Application of lime neutralised phosphogypsum in supersulfated cement

Abstract

The inevitably incorporation of P2O5 impurity results in the poor quality of phosphogypsum (PG), which further hinders the utilisation of PG in manufacturing the supersulfated cement (SSC), an environment-friendly and energy-saving cement made almost entirely from industrial waste. Lime neutralisation provides a sustainable approach to remove the impurity in the PG and improve the quality of SSC. In this study, the effect of neutralisation process under different lime concentration and times on removability of P2O5 in PG was examined. Moreover, both fresh properties, hardened properties and microstructure of PG-based SSC pastes were investigated, and the mechanism behind was explored as well. The results indicated that lime neutralisation successfully removed the P2O5 and improved the pH value of PG, and the minimal requirement to remove P2O5 was only 2% Ca(OH)2. Moreover, for PG-incorporated SSC, the hydration process was significantly accelerated and the setting time was shortened by neutralising the PG with lime. The compressive strength of the PG-incorporated SSC was also improved by lime neutralisation. Under comprehensive consideration, 5% Ca(OH)2 was selected as the optimised content for lime neutralisation of PG, which efficiently improved the compressive strength of SSC by removing the P2O5 impurity in PG.