Frequently Asked Questions – Project Vesta
We utilize Forsterite, the Magnesium rich form of olivine.
Carbon Dioxide (CO2) dissolves into the ocean at a higher rate as the atmosphere contains more CO2
The CO2 is transformed into bicarbonate, and will eventually turn to CaCO3, calcium carbonate, which is used by marine animals like corals for their shells.
Bicarbonate is alkaline and so its creation in the water raises the pH making the water less acidic.
Silicate is the limiting factor for diatoms. Diatoms are a type of plankton that makes up the base of many marine food chains. They are threatened by increasing ocean acidification and nutrient deficiencies. This silicate increases their numbers, and they in turn further sink carbon dioxide through photosynthesis.
Corals use the calcium carbonate to build their shells. Overtime, when as more and more corals build on top of them, they sink and become limestone rock, which is eventually (on geological timescales) is subducted back into the center of the Earth.
Even at the proposed, full-scale yearly CO2 offsetting level, with a volume of 7 km^3 of olivine put on beaches each year for 100 years, it would only raise the magnesium level in the ocean from 1296 to 1296.6 ppm (and bicarbonate from 42 to 45 ppm), which is within normal global ocean water concentration ranges.
Why Use Olivine Vs Other Rocks or Minerals?
“Other rock types can also be used, but they are less effective or less available, although locally, there may be good reasons to use other rock types, such as basalts, anorthosites, or nepheline syenites. In the following weathering reactions, the formula of olivine will be simplified to Mg2SiO4 , although olivine normally is a mixed crystal of Mg2SiO4 and Fe2SiO 4 , with the Mg-endmember usually dominant.” The magnesium-rich end-member of the olivine solid solution series is called Forsterite and is found in large formations called dunite.
R.D. Schuiling, P148-149 – Geoengineering Responses to Climate Change
How fast does stationary and covered rock weather in the real world?
“The rate of weathering of dunite massifs in the tropical zone can be quantified, or at least a minimum rate of weathering can be firmly established. The first example is the dunite massif of Conakry/Guinea. This dunite occupies the entire peninsula on which Conakry, the capital of Guinea, is situated. It has an approximate length of 50 km and an average width of 5 km. Over its entire surface, it is covered by a thick lateritic weathering crust, which is very clearly visible as a purplish red area on satellite pictures (see Fig. 7.5). This lateritic crust, which is the iron-rich insoluble red residue of the dunite after deep tropical weathering, contains virtually no silica, magnesium or calcium oxides which were completely leached out during the weathering process [19]. These components make up around 90% of the original dunite. This means that 1 m of laterite is equivalent to 10 m of dunite, or even more if the remaining components of the laterite were not completely immobile but have also been leached to some extent. The same author presents evidence that iron has in fact been fairly mobile and was partially leached out as well, which means that 1 m of laterite is equivalent to more than 10 m of dunite. The weathering crust has a thickness between 30 and 100 m. The age of the dunite (that is to say the time at which this dunite intrusion formed) has been determined as 195 million years. From these data, it is simple to calculate the minimum rate of weathering as follows: 50 m of laterite is equivalent to 500 m of dunite, 500 m (= 500 million microns) divided by 195 million years is 2.6 mm/year. This is already ten times faster than deduced from laboratory experiments, but the real rate of weathering must have been considerably faster. The rock is an intrusion. That means it was emplaced between rocks at some depth and covered by other rocks, which had to be removed first by erosion before the dunite became exposed and could start its weathering process. If the dunite intrusion has taken place at 2km depth, it would take 100 million years before the dunite massif was entirely laid bare by erosion at an estimated erosion rate of the order of 1–2 cm/1,000 years [20]. This is the average erosion rate for all continents. This correction alone more than
doubles the calculated rate of weathering. That is not the only positive correction that must be made. In more recent times, the weathering process, under such a thick weathering crust, has virtually come to a standstill, as the thick laterite crust effectively shields the underlying rock from further interaction with the atmosphere. This shortens again the time span over which weathering was active, and thereby increases the rate of weathering.
-R.D. Schuiling, Geoengineering Responses to Climate Change P154
How Does the Weathering Rate Differ Between Solid as Opposed to Loose Olivine Grains?
“A further positive correction concerns the difference between weathering of a solid rock as opposed to loose grains. A rock is attacked by weathering from above along a two-dimensional front, whereas loose olivine grains in soil are attacked from all sides. It seems certain that olivine grains in tropical soils dissolve at least at a rate of 10 mm/year, but most likely even faster. Even when their surface retreats only by 10 mm/year, a grain of 100 mm will disappear in 5 years. A similar calculation can be made for the dunite body at Jacupiranga, Brazil [21]. Here, the rock has an age of 130 million years, and it is covered by a weathering crust of >40 m (this is where the drill hole stopped, but at 40 m, the drill was still in lateritic weathering crust). The minimum rate of weathering turns out to be >3.1 mm/year, but the same positive corrections have to be applied as in the Conakry case.”
-R.D. Schuiling, Geoengineering Responses to Climate Change P154
What is the Minimum Yearly Weathering Rate?
From a global balance of weathering and erosion, similar minimum rates of weathering emerge. The average rate of erosion of the continents is 1–2 cm in a 1,000 years [20]. As olivine grains from the interior of the continents do not make it to the oceans, this means that olivine rocks dissolve (= weather) at least at the same speed, which is 10–20 mm/year.
