An experimental study of Mg(OH)2 carbonation

As part of efforts to reduce the greenhouse gas emissions in Finland research around magnesium hydroxide, Mg(OH)2, carbonation takes place at Åbo Akademi University. Converting magnesium silicates, like serpentinite and olivine into Mg(OH)2 is only briefly discussed here, but it is fundamental to a successful mineral carbonation process. Here, the subsequent carbonation of the produced hydroxide is assessed and its experimental setup is discussed in detail together with experimental results. Our focus is on a gas–solid reaction route in a fluidised bed based on the thermodynamic fact that the reaction between solid Mg(OH)2 and gaseous CO2 forming MgCO3 and water releases significant amounts of heat. A lab-scale test-setup was constructed in order to study the accelerated carbonation reaction at elevated pressures. If the reaction becomes fast enough, the process will not require an additional heat input. At high enough temperatures the reaction could provide heat for the proceeding Mg(OH)2 production step and thereby reduce the energy penalty imposed by the Mg(OH)2 production step.

► Carbonation of Mg(OH)2 using a pressurised fluidised bed at elevated temperatures (450–600 °C) has been studied.
► Mg(OH)2 can be produced from abundant resources of serpentinite.
► Fast initial kinetics has been achieved, but complete carbonation is apparently hindered by calcination.
► Supercritical CO2 does not increase the carbonation rate in the temperature range studied.
► Low concentrations (<15%) of water vapour in CO2 do not affect the carbonation significantly.