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e-mail: sabine.petit@univ-poitiers.fr

Synthesis of Clay Minerals and the Relationship between Formation Processes and Crystal Chemistry. Pauline ANDRIEUX Sabine PETIT Alain DECARREAU FRE3114 CNRS, HydrASA Université de Poitiers 40, ave. du Recteur Pineau 86022 POITIERS Cedex FRANCE. e-mail: sabine.petit@univ-poitiers.fr.

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  1. Synthesis of Clay Minerals and the Relationship between Formation Processes and Crystal Chemistry Pauline ANDRIEUX Sabine PETIT Alain DECARREAU FRE3114 CNRS, HydrASA Université de Poitiers 40, ave. du Recteur Pineau 86022 POITIERS Cedex FRANCE e-mail: sabine.petit@univ-poitiers.fr

  2. - determine the experimental conditions which led to mineral crystallization (in very simplified systems) constrain possible conditions of formation for those minerals - obtain good reference minerals with monitored crystal chemistry determine their spectroscopic fingerprint Clays synthesis experiments Interest

  3. Tetrahedral charge Octahedral charge Montmorillonite Fe3+-Montmorillonite Beidellite Nontronite Ternary diagram of octahedral compositions for dioctahedral smectite (after Güven, 1988) (Theoretical)

  4. (Si (4-x) Alx)(Al, Fe3+) 2O10 (OH)2 M+x Beidellite Clay synthesis Chemical series studied (Theoretical) Fe3+- nontronite (Si (4-x)Fe3+x) Fe3+2 O10 (OH)2 M+x (Si (4-x)Al, Fe3+x) Fe3+2 O10 (OH)2 M+x IV VI nontronite

  5. Ditrigonal cavity Tetrahedral sheet R(VI),  OH Octahedral sheet R(IV) O Tetrahedral sheet Ditrigonal cavity Smectite structure (dioctahedral) Ditrigonal cavity R(VI), Tetrahedral sheet OH Octahedral sheet R(IV) O Tetrahedral sheet Ditrigonal cavity dioctahedral (cv) dioctahedral (tv) Schematic representation of the octahedral sheet

  6. h Smectite structure (dioctahedral) R = Al, Fe3+ OH dioctahedral (tv) dioctahedral (cv) O H \/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\

  7. Smectite structure (dioctahedral) R = Al, Fe3+ OH dioctahedral (tv) dioctahedral (cv) H+ O Al Fe3+ vacancy

  8. IR spectroscopy Ferruginous smectite SWa-1 (Si3.70Al0.30 )(Al0.57 Fe3+1.33 Mg0.10) O10(OH)2 Na+0.40 NIR MIR n+d OH dOH region

  9. IR spectroscopy Ferruginous smectite SWa-1 NIR MIR Wavelength (µm) n+d Fe3+2OH d Fe3+2OH 2.29 4361 12.2 820

  10. IR spectroscopy Ferruginous smectite SWa-1 NIR MIR Wavelength (µm) n+d AlFe3+OH 2.24 4464 AlAl 4563 dAlFe3+OH 11.4 875

  11. IR spectroscopy Ferruginous smectite SWa-1 NIR MIR Wavelength (µm) n+d Al2OH d Al2OH 2.19 4563 AlAl 4563 4563 10.87 920 920 AlAl

  12. UV Vis NIR MIR Far IR l(µm) Fundamental vibrations OH overtones OH combination 0.9 2.5 25 nSiO dOH 3nOH 2nOH n+d OH nOH dSiO 11000 4000 400 H2O H2O H2O H2O H2O 2WOH >> W2OH X = 1/2W2OH - WOH = -85.6 cm-1 _ n(cm-1) X : anharmonicity constant Petit et al. (2004) Phys. Chem. Minerals, 31, 585-592. IR spectroscopy

