Clays and Clay Minerals, Vol. 26, No. 5, pp. 361-364, 1978.
A COMPARISON OF THE E F F E C T I V E N E S S OF EIGHT
METHODS FOR THE REMOVAL OF ORGANIC
MATTER FROM CLAY
A. D. VAN LANGEVELD,
S. J. VAN DER GAAST, AND D. EISMA
Netherlands Institute for Sea Research, Texel
(Received 30 September 1977)
Abstract--Organic matter present in clayey sediments may act as a cement between the clay particles as well as a blocking
agent for the swelling of clay minerals like montmorillonite.
Removal of the organic matter is important when a clay sample is to be characterized by X-ray powder diffraction, or
when it is to be separated into the composing minerals on the basis of differences in density.
Eight different methods for the removal of organic matter from a North Sea clay sample have been studied. Of all
methods tried bromine oxidation was found to be the most effective.
Key W o r d s - - C a r b o n disulfide, Hydrogen peroxide, Hypobromite, Montmorillonite, Organic.
EXPERIMENTAL METHODS
To study the effectiveness of various methods for the
removal of organic matter from a North Sea clay sample, the carbon percentages and X-ray powder diffraction patterns were compared before and after removal
of the organic matter.
4)
Pretreatment of the clay
The pretreatment of the clay sample consisted of the
removal of carbonate in a sodium acetate-acetic acid
buffer (pH = 5), followed by extraction of free iron
with sodium dithionite and sodium citrate following
Holmgren (1967). This pretreatment is necessary, because carbonates and iron (as oxide and hydroxide) can
act as a coating and as a cement. Moreover, organic
carbon determinations cannot be made without such
pretreatment. The fraction <0.5 p~ of the pretreated
sample was separated with a centrifuge and freezedried.
7)
Methods for the removal of organic
matter from clay
8)
All sample treatments were carried out on 0.4 g of the
homogenized, pretreated, fractionated, and freezedried sample. After the reactions all samples were thoroughly washed with distilled water and saturated with
Ca ions before X-ray powder diffraction.
The following methods for the removal of organic
matter were applied:
5)
6)
X-ray analysis
1) Oxidation by activated oxygen in a Tracerlab Low
Temperature Asher type S.A. 33 during 16 hr. R F
power 200 watts.
2) Oxidation in 200 ml 0.1% sodium permanganate in
water (Diimmler and Schroeder, 1965) during 2 hr
at 40~ After this the sample was washed with 1 N
oxalic acid in water to remove manganese dioxide
residues.
3) Oxidation by bromine (Mitchel and Smith, 1974).
9 1978, The Clay Minerals Society
The sample was treated during 2 hr at 40~ with a
freshly prepared mixture of 150 ml 5% sodium carbonate and 50 ml of a saturated solution of bromine
in water (pH ~ 7).
Oxidation by sodium hypobromite (Troell, 1976).
The sample was treated for 2 hr at 25~ with a freshly
prepared solution of 2.5 ml bromine in 100 ml 1 N
NaOH in water; then another 100 ml of this solution
was added, and 2 hr later the reaction was stopped.
T h e reaction takes place at pH ~ 12, which implies
that some clay minerals may be partly dissolved.
Extraction by a 1:1 mixture of 0.5 N N a O H in methanol and benzene (Farrington and Quinn, I971), in
which the sample was refluxed during 2 hr. After
this, the sample was washed with ethanol.
A vigorous hydrogen peroxide oxidation. During 2
hr the sample was treated at 90~ in 100 ml of a 20%
hydrogen peroxide solution.
A gentle hydrogen peroxide oxidation. During 24 hr
the sample was treated at 25~ in 200 ml of a 5%
hydrogen peroxide solution.
Triple extractions of 1 hr each at 25~ in 100 ml of
a 1:1 mixture of carbon disulfide and ethanol (de
Lange, 1976). After this the sample was washed with
ethanol.
361
Of the pretreated samples about 40 mg was converted
into a corresponding " C a - c l a y " by washing the samples with a saturated CaCI2 solution. These " C a - c l a y s "
were oriented from a suspension on a slab of ceramic
material by suction (Dfimmler and Schroeder, 1965).
