CO2 Medusa

Review on: Matter et. al., 'Rapid carbon mineralization for permanent disposal of anthropogenic carbon dioxide emissions', Science, 2016, 352, 6291, 1312-1314. [1]

This article [1], just published on the 9^th June issue of Science Magazine, has already received a lot of coverage on the web. Of course, having an intense passion in Chemistry and Geology, I am totally excited by this wonderful work!  It represents the two subjects holding hand-in-hand, contributing towards a better future.

The rising level of CO₂ in the atmosphere has been a serious issue, and many means have been devised to counteract this important factor that leads to global warming. A strategy is known as carbon capture and storage (CCS). It is the process of capturing excess anthropogenic CO₂, and to store and then deposit it to a sink, so that the CO₂ will not enter the atmosphere. The deposition site is usually a geological formation under the ground. Of course, deep ocean storage is not yet a feasible approach, because the introduction of CO₂ into ocean will lead to ocean acidification.

So what rock should we shoot the gas into? Most researchers tend to favor a sedimentary rock, sandstone, as the sink, because of the well-established research experience with this type of rock. Yet, a potential pitfall is that the fissures present in the rock layers of sandstone can lead to the leaching of CO₂ back to the atmosphere.

Thus, the researcher direction in the field has changed.  In this collaborative work, the researchers injected CO₂ into the igneous rock – the extrusive volcanic rock known as basalt. This is a great strategy because the minerals present in basalt can react with CO₂, and through a carbonation reaction, that results in the formation of the mineral calcite, a polymorph of CaCO₃. In this way, the excess CO₂ can thus be mopped up. The reaction rate was much faster than the rates modeled by computational methods. Also, the research represented a nice example of using an isotopic labeling technique (¹⁴C in this case) to characterize the formation of carbonate minerals from CO₂.

This is an impressive idea, yet the researchers also noted a possible obstacle to the generalization of this process is cost. Also, when a scaling up of the process is required, the reaction rate has to be acceptable to compromise the long-term cost. It is quite obvious a better understanding of the mechanism is required to fine-tune the carbonation reaction and to shut down other unproductive pathways – like the sandstone scenarios. To me, it seems that catalysis will be able to contribute to an improvement of the CCS process (Once a chemist, always a chemist?!). Indeed, I have found a paper back in 2013 in ‘Catalysis Science & Technology’, where the authors demonstrated the use of nickel nanoparticles as a catalyst for the mineralization reactions from carbon dioxide. [2] So, it seems that the door has already been opened and there are active research projects towards this direction. If the time course of the carbonation / mineralization reaction can be significantly shortened through the application of a low-cost catalyst, the process will become common place and then this can alleviate the problem of excess CO₂ in the long term.

One final chemical point of view is that we should bear in mind that CO₂ is a potential one-carbon building block. In photosynthesis, CO₂ is used to form the six-carbon sugar, catalyzed by the enzyme complex Rubisco. So, similarly, if CO₂ can be stored efficiently, this can be a great starting substrate for the production of other compounds, often employing organometallic catalysis.

All in all, it is a truly brilliant contribution, and it is more so because it has a great potential to lead to a better future.

by Ed Law

11/6/2016

Reference:

1. Rapid carbon mineralization for permanent disposal of anthropogenic carbon dioxide emissions.

J. M. Matter et. al., Science, 2016, 352, 6291, 1312-1314.

Further commentaries on:

http://www.sciencemag.org/news/2016/06/underground-injections-turn-carbon-dioxide-stone

http://science.sciencemag.org/content/352/6291/1262

2.  Nickel nanoparticles catalyse reversible hydration of carbon dioxide for mineralization carbon capture and storage.

G. A. Bhaduri and L. Siller, Catal. Sci. Technol., 2013, 3, 1234.

Growing out of Copper's Pants

Figure 1. Porphyry copper deposits. 

(Taken from http://pubs.usgs.gov/fs/fs053-03/fs053-03.html)

You see, I always have a strong interest in Geology and Geomorphology, and indeed I have been a tutor of the undergraduate Environmental Chemistry course for some time! I read ‘Nature Geoscience’ regularly and this month I have read a fascinating article about ‘porphyry copper deposit’. [1]

Figure 2. Formation of porphyry copper deposits. Taken from Source [2].

The 'golden child' here is copper (should be called 'copper child?), and these copper deposits indeed have high economical values. These deposits are porphyritic, and intrusive (hence plutonic) in nature. The positions of these deposits are often found near the convergent plate margins, and above the subducting plate. The magmatic (hydrothermal) fluid first rises through the continental crust. When the hydrothermal fluid rises, the rate of its cooling increases gradually, as it passes through the area of the fractures and intrusions. Mineralization leads to the formation of the porphyry copper deposits (Figure 2). [2]

A key theme of the article is about tectonic uplift, which is the 'lifting-up' of the surface of the mountain belts, in opposite to the direction of gravity. One of the components is known as 'exhumation', which is defined as 'the displacement of rocks with respect to surface'. Quantitatively, the rate of exhumation is related to the rate of erosion or the removal of overburden by tectonic processes. So, exhumation comes hand in hand with exogenic denudation processes. Erosion will wear away the mountains, and so the metamorphic rocks or reserves from below will become exposed at the surface.[3]

The Nature Geoscience article shows the relationship between climate and the effects it may cause to the orogenic geomorphology. The researches have studied Cenozoic porphyry copper deposits at convergent tectonic settings. From various data, they have discovered that a higher precipitation, which means a higher erosion rate by rain water, will lead to faster exhumation. The consequence of rapid exhumation is the sparsely distributed porphyry copper deposits, with a relatively younger age. By contrast, lower precipitation, which corresponds to an arid region, will lead to slower exhumation, and the copper deposits are more abundant and relatively aged. Therefore, in a sense the age of the copper deposits is related to the exhumation rates of the active orogens, and so this can serve as a 'sensor' to uncover the geological phenomenon. 

Upon the completion of this article, I have discovered that it also has been covered on the web already. Well, that means this research is really significant for many! [4]

By Ed Law

19/6/2015

  

Reference and sources:

1. A climate signal in exhumation patterns revealed by porphyry copper deposits

Brian J. Yanites and Stephen E. Kesler

Nature Geoscience 2015, 8, 462–465.

doi:10.1038/ngeo2429

2. http://ns.umich.edu/new/releases/22883-a-climate-signal-in-the-global-distribution-of-copper-deposits

3. Surface uplift, uplift of rocks, and exhumation of rocks.

P. England, P. Molnar

Geology, 1990, 1173-1177.

4. http://www.indicoresources.com/s/CopperPorphyryDeposits.asp