EVALUATION OF M g AND K EXCHANGE CATION EFFECTS WITH SIMULATED XRD PATTERNS Aparicio, Patricia 1 and Ferrell, Ray E. 2

1. EVALUATION OF Mg AND K EXCHANGE CATIONEFFECTS WITH SIMULATED XRD PATTERNSAparicio, Patricia1 and Ferrell, Ray E.2 1 Departamento de Cristalografía, Mineralogía y Q. Agrícola. Universidad de Seville, Spain. e-mail:patric@cica.es 2 Department of Geology and Geophysics. Louisiana State University, Baton Rouge, LA 70803-4101, USA. e-mail: rferrell@lsu.edu

2. The use of simulated XRD patterns for interpretation of complex clay mineral assemblages has become essential in modern clay mineral investigations. • Much of the progress is due to the availability of computer programs (i.e., NEWMOD) for the calculation of diffraction effects based on the Mering principle for mixed crystallites. • Additional information can be obtained by comparing actual XRD patterns with those simulating Mg- and K-saturated mixed-layered clays.

3. MATERIALS • Samples from the freshwater marsh in the area of Lake Des Allemands near New Orleans (Louisiana, USA) from a depth between 200-206cm and 290-300cm. • The dark gray samples belong to the Kenner-Allemands soil association. They are typical of the moderately alkaline, fluid clays occurring beneath slightly acid mucks in freshwater marsh environments of the Mississippi River Deltaic Plain.

4. METHOLOGY Sample normal settling by centrifugation <2µ fraction <0.2µ fraction K-saturation Mg-saturation air-dried glycerol-dried air-dried EG-solvation XRD-patterns EG-solvation Heat-treatment at 300°C and 550°C 2q correction 1st qualitative result Layer type determination

5. METHOLOGY 1st qualitative result Layer type determination profile-fitting of Mg-EG patterns Mixed-layered clay mineral identification according to: Moore & Reynolds (1997), Srodon (1984) 2nd qualitative result Mulcalc simulation pattern Clay++ procedure Mulcalc library Assess concordance of experimental and theoretical pattern Qualitative analysis (QR) and Ideal layer percentage of clay minerals Change calculated parameters Bad R2> 0.01 Good R2 ≤ 0.01

6. 9.98 A 16.86 A 3.32 A 4.98 A K-550 12.2 A K-300 9.91 A MgEG 14.5 A 7.2 A MgAD SAMPLE C9, <0.2 micrometers Des Allemands

7. SAMPLE C9, <2 micrometers Des Allemands 3.34 A 9.98 A 13.9 A 4.99 A Qtz 3.57 A K-550 16.8 A K-300 MgEG 15.34 A MgAD

8. Des Allemands Mg- saturated Fine Clay Residual Smoothed composite Individual peaks 23 28 Two theta (Cu)

9. Des Allemands Coarse Clay Residual Individual peaks Smoothed composite 23 28 Two theta (Cu)

10. SIMULATION Crystallite thickness Changes intensity ratios and peak width.

11. SIMULATION Layer types, percentage, and stacking Changes peak intensities, shapes, and positions.

12. SIMULATION Large library of simulated XRD profiles.

13. Decomposition and simulation open new doors to solving the universal problems of qualitative clay mineral determination and quantitative representation with XRD techniques. Peak decomposition provides a better measure of peak position, width and intensity than manual stripping or “eye-ball” methods. Simulation is a reasonable method to account for crystallite size variability, layer composition, and mixed layering. A “computer-fitting-procedure” offers a way to match library and actual XRD patterns.

14. Peak Identities

15. “FIT” Mg-saturated Fine Clay (C9) simulation actual XRD Two theta (Cu)

16. “FIT” K-saturated Fine Clay (C9) actual XRD simulation 5 10 15 20 25 Two theta (Cu)

17. “FIT” Mg-saturated Coarse Clay (C9) simulated actual

18. “FIT” K-saturated Coarse Clay (C9) 5 10 15 20 25 Two theta (Cu)

19. “FIT” Coarse Clay

20. “FIT” Fine Clay

21. <0.2µm Mg and EG treated : 63 wt% R0 I(.5)/S 23 wt% R0 I(.9)/S Minor I and K K and EG treated: 50 wt% R0 V(.7)/I 29 wt% R1 I(.9)/S Minor I, V, K, Ch <2µm Mg and EG treated : 25 wt% R1 I(.9)/S 16 wt% R1 S(.7)/I 15 wt% I, 12 wt% K, 10 wt% V Minor Ch, Q K and EG treated: 38 wt% R0 V(.7)/I 24 wt% I 10 wt% R1 I(.9)/S 11 wt% K, 10 wt%V Minor S, Ch, Q RESULTS (C1)

22. RESULTS (C9) <0.2µm • Mg and EG treated : • 43 wt% R0 I(.5)/S • 21 wt% R0 I(.9)/S • 15 wt% R1 I (.9)/S • Minor I, K, Sm • K and EG treated: • 48 wt% R0 V(.7)/I • 21 wt% R1 I(.9)/S • 13 wt% I, 10 wt% V • Minor K, Sm, Ch <2µm • Mg and EG treated : • 34 wt% R1 I(.9)/S • 19 wt% I • 10 wt% R1 I(.6)/V • 13 wt% K, 8 wt% S • Minor Ch, Q • K and EG treated: • 28 wt% R0 V(.7)/I • 22 wt% I • 11 wt% K, 11 wt% Ch, 8 wt%V • Minor Q

23. RESULTS • QR was obtained with a good statistical value (R2): • R2<0.010 for finer fraction • R2<0.022 for coarse clay • QR in <0.2µm EG-fraction shows the presence of • kaolinite, illite and smectite for Mg treatment • kaolinite, illite, smectite, vermiculite and (chlorite) for K treatment • K treatment produces: illite and smectite • QR in <2µm EG-fraction shows the presence of • kaolinite, illite, smectite, vermiculite, chlorite and quarzt for both treatments • Relative amount of illite, vermiculite and chlorite is higher (smectite amount is lower) with the K treatment

24. CONCLUSIONS • The addition of K alters the characteristics of the 50/50 I/S by limiting the swelling to the 14A spacing attributed to vermiculite (which is not detected with Mg saturated samples) • K further changes the random, I-dominant I/S to an ordered one and stabilizes additional swelling layers so its relative abundance increases (23wt% to 29wt%) • The change in relative abundance and layer types are related to the differing effects of Mg and K on high- and low-charged swelling clays and the presence of hydroxy interlayers