterability of the resulting calcium carbonate. Experiments conducted at 50 °C showed that ammonium carbonate consumption at 100–110% of the stoichiometric requirement significantly affected process efficiency, with gypsum conversion reaching 95–97% under optimal conditions. The 95% confidence interval for gypsum conversion was 94.5% to 97.5%. The recycled ammonium sulfate solution, at concentrations ranging from 15% to 35%, was evaluated for its impact on gypsum conversion and calcium carbonate filterability. Notably, using a recycled ammonium sulfate solution resulted in larger, denser calcium carbonate crystals, thereby improving filterability. The filtration rate increased from 500–600 kg/m²·h to 700–1000 kg/m²·h, with a 95% confidence interval of 680–1020 kg/m²·h, demonstrating a clear improvement in process efficacy. This improvement, when scaled to an industrial level for a 10 m² filter press, could potentially translate into an annual throughput boost of approximately 40–50%, emphasizing the significant industrial value of the process advancement. These results demonstrate both scientific and practical value for optimizing the gypsum–ammonium carbonate conversion process and advancing industrial ammonium sulfate production technologies. Additionally, steps were taken to replicate the experiments under these conditions, strengthening the credibility and reproducibility of the results.