How to fight climate change? Scientists have found a way to get carbon dioxide from the ocean and turn it into rock. Did you know that for every ton of carbon dioxide we pump into the air, about a quarter is absorbed by the ocean? Excess carbon dioxide acidifies the water and seriously endangers the organisms that live in the water. To prevent the situation from deteriorating, carbon dioxide emissions need to be reduced. In addition, carbon dioxide needs to be actively captured in order to reverse the extreme increase in emissions. However, carbon capture is a challenging and costly task.

“You’re talking about removing some 10 to 20 gigatonnes of [carbon dioxide] per year, starting from 2050, probably for the next century,” says Gaurav Sant, a civil and environmental engineering professor and director of the Institute for Carbon Management at the University of California, Los Angeles.

Pulling carbon dioxide out of the environment will be a necessary step

Most carbon capture methods have focused on capturing carbon dioxide from the atmosphere. To make the process more efficient, carbon sequestration in the ocean needs to be addressed. Oceans and other bodies of water hold more than 150 times more carbon dioxide than air. Sant assumes that if we can actively remove carbon from the ocean, the water will be able to absorb more carbon dioxide and thus reach equilibrium. The goal of the scientists is to convert carbon from the ocean into rock, specifically limestone.

How does the process work?

Sea water is rich in calcium and magnesium. When calcium or magnesium ions combine with carbon dioxide, calcite or magnesite is formed. It is a chemical reaction that is similar to one in which different organisms form their shells. When a third ingredient is added to the whole process – electricity, scientists can ensure that the whole process is very fast, efficient and can also be carried out on a large scale. The researchers proposed a technology in which seawater will flow through an electrically charged network and electrolysis will trigger the chemical reactions necessary to form carbonate rocks. Sant and his team created a prototype with dimensions of 1.5×1.5 meters, which is flooded with simulated seawater. This model collects important data and examines the effectiveness of the whole process.

“This is the formative step towards building larger systems and proving the process at a larger scale,” says Sant.

The process resembles the treatment of water, from which carbon is removed and the purified water will travel back to the ocean.

“You are actually returning water that is slightly more alkaline than what you put in,” says Alan Hatton, a chemical engineer at the Massachusetts Institute of Technology who has worked on several unrelated carbon capture technologies. “This more alkaline water could help mitigate the effects of ocean acidification in the immediate vicinity,” he adds.

Hydrogen gas is formed during a chemical reaction

A by-product of this whole chemical reaction is a very useful element – hydrogen gas. Thanks to the production of hydrogen, it is possible to offset the high costs of the entire chemical process. This whole process can still be carbon negative due to this hydrogen gas by-product.

More scientific groups are investigating carbon sequestration in the ocean
While carbon sequestration in the ocean is a new technology, more scientific groups are already experimenting with it, such as Halifax, Nova Scotia-based startup Planetary Hydrogen.

The Planetary Hydrogen scientific group is working on a process that also aims to extract carbon from water. Carbon traps in the solid and indirectly forms hydrogen gas. Instead of electrolysis, however, they do it with hydroxide.

Carbon capture in the ocean is more efficient

Because there is much more carbon dioxide in the water than in the atmosphere, capturing directly in the ocean is a much more efficient and less expensive way. However, it is necessary to figure out how the large amount of rock formed will be handled. Removing 10 gigatonnes of carbon dioxide from the ocean, for instance, would yield 20 gigatonnes of carbonates — at a minimum, says Sant. One option is to produce carbon-neutral cement that can be used in construction. It is not yet clear how the technology would work on a large scale, but it is necessary to constantly work on methods to effectively remove carbon dioxide from the atmosphere and the ocean.

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