Using cemented paste backfill to tackle the phosphogypsum stockpile in China: A down-to-earth technology with new vitalities in pollutants retention and CO₂ abatement

Phosphogypsum (PG), a hard-to-dissipate by-product of the phosphorus fertilizer production industry, places strain on the biogeochemical cycles and ecosystem functions of the storage sites, which is already a pervasive problem worldwide and needs careful stewardship. In this review, we examine the presence of potentially toxic elements (PTEs) in PG and describe their associations with soil properties, anthropogenic activities, and surrounding organisms. We then review different ex-/in-situ solutions for promoting the sustainable management of PG, with an emphasis on in-situ cemented paste backfill, which offers a cost-effective and highly scalable opportunity to advance the value-added recovery of PG. However, the concerns related to the PTEs retention capacity and long-term effectiveness limit the implementation of this down-to-earth strategy. In addition, the technology has recently undergone additional scrutiny in order to meet the climate mitigation ambition of the Paris Agreement and China's Carbon Neutrality Economy, as the large-scale demand for ordinary Portland cement from this conventional option has resulted in significant CO₂ emissions. We therefore next discussed how to integrate innovative strategies, including complementary cementitious materials, alternative binder solutions, CO₂ curing, CO₂ mineralization, and optimization of the supply chain for the profitability and sustainability of PG remediation. Future research will need to bridge the gap between the feasibility of expanding these advanced pathways and the multidisciplinary needs to maximize the co-benefits in environmental, social, and economic.