A large dome-shaped robotic vehicle for collecting polymetallic nodules rests on the bottom of the ocean.

The Metals Company will outfit its nodule-collection robot with lights and cameras, which will document its effects on the ocean floor.

The Metals Company

Last March,BMW and Volvo joined other companies calling for a moratorium on deep-sea mining, one spearheaded by the World Wildlife Fund. These names were significant because the battery in an electric vehicle contains at least a few kilograms of cobalt, a metal that some hope one day to extract from the seabed—to the chagrin of many environmentalists.

This simmering controversy will no doubt reach the boiling point in 2022, when the Metals Company begins testing a system for collecting metal-rich nodules from the ocean floor. Most press coverage will no doubt paint a simplistic picture of the arguments for and against doing so. But the question of whether obtaining cobalt and other valuable metals from the ocean floor would help or hurt the environment overall is, in fact, quite complicated.

A reasoned judgement will hinge on many things, including how much you are concerned by the toll from conventional mining. More than half of the world’s cobalt currently comes from the Democratic Republic of the Congo, which has had a dismal record for protecting the environment and the well-being of the people who live and work around its mines.

Would having another large source available—the deep Pacific—help corporate buyers pressure Congolese mining companies to clean up their act? This and other important questions will remain open for some time, but one critical component in the calculus—the degree of environmental disruption involved in collecting metal-rich nodules from the deep Pacific—should become much clearer after the Metals Company begins pilot operations later this year.

Those operations will be conducted from what formerly served as a petroleum drill ship, rechristened Hidden Gem. The giant vessel is now being outfitted to collect polymetallic nodules, which are gravel- to briquette-size concretions that can be found strewn almost like paving stones on certain parts of the deep-ocean floor. Unlike some other strategies for obtaining metal ores from the seafloor, getting them from nodules is more a matter of collecting than “mining” in the usual sense of the word.

Sometime in 2022, workers on the Hidden Gem will lower into the water a steel pipe of colossal proportions, one segment at a time, with a total length of 4 kilometers. But it won’t simply dangle over the seafloor, hoovering up nodules like a giant underwater vacuum cleaner.

“At the business end is the robotic collector vehicle,” explains Jon Machin, head of offshore engineering at the Metals Company. This vehicle is some 12 meters long and weighs 80 tonnes in air. In water, though, it weighs significantly less—just enough for the vehicle to gain traction as it propels itself, but not so much as to cause it to get mired in the mud.

Compressed air injected into the bottom of the pipe will create countless bubbles, which will help raise the mix of nodules, mud, and seawater.

A flexible conduit will connect the end of the steel pipe with the vehicle. As the vehicle moves over the bottom, it will funnel nodules through this flexible conduit and into the pipe, where they will be sent upward using what Machin calls “an air-lift system”: Compressed air injected into the bottom of the pipe will create countless bubbles, which will help raise the nodules, along with some mud and seawater.

Nodules will be separated from this slurry aboard the Hidden Gem, which will store them in its hold and discard what remains. The best depth to discharge the leftovers is not yet entirely clear. Doing so in shallow water could affect the abundant sea life that lives there, while releasing it too close to the seafloor wouldn’t give the mud an opportunity to spread and thin before settling. This could potentially bury the immobile creatures that reside on the bottom at these depths (albeit at very low densities). The Goldilocks plan is to discharge the seawater and mud through a second pipe at an intermediate depth of about 1,200 meters.

Oceanographers from MIT and elsewhere have been studying the environmental consequences of such operations. They even mounted a research expedition in the Pacific in 2018, during which they pumped a mixture of dye and mud from the bottom into the water. This allowed the researchers to discern whether the fine mud particles would glom together. “It doesn’t look like that’s the case,” says E. Eric Adams, an expert in water-quality monitoring at MIT, who was one of the participants in that study. This experiment also helped the scientists to verify their models of the movement of the resulting turbid plumes. “We showed that you could do a fairly good job with a simple equation,” says Adams.

Oceanographers will have weeks or months to investigate further how well their models match reality when the Metals Company conducts its 2022 tests with the Hidden Gem. Later, Machin says, “we plan to ramp up with bespoke, newly built vessels.” That assumes that the company continues to receive the needed permits from the International Seabed Authority, which has jurisdiction in these waters.

There are many examples of seafloor disruption most people never think about—trawling by fishing vessels, dredging, even the mining of diamonds off the coast of Namibia, to name a few. These actions take place where marine life is far more abundant than at the great depths where nodules form. But given the World Wildlife Fund’s call for a moratorium in deep-seabed mining, it’s likely the Metals Company’s upcoming pilot operations will stir up as much debate as it does mud.

This article appears in the January 2022 print issue as “Deep-Sea Mining Stirs Up Muddy Questions.”

This article was updated on 22 December, 2021

The Conversation (1)
Michel Gelinas29 Dec, 2021

Hi David, The link to sono.nl (i.e. DRC's "dismal record") is not working. The DRC's environnemental record is one of those that will matter.

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