Porous wollastonite granules for CO2 capture and utilization as artificial lightweight aggregates

Mineral carbonation has gained attention as a technology for CO2 capture and utilization (CCU) in construction materials, including artificial aggregates. The synthesis of artificial aggregates by carbonation hardening using reactive mineral precursors is ineffective due to several factors, including densification during granulation, pore closure during carbonation, and ineffective CO2 diffusion into the granule. To improve the CO2 diffusion into a granule, a process of introducing pores using a templating agent (polyvinyl alcohol) and pore-forming agent (potassium persulfate) was developed to produce highly porous granules. The porous granules were carbonated in a CO2 reactor at CO2 partial pressure and temperature of 10 bar and 100 °C respectively. Thermogravimetric analysis coupled with optical microscopy and scanning electron microscopy showed that CO2 penetrated the granule synthesized with 20% persulfate concentration and showed the highest uptake of CO2 of 44 mol%, aided by an interconnected pore network. Morphology and surface geometry of the pores in the granules were studied by fractal theory using the Frankel-Halsey-Hill (FHH) model with N2 adsorption–desorption isotherms. The granules were further enhanced by esterification of the polyvinyl alcohol with citric acid resulting in excellent thermal resistance and water stability. The granules were characterized for use as artificial lightweight aggregates after CO2 capture using strength, density, and water absorption tests. The optimum carbonated granules exhibited high crushing force and low density, and water absorption between 10 – 20%. The mechanical strength indicated that the granules could potentially be utilized as artificial lightweight aggregates. This study demonstrates a new process for synthesizing porous mineral–based absorbents for CO2 capture through the introduction of pores during granulation.
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