A stepwise process for carbon dioxide sequestration using magnesium silicates

This work involves the production of magnesium in the form of Mg(OH)_(2)from serpentinite rock(nickel mine tailing)material followed by conversion into MgCO_(3)using a pressurised fluidised bed(PFB)reactor operating at 400℃-600℃and pressures up to 2.85 MPa.Our approach is rooted in the thermodynamic fact that the reaction between Mg(OH)_(2)and gaseous CO_(2)forming MgCO_(3)and water releases significant amounts of heat.The main problem is,however,the chemical kinetics;the reaction is slow and has to be accelerated in order to be used in an economically viable process for large-scale(~1 Mt/a)CO_(2)sequestration.We have constructed a labscale PFB reactor test-setup for optimising the carbonation reaction.At high enough temperatures and conversion levels the reaction should provide the heat for the proceeding Mg(OH)_(2)production step,making the overall process energy neutral.So far we have been able to achieve a conversion degree of 26%at 500℃and 2.85 MPa after 30 min(particle size 125-212μm).In this paper the test facility and our latest results and progress on CO_(2)mineral carbonation are summarised.Also,the possible integration of the iron as a feedstock for iron and steel production will be briefly addressed.An interesting side-effect of this carbon dioxide capture and storage(CCS)route is that significant amounts of iron are obtained from the serpentinite rock material.This is released during the Mg(OH)_(2)production and can be of great interest to the iron-and steel producing sector,which at the same time is Finland’s largest CO_(2)producer.