Adsorption of barium ions by β-manganese dioxide and its activation in oleate flotation     

M.A Arafa  A.A Yousef  M.A Malati 《International Journal of Mineral Processing》1974,1(3):267-275

The Ba²⁺ ion adsorption isotherms on β-MnO₂ were of the Langmuir type. The endothermic heat of adsorption (40 kJ mol^?1) is ascribed to entropy contributions associated with the $\text{Na}{}^{\mathrm{+}}\text{Ba}{}^{\mathrm{2+}}$ ion-exchange mechanism. The Ba²⁺ ion adsorption density was higher at pH 10 than that at pH 7, due to the more negative surface charge at the higher pH. Ba²⁺ ions were found to reverse the sign of the ζ potential of the MnO₂ particles.More oleate was adsorbed by β-MnO₂ in the presence of Ba²⁺ ions than in their absence. The oleate adsorption isotherms on Ba²⁺-activated MnO₂ were of the Freundlich type and indicated an exothermic process. Hallimond flotation recovery of Ba²⁺-activated MnO₂ was higher at pH 10 than at pH 7, although less oleate was adsorbed at the higher pH. At pH 7, Mn²⁺-activation led to higher recoveries than Ba²⁺-activation. It seems that the attraction between the surface and the activator plays an important rôle in determining the flotation recovery.  相似文献   

Nature of Co-bearing ferromanganese crusts of the Magellan Seamounts (Pacific Ocean): Communication 2. Ion exchange properties of ore minerals     

G. V. Novikov  S. V. Yashina  M. E. Mel’nikov  I. V. Vikent’ev  O. Yu. Bogdanova 《Lithology and Mineral Resources》2014,49(2):138-164

The results of experimental studies of ion exchange properties of Co-bearing ferromanganese crusts in the Magellan Seamounts (Pacific Ocean) are discussed. Maximum reactivity in reactions with the participation of manganese minerals (Fe-vernadite, vernadite) is typical of Na⁺, K⁺, and Ca²⁺ cations, whereas minimum activity is recorded for cations Pb²⁺ and Co²⁺. The exchange complex of ore minerals in crusts is composed of Na⁺, K⁺, Ca²⁺, Mg²⁺, and Mn²⁺ cations. The exchange capacity of manganese minerals increases from the alkali metal cations to rare and heavy metal cations. Peculiarities of the affiliation of Co²⁺, Mn²⁺, and Mg²⁺ cations in manganese minerals of crusts are discussed. In manganese minerals, Co occurs as Co²⁺ and Co³⁺ cations. Metal cations in manganese minerals occur in different chemical forms: sorbed (Na⁺, K⁺, Ca²⁺, Mn²⁺, Co²⁺, Cu²⁺, Zn²⁺, Cd²⁺, and Pb²⁺); sorbed and chemically bound (Mg²⁺, Ni²⁺, Y³⁺, La³⁺, and Mo⁶⁺); and only chemically bound (Co³⁺). It is shown that the age of crust, its preservation time in the air-dry state, and type of host substrate do not affect the ion exchange indicators of manganese minerals. It has been established that alkali metal cations are characterized by completely reversible equivalent sorption, whereas heavy metal cations are sorbed by a complex mechanism: equivalent ion exchange for all metal cations; superequivalent, partly reversible sorption for Ba²⁺, Pb²⁺, Co²⁺, and Cu²⁺ cations, relative to exchange cations of manganese minerals. The obtained results refine the role of ion exchange processes during the hydrogenic formation of Co-bearing ferromanganese crusts.  相似文献   

