Serpentinite Carbonation Using the ÅBo Akademi Routes – Status Update

This paper / presentation reports on recent progress made at Åbo Akademi University (ÅA) with the so-called ÅA routes for stepwise carbonation of serpentinite rock, developing towards large-scale industrial application. The two routes are described that use ammonium sulphate as flux salt for extracting magnesium from rock in a solid/solid reactor, followed either by production and carbonation of magnesium hydroxide as a gas/solid reaction, or by carbonation of magnesium sulphate in aqueous solution.

While the first, original route requires less (waste) heat, the second route is technically less complicated. Another difference is the product obtained, being either magnesite or a hydrated magnesium carbonate, besides iron hydroxyoxide, a silica fraction and unreacted rock.

Essential for either route is that the ammonium sulphate flux salt is recovered and reused: for this purpose membrane-based methods are tested. Membrane electrodialysis using monovalent ion-selective membranes is investigated for the separation of dissolved sulphate from bisulphate: results on separation and energy use will be reported.

Besides this, life cycle assessment (LCA) was used to assess and compare the environmental footprints of the two ÅA routes, including the importance of transport distance for serpentinite rock from a mining site.

Finally, results on designing a system for energy (heat) storage by cycled hydration and dehydration of magnesite and hydrated magnesium carbonate are reported. Combined with solar heat or low temperature district heating heat this can be deployed for heat storage in buildings.