Electrobioleaching of polymetallic ocean nodules

Abstract

In this paper, a novel electrobioleaching process for recovering valuable non-ferrous metals from ocean nodules is described. The key for successful and efficient dissolution of copper, nickel and cobalt from ocean nodules depends on prior reduction of the manganese and ferric oxides with which the above valuable non-ferrous metals are interlocked. We have shown that through the application of negative reduction potential or DC current, significant reduction of manganic and iron oxides in the ocean nodules can be achieved, thus liberating the occluded copper, nickel and cobalt for easy dissolution in an acid medium. Polarization studies using a slurry electrode system indicated that maximum dissolution of iron and manganese due to electrochemical reduction occurred at negative DC potentials of -600 and -1400 mV(SCE). Electroleaching and electrobioleaching of ocean nodules in the presence of Thiobacillus ferrooxidans and T. thiooxidans at the above negative applied 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 involved in electrobioleaching of ocean nodules are discussed. The effect of bacterial metabolites in the dissolution of copper, nickel and cobalt from the ocean nodules is also examined as a function of pH, time and applied potentials. Various electrochemical and biochemical parameters were optimized and the electrobioleaching process so developed is shown to yield almost complete dissolution of all metal values.