Sorption of heavy metal ions by a hydrous manganese oxide     

P. Loganathan  R.G. Burau 《Geochimica et cosmochimica acta》1973,37(5):1277-1293

Sorption of Co, Zn, Ca and Na by δ-MnO₂ was studied at 24.0 ± 0.5°C and pH 4. During the sorption of Co and Zn, Mn was released to the solution phase; however, Mn release was not detected during the sorption of Ca and Na. On the basis of crystal field theory, it is proposed that Zn may interchange with Mn²⁺ in the δ-MnO₂ structure, whereas Co may interchange with both Mn²⁺ and Mn³⁺. It is suggested that the interchangeable Mn²⁺ and Mn³⁺ sites were in the disordered layers in the δ-MnO₂ structure.Sorption of Co, Zn and Ca at pH 4 fitted single-site Langmuir isotherm expressions at all Ca concentrations, but only at concentrations greater than 10^?4 M for Co and Zn. Mn release by δ-MnO₂ at pH 4 during Co and Zn sorption also fitted single-site Langmuir isotherms. An expression for the case of multisite Langmuir sorption was derived and applied to the cases of Co and Zn sorption and to the case of Mn release during Co sorption. The data of these cases were used to calculate statistically the coefficients of multiple regression equations from which the sum of the capacities of all sites in each case were obtained. From all of these derived capacities, it is proposed that there was only one site where Ca interchanged with surface bound H. Zn was postulated to interchange not only with these bound H sites, but also with another site where it interchanged with structural Mn²⁺. Co was postulated to interchange with both of these sites, and additionally, with a third site where it interchanged with structural Mn³⁺.Using a pH-stat set at pH 4, it was determined that approximately 2 moles of H were released per mole of Co or Zn sorbed at bound H sites.  相似文献   

Ferric iron in tourmaline     

Stephanie M. Mattson  George R. Rossman 《Physics and Chemistry of Minerals》1984,11(5):225-234

Red Fe³⁺-rich and black Fe³⁺, Fe²⁺-rich tourmalines have been studied by optical and Mössbauer spectroscopies to determine the optical characteristics of Fe³⁺ in tourmaline. Prominent optical absorption features at 485 and 540 nm are assigned to transitions of multiple exchange-coupled Fe³⁺ pairs in several site combinations. These transitions are more intense than those of isolated Fe³⁺ and are polarized along the vector between the interacting ions, thus permitting site assignments. The 485 nm band occurs at an unusually low energy for Fe³⁺ in silicate minerals. Similar behavior has been observed in the spectrum of coalingite, Mg₁₀Fe ₂ ³⁺ (OH)₂₄CO₃·2H₂O, in which Fe³⁺ occurs in related pairs in edge-shared sheets. These lower energies are proposed to result from magnetic exchange in edge-shared geometries. Antiferromagnetic exchange has been confirmed by a variable temperature magnetic susceptibility study of a Kenyan dravite with 3.36 wt percent Fe. The Mössbauer spectrum of this sample is unusual in that it shows a pronounced decrease in width of component peaks from 298 K to 5 K.  相似文献   

Biogenic wad in Iron Ore Group of rocks of Bonai-Keonjhar belt,Orissa     

B. K. Mohapatra  S. Mishra  P. P. Singh 《Journal of the Geological Society of India》2012,80(1):89-95

Outcrop of wad, about 3–5 m thick, associated with low to medium-grade manganese ore deposits in Iron Ore Group (IOG), is present in large quantum in Bonai-Keonjhar belt, Orissa. It is often inter-bedded with volcanic ash layers. Wad is powdery, fine grained, black to blackish-brown in colour, very soft, readily soils the fingers and its hardness on the Mohs’ hardness scale is 1–3. The wad zone is capped by a thin lateritic zone and overlies manganese ore beds of variable thickness in Dalki, Guruda and Dubna mines. Wad constitutes two mineral phases, viz. manganese oxides (δ-MnO₂, manganite, romanechite with minor pyrolusite) and iron oxides (goethite/limonite and hematite) with minor clay and free quartz. Mixed limonite-clay and cryptomelane-limonite are commonly observed. Under microscope the ore appears oolitic, pisolitic, elipsoidal to globular in shape having small detritus of quartz, pyrolusite / romanechite and hematite at the core. The ore contains around 23% Mn and 28% Fe with ～7% of combined alumina and silica. Wad might have developed in a swampy region due to slow chemical precipitation of Fe-Mn-Co enriched fluid, nucleating over quartz/hematite grains. Influence of a marine environment is indicated from δ-MnO₂ phase. Remnants of some microfossils, like algal filament, bacteria, foraminifera and diatomite are observed in wad sample under SEM. These microorganisms might have been responsible for the oxidation of dissolved Mn²⁺ and Fe²⁺ precipitates. These findings suggest biochemogenic origin of wad in Bonai-Keonjhar belt of Orissa.  相似文献   

