Scientists have turned an Icelandic power plant's carbon dioxide gases into minerals, a discovery that could represent a big step in efforts to curb climate change due to fossil fuels.
"It's a promising result," said Ken Caldeira, a climate scientist at the Carnegie Institution for Science who was not involved in the project. "If this could be done at a large scale and costs could be brought down, then it would be very promising indeed."
The project took place at the Hellisheidi Geothermal Power Station, the biggest thermal power plant in the world and the energy provider for Reykjavik, Iceland's capital. Usually thermal plants don't emit much greenhouse gas, but the facility produces around 5 percent of the emission of a coal-fired plant because it taps into volcanic heat that also emits carbon dioxide.
The volcanic activity has also produced basalt, however, the blackish rock found in lava flows and elsewhere.
An international team of scientists figured out that if they mixed the plant's carbon discharges with water and pumped the mix into the basalt, it became calcite, a component of limestone.
"We need to deal with rising carbon emissions," said Juerg Matter, a geoengineering professor at the University of Southampton in Britain and a co-author of a study about the findings in the journal Science, in a Columbia University press release. "This is the ultimate permanent storage — turn them back to stone."
Under natural circumstance, carbon dioxide can take hundreds or thousands of years to turn into a mineral, but the scientists claim that 95 percent of the 250 tons of carbon dioxide they injected around 2,000 feet underground became harmless calcite in two years.
The scientists in Iceland said their process cost around $30 per ton, whereas other types of carbon dioxide capturing and storage cost around $130 per ton. Those other methods also run the risk of gas or liquid seeping back into the atmosphere, whereas the Icelandic method so far appears to render it inert.
There are two catches, though.
The process needs a hell of a lot of water, around 25 tons for every ton of carbon dioxide. Hellisheidi already pumps up heated water from under the ground, so it had an ample supply. Other power plants might not be so lucky.
Robert Williams, senior research scientist at the Andlinger Center for Energy and the Environment at Princeton University, said the researchers in Iceland were testing to see if they could use salt water in the process. That could make it much easier to adopt elsewhere, he said.
"The huge water requirements are challenging," Williams told VICE News. "Applications might be limited to where ocean water can be used."
It also needs basalt. Iceland is made mostly of basalt. But only around 10 percent of rocks on land are made of the rock, according to the scientists. The ocean floor is largely basalt, however, so power plants might be able to use seawater to pump carbon under the seabed.
But Caldeira noted that it's not clear if the basalt deposits around the world possess fractures that are big enough to accommodate the minerals from solidifying the approximately 40 billion tons of carbon dioxide that power plants spew into the atmosphere annually. He also questioned whether the carbon dioxide and water mix would react with basalt after continuous pumping filled a fissure with hardened calcite.
"They showed they were able to store a fifth of a second's worth of global C02 emissions," said Caldeira. "If they sustain that at a higher volume, 'Will it continue to be effective?' is a big unknown question. Basically you need to do bigger experiments to see if you continually pump this stuff in, will it continue reacting?"
If accessible basalt can accommodate massive amounts of injected carbon dioxide, Caldeira and Williams both raised concerns about destabilizing the ground with water injections and causing earthquakes, a problem that arises from fracking.
Those and other questions suggest the researchers in Iceland and others working on turning carbon dioxide solid have a lot more work to do.
"The concept is far from commercial, largely because there has been so little R&D on the concept," said Williams. "This is not something we are going to be implementing in one year or five years. Whether and when we will be using the technology commercially depends on the success of future R&D — and then only if there is a serious public policy in place to address the global warming challenge."
Despite their reservations, however, Caldeira and Williams emphasized that, if the process was scaled up, it could be a game changer.
India has large deposits of basalt that might be a perfect place to store carbon from the country's many coal-fired plants, for instance, said Williams. "India is potentially the most important application because conventional CO2 storage opportunities are limited there," he said.
Reykjavik Energy, the utility that owns the thermal power plant, is now experimenting with injecting 5,000 tons of the mix underground.
That example could be a blueprint to convincing energy companies to invest in efforts to perfect the technology, said Caldeira.
"We need a big political tent where powerful political forces can see themselves as part of the solution to the problem," he said. "If you tell the fossil fuel industry that under no circumstances do you have any role in any future energy system, then you've created political opponents to doing anything about the climate problem."
While he believed energy providers should embrace wind and solar power, Caldeira said he wouldn't be opposed to keeping fossil fuels around if energy companies could prevent their carbon from reaching the atmosphere.
"If you want to build a power plant, do it without a smokestack," he said.
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