Energy consumption and net CO₂ sequestration of aqueous mineral carbonation

Aqueous mineral carbonation is a potentially attractive sequestration technology to reduce CO₂ emissions. The energy consumption of this technology, however, reduces the net amount of CO₂ sequestered. Therefore, the energetic CO₂ sequestration efficiency of aqueous mineral carbonation was studied in dependence of various process variables using either wollastonite (CaSiO₃) or steel slag as feedstock. For wollastonite, the maximum energetic CO₂ sequestration efficiency within the ranges of process conditions studied was 75% at 200°C, 20 bar CO₂, and a particle size of <38 μm. The main energy-consuming process steps were the grinding of the feedstock and the compression of the CO₂ feed. At these process conditions, a significantly lower efficiency was determined for steel slag (69%), mainly because of the lower Ca content of the feedstock. The CO₂ sequestration efficiency might be improved substantially for both types of feedstock by, e.g., reducing the amount of process water applied and further grinding of the feedstock. The calculated energetic efficiencies warrant a further assessment of the (energetic) feasibility of CO₂ sequestration by aqueous mineral carbonation on the basis of a pilot-scale process.