Petrology of a piemontite-bearing gneiss,San Gorgonio Pass,California     

Douglas Smith  Arden L. Albee 《Contributions to Mineralogy and Petrology》1967,16(3):189-203

Equilibria between different valence states of Fe and Mn have been studied in a microcline-plagioclase-quartz gneiss which locally contains ferromagnesian minerals unusually high in Mn⁺³ and Fe⁺³ and low in Fe⁺². The compositions of coexistent minerals have been determined by chemical and microprobe analyses. The minerals in some layers were formed under highly-oxidizing conditions, as indicated by extremely low Fe⁺²/Fe⁺³ ratios in the silicates, by the presence of hematite, and by the occurrence of piemontite, which requires Mn⁺³ for its formation. The minerals in other layers were formed under less-oxidizing conditions, as indicated by the fact that epidote, rather than piemontite, crystallized with Mn-rich garnet and by the presence of biotite rather than phlogopite. In the less-oxidized layers Mn⁺³ appears to be absent. The differences in oxidation of Fe and Mn occur between adjacent layers and probably reflect sedimentary differences preserved despite the metamorphism.Iron and manganese with different valences are sharply partitioned between the coexisting phases. In highly-oxidized layers, muscovite contains more iron (as Fe⁺³) than coexistent phlogopite; in piemontite most of the manganese is Mn⁺³, while in coexistent garnet most of the manganese is Mn⁺². In less-oxidized layers, epidote contains no Mn⁺³ and contains less Mn⁺² than coexistent garnet, biotite, or amphibole. Analytical data, crystal-chemical arguments, and characteristics of Fe and Mn L-spectra indicate that in coexistent garnet and piemontite, Fe⁺², Fe⁺³, Mn⁺², and Mn⁺³ are present, in spite of the fact that trivalent manganese strongly oxidizes divalent iron in aqueous solution under normal conditions.Contribution No. 1468.  相似文献   

The redox chemistry of Pu(V)O₂⁺ interaction with common mineral surfaces in dilute solutions and seawater     

Wendy L. Keeney-kennicutt  John W. Morse 《Geochimica et cosmochimica acta》1985,49(12):2577-2588

It has long been recognized that the Pu⁴⁺ ion can be readily adsorbed on solid surfaces, but it has been assumed that the generally more abundant Pu(V)O₂⁺ ion should have little affinity for surfaces. Our results indicate that Pu(V)O₂⁺ can be adsorbed from dilute solutions and seawater on goethite, aragonite, calcite, and δ-MnO₂. Adsorption on δ-MnO₂ is severely depressed in seawater, probably as a result of site competition with seawater cations.The sorption behavior of PuO₂⁺ is influenced by oxidation-reduction reactions occurring on the mineral surfaces. Adsorption on δ-MnO₂ results in oxidation of adsorbed Pu(IV) and Pu(V) to Pu(VI). However, adsorption on goethite results in a reaction in which Pu(IV) and Pu(VI) are formed on the mineral surface. The Pu(VI) is slowly reduced to Pu(IV), leaving Pu(IV) as the dominant surface Pu species. This reaction can be photochemically catalyzed. PuO₂⁺ adsorbed on carbonate minerals behaves similarly to Np(V)O₂⁺ and undergoes little change in oxidation state after adsorption.  相似文献   

Low temperature spectral studies of Mn3+-bearing andalusite and epidote type minerals in the range 30000–5000 cm−1     

Smith  G.  Hålenius  U.  Langer  K. 《Physics and Chemistry of Minerals》1982,8(3):136-142

Polarized absorption spectra of natural piemontite (Ca_1.802Mn ²⁺_0.178 Mg_0.025) (Mn ³⁺_0.829 Fe ³⁺_0.346 Al_1.825) [(Si_2.992Al_0.008) O₁₂OH], viridine (Al_1.945Mn ³⁺_0.033 Fe ³⁺_0.063 Mg_0.003) [O|Si_0.970 O₄], and kanonaite (Al_1.291Mn ³⁺_0.682 Fe ³⁺_0.019 ) [O|Si_1.006 O₄] were measured at 295 and ca. 100 K. For piemontite, lowering the temperature resulted in a sharpening of broad bands in the 10 000–25 000 cm⁻¹ region supporting their assignment to single ion Mn³⁺ in M3 non-centrosymmetric sites.

