CO2 sequestration with serpentinite and metaperidotite from Northeast Portugal

• Portuguese serpentinite has a theoretical CO2 sequestration capacity ∼3.4 Gt.
• Ammonium sulphate and bisulphate extracted 60% and 80% Mg, respectively.
• Mg(OH)2 carbonation is dependent on temperature and particle size.
• A maximum of 70 % of Mg(OH)2 carbonation was achieved at 19–21 bar and 510 °C.
• The process is suitable for CO2 mineralisation for application in Portugal (and Spain).

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.