EVALUATION OF Mg AND K EXCHANGE CATION EFFECTS WITH SIMULATED XRD

PATTERNS

Aparicio, Patricia1 and Ferrell, Ray E.2

1 Departamento de Cristalografía, Mineralogía y Q. Agrícola. Universidad de Seville, Spain.

e-mail:patric@cica.es2 Department of Geology and Geophysics. Louisiana

State University, Baton Rouge, LA 70803-4101, USA. e-mail: rferrell@lsu.edu

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 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.

METHOLOGYSample

<2µ fraction <0.2µ fraction

normal settling by centrifugation

K-saturation

air-dried

glycerol-dried

EG-solvation

air-dried

EG-solvationHeat-treatment

at 300°C and 550°C

XRD-patterns

2 correction

Layer type determination 1st qualitative result

Mg-saturation

METHOLOGYLayer type determination

1st qualitative result

profile-fitting of Mg-EG patterns

Mixed-layered clay mineral identification according to: Moore & Reynolds (1997), Srodon (1984)

Mulcalc simulation pattern

Mulcalc libraryClay++ procedure

2nd qualitative result

Qualitative analysis (QR) and

Ideal layer percentage of clay minerals

BadR2> 0.01

Assess concordance of experimental and theoretical pattern

Change calculated parameters GoodR2 ≤ 0.01

SAMPLE C9, <0.2 micrometers

Des Allemands

MgAD

K-550

K-300

MgEG

3.32 A4.98 A

9.98 A

7.2 A

14.5 A

16.86 A

12.2 A

9.91 A

K-550

K-300

3.34 A

MgAD

MgEG

13.9 A

9.98 A

4.99 A Qtz 3.57 A

15.34 A

16.8 A

SAMPLE C9, <2 micrometers

Des Allemands

Des Allemands Mg- saturated Fine Clay

23 28

Residual

Smoothed composite

Individual peaks

Two theta (Cu)

Des Allemands Coarse Clay

23 28

Residual

Smoothed composite

Individual

peaks

Two theta (Cu)

SIMULATIONCrystallite 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.

dhkl (Å) I (c) H(Ä) Identification 22.286 214 0.844 R1 illite (0.3)/smectite 19.479 422 0.499 17.975 662 0.374 16.965 1057 0.348 R0 illite (0.1)/smectite

16.1660 539 0.370 R1 illite (0.2)/smectite 15.298 252 0.481 R1 illite (0.3)/smectite 14.297 196 0.788 R1 illite (0.3)/smectite 10.227 62 0.231 R0 illite (0.1)/vermiculite; R0 illite (0.9)/vermiculite 10.096 132 0.118 R1 illite (0.9)/smectite 9.9852 249 0.116 R0 illite (0.9)/smectite 9.8775 138 0.119 R0 illite (0.9)/smectite 9.7604 76 0.156 9.5311 67 0.535 8.5769 55 0.488 R0 illite (0.1)/smectite 9.0510 55 0.619 7.3395 82 0.275 7.2482 117 0.126 7.1811 332 0.109 7.1279 351 0.106 7.0698 171 0.152 5.6545 51 0.736 R0 illite (0.1)/smectite 5.3776 32 0.845 5.1493 39 0.647 R1 illite (0.9)/smectite 5.0263 48 0.247 R0 illite (0.9)/smectite 4.9844 118 0.252 R0 illite (0.1)/vermiculite; R0 illite (0.9)/smectite

Peak Identities

0

1000

2000

3000

4000

5000

6000

4 9 14 19 24 29

“FIT” Mg-saturated Fine Clay (C9)

actual XRD

simulation

Two theta (Cu)

0

500

1000

1500

2000

2500

3000“FIT” K-saturated Fine Clay (C9)

5Two theta (Cu)

10 15 20 25

simulation

actual XRD

“FIT” Mg-saturated Coarse Clay (C9)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

4 9 14 19 24 29Two theta (Cu)

simulated

actual

“FIT” K-saturated Coarse Clay (C9)

5

Two theta (Cu)

10 15 20 25

Clay composition %wt

Dimica Dismectite Divermiculite Sample R2 Phases presented

Fe K Fe Fe

Chlorite * 4.6

Illite 1 0 0.3

Illite 1 1 8.4

Kaolinite 5.1

Smectite 1.5 2.3

Vermiculite 1.5 1.0

R1 smectite (0.7)/illite 0.2 1 0.2 21.0

R1 illite (0.9)/smectite 1 1 1 9.5

R1 smecttite(0.9)/illite 1 1 1 7.9

R1 illite (0.6)/vermiculite 1 1 1 2.6

Quartz 1.3

C1

200-206

<2µm

0.009

Glass slide 36.1

“FIT” Coarse Clay

“FIT” Fine Clay

Clay composition %wt

Dimica Dismectite Divermiculite Sample R2 Phases presented

Fe K Fe Fe

Chlorite* 2.9

Illite 1 0 3.7

Illite 1 1 1.0

Kaolinite 2.6

Smectite 1.5 4.9

R0 illite (0.5)/smectite 0.5 1 0.5 27.6

R0 smectite (0.7)/illite 0.2 1 0.2 8.3

R0 illite (0.9)/smectite 0.5 1 0.5 8.5

C1

200-206

<0.2µm

0.017

Glass slide 43.4

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 (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

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