Development and optimization of phosphogypsum-based geopolymer cement

Phosphogypsum (PG) is a solid waste product that is generated in the phosphoric acid manufacturing process, most of which is currently sent to landfills rather than reused. In this study, beta-hemihydrate phosphogypsum (beta-HPG), slag, fly ash (FA) and alkali activator were mixed to form a phosphogypsum-based geopolymer (PBG) cement. The effects of the slag and FA content, citric acid (CA) dosage, sodium metasilicate (SM) dosage, and water addition process were investigated. The results indicated that the 28-day unconfined compressive strength (UCS) of the cement can exceed 60 MPa when a reasonable mix proportion is adopted. The hydration products and strength formation mechanism of the PBG cement were assessed using XRD-Rietveld and SEM-EDS. The micro-analysis results indicated that the main hydration products were dihydrate phosphogypsum, ettringite, and C-S-H gel, which jointly provided the strength for the PBG cement. The PBG cement may improve the utilisation prospects of PG waste.

Automated summary

In this study, a phosphogypsum-based geopolymer (PBG) cement was created by mixing beta-hemihydrate phosphogypsum (beta-HPG), slag, fly ash (FA), and alkali activator. The effects of slag and FA content, citric acid and sodium metasilicate dosage, and water addition process were investigated. The results showed that the cement could achieve a 28-day unconfined compressive strength (UCS) exceeding 60 MPa with a reasonable mix proportion. The main hydration products of the PBG cement were dihydrate phosphogypsum, ettringite, and C-S-H gel, which collectively contributed to its strength.