Using cemented paste backfill to tackle the phosphogypsum stockpile in China:A down-to-earth technology with new vitalities in pollutant retention and CO_(2) 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 storage sites.This pervasive problem is already widespread worldwide and requires careful stewardship.In this study,we review the presence of potentially toxic elements(PTEs)in PG and describe their associations with soil properties,anthropogenic activities,and surrounding organisms.Then,we 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,concerns related to the PTEs'retention capacity and long-term effectiveness limit the implementation of this strategy.Furthermore,given that the large-scale demand for ordinary Portland cement from this conventional option has resulted in significant CO_(2) emissions,the technology has recently undergone additional scrutiny to meet the climate mitigation ambition of the Paris Agreement and China's Carbon Neutrality Economy.Therefore,we discuss the ways by which we can integrate innovative strategies,including supplementary cementitious materials,alternative binder solutions,CO_(2) mineralization,CO_(2) curing,and optimization of the supply chain for the profitability and sustainability of PG remediation.However,to maximize the co-benefits in environmental,social,and economic,future research must bridge the gap between the feasibility of expanding these advanced pathways and the multidisciplinary needs.

Leaching characteristics of heavy metals during cement stabilization of fly ash from municipal solid waste incinerators

The leaching characteristics of heavy metals in products of cement stabilization of fly ash from a municipal solid waste incinerator were investigated in this paper.The stabilization of heavy metals such as Cd,Pb,Cu,and Zn in fly ash from such incinerators was examined through the national standard method in China based on the following factors:additive quantity of cement and Na_(2)S,curing time,and pH of leaching liquor.The results showed that as more additives were used,less heavy metals were leached except for Pb,which is sensitive to pH of the leachate,and the worse effect was observed for Cd.The mass ratio of cement to fly ash=10% is the most appropriate parameter according to the national standard method.When the hydration of cement was basically finished,stabilization of heavy metals did not vary after curing for 1 d.The mixtures of cement and fly ash had excellent adaptability to environmental pH.The pH of leachate was maintained at 7 when pH of leaching liquor varied from 3 to 11.