Influence of Dissolved\nIron in Solution on MgO Hydroxylation\nand Carbonation

MgO (periclase) is a promising material for direct air\ncapture\nof CO<sub>2</sub> using a mineral looping process, but it is unknown\nhow impurities in the environment will affect the CO<sub>2</sub> uptake\nand hence process economics. Here, we investigated the effects of\ndissolved iron on the extents of MgO hydroxylation and subsequent\ncarbonation reactions to determine if this has a beneficial or detrimental\neffect. On single-crystal MgO, dissolved iron prevented hydration\nof MgO to Mg(OH)<sub>2</sub> (brucite) and instead formed a shell\nof lepidocrocite (γ-FeOOH). This did not passivate the MgO as\ndissolution below the shell was observed. During hydroxylation of\nMgO powders in the presence of dissolved iron, formation of brucite\ncontaining Fe(II) was observed. In addition, formation of nanoscale\niron oxides containing Fe(III) was observed using magnetometry and\nMössbauer spectroscopy. Subsequent carbonation experiments\nshowed increased carbonation of MgO hydroxylated in the presence of\niron. Our results indicate that the presence of dissolved solute impurities\nduring hydroxylation may be beneficial for carbonation of hydroxylated\nMgO.