Beyond CO₂ uptake: A comprehensive review of the stability paradox in carbonated alkaline waste-derived construction...

Accelerated carbonation of alkaline industrial wastes is promoted as a dual-purpose strategy: sequestering CO₂ while valorizing residues as construction materials. Yet the assumption that carbonated products remain geochemically stable after demolition has rarely been systematically examined. This review synthesizes evidence from 24 studies evaluating end-of-life leaching behavior and reveals a stability paradox: carbonation immobilizes cationic metals with 90-99.9% efficiency through carbonate precipitation yet simultaneously remobilizes oxyanionic species like chromium (VI), vanadium, arsenic, and molybdenum, with vanadium leaching increasing by 334-470% where quantifiable baselines exist. The paradox is well-evidenced for steel slag and MSWI fly ash; evidence for phosphogypsum, red mud, and other wastes is consistent but derived from fewer studies. Cementitious matrices reduce leaching by one to four orders of magnitude, though this protection is compromised by end-of-life crushing. Current regulatory frameworks, which evaluate single-metal compliance without end-of-life scenario testing, are not designed for these divergent outcomes. Priority actions include standardized end-of-life leaching protocols with crushing simulation, addition of vanadium to regulated element suites, tiered permanence factors for carbon credits, and multi-indicator life cycle assessment extending beyond global warming potential.