Carbon dioxide sequestration by mineral carbonation Literature review update 2005–2007
The field of mineral sequestration for the long-term storage of carbon dioxide is a CCS (carbon dioxide capture and storage) option that provides an alternative for the more widely advocated method of geological storage in underground cavities, especially at locations where such underground cavities are not available, where the risk of leakage of the CO2 stored underground is considered unacceptable, or where large resources of material suitable for carbonation are present. Although the state of the art of mineral carbonation processing technically suffers from too slow chemical kinetics and poor energy economy, the driving forces for continued attention for this CCS route are its sheer capacity (dwarfing other CCS methods), the fact that it gives compact and leakage-free CO2 fixation that needs no post-storage monitoring and finally the potential of operating at a zero (or negative) net energy input, provided that the process is properly optimised, and utilises the benefits of favourable thermodynamics. Despite partial successes and promising process ideas, so far the keys to success have not been found. While work on this subject did not start until the 1990s, earlier literature reviews have considered the period until 2000 [1†], the period until 2003 [2†] and the years 2003-2004 . As already noted in the previous review, the increasing worldwide interest in mineral carbonation (demonstrated, for example, by the number of contributions to the latest GHGT conferences) has motivated the prompt production of the next literature review. The information collected and presented here shows that mineral carbonation R&D found its way to an increasing number of countries, and that besides carbonation of magnesium- or calcium-based minerals especially the carbonation of waste materials and industrial by-products is expanding. Currently the main route for carbonation uses aqueous solutions, either “direct”, where an additive is used to achieve the required chemical reaction rate, or “indirect” where extraction of Mg or Ca and the subsequent carbonation of that are separate process steps that are optimised independently. Depending on whether purpose of the goal is to bind large amounts of CO2, or produce a carbonate material, the methods, process parameters, input materials and additives vary widely depending on what cost level is considered acceptable. One aspect addressed in some more detail in this report is energy efficiency, showing that the costs of process heat input are significantly over-estimated when charged the same way as power input, giving a false impression of overall process economics. For large-scale CO2 sequestration using magnesium silicates the aqueous route developed in the U.S. is still the most successful one, with a cost level at above 40 €/t CO2. Work on stepwise carbonation of serpentine with the exothermic carbonation step conducted at high temperatures and pressures is ongoing in Finland.