  13. Wavenumber (cm-1) 4600 4350 4100 Reflectance 4464 4361 2.24 SWa-1 2.29 2.17 2.30 2.44 Wavelength (µm) Reflects different conditions of formation Scale of heterogeneity in clay minerals (Al2OH) AlFeOH Fe2OH NIR is most often not self – sufficient but it could help

  14. Use an amorphous gel with the clay stoechiometry Clays synthesis experiments The starting material Requirements: - minimize the variables of the system - reproducibility - homogeneous and definite chemical composition

  15. Basic reaction : silica source: SiO2Na2O metal source: salt (chloride, nitrate…) equilibrated agent: HCl, NaOH, ….. Ex: nontronite 4 SiO2Na2O + 2 FeCl3 + 2 HCl  8 NaCl + H2O + Si4 Fe2 O11 beidellite 4 SiO2Na2O + 2 AlCl3 +2 HCl  8 NaCl + H2O + Si4 Al2 O11 Clay synthesis experiments Protocol Coprecipitation of gel with the clay stoechiometry Decarreau (1983) ’s protocol

  16. Clays syntheses experiments Protocol The coprecipitate is: - centrifuged and washed - dried and crushed (or frieze dried) The starting material is ready to use.

  17. The rate constant of an heterogeneous chemical reaction in aqueous phase is given by : k = A.exp - (E/RT) Ageing time of clay synthesis can be minimized by an increase of T. Clay synthesis experiments Starting material Aim: Reproduce in laboratory clay formation Problem: we cannot use geological times ! From kaolinite syntheses performed at several temperatures (180-300°C), Rayner [1962] calculated a half-reaction time of 16.104 years at 20°C. Clays similar to clays formed at the earth surface are synthesized by hydrothermal treatment at T <= 250°C (at equilibrium water P)

  18. Starting material (300-500 mg) + distilled water (30 cc) (+ HCl or NaOH) Teflon Metal Clay synthesis Experimental conditions < 100°C : PFA reactors (copolymer of ethylene tetrafluor) From 100 to 240°C : reactors with metal bodies and removable Teflon liners

  19. Clay synthesis Chemical series studied (Theoretical) Fe3+- nontronite (Si (4-x)Fe3+x) Fe3+2 O10 (OH)2 M+x nontronite

  20. Synthesis of nontronite Partially reducing conditions (Decarreau et al. Clays&Clay Min. 322-337, 2008) Starting from Fe2+: 2 SiO2Na2O + FeCl2 Si2FeNa2O6 + 2 NaCl after drying the gel, iron is oxidized pH is adjusted to 12.5 with NaOH ageing time 4 weeks T = 75, 90, 100, 125, 150 °C * *aegirine (Na Fe3+Si2O6 ) is obtained at higher temperatures (Decarreau et al. Eur. J. Mineral. 16, 85-90, 2004)

  21. 001 02-11 T (°C) 150 125 110 100 90 75 gel 004 13-20 06-33 15-24-31 Synthesis of nontronite X-Ray Diffraction patterns Si3.25Fe3+0.75 Fe3+2 O10(OH)2 Na+0.75 (Decarreau et al. Clays&Clay Min. 322-337, 2008)

  22. Synthesis of nontronite Partially reducing conditions NIR spectra Wavelength (µm) H2O 65 1.43 60 H2O n+d Fe3+2OH 55 1.92 ? 50 2.29 45 2.41 4144 %Réflectance (Offset) 40 35 fresh gel starting gel nontronite 30 6975 5198 25 2nFe3+2OH 4373 20 7500 7000 6500 6000 5500 5000 4500 Wavenumber (cm-1)

  23. Synthesis of nontronite Partially reducing conditions NIR spectra 1.43 1.47 Wavelength (µm) 1.92 ? 2.29 80 2.41 75°C 90°C 76 %Reflectance (offset) 100°C 72 110°C 125°C 68 150°C 64 6800 H2O 60 Wavenumber (cm-1) 7000 6000 5000 6982 5204 4373 4144 2n Fe3+2OH H2O n+d Fe3+2OH

  24. 3+ Synthesis of Fe -nontronite Conclusion - Well crystallized nontronite can be synthesized under either oxidizing or partially reducing conditions. - the range of synthesis pH is narrow (12 to 12.5) - at lower pH hematite or hisingerite are formed - at higher pH and for temperatures >180°C aegirine is formed Thermodynamic equilibrium diagram of aegirine with 2:1 phyllosilicates with the following structural formula: Si (4-x) Fe3+x Fe3+2 O10 (OH)2 Na+x after Decarreau et al. (2004) Eur. J. Mineral., 85-90.

