Chemical conversion of carbon dioxide via target metal separation using seawater-derived wastewater

This study investigated the capture of carbon dioxide (CO₂) and its chemical conversion to high-purity calcium carbonate salt, which has potential uses in a range of industrial sectors. Indirect inorganic aqueous carbonation methods were used, with seawater-based industrial wastewater as the source of metal ions. The alkanolamine absorbent solutions of monoethanolamine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA) were used at typical industrial concentrations of 30 wt%. Calcium ions from industrial wastewater were extracted in the form of gypsum. Subsequently, a carbonation reaction afforded high-purity calcium carbonate salt. The conversion yields of 33.16% for monoethanolamine, 33.86% for diethanolamine, and 55.18% for methyldiethanolamine were achieved. Thermogravimetric analysis demonstrated the purity of the product to be 93.6, 95.2 and 92.8 wt%, respectively. X-ray diffraction and scanning electron microscopy showed the crystal structure of the products to be aragonite mixed with vaterite. Furthermore, the CO₂ capture capacity of each absorbent and the amount of CO₂ desorbed by the carbonation reaction were investigated. The results may support the design of carbon capture and utilization plants and potential market research.