EVALUATION AND ACTIVATION OF CAMBALPUR BENTONITE FOR
INDUSTRIAL UTILIZATION
Shagufta Nasreen*
P.C.S.I.R. Laboratories Complex, Jamrud Road, 25120- Peshawar, Pakistan.
Tel:091-9216240, Ext: 234, Fax: Tel:091-9216232, shnasreen@yahoo.com
Abdul Ghani
Dimension Stone Center P.C.S.I.R. Laboratories Complex, Jamrud Road, 25120Peshawar, Pakistan. Tel:091-9218557, Fax: Tel:091-9218559
Sohail Noor
P.C.S.I.R. Laboratories Complex, Jamrud Road, 25120- Peshawar, Pakistan.
Tel:091-9216240, Ext: 234, Fax: Tel:091-9216232, sohailpcsir@yahoo.com
Abstract
Bleaching or decolorization is an integral part of processes practiced in petro-chemical and edible oil/ghee
industries and this is usually done with the application of activated clays. The indigenous industries import
these clays while appreciable deposits of clays occur in different vicinities of NWFP, Punjab, Sindh, and
Azad Kashmir. These clays (mostly Bentonite) can be used as a substitution of importing ones after
activating these by simple treatment with either hydrochloric acid or sulphuric acid by keeping an
appropriate control over process variables. In the ensuing paras an experimental study of the bentonite
clays of Cambalpur (Attock) area towards the said end is being presented.
Key Words
Cambalpur, bentonite, clay, and activation.
Introduction
Naturally occurring clays are known to exhibit excellent adsorbing and decolorizing properties. One of the
most common clays used in this field is bentonite, a rock in which smectite minerals are the dominant
constituent. The term smectite is applied as name for a group of sodium, calcium, magnesium, iron and
lithium aluminium silicates. Industrial quality bentonites are pre-dominantly composed of either sodium or
calcium montmorilonite, nontronite, (iron smectite), saponite (magnesium smectite) and to much lesser
extent hectorite (Lithium Smectite) [1]. Bentonite is derived from degeneration of volcanic ashes. This is
chemically an aluminium hydrosiclicate in which the ratio of silicilc acid to alumina is 4:1 [2]. The
bleaching properties of clay can further be enhanced by treating clay with a suitable mineral acid leading to
clay activation. The acid activation of clay is often accompanied by the change in key physical properties
of clay e.g surface acidity, surface area and surface volume etc. These activated bentonite clays are used for
decolorizing or bleaching of various oils such as mineral oils, vegetable oils, various fractions from
petroleum especially lubricating oils and purification of melted animal fats and beeswax.
For bleaching edible oils the desirable properties of clay are as follows [3].
i.
The clay should be able to bleach the oils so thoroughly that these do not revert to the original
color on standing
ii.
The oil should filter easily
iii.
The clay should not impart any order to the oil. The quantity of the oil retained by the earth
should be small.
iv.
No spontaneous ignition should occur either in the filter press or in the waste pits.
In Pakistan the bentonite deposits occurs at few localities in NWFP, Punjab, Sindh and Azad
Kashmir. The deposits at Karak (NWFP) were investigated by engineers combined limited in 1976 for the
government of NWFP. [4]. In Punjab reasonably big deposits have been found at Dera Gahzi khan and
Cambulpur. [5]. The later occurs near the villages named Dherikot and Dheri Chohan. These two villages
are one mile apart. Dherikot village is on the left bank of Haro River, which is a tributary of the river Indus.
The area is easily accessible. The estimated reserve of bentonite deposit is around one million tons [6]. The
indigenous occurrence of bentonite in appreciable quantities and the high prices of imported varieties are
the reasons for exploring the possibilities of activation and consumption in vegetable ghee and other
industries.
Material and Method:
The experimental part consists of the following:
The lumps of the clay were dried in air at room temperature. The clay is cleaned manually to remove
stones, particles with metallic iron material which are generally dark radesh brown and can be removed
easily by color sorting. The dried and cleaned clay is ground to pass through 100 British Standard Sieve
(BSS) and tested for Methylene Blue value, which indicates its original ion exchange capacity.

Determination of the caution exchange capacity (C.E.C) of the bentonite clay with Methylene blue
dye adsorption.
The sample was placed in a 2 cz screw top bottle and added 20 ml distilled water. Shaken for 1-2
hours and left overnight. Washed contents of bottle into 100 ml flask and added 1 ml 5N- Sulphuric
acid (This improves the end-point in some cases). From a 50 ml burette added 2 ml at a time 0.082 N
solution of methylene blue. Immediately after adding the dye swirled the contents of the flask and
spotted a small portion of the suspension on a filter paper (whatman No.41) by means of a glass rod.
