Simultaneous CO₂ utilization and rare earth elements recovery by novel aqueous carbon mineralization of blast furnace slag

Carbon mineralization is recognized as a promising strategy for large-scale CO₂ storage and utilization. To practically employ the carbon mineralization technology on a large scale, producing value-added solid carbonates is the key to reduce the overall costs. In this paper, we propose a novel concept not only for CO₂ fixation but also recovery of rare earth elements (REEs) via the pH swing-assisted carbonation process. The blast furnace slag was selected as a feedstock, and NaOH and oxalic acid were adopted as the precipitation agent. The results revealed that the maximum REEs can be obtained in NaOH and oxalic acid-assisted pH swing carbonation and were 1986.1 and 9349.2 ppm, respectively. The CO₂ storage capacities for NaOH and oxalic acid-assisted pH swing carbonation were also calculated to 107.38 and 117.89 kg CO₂/ton-blast furnace slag, respectively, and both cases produced calcite of high purity. Conclusively, oxalic acid-assisted pH swing carbonation was advantageous over the case of NaOH for both simultaneous CO₂ storage and REE recovery. These findings confirm that the pH swing carbonation process can contribute to building the waste-to resource supply chain as well as to improving CO₂ storage and utilization.