Synthetic Stones Capture Carbon

While scrubbers in smokestacks at coal plants can pull out toxic gases like sulfur dioxide, scientists haven’t yet developed a cost-effective technology to remove carbon dioxide from industrial exhaust. Now European researchers have tinkered with the chemical composition of limestone to produce a material that absorbs almost twice as much CO2 as the natural mineral can (Environ. Sci. Technol., DOI: 10.1021/es2034697).

Small-scale carbon-scrubbing operations currently rely on amine-based materials. But these materials lose some of their absorbency after repeated use. Dolomitic limestone, CaMg(CO3)2, is an alternative. As early as the 1970s, scientists noticed that when they heated it, the mineral could absorb CO2 from the mixture of gases emitted by coal power plants and later release it as a purified gas, ready to compress and store. It doesn’t absorb as much CO2 as amine-based materials, but it can survive more absorption-release cycles.

To improve on dolomitic limestone’s carbon-absorbing properties, Christoph Müller of the Swiss Federal Institute of Technology, Zurich (ETH), and his colleagues wanted to minimize the amount of magnesium in the material. Magnesium helps form microscopic pores in the mineral, which expose more surface area of the calcium component to CO2. But magnesium doesn’t react with CO2. With more of the element, the limestone becomes heavier and requires more heat to drive the calcium to react with CO2.

So Müller and his colleagues created a series of synthetic limestones by mixing different ratios of calcium and magnesium, precipitating the mineral with different bases, and using different crystallization times. They found that a calcium-to-magnesium ratio of about 7:3, precipitation with a nitrate base, and 14 days of crystallization produced the best-performing material.

Per gram of material, the material absorbed about 0.56 g of CO2, while natural dolomitic limestone absorbs 0.38 g CO2. The synthetic material also performed better after repeated cycles of absorption and release. After 15 such cycles, a gram of the synthetic limestone could still grab about 0.51 g of CO2, while the natural mineral could absorb only 0.26 g.

When the scientists studied the best-performing synthetic mineral’s crystal structure using a scanning electron microscope, they found that the magnesium and calcium atoms were mixed evenly throughout the crystal lattice, similar to dolomitic limestone’s structure. Meanwhile, in the poor-performing materials, the two elements formed separate mini-crystals. The team speculates that the precipitation technique and crystallization time allowed the material to form more pores despite the low amount of magnesium.

Carlos Abanades, a chemical engineer at the National Coal Institute in Oviedo, Spain, says that the material is promising and adds that the researchers next should test whether a scaled-up version of the material will cost less than existing amine technologies.

Edward J. Anthony, a chemical engineer at the University of Ottawa, calls the study “very intriguing work.” He says the next step will be to test whether the new material performs as well after even more cycles and in the hot conditions found in industrial settings. Müller says his team plans to test the material under those conditions.

First published by Chemical & Engineering News: [html] [pdf]

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Jaegihorn incident report

Messieurs Goldman and Davenport, in Switzerland for the McCombie nuptials, invited Ms Crockett and Mr Laursen to an attempt on the Jaegihorn, above Saas Grund in the Swiss Valais region. Goldman and Davenport charmed the hut mistress into providing extra victuals. With full bellies and a 4am start, Laursen led the team on a circular tour of a neighbouring moraine in a suspected effort to escape the climb.

When the fog cleared and the sun rose, however, the team identified the start of the Alpendurst route and commenced climbing activities culminating in a successful summit. From here the evidence grows patchier. The two rope teams lost sight of one another. Subsequent reports from CUMC Zurich stationmaster Kavanaugh place Goldman and Davenport on a dance floor at a castle outside Basel ca. 3am. Davenport failed to report to the post-climb debriefing in Dietikon while Goldman reported to Dietlikon instead. Kavanaugh relieved all parties of their duties in disgust.

See the original as it appeared in Cambridge Mountaineering: [pdf]

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Mantle Recycles Far Faster Than Thought

The magma that rises from the mantle, forming new islands, may blast more than it bubbles. Where those plumes of magma originate — at the core-mantle boundary or the mantle-crust boundary — and how fast they rise to the surface are still open questions among volcanologists. But now a new study of minerals from the volcano Mauna Loa on the Big Island of Hawaii suggests that some elements made a 2,900-kilometer-long journey from the core-mantle boundary to Earth’s surface in as little as half a million years — quadruple the speed found by previous studies.

Alexander Sobolev, a geochemist at Joseph Fourier University in France, and his colleagues examined hundreds of miniscule inclusions in tiny grains of olivine in basaltic lava erupted from Mauna Loa. By measuring the amount of rubidium, which decays into strontium at a predictable pace, and the amount of strontium in the samples, Sobolev and his team concluded that there was too much strontium, given previously assumed mantle recycling rates.

