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Topotactic formation of ferrisicklerite from natural triphylite under hydrothermal conditions |
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| Authors: | Peter Schmid-Beurmann Luisa Ottolini Frédéric Hatert Thorsten Geisler Magdalena Huyskens Volker Kahlenberg |
| Institution: | 1. Institut für Mineralogie, Universit?t Münster, Corrensstr. 24, 48149, Münster, Germany 2. C.N.R.- Istituto di Geoscienze e Georisorse (IGG), Unità di Pavia, Via A. Ferrata 1, 27100, Pavia, Italy 3. Laboratoire de Minéralogie, Département de Géologie, Université de Liège, Batiment B18, 4000, Liège, Belgium 4. Universit?t Bonn, Steinmann-Institut für Geologie, Mineralogie und Pal?ontologie, Poppelsdorfer Schlo?, 33115, Bonn, Germany 5. Universit?t Innsbruck, Institut für Mineralogie und Petrographie, Innrain 52, 6020, Innsbruck, Austria |
| Abstract: | The topotactic oxidation and delithiation reaction from triphylite, Li(Fe,Mn)PO4, leading to ferrisicklerite, Li<1(Fe3+,Mn2+)PO4, was investigated under hydrothermal conditions. A cuboid cut from a triphylite single-crystal (Palermo Mine, New Hampshire, USA) with the composition Li0.93(3)(Fe2+ 0.733(6),Fe3+ 0.015(1),Mn2+ 0.210(4),Mg0.063(2))1.021(8)P1.00(2)O4 in addition with ground bulk material were treated with KMnO4 and 30 % H2O2(aq) as oxidizing agent in a 0.1 N hydrochloric acid solution in the temperature range between 60 and 200 °C. At 120 °C a rim of 0.1 mm thickness of ferrisicklerite had formed around the core of unreacted triphylite. The sharp reaction boundary was clearly visible, due to the reddish brown absorption colors of ferrisicklerite, compared to colorless triphylite. Using single-crystal X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), electron probe micro-analysis (EPMA) and 57Fe-Mössbauer spectroscopy the product ferrisicklerite was characterized and its composition determined as Li0.30(7)(Fe2+ 0.049(1)Fe3+ 0.65(2)Mn2+ 0.218(5)Mg0.062(2))0.98(1)P1.01(3)O4, with unit cell parameters a?=?4.795(1), b?=?9.992(4), and c?=?5.886(2) Å. EPMA investigations across the reaction boundary showed no changes in the concentrations of Fe, Mn, Mg, and P. In contrast, SIMS measurements clearly proved the delithiated state of the ferrisicklerite product. Polarization microscopy revealed that the orientation of the ferrisicklerite rim was the same as that of the original triphylite single-crystal, confirming the strictly topotactic character of the reaction. |
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