Taking carbon out of the atmosphere will be crucial if we are to slow the progress of climate change. As technologies to capture carbon improve, some are already thinking about what we will do with all that CO2.
Storage in geological formations underground is one option. Better yet, what if we could make useful stuff out of it, such as biofuels, plastics or building materials?
Several initiatives to explore such ideas are under way. Canadian company Carbon Engineering is combining captured CO2 with hydrogen gas to generate synthetic gasoline at its pilot plant north of Vancouver. And Newlight Technologies, based near Los Angeles, California, is using the greenhouse gas methane to manufacture plastic products such as mobile-phone cases and chairs.
Another project started last week; it will research ways to turn CO2 into common building materials.
A pilot plant at the University of Newcastle near Sydney will test the commercial potential of mineral carbonation. This is a process that chemically binds CO2 with calcium- or magnesium-containing minerals to form stable materials. The plant will bind CO2 with crushed serpentinite rocks to create magnesium carbonate, which can be used to produce building and construction materials such as cement, paving stones and plasterboard.
This carbonation process could be a way of “permanently and safely disposing of CO2, and making useful products in the process”, says Klaus Lackner, director of the Center for Negative Carbon Emissions at Arizona State University, Tempe, who pioneered laboratory studies of mineral carbonation.
The process happens naturally when rocks are exposed to CO2 in the air. This gradual weathering helped cut down CO2 in the ancient atmosphere to levels that were low enough for life to flourish, says Geoff Brent, senior scientist at Orica, an explosives manufacturer that will supply the pilot plant with CO2 – a by-product of its manufacture of ammonium nitrate.
But we don’t have millions of years to wait for geology to rid the atmosphere of excess carbon. “It’s about turning the natural process into a large-scale industrial process on our required time scale — which is extremely urgent,” says Brent.
There are several challenges in achieving this. Mining for serpentinite is itself energy-intensive and damaging to the environment. But Brent says an advantage is that the rock is one of the most common on Earth, and carbonation plants could be built near mining areas.
Another objection is that the carbonisation process still costs too much, whereas simply storing CO2 undergroundwould be cheaper and require less energy.
However, Brent says that suitable underground repositories are hard to find and that carbon dioxide may escape back into the atmosphere even after being stored.
“Carbonation is more secure in the long term, because there is no danger of leakage and no need to maintain long gas pipelines and transportation infrastructure to move the CO2, since we will be obtaining it on-site,” says Brent.
And if the chemical reactions could be sped up and maintained with less heat, carbonation could become commercially competitive with underground injection storage of CO2.
“The whole point of the project is to get the price down low enough,” says Marcus Dawe, CEO of Mineral Carbonation International, the group coordinating the effort. “It is all about how we can make this economical.”
Dawe and his team are optimistic that they will make progress by the end of their initial 18-month project period, but whether their trials yield anything that can be scaled up on a meaningful level remains to be seen.
For mineral carbonation to take off, there will need to be a higher price on carbon, says Dawe, because right now “nothing is more economical than putting CO2 in the air”.
He is looking to China as one place where large-scale mineral carbonation might eventually take off. The country is developing a carbon-trading system that is expected to go into effect next year, and is also scrambling to find ways to cut emissions causing its massive urban air-pollution problem, says Dawe.