Evolution Process of Ferroan Brucite under Humid Conditions with CO2 and O2

Ferroan brucite, Mg1–XFeX(OH)2 (0.05 < x < 0.35) was a common mineral product preserved in serpentinized peridotites. Studying the evolution of Mg1–XFeX(OH)2 with different doping amounts of Fe2+ was beneficial to reveal the role of Fe2+ in forming different kinds of evolution products and the reasonable utilization of Mg1–XFeX(OH)2 resources. In this study, Mg1–XFeX(OH)2 with x being 0.05, 0.1 0.15, 0.2, and 0.3 were successfully prepared, characterized, and structurally refined in detail. The evolution products of Mg1–XFeX(OH)2 in the presence of H2O, CO2, and O2 were clearly investigated to assess the evolution process and the role of Fe2+. The evolution products were mainly CO32– intercalated MgFe-layered double hydroxides (MgFe–CO32–-LDHs) and MgCO3·3H2O. The content of MgFe–CO32–-LDHs in the evolution products increased with the Fe2+ doping content increased. While the content of MgCO3·3H2O changed in the opposite direction and completely disappeared as the doping content of Fe2+ was 20%. Accordingly, the evolution mechanism of Mg1–XFeX(OH)2 was afforded based on various characterization and calculation on the deformation and system energy of the products by molecular simulation. In the evolution process, the oxidization of Fe2+ to Fe3+ in Mg1–XFeX(OH)2 by O2 forced the entrance of CO32– into the interlayers. Meanwhile, high content of doping Fe2+ in Mg1–XFeX(OH)2 resulted in the easy formation of MgFe–CO32–-LDHs. Correspondingly, the change of surface charge, magnetic property, and adsorption ability toward Congo red was tested after evolution.