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What is bulk marine sediment mining?

New methods and technologies have led ‘to exponential increases in the achievable mining rate of the sea floor’. This has culminated in a technology named Trailing Suction Hopper-Dredge (TSHD). This involves dredging and removing sediment on the seafloor at an alarming rate, removing a layer of sediment of up to 3 meters deep.

A dredge-head of around 11m wide is dragged on the seafloor, cutting a trench. The dredge-head has cutting teeth and water jets that crush hard sediment. The sediment is then suctioned by a tube where it is distilled, separating larger sediment from fine particulates. Any excess water and fine particulates are released back into the water column. This creates a giant plume of sediment, equivalent to a dust cloud that covers an area far greater than the mined area, burying and smothering seabed ecosystems.

This technology can dredge more than 100 000 m2 of sediment per day. A proposed marine phosphate mining project in Namibia, called the Sandpiper Project is expected to remove up to 5.5 million tonnes of sediment annually. If mining were to proceed in the areas currently under prospecting rights in South Africa, it would in all likelihood involve such technology.