As for tonnage of mineral no sure if this effects your calc, but isn't the reaction: CO2 + CaSiO3 --> CaCO3 + SiO2 or more likely with silicate minerals: CO2 + MgSiO3 --> MgCO3 + SiO2.
If you are really worried about mineral tonnage, why not get more bang for the buck with: 2CO2 + H2O + CaSiO3 --> Ca(HCO3)2 + SiO2 plus adding dissolved Ca(HCO3)2 to the ocean could help mitigate ocean acidification. Silicate weathering is the ultimate consumer of excess atmos CO2 over 100kyr time scales, so the capacity is indeed there. Lets see if there are safe, cost effective ways of accelerating this. -Greg ________________________________________ From: [email protected] [[email protected]] On Behalf Of John Gorman [[email protected]] Sent: Sunday, July 10, 2011 1:22 AM To: geoengineering Subject: [geo] Large scale CCO2 removal from atmosphere Whatever happens with emissions we will have a lot of CO2 to remove from the atmosphere after mid centaury so it was good to hear in the recent Bakerian lecture at the Royal Society that there are saline aquifers about a mile down in the earth over much of the land mass of the planet. These could hold enough CO2. However, after what happened at that South American lake, I cant see people wanting any CO2 stored within a thousand miles of their homes. I would much rather see the CO2 locked up for good. The chemical solution exists and has been discussed here on various threads. 2 CO2 + Ca2SiO4 = SiO2 + 2 CaCO3 There is unlimited calcium silicate, (together with magnesium silicate as peridotite) in various places in the world. (eg northern Iran) because it is the main constituent of magma. Also the reaction is exothermic. So lets look at the practicalities of such a "plant" (facility -it could be more than one but lets look at one for now). First -how big? well if it was up and running in 2050 say, emissions might have peaked by 2035, say and be about the same as now, falling towards 2100. So if the plant balances current emissions in 2050, it will start to lower the concentration thereafter. (Concentration will then peak at about 500 ppm in 2050) So to balance the current 30 billion tons of CO2 we need to mine 90 billion tons of peridotite each year. What ! 90,000,000,000 tons -that's impossible! Well actually its only about ten times the annual world production of coal, its all on the surface and it wont have to be transported very far, so its not impossible. How much CO2 do we have to remove? Lets assume the plant removes 40 billion tons per year. If it has a life of 50 years while the emissions drop linearly to near zero in 2100. the net removal will be 1500 billion tons which is just about the excess that 500 ppm is over preindustrial at 280. So this brings us back to normal in 2100. How big would the site be to achieve this? specific gravity of the solid peridotite will be about 3 so one cubic metre weighs about 3 tons. So 2000 billion tons will have a volume of about 700 billion cubic metres which is 700 cubic kilometres. If we opencast mine to a depth of 500 metres that requires a land area of 1400 square km, which is a circle of radius only about 20 kilometres. So a combined mining and processing facility only about 25 miles across could deal with the whole of the CO2 problem for good ! It would need a nuclear power station or two for the transport, crushing etc but the reaction is exothermic so it would be self sustaining once up to temperature. The calcium/ magnesium carbonate would be dumped int the same hole that the peridotite is taken out of, working in a circle round the central processor for 50 years. This " back of an envelope" calculation is produced for comment. I hope I haven't lost a few factors of 10 ! Could any chemical process engineer suggest how the actual processing plant might look. john gorman -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
