Presentation on theme: "EVALUATION OF Mg AND K EXCHANGE CATION EFFECTS WITH SIMULATED XRD PATTERNS Aparicio, Patricia 1 and Ferrell, Ray E. 2 1 Departamento de Cristalografía,"— Presentation transcript:
EVALUATION OF Mg AND K EXCHANGE CATION EFFECTS WITH SIMULATED XRD PATTERNS Aparicio, Patricia 1 and Ferrell, Ray E. 2 1 Departamento de Cristalografía, Mineralogía y Q. Agrícola. Universidad de Seville, Spain. 2 Department of Geology and Geophysics. Louisiana State University, Baton Rouge, LA , USA.
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.
MATERIALS Samples from the freshwater marsh in the area of Lake Des Allemands near New Orleans (Louisiana, USA) from a depth between cm and cm. 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.
METHOLOGY Sample <2µ fraction<0.2µ fraction normal settlingby centrifugation K-saturation air-dried glycerol-dried EG-solvation air-dried EG-solvation Heat-treatment at 300°C and 550°C XRD-patterns 2 correction Layer type determination 1 st qualitative result Mg-saturation
METHOLOGY Layer type determination 1 st qualitative result profile-fitting of Mg-EG patterns Mixed-layered clay mineral identification according to: Moore & Reynolds (1997), Srodon (1984) Mulcalc simulation pattern Mulcalc library Clay++ procedure 2 nd qualitative result Qualitative analysis (QR) and Ideal layer percentage of clay minerals Bad R 2 > 0.01 Assess concordance of experimental and theoretical pattern Change calculated parametersGood R 2 ≤ 0.01
SAMPLE C9, <0.2 micrometers Des Allemands MgAD K-550 K-300 MgEG 3.32 A 4.98 A 9.98 A 7.2 A 14.5 A A 12.2 A 9.91 A
K-550 K A MgAD MgE G 13.9 A 9.98 A 4.99 A Qtz 3.57 A A 16.8 A SAMPLE C9, <2 micrometers Des Allemands
Des Allemands Mg- saturated Fine Clay 2328 Residual Smoothed composite Individual peaks Two theta (Cu)
Des Allemands Coarse Clay 2328 Residual Smoothed composite Individual peaks Two theta (Cu)
SIMULATION Crystallite thickness Changes intensity ratios and peak width.
SIMULATION Layer types, percentage, and stacking Changes peak intensities, shapes, and positions.
SIMULATION Large library of simulated XRD profiles.
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.
“FIT” Mg-saturated Fine Clay (C9) actual XRD simulation Two theta (Cu)
“FIT” K-saturated Fine Clay (C9) 5 Two theta (Cu) simulation actual XRD
“FIT” Mg-saturated Coarse Clay (C9) simulated actual
“FIT” K-saturated Coarse Clay (C9) 5 Two theta (Cu)
“ FIT” Coarse Clay
“ FIT” Fine Clay
RESULTS (C1) <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 (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
RESULTS QR was obtained with a good statistical value (R 2 ): R 2 <0.010 for finer fraction R 2 <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
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