Simultaneous CO2 Utilization and Rare Earth Elements Recovery by Novel Aqueous Carbon Mineralization of Blast Furnace Slag

Abstract

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.