Deep-sea mining 'poses environmental risks': Study

The study compares the waste streams of land mining and deep-sea mining.
Deep-sea mining 'poses environmental risks': Study Deep-sea mining 'poses environmental risks': Study Deep-sea mining 'poses environmental risks': Study Deep-sea mining 'poses environmental risks': Study Deep-sea mining 'poses environmental risks': Study

A new study assesses the environmental impact of nodule collection.

A new peer-reviewed study published by Yale Journal of Industrial Ecology found that deep-sea mining presents risks for deep-sea habitats, but may have benefits over land-based mining.

The paper compares the waste streams of land mining and deep-sea mining to meet demand for one billion 75KWh electric vehicle batteries, which contain 80% nickel, 10% manganese, and 10% cobalt.

The comparison of waste tonnage and impacts shows that the use of nodules from the Clarion Clipperton Zone for mining may reduce the amount of waste produce, and reduce impact-risk severities when compared to mining on land.

The Metals Company is looking to extract polymetallic nodules from the CCZ, in international waters located 5,285 miles from the coast of the Pacific island nation of Nauru.

The authors of the study caution that much remains unknown, and that is impossible to anticipate actual waste profiles of nodule producers for some years.

There is "substantial uncertainty" around the impact of sediment plumes, resulting from nodule extraction from the seafloor.

The harm created by this mine waste "will likely be significant", the report said, while cautioning that  "many investigations are underway to understand and mitigate its effects."

"In our analysis, sediment plume is the single biggest waste stream that would be generated by metal production from nodules," one report author, Dr Steven Katona from the College of the Atlantic, said.

There are ongoing scientific analyses to better understand the impacts of plumes, the report said.

"A number of studies have already been published in this regard, including one by MIT focussing on the midwater sediment plume which found that the ocean mixing processes prevented sediment particles from flocculating, resulting in the rapid dilution of the discharge by around 1,000 times to near background levels - leaving what is essentially clear water to the naked eye," a TMC spokesperson told Mining Magazine.

Nodule mining may also result in "long-lasting habitat degradation", the report found, acknowledging that there will be variations in impact and recovery time for habitats and organisms.

The report also notes that the removal of the nodules, which provide a base on which organisms live, may have "one of the strongest negative environmental impacts" of the nodule mining process.

Tailings in nodule mining are of lesser quantity, the report said. However, in the worst-case scenario where the industry adopts the highest-waste flowsheet, this would no longer be the case, it added.

Nodule mining is likely to produce less severe by-products than those generated by land mining, due to the dearth of high levels of toxic elements, the report said.

There are several ways by which nodule mining could mitigate and lessen its impact.

Miners extracting nodules can optimise collector machines by using hydraulic collectors and improve hydraulic jet controls to allow them to collect more nodules while limiting sediment disruption.

Tests are underway on the use of artificial substrates, and nodule mining companies can also spread out their nodule collection over time and space, the report said.

The impact of returned material to the seafloor can be lessened by choosing a single discharge point, which would minimise disruption. The discharge would need to occur far below the current recommended point so as not to impact the biosystem, the report said.

Metallurgical designs should also use fewer reagents, and use a closed-loop system which allows for the internal recycling of residues.

The report warns that the main challenge in deep-sea mining of polymetallic nodules is in balancing new scientific knowledge about the process and the deep-sea environment with industrial needs.

Scientists at other institutions have cautioned that because so little is known about deep-sea environments, it is difficult to accurately assess what kind of damage would be done by mining activities on the seafloor.

Deep-sea mining advocates maintain that deep-sea operations are necessary to meet metals demands for the transition to decarbonisation.

The study was authored by Dr. Daina Paulikas, Dr. Steven Katona, Dr. Saleem Ali, and The Metals Company's head of strategy and business development Erika Ilves.

The study was financed by The Metals Company.

The article has been updated to include commentary from TMC.

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