Abidin Kaya

ZETA POTENTIAL OF KAOLINITE IN THE PRESENCE OF ALKALI, ALKALINE EARTH AND HYDROLYZABLE METAL IONS

Electrokinetic remediation is one of the promising subsurface clean up techniques whose efficiency is directly affected by the zeta potential of clay minerals. To determine the factors affecting the zeta potential, in turn, electrokinetic remediation, the zeta potential of kaolinite is determined usingelectrophoretic mobility in the salt and heavy metals ions asfunctions of pH and concentration. The zeta potential of kaolinite ranged from -25 mV (pH 3) to -42 mV (pH 11) in water. The zeta potential of kaolinite became more negativewith increasing pH. The zeta potential of kaolinite was also found to be sensitive to the valence of ions. Results, furthermore, revealed that kaolinite has higher zeta potentialvalues in the presence of NaCl and LiCl than in water. However, the zeta potential of kaolinite decreased with divalent cationssuch as Ca2+ and Mg2+. The zeta potential of kaolinitewith heavy metal ions such as Cu2+, Co2+ and Pb2+ showed a similar trend, i.e., increase in the concentration ofthese ions caused a decrease in the zeta potential up to neutral pH, then it became positive. In highly basic environments, thezeta potential became negative again, giving two apparent pzcs. One of two apparent pzcs was attributed to kaolinite and the other one to the precipitation of these ions in highly basic solutions (pH ≥ 9).

THE EFFECT OF YATAGAN THERMAL POWER PLANT (MUGLA, TURKEY) ON THE QUALITY OF SURFACE AND GROUND WATERS

Yatagan thermal power plant consumes annually 5.4 million tons of coal and the annual production capacity of the plant is 3.78 billion KWh. The thermal power plant uses 15 000 tons of coal and discharges 5000 tons of fly and bottom ash daily to the disposal site. The waste is dumped using conveyer belts and pipes into a dam founded on metamorphic rocks. However, as the waste hills formed, the water level reached the karstic marbles that over lay schist. Water leaches through dried waste hills and karstic marbles, ultimately adversely affecting the quality of ground and surface waters. The concentrations of major and minor ions were determined on water samples taken at 2 points in the dam, 5 points in surface water and at 21 points in groundwater located in the vicinity of the waste disposal site, total of 28 samples, for three years. The chemical analyses revealed that the concentrations of Ca2+, Cd2+, Pb2+, Sb2+ and SO42- in some samples exceed the Turkish Drinking Water, the U.S. EPA and WHO limits. Isotope analyses were carried out to determine the origins of waters, which showedthat contamination is taking place in the vicinity of the waste disposal site.

Settling of Kaolinite in Different Aqueous Environment

Settling characteristics of soils carry great importance for geotechnical engineers since sediments properties are formed during the settling of soil particles in an aqueous environment. In this study, settling characteristics of kaolinite are investigated. Different ionic strengths of NaCl, CaCl2 and AlCl3 were considered as a function of pH in aqueous environment of varying solid concentrations. Factors affecting the settling characteristics and fabric of kaolinitic sediments have been identified. The results of the study reveal that kaolinite settles in either flocculated or dispersed forms depending on pH and ion concentration. Flocculated settling occurs in acidic pH due to formation of flocs in edge-to-face structure with increasing positive charges at the particle edges. Dispersed settling occurs in alkaline pHs when ionic strength is low. When ionic strength is increased in alkaline pHs, kaolinite particles settle in flocculated form. Furthermore, the results show that pH has a significant role on the final sediment thickness or void ratio of kaolinite. Densely packed structures in alkaline and loosely packed structures in acidic aqueous environments are formed depending on pH level. Results also show that as the solid concentration increases, the settling rate decreases due to buoyancy effect. Finally, the zeta potential of kaolinite is correlated with the final sediment thickness or void ratio of kaolinite as a function of pH. This correlation proves that there is a good agreement between zeta potential and the final sediment thickness or void ratio, especially when the soil is settled in a dispersed form.

