Deep-Sea Manganese Nodules

Deep-sea manganese nodules occur mainly in deep-ocean basins characterized by low sedimentation rates (i.e. 5 mm ka ) where inputs of calcareous ooze, 

In the following section, the distribution, mineralogy and composition of manganese nodules from three of these regions is considered in order to illustrate the different modes of formation of nodules in different settings. A detailed comparison of the characteristics of the nodnles from these three regions has already been presented by Glasby et al. (1983). 

Descriptive classification of manganese nodule types (after Glasby etal. 1980). 

Southwestern Pacific Basin nodules are considered to be hydrogenous in origin based on their average Mn/Fe ratio of about unity, Ni+Cu contents of 1%, 5Mn02 as the principal Mn oxide phase and growth rates of 1-2 mmMa (Dymondetal. 1984). 

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Deep-Sea Manganese Nodules. A potentially important future source of manganese is the deep-sea nodules found over wide areas of... 

Deep-sea manganese nodules represent a significant potential mineral resource. Whereas the principal constituent of these deposits is manganese, the primary interest has come from the associated metals that the nodules can also contain (see Ocean rawmaterials). For example, metals can range from 0.01—2.0% nickel, 0.01—2.0% copper, and 0.01—2.25% cobalt (12). Recovery is considered an economic potential in the northwestern equatorial Pacific, and to a lesser degree in the southern and western Pacific and Indian Oceans (13—18). 

HydrometaHurgical processes for copper can be categorized as (/) acid extraction of copper from oxide ore (2) oxidation and solution of sulfides in waste rock from mining, concentrator tailings, or in situ ore bodies (J) dissolution of copper in concentrates to avoid conventional smelting and (4) extraction of copper from deep-sea manganese nodules. 

The combination of physical and chemical characteristics of nodules make impossible the application of methods of physical beneficiation such as flotation and magnetic separation to produce concentrates of valuable metals, and so chemical processing must be used. Their processing also tends to be much more energy-intensive, vis-a-vis that of conventional land-based ores. Deep-sea manganese nodules are quite unlike any terrestrial ores, both with respect to their physical characteristics and to their mineralogical and chemical compositions new processes are, therefore, required. 

Jana, R. K. Pandey, B. D. Premchand Ammoniacal leaching of roast reduced deep-sea manganese nodules. 

Deep-cone thickener, 22 65-66 Deep-sea manganese nodules, 15 542, 566-567... 

Bums, R. G. Bums, V. M. (1977) The mineralogy and crystal chemistry of deep sea manganese nodules, a polymetallic resource of the 21st century. Phil. Trans. Royal Soc. (London), A286,283-301. 

We know that manganese nodules near the continent have a lower manganese and higher iron content than deep-sea manganese nodules. Iron hydroxide colloids coagulate, as already described, earlier than those of man nese hydroxides. Therefore the first precipitation from the river impact near the continental border should Iw enriched in iron, and the precipitates more distant from the continental border should have lower iron and higher manganese contents. 

Because of the different supply of ions for adsorption in the changing environment, and because of different growth rates of mangane nodules (different time for adsorption) it could be expected that the ratio of adsorbed ions to manganese or to iron hydroxide would be regionally different. There are, anyway, some rules which seem to be valid for the greater part of deep-sea manganese nodules ... 

There is a lot of confusion in the mineralogical data about manganese nodules. The most frequent manganese mineral in deep-sea manganese nodules is an 10 A manganate... 

Deep-sea manganese nodules can widely be observed in all oceans. The majority of them is located on the sediment surface so that the upper side is in contact with the sea-water and the lower side in the nearly liquid mud of the sediment/water interface. Only a small part of nodules gets buried during their growth. 

The growth rates of deep-sea manganese nodules lie between 4-9 nun in one million years . These growth rates are much lower than the sedimentation rate of the sediment on which the manganese nodules are located. Thus, they should actually get buried within a relatively short period of time. 

Within the last twenty years deep-sea manganese nodules (which have already been known for about one hundred years) have come to discussion as a multielement ore of the future. The interesting metals in this ore are copper, nickel, cobalt, and manganese. Zinc and molybdenum could also be used as by-products. 

Burns V. M. and Burns R. G. (1978b) Diagenetic features observed inside deep-sea manganese nodules from the north equatorial Pacific. Scan. Electr. Micros. 1978, 245-252. 

Crerar D. A. and Barnes H. L. (1974) Deposition of deep-sea manganese nodules. Geochim. Cosmochim. Acta 38, 279-300. 

A, J. Monhemius, The Extractive Metallurgy or Deep-Sea Manganese Nodules, in R. Burkin... 

The stability field of Fe in seawater is best illustrated by the use of an Eh, pH diagram (Fig. 11.4). Solid Fe(OH)3 is shown as the metastable form of iron at the conditions prevalent in sea-water (Eh +0.4 V, pH 8). Actually, akageneite (P-FeOOH) is the more stable form found in deep-sea manganese nodules (see Sect. 11.4.8) but its free energy of formation has not been determined. 

Deep-sea Mn nodnles and crusts are amongst the slowest growing minerals on Earth (Manheim 1986). They have a minimum growth rate of 0.8 mm Ma (Puteanus and Halbach 1988) which is eqnivalent to the formation of about one unit cell every year. Shallow-water concretions grow about 10 times faster. Several methods have been used to date deep-sea manganese nodules and crusts (Ku 1977 Mangini 1988). 

The economic potential of marine manganese deposits and the potential of these deposits as paleoenvironmental indicators are directly related to the chemistry of manganese, its associated transition metals and other key elements adsorbed on to the surface of these deposits. It is this complex interplay of these factors which makes the study of marine manganese deposits so intriguing. Unfortunately, research on deep-sea manganese nodules and crasts has been held hostage to the economic potential of these deposits. Time will tell if these deposits are to become a major source of metals for the world as was once thought. 

Radiometric dating has revealed wide variations (by four orders of magnitude) for the growth rates of marine manganese deposits Co-rich Mn cmsts (0.8 mm Ma Puteanus and Halbach 1988), deep-sea manganese nodules on red clay substrates (1-2 mm Ma Hu and Ku 1984), deep-sea manganese nodules on siliceous ooze substrates (3 -8 mm Ma" Hu and Ku... 

Usui, A., 1979. Nickel and copper accumulation as essential elements in lOA manganite of deep-sea manganese nodules. Nature, 279 411-413. 

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