On Al Jazeera, of all places, they had a story on praising all sorts of folks working to fix “Climate Change”. One of them was an Icelandic project to fix CO2 underground. This is different from other programs in that it is not just pumping CO2 into underground storage, it is placing it where it will react with one kind of rock, basalt, and make another, calcium carbonate. The “feature” is that it permanently places the CO2 in the form or rock where it can not leak out (nor, for that matter, be effectively recovered…)
The process is to take steam, from geothermal wells, and use it to generate electric power, then hot water for homes. Along the way, a very small part of what is produced is H2S and CO2. They use a cold water counter current stripper to absorb the CO2 and H2S from the gasses from the wells, and then inject this acidic water into a basalt rock layer underground.
After about 2 years, the CO2 has reacted with the basalt and formed Calcium Carbonate rock. This is then permanently stuck underground and can’t leak out.
Basalt is found as the bottom of the ocean floor, and in volcanic rocks all over the world.
Basalt (pronounced /bəˈsɔːlt/, /ˈbæsɒlt/ or /ˈbæsɔːlt/) is a common extrusive igneous (volcanic) rock formed from the rapid cooling of basaltic lava exposed at or very near the surface of a planet or moon. Flood basalt describes the formation in a series of lava basalt flows.
By definition, basalt is an aphanitic (fine-grained) igneous rock with generally 45-53% silica (SiO2) and less than 10% feldspathoid by volume, and where at least 65% of the rock is feldspar in the form of plagioclase. This is as per definition of the International Union of Geological Sciences (IUGS) classification scheme. It is the most common volcanic rock type on Earth, being a key component of oceanic crust as well as the principal volcanic rock in many mid-oceanic islands, including Iceland, the Faroe Islands, Réunion and the islands of Hawaii. Basalt commonly features a very fine-grained or glassy matrix interspersed with visible mineral grains. The average density is 3.0 g/cm3.
Basalt is defined by its mineral content and texture, and physical descriptions without mineralogical context may be unreliable in some circumstances. Basalt is usually grey to black in colour, but rapidly weathers to brown or rust-red due to oxidation of its mafic (iron-rich) minerals into hematite and other iron oxides and hydroxides. Although usually characterized as “dark”, basaltic rocks exhibit a wide range of shading due to regional geochemical processes. Due to weathering or high concentrations of plagioclase, some basalts can be quite light-coloured, superficially resembling andesite to untrained eyes. Basalt has a fine-grained mineral texture due to the molten rock cooling too quickly for large mineral crystals to grow; it is often porphyritic, containing larger crystals (phenocrysts) formed prior to the extrusion that brought the magma to the surface, embedded in a finer-grained matrix. These phenocrysts usually are of olivine or a calcium-rich plagioclase, which have the highest melting temperatures of the typical minerals that can crystallize from the melt.
Relative to most common igneous rocks, basalt compositions are rich in MgO and CaO and low in SiO2 and the alkali oxides, i.e., Na2O + K2O, consistent with the TAS classification.
Basalt generally has a composition of 45–55 wt% SiO2, 2–6 wt% total alkalis, 0.5–2.0 wt% TiO2, 5–14 wt% FeO and 14 wt% or more Al2O3. Contents of CaO are commonly near 10 wt%, those of MgO commonly in the range 5 to 12 wt%.
High-alumina basalts have aluminium contents of 17–19 wt% Al2O3; boninites have magnesium contents of up to 15 percent MgO. Rare feldspathoid-rich mafic rocks, akin to alkali basalts, may have Na2O + K2O contents of 12% or more.
So this stuff is everywhere volcanic (which is a huge part of the earth) and is very rich in alkaline chemicals including calcium and magnesium oxides. It will react readily with anything in an acidic solution.
Now the first thought that comes to mind is that with the ocean floor being up to 6% alkalis and another 15% to 25% alkaline oxides that are highly reactive with even very weakly acidic species, just how in the heck could the ocean ever become acidic? It just can’t. Ever. The ocean floor would neutralize it.
So why is basalt like that? Because it was cooked by volcanic heat that drove out any water of hydration and decomposed any carbonates to oxides and silicates. In the process, releasing lots of CO2 to the environment. That’s why all those global volcanoes emit lots of CO2 and why all the “mid-ocean ridges” similarly vent lots of CO2.
Given just how massive is the global inventory of basalt, it’s pretty clear that the chemistry of the planet is dominated by an alkaline / basic bias. Only a trivial part is able to become acidic. Some of the air, and surface waters on land. A little bit of stuff that becomes life. Once those acidic bits come back in contact with the alkaline rocks, like basalt, they react again and are neutralized. In the process, the basalt weakens and breaks down into those reddish iron rich soils seen in many places on the continental surface.
Once those soils, muds, and other deposits get subducted back under a continent, then they are again melted and cooked to release the trapped CO2, water and other light gases (that H2S) and reform lava that becomes basalt.
That is the great cycle of CO2, and of rocks. That is the core of the “Carbon Cycle”. What people do is essentially irrelevant.
So let that sink in for a minute. Just what basalt means about the world. All those megatons of essentially alkaline material making up the ocean floor and gigantic expanses of volcanic rocks globally. The CO2, cycling between the air and rocks then subducted and moving from rocks to volcanic gasses, then back to the air to be again consumed by eroding basalt.
CarbFix is a collaborative research project led by Reykjavik Energy, that aims at developing safe, simple and economical methods and technology for permanent CO2 mineral storage in basalts. It was founded in 2007 by Reykjavík Energy, CNRS, the University of Iceland, and Columbia University.
Now the fascinating thing to me is that neither the wiki, nor their web site, can I find them describing their water based CO2 stripping process. It was described in the Al Jazeera video. Basically a cold water shower through the gasses absorbs the CO2 and H2S. That’s all it takes.
Now, think just a minute… Cold rain, falls through the air, and onto a basalt rock surface. Sounds a whole lot like natural process that make carbonic acid in rain and weathers natural rocks.
Natural Acidity of Rainwater
Pure water has a pH of 7.0 (neutral); however, natural, unpolluted rainwater actually has a pH of about 5.6 (acidic).[Recall from Experiment 1 that pH is a measure of the hydrogen ion (H+) concentration.] The acidity of rainwater comes from the natural presence of three substances (CO2, NO, and SO2) found in the troposphere (the lowest layer of the atmosphere). As is seen in Table I, carbon dioxide (CO2) is present in the greatest concentration and therefore contributes the most to the natural acidity of rainwater.
So natural cold rain strips CO2 from the air. Acid rain water falling on volcanic rocks reacts to break down the rocks and fix the CO2. All without human interaction. The CarbFix folks even go so far as to call their process “accelerated weathering”.
So tell me again just why we need this process? Since as soon as the air gets a bit colder as we enter the cooling phase of the next glacial, that cold air CO2 stripping process will increase a lot and atmospheric CO2 levels ought to once again drop to the near plant starvation levels seen in the last cold glacial period. At 180 ppm plants suffer greatly. Even at 220 ppm they have some trouble. It isn’t until you reach levels of 1000 to 2000 ppm that the plants are really fully happy and growing at their best. That is the level that existed when most of the plants evolved their photosynthesis. At the present 400 ppm, we are still far below the best level of the plants. We are on the cusp of the end of the Holocene, and when that happens and the cold air stripping returns, there will be very significant food production issues as the plants again struggle just to survive.
Do we really want to have locked away large amounts of CO2 in vast depths of basalt?