CO2 sequestration by wet carbonated magnesium slag with high-content aragonite whiskers for improving cement performance as underground filling material

Magnesium slag (MS) is an alkaline waste residue from magnesium smelting processes. This study aimed to utilize the magnesium oxide in MS and adopt MgCl2 as the calcium carbonate crystal modifier to prepare high length-to-diameter ratio aragonite whiskers via wet carbonation, which can achieve high-value recovery of MS while capturing CO2 and enhancing cement as underground filling material. The effects of MgCl2 concentration on the carbonation process, composition, microstructure, and morphology were systematically investigated. With increasing MgCl2 concentration, more aragonite was obtained, reaching 94.9 % at 0.5 M MgCl2. Notably, at 0.1 M MgCl2, high length-to-diameter ratio aragonite whiskers with 16 were achieved. Introducing 1 wt% MS carbonated at optimal 0.1 M MgCl2 into cement increased the 3 d and 28 d compressive strengths by 17.8 % and 22 %, respectively. Moreover, an excellent CO2 sequestration capacity of up to 20.33 g CO2 per 100 g MS was obtained for the carbonated MS. Therefore, wet carbonated MS with high content aragonite whiskers is a promising method for MS high-value utilization while reducing cement usage and CO2 emission, as well as improving cement performance as underground filling material.