Response of fly ash-bentonite based landfill liner to chemical solutions
Presented by
E LAKSHMI SURESH BABU
INTERNATIONAL CONFERENCE ON
INNOVATIVE TRENDS IN CIVIL ENGINEERING FOR SUSTAINABLE DEVELOPMENT (ITCSD - 2019)
OUTLINE
• Introduction
• Past studies
• Objective
• Materials
• Methodology
• Results
• Conclusions
• References
Introduction
• Hydraulic barriers are a part of lining systems which are responsible for preventing a potential pollutant present in the waste containment from migrating to groundwater and thus polluting them.
• Permeability criteria to be satisfied by a liner material is k ≤ 10
-7cm/sec.
• Although bentonite alone satisfies the permeability criteria of a liner material,
• being highly plastic in nature,
• shows a high change in volume with the variation of water content and
• possess low strength.
• Hence, cohesion-less soils (sands) were mixed with bentonite clay in the right proportions to increase the strength and enhance the volume change characteristics without compromising the overall hydraulic conductivity.
• Fly ash can be used along with bentonite as a replacement for sand,
thus addressing the problem of effective disposal of fly ash and
conserving natural resources.
Past Studies
Author(s) Findings
Mesri and Olson (1971) Hydraulic conductivity of Na-bentonite is five times lower than Ca-bentonite at similar void ratios
• Sposito (1981)
• McBride (1994)
Na-bentonites are more prone to cation exchange when permeated with solutions containing divalent and trivalent cations
Quigley (1993) Change in diffused double layer thickness (resulting in flocculation of the clay particles) attributed to the variation of permeability
• Mitchell (1993)
• Sharma and Lewis (1994)
Di-electric constant, cation valence attributed to the variation of hydraulic conductivity
Kayabali et al. (1998) Chemical properties of landfill leachate
• Arasan and Yetimoglu (2006)
• Yilmaz et al. (2008)
Chlorides and Sulphates are widely distributed in nature and are common constituents in the leachate
OBJECTIVE
Chemical Compatibility of Fly ash-bentonite based Hydraulic Barrier
Materials
• Fly ash collected from Aditya Alumina Ltd. situated in Lapanga town of Sambalpur district, Odisha.
• Commercially available sodium based bentonite from the local market, Odisha.
• Different concentrations of Hydrochloric acid, Sodium chloride and
Sodium hydroxide, Sulphuric acid, calcium chloride and ferric chloride.
Methodology
• The basic geotechnical characteristics of the materials were found out by performing different laboratory tests.
• In order to assess the chemical characteristics, hydraulic conductivity tests were carried out on different trial mixes of fly ash and bentonite.
• The bentonite content in the fly ash-bentonite mixture was taken up to 15% @ 5% increment starting from 5%.
• The permeant solutions used include NaCl, NaOH, HCl, CaCl
2, H
2SO
4and FeCl
3at different concentrations i.e. 0M (water), 0.01M, 0.1M,
0.5M and 1M (where ‘M’ represents Molarity), which were chosen to
best represent the acidic, basic and neutral nature of the landfill
leachate.
Results
Geotechnical Properties
Sl. No. Property Fly ash Bentonite
1. Specific Gravity 2.08 2.74
2. Liquid limit, LL (%) - 268
3. Plastic limit, PL (%) - 54
4. Linear Shrinkage, L
s- 29
5. Plasticity Index, PI (%) - 214
6. Differential Free Swell Index, DFSI (%) 0 400
SEM image of fly ash SEM image of bentonite
Grain size distribution curves of bentonite and fly ash
Water content-dry density relation for FA: B
mixtures from Standard Proctor method
FA+B mixture (FA: B)
Liquid Limit, LL (%)
Plastic Limit, PL (%)
Plasticity Index, PI (%)
95:05 40.84 15.79 25.05
90:10 56.44 27.37 29.07
85:15 62.15 31.68 30.47
Consistency Limits of Fly ash-bentonite mixtures
Hydraulic conductivity of fly ash and bentonite mixtures with water as permeant
Sl. No. Trial Mix Type of compaction Permeability,
k (cm/sec) Average Permeability, k (cm/sec)
1. FA+B (95:05) Standard Proctor
2.58×10-6
1.87×10-6 1.85×10-6
1.60×10-6 1.46×10-6 2. FA+B (90:10) Standard Proctor
0.90×10-6
0.70×10-6 0.63×10-6
0.77×10-6 0.50×10-6 3. FA+B (85:15) Standard Proctor
4.12×10-8
3.64×10-8 3.16×10-8
3.60×10-8 3.68×10-8
Effect of bentonite content and NaCl Effect of bentonite content and HCl
Effect of bentonite content and NaOH concentration on the permeability of FA:B
mixture
Effect of bentonite content and
CaCl
2concentration on the permeability of FA:B mixture
Effect of bentonite content and
H
2SO
4 Effect of bentonite content andFeCl
35% bentonite 10% bentonite 15% bentonite 0.0E+00
2.0E-06 4.0E-06 6.0E-06 8.0E-06 1.0E-05 1.2E-05 1.4E-05 1.6E-05
Permeability (cm/sec)
Normal Water 0.01M FeCl3 0.1M FeCl3 0.5M FeCl3 1M FeCl3
100% stacked column showing the effect on permeability with different chemicals at varying concentrations @ 5% bentonite
• The plot shows that the effect on permeability is more in case of H2SO4 compared to other chemicals.