Alternatively, in kanonaite, temperature behaviour pointed to a slightly stronger influence of vibronic coupling on strong bands near 16 000 and 22 000 cm⁻¹, which supported an interpretation of Mn³⁺ in nearly centrosymmetric M1 sites. Measurements at ca. 100 K show pronounced fine structure in the viridine spectra which is attributed to Fe³⁺. The ɛ values for Mn³⁺ spin-allowed bands in the three minerals lie in the range 18 to 227 [1·g-atom⁻¹·cm⁻¹].

For the same band and polarisation, ɛ values in Mn³⁺-bearing andalusite-type minerals viridine and kanonaite are the same, which indicates an absence of strong magnetic coupling effects between Mn³⁺ ions in the andalusite type structure down to ca. 100 K.

In silicates, the high ɛ values for Mn³⁺ spin-allowed bands, in comparison to those obtained for Fe²⁺ spin-allowed bands from sites of “similar distortion”, is attributed to a higher degree of covalency in the Mn³⁺-O bonds compared to the Fe²⁺-O bonds, as a result of the higher valence state of manganese.

  相似文献   

On the model of Mn,Fe, Ni,Co ore formation in recent basins: Experiments with the synthesis of Me-hydroxide phases on Mn3O4     

I. M. Varentsov  N. V. Bakova  Yu. P. Dikov  T. S. Gendler  R. Giovanoli 《Mineralium Deposita》1979,14(3):281-296

Experiments on the sorption of dissolved Ni, Co, Mn, Fe from seawater by Mn₃O₄ reveal a sequence of reactions taking place: Ion exchange, hydrolysis, then autocatalytic oxidation and layer formation on the interface. The composition of the new compounds depends on the kinetics of i) sorption, and ii) interface oxidation. The highest oxidized Me ions accumulate at low sorption rates, i. e. when sorption does not inhibit interface oxidation: 60% Mn⁴⁺, 30% Ni³⁺ & 30% Co³⁺ are a representative example for that layer type. Iron is present in this layer as amorphous FeOOH·xH₂O according to Mössbauer spectra. Specific for the Me sorption by Mn₃O₄ is the interaction of Ni & Co with Mn²⁺ and Mn³⁺ of the sorbent lattice. Mn is found in the solute phase equivalent to 16, 14% of the adsorbed Co or 17, 96% of the adsorbed Ni. These results confirm the earlier presented model on the transition metal accumulation in recent basins as taking place in distinct stages with interface autocatalysis for the Me oxidation playing the main role.  相似文献   

57Fe-Mössbauer spectroscopy on natural eosphorite-childrenite-ernstite samples     

Geraldo Magela da Costa  Ricardo Scholz  Joachim Karfunkel  Vladimir Bermanec  Mário Luiz de Sá Carneiro Chaves 《Physics and Chemistry of Minerals》2005,31(10):714-720

Samples of the eosphorite-childrenite [(Mn²⁺, Fe²⁺)AlPO₄(OH)₂H₂O] series from Divino das Laranjeiras and Araçuaí (Minas Gerais State) and Parelhas (Rio Grande do Norte State) pegmatites have been investigated by X-ray diffraction, microprobe analysis and Mössbauer spectroscopy at 295 and 77 K. The Mössbauer spectra of ernstite [(Mn²⁺, Fe³⁺)AlPO₄(OH)_2-xO_x] showed the existence of ferric ions in both A and B sites, whereas ferrous ions seem to be located exclusively in the A site. Nonoxidised samples show ferrous ions located in both sites, and no Fe³⁺ could be detected. The interpretation of the Mössbauer spectra of both, oxidised and nonoxidised samples, is difficult because the hyperfine parameters of these minerals are rather similar, rendering it difficult to make proper site assignments.  相似文献   

Contributions to the mineralogy of authigenic manganese phases from marine manganese deposits     

F. V. Chukhrov  A. I. Gorshkov  V. V. Beresovskaya  A. V. Sivtsov 《Mineralium Deposita》1979,14(3):249-261

The formation of authigenic manganese minerals and ores in the pelagic regions of the ocean is related to oxidation of Mn²⁺ extracted from basalts and other rocks with heated seawater. For littoral parts of the ocean and lakes mobilization of Mn²⁺ and Fe²⁺ is admitted finding its way to the bottom sediments (along with the organic substances) from land in the form of Mn⁴⁺. The main manganese mineral of oceanic and continental basins is vernadite. Its deposition is considered a result of the activity of microorganisms.  相似文献   

