Experimental study of enhanced phosphogypsum carbonation with ammonia under increased CO2 pressure

• Waste phosphogypsum and greenhouse gases CO2 are utilized simultaneously.
• CO2 partial pressure and stirring speed significantly affect the reaction rate.
• 97% of phosphogypsum conversion is achieved in 5 min with increased CO2 pressure.
• Ammonium sulfate fertilizer and calcium carbonate are obtained at the same time.

Phosphogypsum is the byproduct discharged from phosphate industry. A novel process was proposed for converting phosphogypsum into ammonium sulfate via phosphogypsum carbonation with ammonia. The effects of stirring speed, reaction time, initial temperature, CO2 partial pressure, liquid–solid ratio and excess ammonia ratio were evaluated. The main phases presented before and after the carbonation process were identified using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and carbon-sulfur (CS) analytical techniques. The phosphogypsum was found to have the highest carbonation conversion of approximately 97% in 5 min. The product collected from the reaction was characterized as calcite with the average particle size smaller than the raw phosphogypsum.