• Effect in case of NaOH is very less comparatively.
4%2% 4%2% 9% 8%
2% 1%
9% 9% 8%
6%
6% 9%
13%
11%
72% 65% 53% 61%
7% 11% 15% 13%
0.01M 0.1M 0.5M 1M
0 20 40 60 80 100
5% bentonite FeCl3
H2SO4 CaCl2 HCl NaOH NaCl
Effect on permeability (%)
Concentration
• The plot shows that the effect on permeability is more in case of H2SO4 compared to other chemicals.
• Relatively, the effect of NaCl and NaOH remained same irrespective of the change in concentration.
6% 6% 6% 5%
3% 3% 2% 2%
10% 10% 8%
6%
9% 12% 18%
15%
67%
52% 46%
55%
5%
18% 19% 17%
0.01M 0.1M 0.5M 1M
0 20 40 60 80 100
Effect on permeability (%)
FeCl3 H2SO
4
CaCl2 HCl NaOH NaCl
10% bentonite
Concentration
• Comparatively the effect of FeCl3 and CaCl2 has increased at 15% bentonite
• The effect of HCl kept on reducing in every case with increasing concentration.
6% 4% 3% 3%
26%
15% 11% 11%
7%
5%
4% 3%
16%
21% 25% 30%
30%
22% 30% 26%
14%
33% 27% 27%
0.01M 0.1M 0.5M 1M
0 20 40 60 80 100
15% bentonite FeCl3
H2SO4 CaCl2 HCl NaOH NaCl
Effect on permeability (%)
Concentration
100% stacked column showing the effect on permeability with different chemicals at varying concentrations @ 15% bentonite
Conclusions
• Irrespective of the nature of the permeant solution (acidic/basic/neutral), the hydraulic conductivity of all the fly ash-bentonite mixtures increased with an increase in chemical concentrations.
• At lower bentonite content, the effect of H2SO4 was predominant but as the bentonite content increased the effect of FeCl3 and CaCl2 was predominant.
• Monovalent cations showed less effect on the permeability compared to the divalent and trivalent cations.
• Overall, the increase in permeability might be attributed to the following reasons.
• decrease in double layer thickness (flocculation)
• pH effect on ionisation
• Di-electric constant of chemicals.
References
Akcanca F, Aytekin M (2014) Impact of wetting-drying cycles on the hydraulic conductivity of liners made of lime-stabilized sand-bentonite mixtures for sanitary landfills. Environmental earth sciences 72(1):59-66
Alla V, Sasmal SK, Behera RN, Patra CR. Development of alternate liner material by blending fly ash, local soil and bentonite. In: Proceedings of Indian Geotechnical Conference GeoNEst, 14-16 December 2017, IIT Guwahati, India, 95
Arasan S (2010). Effect of chemicals on geotechnical properties of clay liners: a review. Research Journal of Applied Sciences, Engineering and Technology 2(8):765-775
Arasan S, Yetimoglu T (2006) Effect of leachate components on the consistency limits of clay liners.
In: 11th National Soil Mechanic and Foundation Engineering Congress, Trabzon, Turkey (pp. 439- 445)
Kayabali K, Kezer H (1998) Testing the ability of bentonite-amended natural zeolite (clinoptinolite) to remove heavy metals from liquid waste. Environmental Geology 34(2-3):95-102
McBride MB. Environmental chemistry of soils. Oxford University Press. New York; 1994.
Mesri G, Olson RE (1971) Mechanisms controlling the permeability of clays. Clays and Clay Minerals
Mitchell JK. Fundamentals of soil behavior. John Wiley & Sons, New York. Fundamentals of soil behavior. 2nd ed. John Wiley and Sons, New York; 1993.
Quigley RM (1993) Clay minerals against contaminant migration. Geotechnical News 11(4):44-46 Sharma HD, Lewis SP (1994) Waste containment systems, waste stabilization, and landfills:
design and evaluation. John Wiley & Sons.
Sposito G. The thermodynamics of soil solutions. Oxford University Press; 1981.
Yılmaz G, Yetimoglu T, Arasan S (2008) Hydraulic conductivity of compacted clay liners permeated with inorganic salt solutions. Waste Management & Research 26(5):464-473.