Mössbauer spectra of kyanite,aquamarine, and cordierite showing intervalence charge transfer     

Kathleen M. Parkin  Bruce M. Loeffler  Roger G. Burns 《Physics and Chemistry of Minerals》1977,1(3):301-311

The blue colors of several minerals and gems, including aquamarine (beryl, Be₃Al₂Si₆O₁₈) and cordierite (Al₃(Mg, Fe)₂Si₅AlO₁₈), have been attributed to charge transfer (CT) between adjacent Fe²⁺ and Fe³⁺ cations, while Fe²⁺→Ti⁴⁺ CT has been proposed for blue kyanites (Al₂SiO₅). Such assignments were based on chemical analyses and on polarization-dependent absorption bands measured in visible-region spectra. We have attempted to characterize the Fe cations in each of these minerals by Mössbauer spectroscopy (MS). In blue kyanites, significant amounts of both Fe²⁺ and Fe³⁺ were detected with MS, indicating that Fe²⁺→Fe³⁺ CT, Fe²⁺→Ti⁴⁺ CT, and Fe²⁺ and Fe³⁺ crystal field transitions each could contribute to the electronic spectra. In aquamarines, coexisting Fe²⁺ and Fe³⁺ ions were resolved by MS, supporting our assignment of the broad, relatively weak band at 16,100 cm^?1 in E∥c spectra to Fe²⁺→Fe³⁺ CT between Fe cations replacing Al³⁺ ions 4.6Å apart along c. A band at 17,500 cm^?1 in E⊥c spectra of cordierite is generally assigned to Fe²⁺ (oct)→Fe³⁺ (tet) CT between cations only 2.74 Å apart. However, no Fe³⁺ ions were detected in the MS at 293K of several blue cordierites showing the 17,500 cm^?1 band and reported to contain Fe³⁺. A quadrupole doublet with parameters consistent with tetrahedral Fe³⁺ appears in 77K MS, but the Fe³⁺/Fe²⁺ ratios from MS are much smaller than values from chemical analysis. These results sound a cautionary note when correlating Mössbauer and chemically determined Fe³⁺/Fe²⁺ ratios for minerals exhibiting Fe²⁺→Fe³⁺ CT.  相似文献   

Electron paramagnetic resonance study of iron(III) and manganese(II) in the glassy and crystalline environments of synthetic fayalite and tephroite     

Sandip K. Sur  Thomas F. Cooney 《Physics and Chemistry of Minerals》1989,16(7):693-696

Crystals of the olivine minerals, tephroite (Mn₂SiO₄) and fayalite (Fe₂SiO₄) containing manganese(II) and iron (II and trace of III), respectively, were synthesized. Glasses were prepared from these crystalline materials by a splat-quench technique. Measurement of electron paramagnetic resonance (EPR) of all these powdered samples at room temperature show that the g-factors of Mn²⁺ in both glassy and crystalline environments (g_eff = 2.004) are the same, although the EPR linewidths (for glass, ΔH_pp = 200 G; for crystals ΔH_pp = 287 G) suggest less clustering of paramagnetic Mn²⁺ ions in the glass. Mn²⁺ probably occupies a distorted octahedral site in the tephroite crystal structure, although a four-fold coordination is suggested from other spectroscopic investigation on this glass. The EPR parameters of Fe³⁺ in synthetic fayalite glass (g_eff = 2.01 and 6.00; ΔH_pp=150 and 1375 G, respectively, for the high and low field resonances) and powdered crystals (g_eff = 3.31 and ΔH_pp = 900 G) indicated that Fe³⁺ ion in the crystals, is probably located in a distorted tetragonal site M2 and an axial environment has been proposed in the glassy system.  相似文献   

Metal cation exchange reactions of ore minerals in Fe–Mn crusts of the Marcus Wake Rise (Pacific Ocean) in aqueous–salt solutions     

G. V. Novikov  O. Yu. Bogdanova  M. E. Melnikov  A. N. Drozdova  N. V. Lobus  N. A. Shulga 《Doklady Earth Sciences》2017,477(2):1414-1418

