I think that not everybody realizes that some 300 million tons of CO2 are captured every year by the weathering of basic silicates, notably the most common one, olivine. To demonstrate this, the diagram below shows the analytical data of some 20 spring water samples in olivine rocks in Turkey. It shows what happens when rain falls on soils on top of olivine rocks. The rainwater contains essentially only some CO2 and has a pH in the order of 6. Then it penetrates the soil, which has much higher CO2 concentrations in the soil atmosphere than in the atmosphere above. Dead plant material is decaying, the soil fauna is breathing, both releasing CO2, so the CO2 concentration of the soil atmosphere is often hundred times or more higher than in the atmosphere. The water equilibrates with this high CO2 concentration. Then it seeps into the rock, and reacts with it, releasing magnesium to the solution, and the pH rises to values around 7.5 to 8.5. This weathering reaction can be written as
Mg2SiO4 + 4 CO2 + 4 H2O --> 2 Mg2+ + 4 HCO3- + H4SiO4 (so the CO2 is captured as bicarbonate in solution). At some point this water is emitted again as a spring. This spring water is very healthy, and we often had to wait in line for the many people who collect this spring water in containers and jerrycans to bring home. Most of the water flows away in small brooks, and finally reaches the sea, where the calcium and magnesium are used by plankton, corals and shellfish to form limestones and dolomites, the ultimate sustainable storage of the CO2. Just as an afterthought: so if we irrigate semi-arid land on top of olivine massifs, we have a cheap way to fix CO2 by increasing the number and the volume of springs in such rocks, Olaf Schuiling I attach the paper in which these data were published \ [cid:[email protected]] ® Fig.1: Concentration in meq [Ca2+ + Mg2+] in spring waters. Total carbon as mg CO2. ® composition of rain water. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout.
image001.emz
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olivine hills.doc
Description: olivine hills.doc
