Cation and anion ordering in synthetic lepidolites and lithian muscovites: influence of the OH ∕ F and Li ∕ Al ratios on the mica formation studied by NMR (nuclear magnetic resonance) spectroscopy and X-ray diffraction
<p>A large number of lepidolites K(Li<span class="inline-formula"><sub><i>x</i></sub></span>Al<span class="inline-formula"><sub>3−<i>x</i></sub></span>)[Si<span class="inline-formula">&l...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-03-01
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| Series: | European Journal of Mineralogy |
| Online Access: | https://ejm.copernicus.org/articles/35/199/2023/ejm-35-199-2023.pdf |
| Summary: | <p>A large number of lepidolites
K(Li<span class="inline-formula"><sub><i>x</i></sub></span>Al<span class="inline-formula"><sub>3−<i>x</i></sub></span>)[Si<span class="inline-formula"><sub>2<i>x</i></sub></span>Al<span class="inline-formula"><sub>4−2<i>x</i></sub></span>O<span class="inline-formula"><sub>10</sub></span>](OH)<span class="inline-formula"><sub><i>y</i></sub></span>F<span class="inline-formula"><sub>2−<i>y</i></sub></span>
and Li-muscovites K(Li<span class="inline-formula"><sub><i>x</i></sub></span>Al<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi/><mrow><mn mathvariant="normal">2</mn><mo>-</mo><mi>x</mi><mo>/</mo><mn mathvariant="normal">3</mn></mrow></msub><msub><mo>□</mo><mrow><mn mathvariant="normal">1</mn><mo>-</mo><mn mathvariant="normal">2</mn><mi>x</mi><mo>/</mo><mn mathvariant="normal">3</mn></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="62pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="5e45994ef1330b1cb9444f3c04d701de"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-199-2023-ie00005.svg" width="62pt" height="14pt" src="ejm-35-199-2023-ie00005.png"/></svg:svg></span></span>)[Si<span class="inline-formula"><sub>3</sub></span>AlO<span class="inline-formula"><sub>10</sub></span>](OH)<span class="inline-formula"><sub><i>y</i></sub></span>F<span class="inline-formula"><sub>2−<i>y</i></sub></span> were synthesised by a gelling method in combination with hydrothermal
syntheses at a pressure of 2 kbar and a temperature of 873 K. The nominal
composition ranged between <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">0.0</mn><mo>≤</mo><mi>x</mi><mo>≤</mo><mn mathvariant="normal">2.0</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="22dcaaadbbc3f512e7e4c1906bb9bf54"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-199-2023-ie00006.svg" width="64pt" height="11pt" src="ejm-35-199-2023-ie00006.png"/></svg:svg></span></span> and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">0.0</mn><mo>≤</mo><mi>y</mi><mo>≤</mo><mn mathvariant="normal">2.0</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="25930b3602645311922ba016021999ae"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-199-2023-ie00007.svg" width="64pt" height="12pt" src="ejm-35-199-2023-ie00007.png"/></svg:svg></span></span>, i.e. from polylithionite
K[Li<span class="inline-formula"><sub>2.0</sub></span>Al][Si<span class="inline-formula"><sub>4.0</sub></span>O<span class="inline-formula"><sub>10</sub></span>](OH)<span class="inline-formula"><sub><i>y</i></sub></span>F<span class="inline-formula"><sub>2−<i>y</i></sub></span> over
trilithionite
K[Li<span class="inline-formula"><sub>1.5</sub></span>Al<span class="inline-formula"><sub>1.5</sub></span>][AlSi<span class="inline-formula"><sub>3.0</sub></span>O<span class="inline-formula"><sub>10</sub></span>](OH)<span class="inline-formula"><sub><i>y</i></sub></span>F<span class="inline-formula"><sub>2−<i>y</i></sub></span> to muscovite K[Al<span class="inline-formula"><sub>2.0</sub>□</span>][AlSi<span class="inline-formula"><sub>3.0</sub></span>O<span class="inline-formula"><sub>10</sub></span>](OH)<span class="inline-formula"><sub><i>y</i></sub></span>F<span class="inline-formula"><sub>2−<i>y</i></sub></span>. <span class="inline-formula"><sup>1</sup></span>H, <span class="inline-formula"><sup>19</sup></span>F,
<span class="inline-formula"><sup>29</sup></span>Si and <span class="inline-formula"><sup>27</sup></span>Al magic-angle spinning nuclear magnetic resonance (MAS
NMR) and <span class="inline-formula"><sup>27</sup></span>Al multiple-quantum magic-angle spinning (MQMAS) NMR
spectroscopy has been performed to investigate the order and/or disorder state of
Si and Al in the tetrahedral layers and of Li, Al, OH and F in the
octahedral layer. The synthetic mica crystals are very small, ranging from
0.1 to 5 <span class="inline-formula">µ</span>m. With increasing Al content, the crystal sizes
decrease. Rietveld structure analyses on 12 samples showed that nearly all
samples consist of two mica polytypes (1M and 2M<span class="inline-formula"><sub>1</sub></span>) of varying
proportions. In the case of lepidolites, the 1M <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M41" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="dec69c2f61a2c3df83845e73f901bed1"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-199-2023-ie00008.svg" width="8pt" height="14pt" src="ejm-35-199-2023-ie00008.png"/></svg:svg></span></span> 2M<span class="inline-formula"><sub>1</sub></span> ratio depends on
the <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M43" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">Li</mi><mo>/</mo><mi mathvariant="normal">Al</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="27pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="46437f94bb53152da39d7025522632f0"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-199-2023-ie00009.svg" width="27pt" height="14pt" src="ejm-35-199-2023-ie00009.png"/></svg:svg></span></span> ratio of the reaction mixture. The refinement of the occupancy
