This document discusses a study on the effect of leachate on the engineering properties of different types of bentonite. Five bentonites were tested: calcium bentonite and four sodium-activated bentonites. The bentonites were exposed to varying concentrations of acetic acid and calcium chloride solutions to simulate leachate components. Testing showed the liquid limit, plastic limit, plasticity index, free swell, percentage swell, and hydraulic conductivity of the bentonites changed when exposed to the chemical solutions. In general, properties were most affected by calcium chloride. The study developed mathematical models to predict hydraulic conductivity from other properties. Percentage swell showed the best correlation with hydraulic conductivity.

1. Effect of Leachate on the Engineering Properties
of Different Bentonites
Evangeline, Y. Sheela John, Raji Ann
Assistant Professor Postgraduate Student
e-mail: sheelabala2000@yahoo.com e-mail: raji_annjohn@yahoo.co.in
Department of Civil Engineering, College of Engineering, Trivandrum, Kerala
ABSTRACT
Bentonite is a naturally occurring clay mineral derived from in situ chemical alteration of volcanic ash. The
engineering properties of bentonite get modified on interaction with contaminants in leachate produced from the
waste. In the present study effect of leachate on calcium bentonite and four types of sodium activated bentonites
are determined. Acetic acid and calcium chloride were used to represent the components of leachate. The variations
of properties like Atterberg’s limits, swell index, percentage of swell and hydraulic conductivity with various
concentrations of the chemicals were studied. The results indicate that the index properties and hydraulic
conductivity get altered due to the reaction with acetic acid and calcium chloride. Mathematical model is developed
with liquid limit, plasticity index, free swell and percentage swell as independent variable and hydraulic conductivity
as dependant variable for all types of bentonite.
Indian Geotechnical Conference – 2010, GEOtrendz
December 16–18, 2010
IGS Mumbai Chapter & IIT Bombay
1. INTRODUCTION
Landfill is one of the most widely employed methods for
the disposal of municipal solid waste (MSW). About 95%
of total MSW collected worldwide is disposed in landfills.
After landfilling, solid waste undergoes physico-chemical
and biological changes. Consequently, the degradation of
the organic fraction of the wastes in combination with
percolating rainwater leads to the generation of a highly
contaminated liquid called “leachate”. The concentration
of these in the leachate depends on the composition of
wastes.
To prevent contamination of the surrounding soil and
underlying groundwater byleachate, landfills are lined and
covered with an impermeable material. Compacted clayey
soils or geosynthetic clay liners (GCLs) are predominantly
used in the construction of landfill liners.Both contains
bentonite. Bentonite is a naturally occurring clay mineral
derived from in situ chemical alteration of volcanic ash. It
is very highly plastic swelling clay of the smectite mineral
group, and is mineralogicallyknown as “montmorillonite”.
The properties of bentonite are greatly affected by
interaction between its particles andleachate. The net
electrical charge on bentonite is negative, which causes
dissolved cations in the surrounding pore water to be
attracted to the surface of the clay (Arasan and Yetimoglu,
2008 and Muhammed, 2004).
Acetic acid and calcium chloride are two chemicals
that are usually present in an Indian MSW leachate. In the
present study the effects of these chemicals on the
engineering properties of different bentonites are studied.
The different bentonites are calcium bentonite and four
types of sodium activated bentonites.
2. MATERIALS
Calcium Bentonite
Commerciallyavailable calcium bentonite is chosen for the
study. and it is designated as Type I. The index properties
of calcium bentonite are presented in Table 1.
Table 1: Properties of Calcium Bentonite
Sl No Property Value
1 Liquid Limit (%) 234
2 Plastic Limit (%) 54
3 Plasticity Index 180
4 Specific Gravity 2.67
5
Coefficient of permeability
(cm/s)
1.537 × 10-8
6 Free swell (ml/2g) 16

2. 378 Y. Sheela Evangelinen and Raji Ann John
Sodium Activated Bentonites
In an attempt to find the best sodium activated bentonite to
be used as a component of GCL, calcium bentonite was
treated with sodium carbonate, sodium hydroxide, sodium
chloride and sodium silicate. Bentonite with lowest
permeability could be obtained when treated with 7.5%
sodium carbonate, 2.5% sodium hydroxide, 2.5% sodium
chloride and 2.5% sodium silicate (Vinod, 2009). Hence
for investigation sodium activated bentonite treated with
7.5% sodium carbonate, 2.5% sodium hydroxide, 2.5%
sodium chloride and 2.5% sodium silicate are used for the
study. Sodium activated bentonites are prepared in the
laboratorybyboiling required quantityof sodium compound
and calcium bentonite in water for one hour. The boiled
solution was cooled, diluted, washed and allowed to settle.