Whilst the dye was being adsorbed by the clay there was a sharp boundary on the filter, paper
between blue clay/dye spot and the accompanying water which radiates from this. As the end point
is approached excess dye formed a lighter blue hallow around the spot. The Cationic Exchange
capacity was calculated as follows:
C.E.C =
100xVolume of methylene bluex0.0082
Weight of clay (dried at 1050C)
As the minimum cationic exchange capacity of monmorilonite is 80 milliequivalent (meq)/100g,
hence only five samples, having C.E.C. >60 meq/100g were selected for chemical analysis and
activation studies.
Chemical Evaluation
Chemical analysis was carried out according to standard silicate analysis procedure [7]. All
chemicals used were A.R grade BDH chemicals.

Acid treatment for activation of bentonite
Though earth particles of finer size offer a greater surface area for activation, the material passing
through 100 mesh is found to be satisfactory for activation with respect to both decolorizing power
and filterability. The next step is mixing with acid (Hydrochloric/Sulphuric). The acid treatment
replaces part of exchangeable bases by hydrogen thereby increasing their activity. The heating vessel
was fitted with condenser to prevent the loss of water. After completion of the heating period the
reaction was presumed to be completed. The treated mixture after the bulk of the acid had been
consumed was dumpled into fresh water and washed on a Buchner filtering funnel or by decantation
until substantially free from excess acids and salts. The washed product is dried to remove free
moisture. Further heat activation at 3000C considerably improves the decolorizing power of the
material. This is presumed to be due to the dehydration of silica gel and aluminium hydroxide
formed during acid treatment and subsequent washing.

Preliminary testing of activated clay with methylens blue dye
1 gm methylene blue dye was dissolved in 1 litre warm distilled water to give standard methylene
blue dye solution (1ml=1mg). 1 gm activated bentonite was taken in a beaker and standard
methylene blue was added from 50 ml burette and added 2 ml at a time. The volume of standard
methylene blue decolorized was determined.
Preliminary test for activity of clay sample was determined by methylene blue solution. Those
samples showing good bleaching with methylene blue solution were further treated with cotton seed
oil. Imported activated clay was also treated likewise, and bleaching values compared with the
samples prepared in the laboratory.

Cotton Seed Oil And Activated Clay Reaction test
This test was performed according to the method reported earlier [8]. About 200g of crude cotton
seed oil was heated to 45C on a hot plate and to this 3 ml of 150 Be NaOH was added and stirred
for 15 minutes. After heating upto 65C the oil was filtered through Whatman No. 1. This refined
cottonseed oil was then reacted with the activated bentonite in order to determine the bleaching
ability of the prepared activated clay samples.
2 gms of bentonite clay sample reacted with 100 gms of refined oil, heated to 85C with continue
stirring for 15 minutes. The clay was filtered out of oil and decolonization was measured by
tintometer. Tintometric colour readings of the bleached oil was taken in 1″ and 5 1/2″ for
comparison and the units of yellow and red pigments for unbleached oil were taken as 100% colour
for the sake of calculations.
Result and Discussion:
Before going in to the activation studies the catinionic exchange capacity (C.E.C) of the clay samples were
determined by Methylene blue method. The results show that five samples have C.E.C value of more than
60, which indicates the absence of non-expainding three layer illites that have C.E.C between 20 and 40
[5].
Chemical Analysis
Chemical analysis reveals little about the mineralogical composition of the clay because of the
isomorphous replacements of elements and the possibility of the occurance of more than one clay mineral
in the same clay deposit. Analysis of mountmorillonite mineral frequently shows high values of H 2O, SiO2,
R2O3 ratios (4:1or more) and low K 2O. About 20 percent Fe2O3 is indicative of pure nontronite and less the
1 percent MgO while 10% Fe2O3 is indicative of biedelite [9]. Illite or hydrous mica contains appreciable
amounts of potash, approximately 6% as K2O. In attapulgite-sepiolite minerals, magnesium is predominant.
In attapulgite Al2O3 and MgO are in equal proportion, whereas sepiolite is the magnesium end member and
contains little alumina [10].
The chemical analysis (Table-I) reveals that the clay is montmorillonite type as the ratio of silica (SiO 2,
R2O3) is greater than 4 in all samples. Presence of high magnesium indicates that the clay may contain some
Saponite. The average specific gravity of the clay was found to be 1.90. Presence of alakalies in all samples
confirms their swelling characteristics. The higher concentration of alumina and low concentration of iron
indicates that the clay is aluminous in nature rather than ferroaluminous.
Since the clays containing minerals of montmorillonite group are usually activated by acid treatment.
Therefore, the best activation method as considered to be the acid activation.
