Electrobioleaching of polymetallic ocean nodules

In this paper, a novel electrobioleaching process for recovering valuable n on-ferrous metals from ocean nodules is described. The key for successful a nd efficient dissolution of copper, nickel and cobalt from ocean nodules de pends on prior reduction of the manganese and ferric oxides with which the above valuable non-ferrous metals are interlocked. We have shown that throu gh the application of negative reduction potential or DC current, significa nt reduction of manganic and iron oxides in the ocean nodules can be achiev ed, thus liberating the occluded copper, nickel and cobalt for easy dissolu tion in an acid medium. Polarization studies using a slurry electrode syste m indicated that maximum dissolution of iron and manganese due to electroch emical reduction occurred at negative DC potentials of -600 and -1400 mV(SC E). Electroleaching and electrobioleaching of ocean nodules in the presence of Thiobacillus ferrooxidans and T thiooxidans at the above negative appli ed DC potentials resulted in significant dissolution of copper, nickel and cobalt in 1 M H2SO4 and in sulphuric acid at pH 0.5 and 2.0. Mechanisms inv olved in electrobioleaching of ocean nodules are discussed. The effect of b acterial metabolites in the dissolution of copper, nickel and cobalt from t he ocean nodules is also examined as a function of pH, time and applied pot entials. Various electrochemical and biochemical parameters were optimized and the electrobioleaching process so developed is shown to yield almost co mplete dissolution of all metal values. (C) 2001 Elsevier Science B.V. All rights reserved.