Extraction of Mg(OH) sub(2) from Mg silicate minerals with NaOH assisted with H sub(2)O: implications for CO sub(2) capture from exhaust flue gas

The utilisation of Mg(OH) sub(2) to capture exhaust CO sub(2) has been hindered by the limited availability of brucite, the Mg(OH) sub(2) mineral in natural deposits. Our previous study demonstrated that Mg(OH) sub(2) can be obtained from dunite, an ultramafic rock composed of Mg silicate minerals, in highly concentrated NaOH aqueous systems. However, the large quantity of NaOH consumed was considered an obstacle for the implementation of the technology. In the present study, Mg(OH) sub(2) was extracted from dunite reacted in solid systems with NaOH assisted with H sub(2)O. The consumption of NaOH was reduced by 97% with respect to the NaOH aqueous systems, maintaining a comparable yield of Mg(OH) sub(2) extraction, i.e. 64.8-66%. The capture of CO sub(2) from a CO sub(2)-N sub(2) gas mixture was tested at ambient conditions using a Mg(OH) sub(2) aqueous slurry. Mg(OH) sub(2) almost fully dissolved and reacted with dissolved CO sub(2) by forming Mg(HCO sub(3)) sub(2) which remained in equilibrium storing the CO sub(2) in the aqueous solution. The CO sub(2) balance of the process was assessed from the emissions derived from the power consumption for NaOH production and Mg(OH) sub(2) extraction together with the CO sub(2) captured by Mg(OH) sub(2) derived from dunite. The process resulted as carbon neutral when dunite is reacted at 250 degree C for durations of 1 and 3 hours and CO sub(2) is captured as Mg(HCO sub(3)) sub(2).