The effects of NaOH addition on the mechanochemical pre-treatment of wollastonite and their performances as carbonated mineral product

The increasing demand for sustainable cement production has driven research into alternative CO2 sequestration and mineral utilisation strategies. This study investigated wollastonite as a reactive phase frequently found in a wide range of industrial mineral waste streams. The solvent-free mechanochemical activation of wollastonite and its performance in direct mineral carbonation were evaluated to explore its potential for CO2 capture and cement replacement. The influence of NaOH addition (up to 20%) during pre-treatment was assessed. Mechanochemical activation reduced crystallite size and promoted depolymerisation of the silica chain structure of wollastonite, enhancing its carbonation reactivity. NaOH addition accelerated early-stage CO₂ uptake and uptake efficiency (at 1 day), where the best 1-day CO2 uptake performance (10.3 g per 100 g wollastonite) was achieved with 20% NaOH addition and 20 minutes of activation. However, the addition of NaOH resulted in lower overall carbonation efficiency and wollastonite conversion rate after 10 days, likely due to limited conversion to CO32- species in the presence of NaHCO3. The best 10 days performance was achieved with 20 minutes of milling without NaOH, resulting in a fourfold increase (compared to untreated material) in CO2 uptake (12.6 g per 100 g wollastonite) and a wollastonite conversion rate of 33.2%. When used as a partial cement replacement, the carbonated product was able to achieve compressive strength equivalent to general-purpose CEM II/B-L 32.5 N cement. These findings offer valuable insights for optimising mechanochemical activation processes in sustainable cement and CO2 mineralisation technologies.