Mitigating acid rain effects on stabilized soils: the role of phosphogypsum in leaching resistance
Xia Bian, Jianyu Xiao, Tao Zhang, Lingling Zeng
Abstract
Phosphogypsum, an industrial solid waste, is an effective binder for partially replacing cement in stabilizing dredged sediments. Acid rain, as a worldwide ecological problem, also affects the long-term stability and sustainability of geotechnical materials and structures. However, the research on leaching effects and long-term durability of phosphogypsum-stabilized soils under acid rain conditions is limited and remains a significant challenge for practical applications. This study investigates the leaching effects and long-term durability of phosphogypsum-stabilized soils by simulating acid rain erosion through semi-dynamic leaching tests. Key parameters, including leached Ca 2+ concentration, leachate pH, and unconfined compressive strength after leaching, were evaluated. Microscopic analyses with X-ray diffraction (XRD) and scanning electron microscopy (SEM) were also conducted to explore the underlying mechanisms. The results indicate that the presence of phosphogypsum in stabilized soil with high water content shows a significant improvement in leaching resistance subjected to acid ions, evidencing a lower Ca 2+ concentration and pH value in the leachate, and a higher strength after leaching compared to those samples without phosphogypsum. SEM images and XRD analysis revealed that samples with higher phosphogypsum content possess denser structures due to more needle-shaped ettringite and other minerals in the soil matrix, contributing to improved strength and leaching resistance. The enhanced strength and leaching resistance of phosphogypsum-stabilized soil can be attributed to additional gel formation, a rise in swelling potential, ettringite bridging, and a denser microstructure, which reduces Ca 2+ availability for leaching in acidic environments.