Mineral carbonation of cement-plant residues and industrial by-products: Process pathways, cement-kiln flue-gas integration and technology readiness

Cement production generates concentrated CO 2 -bearing flue gas and alkaline residues that could be coupled through mineral carbonation to support partial sectoral decarbonisation. This review evaluates carbonation pathways for internally generated cement-plant residues, such as cement kiln dust, cement bypass dust, off-specification clinker, and spent refractories, as well as externally sourced blast-furnace slag, steel slag, and fly ash. The feedstocks and associated pathways are comparatively assessed by origin, reactive Ca/Mg accessibility, processing requirements, demonstrated carbonation performance, product destination, and technology readiness. Dry or moisture-assisted gas-solid and direct aqueous routes are most applicable to residues containing accessible free CaO or Ca(OH) 2 , whereas silicate-, aluminosilicate-, and dead-burned MgO-rich materials generally require longer residence times or mechanical, chemical, thermal, or pressure-assisted intensification. Cement kiln dust and bypass dust show the strongest near-term integration potential because they may combine accessible calcium with on-site availability, although their composition and net availability are plant-specific. External slags and fly ash can expand feedstock capacity but introduce transport, competing-use, and burden-allocation considerations, while spent refractories remain insufficiently validated. The review further shows that gross CO 2 uptake, final CO 2 content, carbonation degree, extraction, and carbonate-recovery efficiencies are not interchangeable, and that mitigation depends on process energy, reagent recovery, product qualification, market demand and end-of-life fate. Plant-specific characterisation, consistent carbon accounting and integrated pilot demonstrations are therefore essential for translating carbonation performance into credible emissions reductions.