Thermally activated serpentine leaching under flue gas conditions in a bubble column reactor operated at ambient pressure and temperature

Mineral carbonation of serpentine in the aqueous phase traditionally required high temperatures and pressures or additives to dissolve the mineral. This was accompanied by significant costs and important environmental burdens. This paper aims to demonstrate the feasibility of thermally activated serpentine leaching under ambient temperature and pressure. A simulated cement flue gas effluent with a CO2 content of 18.2% on a volume basis was used. The reaction was performed in a bubble column operated under a homogeneous regime. Agitation was required to improve solution mixing and CO2 diffusion. Results showed that the extent of Mg leaching was limited by the low solubility of silica in the aqueous solution. Once the solution was saturated with silica, CO2 dissolution acted only to cause precipitation of magnesium carbonate. Successive leaching with fresh water partially limited the problem as serpentine leaching declined with time. A total of 32% of the serpentine magnesium content was recovered from the solution after six successive leaching stages. For comparison, 33% of the content of the same material was dissolved when the reaction was performed in a batch reactor operated under 11.5 bar total pressure. In addition to costs and environmental improvements, these results have positive consequences on reducing complexity and retrofit issues for the application of mineral carbonation with serpentine. It was also shown that improving CO2 mass transfer through increasing agitation or superficial gas velocity accelerated serpentine leaching, highlighting the synergistic effect between the two reactions.