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Electrochemistry of Porous Oxides and Related Materials
Published in Antonio Doménech-Carbó, Electrochemistry of Porous Materials, 2021
A number of metal oxides can be described as porous materials. For instance, porous manganese oxides define octahedral molecular sieves that have been introduced in the last years as possible materials for batteries, separations, and chemical sensing [3]. Interestingly, metal oxides and related materials can eventually be obtained electrochemically. This is the case with MnO2, which is deposited on solid electrodes upon oxidation of Mn2+ salts in aqueous media. The two basic MnO2 forms, pyrolusite and ramsdellite, are constituted with MnO6 octahedral units with edge or corner-sharing resulting in 1 × 1 (pyrolusite) or 1 × 2 (ramsdellite) tunnels. The oxidation process can be represented as: Mnaq2++2H2O→{MnO2}solid+4Haq++2e−
Petroleum Geochemical Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
An oxide mineral consists of a closely packed structure of oxygen atoms in which positively charged cations are located in the interstices (narrow space). Silicon dioxide (SiO2) is the most important and abundant oxide existing in nature. The purest form of silicon dioxide is quartz. The next most important oxide is aluminum oxide (Al2O3), known as alumina. Both silicon and aluminum oxides are found in earth in different polymorphic forms. Sand is the crushed form of quartz. Sandstone consists of sand particles bonded together. Kieselguhr rock is made of silicon dioxide which is the remains of siliceous marine organisms. The bond between silicon and oxygen is covalent. Silicon atoms are bonded tetrahedrally to four oxygen atoms. Silicon dioxide is very hard, having a high melting point. It is the hardest substance having a crystalline structure used as a semiconductor. Aluminum oxides occur naturally in several crystalline polymorphic forms. The precious gemstones ruby and sapphire are polymorphic forms of alumina. Hematite and magnetite are well-known iron oxide minerals. Magnesium oxide (magnesia) is a white hygroscopic mineral. Pyrolusite` and ramsdellite are polymorphic minerals of manganese dioxide. In addition to these, several hundred natural oxides of various types are known. Oxides are formed either by covalent linkage or by ionic bond between oxygen free radicals (O)–2 and one or more metallic free radicals (cations). The carborundum mineral is silicon carbide (SiC) and occurs in nature as traces.
In Situ Metal Immobilization and Phytostabilization of Contaminated Soils
Published in Norman Terry, Gary Bañuelos, of Contaminated Soil and Water, 2020
M. Mench, J. Vangronsveld, H. Clijsters, N. W. Lepp, R. Edwards
Hydrous ferric and manganese oxides have coherent small-sized scattering domains composed of mixed cubic and hexagonal anionic packing, where each pair of the anionic layer contains, on average, the same number of cations (Manceau et al., 1992b; Charlet and Manceau, 1993). At least rive distinct local structures (-0.5 -1 nm) have been reported for hydrous Fe oxides, i.e., ferric gels with a lepidocrocite-like local structure, so-called “2-line” gels that possess either a goethite-like (αFeOOH) or akaganeite-like (βFeOOH) local structure and that, either aged at neutral pH or heated, converted into a feroxyhite-like (δFeOOH) form, followed by further transformations into hematite. The feroxyhite structure is similar to that of hematite, but shows octahedral vacancies and layer defaults. “2-line ferrihydrite” (HFO) was described as a mosaic of single and double octahedral chains of varying length, ranging from 1 - n octahedra, linked at the corners of the chains (Spadini et al., 1994). The large number of high affinity-free edges found in HFO results from the extreme shortening of these octahedral chains. In contrast, the local structure of hydrous Mn oxides (HMO) does not seem to be related to that of a well-crystallized MnO2 polymorph (e.g., pyrolusite, ramsdellite, todorokite, chalcophanite). A three-dimensinal framework of randomly distributed edge- and corner-sharing MnO2 octahedra is the most probable structure.
Release Characteristics of Manganese in Soil under Ion-absorbed Rare Earth Mining Conditions
Published in Soil and Sediment Contamination: An International Journal, 2020
Zuwen Liu, Chenbin Lu, Shi Yang, Jinfeng Zeng, Shiyun Yin
The mineral composition of the soil sample was made clear by an X-ray powder diffractometer. The X-ray diffraction pattern (Figure 2) showed that kaolinite (Al2O3∙2SiO2∙2H2O), quartz (SiO2) and orthoclase (K2O∙Al2O3∙6SiO2) were the main mineral components in the soil sample, which is essentially in agreement with a previous research (Liu et al. 2019). The principal manganese-bearing minerals in the sample were rhodonite (MnSiO3) and ramsdellite (MnO2), indicating that the manganese existed in the forms of silicate bound and oxide. This does not exclude the possibility that manganese also presents in dispersed forms in the sample, such as absorbed ions on the surface of minerals. Some unidentified small diffraction peaks in Figure 2 show that the presence of other minerals. These minerals could not be identified because their quantities were too little to reach the minimum detection limit of the instrument.
Performance of selective catalytic reduction of NO with NH3 over natural manganese ore catalysts at low temperature
Published in Environmental Technology, 2018
Tao Wang, Chengzhu Zhu, Haibo Liu, Yongpeng Xu, Xuehua Zou, Bin Xu, Tianhu Chen
In this work, we investigated some natural manganese ores, which was composed of various metal oxides (mainly manganese oxides), had the potential to be used as a SCR catalyst, and it was low cost and did not require pretreatment, except for crushing. The main form of manganese oxides in a natural manganese ore was ramsdellite (γ-MnO2), with other metal oxides such as Fe2O3, Al2O3 and CuO from Qingyang, Anhui, which is due to the formation of the amorphous MnOx, high concentration of lattice oxygen and surface-adsorbed oxygen groups and a lot of reducible species as well as adsorption of the reactants, which brought about excellent SCR performance. NO conversion was above 85% at 150–300°C when used for denitrification experiment and the initial NO concentration was 1000 ppm, and it had good low-temperature activity and high N2 selectivity. Neither the presence of H2O (10%) nor SO2 (100 and 200 ppm) had an adverse effect on the activity. It can be used as a novel catalyst in terms of stability, good efficiency, environment friendliness and lower cost.
Effect of slag basicity in ferromanganese production using medium-grade manganese ore from East Java-Indonesia
Published in Mineral Processing and Extractive Metallurgy, 2018
Fajar Nurjaman, Eka Bobby Saputra, Deni Ferdian, Bambang Suharno
Figure 1 shows that the manganese ore in this experiment consisted of quartz (SiO2), manganite (MnO2), pyrolusite (MnO2), and ramsdellite (MnO2). Table 1 shows that the Mn/Fe ratio of this manganese ore was 13.6 and it exceeds the minimum Mn/Fe ratio for producing ferromanganese from manganese ore, which is 6.0 (Lee and Tangstad 2010). The medium-grade manganese ore consists of 35–40% Mn, while high-grade manganese ore consists of more than 48% Mn content (Gasik 2013). Thus, the manganese ore in this experiment was categorised as medium-grade manganese ore.