Formation Of Ferromanganese Nodules Research Articles

Micromorphology, mineralogy, and geochemistry of ferromanganese nodules in tropical soils and their impacts on heavy metal sequestration

Ferromanganese nodules (FMNs) are important products of soil-forming processes that can reflect the historical pedogenic environment and affect the elemental cycle in the soil. Despite extensive investigations on the morphology, microstructure, and components of FMNs, non-destructive observation of the 3D microstructure and elemental distribution feature of FMNs remains difficult, owing to the limitations of conventional measurement techniques and instrumental accuracy. In this study, the micromorphological, mineralogical and geochemical characteristics of FMNs in basalt-derived soils in tropical China were examined using different techniques, including scanning electron microscopy, X-ray diffraction, chemical extraction, and synchrotron radiation-based X-ray microtomography and microfluorescence mapping. Mn and Fe in FMNs were found to be inversely distributed in concentric rings, with Mn mainly enriched in the interior and Fe mainly distributed at the edge of the nodule. A line scan of the cross-section of FMNs revealed symmetrical distributions of the peak Fe and Mn contents and Fe:Mn ratios, indicating alternating dry/wet conditions and oxidation/reduction reactions during the formation of FMNs. FMNs were significantly enriched in P and various heavy metals, including Ba, Co, Cu, and Ni. The enrichment factors of P, Ba, Co, Cu, and Ni were in the range of 1.20–4.68, 8.34–27.12, 12.92–24.74, 2.51–3.55, and 2.75–3.58, respectively, reflecting the potential of FMNs to influence the soil nutrient cycle and heavy metal sequestration. Factor analysis further verified the adsorption of heavy metals by FMNs and indicated that the formation of FMNs was accompanied by an increase in Mn-bearing mineral and a decrease in phyllosilicate. Our study demonstrates that FMNs provide important information for understanding changes in pedogenic environment and heavy metal behavior in tropical soils.

Iron isotope fractionation during the formation of ferromanganese nodules under different conditions of hydromorphism

Hydromorphic soils are often characterized by redoximorphic pedofeatures like ferromanganese nodules. As the highly varying properties of the nodules are sensitive indicators of the pedogenic processes and redox history of the soil, their isotopic study may get a deeper insight into the soil genesis. In this study, the Fe isotopic characteristics, fabric, and mineralogy of ferromanganese nodules formed in six hydromorphic soil profiles were investigated using MC-ICP-MS, EPMA, and XRD analyses. We aimed to relate the Fe isotopic composition of the bulk soils and nodules to the varying conditions of hydromorphism and the various properties of the nodules.Although the extent of hydromorphism could be related to the nodules' properties, such a relationship was not found with their Fe isotopic characteristics. The reductive dissolution of primary Fe minerals resulted in similar Fe isotope distribution characteristics for the bulk soils. However, specific features of hydromorphic conditions (like frequency of the redox cycles, relocation of water fluctuation zone, external Fe input, and inhibition of leaching) affected the Fe isotope characteristics of both bulk soils and nodules. The minimum δ 56Fe value within the soil profile indicated the deepest part where precipitation of light Fe may dominate over its leaching. Above this depth, the isotopically light Fe precipitated to form the nodules. However, the higher frequency of the reductive conditions was responsible for the higher mobilization of isotopically light Fe below this depth. The isotopic characteristics of the nodules supported that authigenic Fe-oxyhydroxides were enriched in the light Fe isotope.The Fe isotope composition of a given soil horizon and its nodules result from a complex interaction of different processes whose effect varies from profile to profile. The integrated study of the Fe isotope characteristics of hydromorphic soils and their nodules may help follow several pedogenic processes and conditions.

