Hydrotalcite-pyroaurite solid solution in cement system: Molecular structure and thermodynamic properties
Dengquan Wang, Yue Zhang, John L. Provis, Barbara Lothenbach, Sergey V. Churakov, George-Dan Miron, Zeyu Zhou, Jing Guan, Jiaxing Ban, Bin Ma
Abstract
Hydrotalcite-pyroaurite solid solutions, which are common minerals both in nature and in modern cementitious materials, hold significant potential for waste immobilization and cement properties yet remain insufficiently studied. In this work, we first synthesized a series of hydrotalcite (Mg 6 Al 2 (OH) 16 CO 3 ·nH 2 O) and pyroaurite (Mg 6 Fe 2 (OH) 16 CO 3 ·nH 2 O) solid solutions and conducted comprehensive characterizations. Synchrotron-based X-ray absorption spectroscopy was further employed to elucidate the molecular structure, while molecular simulations explored changes in charge density induced by Fe substitution. The results reveal that Fe substitution for Al reduces the thermal stability and induces structural changes. Specifically, the larger ionic radius of Fe 3+ compared to Al 3+ increases the unit cell parameters and elongates the Fe O and Fe Mg distances in the local structure. Fe substitution also leads to localized positive charge accumulation within the layer. Additionally, thermodynamic parameters were obtained, and a solid solution model was established to supplement the existing thermodynamic database.