Deep-ocean polymetallic nodules as a resource for critical materials

Abstract

Deep-ocean polymetallic nodules form on or just below the vast, sediment-covered, abyssal plains of the global ocean. Polymetallic nodules primarily consist of precipitated iron oxyhydroxides and manganese oxides, onto which metals such as nickel, cobalt, copper, titanium and rare earth elements sorb. The enormous tonnage of nodules on the seabed, and the immense quantities of critical metals that they contain, have made them a target for future mining operations. Mining of polymetallic nodules has been spurred by the need for critical metals to support growing populations, urbanization, high-technology applications and the development of a green-energy economy. Nevertheless, an improved understanding of the affected ecosystems and their connectivity, as well as the environmental impacts of deep-ocean mining, is required before operations begin. Opportunities exist, however, to ensure that this new industry applies adaptive management to continually refine operations with the goal of environmental protection and invests in the development of green technologies for extractive metallurgy and mining. In this Review, we explore the chemical processes that control the concentration of critical metals in deep-ocean polymetallic nodules, discuss the mining and metallurgical techniques required, and highlight the opportunities and potential risks that are presented by this new industry.