Carbon dioxide sequestration using NaHSO₄ and NaOH: A dissolution and carbonation optimisation study

The use of NaHSO₄ to leach out Mg fromlizardite-rich serpentinite (in form of MgSO₄) and the carbonation of CO₂ (captured in form of Na₂CO₃ using NaOH) to form MgCO₃ and Na₂SO₄ was investigated. Unlike ammonium sulphate, sodium sulphate can be separated via precipitation during the recycling step avoiding energy intensive evaporation process required in NH₄-based processes. To determine the effectiveness of the NaHSO₄/NaOH process when applied to lizardite, the optimisation of the dissolution and carbonation steps were performed using a UK lizardite-rich serpentine. Temperature, solid/liquid ratio, particle size, concentration and molar ratio were evaluated. An optimal dissolution efficiency of 69.6% was achieved over 3 h at 100 °C using 1.4 M sodium bisulphate and 50 g/l serpentine with particle size 75–150 μm. An optimal carbonation efficiency of 95.4% was achieved over 30 min at 90 °C and 1:1 magnesium:sodium carbonate molar ratio using non-synthesised solution. The CO₂ sequestration capacity was 223.6 g carbon dioxide/kg serpentine (66.4% in terms of Mg bonded to hydromagnesite), which is comparable with those obtained using ammonium based processes. Therefore, lizardite-rich serpentinites represent a valuable resource for the NaHSO₄/NaOH based pH swing mineralisation process.