Extraction of Mg(OH)2 from Mg silicate minerals with NaOH assisted with H2O: implications for CO2 capture from exhaust flue gas

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