Rapid CO₂ mineralization by zeolite via cation exchange

This study illuminates the mineral carbonation potential of zeolite minerals. Zeolite minerals are common alteration products of basaltic rocks and are known for their ability to rapidly exchange their interstitial cations with those in aqueous solutions. A series of closed system batch reactor experiments was conducted at 60 °C by combining stilbite, a Ca-bearing zeolite, with 0.1 mol/kg_w aqueous sodium carbonate solutions. The individual batch reactor experiments ran from 2 to 225 days. Scanning electron microscope images of the solids recovered from the experiments reveal the presence of extensive calcite crystals, suggesting rapid and efficient carbonation. The total mass of CO₂ mineralized during the experiments, determined from the direct analysis of the solids by thermogravimetric analysis and organic carbon analysis, equaled more than 5% of that of the original stilbite within a month. This is approximately equal to maximum CO₂ mineralization possible if all of the Ca in the original stilbite was incorporated into calcite. Chemical analysis of reacted stilbite shows that approximately 2 Na atoms were incorporated into stilbite for each Ca atom incorporated into the precipitated calcite. These observations indicate that the carbon removal by stilbite proceeded by the rapid exchange of Na for Ca in its structure. This process results in carbonation rates that are far faster than those achieved by a silicate dissolution-carbonate precipitation mechanism. These results, consequently, compel consideration of targeting subsurface mineral carbonation efforts into zeolite-rich rocks.