Utilization of magnesium hydroxy-carbonate hydrate (MHCH) materials formed by precipitation of CO₂ in alkaline aqueous solutions

CO₂ capture from mixed gaseous emissions and subsequent utilisation has proven to be possible in many ways and at different points in the cycle. This paper describes a relatively simple route for the capture of CO₂ and its conversion to useful solid construction products. CO₂ from a combustion gas waste stream {e.g. from a cement plant) containing N₂ and water vapour is selectively dissolved into an alkaline aqueous solution at ∼ 25 °C and 1 atm. The carbonate and bicarbonate ions thus formed react with Mg ions (e.g. from a seawater desalination brine) and precipitate Magnesium Hydroxy-Carbonate Hydrate (MHCH) phases; the presence of NaCI does not interfere significantly with the precipitation process. Nesquehonite, MgCO₃.3H₂O, is the preferred product obtained at ∼ 25 °C and 1 atm and typically occurs as micrometric well crystallized prismatic needles. After its thermal activation, the powder is mixed with water and the mix can be shaped into panels or blocks. The hardened materials contain ∼ 30 wt% CO₂ and their properties depend on the applied parameters; they are non-toxic, non-combustible and can be recycled at end of life.