Stepwise selective rare earth elements recovery from blast furnace slag and CO2 utilization via highly integrated pH swing process

Abstract

Ex-situ carbon mineralization converts CO2 into thermodynamically stable solid carbonate phases while providing a means of utilizing of alkaline earth metal–rich industrial residues. Among such industrial wastes, blast furnace slag (BFS) is a major industrial byproduct of the ironmaking process and often contains not only alkaline earth metals but also precious metals, including rare earth elements (REEs). This study explored a pH swing-assisted hydrometallurgy process comprising leaching, precipitation, and carbonation to enable recovery of REEs and production of solid carbonate from the BFS. The leaching behavior and kinetics were evaluated using two different slurry densities (0.03 and 5 wt%). The results indicated that both leaching efficiency and kinetics are highly dependent on the silicate structure of BFS. By employing a stepwise-pH swing process, cerium was selectively concentrated to approximately ten times its original abundance, reaching a final concentration of 2.1 wt% at pH 7. Following cerium precipitation, a calcium– and magnesium–rich solution was obtained and subsequently utilized for carbon mineralization. The calculated carbon storage capacity was 132 kg CO2/ton of slag. These findings demonstrate that the proposed BFS–based process can offset landfill demand and mitigate the carbon footprint of iron and steel production, while simultaneously enabling the recovery of valuable metals from industrial waste.