The settled clay was dried and used for the study (Yildiz
et. al., 1998). Sodium activated bentonites prepared from
sodium carbonate; sodium hydroxide, sodium chloride and
sodium silicate were designated as Type II, type III, Type
IV and Type V respectively. The properties of the bentonite
used for the study are listed in Table 2.
Pore Fluids
Acetic acid and calcium chloride solutions of molarity
0.25M, 0.5M, 1M and 2 M were used for the study as
leachate.
Table 2: Properties of Various Types of Bentonites
Properties
Soil Types
LL
(%)
PL
(%)
PI (%)
Free Swell
(ml/2g)
Type I 234 54 180 16
Type II 448 69 379 21
Type III 400 52 348 18
Type IV 315 65 250 14
Type V 260 60 200 16
3. EXPERIMENTAL PROGRAMME
The engineering properties of bentonite soils get modified
upon contamination with different chemicals in the
leachate. Tests were conducted in the laboratory to found
the variation in properties of bentonite such as liquid limit,
plastic limit, plasticity index, free swell, hydraulic
conductivity and percentage of swell with different
concentrations of acetic acid and calcium chloride solutions.
4. ATTERBERGS LIMITS TESTS
The liquid limit was determined as per IS 2720 (Part V).
For the liquid limit tests, the specimens were prepared by
mixing an air-dried clay mass with each acetic acid and
calcium chloride solution.
5. FREE SWELL TESTS
Free swell of the bentonite was determined as per ASTM
D 5890-02 standard. To perform the tests, a 2g sample of
dried and finely powdered bentonite is dispersed into a 100
ml graduated cylinder in 0.1g increments over a period of
30 minutes. The sample was then kept for a period of 24
hours and the swell volume was noted. The free swell is
expressed in ml/2g of bentonite
6. HYDRAULIC CONDUCTIVITY TESTS
Hydraulic conductivity of all types of bentonite while
permeating with water and different concentrations ofacetic
acid and calcium chloride were found using consolidometer.
The dry powdered samples were carefully filled in the
consolidation mould at a density of 1.2g/cc and they were
fully saturated, applied a seating load of 0.05Kg/cm2
.
7. PERCENTAGE SWELL TESTS
The percentage swell was determined using consolidometer.
The dry powdered bentonite was filled in the consolidation
mould at a density of 1.2g/cc and allowed to saturate either
with water, acetic acid or calcium chloride solution. The
thickness of the sample was noted continuously using a
dialguage
8. RESULTS AND DISCUSSION
Variation in LL, PL and PI with Acetic Acid
The liquid limit, plastic limit and plasticityindex tests were
conducted on calcium bentonite and four types of sodium
activated bentonite samples. Different concentrations of
acetic acid solutions used were 0.25M, 0.5M, 1M and 2M.
The results of the LL, and PI tests are presented in Fig 1
and 2.
The results show that the liquid and plastic limit values
reduced drastically due to reaction with acetic acid.
Variation is least for calcium bentonite and followed by
sodium bentonite prepared with sodium chloride. For
calcium bentonite (Type I) the liquid limit, plastic limit
and plasticity index were reduced by 81%, 2% and79%
respectively with 0.25M acetic acid solution. As the
concentration of acetic acid increase the plasticity index
also reduces. The highest reduction in plasticity index is
332% for bentonite activated with sodium carbonate (Type
II) with 2M acetic acid solution.
Fig. 1: LL of Various Types of Bentonites with Different
Concentrations of Acetic Acid Solutions

3. Effect of Leachate on the Engineering Properties of Different Bentonites 379
Fig. 2: PI of Various Types of Bentonites with Different
Concentrations of Acetic Acid Solutions
Variation in LL and PI with Calcium Chloride
The results of tests conducted with different concentrations
of calcium chloride solutions on calcium bentonite and four
types of sodium activated bentonite samples are presented
in Fig. 3 and 4.
The liquid and plastic limit values reduced with
calcium chloride solutions for all types of bentonites. Here
also variation is least for calcium bentonite and followed
by sodium bentonite prepared with sodium chloride. For
calcium bentonite (Type I) the liquid limit, plastic limit
and plasticity index were reduced by 117%, 2% and 115%
respectively with 0.25M calcium chloride solution. As the
concentration of calcium chloride increase the plasticity
index also reduces. Bentonite activated with sodium
carbonate (Type II) shows the highest reduction in plasticity
index of 336%.
