Resource recycling of industrial waste phosphogypsum in cementitious materials: Pretreatment, properties, and applications

Phosphogypsum (PG), is a common by-product of the phosphate fertilizer industries using the wet acid process, which produces significant amounts of PG along with the complexities associated with its disposal. Economic and technical constraints often lead to suboptimal handling practices, such as indiscriminate disposal and indefinite storage, which consume valuable land and arouse environmental risks (Pliaka and Gaidajis, 2022; Rashad, 2017; Wan et al., 2024) because PG waste includes a variety of contaminants (Bilal et al., 2023; Silva et al., 2022). The inappropriate disposal of PG can lead to soil contamination, water pollution, and airborne dust from wind-blown PG particles, causing widespread ecological impact (Meng et al., 2022; Yang et al., 2019). The global stockpile of PG is estimated to be between 3 and 4 billion tons, with an annual increment of approximately 300 million tons, a significant portion of which is discharged into marine environments (Arhouni et al., 2023; Hassoune et al., 2021). This burgeoning accumulation underscores a critical challenge for the sustainable development of the phosphorus processing industry (Akfas et al., 2023). Hence, the imperative to mitigate the environmental impact of PG has catalyzed research efforts to devise effective management strategies and reduce the ecological burdens of PG waste.

Recent policy interventions have been pivotal in fostering the global advancement of PG recycling, addressing the pressing environmental challenges of solid waste management (Lu et al., 2024; Mohammed et al., 2018; Wu, 2023). Notably, the construction industry has demonstrated a growing interest in using PG for eco-efficient cementitious materials (Amrani et al., 2020; Gijbels et al., 2019a; Xu et al., 2024). Data from Scopus between 2014 and 2024, as depicted in Fig. 1, reveal a steady escalation in research into PG recycling for cementitious material development. For instance, there is a lot of research about the application of PG in fabricating PG-based cementitious materials (PBCMs) (Chen P. et al., 2023; Harrou et al., 2020; Pratap et al., 2023a), including cemented backfill, burn-free bricks, supersulfated cement, alkali-activated materials, waste binder, foam concrete, and artificial aggregate, etc., in developing countries (e.g., India and China). Similarly, developed countries, including the United States, Australia, Spain, etc., have lots of stockpiling PG and consider industrial waste phosphogypsum as a resource recycling in developing eco-efficient PBCMs (Amrani et al., 2020; Gijbels et al., 2019a; Islam et al., 2017).

However, several impediments thwart the effective recycling of PG into cementitious materials (Ajam et al., 2019; Tsioka and Voudrias, 2020; Wang et al., 2023a): (a) Diverse origins of PG from various countries and regions result in variable chemical compositions, physical properties, and levels of radioactivity, thereby challenging the uniform application in cementitious materials (Murali and Azab, 2023); (b) The presence of contaminants, notably fluoride and phosphate, in the recycled PG can adversely affect the cement hydration process, significantly undermining the mechanical integrity and durability of PBCMs (Chen et al., 2023); (c) The heterogeneous characteristics of PG sourced from different origins impact the workability, mechanical attributes, and longevity of PBCMs, constraining their applicability across various engineering contexts (Gijbels et al., 2019b); (d) Future research is warranted to classify PBCMs according to their specific uses to optimize the required recycling efforts (Cao et al., 2022; Haque et al., 2020). In response to these challenges, researchers strive to mitigate these barriers and broaden the practical deployment of PG recycling in engineering practices.

Therefore, we conduct an extensive and critical review of PG recycling in cementitious materials for construction, aiming to elucidate the feasibility of its large-scale application in practical engineering works. Although previous reviews summarized the reuse of PG in various contexts (Men et al., 2022; Thakur et al., 2023; Wu F. et al., 2022), our study positions itself by providing a comparative and critical analysis of the latest advancements in PG recycling for cementitious material development. For example, Wu et al. (2022) reported that PG can be used in multi-directional resource utilization paths, including the application in agriculture, chemical raw materials, environmental functional materials, fill materials, etc. Thakur et al. (2023) summarized the applications of PG as geomaterial, while Akfas et al. (2023), Murali and Azab (2023), and others underscored the potential of PG as a resource. Our review takes a step further by evaluating the impediments to its effective utilization in cementitious composites and proposing viable solutions for overcoming these challenges.

The organizational flow of our review is depicted in Fig. 2. Specifically, we address the variability in PG’s chemical composition, physical performance, and radioactivity due to its diverse origins, which complicate its standardization for use in cementitious materials. Our review elucidates the properties and pretreatment methodologies for PG and critically assesses its applications in terms of the durability, workability, and mechanical properties of PBCMs. Furthermore, we explore burgeoning applications of PBCMs in large-scale engineering projects, offering novel perspectives on the holistic integration of PG recycling in eco-efficient construction practices. This review presents a forward-looking discussion on the scalable potential of PG in the construction sector, aiming to inspire interdisciplinary research and technological innovation for sustainable urban development.