It is shown that the reaction ability of metal cations of ore minerals in Fe–Mn crusts of the Marcus Wake Rise increases in the following manner: (Co²⁺ < Cu²⁺ < Ni²⁺) < (Mg²⁺ < Mn²⁺ < K⁺ ≈ Ca²⁺ ≈ Na⁺). The composition of the exchange complex of the ore minerals is constant and includes these metal cations. Ca²⁺ and Na⁺ are major contributors to the exchange capacity of the ore minerals. The capacity of the ore minerals by cations of alkali and base metals is 0.43–0.60 and 2.08–2.70 mg-equiv/g, respectively. The exchange capacity of the ore minerals by cations of base metals increases linearly with the increase in the MnO₂ content of the crust and does not depend on the geographical locations of the Marcus Wake guyots.  相似文献   

Electronic structures of iron(III) and manganese(IV) (hydr)oxide minerals: Thermodynamics of photochemical reductive dissolution in aquatic environments   总被引：2，自引：0，他引：2  

David M. Sherman 《Geochimica et cosmochimica acta》2005,69(13):3249-3255

Sunlight-induced reduction and dissolution of colloidal Fe-Mn (hydr)oxide minerals yields elevated concentrations of Fe²⁺ and Mn²⁺ in natural waters. Since these elements may be biolimiting micronutrients, photochemical reactions might play a significant role in biogeochemical cycles. Reductive photodissolution of Fe (hydr)oxide minerals may also release sorbed metals. The reactivity of Fe-Mn (hydr)oxide minerals to sunlight-induced photochemical dissolution is determined by the electronic structure of the mineral-water interface. In this work, oxygen K-edge absorption and emission spectra were used to determine the electronic structures of iron(III) (hydr)oxides (hematite, goethite, lepidocrocite, akaganeite and schwertmannite) and manganese(IV) oxides (pyrolusite, birnessite, cryptomelane). The band gaps in the iron(III) (hydr)oxide minerals are near 2.0-2.5 eV; the band gaps in the manganese (IV) oxide phases are 1.0-1.8 eV. Using published values for the electrochemical flat-band potential for hematite together with experimental pH_pzc values for the (hydr)oxides, it is possible to predict the electrochemical potentials of the conduction and valence bands in aqueous solutions as a function of pH. The band potentials enable semiquantitative predictions of the susceptibilities of these minerals to photochemical dissolution in aqueous solutions. At pH 2 (e.g., acid-mine waters), photoreduction of iron(III) (hydr)oxides could yield millimolal concentrations of aqueous Fe²⁺ (assuming surface detachment of Fe²⁺ is not rate limiting). In seawater (pH 8.3), however, the direct photo-reduction of colloidal iron(III) (hydr)oxides to give nanomolal concentrations of dissolved, uncomplexed, Fe²⁺ is not thermodynamically feasible. This supports the hypothesis that the apparent photodissolution of iron(III) (hydr)oxides in marines systems results from Fe³⁺ reduction by photochemically produced superoxide. In contrast, the direct photoreduction of manganese oxides should be energetically feasible at pH 2 and 8.3.  相似文献   

Pyrolusite surface transformations measured in real-time during the reactive transport of Co(II)EDTA2−     

《Geochimica et cosmochimica acta》1999,63(19-20):3049-3057

Oxidation of Co(II)EDTA²⁻ to Co(III)EDTA⁻ by manganese and iron hydrous oxide minerals enhances the transport of ⁶⁰Co in subsurface environments. Until now, reduction of the oxidant MnO₂ has not been identified in hydrodynamic systems, leaving the fate and transport mechanisms involving ⁶⁰Co in natural environments unresolved. We investigated the transport of Co(II)EDTA²⁻ through packed beds of β-MnO₂ and identified the reaction mechanism using a novel hydrodynamic flow cell coupled with X-ray absorption near edge structure (XANES) spectroscopy. Using this technique we are able to determine both solution and solid-phase species of cobalt and manganese in real-time. Co(II)EDTA²⁻ is produced while Mn(IV) is reduced to Mn(III) which forms an α-Mn₂O₃layer on pyrolusite. This layer passivates the surface after an initial reaction period and ultimately limits the production of Co(III)EDTA⁻. As a consequence, the enhanced transport of ⁶⁰Co by oxidative processes may be diminished by continual exposure to pyrolusite—an advantage from an environmental quality perspective. It has also been clarified that Mn(III) is formed rather than Mn(II) resulting in formation of a stable trivalent manganese solid (α-Mn₂O₃).  相似文献   

