Phosphogypsum carbonation study: high calcium extraction doesn't guarantee CO2 storage efficiency

A new study in Case Studies in Construction Materials tests four chemical activators for pulling calcium out of phosphogypsum waste to feed mineral carbonation. Surprisingly, sodium gluconate extracts the most calcium, up to 98.5% of available calcium, but it performs worst at actually converting CO2 into solid calcite. Its calcium remains bound in complexes, so only about 86% of the dissolved calcium gets consumed, versus over 98% for ammonium chloride and acetate-based leachates. The research shows that a high dissolved calcium level on paper does not mean the calcium is chemically available for carbonation. Ammonium chloride emerges as the balanced option, releasing moderate calcium while producing clean calcite products that mineralize an estimated 14.4 kg of CO2 per tonne of phosphogypsum. The authors stress that engineers need to evaluate the full chain from calcium release to carbonate formation, not just the extraction step.