Mineral Sequestration of CO2 and Recovery of the Heat of Reaction

Apart from saving energy, sequestration of CO2 is the most direct way of combating the excessive greenhouse effect. Current approaches focus mainly on CO2 storage in gaseous form in abandoned gas fields or aquifers. Sequestration in mineral form is still in its infancy, because the dry carbonation of common Mg- or Ca-silicates is unsuccessful. It can be deduced from natural examples that wet sequestration, combining hydration and carbonation is likely to be more successful. Several approaches are explored in this paper, either in situ in dunite massifs (olivine-rich rocks), or by reacting crushed olivine off-site in contained spaces with the off gases of thermal plants. The reaction produces a large amount of heat, which can be recovered as high enthalpy steam. In order to be effective, however, it should only be applied to large volumes of olivine, in a typical macro-engineering fashion, as the heat losses become unacceptably high in small systems with a high surface to volume ratio. One possibility would be to fill half of abandoned deep opencast mines with ground olivine and cover it by backfill. In the bottom part a mixture of hot CO2 and steam is injected in order to set up a convective system similar to geothermal systems