Coupling Solvay process with carbon mineralization in stilbite: an innovative approach for carbon dioxide storage

Geological storage of CO 2 through carbon mineralization is an efficient approach to reverse climate change, especially in stilbite-bearing formations such as basalts. However, integrated process routes that directly couple industrial CO 2 utilization with reactive mineral phases remain underexplored. Thus, this study presents a novel integrated pathway that couples CO 2 utilisation and permanent storage by linking a Solvay-type Na 2 CO 3 production loop directly to mineral carbonation in stilbite. Stilbite, a Ca-rich secondary zeolite, is evaluated as a reactive medium for CO 2 fixation via Na–Ca cation exchange using Na 2 CO 3 generated from the Solvay process. Stilbite samples collected from the Rajkot region (Gujarat, India) were reacted with Na 2 CO 3 solution in an in-house fabricated reactor at 60 °C and 1 bar for 30 days. The post-reaction products were characterised using XRD, XRF, FE-SEM and TGA. Post-reaction XRD confirms calcite precipitation, and XRF data reveal substantial Na enrichment (0.51–7.74 wt%) and Ca depletion (7.34–5.88 wt%), indicating a dominant Na–Ca exchange mechanism for CO 2 storage. The variation in the wt% in stilbite indicates Na-Ca exchange at the cation level, atomic mass differences, partial desilication, and secondary calcite precipitation within the solid matrix. FESEM imaging shows roughened stilbite surfaces and abundant secondary calcite crystals, confirming mineralogical immobilisation of CO 2 as calcite directly on and around the host zeolite. The Na-Ca exchange-driven calcite precipitation quantified by TGA shows a 5.76% mass loss between 800 °C and 950 °C, with a further calculation of CO 2 uptake of 57.6 g CO 2 kg -1 for stilbite. The novelty of this work lies in demonstrating a coupled Solvay–stilbite route to store CO 2 and drive rapid carbon mineralization.