(Table 1, page 67) Chemical analyses and XRD determined mineralogy of manganese nodules from the Pacific Ocean and Southern Ocean

The uptake of Ni and Co in the hydrous Mn oxide or the amorphous Fe-oxide phases of ferromanganese deposits in the oceans was studied by electron-microprobe analyses of 17 natural manganese nodules and by experiments on desorption-dissolution of these metals from synthetic Fe oxide or Mn oxides and natural nodule material. Ni was found to occur nearly always in the Mn-oxide phases of natural nodules, while Co occurs both in the Mn-oxide and Fe-oxide phases, with a slight preference for the latter. The solubility of Ni and Co (from coprecipitates of these metals with Fe hydroxides after aging) in seawater was found to depend strongly on the crystallinity of the host phase. The adsorption of Co by the synthetic Mn oxides from seawater was higher than that of Ni. The experimentally determined solubility of Ni and Co in seawater from natural nodule material is extremely low and matches the concentration range of these metals in ocean water