Prediction of cation exchange capacity from soil index properties

Abstract In many areas of geotechnical engineering it is necessary to have an estimate of the cation exchange capacity (CEC) of a soil in order to allow preliminary design estimates. Standard methods of CEC determination are time-consuming and involve several steps (e.g. displacement of the saturating cation requires several washings with alcohol). Therefore, a rapid method of CEC estimation would be very useful. During preliminary site investigations, the soil engineering parameters can be estimated from the considerable number of correlations available in the literature. In this study, relationships between CEC and various other soil engineering properties have been investigated, resulting in a quick method for estimating CEC. Simple correlations were developed between CEC and specific surface area (SSA), soil organic matter (OM), clay fraction (CF), activity (A), Atterberg limits (liquid (LL), plastic (PL), and shrinkage (SL)), and modified free swell index (MFSI) of the soils. Strong correlations are observed between the CEC values and those for ethylene glycol monoethyl ether (EGME) uptake and methylene blue (MB) titration. However, no significant correlation was found between CEC and N2_SSA. No unique relationship was seen between CEC and CF (r2 <0.5). No relationship was observed between CEC and OM in this study. The best correlation coefficient between the CEC and Atterberg limits exists between CEC and LL (r2 = 0.61). No significant relationship was seen between CEC and PL or SL. The correlation coefficient between CEC and MFSI was 0.65. Multiple linear regression analyses were developed to investigate the contributions of different soil parameters to CEC. These analyses show that EGME_SSA, in combination with LL, accounted for 91% of the variation in CEC. Correlations between CEC and EGME_SSA, MB_SSA and LL appear to be sufficiently good to enable an indication of CEC to be estimated from these parameters.

Some engineering aspects of homoionized mixed clay minerals.

Many studies have been conducted to investigate thephysicochemical behavior of pure clay minerals and predicttheir engineering performance in the field. In this study, thephysicochemical properties of an artificial mixture of differentclay minerals namely, 40-50% montmorillonite, 20-30% illite and 10-15% kaolin were investigated. The mixture was homoionized with sodium, Na+; calcium, Ca2+; andaluminum, Al3+. The engineering properties studied wereconsistency limits, sediment volume, compressibility behavior,and hydraulic conductivity. The results revealed that theliquid, plastic and shrinkage limits of soil increased withincreasing cation valence. The hydraulic conductivity of thesoil also increased with an increase in the valence of thecation at any given void ratio. Aluminum and sodium treatedclays had the highest and the lowest modified compressionindex values, respectively. Furthermore, trivalent cationsaturated clayey soil consolidates three times faster thanthat of monovalent and two times faster than that of divalent.These properties of the soils determined were, in general,similar to those of kaolinite rather than those ofmontmorillonite. The comparison of the results obtained withthe published data in the literature revealed that thephysicochemical behavior of the tested clay soil was, ingeneral, similar to that of kaolinite.

INTERFACIAL PARAMETERS AND WORK OF ADHESION IN SOIL-LIQUID SYSTEMS

The surface/interfacial properties and soil-liquid interaction are studied to serve as a preliminary study to interpret engineering behavior of soils. To fully understand the nature of fine-grained soil-pore fluid interaction, the work of adhesion of liquids on kaolinite and bentonite is determined by means of measuring soil-liquid contact angle by the Wilhelmy Plate technique and horizontal capillarity. The results reveal that work of adhesion of soils with organic liquids varies considerably depending on the surface tension of the organic liquids (cohesive forces) as well as the liquid-soil adhesive forces. Further, surface parameters of the soils, such as the Lifshitz-van der Waals component of solid surface tension, the acidic component of solid surface tension, and the basic component of solid surface tension, are determined and compared with the values reported in the literature. The results reported in this study are compared with the previous ones in the literature. The agreement between the results of this study and reported results in the literature is good. Results also revealed that when the soil particles are wetted with water, organic liquids could not displace water molecules and change the soil microstructure. Based on the obtained results, it is concluded that studying the work of adhesion is a very useful way of understanding soil-liquid interaction and predicting engineering behavior of soils.

