Development of Ultrafine Mineral Admixture from Magnesium Slag and Sequestration of CO₂

Abstract

To upcycle magnesium slag solid waste (MS) as well as sequester CO2, a new wet carbonation process was proposed to activate the volcanic ash activity of MS and use it as an ultrafine mineral admixture for cement. The effects of different carbonation times on the activity of MS were investigated, and the phase assemblage, as well as the changes in the microstructure and pore structure during the carbonation process, was also characterized using multiple techniques, such as TG-DTG, XRD, FT-IR, 29Si NMR spectrum, SEM, and BET, to further reveal the carbonation activation mechanism of MS under wet carbonation. Moreover, the effects of MS before and after carbonation on the compressive strength of the composite cement paste were investigated to verify the feasibility of carbonated MS as an ultrafine mineral admixture. The results show that the products of MS generated after a short carbonation reaction were mainly highly polymerized calcium–silicate–hydrate gel and a large amount of calcium carbonate in the form of calcite and aragonite with a size of about 1 μm. The CO2 sequestration rate of MS reached 22.14%. Compared to pure cement, carbonated MS can replace 30% of the cement clinker without compromising compressive strength. The above results offer potential possibilities for upgrading the utilization of MS and CO2 sequestration in the cement industry.

Keywords

• magnesium slag
• wet carbonation
• CaCO₃
• microstructure
• calcium–silicate–hydrate (C-S-H)