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 MgCO3 using a pressurised fluidised bed (PFB) reactor operating at 400°C–600°C and pressures up to 2.85 MPa. Our approach is rooted in the thermodynamic fact that the reaction between Mg(OH)2 and gaseous CO2 forming MgCO3 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) CO2 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°C and 2.85 MPa after 30 min (particle size 125–212 μm). In this paper the test facility and our latest results and progress on CO2 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 CO2 producer.
Keywordsmineralisation serpentinite mineral carbonation magnesium carbonate fluidised bed
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