Shiro Okabe

Factors controlling the chemical composition of marine manganese nodules and crusts: a review and synthesis

Abstract The contents of cationic transition metals in manganese oxide deposits of different origins are explained by the supply of these metals, the sorptive and crystallo-chemical properties of the manganese oxides and the chemical forms of the metals in seawater in contact with the deposits. This assumes that the manganese oxide phases are in equilibrium with seawater or interstitial water for the deposits of hydrogenous and oxic diagenetic origins. The growth of suboxic diagenetic nodules is assumed not to be in a steady state.

The partition of vanadium and molybdenum between manganese oxides and sea water

Abstract The partition of V and Mo between manganese oxides and sea water was investigated in the sea water supply system for aquaria at the Marine Science Museum, Tokai University, where both todorokite and birnessite are precipitated from aerated well sea water. The distribution coefficient of V was an order of magnitude higher than that of Mo. Assuming that the distribution coefficients can be applied to marine environments and that manganese oxides are precipitated from sea water, the calculated contents of these oxyanionic elements in manganese oxides were comparable to those in marine manganese nodules.

Uptake of selenium and other oxyanionic elements in marine ferromanganese concretions of different origins.

The concentration of selenium in marine ferromanganese concretions varies between 0.02 and 1.2 mg kg−1, with an average of 0.6 mg kg−1. This is about two orders of magnitude lower than previously reported. In contrast to minor cationic elements, the concentrations of selenium are relatively uniform between ferromanganese concretions of different origins, except for hydrothermal crusts. It shows the same trends of element enrichment as other oxyanionic elements. The incorporation of selenium into ferromanganese concretions is attributed to adsorption of selenate on iron and manganese oxides.

The formation of todorokite and birnessite in sea water pumped from under ground

Abstract Manganese oxides precipitated from aerated well sea water at the Marine Science Museum, Tokai University, have been analyzed chemically and mineralogically. The O Mn ratios are lower in todorokite than in birnessite but these minerals have similar contents of minor transition metals, which can be taken up additionally from sea water after the precipitation of Mn oxides. On the basis of these results, the genesis of Mn minerals is discussed in relation to marine Mn nodules.

The determination of Mn, Fe, Ni, Cu and Zn in seawater by atomic absorption spectrometry after coprecipitation with lanthanum hydroxide

A simple and rapid coprecipitation method for the determination of several trace metals in seawater is presented. These metals are coprecipitated with lanthanum hydroxide, the precipitate is dissolved, and then the metals are determined by atomic absorption spectrometry. Lanthanum hydroxide was chosen as a coprecipitant for the following reasons, (a) lanthanum hydroxide has a sufficiently low solubility and forms an easily filterable flocculate at about 80‡C, and (b) lanthanum has an absorption wavelength that is sufficiently separated from those of the other elements to be analysed, i.e., Mn, Fe, Ni, Cu and Zn. Experimental results show that these metals are coprecipitated by the present method with excellent recoveries.

The partition of minor transition metals between manganese oxides and seawater

The behavior of transition metals (Co, Ni, Cu and Zn) on precipitation of manganese oxides from seawater pumped up from a well at the site of the Marine Science Museum, Tokai University, and collected from several tanks along the water supply system to an aquarium was investigated. The distribution coefficients of cobalt and nickel between manganese oxides and seawater were different at different sampling points along the water supply system. At sampling points with high rates of manganese oxide precipitation, the distribution coefficients were about one order of magnitude smaller than those at the points with low precipitation rates, while there were no remarkable differences in the distribution coefficients of copper and zinc among the sampling points. The distribution coefficients of minor transition metals, with the exception of copper, observed at the points with low precipitation rates were comparable to those measured experimentally using manganese dioxides.

Todorokite formation in seawater by microbial mediation

Microbial manganese oxidation in seawater was carried out in enrichment cultures which were obtained from the seawater supply system at the Marine Science Museum, Tokai University (Shimizu-shi, Japan). The manganese oxide formed was well-crystallized todorokite. The major element composition was within the range of marine manganese concretions and the O/Mn molar ratio was 1.8. The conditions for formation of manganese oxide minerals in marine environments are discussed on the basis of these results.

Factors regulating the distribution of elements in marine sediments predicted by a simulation model

The contents of oxyanionic elements (V, Se and Mo) and cationic transition metals (Mn, Fe, Co, Ni, Cu and Zn) in sediments from near-shore to deep-sea environments were measured to clarify factors regulating the distribution of these elements in marine sediments. For cationic transition metals of which contents increase from near-shore to deep-sea environments, the chemical composition of pelagic clays is modeled by a mixture of aluminosilicates having the chemical composition of average shale and Fe−Mn oxides having the chemical composition of associated manganese nodules. The content of V is fairly constant in sediments from near-shore to deep-sea areas. The mixture model of average shale and manganese nodules holds also for V, although most of the V is located in the aluminosilicate lattices. The content of Se in the near-shore sediments is higher and that in the deep-sea sediments is lower than that in average shale. The high content in the near-shore sediments is interpreted as the addition of biogenic materials to aluminosilicates with average shale composition and the low content in deep-sea sediments is explained by oxidative release of Se from aluminosilicates. The content of Mo in sediments increases from near-shore to deep-sea environments. The general distribution of Mo in marine sediments is expressed by the mixture model. An anomalously high content of Mo in a near-shore sediment is attributed to adsorption of molybdate on manganese oxides.

Major elements in manganese and iron oxides precipitated from seawater

Abstract manganese and iron oxides precipitated from aerated well-seawater at aquaria in Japan were analyzed for their mineralogy and alkaline earth and alkali metal contents. Todorokite-rich manganese oxides were enriched in Na and Ca and depleted in K and Mg relative to birnessite-rich manganese oxides. The concentrations of alkaline earths and alkali metals in the iron oxide were lower than in the manganese oxides; this is especially true of the alkali metals. On the basis of these results, mineralogical control on the major element composition and the charge-balancing cations of marine ferromanganese oxide deposits are discussed.

Metal-organic complexes in seawater pumped up from under the ground

Metal-organic complexes of transition elements removed by Amberlite XAD-2 resin from seawater pumped up from under the ground were determined. The proportions of iron, copper and zinc retained on the resin to dissolved forms of these metals were about 70, 40 and 5%, respectively, while manganese, cobalt and nickel were not retained on the resin. These results suggest that although iron may be retained in colloidal form, a significant fraction of copper is present in some organic form(s).