Activation
Activation by partial leaching with mineral acid appears to be a very simple process but in practice, it
requires an extreme degree of control of process variables in order to obtain a product of requisite
bleaching power. A variety of processes have been patented but very little information is available on the
actual industrial processes except those given in the classical article by Burghardt [11] and thereafter by
Rich P [10].
Activation depends on various factors such as strength of acid, temperature, heating time and proper
washing of the clay after acid treatment. Hence the activation initiated with an acid of lower strength that is
1 N and progressively raised up to strength of 5 N (table 2 and 3) and like wise time period of heating was
raised from 1 hour to 5 hours. These tables show that the initial activity of heating increases with increased
acid strength and time period of heating. While the activation become stabilize when the acid strength is 4
N and heating time is 3 hours and no significant enhancement in activation has been observed on increase
of acid strength and heating time. It is clear from the Table 2 and 3 that both Hydrochloric (HCl) and
Sulfuric (H2SO4) acids are capable of activating the clay to a conducive level for industrial utilization.
H2SO4 proves to be a comparatively better activating agent. The rest of the samples were activated by
reacting with 4N H2SO4 for 3hrs.
Activity test
The washed and dried activated clay was subjected to decolarization of methylene blue die and cotton seed
oil [Table-4, 5] decolarization. Results of bleaching activity indicates that the bleaching properties of the
clay activated with sulfuric acid compares favorably with the imported German variety (Terrana).
Conclusion
The indigenous petro-chemical and edible oil/ghee industries use a variety of imported clays (activated) for
bleaching/decolorisation. These activated clays can be produced by simple treatment of locally available
clays. This simple treatment includes steps like grinding, meshing, washing and activation with either
hydrochloric or sulphuric acid for the specific time. However, parameters of these processes like time,
temperature and strength of acid (Normality) have to be set for a single clay deposit or say for clay of a
specific composition. The activation studies carried out for the clay deposit of Attock area, as narrated in
the preceding paras, show that the clay dominantly composed of montmorillonite and allied members of
clay group respond actively to both the treatment by hydrochloric acid and sulphuric acid. However, the
response to he sulphuric acid is more than to hydrochloric acid.
This may be codified from the above studies that experimentation on any local bentonite clay in
perspectives of temperature, time and strength of the acid (to be used for activation) may result in setting a
set of these parameters for activation. By standardizing these parameters, we can produce industrially
activated clays, which may replace the imported ones. This may be helpful in curbing the import of
activated clays and thus saving the valuable foreign exchange.
References
1.
Encyclopedia of Chemical Technolog, 2004, 5th Edn., John Willey & Sons, Inc. Hoboken, New
Jersey, Vol. 6, p. 696
2.
http://www.pncil.com.pk/Raw_Material.htm, 2004.
3.
Ahmad Z., Ahmad R., 1992, Minerals & Rocks for Industry, Geological Survey of Pakistan.
Quetta, Vol. I, p. 207.
4.
Odom I. E., 1984, Philos. Trans. R. Soc. London, Ser. A., 311: 207.
5.
Yousaf M. et al, 1989, Pak. J. Sci. Ind. Res. 32: 798.
6.
Information Received through Communication with the mine-ownwer of Bentonite Clay deposits
of Cambelpur district M/s Pakistan, Pakistan Mineral Products, Lytton street, Lahore.
7.
ASTM, 2002, Annual book of ASTM, Vol. 4.01, 10-38,
8.
Ahmad N et al, 1987, Pak, J. Sci. Ind. Res, 30: 10.
9.
Makenzie R.C., 1957, Differential Thermal Investigation of Clays Minerological Society, London.
10.
Robertson R. H. S., 1950, Clay Min. Bull., 4: 125.
11.
Burghart O., 1931, Industr. Enggng. Chem. 23: 800.
12.
Rich A. D., 1949, Industrial Minerals and Rocks, (The American Institute of Mining and
Metallurgical Engineers), NewYork, Ind. p.127.
Table-1
Chemical analysis of Attock bentonite
% Chemical
1
2
3
4
5
SiO2
52.49
58.60
52.10
52.20
57.14
Al2O3
17.17
12.17
15.85
16.77
13.98
Fe2O3
2.02
4.36
3.07
3.13
2.49
TiO2
0.30
0.72
0.70
0.49
0.60
MnO
Trace
Nil
0.20
0.11
0.10
P2O5
Nil
0.064
0.09
Trace
0.02
CaO
3.65
1.59
3.12
3.97
4.10
MgO
3.2
2.15
1.10
3.85
1.61
Na2O
1.00
0.20
3.90
1.98
3.99
K2O
0.47
0.55
2.20
1.44
2.10
Loss on
18.66
19.45
17.99
16.37
14.10
Composition
Ignition
Table-2
Activation of Bentonite Clay with hydrochloric Acid (Varying acid concentration a well as time
period of reaction).
