(663b) Carbon Mineral Sequestration Integrated with the Recovery of Rare Earth Elements from Alkaline Industrial Wastes and Silicate Minerals

The ever-increasing atmospheric CO₂ concentration has become one of the most difficult environmental issues in recent years. In order to reduce the atmospheric CO₂ concentration, various technologies to capture, utilize and store CO₂ (CCUS) are being developed. One of the CCUS technologies that can permanently immobilize CO₂ and keep CO₂ away from the atmosphere is called mineral carbonation, where CO₂ reacts with Mg or Ca-bearing silicate materials to produce stable, environmentally benign and insoluble carbonates. In a typical pH swing process for mineral carbonation, Ca and Mg in the silicate minerals are extracted by acidic solvents, with silica left in the solid phase. Subsequently, by bubbling CO₂-containing gas streams while adding base into the leachate, solid carbonates are precipitated out.

Serpentine ((Mg, Fe)₃(OH)₄Si₃O₅) is a hydrated magnesium silicate mineral which has a large enough CO₂ mineralization capacity to sequester significant amounts of anthropogenic CO₂. Apart from silicate minerals, alkaline industrial solid wastes are also good resources for mineral carbonation. Iron slags and steel slags are particularly interesting because aside from Ca and Mg, iron slags and steel slags can also contain other valuable metals, including Fe, Al, Cr, V, Mn, Ti and rare earth elements (REE). The integrated recovery of these elements during the mineral carbonation process can maximize the exploitation and valorization of the slags, while contributing to the reduction of CO₂ emissions and the sustainable utilization of energy. In this study, the fate of REE in the iron slags and steel slags is investigated during the pH swing process for carbon mineralization. Both dissolution and carbonation kinetics of Ca and Mg in silicate minerals and slags are studied while monitoring the leaching behaviors of REEs. Additionally, the precipitation behaviors of REE are studied under various pH conditions.