Brucite Mg(OH)2 is a promising sorbent for carbon dioxide removal (CDR) due to its availability and low calcination temperatures. However, natural and synthetic brucites tend to contain metal impurities, such as iron or manganese, and how these impurities affect the interfacial chemical reactivity is uncertain. Here, the impact of low concentrations of iron and manganese impurities on the carbonation efficiency of Mg(OH)2 was examined. Mg(OH)2 with small amounts (1–5 mol %) of Fe and Mn was synthesized. The increasing substitution of Fe into Mg(OH)2 was accompanied by the oxidation of Fe. The phase transformation sequence during the carbonation was found to be brucite Mg(OH)2 → amorphous magnesium carbonate (MgCO3·nH2O) → nesquehonite (MgCO3·3H2O), regardless of impurity concentration. Both the Fe- and Mn-doped Mg(OH)2 samples were more reactive than endmember Mg(OH)2, possibly due to their higher surface areas and lower stabilities. During carbonation, 3 mol % Fe- and Mn-doped Mg(OH)2 showed the highest reactivity. The variance in reactivity for Mn-doped Mg(OH)2 was less than that of Fe-doped Mg(OH)2. These results suggest that natural or industrial waste Mg(OH)2 with less than 5 mol % Fe and Mn impurities may be targeted as more effective CDR sorbents than endmember Mg(OH)2.
Chung et al. (Mon,) studied this question.