The rubidium-strontium ratio is “the opposite of what you’d expect” for rocks formed from subducting seafloor only, says geochemist Tim Elliott of Bristol University of England, who was not part of the research team. So the strontium is likely from seawater, instead: As oceanic crust is subducted into the mantle, it brings seawater with it. Researchers know how strontium levels have changed in seawater over the Earth’s history, so once Sobolev and colleagues decided to assume that their strontium came from seawater, the age of the samples could be extracted from tables showing the concentration of strontium in seawater of different ages.

The strontium concentrations indicated an age of between 650 million and 200 million years, they reported in Nature. Assuming that the samples must have risen from the core-mantle boundary, which is much deeper than the 600-kilometer mantle-crust boundary, the scientists calculated a crustal recycling rate of between 1 and 3 centimeters a year, four times faster than what other research has suggested.

“It’s provocative and it’s an important break-through if it turns out to be confirmed,” says Dominique Weis of the University of British Columbia in Canada. “What’s exciting is that it’s proof that something that was near the surface went into the mantle and was then brought back up,” Weis says, adding that she would like to see more evidence of the timing of the cycle.

Weis and Elliott both say they’d like further proof of the faster recycling rate through examples from elsewhere in Hawaii or from other volcanic islands. “Mauna Loa is special,” Weis says. Lead isotopes have also shown anomalies on that volcano. “What I think should be done is to do analysis of more lava from other volcanoes,” she adds. Indeed, Sobolev’s “model would predict it’s a common occurrence,” Elliott says, so it should be possible to test the model by collecting and analyzing more samples elsewhere.

See this news story as it appeared in EARTH Magazine: [pdf]

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Extreme Weather More Frequent in Northern Europe

Northern Europe may have gotten stormier since the late Victorian Era. Looking at a fresh analysis of old atmospheric pressure data, researchers found that the annual number of windy days may have risen by one to five days per century in parts of northern Europe, and the intensity of such storms may have grown too.

Markus Donat, a climate modeler at the University of New South Wales in Australia, and his colleagues wanted to calculate the frequency and intensity of wind storms across Europe to search for trends lasting longer than a decade, something several research groups are pursuing. Donat and his team used the 20th-Century Reanalysis, a global model released earlier this year that incorporates pressure readings from 1871 to 2008.

In a reanalysis model, researchers take a weather model and mix in real-world observations to try to reconstruct historic weather patterns. The way they incorporate the real-world observations can make a difference in the outcome of their reconstructions though, because each type of weather observation requires customized corrections that may introduce incompatible errors.

The errors in the 20th-Century Reanalysis model are easier to understand than in other reanalysis models, Donat says, because it only uses one type of weather observation: pressure readings. Most reanalyses use several kinds of weather measurements, such as those taken by weather balloons and satellites. Furthermore, the 20th- Century Reanalysis model takes into account a longer time period than most such models, he says, which gives the new study “better sensitivity” than other studies that have looked for such trends over shorter time periods.

Donat and his colleagues used the pressure values from the reanalysis model to predict daily wind speeds throughout Europe over the duration of the reanalysis. Then they searched for long-term trends and found an increase in maximum wind speeds and in the frequency of extra-windy days, as they reported in Geophysical Research Letters.

The study appears to show a small trend above natural decadal variability, says climate modeler Len Shaffrey of the University of Reading in England. But identifying trends, or the hints of trends, is one thing; explaining them is another. “Although they’ve characterized these trends, the reason why the trends are there is uncertain,” Shaffrey says.

Part of the uncertainty arises because there were fewer pressure observations early in the period covered by the 20th-Century Reanalysis, so assumptions made in integrating the data with the meteorological model may distort the weather reconstructions, says meteorologist Kevin Hodges of the University of Reading. “I’m not sure if you can get more [data] going back to 1871,” Hodges says, “but it motivates the need to try to improve the data record.”

Gilbert Compo of the University of Colorado at Boulder, one of the creators of the 20th-Century Reanalysis, says that this is “the sort of study we hoped would get done” with the data. But he also notes that he would be more convinced of the trend Donat and colleagues found if there were an independent comparison covering the same time period, such as ground wind speeds. “Not that that’s an easy thing to do,” he adds, “because you have to account for ground drag and all kinds of other effects.”

Donat says that “a very important next step would be an attribution of mechanisms,” and he and his colleagues will next look for connections between this trend and changes in the other regional climate patterns such as the North Atlantic Oscillation or the El Niño/Southern Oscillation.

See this news story as it appeared in EARTH Magazine: [pdf]

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