Research on the method of improving carbon storage capacity of a new low calcium CO2 storage binder: Based on the recycling of heavy metal Ba ions

The novel low calcium CO 2 storage binder (LCCSB) containing α-CS, C 3 S 2 and C 2 AS as the primary minerals shows promise as a carbon fixation material, but exhibits low carbonation activity. This study aims to enhance the carbonation activity of LCCSB through barium (Ba) doping, investigate the impact of Ba doping on its carbonation behavior, and elucidate its mechanism. Density functional theory (DFT) simulation, scanning electron microscope test and X-ray diffraction results indicate that Ba ions preferentially substitute Ca atoms within α-CS, followed by Ca sites in C 3 S 2 , with a maximum solid solubility of 1mol%. Following Ba ion solid solution into LCCSB, there is an increase in carbonation reaction products along with elevated levels of calcite and aragonite. Additionally, small particles are formed to fill mineral matrix and pores leading to increased porosity and enhanced hardening strength. DFT calculations reveal that Ba ion doping reduces the total bond sequence density TBOD of the LCCSB system while weakening the bond strength of Ca–O bonds thereby accelerating the dissolution of Ca ions. Furthermore, average bond length, volume and distortion index of Ca–O polyhedra increase after Ba ion doping indicating structural distortion resulting in more active sites for potential high carbonation reactivity. This study presents a new research approach for achieving high carbonation activity in LCCSB preparation while also offering insights into the potential for clarifying the carbonation mechanism based on ion-doped LCCSB which could lead to improved environmental and economic benefits for CO 2 storage within the cement industry.