Mineral carbonation to produce magnesite: a practical solution for long-term CO₂ sequestration in the great Serpentine Belt, NSW, Australia

New South Wales requires a range of sequestration options for its annual stationary emissions of C0₂ from energy generation. With inadequate sequestration capacity in depleted hydrocarbon reservoirs or porous aquifers at requisite depths for supercritical injection, mineral carbonation is an additional method of sequestration for carbon dioxide emissions. Mineral carbonation replicates the natural weathering process of magnesium-rich silicate rocks to form principally insoluble magnesite (MgC0₃), binding C0₂ chemically in a form that is stable over geological time. The reactions are exothermic, and occur naturally over extended periods. This study assessed the properties of the ultramafic rocks of the Great Serpentine Belt between Bingara and Barraba, NSW, for their mineral carbonation potential. Although dunites have the fastest reaction time and highest conversion rate, the more abundant serpentinites, although hydrated, are attractive targets for mineral carbonation. Serpentinite volumes calculated to a maximum mineable depth of 500 fil have the potential to sequester ex situ more than 300 years of stationary emissions for NSW at 2007 levels. Geomagnetic modelling indicates serpentinites extend to 2 km depth, which may add significant in situ sequestration capacity. Current research aims to decrease the overall cost of storage of C0₂ in serpentinite from $70 to $40 per tonne of net fixed C0₂. Costs will be offset with saleable end-products such as magnesite refractories, magnetite separated during processing, chromium in the form of chromite and spinel, nickel as an accessory element in serpentine minerals, as well as silica and exothermic heat. Commercially viable mineral sequestration requires the carbonation reaction rate to be accelerated. Current research focuses on reducing energy penalty by accelerating the aqueous weathering reactions occurring naturally in serpentinites and pursuing biologically-mediated sequestration by microbes