Preparation of high-purity nano-CaCO₃ from steel slag

Indirect carbonation is a suitable method for carbon dioxide (CO₂) removal from the environment, and it requires an acid to dissolve the calcium ions and a base to precipitate the formed calcium carbonate (CaCO₃). We herein report a new method to produce high-purity nano-CaCO₃(nCaCO₃) from steel slag using hydrochloric acid (HCl) and sodium hydroxide (NaOH). The rate equation for the dissolution of calcium (Ca) in the slag was derived using a range of variables, such as temperatures, solid-to-liquid (S/L) ratio, and HCl concentration. The purified calcium hydroxide (Ca(OH)₂) was converted into nCaCO₃(size: 80–120 nm, purity: 98.5%) by carbonation with CO₂, after impurities, such as iron (Fe), aluminum (Al), and Mg, were completely removed. An efficiency of 73% was obtained for the dissolution and precipitation steps when 0.50 M HCl and 1.0 M NaOH were employed to produce 1 ton/h of nano-CaCO₃with a purity of 98.5 wt%. Recently, a sodium chloride (NaCl) electrolysis system with low energy requirement was proposed to simultaneously produce HCl and NaOH. Assuming 90% faradic efficiency in the aforementioned NaCl electrolysis, process energies of 916 kWh/tCaCO₃and 1462 kWh/tCaCO₃were obtained at potentials of 0.83 V and 1.50 V, respectively.