Mechanochemical activation for improving the direct mineral carbonation efficiency and capacity of a timber biomass ash

Biomass ashes generated from the combustion process of timber materials have the capacity to be used as sustainable feedstock materials for CO2 utilisation through mineral carbonation. However, the CO2 uptake capacity and efficiency of biomass bottom ash are normally quite limited under ambient conditions due to the low reactivity of the materials. This study investigates the use of timber biomass bottom ash for direct mineral carbonation, and the effects of mechanochemical activation as a pre-conditioning treatment. The effects of different mechanochemical activation conditions (i.e., milling time, the ball to sample mass charge ratio, and the water addition content) were systematically assessed. The mechanochemically activated biomass bottom ash samples before and after carbonation were characterised using X-ray diffraction, Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and thermogravimetric analysis (coupled with mass spectroscopy). The results show that mechanochemical pre-conditioning can effectively improve both the mineral carbonation efficiency (kinetics) and capacity, most likely by increasing the reactivity of calcium (magnesium) silicate for mineral carbonation even at ambient temperature and pressure. The maximal CO2 uptake capacity has doubled at the optimised mechanochemical treatment conditions. Comparison of performances reported in literature using biomass ash with similar chemical compositions was carried out, where mechanochemical activation pre-treatment exhibited superior performances. The outcomes of this study also suggest that mechanochemical activation might also be effective for improving the mineral carbonation capacity of other alkali industrial waste containing calcium (magnesium) silicates.