Enhanced carbon sequestration via phosphogypsum utilization in Conjunction with concrete wastewater treatment

The simultaneous utilization of concrete wastewater (CW) and phosphogypsum (PG) to mineralize CO₂ for carbon reduction is a green and low-carbon treatment method. In this work, the combined carbonation process of CW and PG and the role of ammonia as an additive were investigated. The addition of ammonia balances the excess cations, inhibits CaCO₃ resolvation, and enhances the gas–liquid mass transfer. The higher pH and ionic strength of CW help to accelerate the PG dissolution and increase the PG conversion rate. Simultaneously, a decalcification efficiency of 100 % for CW and a PG conversion rate of 98.00 % were achieved. This process resulted in a CO₂ capture of 215.76 g CO₂/kg PG, with the pH of the synergistically treated wastewater ranging from 6.43 to 7.54. Additionally, the common ionic effect of Ca²⁺ and SO₄²⁻, the salting effect of CW, and the salting-out effect of CO₂ influenced the reaction. The formation of vaterite under pressurized conditions was primarily governed by pH, which played a key role in determining the crystal morphology. The interaction between CW and PG was further confirmed in 5 L scale-up experiments, during which ammonia recycling was also achieved. This study fully utilized CW, combining it with PG to efficiently repurpose wastewater and solid waste for resource recovery.