Neutron Spectroscopic Study of Synthetic Alunite and Oxonium-Substituted Alunite

Lager, G. A.; Swayze, Gregg A.; Loong, C.‐K.; Rotella, F. J.; Richardson, James W.; Stoffregen, Roger E.

doi:10.2113/gscanmin.39.4.1131

Cited by 24 publications

(26 citation statements)

References 17 publications

(15 reference statements)

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“…On the basis of the changes in K w with temperature and pressure, it is proposed that the formation of pentagonite or cavansite depends on whether or not the hydrothermal solution is in supercritical condition (above 300 °C). Such a difference in the formation of cavansite and pentagonite cannot be verified by comparing the crystallization temperatures of H 3 O + -bearing minerals such as jarosite -alunite groups (Ripmeester et al, 1986;Lager et al, 2001), hydrated uranates (Demartin et al, 1991;Chukanov et al, 1999;Chukanov et al, 2004), and clay min- Table 9. Assignment of hydrogens to the refined oxygens using the difference in bond -valence sum of cavansite Polymorphic relation between cavansite and pentagonite erals (Jiang et al, 1994).…”

Section: Polymorphic Relation Between Cavansite and Pentagonitementioning

confidence: 99%

Polymorphic relation between cavansite and pentagonite: Genetic implications of oxonium ion in cavansite

Ishida

Kimata

Nishida

et al. 2009

Journal of Mineralogical and Petrological Sciences

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The chemical compositions of cavansite and pentagonite, in which H 2 O contents and vanadium (in an unknown oxidation state) are present, were determined by thermogravimetry -differential thermal analysis (TG -DTA), electron spin resonance (ESR), and electron microprobe analysis (EMPA). Furthermore, the mechanism of dehydration of the minerals and presence of the hydrous species such as H 2 O, H 3 O + , and OH − in the aforementioned minerals have been investigated by TG -DTA, high -temperature X -ray diffraction (HT -XRPD) analysis, Fourier -transform infrared (FTIR) spectroscopy, and single -crystal XRD analysis. The results of TG -DTA and HT -XRD revealed that no reversible transitions occur between cavansite and pentagonite when they are heated in air and that no intermediate amorphous phase exists in these two minerals. Gradual dehydration of cavansite in the temperature range of 225 -550 °C was attributed to the removal of both oxonium (H 3 O + ) and hydroxyl ions (OH − ); the IR absorption bands of cavansite observed at 3186 and 3653 cm −1 were assigned to H 3 O + and OH − stretching vibrations, respectively. Moreover, the exact distribution of hydrogens in the crystal structure of the cavansite refined in this study was determined by applying the valence -matching principle; the results showed the existence of H 3 O + and OH − . Thus, the structural formula of cavansite should be revised to Ca(VO)(Si 4 O 10 )·(H 2 O) 4−2x (H 3 O) x (OH) x , in contrast to that of pentagonite, Ca(VO)(Si 4 O 10 )·4H 2 O. The changes in the ion product constant of water with temperature and pressure suggest that pentagonite is formed when the hydrothermal fluid is in supercritical condition (>300 °C), while cavansite is formed when the hydrothermal fluid is not in supercritical condition. Thus, cavansite is identified as a low -temperature form and pentagonite as a high -temperature one.

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Section: Polymorphic Relation Between Cavansite and Pentagonitementioning

confidence: 99%

Polymorphic relation between cavansite and pentagonite: Genetic implications of oxonium ion in cavansite

Ishida

Kimata

Nishida

et al. 2009

Journal of Mineralogical and Petrological Sciences

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“…The extent of this replacement depends on temperature and solution composition. [9][10][11][12][13][14] Natural alunites contain Al, K, and Na, which can be recovered as K 2 SO 4 , Na 2 SO 4 , Al 2 O 3 , Al 2 (SO 4 ) 3 , or potassium alum KAl(SO 4 ) 2 . 6 The main method of alunite processing and recovering its valuable products is hydrometallurgy.…”

Section: Introductionmentioning

confidence: 99%

Kinetics of Direct Leaching of Natural Alunite in KOH

Mohammadi

Salarirad

2013

Ind. Eng. Chem. Res.