Fig. 3: LL of Various Types of Bentonites with Different
Concentrations of Calcium Chloride Solutions
Fig. 4: PI of Various Types of Bentonites with Different
Concentrations of Calcium Chloride Solutions
Variation of Free Swell with Acetic Acid
The free swell tests were done as per ASTM D 5890 - 02.
The free swell of five different types of bentonite found
with different concentrations of acetic acid solution is shown
in Fig. 5. The calcium bentonites have a free swell of 16ml/
2g and bentonites activated with sodium carbonate has a
free swell of 21ml/2g in water.
Fig. 5: Free Swell Values for Various Types of Bentonites at
Different Concentrations of Acetic Acid Solutions
With acetic acid the free swell values are reduced.
There is only slight variation in free swell value with the
increase in concentration of the acetic acid solution. The
lowest reduction is for calcium bentonite (Type I) and is
25% with 0.25M acetic acid solution. The largest reduction
of 63% is for bentonite activated with sodium silicate (Type
V) with 0.25M acetic acid solution.
Variation of Free Swell with Calcium Chloride
The free swell values of all the five types of bentonites
were found with different concentrations of calcium chloride
solutions. The results are shown in Fig 6
Fig. 6: Free Swell Values for Various Types of Bentonites at
Different Concentrations of Calcium Chloride Solutions.
Results shows that the free swell values are reduced to
a large amount due to the reaction with calcium chloride.
There is only slight variation in free swell value with the
increase in concentration of the calcium chloride solution.
The lowest reduction is for bentonite activated with sodium

4. 380 Y. Sheela Evangelinen and Raji Ann John
chloride (Type IV) of 43% with 0.25M calcium chloride
solutions. The free swell value of calcium bentonite (Type
I) is reduced by 62% in calcium chloride solution. In
general, variation in liquid limit, plasticity index and free
swell are more for calcium chloride than with acetic acid
solutions.
Variation in Hydraulic Conductivity with Acetic Acid
and Calcium Chloride
The variations in hydraulic conductivity of different types
of bentonites with acetic acid is shown in Fig 7.
Fig. 7: Variations in Hydraulic Conductivity of Different Types
of Bentonites with Acetic Acid Solutions
Results show that hydraulic conductivity increased due
to the reaction with solution and also with increase in
molarity. The maximum increase was of the order of 3 for
bentonite activated with sodium carbonate (Type II) with
2M acetic acid.
Variation of Percentage Swelling due to Acetic Acid
and Calcium Chloride
Percentage increase in thickness for all types of bentonite
due to permeation with water and different concentrations
of acetic acid and calcium chloride solutions were dound.
Results showthat as the concentration of solutions increases
percentage swelling decreases. Lowest reduction is for
bentonite activated with sodium carbonate (Type II) of 11%
at 0.25M acetic acid solution
Prediction of Hydraulic Conductivity
Linear and non linear regression analysis using SPSS
(Statistical Package for the Social Sciences) iwas done to
develop a relation between Liquid Limit, Plasticity Index,
Free Swell and Percentage Swell with Hydraulic
Conductivity for all types of soil. The linear relation
generated does not seem to be reliable for most of the
bentonite types. The nonlinear analysis leads to the
generation of very complex equations for all types of soil.
So curve fitting is done with Liquid Limit, PlasticityIndex,
Free Swell and Percentage Swell as independent variable
and Hydraulic Conductivity as dependant variable
For all types of soil percentage swell and hydraulic
conductivity relation gives the highest R2
value. So we can
say that percentage swell can be used as the independent
variable for the better prediction of hydraulic conductivity
for most of the bentonite types. The expression, which gives
highest R2 value of 0.959, is for Type IV soil with
percentage swell as independent variable
9. CONCLUSIONS
From the study the following conclusions can be
drawn
Liquid limit, plasticity index, free swell and percentage
swelling of all types of bentonite reduced due to the effect
of acetic acid and calcium chloride solutions. For all types
of bentonites the hydraulic conductivity increase as the
concentration of the acetic acid increases. For all types of
bentonites the variation in liquid limit, plasticity index,
free swell, percentage swelling and hydraulic conductivity
are comparativelyhigh with calcium chloride than to acetic
acid solution. Calcium bentonite would be more resistant
than sodium bentonite to chemical constituents in the
permeating fluids. Percentage swell is seems to be the most
suitable independent variable for the better prediction of
hydraulic conductivity for most of the bentonite types.
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