Parameters optimization for direct flue gas CO_2 capture and sequestration by aqueous mineral carbonation using activated serpentinite based mining residue

摘要

Naturally occurring mineral carbonation can significantly reduce GHG emissions. Adapting the reaction in order to sequester post combustion CO_2 is a potential industrial mitigation pathway, but such a process must be chemically and economically efficient. Research to date has focused on reacting a concentrated CO_2 stream with alkaline rocks. Significant carbonation rates where reached but required a system operating at high pressure and temperature. This article describes the parameter optimization for direct flue gas CO_2 capture and sequestration when using finely-ground, heat-activated serpentine derived from mining residues. The gas is contacted with the minerals in an aqueous phase at ambient temperature and moderate pressure (10.5 bar). Once the solution is saturated with dissolved CO_2 and Mg, it is filtered and carbonates precipitated in a downstream operation. The solid is mixed with fresh water and recirculated to treat more gas until no further Mg can be leached from the solid media. Reaction parameters such as the pulp density, the volumetric ratio of gas to liquid, the reaction time and the particle size were investigated with a 18.2% CO_2 gas stream in a batch mode. This innovative approach permits the use of moderate temperature and pressure conditions and the production of pure MgCO_3 with a potential sale value. After parameter optimization, batch mode tests showed that 64 wt.% of the Mg could be leached from the solid and that 62.5 wt.% of the CO_2 removed from the gas phase giving a ratio of 0.28 kg of CO_2 sequestered per kg of residues.