Annotated record and illustrations of Mn nodules retrieved during cruise KH-73-4 of the R/V Hakuho Maru and cruises GH76-1 and GH77-1 of the R/V Hakurei Maru

Deep sea manganese nodules from the Central Pacific Basin are mainly composed of 10Ã… manganite and d-MnO2 Two zones equivalent to the minerals are evidently distinguishable according to their optical properties. Microscopic and microprobe analyses revealed quite different chemical compositions and textnral characteristics of the two zones. These different feature of the two zones of nodules suggest the different conditions under which they were formed. Concentrations of 11 metal elements in the zones and inter-element relationships show that the 10Ã… manganite zone is a monomineralic oxide phase containing a large amount of manganese and minor amounts of useful metals, and that the d-MnO2 zone which is apparently homogeneous under the microscope is a mixture of three or more different minerals. The chemical characteristics of the two zones can explain the variation of bulk composition of deep sea manganese nodules and inter-element relationships previously reported, suggesting that the bulk compositions are attributable to the mixing of the 10Ã… manganite and d-MnO2 zones in various ratios. Characteristic morphology and surface structure of some types of nodules and their relationships to chemistry are also attribut able to the textural and chemical features of the above mentioned two phases. Synthesis of hydrated manganese oxides was carried out in terms of the formation of manganese minerals in the ocean. The primary product which is an equivalent to d-MnO2 was precipitated from Mn 2+ -bearing alkaline solution under oxigenated condition by air bubbling at one atmospheric pressure and room temperature. The primary product was converted to a l0Ã… manganite equivalent by contact with Ni 2+, Cu 2++ or CO2+ chloride solutions. This reaction caused the decrease of Ni2+, Cu2+ or CO2+ concentrations and the increase of Na+ concentration in the solution. The reaction also proceeded even in diluted solutions of nickel chloride and resulted in a complete removal of Ni2+ from the solution. Reaction products were exclusively 10Ã… manganite equivalents and their chemical compositions were very similar to those of 10Ã… manganite in manganese nodules. The maximum value of(Cu+Ni+Co)/Mn ratio of 10Ã… manganite zones in manganese nodules is 0.16, and the Ni/Mn ratio of synthetic 10Ã… manganite ranges from 0.15 to 0.18 with the average of 0.167.

Contents of metal cations exchange capacity of ore minerals in ferromanganese micronodules from the Atlantic, Indian and Pacific Oceans

Results of experimental studies of ion exchange properties of manganese and iron minerals in micronodules from diverse bioproductive zones of the World Ocean were considered. It was found that sorption behavior of these minerals was similar to that of ore minerals from ferromanganese nodules and low-temperature hydrothermal crusts. The exchange complex of minerals in the micronodules includes the major (Na**+, K**+, Ca**2+, Mg**2+, and Mn**2+) and subordinate (Ni**2+, Cu**2+, Co**2+, Pb**2+, and others) cations. Reactivity of theses cations increases from Pb**2+ and Co**2+ to Na**+ and Ca**2+. Exchange capacity of micronodule minerals increases from alkali to heavy metal cations. Capacity of iron and manganese minerals in oceanic micronodules increases in the following series: goethite < goethite + birnessite < todorokite + asbolane-buserite + birnessite < asbolane-buserite + birnessite < birnessite + asbolane-buserite < birnessite + vernadite ~= Fe-vernadite + Mn-feroxyhyte. Obtained data supplement available information on ion exchange properties of oceanic ferromanganese sediments and refine the role of sorption processes in redistribution of metal cations at the bottom water - sediment interface during micronodule formation and growth.

Annotated record of the detailed examination of Mn deposits from R/V Xiang Yang Hong 16 stations (1983) in the Pacific Ocean

Electron microprobe and X-ray diffraction data for north Pacific manganese nodules reveal that the transition metal distributions are controlled by the mineralogy. Microlayers rich in 10Ã…-manganates generally have high Mn/Fe ratios and positive correlations between Ni, Cu and Mn, and between Co and Fe. Microlayers rich in vernadite, on the other hand, show low Mn/Fe ratios, and Co, Ni and Cu all show positive correlations with Mn. The 10Ã…-manganates form mainly in porewaters with high Mn/Fe ratios. The Ni2+ and Cu2+ ions are post-depositionally incorporated into the interlayers of the manganates, whereas Co3+ is substituted for Fe3+ in ferric oxyhydroxides. In seawater with a low Mn/Fe ratio, on the other hand, the adsorption of positively charged ferric oxyhydroxides on negatively charged [MnO6] octahedral layers suppresses the growth of 10Ã…-manganates, enhancing the formation of vernadite. Positively charged hydroxides of Co3+, Ni2+ and Cu2+ are also adsorbed on the [MnO6] layers. These mechanisms of mineral formation and metal uptake are corroborated by data for other oceanic non-hydrothermal manganese nodules and crusts.