Scientists find an easier way to trap carbon dioxide in rock | Science News for Students

Scientists find an easier way to trap carbon dioxide in rock

If they can scale it up, this process could someday help curb climate change
Sep 20, 2018 — 6:40 am EST
a piece of magnesite, a gray and white mineral, on a black table and against a black background

In nature, this magnesite takes thousands of years to form. Now researchers can make tiny amounts of this mineral in the lab. And it only takes three months to form.

A_Pobedimskiy/iStockphoto

Scientists have suggested trapping carbon dioxide in rocks as one way to slow the rate of climate change. But they hadn’t come up with an easy way to do it. All their proposed tactics appeared to be difficult, costly or require too much energy. Until now, anyway. Researchers in Canada have just proposed a new technology to collect and trap the greenhouse gas.

Limestone and other minerals already store a lot of carbon dioxide (CO2) on Earth, notes Ian Power. He’s a geoscientist at Trent University in Peterborough, Canada. The problem: This natural process is slow. It can take thousands or even millions of years. At present, he explains, “We’re emitting so much CO2 now that Earth can’t keep up.”

But Power’s team has just reported a way to quickly do what nature does slowly. A mineral called magnesite (MAG-nuh-syte) locks up CO2. A metric ton of this mineral (also known as magnesium carbonate) can store about half a metric ton of CO2. The chemical normally takes thousands of years to form. But in their lab, Power’s group made it happen in just a few months.

On August 14, Power described how his team did this at the Goldschmidt geochemistry conference in Boston, Mass.

How the lab cooked up this CO2 ‘sponge’ so quickly

Ions are electrically charged atoms or molecules. Power’s group combined positively charged magnesium ions and negatively charged carbonate ions. (Carbonate ions form when carbon dioxide mixes with water.) Magnesite naturally can hold a lot of CO2.

Magnesite occurs naturally. But the process by which it forms on Earth’s surface is very, very slow. Researchers had thought about pumping CO2 deep inside the Earth. How deep? Kilometers (miles) down into the mantle. There, rocks called olivine contain magnesium. It’s also quite hot there. Gases would get squished under high pressure, allowing magnesite to form faster there. But this process would be quite difficult and costly. Scientists first would have to find transport and store the CO2 that they hoped to trap in the rock. They’d also have to identify good places underground for inserting the CO2.

Power’s group opted to do it differently — in their lab.

To learn what they’d need to do, Power and his team investigated how Mother Nature makes magnesite. And to do that, they went to one place where they knew this mineral forms near Earth’s surface. It was a northern site in Canada’s western province of British Columbia.

At dry basins there known as playas (PLY-uhs), groundwater flows through rocks. Along the way, it picks up magnesium and carbonate ions. Over time, those ions react to make magnesite. The mineral slowly settles out of the water, creating rock.

“We knew it was slow,” Power says of the natural process. “But no one had ever measured the rate.” In British Columbia, the process began as far back as 11,000 years ago, he notes.

Scientists can combine rocks and CO2 using lots of heat in the lab. That could make the mineral quickly — but only by using a lot of costly energy, Power says. And that’s because water gets in the way. When magnesium ions are in water, the water molecules form a “shell” around the ions. This keeps the magnesium from bonding to carbonate ions. “It’s difficult to strip away those water molecules,” Power says. But unless you do, he adds, the magnesite will take a very long time to form.

To get around the problem, the researchers stripped water from the magnesium. To do this, they added thousands of little plastic balls, or microspheres. Each was about 20 micrometers (8 ten-thousandths of an inch) in diameter. Made out of polystyrene (Paal-ee-STY-reen), the tiny balls were coated with molecules that attract the water. As they tied up the water, the leftover magnesium ions now were free to bond with the carbonate.

Using the microballs, the researchers produced magnesite in 72 days, Power says. And the good news: The same microspheres could also be reused over and over, he says.

Still a long way to go

So far, the scientists have made only a tiny amount of magnesite in the lab. Their total — one microgram — is about one millionth the weight of a paper clip. So the process needs a lot of improvement before it can begin trapping the millions of tons of CO2 produced each year, Powers says.

But a big concern has been hurdled, he says. They’ve shown it is possible to do this at room temperature and pressure. Now the team can explore how to make the process more efficient.

“The result really surprised me,” says Patricia Dove. She is a geochemist at Virginia Tech in Blacksburg. It’s not clear how costly or efficient this process might be, she says. But she finds it “certainly very intriguing.”

Power Words

(for more about Power Words, click here)

atom     The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

basin     (in geology) A low-lying area, often below sea level. It collects water, which then deposits fine silt and other sediment on its bottom. Because it collects these materials, it’s sometimes referred to as a catchment or a drainage basin.

bond     (in chemistry) A semi-permanent attachment between atoms — or groups of atoms — in a molecule. It’s formed by an attractive force between the participating atoms. Once bonded, the atoms will work as a unit. To separate the component atoms, energy must be supplied to the molecule as heat or some other type of radiation.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

carbonate     A group of minerals, including those that make up limestone, which contains carbon and oxygen.

carbon dioxide (or CO2)     A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

climate change     Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

diameter     The length of a straight line that runs through the center of a circle or spherical object, starting at the edge on one side and ending at the edge on the far side.

geochemistry     A science that deals with the chemical composition of and chemical changes in the solid material of Earth or of another celestial body (such as the moon or Mars). Scientists who study geochemistry are known as geochemists.

greenhouse gas     A gas that contributes to the greenhouse effect by absorbing heat. Carbon dioxide is one example of a greenhouse gas.

groundwater     Water that is held underground in the soil or in pores and crevices in rock.

ion     (adj. ionized) An atom or molecule with an electric charge due to the loss or gain of one or more electrons. An ionized gas, or plasma, is where all of the electrons have been separated from their parent atoms.

limestone     A natural rock formed by the accumulation of calcium carbonate over time, then compressed under great pressure. Most of the starting calcium carbonate came from the shells of sea animals after they died. However, that chemical also can settle out of water, especially after carbon dioxide is removed (by plants, for instance).

magnesium     A metallic element that is number 12 on the periodic table. It burns with a white light and is the eighth most abundant element in Earth’s crust.

magnesium carbonate     A white solid mineral. Each molecule consists of a magnesium atom linked to a group with one carbon and three oxygen atoms. It is used in fireproofing, cosmetics and toothpaste. Climbers and gymnasts dust magnesium carbonate as a drying agent on their hands to improve their grip.

mantle     (in geology) The thick layer of the Earth beneath its outer crust. The mantle is semi-solid and generally divided into an upper and lower mantle.

micrometer     (sometimes called a micron) One thousandth of a millimeter, or one millionth of a meter. It’s also equivalent to a few one-hundred-thousandths of an inch.

mineral     Crystal-forming substances that make up rock, such as quartz, apatite or various carbonates. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in regular three-dimensional patterns).

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

plastic     Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.

playa     A flat-bottomed desert area that periodically becomes a shallow lake.

polystyrene     A plastic made from chemicals that have been refined (produced from) crude oil and/or natural gas. Polystyrene is one of the most widely used plastics, and an ingredient used to make a widely used white, rigid foam (often sold under the name Styrofoam).

pressure     Force applied uniformly over a surface, measured as force per unit of area.

Citation

Meeting:​​ ​ Power et al. Magnesite formation at Earth’s surface. Goldschmidt conference. Boston, August 14, 2018.

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