Synthesis of high-strength porous particles based on alkaline solid waste: a promising CO2-capturing material for mine goafs

Using porous materials as a carrier to adsorb and store CO2 in the vast underground mine goaf is a feasible and effective route to achieve "emission peak" and "carbon neutrality", because this method boasts the advantages of a large storage capacity and remarkable safety. In this research, first, alkaline waste carbide slag was adopted to mineralize and store CO2. Afterward, a new type of environmentally friendly porous particles for efficiently adsorbing and storing CO2 in the mine goaf was prepared through the one-step synthesis method using mineralized carbide slag (CS) as the aggregate, oleic acid (OA) as the anionic surfactant, cetyl trimithyl ammonium bromide (CTAB) as the cationic surfactant and sodium hypochlorite (NaClO) as the foaming agent. According to the single-factor experiment results, the optimal ratio of porous particles with a high porosity and a large specific surface area was concluded, i.e., CS = 65-67.5 wt%, OA = 2.75-3.25 wt%, CTAB = 0.2-0.28 wt%, NaClO = 4.25-4.5 wt% and H2O = 40 wt%. Under this ratio, the particles enjoy excellent compressive strength and CO2 static adsorption capacity, i.e., 102.4-110.7 N and 213.7-321.4 cm(3)/g, respectively. By adding the amount of CO2 mineralized by alkaline waste (0.41 g/g) and the CO2 adsorption capacity of waste-based porous particles (321.4 cm(3)/g), it is calculated that one ton of solid waste can absorb about 1 tons of CO2. This research discloses the effects of various factors on the compressive strength and CO2 adsorption capacity of porous particles and provides important guidance for the development of high-performance porous CO2 adsorbents in the goaf.