The 001 reflections of the samples were measured from
2 0 = 3~ ~ under the following experimental conditions: 1) saturated with glycerol ( " G L Y " ) , 2) saturated
with water ( " H 2 0 " ) , 3) dried in air (65% relative humidity) ( " A D R " ) , 4) at lowered pressure, 0.7 cm Hg
("0.7 Hg"), and 5) after heating the sample at 350~
during 0.5 hr ("350"). CoK~L z radiation (h = 1.7902 A)
362
Clays and Clay Minerals
Langeveld, van der Gaast, and Eisma
prelreated
IH
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X-ray diffractograms of a pretreated clay sample before and after applying the most effective methods for removal of organic material.
was used. The goniometer was supplied with a vacuum
housing and a graphite monochromator.
Carbon analysis
The carbon analysis was carried out in a Coleman
Carbon Hydrogen Analyzer, type 33, on 40-100 mg of
the freeze-dried sample.
EXPERIMENTAL RESULTS
All the results of the various methods are summarized in Table 1. F r o m top to bottom the table shows:
the relative intensity of the montmorillonite 002 peak
with regard to the montmorillonite 001 peak (corrected
for the chlorite 001 peak), for the samples saturated
with water (H20 ~002/Io00 (I) and (GLY ~002/I0oJ (II);
the increase of the intensity of the 10 A peak (Ill) (with
regard to the air dry sample), AI,,10~.. = I ( 3 5 0 ) I(ADR)/I(ADR), as a result of the dehydration of montmorillonite after the heat treatment at 350~ during 0.5
hr. Montmorillonite blocked by organic matter does not
collapse; the doo~ spacing values (/~), corresponding
with the peak maxima of the montmorillonite 001 reflections, were measured for the samples saturated with
water (d0ol H20) (IV), with glycerol (do01GLY) (V), and
at lowered pressure (0.7 cm Hg) (dool 0.7 Hg) (VI); the
carbon percentage (VII).
For a clean, water- or glycerol-saturated montmorillonite one may expect a higher relative intensity of the
002 peak than for montmorillonite partially blocked by
organic material. For the samples saturated with water
only, the samples which had been treated with bromine
and with hypobromite exhibited a strong enhancement
of the relative montmorillonite 002 peak as compared
with the pretreated sample, just like the samples saturated with glycerol.
The greatest enhancement of the 10 -~ peak was
found in the sample extracted with sodium hydroxide
in methanol and benzene, followed by a smaller enhancement for the samples treated with bromine, hypobromite, and activated oxygen. A montmorillonite
Vol. 26, No. 5, 1978
Table h
R e m o v a l of organic ma t t e r from clay
363
X-ray diffraction and carbon content data of a clay sample before and after applying various methods for removal of organic matter.
pretreated
Low
Temp.
Asher
NaMno 4
Br 2
NaBrO
NaOH in
methanol/
benzene
H202
H202
vigour,
gentle
C.S2
in
ethanol
I
H201002/I001
0,04
0,09
0,05
0,16
0,II
0,02
0,08
0~03
0,07
II
GLyIo02/Io01
0,14
0,25
0,05
0,35
0,33
0,05
O,lO
0,02
0,13
III
I,,i0~,,
1,2
1,8
0,4
1,6
1,8
2,3
0,9
0,9
1,2
IV
do01(~), H20
14,41
14,37
14,25
18,65
18,52
14,66
14,35
14,25
14,58
V
do01(~), GLY
14,37
17,69
14,25
17,75
17,81
15,18
14,37
14,25
14,58
VI
do01(~), 0,7 Hg
12,83
14,10
12,77
11,75
11,99
12,99
12,59
13,26
12,83
VII
%C
6,1
1,8
4,3
1,8
1,8
4,2
1,6
5,0
5,4
saturated with water will swell until a d001 value of at
most 18.9 ]k is reached (Brown, 1961); only the samples
treated with bromine and hypobromite show this.
