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

Rapid industrialization in China has led to significant environmental challenges, particularly the heavy metal pollution from mine tailings. Toxic heavy metals such as lead (Pb), cadmium (Cd), and mercury (Hg) cause pollution during the processing of mining wastewater, and leaching from mine tailings. Cementitious materials are widely used for solidification/stabilization of heavy metals owing to their excellent physicochemical properties. Cementitious materials immobilize heavy metals through two distinct mechanisms. Physically, their favorable characteristics such as high mechanical strength, low porosity, and durable matrix create effective barriers. Chemically, the alkaline environment facilitates the precipitation of metal hydroxides/carbonates (such as Pb²⁺, and Cd²⁺), while hydration products (C-S-H gels and ettringite) contribute to immobilization through adsorption and physical encapsulation. The present study systematically investigates the migration mechanisms of heavy metal contaminants in mine tailings. Additionally, the study elucidates the multifaceted immobilization pathways of cementitious materials, which involve synergistic adsorption, precipitation, and encapsulation by hydration products, combined with homo-crystalline substitution. Comprehensive analysis indicates that cementitious materials significantly reduce the mobility and bioavailability of heavy metals. However, their long-term stability and potential environmental impacts require further investigation. The present study aims at providing theoretical support for environmental management, sustainable resource utilization, and broader application potential of cementitious technology in heavy metal stabilization. The study also provides a theoretical foundation for future research on heavy metals in low-cement solidified/stabilized tailings.