High-resolution parallel electron energy-loss spectroscopy of Mn L2,3-edges in inorganic manganese compounds   总被引：1，自引：0，他引：1  

L. A. J. Garvie  A. J. Craven 《Physics and Chemistry of Minerals》1994,21(4):191-206

Parallel electron energy-loss spectroscopy (PEELS) in a scanning transmission electron microscope (STEM) was used to record the Mn L_2,3-edges from a range of natural and synthetic manganese containing materials, covering valences 0, II, III, IV and VII, with an energy resolution of ca. 0.5 eV. The Mn L_2,3 electron-loss near-edge structure (ELNES) of these edges provided a sensitive fingerprint of its valence. The Mn²⁺ L_2,3-edges show little sensitivity to the local site symmetry of the ligands surrounding the manganese. This is illustrated by comparing the Mn L_2,3-edges from 4-, 6- and 8-fold coordinated Mn²⁺. In contrast, the Mn L₃-edges from Mn³⁺ and Mn⁴⁺ containing minerals exhibited ELNES that are interpreted in terms of a crystal-field splitting of the 3d electrons, governed by the symmetry of the surrounding ligands. The Mn L₃-edges for octahedrally coordinated Mn²⁺, Mn³⁺ and Mn⁴⁺ showed variations in their ELNES that were sensitive to the crystal-field strength. The crystal-field strength (10Dq) was measured from these edges and compared very well with published optically determined values. The magnitude of 10Dq measured from the Mn L₃-edges and their O K-edge prepeaks of the manganese oxides were almost identical. This further confirms that the value of 10Dq measured at the Mn L₃-edge is correct. Selected spectra are compared with theoretical 2p atomic multiplet spectra and the differences and similarities are explained in terms of the covalency and site symmetry of the manganese. The Mn L₃-edges allow the valence of the manganese to be ascertained, even in multivalent state materials, and can also be used to determine 10Dq.  相似文献   

Mie scattering and charge transfer phenomena as causes of the UV edge in the absorption spectra of natural and synthetic almandine garnets     

V. M. Khomenko  K. Langer  R. Wirth  B. Weyer 《Physics and Chemistry of Minerals》2002,29(3):201-209

 The UV edge in the electronic absorption spectra of minerals, in many cases influencing their colour, is generally interpreted as the low-energy wing of very strong UV bands caused by ligand–metal charge transfer (CT) transitions (e.g. Burns 1993). However, Mie scattering theory shows that the presence of randomly distributed submicroscopic inclusions with narrow size distribution and a refractive index n _i in a matrix with different refractive index n _m may give rise to a λ-dependent, band-like scattering (e.g. Kortüm 1969). Such scattering bands have so far not been considered as contributing to the UV edge. Single-crystal electronic absorption spectra of eight natural almandine-rich garnets (Alm₆₀–Alm₈₈), two synthetic almandine samples (Alm₁₀₀), all of different colours, and synthetic spessartine were studied by means of a Zeiss microscope-spectrometer in the range 40 000–20 000 cm⁻¹. Special techniques of spectral measurements with crossed analyzer and polarizer, which enable the registration of the scattering effect directly, were used as well. Four of the above garnets were also investigated using transmission electron microscopy. Different types of inclusions, from 10 to several 100 nm in size, were observed in the garnet matrices. They are abundant in cores of synthetic garnets, but very rare in most natural almandines studied. Electronic absorption spectra of the natural almandine garnets show largely varying UV edge position and, hence, intensity at a given wavenumber which correlates with the intensities of spin-forbidden dd bands of Fe³⁺ ions at 27 000 and 28 000 cm⁻¹, superimposed on the long energy slope of the UV absorption. There are also positive correlations between Ti⁴⁺ and Fe³⁺ content, the latter recalculated on the basis of garnet stoichiometry, and UV edge intensity. Thus, the presence of Ti⁴⁺ and Fe³⁺ ions in octahedra, even in very low concentrations (0.0n at. pfu), leads to CT phenomena, that probably involve Fe²⁺ ions in edge-shared dodecahedral position and intensifies ligand- to-metal CT. The different colours of natural almandine garnets with similar Fe²⁺ contents studied here are caused by this effect. Consistent with the absence of inclusions in most natural garnets studied, λ-dependent scattering plays no role in their UV absorption. In contrast, in synthetic almandine and spessartine crystals, a different intensity of UV absorption was observed in inclusion-free rims and inclusion-enriched cores. Some of the latter demonstrate typical scattering patterns when measured at crossed polarizers. Received: 10 April 2001 / Accepted: 27 September 2001  相似文献   

