The extent of the influence of leachate on bentonite behavior also varies from bentonite to bentonite, depending on its mineralogical composition. The results showed that salt has a certain influence on free swelling, swelling potential, swelling pressure, hydraulic conductivity of compressed bentonite. The liquid limit, free swelling, swelling potential and swelling pressure of bentonites decreased with increasing salt or heavy metal ion concentration.
Regardless of the salt solution present in pore water, it was found that cv decreased while t90 increased with increase in the consolidation pressure. This study concludes that the effect of the salt on the properties of the bentonite depends on the salt type, salt concentration and initial compaction state of the bentonite.
80 4.20 Hydraulic conductivity vs. swelling pressure for bentonite-A and -B 81 4.21 Graphical relationship between void and pressure of bentonite-A and -B for MDD and OMC at. 104 4.41 The effect of salt concentration on the compression index of bentonite-A and -B 106 4.42 Graph between the compression index and the liquid limit of bentonites 107 5.1 The liquid limits of bentonite-A and -B in the presence of different. 170 6.12 Graph for the extent of increase in hydraulic conductivity of Bentonite-A 170 6.13 Comparison graphs of void ratio and hydraulic conductivity of the combination.
171 6.14 Graphical representation of the range of increase in hydraulic conductivity of bentonite-B 172 6.15 Graphical representation of the relationship between void and pressure of bentonite-A in the presence of combination.
LIST OF TABLES
Symbols Used
INTRODUCTION
- GENERAL
- ORGANIZATION OF THE THESIS
With the rapid growth of population and standard of living, the total amount of municipal solid waste (MSW) that is generated has increased many times and has become one of the serious environmental issues in both developed and developing countries (Beede and Bloom, 1995; Suocheng et al., 2001). To prevent groundwater contamination from these seeps, a very low permeability clay layer is provided at the bottom of the landfill, which acts as a barrier between the leachate and the groundwater (Daniel, 1984). In addition to salt solution, a change in mineralogical composition such as montmorillonite content, cation exchange capacity, specific surface area, percentage of exchangeable sodium of bentonite also significantly affects its swelling and therefore hydraulic conductivity (Lee and Shackelford, 2005; Mishra et al., 2009).
Like hydraulic conductivity, compressibility is one of the most important properties that help evaluate the settlement of the liner material due to the weight of waste in the landfill (Mishra et al., 2010). Very few of the previous studies have focused on the effect of the brine and mineralogical parameters on the swelling and consequently on the hydraulic conductivity and compressibility behavior of bentonite together; where most previous studies mainly focused only on the study of hydraulic conductivity of bentonite (Quirk and Schofield, 1955; Lee and Shackelford, 2005) or soil-bentonite mixtures (Mishra et al., 2009).
Therefore, the main purpose of this study was to investigate the effect of mineralogical solutions and salts of different concentrations on the swelling, hydraulic conductivity and consolidation behavior of bentonite. Bentonites were studied for their change in properties of index, swelling, swelling potential, swelling pressure, hydraulic conductivity and consolidation parameters due to the presence of different inorganic salts and heavy metals of different concentrations, individually as well as in combination of each other.
BACKGROUND AND LITERATURE REVIEW
- GENERAL
- PRESENT SITUATION OF WASTE MANAGEMENT AND DISPOSAL
- LANDFILL LINERS
- LANDFILL DESIGN METHOD ADOPTED IN DIFFERENT COUNTRIES
- GENERATION OF LEACHATE FROM MSW
- Composition of leachate
- Effect of leachate on liner material
- DESIGN PARAMETERS FOR LANDFILL LINERS 1. Hydraulic conductivity
- Shear Strength
- Volumetric shrinkage
- BENTONITE 1. Introduction
- Structure of Montmorillonite
- Swelling Behaviour of Bentonite
- DIFFUSE DOUBLE LAYER
- Factors affecting diffuse double layer (DDL) thickness
- SWELLING PRESSURE
- SWELLING POTENTIAL
- COMPRESSIBILITY
- HYDRAULIC CONDUCTIVITY
- Influence of salt on hydraulic conductivity of clay
- Effect of bentonite waste interaction on hydraulic conductivity
- REVIEW OF LITERATURES ON INTERACTION OF CLAY WITH SALT SOLUTIONS
- HEAVY METALS
- REVIEW OF LITERATURES ON INTERACTION OF CLAY WITH HEAVY METALS
- SUMMARY AND CRITICAL APPRAISAL OF LITERATURE REVIEW
- OBJECTIVES OF THE PRESENT STUDY
- SIGNIFICANCE OF THE STUDY
These factors contribute to the bentonite's high swelling, low hydraulic conductivity, and contaminant adsorption capacity. The polarity of the water molecule is an important factor in the inner crystalline swelling of clay. Their results showed that the liquid limit of the mixtures decreases as the salt concentration increases.
Consolidation tests were performed on the mixtures to evaluate the effect of the mineralogical composition of the bentonite on the hydraulic conductivity (k) of the mixture in the presence of different salt concentrations. The changes in the fluid limit, compression index, and hydraulic conductivity of the backfills with respect to Pb concentration were attributed to the contraction of the diffuse bentonite double layer.