SAMPLE
NORMATLITY OF
TIME PERIOD
VALUME OF METHYLENE
NUMBER
HYDROCHLORIC ACID
OF REACTION
BLUE SOLUTION ADSORBED
PER GRAM (Img-1 mg Methylene
Blue)
Representative
Sample No.1
“
1 N HCl
1 hour
14.00 ml
“
1 N HCl
2 hours
14.00 ml
“
1 N HCl
3 hours
15.00 ml
“
1 N HCl
4 hours
15.00 ml
“
1 N HCl
5 hours
15.00 ml
“
2N HCl
1 hour
26.00 ml
“
2N HCl
2 hours
28.00 ml
“
2N HCl
3 hours
29.00 ml
“
2N HCl
4 hours
29.00 ml
“
2N HCl
5 hours
29.00 ml
“
3N HCl
1 hour
57.00 ml
“
3N HCl
2 hours
61.00 ml
“
3N HCl
3 hours
63.00 ml
“
3N HCl
4 hours
63.00 ml
“
3N HCl
5 hours
63.00 ml
“
4N HCl
1 hour
71.00 ml
“
4N HCl
2 hours
73.00 ml
“
4N HCl
3 hours
75.00 ml
“
4N HCl
4 hours
75.00 ml
“
4N HCl
5 hours
75.00 ml
“
5N HCl
1 hour
71.00 ml
“
5N HCl
2 hours
74.00 ml
“
5N HCl
3 hours
75.00 ml
“
5N HCl
4 hours
75.00 ml
“
5N HCl
5 hours
75.00 ml
Table-3 Activation of Bentonie Clay with Sulphuric acid (Varying acid concentration as well as time
period of reaction), Representative value for sample No. 1.
SAMPLE
NORMATLITY OF
TIME PERIOD
VALUME OF METHYLENE BLUE
NUMBER
SULPHURIC ACID
OF REACTION
SOLUTION ADSORBED PER GRAM
(Img-1 mg Methylene Blue)
Representative
Sample No.1
“
1 N H2SO4
1 hour
21.00 ml
“
1 N H2SO4
2 hours
22.00 ml
“
1 N H2SO4
3 hours
22.00 ml
“
1 N H2SO4
4 hours
22.00 ml
“
1 N H2SO4
5 hours
22.00 ml
“
2 N H2SO4
1 hour
37.00 ml
“
2 N H2SO4
2 hours
39.00 ml
“
2 N H2SO4
3 hours
39.00 ml
“
2 N H2SO4
4 hours
39.00 ml
“
2 N H2SO4
5 hours
39.00 ml
“
3 N H2SO4
1 hour
65.00 ml
“
3 N H2SO4
2 hours
67.00 ml
“
3 N H2SO4
3 hours
71.00 ml
3 N H2SO4
4 hours
70.00 ml
3 N H2SO4
5 hours
66.00 ml
“
4 N H2SO4
1 hour
80.00 ml
“
4 N H2SO4
2 hours
89.00 ml
“
“
“
“
4 N H2SO4
3 hours
101.00 ml
“
4 N H2SO4
4 hours
95.00 ml
“
4 N H2SO4
5 hours
91.00 ml
5 N H2SO4
1 hour
81.00 ml
5 N H2SO4
2 hours
89.00 ml
“
5 N H2SO4
3 hours
98.00 ml
“
5 N H2SO4
4 hours
93.00 ml
“
5 N H2SO4
5 hours
85.00 ml
“
“
Table –4
Testing of Activated Bentonite with Methylene Blue dye
SAMPLE NUMBER
WT. OF SAMPLE TAKEN
VOLUME OF METHLYLENE
BLUE (1ml-1mg)
DECOLORISED
1
1 gm
88.00 ml
2
1 gm
90.00 ml
3
1 gm
93.00 ml
4
1 gm
92.00 ml
5
1 gm
93.00 ml
Terrana (German Bentonite)
1 gm
115.00 ml
Table-5
Optimised Sulphuric acid activation tests (Oil Bleaching) (Tintometric Results)
Reference Oil:
Naturalized Cotton seed oil with colour content as
Yellow Unit : 30
Red Unit
Sample No.
Percentage
: 3.7
Colors retained
Percentage of colors
of clay in
oil clay
Bleached
Yellow unit
Red unit
Yellow unit
Red unit
mixture
1
2
8.10
0.80
73.00
78.38
2
2
7.90
0.71
73.66
80.81
3
2
8.10
0.68
73.00
81.62
4
2
7.80
0.69
74.00
81.35
5
2
8.00
0.70
73.33
81.08
Terrana
2
4.10
0.50
86.48
86.33
(Imported
German)