CO2 sequestration with serpentinite and metaperidotite from Northeast Portugal

The application of a staged process for CO₂ sequestration by mineralisation, studied at Åbo Akademi University (ÅA), to abundant minerals from Northeast Portugal, is presented. Mg is extracted from magnesium silicates using recoverable ammonium salts (ammonium sulphate – AS and ammonium bisulphate – ABS), precipitated in the form of Mg(OH)₂ and subsequently carbonated at 20 bar CO₂ partial pressure. The concept of the process is promising since the Mg extraction requires heat at ∼450 °C while the Mg(OH)₂ carbonation produces heat at ∼500 °C. Samples of serpentinite and metaperidotite were collected from Bragança and their theoretical capacity for CO₂ mineralisation, in Northeast Portugal, was estimated to be 3.4 Gt of CO₂. All the samples were mineralogically and physically characterized using X-ray diffraction and ICP-OES techniques and microscopic observation of thin sections. The reactivity of the samples, for Mg(OH)₂ production, was tested at different temperatures (350–500 °C) with AS and ABS, in different mixing conditions and both in the presence and absence of water. Metaperidotite was shown to be more reactive than serpentinite. The produced Mg(OH)₂ was carbonated in a pressurized fluidized bed at ÅA. The maximum Mg extraction (using ABS) and Mg(OH)₂ carbonation levels reached were 80% and 70%, respectively.