Saturation of a clean montmorillonite with glycerol
results in a d001 value of about 17.7/~ at most (Brown,
1961); only the samples treated in the low temperature
asher, or with the bromine and hypobromite showed
this. When the diffraction pattern of a clean montmorillonite is measured at lowered pressure (0.7 cm Hg),
the d001 value will be about 11.40-11.90/~, depending
on the montmorillonite measured. Only the samples
treated with bromine and hypobromite showed a decrease of this size.
As an illustration of the different nature of the samples, the diffraction patterns of the pretreated sample,
and of the samples after the bromine, the hypobromite,
the low temperature asher, and the vigorous hydrogen peroxide treatment, are shown in Figure 1.
According to the carbon percentages of the samples,
the removal methods can be separated into two groups,
one removing at most 30% of the carbon present in the
pretreated sample, and a group removing about 70% of
the carbon. The low temperature asher, the bromine,
the hypobromite, and the vigorous hydrogen peroxide
treatment remove about 70% each.
DISCUSSION
Remarkably, the X-ray analysis is a more sensitive
method to check the cleanness of montmorillonite than
the determination of carbon. The low temperature asher oxidation resulted in a montmorillonite sensitive
only to saturation with glycerol and dehydration, while
the so widely used vigorous hydrogen peroxide oxidation had nearly no positive effect on the montmorillonite blocked by organic material. The latter method,
however, destroyed a considerable part of the montmorillonite, which is possibly enhanced by the presence of organic material (Douglas and Fiessinger,
1971). The results of the bromine and hypobromite
treatment were very similar, the only exception being
the montmorillonite 001 peak for the sample saturated
with water, which was more sharply defined after the
bromine treatment than after the hypobromite treatment. This suggests a cleaner internal surface of the
montmorillonite after bromine treatment.
The carbon percentage found after the bromine oxidation (1.8%), may in part be caused by carbonates adsorbed from the sodium carbonate solution. Carbonate
removal with a sodium acetate-acetic acid buffer after
the bromine oxidation lowered the carbon percentage
to 1.2%. Because the carbon content of the original pretreated sample is 6.1%, even the most effective removal
method left about 20% of the noncarbonate carbon in
the sample.
CONCLUSION
Of all methods tried for the removal of organic matter
from clay, bromine oxidation was the most effective.
This result should be considered as somewhat preliminary because only one clay sample from one environment of deposition was tested.
ACKNOWLEDGMENTS
We are indebted to Mr. B. Verschuur for the drawings and to Mr. J. Kalf and Mrs. R. Gieles-Witte for
carrying out organic matter analyses.
REFERENCES
Brown, G. (1961) The X-ray Identification and Crystal Structures of
Clay Minerals: Mineral. Soc., London, 544 pp.
de Lange, G. J. (1976) Rrntgen diffractie aan kleimineralenvan enkele
Noordzee monsters: Internal Report N.I.O.Z., 1976-6, 25 pp.
Douglas, A. L. and Fiessinger, F. (1971) Degradation of clay minerals
by H~O~treatments to oxidize organic matter: Clays & Clay Minerals
19, 67-68.
D/immler, H. and Schroeder, D. (1965) Zur qualitativen und quantitativen riSntgenographischen Bestimmung von Dreischicht-tonmineralen in Bfden: Z. Pflanzenernaehr. Dueng. Bodenk. 109, 35--47.
364
Langeveld, van der Gaast, and Eisma
Farrington, J. W. and Quinn, J. G. (1971) Comparison ofsamplingand
extraction techniques for fatty acids in recent sediments: Geochim.
Cosmochim. Acta 35, 735-741.
Holmgren, C. G. S. (1967) A rapid citrate-dithionite extractable iron
procedure: Soil Sci. Soc. Am. Proc. 31, 210--211.
Clays and Clay Minerals
Mitchel, B. D. and Smith, B. F. L. (1974) The removal of organic
matter from soil extracts by bromine oxidation: J. Soil Sci. 25,
239--241.
Troell, E. (1976) The use of sodium hypobromite for the oxidation of
organic matter in the mechanical analysis of soils: J. Agric. Sci.
Cambz. 21, 476--483.
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