Insights into conversion of Mg(HCO3)2 to MgCO3·3H2O in solvent-mediated CO2 mineralization from bischofite waste

The excessive accumulation of bischofite waste following potassium extraction poses a significant threat to the ecological environment of chloride-type salt lakes, while CO 2 mineralization of Mg-rich minerals shows great potential for achieving carbon neutrality. Previous studies have identified Mg(HCO 3 ) 2 as an inevitable intermediate in the synthesis of the high-value MgCO 3 ·3H 2 O product from bischofite waste, yet the atomic-level mechanism of Mg(HCO 3 ) 2 converting to MgCO 3 ·3H 2 O remains unclear. In this study, the decomposition-crystallization process and solvent effects were systematically investigated by integrating molecular dynamics (MD) simulations, DFT calculations, in-situ, and ex-situ characterization methods. In-situ analysis using ATR-FTIR, pH, and conductivity measurements indicated that the ionization of Mg(HCO 3 ) 2 is the primary kinetic obstacle, followed by zeroth-order kinetics. EtOH accelerated the ionization rate of Mg(HCO 3 ) 2 and reduced the average aspect ratio of MgCO 3 ·3H 2 O crystals from 21.6 to 7.5. MD simulations quantitatively proved that EtOH could replace H 2 O molecules in the first solvation shell of Mg(HCO 3 ) 2 and disrupt the bulk H 2 O-H 2 O hydrogen-bond network. DFT calculations revealed that the O C adsorption mode of the growth unit on the (0 1 1) surface was predominant, causing the (0 1 1) surface to evolve into the axial faces of acicular MgCO 3 ·3H 2 O crystallite. EtOH inhibited the axial growth by altering the relative growth rates of crystal surfaces, rather than by adsorbing onto the (0 1 1) surface to impede growth. These findings offer mechanistic understanding of MgCO 3 ·3H 2 O morphology control, enhancing the CO 2 mineralization efficiency and Mg-rich resources sustainability.