CO2 resource utilization in red mud modified phosphogypsum cementitious material: Strength development mechanism, heavy metals evaluation and carbon emission reduction effect

• CO 2 curing mechanism of RMPCM was carried out. • Characteristic heavy metals were analyzed. • Carbon emission reduction effect was presented. Carbon dioxide (CO 2 ) utilization in red mud modified phosphogypsum cementitious material (RMPCM) as a curing atmosphere can shorten the curing cycle of cementitious materials, improve their compressive strength, and enable CO 2 capture and storage. This approach offers significant potential for CO 2 capture and utilization, with promising industrial applications. In this study, the literature was visualized and analyzed, and the stress development mechanism, heavy metals (HMs) evaluation, and carbon emission reduction effect of RMPCM under standard CO 2 curing were systematically investigated using advanced scientific testing technologies and methods. Based on these findings, a safety control system for RMPCM under CO 2 curing was established to support the development of low-carbon, environmentally friendly materials for solid waste resource utilization. The analysis revealed that current research on CO 2 -cured waste-based materials mainly focuses on material properties, while environmental aspects such as carbon emissions, HMs leaching, and life cycle assessments are underexplored. The compressive strength of RMPCM improved with various CO 2 curing concentrations and curing times. This improvement was attributed to the carbonation product CaCO 3 , which played a filling, crystal nucleating, and chemical activation role during accelerated carbonation and subsequent hydration. Additionally, silica gel formed during carbonation reacted with the hydration product Ca(OH) 2 to produce secondary C-S-H gel, which effectively repaired internal pores and enhanced the material’s strength. However, excessive CO 2 curing time caused free CO 2 to combine with residual water in the specimen, forming weakly acidic carbonic acid, which eroded the material and damaged its structure.The compressive strength of the specimen reached 31.6 MPa after 28 h of curing at 20 % CO 2 concentration, meeting the strength requirements for cementitious materials. Leaching tests of HMs in RMPCM before and after CO 2 curing showed that only chromium (Cr) exceeded 1 ppm, while the content of the other seven HMs sharply decreased after 15 min of dissolution. XRD and HMs content tests indicated that mineralization reactions significantly reduced HMs content in RMPCM. Risk assessment results identified chromium, mercury, and cadmium as key HMs to monitor in RMPCM. A risk control value for RMPCM application was proposed. Finally, life cycle analysis revealed that CO 2 -curing of bulk solid waste for high-performance product production significantly reduced carbon emissions.