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Alunite is a potential resource for production of alumina and potassium sulfate.Hydrometallurgy is the conventional process employed for this purpose and direct leaching in KOH is suitable as one of the process steps because it does not require prior calcination. In this paper dissolution kinetics of pure natural alunite in KOH is described. Kinetics of dissolution of alunite in potassium hydroxide follows the shrinking core model. The rate of reaction is controlled by surface chemical reaction step and the order of reaction with respect to KOH is 1.327. The activation energy of this reaction was estimated as 94.18kJ/mol and the following kinetic model for alunite dissolution in potassium hydroxide was obtained:

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“…The monovalent ions are coordinated by 12 O atoms or hydroxyl groups. There are weak hydrogen bonds between the Al 2 -OH groups and the O atoms in the sulfate tetrahedron that point towards the cavity (Wang et al 1965;Schukow et al 1999;Lager et al 2001).…”

Section: Introductionmentioning

confidence: 99%

“…The structure also contains a single A (A = Na + , K + , H 3 O + ) site (Wang et al 1965;Schukow et al 1999;Lager et al 2001). Thus, the 27 Al, 23 Na, and 39 K NMR spectra of a stoichiometric alunite will each consist of a single NMR resonance.…”

Section: Introductionmentioning

confidence: 99%

Characterization of defects and the local structure in natural and synthetic alunite (K, Na, H3O)Al3(SO4)2(OH)6 by multi-nuclear solid-state NMR spectroscopy

Nielsen

Majzlan

Phillips

et al. 2007

American Mineralogist

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The local structural environments in a series of natural and synthetic alunite samples [ideally AAl 3 (SO 4 ) 2 (OH) 6 , A = H 3 O + , D 3 O + , Na + , and K + ] have been probed by solid-state 1 H, 2 H, 23 Na, 27 Al, and 39 K NMR spectroscopy. The natural alunite [KAl 3 (SO 4 ) 2 (OH) 6 ] and synthetic hydronium alunite samples contain few structural defects, whereas the synthetic natroalunite and alunite samples have ca. 10% Al vacancies based on 27 Al NMR. A new 27 Al local environment (Al D ) was observed and assigned to Al with one Al vacancy in the fi rst cation sphere. Three different proton environments, Al 2 -OH, Al-OH 2 , and H 3 O + are detected by 1 H and 2 H MAS NMR. The hydronium ion (H 3 O + ) is only observed in hydronium alunite, and is associated with the stoichiometric regions of the sample. It was not detected in 1 H and 2 H NMR spectra of alunite and natroalunite despite K (Na) occupancies of signifi cantly less than 100%, as determined from elemental analysis. Thus, our NMR results suggest that the common assumption, namely that an A vacancy and an Al 3+ vacancy are compensated by adding an H 3 O + and 3 H + (creating 3 Al-OH 2 groups), respectively, is too simplistic. Instead, a signifi cant fraction of the Al 3+ vacancies are compensated for by 4 H + ions, resulting in 4 Al-OH 2 groups per vacancy. This substitution is accompanied by the simultaneous deprotonation of a H 3 O + ion present on the A site. The resultant H 2 O molecule is unnecessary for charge balance, accounting for the A-site defi ciency often observed. The presence of Al 3+ and A + vacancies appears closely correlated based on NMR.

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Neutron Spectroscopic Study of Synthetic Alunite and Oxonium-Substituted Alunite

Cited by 24 publications

References 17 publications

Polymorphic relation between cavansite and pentagonite: Genetic implications of oxonium ion in cavansite

Polymorphic relation between cavansite and pentagonite: Genetic implications of oxonium ion in cavansite

Kinetics of Direct Leaching of Natural Alunite in KOH

Characterization of defects and the local structure in natural and synthetic alunite (K, Na, H3O)Al3(SO4)2(OH)6 by multi-nuclear solid-state NMR spectroscopy

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