Production of Mg(OH)₂ for CO₂ emissions removal applications: Parametric and process evaluation

Technological processes that accelerate natural and geochemical weathering of abundantly available Mgsilicate minerals have the potential for large-scale, safe and permanent storage of CO2. One of these CO2 sequestration routes involves as a first step the production of reactive Mg(OH)2 from Mg-silicates using recoverable ammonium sulfate (AS) salt. This route avoids the very slow kinetics of carbonating magnesium silicates. A recently identified Mg(OH)2 production process involves a closed loop, staged process of Mg extraction followed by Mg(OH)2 precipitation and reagent (AS) recovery. This process has been applied to different Mg-silicate (serpentinite and olivine rocks in particular) minerals from worldwide locations, having varying physical and chemical properties. Experimental results showed some dependence of Mg extraction and mass of the Mg(OH)2 product on the reaction parameters: mass ratio of Mg-silicate mineral (S) to AS salt reacted, reaction temperature (T) and time (t). This paper statistically evaluates the contribution of these effects and their interactions using a 2n-1 factorial experimental design. Both Mg(OH)2 production and carbonation were simulated using Aspen Plus® software while process heat integration was done by pinch analysis. Process energy evaluation, on an exergy basis, gives 3.88 GJ of energy requirement for 1t-CO2 sequestered (for Finnish serpentinite). This value is ~ 0.5 GJ/t-CO2 (10 % points) less than the energy requirement of the process in a previous model. The results of this analysis would be beneficial for optimization and pilot scale studies of this process.