A green integrated process for phosphogypsum recycling: CO2 sequestration combined with SO2 recovery.

An integrated process was constructed combining ammonia-enhanced CO₂ sequestration and low-temperature preparation of SO₂ to achieve efficient recovery and comprehensive utilization of the main element in phosphogypsum (PG). The entire integrated process could mitigate the environmental issue of PG stacking and the CO₂ concentration, as well as yield high value-added product of SO₂. PG obtained its maximum carbonation ratio of 91% within 40 min, and transformed to micro-sized fine CaCO₃. The carbonation by-product of ammonium sulfate was used to stepwise recover NH₃ and SO₂, with the catalyze of iron scales. Under optimal conditions, SO₂ recovery of 97% was attained and 84% of NH₃ can be recycled for CO₂ sequestration. Furthermore, the techno-economic efficiency was preliminarily assessed. During the entire process, the effective utilization rates of calcium and sulfur, the main elements of phosphogypsum, were 92% and 88%, respectively. Additionally, the recycling efficiency of ammonia water reached 84%. Furthermore, the techno-economic benefit was preliminarily assessed. Each ton of raw PG treated by the integrated process would capture 0.23 t of CO₂ and yield economic benefit of 132 yuan, which has great advantages in industrial solid wastes with similar calcium content by direct wet mineralization. This integrated process offers a novel technological reference for current PG management and sulfuric acid manufacturing processes.