Geochemical constraints and heritage conflicts during cadmium stabilization of Zn-Pb-Ag tailings at a UNESCO World Heritage site

) exhibits lability, with up to 74% partitioned in exchangeable (up to 13%) and carbonate (up to 61%) fractions. Although aqueous leaching demonstrates negligible current mobilization, this partitioning poses a latent risk of release due to localized rhizosphere acidification or microenvironmental carbonate depletion. Furthermore, heritage status effectively restricts the potential extraction of an estimated 150 tons of Ag, 123,000 tons of Zn, and 19,800 tons of Pb. We propose a conceptual dual-zone sustainable management model: (1) Assisted phytostabilization using native calcicolous species for stable slopes; and (2) 'invisible' chemostabilization using Fe-modified biochar amendments for protected zones where vegetation would compromise historical industrial aesthetics. Engineered biochar effectively immobilizes labile Cd while preventing the secondary mobilization of background As, a risk typically associated with conventional biochar. Concurrently, it reduces wind erosion without altering the waste's visual character. These findings provide a scalable conceptual framework for reconciling pollution control with the preservation of Outstanding Universal Value at carbonate-hosted mining legacies globally.