ORIGIN OF AND CHARACTERIZATION OF GLAUCONITE RICH SEDIMENTS FOR CO2 MINERAL TRAPPING, STATE OF THE ART WITH ANALOGS TO LOWER CRETACEOUS, MANGISTAU, KAZAKHSTAN

Abstract

This present study investigates the potential of glauconite—a green, iron- and potassium-rich clay mineral—for carbon dioxide (CO₂) sequestration via mineral trapping. Recent interest has emerged in utilizing glauconite-rich sediments for permanent CO₂ immobilization, primarily through a process involving glauconite dissolution in a CO₂-rich aqueous environment, followed by the release of ferrous iron (Fe²⁺) that subsequently reacts with CO₂ to form stable carbonate minerals, such as siderite. A comprehensive review of experimental and geochemical literature was conducted to identify the favorable conditions for effective CO₂ mineral trapping in glauconite-bearing systems. Particular attention was given to the Fe²⁺/Fe³⁺ ratio, which plays a critical role in carbonation potential. Furthermore, glauconite with lower potassium content was found to be more reactive and thus more conducive to carbonation processes. To apply this concept, glauconite-rich Albian sandstones with a marine depositional origin from the Mangystau region of Kazakhstan were studied. Detailed sedimentological and petrographic analyses were conducted to delineate lithofacies with elevated glauconite content. Notably, these sandstones host large, meter-scale, spherical concretions cemented by carbonates, which may serve as natural analogues for CO₂ mineral trapping. Sedimentological results revealed a prominent fining-upward trend in the sandstone sequence, with glauconite concentrations increasing within the finer-grained fractions. Glauconite grains exhibited variable maturities between the host sediments and the concretions; however, the nascent variety—characterized by lower potassium content—was more prevalent. The concretions were predominantly cemented by calcite and retained a high intergranular volume (IGV), suggesting early diagenetic cementation, likely preceding significant glauconite dissolution. Textural observations also indicate close spatial relationships between glauconite and pyrite, implying a possible enrichment in Fe²⁺/Fe³⁺ ratios that may enhance carbonation potential. To experimentally validate these findings, a batch reactor experiment was performed using the glauconitic sandstone and CO₂-enriched water. The experiment revealed initial glauconite dissolution accompanied by a rapid release of ions. X-ray diffraction (XRD) analyses before and after the experiment showed minor siderite formation, indicating the onset of mineral carbonation. These preliminary results confirm that glauconite from the studied region is geochemically reactive and exhibits promising potential for CO₂ sequestration via mineral trapping.