Utilisation of electrolytic manganese residue and phosphogypsum in calcium sulfoaluminate cement

This study pioneers a novel methodology to assess the feasibility of utilising industrial byproducts in calcium sulfoaluminate (CSA) cement systems through simulated alkaline environments, specifically employing phosphogypsum (PG) and electrolytic manganese residue (EMR) stabilisation by way of struvite precipitation. The stabilisation protocol comprised two phases. In the first phase, struvite synthesis was optimised using an EMR-to-PG mass ratio of 2:1, a solid-to-liquid ratio of 1:0.7, and pH 9.0 adjusted by magnesium oxide/magnesium sulfate supplementation, followed by 20 days of curing to achieve optimal precipitation. Subsequently, a calcium hydroxide solution-based simulation system replicating CSA hydration conditions (pH <10.5) was established to evaluate the long-term stability of stabilised/solidified (S/S) composites over equivalent 20-day periods. Fourier-transform infrared spectroscopy indicated that the characteristic absorbances of phosphate and nitrogen–hydrogen were markedly intensified after the 20-day S/S treatment and remained stable following alkali exposure. Compressive strength at 14 days (44.4 MPa) was comparable to the control, confirming that 10% cement replacement by the S/S composite does not reduce the later mechanical performance of CSA. These findings significantly advance the application of PG and EMR in CSA.