Facile and cost-efficient indirect carbonation of blast furnace slag with multiple high value-added products through a completely wet process

Abstract

Mineral carbonation of blast furnace slag (BFS) has been proposed as a comprehensive method for carbon capture and storage and utilization of the industrial solid waste. However, the challenge for this technology to be applied practically is how to reduce the cost of process. A completely wet process combining a CO2-mineralization cell for CO2 capture and membrane electrolysis for recovery of carbonated mother liquor is proposed to simultaneously fix CO2 and produce multiple value-added products. In this process, Ca, Mg, Al, and Si are extracted from BFS with an NH4HSO4 solution prepared from H2SO4 and (NH4)2SO4 with extraction ratios of 97.3%, 98.8%, 96.4%, and 94.3% under optimized conditions, respectively. The extracted Al and Si are then recovered as NH4Al(SO4)2·12H2O (99.59 wt%) and SiO2 (97.70 wt%) with 93% and 98.1% yield, respectively. The CaSO4-rich leaching residue and MgSO4-rich leachate after complete depletion of the residual Al and Si are successively carbonated with an NH4HCO3 solution obtained from a CO2-mineralization cell with total CO2 capacity up to 361 kg-CO2 per tonne BFS. The preliminary economic evaluation shows that the present carbonation route is a cost-efficient method to comprehensively utilize BFS and reduce CO2 emissions.