Accelerated phase transition and synthesis of magnesite from hydromagnesite in aqueous mono-ethylene glycol solution

•Magnesite with mode size of of 1 ~ 10 µm was synthesized at 393 K and PCO2 = 0.5 MPa within 5 h.•The effect of adding NaCl, Na2CO3 and MEG on water activity was revealed.•Phase diagrams for magnesium carbonate in MEG solution were constructed.•A thermodynamic framework for the system Mg2+-Na+-Cl-–CO32-–CO2-MEG-H2O was established.•Solubility of MgCl2·6H2O in the aqueous MEG solution was determined. Magnesite was successfully synthesized from hydromagnesite by undergoing a phase transition process in mono-ethylene glycol (MEG) solution. The process can be achieved at 393 K under 0.5 MPa of CO2 in 5 h, and the formed particle size of magnesite ranges from 1 to 10 µm depending on the synthesis temperature. This study discloses the effect of MEG concentration with adequate amount of sodium chloride (NaCl) or sodium carbonate (Na2CO3) on the magnesite synthesis process, both of which accelerates the mass transfer rate of CO2 during the transition process. The mixed-solvent electrolyte (MSE) model was applied by constructing the phase diagram of hydromagnesite -magnesite in the Mg-Na-Cl-CO3-CO2-MEG-H2O system. Both the experimental and the calculated results unveiled that the addition of MEG reduces the water activity significantly, which allowed for the phase transition to occur. Additionally, rhombic magnesite can be obtained from hydromagnesite in an aqueous solution at a condition that contains 95 wt% of MEG, 1 mol/kgw. NaCl and 0.285 mol/kgw. of Na2CO3.