Indirect Multistep Process Routes

Indirect (Multistep) Process Routes 14.4.3.1 Cas-Solid Processes 

Following efforts to directly carbonate magnesium silicate, studies conducted in the US during the late 1990s shifted to MgO extraction from magnesium silicates 

In Finland, investigations into stepwise carbonation processes initially involved the use of Finnish serpentine and (calcined) magnesium hydroxide powder ( 20gm, 99% pure) in a PTGA with humid C02, at 0.1 to 3.5 MPa pressure. The materials were first heated to 1273 K, and then cooled in (mainly) C02/N2 mixtures. Tests conducted at elevated pressures did not produce the expected increase in MgO carbonation rate, as the final carbonation conversions fell from 5.6% at 0.1 MPa to 2.9% at 3.5 MPa in 99%/l% C02/H20. Hence, the decision was taken to proceed with Mg(OH)2 under test conditions where MgO formation was thermodynamically unfavorable [85, 96]. 

Raw material can be found in vast amounts in Finland besides hoisted material, the serpentinites in Eastern Finland (the Outokumpu-Kainuu ultramafic rock belt) alone could provide sufficient material for 200-300 years of CCS processing (based on a current C02 emission excess in Finland of -llMt per year, with respect to the 1997 Kyoto Protocol commitments) [24]. 

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