Pyrochemical Extraction of Transition Metals from Pacific Ocean Deep Sea Nodules

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Abstract
Considerable success has been achieved in lixiviation transition metals from Pacific Ocean deep sea nodules. These nodules typically contain ∼30 wt% Mn, ∼7 wt% Fe, ∼1 wt% Ni, ∼1 wt% Cu, and ∼0.3 wt% Co. Samples of the nodules have been subjected to extraction tests at 450°C using LiCl-KCl eutectic and MgCl2-NaCl-KCl eutectic. The most impressive results came from studies using the Mg, Na, K/Cl eutectic. With this salt, nearly 100% of the Co, Cu, Fe, Mn, and Ni are brought into solution. The dissolution reaction is quite vigorous, with nearly complete extraction occurring in a very short time (minutes) following melting of the eutectic. Quantitative recovery of cobalt is achieved with nodule-to-salt weight ratios as high as 1:3. Electronic absorption spectroscopy (carried out on the molten extract solution at the test temperature) showed that the oxidation states of the dissolved transition metals are Co2+, Cu2+, Fe3+, Mn2+, and Ni2+. At temperatures ≥450°C, the Fe3+ and Cu2+ distill out of the extract solution at a rapid rate and condense as binary halides or halide complexes. Using a combination of distillation followed by electrochemical reduction of the Co2+ and Ni2+ in the extract salt, it appears possible to recover a fairly high grade of cobalt metal and nickel metal as well as high grade Cu2+, Fe2+, and Mn2+ in the form of a halide salt (CuCl2, FeCl3) or an oxide precipitate (Mn2O3).