Comparative effectiveness and mechanisms of different cement types in solidifying/stabilizing copper ions

This study compares the effectiveness of four cement types-Ordinary Portland Cement (OPC), Steel Slag-based Portland Cement (SSPC), Calcium Aluminate Cement (CAC), and Magnesium Phosphate Cement (MPC)-in the solidification/stabilization (S/S) of copper ions (Cu²⁺). A simplified model system isolated the intrinsic interactions between the cement matrices and the heavy metal. A comprehensive suite of macro- and micro-analytical techniques, including semi-dynamic leaching, toxicity characteristic leaching procedure, unconfined compressive strength, BCR sequential extraction, scanning electron microscopy and energy dispersive spectroscopy combined analysis, and X-ray diffraction analysis, was utilized. Results demonstrated that SSPC performed best overall, with negligible Cu²⁺ leaching, high residual strength, and the highest proportion of stable chemical species. Its superiority stemmed from a synergistic triple-mechanism: physical encapsulation by a dense microstructure, chemical precipitation under high pH, and lattice fixation within iron-aluminate phases from steel slag. In contrast, OPC showed reliable but lesser performance, whereas CAC and MPC suffered from early-stage instability and high acidity susceptibility, respectively. Therefore, SSPC is recommended as the optimal S/S binder for Cu²⁺, combining exceptional immobilization capacity with the environmental benefit of recycling industrial solid waste. This work provides critical mechanistic insights and a scientific basis for selecting and developing high-performance cementitious materials for heavy metal remediation.