-R.D. Schuiling, Geoengineering Responses to Climate Change P155
What is the Weathering Rate of Stationary Piles of Ground Up Olivine?
The most dramatic evidence for fast weathering of crushed magnesium silicate rocks comes from observations of weathering rates of mine dumps of such rocks [22]. By measuring the amount of a suite of newly formed Mg carbonates, it was shown that the mine tailings of
two abandoned asbestos mines in British Columbia weather extremely fast. In this case, it does not involve fresh olivine, but its hydration product serpentine (Mg 3 Si 2 O 5 (OH) 4 ) that weathers and produces carbonates. This carbonation proceeds as follows:
Mg3Si2O5(OH)4 + 3CO2 + 2H2O —> 3MgCO3 + 2H4SiO4
At low temperatures, magnesite seldom forms, but in its place, hydrated magnesium carbonates, like nesquehonite Mg(HCO3)(OH)*2H2O, are found instead
In order to make sure that these carbonates have indeed newly formed, Carbon 14 analyses were performed on these carbonates which gave an age of about 0, showing that the carbon in these minerals really represents the sequestration of present-day atmospheric carbon [23]. In one of the cases, the mine dump, occupying a surface area of 0.5 km 2 , had captured 82,000 t of CO 2 between 1978
and 2004, more than 50 times the maximum ever recorded for natural weathering under the most favorable conditions. The real rate of weathering is even higher because the authors have only taken the solid products into account, whereas the waters that percolate through the mine dumps carry an additional load of dissolved weathering products. These waters become quite alkaline, and their high silica content leads to small diatom blooms in a pool at the foot of the tailings dump and in at least one of the mine pit.
-R.D. Schuiling, Geoengineering Responses to Climate Change: Carbon Dioxide Sequestration, Weathering Approaches P155-156
How is Weathering Olivine on Beaches and in Shallow Seas Different?
“To understand what happens to olivine upon weathering we must distinguish between the chemical reaction of olivine with seawater and mechanical impacts during grain transport…The surf is clearly the world’s largest, most efficient and cheapest ball mill. The experiments also showed that a mixture of different grain sizes of olivine wears down more quickly than single grain sizes.”
-R.D. Schuiling, Geoengineering Responses to Climate Change: Carbon Dioxide Sequestration, Weathering Approaches P157-158
Why Are Abiotic Lab Experiments Wrong?
“In abiotic laboratory experiments, it was found that the surface of olivine grains retreats at a few tenths of a micron per year [18]. This is described by the shrinking-sphere concept. Such low rates would make it difficult to use enhanced weathering to mitigate the greenhouse effect. Fortunately, there is observational evidence on rates of weathering of olivine in the real world (see below), which shows that the rates are more than tenfold, and probably 100-fold larger, than those found in the laboratory. Qualitative information on fast rates of weathering is obtained from volcanic terrains with rocks containing olivine. When volcanism started in the Eifel/Germany, synchronous Rhine sediments downstream in the Netherlands immediately started to contain a wealth of volcanic minerals, but no olivine, despite the fact that these volcanic rocks contain plenty of that mineral. Contrary to the there minerals of volcanic origin, olivine has not survived the short trip from Bonn to the Dutch border. Similar observations are reported from many other volcanic
terrains in the world. Although suggestive of fast weathering, this evidence is difficult to quantify.”
-R.D. Schuiling Geoengineering Responses to Climate Change p153
What Are the Experimental Results of Small Scale Testing of Mechanical Activation of Olivine?
“In a recent experiment, this surf action was reproduced [30]. Grains of olivine were rotated in conical flasks. Within 24 h, the crushed olivine grains that were originally angular, with a rough surface, had transformed into rounded and polished grains (Fig. 7.8).
The clear water at the start had become an opaque white suspension of very tiny olivine slivers, half of which had a grain size of less than 5 mm. The system reacts fast, the pH shoots up to 9.4, and a clay-type magnesium mineral is newly formed… The experiments also showed that a mixture of different grain sizes of olivine wears down more quickly than single grain sizes.”
-R.D. Schuiling, Geoengineering Responses to Climate Change: Carbon Dioxide Sequestration, Weathering Approaches P157-158
What Do Criticisms of Beach Weathering of Olivine Get Wrong About the Weathering Rate?
“The mechanical action, the grinding down of olivine grains, by waves and currents largely determines the rate of weathering of olivine on beaches and in shallow seas with strong bottom currents. The papers in which the rate of weathering of olivine grains on beaches is calculated [29], are based on theoretical modeling and overlooks the mechanical consequences of the surf, where grains are wearing down by the constant rubbing and bumping against each other.”
-R.D. Schuiling, Geoengineering Responses to Climate Change: Carbon Dioxide Sequestration, Weathering Approaches P157
How Much Olivine Is Needed For Total Yearly CO2 Emission Removal, What Size, and How Would It Be Distributed?
7 km^3 volume of olivine rock would be crushed and milled to grains of around 100 mm in diameter. If 7 km^3 is spread over an area of 10 million km^2, it will occupy a layer of 0.7-mm thickness. Grains of olivine of 100 mm will weather in approximately 5 years in tropical soils. It will, therefore, be cheaper to spread a layer of 3.5-mm thickness each year over an area of 2 million km^2, shift to the next area in the following year, and come back to the first after 5 years.