MATERIALS AND METHODS
- GENERAL
- MATERIALS USED IN THE STUDY 1. Bentonite
- Permeant liquids
- TESTING METHODOLOGY 1. Atterberg limits
- Compaction test
- Specific Surface Area (SSA)
- Consolidation test
- INTRODUCTION
- RESULTS AND DISCUSSION 1. Atterberg limits
- Free swelling
- Time swelling relationship
- Swelling potential
- Swelling pressure
- Hydraulic conductivity
- Consolidation characteristics 1. Void ratio-pressure relationship
- SUMMARY
The data show that the fluid limits of both bentonites decreased with an increase in salt concentrations. The free swelling of Bentonite-B was found to decrease significantly with the increase in salt concentration compared to Bentonite-A. Regardless of the initial water content, the swelling potential of bentonite decreased as the salt concentration increased.
The increase in hydraulic conductivity with salt concentration was more prominent at higher salt concentrations. The hydraulic conductivity of the bentonites was found to decrease as the swelling pressure of the bentonites increased. However, the difference between the CV values for the two bentonites decreased with the increase in salt concentration.
The graph also shows that regardless of the consolidation pressure, t90 increased with increasing bentonite yield strength. The graph shows that the t90 for the bentonites increased as the swellability of the bentonites increased. As the salt concentration increases, the orientation of the clay particles becomes better.
A comparison of the swelling potential values for both bentonites showed that the swelling potential of Bentonite-B was greatly affected by the increase in salt concentration. The results also showed that the swelling potential of bentonites increased with increasing liquid limit and free swelling. The results showed that the swelling pressure of bentonite decreased with increasing salt concentration.
A comparison of the swelling pressure for the two bentonites showed that the swelling pressure of Bentonite-B decreased significantly due to increase in the salt concentration compared to Bentonite-A. The results for the compression index (Cc) showed that the Cc decreased with an increase in the salt concentration.
EFFECT OF HEAVY METALS ON BEHAVIOUR OF BENTONITES
- INTRODUCTION
- RESULTS AND DISCUSSIONS 1 Atterberg limits
- Free swelling
- Swelling pressure
- Swelling potential
- Time swelling relationship
- Hydraulic conductivity
- Consolidation characteristics 1. Void ratio-pressure relationship
- SUMMARY
Similar to the results obtained for the inorganic salt solution, the graph also shows that the yield stress of bentonites decreased with increasing heavy metal ion concentration and the decrease was more pronounced for Bentonite-B compared to Bentonite-A. The graph in the figure shows that the free swelling of bentonites decreased with increasing concentration of heavy metal ions. It was found that the free swelling of bentonite-B decreased significantly due to the increase in metal ion concentration compared to bentonite-A.
The graph shows that the swelling pressure for both bentonites decreased with the increase of the metal ion concentration in the pore fluid. It can be observed that the increase in hydraulic conductivity was prominent at higher concentrations. With the increase in the concentration of the heavy metals in the pore fluid, a lower value of the theoretically calculated void ratio was obtained for both bentonites.
The plot also shows that the mv for the bentonites decreased with the increase in the heavy metal ion concentration. The plot shows that, regardless of the consolidation pressure, the cv decreased with the increase in the free swelling of the bentonite. The decrease in cv with increase in the free swelling was significant for Bentonite-A compared to that of Bentonite-B.
The reduction in cv with an increase in free swelling was higher for samples compacted in dry OMC. For Bentonite-A, samples compacted in OMC-MDD and in the presence of Zn+2 solution, cv. For both bentonites, t90 decreases with an increase in the concentration of heavy metal ions in the pore fluid.
The results showed that the liquid limit of the bentonites decreased as the heavy metal concentrations increased and the effect was more prominent for Bentonite-B. The free swelling of Bentonite-B was found to decrease significantly due to the increase in metal ion. concentration compared to Bentonite-A.
COMBINED EFFECT OF INORGANIC S ALTS AND HEAVY METALS ON
- INTRODUCTION
- Various combinations of salts used for the study
- Free swelling
- Swelling pressure and Swelling potential
- Time swelling relationship
- Hydraulic conductivity
- Consolidation parameters
The data also show that the difference in liquid limit of the two bentonites is significantly reduced due to the combined effect of the NaCl and CaCl2 solutions. Similarly, the data in Table 6.2 show that the combined effect of heavy metals on the liquid limit of bentonites was significant compared to the individual effect. The swelling pressure data for both bentonites in the presence of heavy metals show that the combined effect of the heavy metals was quite significant compared to the individual effect.
Figures 6.1 and 6.2 show the swelling percentage versus time elapsed for the bentonites in the presence of the mixture of different salt solutions. Regardless of the bentonite quality, it was found that swelling was the least in the presence of combination of the high concentration solutions. The difference in the swelling values for both the bentonites decreased with the increase in concentration of the mixed salt solutions.
Figures 6.3 to 6.4 and 6.5 to 6.8 compare the hydraulic conductivity of bentonites in the presence of combinations of inorganic salts or combinations of heavy metals with their individual type; while, Fig. A comparison between the two bentonites showed that the hydraulic conductivity of bentonite-B was greatly affected compared to bentonite-A due to the presence of combined solutions. Figures 6.15 and 6.16 show the relationship between void and pressure of bentonite in the presence of a mixture of different salt solutions.
Figures 6.19 and 6.20 show the relationship between the consolidation coefficient and the consolidation pressure of bentonites in the presence of inorganic salts and heavy metal solutions mixed in different combinations. The graphs show that as the consolidation pressure increases, the t90 for the sample increases in the presence of salt solutions. However, the increase in t90 with consolidation pressure was less in the presence of salt solutions compared to DI water.
