Preparation of CO2 sequestration materials from semi-dry carbonized carbide slag and coal gasification slag: Study on carbon fixation performance of multistage carbonation

In order to solve the problems of coal-based solid waste disposal and carbon emission reduction, this study used carbide slag (CS) and coal gasification slag (CGS) as raw materials to prepare CO 2 storage materials (CSGS-CO 2 ) with low cost and high carbon fixation performance by a semi-dry carbonation process, and systematically explored its mineralization mechanism and carbon fixation characteristics. The effects of carbonation stage, CS content and curing age on the properties of the materials were analyzed by X-ray diffraction (XRD), thermogravimetric analysis (TG-DTG), scanning electron microscopy (SEM), infrared spectroscopy (FTIR) and mercury intrusion (MIP). The study found that, (1) The carbon fixation rate of CSGS-CO₂ gradually increased with the increase of CS content, reaching a maximum of 38.86 %. However, the mineralization efficiency of CSGS-CO 2 showed a trend of first increasing and then decreasing as the CS content rose. When the CS content was 90 % and the CGS content was 10 %, the mineralization efficiency reached the maximum value of 53.36 % (under 14-day single-stage carbonation). (2) Although the stirring carbonation treatment in double-stage carbonation improved the carbon fixation rate in the early stage of curing (an increase of 11.98 % at 1 d), due to the formation of a dense product layer and the pore backfilling effect, the carbon fixation rate and mineralization efficiency at 14 d were both 23.31 % lower than those of single-stage carbonation. Therefore, for scenarios such as mine backfilling that require long-term stable carbon fixation, single-stage carbonation, with higher total carbon fixation amount and mineralization efficiency, is more applicable. (3) Microstructural analysis indicated that the main product of the carbonation reaction is calcite-type calcium carbonate. Single-stage carbonation led to the formation of a stacked structure of the calcite generated by the carbonation reaction, whereas in the double-stage carbonation samples, the calcite crystals produced exhibited an overall random scattered distribution due to the stirring shear effect. (4) The carbonation stirring process in double-stage carbonation significantly reduced the porosity of the samples, resulting in the blockage of CO 2 diffusion channels during the later stage of carbonation curing. In contrast, the porous characteristics of CGS can optimize the pore structure, providing channels for CO 2 transport. This is conducive to enhancing the long-term stability and air tightness of the material, thereby supporting its application as a CO 2 sequestration material.