Location, valence states, and oxidation mechanisms of iron in eudialyte-group minerals from Mössbauer spectroscopy     

A. P. Khomyakov  V. V. Korovushkin  Yu. D. Perfiliev  V. M. Cherepanov 《Physics and Chemistry of Minerals》2010,37(8):543-554

A representative collection of structurally characterized eudialyte-group minerals (EGM) with varying relative concentrations of Fe²⁺ and Fe³⁺ ions from several localities was investigated at room temperature by ⁵⁷Fe Mössbauer spectroscopy coupled with magnetometric, optical, and X-ray powder diffraction methods. To refine the Mössbauer parameters of isomer shift and quadrupole splitting for Fe²⁺ and Fe³⁺ in different types of coordination polyhedra (planar quadrangle, square pyramid, and distorted octahedron) in EGM structures, we also collected Mössbauer parameters for gillespite and labuntsovite. The main purpose of this work is to determine the location of Fe³⁺ in different sites in typical eudialyte, rastsvetaevite, georgbarsanovite, and some of their naturally hydrated and heat-treated analogs, and investigate the kinetics and oxidation mechanisms of iron ions in their structures. Our study has confirmed the presence of Fe²⁺ ions in the planar quadrangle and square pyramid in primary eudialytes, as well as the presence of Fe³⁺ ions in the square pyramid and distorted octahedron in primary, naturally hydrated, and heat-treated eudialytes. According to this study, hydrated eudialytes are characterized by the location of Fe³⁺ ions mainly in octahedra with OH groups and/or water molecules at trans vertices, while heat-treated eudialytes are characterized by their location in square pyramids with an O^2? anion at the apical vertex.  相似文献   

Reactive transport impacts on recovered freshwater quality during multiple partially penetrating wells (MPPW-)ASR in a brackish heterogeneous aquifer     

《Applied Geochemistry》2016

The use of multiple partially penetrating wells (MPPW) during aquifer storage and recovery (ASR) in brackish aquifers can significantly improve the recovery efficiency (RE) of unmixed injected water. The water quality changes by reactive transport processes in a field MPPW-ASR system and their impact on RE were analyzed. The oxic freshwater injected in the deepest of four wells was continuously enriched with sodium (Na⁺) and other dominant cations from the brackish groundwater due to cation exchange by repeating cycles of ‘freshening’. During recovery periods, the breakthrough of Na⁺ was retarded in the deeper and central parts of the aquifer by ‘salinization’. Cation exchange can therefore either increase or decrease the RE of MPPW-ASR compared to the RE based on conservative Cl⁻, depending on the maximum limits set for Na⁺, the aquifer’s cation exchange capacity, and the native groundwater and injected water composition. Dissolution of Fe and Mn-containing carbonates was stimulated by acidifying oxidation reactions, involving adsorbed Fe²⁺ and Mn²⁺ and pyrite in the pyrite-rich deeper aquifer sections. Fe²⁺ and Mn²⁺ remained mobile in anoxic water upon approaching the recovery proximal zone, where Fe²⁺ precipitated via MnO₂ reduction, resulting in a dominating Mn²⁺ contamination. Recovery of Mn²⁺ and Fe²⁺ was counteracted by frequent injections of oxygen-rich water via the recovering well to form Fe and Mn-precipitates and increase sorption. The MPPW-ASR strategy exposes a much larger part of the injected water to the deeper geochemical units first, which may therefore control the mobilization of undesired elements during MPPW-ASR, rather than the average geochemical composition of the target aquifer.  相似文献