Preparation of magnesium hydroxide from serpentinite by sulfuric acid leaching for CO2 mineral carbonation

• Leaching yield of Mg increased with H2SO4 dosage, limited by a product layer.
• Agitation and ultrasonication effectively controlled the thickness of product layer.
• About 84% of Mg was recovered in Mg(OH)2-rich powder for CO2 mineral carbonation.
• About 95% of Fe was recovered by solvent extraction and magnetic separation.
• Magnetite concentrate and Fe2O3 were obtained as by-products.

Carbon capture and storage (CCS) by mineral carbonation is a promising way for CO2 emissions mitigation that has been under studied for decades. In this work, the preparation of magnesium hydroxide from Finnish serpentinite using sulfuric acid leaching as the first step of a CO2 mineral carbonation process was studied. Some details of leaching behavior of the ore were revealed and a valuable metal was recovered in this study. It was found that leaching yield of magnesium increased with sulfuric acid dosage, limited by a product layer formed on the ore particles, resulting in incomplete serpentinite decomposition. Agitation and ultrasonication were demonstrated to be effective in controlling the thickness of product layer. About 95% of iron was recovered from the leachate and leaching residues and valuable Fe-rich substances were obtained as by-products. After the iron extraction, a fine Mg(OH)2-rich powder could be prepared from the Mg-rich solution by precipitation using sodium hydroxide solution.