Presentation on theme: "EVALUATION OF Mg AND K EXCHANGE CATION EFFECTS WITH SIMULATED XRD PATTERNS Aparicio, Patricia1 and Ferrell, Ray E.2 1 Departamento de Cristalografía,"— Presentation transcript:
1EVALUATION OF Mg AND K EXCHANGE CATION EFFECTS WITH SIMULATED XRD PATTERNS Aparicio, Patricia1 and Ferrell, Ray E.21 Departamento de Cristalografía, Mineralogía y Q. Agrícola. Universidad de Seville, Spain.2 Department of Geology and Geophysics. Louisiana State University, Baton Rouge, LA , USA.
2The 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.
3MATERIALSSamples 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.
4Layer type determination METHOLOGYSamplenormal settlingby centrifugation<2µ fraction<0.2µ fractionK-saturationMg-saturationair-driedglycerol-driedair-driedEG-solvationXRD-patternsEG-solvationHeat-treatmentat 300°C and 550°C2q correction1st qualitative resultLayer type determination
5Qualitative analysis (QR) and Ideal layer percentage of METHOLOGY1st qualitative resultLayer type determinationprofile-fitting of Mg-EG patternsMixed-layered clay mineral identification according to:Moore & Reynolds (1997), Srodon (1984)Mulcalc simulation pattern2nd qualitative resultClay++ procedureMulcalc libraryAssess concordance of experimental and theoretical patternQualitative analysis (QR) andIdeal layer percentage ofclay mineralsChange calculated parametersBadR2> 0.01GoodR2 ≤ 0.01
6SAMPLE C9, <0.2 micrometers Des AllemandsMgADK-550K-300MgEG3.32 A4.98 A9.98 A7.2 A14.5 A16.86 A12.2 A9.91 A
10SIMULATION Crystallite thickness Changes intensity ratios and peak width.
11SIMULATION Layer types, percentage, and stacking Changes peak intensities, shapes, and positions.
12SIMULATIONLarge library of simulated XRD profiles.
13Decomposition 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.
21RESULTS (C1) <0.2µm <2µm Mg and EG treated : Mg and EG treated : 63 wt% R0 I(.5)/S23 wt% R0 I(.9)/SMinor I and KK and EG treated:50 wt% R0 V(.7)/I29 wt% R1 I(.9)/SMinor I, V, K, Ch<2µmMg and EG treated :25 wt% R1 I(.9)/S16 wt% R1 S(.7)/I15 wt% I, 12 wt% K, 10 wt% VMinor Ch, QK and EG treated:38 wt% R0 V(.7)/I24 wt% I10 wt% R1 I(.9)/S11 wt% K, 10 wt%VMinor S, Ch, Q
22RESULTS (C9) <0.2µm <2µm Mg and EG treated : 43 wt% R0 I(.5)/S Minor I, K, SmK and EG treated:48 wt% R0 V(.7)/I21 wt% R1 I(.9)/S13 wt% I, 10 wt% VMinor K, Sm, Ch<2µmMg and EG treated :34 wt% R1 I(.9)/S19 wt% I10 wt% R1 I(.6)/V13 wt% K, 8 wt% SMinor Ch, QK and EG treated:28 wt% R0 V(.7)/I22 wt% I11 wt% K, 11 wt% Ch, 8 wt%VMinor Q
23RESULTS QR was obtained with a good statistical value (R2): R2<0.010 for finer fractionR2<0.022 for coarse clayQR in <0.2µm EG-fraction shows the presence ofkaolinite, illite and smectite for Mg treatmentkaolinite, illite, smectite, vermiculite and (chlorite) for K treatmentK treatment produces: illite and smectiteQR in <2µm EG-fraction shows the presence ofkaolinite, illite, smectite, vermiculite, chlorite and quarzt for both treatmentsRelative amount of illite, vermiculite and chlorite is higher (smectite amount is lower) with the K treatment
24CONCLUSIONSThe 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