source：ChemEngOnline
Small-scale pilot testing has begun for a process that extracts nickel, manganese, cobalt and copper from nodules collected from the surface of the Pacific Ocean seafloor. Obtaining the metals from the seabed nodules has advantages over mining land-based ores because the nodules contain far less toxic heavy metals and can be processed with zero tailings, according to process developer DeepGreen Metals Inc. (Vancouver, B.C.; www.deep.green).
The nodules are formed on the seafloor four to six km deep in the Clarion-Clipperton Zone, a region of the Pacific Ocean between Hawaii and Mexico where the conditions permit precipitation of metal compounds onto nuclei of silica or calcium carbonate particles. The nodules contain around 30% Mn, 1.38% Ni, 1.17% Cu, 0.13% Co, and small amounts of zinc and rare-earth elements, explains Jeff Donald, head of onshore development at DeepGreen. Using robotic technology inspired by the undersea-cable-laying industry, DeepGreen harvests the nodules from the seafloor and raises them for further processing.
“The nodules contain metals in combinations that don’t exist in typical ore bodies on land… “So we had to adapt existing metallurgical processes in novel ways to extract and refine the nodule metals.” Using methodology from the nickel industry, DeepGreen devised a specialized pyrometallurgical process of calcining and smelting that is designed to obtain the desired metal compounds. This is followed by a series of refining steps using leaching and hydrometallurgy techniques. “The only real waste stream from the process is an iron-rich slag that can be used as aggregate for road building,” Donald says, so the nodules are fully utilized.
Ni and Co are obtained as battery-grade sulfates that can be used in batteries for electric vehicles, while the Mn can be used for alloying steel, and Cu as wiring. Donald says the company is currently working with the International Seabed Authority on environmental impact studies and continuing pilot testing for the on-shore process.