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Mn, 25]
Published in Alina Kabata-Pendias, Barbara Szteke, Trace Elements in Abiotic and Biotic Environments, 2015
Alina Kabata-Pendias, Barbara Szteke
Manganese occurs mainly at +2 oxidation stage, but may change valences up to +7. It is a member of the Fe family, and is highly associated with Fe, in all geochemical processes. There are many Mn minerals, mainly together with other metals, especially with Fe. The most common is pyrolusite, β-MnO2; other minerals are manganite, γ-MnOOH; hausmannite, Mn3O4; and rodochrozite; MnCO3. The Mn oxide mineral birnessite, (Na0.3Ca0.1K0.1)(Mn4+,Mn3+)2O4·1.5 H2O, of an unconfirmed composition, is formed due to precipitation in lakes, oceans, and groundwater. It is a major component of desert varnish and deep sea Mn nodules, exhibits a large adsorption capacity to several metals (Cd, Co, Cu, Pb, and Zn), and has a high oxidizing potential (Feng et al. 2007). Sorption capacity of MnO2 for several metals is comparable to that of goethite and hematite.
Geochemistry of Contaminant Mobility
Published in William J. Deutsch, Groundwater Geochemistry, 2020
Under reducing conditions with sulfide present, Fe and Hg form insoluble sulfide minerals. Manganese may be present in the solid phase as manganite (MnOOH), Mn2O3, or rhodochrosite (MnCO3). The chromium hydroxide mineral Cr(OH)3 may still be the stable phase or, if sufficient iron is present, an iron-chrome mineral (FeCr2O4) may be stable. Copper may form the cuprous ferrite mineral Cu2Fe2O4).
Simulation of magnesium chloride vertical transport in column experiments
Published in Human and Ecological Risk Assessment: An International Journal, 2020
Yan Dou, Mengyao Li, Zhaoyu Liu, Renjie Fang, Kaixi Yan
Heavy metals are widely distributed in environmental media such as water, soil and sediments (Li et al. 2015a). Toxic metals are harmful to ecological diversity and human health because of their bioaccumulation (He and Wu 2019; He et al. 2019). The sources of heavy metals can be geogenic or anthropogenic (Li et al. 2016). Heavy metals may transport from one medium to another, such as from soil/sediments to water, inducing serious water contamination. Manganese (Mn) is the eleventh most common element in the Earth’s crust (Li et al. 2014), with an average concentration of 0.09%. In nature, manganese exists in various minerals in the form of oxides, including pyrolusite (MnO2), psilomelane (mMnO·MnO2·nH2O), manganite (MnO2·Mn(OH)2), Hausmannite (Mn3O4), and so forth. These oxides are naturally insoluble in water; however, they are the most efficient electron acceptors (after O2 and NO3) in the sequence of organic matter respiration (Champ et al., 1979), and Mn2+ is the predominantly reduced form and is mobilized with water flow.
Synthesis and characterization of (1 − x)(La0.6Ca0.4MnO3)/x(Sb2O3) ceramic composites
Published in Phase Transitions, 2019
N. Amri, M. Nasri, M. Triki, E. Dhahri
In the case of the composite manganite which represents a line of highly strategic research for various industries, the main goal is to synthesize a material which has an important value of magnetoresistance (MR) in low field and close to room temperature. The composite manganite, representing a variation of material synthesized from two materials (or more) by introducing secondary phase into the manganite matrix [4–6], forms an interesting system to study the magneto-transport in low magnetic field. The improvement in MR is due to the effect of grain boundaries (GBs). Enhanced low field magnetoresistance (LFMR) has been achieved by producing artificial GBs, increasing the electronic barrier in the GBs by governing doping, and by the insertion of nanophase inclusions (commonly non-magnetic or an antiferromagnetic inorganic insulating phase) into the bulk ferromagnetic manganite matrix. In this context, the effect of Sb2O3 addition on the structural, magnetic, electric and magnetocaloric properties of LCMO are investigated. This improvement in LFMR has been mostly attributed to the spin-polarized tunneling between GBs or spin-dependent scattering at the grain boundaries [7–9].