Converting olivine into a novel Mg-based cement for carbon sequestration

Natural Mg-rich olivine could potentially serve as a scalable feedstock for Mg-based cements with zero CO2 emissions. This study explores an innovative synthesis of a Mg-based cement by directly reacting olivine with oxalic acid (H2C2O4). The hydration behaviors and cementitious properties of olivine–oxalic acid blends are investigated, as a function of olivine-to-oxalic acid (OL/OA) weight ratio. Higher OL/OA ratio results in faster hydration, while the best compressive strength with up to 32 MPa is obtained at a moderate OL/OA ratio of 3.5 after 28 days. The obtained cements are composed of residual olivine minerals and a dense and compact glushinskite (MgC2O4·2H2O) matrix intermixed with randomly dispersed amorphous silica nanoparticles. The acid–base reaction between Mg-rich olivine and oxalic acid also provides an efficacious strategy for carbon sequestration, as up to 25 wt% of CO2 equivalent can be taken up in hydrated solid phase, potentially rendering this cementitious system carbon negative.