factors of octahedral sites shows that lepidolites (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M44" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">1.5</mn><mo>≤</mo><mi>x</mi><mo>≤</mo><mn mathvariant="normal">2.0</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="cac6f10755284e66077552368c0f88c0"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-199-2023-ie00010.svg" width="64pt" height="11pt" src="ejm-35-199-2023-ie00010.png"/></svg:svg></span></span>)
represent a solid solution series with polylithionite and trilithionite as
the endmembers. In the case of the Li-muscovites (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M45" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">0.0</mn><mo>≤</mo><mi>x</mi><mo>≤</mo><mn mathvariant="normal">1.5</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="e7b7c9056c57963fa804a3f08d7a3a68"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-199-2023-ie00011.svg" width="64pt" height="11pt" src="ejm-35-199-2023-ie00011.png"/></svg:svg></span></span>),
the 1M <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M46" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="2251cbae0b7d78a459605b060cf1ad8c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-199-2023-ie00012.svg" width="8pt" height="14pt" src="ejm-35-199-2023-ie00012.png"/></svg:svg></span></span> 2M<span class="inline-formula"><sub>1</sub></span> ratio depends on the number of impurity phases like
eucryptite or sanidine depleting the reaction mixture of Li or Al. There is
no solid solution between trilithionite and muscovite; instead, the
Li-muscovite crystals consist of domains differing in the relative
proportions of muscovite and trilithionite.</p>
<p><span id="page200"/>The overall composition of the synthesised micas which consist of two
polytypes can be characterised by <span class="inline-formula"><sup>29</sup></span>Si, <span class="inline-formula"><sup>1</sup></span>H and <span class="inline-formula"><sup>19</sup></span>F MAS NMR
spectroscopy. The <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M51" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">Si</mi><mo>/</mo><mi mathvariant="normal">Al</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="28pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="338a392124e9390f7d065bad69fd7727"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-199-2023-ie00013.svg" width="28pt" height="14pt" src="ejm-35-199-2023-ie00013.png"/></svg:svg></span></span> ratio in the tetrahedral layers and thus the content
of <span class="inline-formula"><sup>[4]</sup></span>Al were calculated by analysing the signal intensities of the
<span class="inline-formula"><sup>29</sup></span>Si MAS NMR experiments. The Li content <span class="inline-formula"><i>x</i><sub>est</sub></span> was calculated from
the measured tetrahedral <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M55" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">Si</mi><mo>/</mo><mi mathvariant="normal">Al</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="28pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="c94797c623eb66c17584d7c514d1ecc7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="ejm-35-199-2023-ie00014.svg" width="28pt" height="14pt" src="ejm-35-199-2023-ie00014.png"/></svg:svg></span></span> ratio of the <span class="inline-formula"><sup>29</sup></span>Si MAS NMR signals. The
calculated Li contents <span class="inline-formula"><i>x</i><sub>est</sub></span> of samples between polylithionite and
trilithionite agree with the expected values. The F-rich samples show slightly
increased values and the OH samples lower values. Lepidolites with only F
(<span class="inline-formula"><i>x</i></span> <span class="inline-formula">=</span> 1.5 to 2.0, <span class="inline-formula"><i>y</i></span> <span class="inline-formula">=</span> 0.0), but not lepidolites with only OH (<span class="inline-formula"><i>x</i></span> <span class="inline-formula">=</span> 1.5 to 2.0
and <span class="inline-formula"><i>y</i></span> <span class="inline-formula">=</span> 2.0), were observed after synthesis. With decreasing Li content, <span class="inline-formula"><i>x</i>≤1.2</span>, Li-muscovites containing mostly hydroxyl (<span class="inline-formula"><i>y</i>>1.0</span>) are
formed. It was possible to synthesise fluorine containing micas with a
Li content as low as 0.3 and <span class="inline-formula"><i>y</i></span> <span class="inline-formula">=</span> 0.2 to 1.8. The <span class="inline-formula"><sup>19</sup></span>F and <span class="inline-formula"><sup>1</sup></span>H MAS NMR
experiments reveal that F and OH are not distributed statistically but local
structural preferences exist. F is attracted by Li-rich and OH by Al-rich
environments. The quadrupolar coupling constant which represents the
anisotropy of the Al coordination is low for polylithionite with <span class="inline-formula"><i>C</i><sub>Q</sub>=1.5</span> MHz and increases to <span class="inline-formula"><i>C</i><sub>Q</sub>=3.8</span> MHz for trilithionite. For
tetrahedral Al a smaller increase of <span class="inline-formula"><i>C</i><sub>Q</sub></span> from 1.7 to 2.8 MHz is
observed. Advancing from trilithionite to muscovite both quadrupolar
coupling constants decrease to 2.5 MHz for octahedral and 1.5 MHz for
tetrahedral Al. In polylithionite there is the most isotropic environment
for octahedral Al; there are only Li<span class="inline-formula"><sub>2</sub></span>Al sites coordinated by F in the
octahedral sheets and O from the tetrahedral sheets which are regular,
containing only Si. The distortion and anisotropy for Al in tetrahedral
as well as octahedral sheets increases with rising Al content. The most anisotropic
environment can be found in trilithionite, especially for octahedral Al.</p> |
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| ISSN: | 0935-1221 1617-4011 |