Enhanced Hydromagnesite Process for CO₂ Sequestration by Desilication of Serpentine Ore in NaOH Solution

A new CO₂ fixation process was highly enhanced by desilication of serpentine ore with concentrated NaOH solution and NH₃ recycling. In the process, desilicated serpentine containing up to 83 wt % MgO after leaching is treated by NH₄Cl solution, from which MgCl₂ solution and NH₃ gas are generated and are used to capture CO₂. Hydromagnesite is produced from the reaction between ammonium carbonate and MgCl₂ solution at ambient temperature. The Phase-transition diagram of magnesium carbonate was constructed with the OLI-based chemical model. The leaching behavior of serpentine in concentrated NaOH was systematically studied. Parameters including the initial NaOH concentration, leaching temperature, solid-to-liquid ratio, and reaction time were investigated to achieve efficient separation of Si and Mg. The validity of the proposed process is successfully verified step by step and the target product of hydromagnesite is obtained. The synthetic hydromagnesite exhibit the same structure and similar morphology as natural hydromagnesite. Moreover, valuable 2% Ni-bearing minerals were also produced.