Phosphogypsum-Based Cold-Bonded Aggregates with Ferroaluminate Cement: Preparation, Properties, and Environmental Impact

This study presents a strategic solution to the dual global dilemmas of phosphogypsum (PG) accumulation and natural aggregate scarcity by investigating the feasibility of employing ferroaluminate cement (FAC) as a binder for preparing high-performance phosphogypsum cold-bonded aggregates (PCBAs) with a PG content ranging from 60% to 90%. A comprehensive suite of characterizations, encompassing physical, mechanical, microstructural, and environmental assessments, revealed the distinctive merit of FAC in facilitating early strength development, with PCBAs attaining over 95% of their maximum strength within 7 days, attributed to the formation of ettringite and calcium-silicate-hydrate (C─S─H) gel and the completion of the majority of hydration reactions within 3 days; however, an excessive dosage of FAC was found to induce a late-stage strength decline, primarily due to internal structural deterioration caused by the formation of secondary ettringite. Environmentally, PCBAs exhibited effective immobilization of heavy metals and phosphorus via ettringite encapsulation, thereby mitigating leaching risks. This research confirms the practical feasibility of FAC-based PCBAs, offering a high-value solution for large-scale PG recycling, advancing the development of low-carbon, ecofriendly construction materials, and contributing to the promotion of a circular economy.