Solidification/stabilization mechanisms of heavy metal ions in cemented paste backfill for green mine operations: A review

Rapid industrialization in China has caused significant environmental challenges, particularly heavy metal pollution from mine tailings. Toxic heavy metals such as lead (Pb), cadmium (Cd), and mercury (Hg) are released during the processing of mining wastewater and leaching of mine tailings. Owing to their excellent physicochemical properties, cementitious materials are widely used for the solidification/stabilization of heavy metals, immobilizing heavy metals via two distinct mechanisms. Physically, their favorable characteristics, including high mechanical strength, low porosity, and durable matrix, create effective barriers. Chemically, the alkaline environment facilitates the precipitation of metal hydroxides/carbonates. Conversely, hydration products (calcium silicate hydrate gels and ettringite) contribute to immobilization through adsorption and physical encapsulation. This study systematically investigated the migration mechanisms of heavy metal contaminants in mine tailings; further, it elucidated the multifaceted immobilization pathways of cementitious materials, which involve synergistic adsorption, precipitation, and encapsulation by hydration products combined with homocrystalline substitution. A comprehensive analysis indicated that cementitious materials significantly reduced the mobility and bioavailability of heavy metals. Nonetheless, their long-term stability and potential environmental impact require further investigation. This study aims to provide theoretical support for environmental management and sustainable resource utilization, and to explore the broader application potential of cementitious technology for heavy metal stabilization, thereby establishing a theoretical foundation for future research on heavy metals in low-cement solidified/stabilized tailings.