Tectonic and paleoceanographic conditions during the formation of ferromanganese nodules from the northern South China Sea based on the high-resolution geochemistry, mineralogy and isotopes

Deep-water ferromanganese (Fe-Mn) nodules cumulate trace elements from the underlying sediment pore-water and seawater during the concentric mineral layers' growth process over millions of years. They can record long-term tectonic movements and paleoceanographic changes. To systematically ascertain paleoceanographic evolution of the deep South China Sea (SCS) since the last 3.2 Ma, we comprehensively investigated microstructure, mineralogy, geochemical element concentrations as well as Sr, Nd and Pb isotopic compositions in the Fe-Mn nodules nearby the Dongsha Islands in the northern SCS. Results indicate that these deposits were formed in a continental marginal environment by a mixture of diagenetic and hydrogenetic processes. Overall, the studied nodules can be divided into three stages with different microstructures and chemical compositions, which indicate different formation environments. Stage 1a is the innermost and oldest layer with a porous mottled texture, and has the lowest Mn/Fe ratio, Cu, Ni and Zn, which implies comparatively high oxidization conditions. In contrast, the Mn mineralogy of Stage 2 shows conditions similar to those of buserite formed under less oxidative conditions. Between Stage 1a and 2, Stage 1b represents a mixture of Stage 1a and 2 and has inhomogeneous growth structures. Based on the Nd and Sr isotopic composition of the detrital phases and Pb isotopes, three potential terrigenous source regions including South China, Luzon and Taiwan that discharge into the northern SCS from 3.2 Ma to 1.06 Ma. After 1.06 Ma, the terrigenous fraction in the Fe-Mn deposits on the northern slope of the SCS is a two end-members mixture of fluvial input from Taiwan Islands and eolian dusts from the Chinese loess. Our study indicates that SCS bottom water variation occurred at ~3.2 Ma, 2.1 Ma, and 1.06 Ma, respectively, which could be attributed to global cooling and the influence of Luzon arc-forearc uplift.

The formation of ferromanganese nodules in the southwest Indian Ocean; an abiotic process

AbstractFerromanganese nodules have been recognized widely as potentially important resources for strategic metals. However it remains unclear if the formation of these nodules is purely an abiotic process or if microorganisms are involved in their formation. To determine the microbial contributions, detailed organic geochemical analyses were performed on ferromanganese nodules collected from across the southwest Indian Ocean. These analyses reveal the presence of specific terrestrial, marine and petroleum derived biomarkers, consistent with formation in a marine setting with a substantial influx of terrestrially derived (higher plant detritus) and naturally occurring petroleum-related organic matter. In contrast, only trace amounts of general bacterial biomarkers, commonly present in these types of depositional environments, were present. This indicates that the formation of these ferromanganese nodules is predominantly an abiotic process although a minor contribution from microbial mediated processes to the growth of these nodules cannot be completely ruled out.

Conditions of formation of ferromanganese nodules in the bottom sediments of lakes in the Baltic shield

Conditions of formation of ferromanganese nodules in the bottom sediments of lakes in the Baltic shield

Ion exchange properties of oceanic ferromanganese nodules and enclosing pelagic sediments

Results of the experimental study of ion exchange properties of deep-sea pelagic sediments and related ferromanganese nodules (FMN) are considered. The exchange complex of sediments and nodules includes Na+, K+, Ca2+, and Mg2+ cations. The FMNs also include Mn2+ cations. Series of reactivity of metal cations during exchange reactions in different types of pelagic clayey sediments and diagenetic-sedimentary FMN are compiled. Series of exchange capacity of the sediments and FMN for alkali and heavy metal cations are also presented. The exchange capacity of FMN is always higher than that of enclosing sediments. Sediments are characterized by reversible equivalent sorption of cations of both alkali and heavy metals. Irrespective of the mineral composition, the FMNs are characterized by the reversible equivalent sorption of alkali metal cations, whereas sorption of heavy metal cations is only partly reversible. More over, alkali metal cations do not replace heavy metal cations. The results obtained refine the role of ion exchange processes in the redistribution of heavy metal cations at the water-bottom sediment interface during the diagenetic-sedimentary formation of ferromanganese nodules.

Manganese ore potential related to hydrosulfuric pollution of bottom waters (with the Black Sea as an example)

Conditions and scales of the accumulation of dissolved manganese in waters of marine basins with hydrosulfuric contamination are considered. It is shown that the Kalamit ferromanganese nodule field, most probably, originated due to the delivery of manganese from the hydrosulfuric zone of the Black Sea. Precisely this source converts the normal diagenetic process of material redistribution into the ore process. It is demonstrated that the formation of ferromanganese nodules in the Black Sea represents an embryonic manganese ore process. Its full-scale development seems to have taken place in the Early Oligocene Maikop basin owing to the spatiotemporal coincidence of a series of favorable conditions.