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.