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Survey of Types of Solid Electrolytes
Published in P.J. Gellings, H.J.M. Bouwmeester, Electrochemistry, 2019
Compounds in the hollandite family also serve as Na+ or K+ conductors. Hollandite is a mineral with a composition BaxMn8O16 (x ≤ 2), in which Ba2+ ions are located in onedimensional tunnels formed along the c-axis of a pseudotetragonal framework structure composed of MnO6 octahedra. Mixed titanates, Ax(B,Ti)8O16 (priderite, A: alkaline metal, B: Mg, Al, Ga, etc.), are isostructural and exhibit one-dimensional ionic conduction along the tunnel. For example, a single crystal sample of Kx(Mg,Ti)8O16 (KMTO) shows K+ conductivity as high as 0.1 S cm−1 at 293 K along the c-axis in the very high-frequency region, though it rapidly decreases as the measuring ac frequency is lowered, as shown in Figure 6.9.75 High-frequency conductivity may represent short-range motion of K+ between bottlenecks in the tunnel. It is believed that such bottlenecks are generated due to large impurity ions, like Rb, and/or excess oxygens occupying the tunnel sites. Moreover, it is noted that the shortest diameter of the tunnel is about 2.4 Å, which is not large enough for K+ migration. Analogous compounds, such as KxGa8Ga8+xTi16−xO56, show a better conductivity because their tunnel is larger in diameter.76
Geometallurgical characterisation of Mn ores
Published in Applied Earth Science, 2021
Michael John Peterson, James Robert Manuel, Sarath Hapugoda
As this was the first attempt at a geometallurgical Mn ore classification scheme, the distinction of various Mn oxide mineral/textural types was quite conservative, e.g. no attempt was made to distinguish hollandite from hard, dense cryptomelane and todorokite from microporous earthy cryptomelane during point counting. As supergene todorokite is often poorly microcrystalline, it can be difficult to reliably distinguish using optical microscopy alone (e.g. Frenzel 1980; Ostwald 1988). Hollandite was considered most likely to be present in group 3a particles, while todorokite was considered most likely to be present in group 2b particles (see Figure 1(e)), due to its association with porous cryptomelane and pyrolusite in higher porosity (i.e. >10%) particles. Furthermore, no attempt was made to distinguish nsutite during point counting and thus it was counted as pyrolusite, as very fine grained pyrolusite can appear similar to nsutite under the microscope (e.g. Zwicker et al. 1962; Ostwald 1984). Nsutite was considered most likely to be present in group 3a particles (see Figure 1(f)) due to its common association with cryptomelane in low porosity (i.e. ≤10%) particles (and perhaps also some higher density particles) (cf. Sorem and Cameron 1960; Ostwald 1984, 1988).
Mn concentration and mycorrhizal colonization in understory native species grown at areas of manganese mine tailings disposal
Published in International Journal of Phytoremediation, 2019
Elzane Freitas Leite Silva, Fatima Maria de Souza Moreira, Jose Oswaldo Siqueira
The total Mn contents at PS location were higher than T and FN and similar to TL (Table 2). The high Mn contents in these substrates can be related to the processing of Mn ore, which can generate a residue with about 63% of the metal, which allows its recovery (Lima et al. 2008). Souza et al. (2016) found the following chemical composition of tailings coming from the Azul Mn mine (%): 7.1 Mn; 34.2 silica; 29.7 alumina, and 7.3 Fe, and mineralogical constitution (in weight): kaolinite (71%), cryptomelane-hollandite (17%), goethite (3.7%), bixbyite (3.1%), and quartz (0.7%). In the same region, Azevedo et al. (2016) evaluated Mn tailings from the Kalunga dam and observed mineralogical composition mainly formed by kaolinite, gibbsite, goethite, birnessite, todorokite, and quartz.
Phanerozoic history of the Pilbara region: implications for iron mineralisation
Published in Australian Journal of Earth Sciences, 2022
C. S. Perring, J. M. A. Hronsky, M. Crowe
Dammer et al. (1999) found that the ages of K-bearing Mn oxides (of the cryptomelane–hollandite series) varied from 36 to 0 Ma. Importantly, the older ages occurred in the central part of the Yilgarn whereas the younger ages were obtained from the southern and southwestern coastal areas. A sample from Mundijong near Perth returned an age of 1.4 ± 1.4 Ma, indicating that Mn oxide formation may still be ongoing there, probably because rainfall is still relatively high.