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Semi-pilot-scale vaterite production, CO2 storage, and zero-waste processing using oyster shells and seawater: Process and cost assessment

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This study focuses on the semi-pilot-scale production of vaterite from oyster shells and seawater, with by-product reutilization. Previous research on vaterite synthesis via indirect carbonation using oyster shells was limited to the laboratory scale, and seawater or process by-products were not utilized. The objective of this study is to overcome these limitations through a semi-pilot-scale process involving (1) indirect carbonation of calcined oyster shells using seawater and (2) direct carbonation of the residual by-products obtained from indirect carbonation. Calcium carbonate with 99 % vaterite content and particles 2.7 μm in size was produced through indirect carbonation in 0.2 m3 reactors. Direct carbonation of the residual by-products yielded a mixture of calcite-type calcium carbonate and nesquehonite (MgCO3·3H2O). The total carbon dioxide stored during calcination, indirect carbonation, and direct carbonation was 227 kg-CO2 per ton of calcined shell. This net storage is attributable to the conversion of the Mg in seawater into nesquehonite. This method is simple and cost-effective, with the potential for substantial CO2 sequestration and the production of high-value materials such as vaterite and a calcite–nesquehonite mixture, with zero waste. This study also includes a comprehensive cost assessment, highlighting the economic viability of the process. Full-scale implementation of the process should be investigated in future research.