  25. (Si (4-x) Alx)(Al, Fe3+) 2O10 (OH)2 M+x Beidellite Clay synthesis Chemical series studied (Theoretical) Fe3+- nontronite (Si (4-x)Fe3+x) Fe3+2 O10 (OH)2 M+x (Si (4-x)Al, Fe3+x) Fe3+2 O10 (OH)2 M+x IV VI nontronite

  26. Synthesis of smectite Al-Fe - chemical series 3+

  27. XRD powder pattern 3.64 Å 6000 5000 4000 3000 2000 1000 15.9 Å Wavelength (µm) 4.52 Å 100 2.58 Å 1.919 Å 1.528 Å 95 90 Counts 85 80 % Reflectance 75 1.46 6833 70 2.29 4373 65 1.43 6980 H2O 60 1.91 5224 Position (°2Theta) Cuka 55 2n Fe3+2OH 50 2.22 4510 H2O 45 • 13 23 33 43 53 63 40 7500 7000 6500 6000 5500 5000 4500 Wavenumber (cm-1) n+d Fe3+2OH Hisingerite

  28. Synthesis of smectite Al-Fe - chemical series 3+

  29. Synthesis of smectite Al-Fe - chemical series 3+ Wavelength (µm) 2n Al3+2OH 2n Fe3+2OH 1.41 H2O 1.43 H2O 1.47 1.92 n+d R3+2OH 1.8Al0.2Fe %Reflectance (Offset) 1Al1Fe pHi=6.3, pHf=6.7 1Al1Fe pHi=8.4, pHf=10.4 6800 0.4Al1.6Fe 7100 5204 0.2Al1.8Fe 6982 2Fe 8000 7500 7000 6500 6000 5500 5000 4500 Wavenumber (cm-1)

  30. Synthesis of smectite Al-Fe - chemical series 3+ n+d AlFe3+OH n+d Al2OH 2.24 n+d Fe3+2OH 2.19 Wavelength (µm) 2.29 1.8Al0.2Fe % Reflectance (Offset) 1Al1Fe pHi=6.3, pHf=6.7 1Al1Fe pHi=8.4, pHf=10.4 0.4Al1.6Fe 4566 4462 0.2Al1.8Fe 4373 2Fe 4800 4600 4400 4200 Wavenumber (cm-1)

  31. Synthesis of smectite Possible implications for Mars • nontronite can crystallize under partially reducing or oxidizing conditions if available water, Si, Fe and alkaline pH without biology and organic acids • poorly crystalline nontronite can be obtained for days at low temperature • - however, the pH conditions range is narrow • - the range increases when Al increases (same with Mg) • - pH conditions hardly control crystal-chemistry of synthesized clays • - high T are not convenient for nontronite • nontronite/zeolite paragenesis may correspond to the same geochemical conditions What is the «stability » of nontronite (or hingerite) under rather acidic atmosphere ? (no H+ activity ?)

  32. Synthesis of smectite Possible implications for Mars • YESTERDAY topic • (Identification of phyllosilicates) • poorly crystalline nontronite give the same NIR signal than well crystallized one (width of the OH combination band does not decrease significantly) • doublet (or triplet) in the 2.2 µm region does not necessarily reflect the presence of several minerals (… and is the mystery of the doublet at 2.2 and 2.28 µm solved? ) • NIR alone is most often not enough to characterize muti-component samples unambiguously

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