Determination of Cylindrical Soil Specimen Dimensions by Imaging with Application to Volume Change of Bentonite-Sand Mixtures

Volumetric shrinkage of compacted bentonite and sand mixtures has been continuously monitored at small strain levels (i.e., <5 %) using a digital image processing technique. A special digital measurement setup and a computer algorithm have been developed in order to identify volume of the drying specimens. Volume change of three compacted bentonite-sand mixtures at different initial moisture contents were recorded during drying by means of vernier caliper and digital measurements. Continuous monitoring of the volumetric shrinkage of specimens using digital images proved that digital measurement and data reduction methodology developed herein is capable of determining the shrinkage amount with desired accuracy. It is shown in the study that consistent volumetric shrinkage strain readings can be taken using this cost effective, nondestructive, and operator independent measurement setup, which may have become the preferred shrinkage measurement methodology in soil mechanics laboratory practice with some added features.

Removal of TDS from Cooling Tower Water by Using EDTA-Modified Bagasse Fibers

Modified by ethylenediaminetetraacetic acid (EDTA) salts and unmodified bagasse fibers were tested for the removal of total dissolved solids (TDSs) from cooling tower water. Parameters such as hydrogen ion concentration (pH), particle size of bagasse fibers, and the concentrations of adsorbent and adsorbate were studied to optimize the conditions to be applied on a commercial scale for the decontamination of effluents of cooling tower water. The optimum pH for TDS removal was between 6 and 6.5. The efficiency of TDS removal increased when the size of fiber particles decreased ( 100 μm ) and when the concentration of EDTA salt increased to reach 78 mg/g of modified bagasse fibers. The adsorption parameters were determined using both Langmuir and Freundlich isotherms. The preferential mechanisms for the retention of TDSs are a complexation process between the TDSs and chemical functions present on the surface of fibers, and the chelation process with the EDTA attached to the fibers. The results obtained cou...

Geomechanics of Landfills—Innovative Technology for Liners

Cracks in clayey landfill liner, which cannot be closed up upon re-wetting, affect the long-term performance of a landfill. In this paper, the mixture bentonite-zeolite (BEZ) is presented as a potential liner material due to its plastic properties. Also, it may fulfill an existing demand, in developing countries, for liners that are cost-effective, natural and in compliance with environmental regulations. Traditional liners have shortcomings: (i) clayey soil is suitable for liners if the temperature and moisture fluctuations are not high; otherwise, they may form cracks; (ii) geomembranes, considered as the best alternatives for liners, are out of reach of most underdeveloped countries for their high price, and do not last more than 4 years; (iii) the interface of a CGL (clay geosynthetic liner) is susceptible to sliding. In the studies performed, the low volumetric shrinkage of the BEZ indicates that it is not affected by moisture content fluctuations, and its hydraulic conductivity in the order of 10 −10 cm/s meets regulatory agency requirements. Also, its inherent chemical properties (specially clinoptilolite zeolite) and its natural selectivity indicates that it will adsorb heavy metals such as Pb 2+ , Zn 2+ , Cd 2+ , Ni 2+ ,Fe 2+ , and Mn 2+ that may be present in leachate. Therefore, BEZ is a potential innovative material for liners in landfills.

Discussion of “Swelling characteristics of bentonite in artificial seawater”Appears in Canadian Geotechnical Journal, 46(2): 177–189.

The authors have to be congratulated for presenting such interesting research. The results are important not only in terms of buffer material to fill disposal facilities, but also in terms of understanding the effect of rising seawater level and regression of seawater inland due to excessive fresh water withdrawal at coastal areas (Yukselen et al. 2008). Thus, the discussers are very interested in the results presented in this paper, and would like to offer the following comments on the authors’ interpretations. The experimental results reveal that the maximum swelling pressures of bentonites B–E are affected by artificial seawater to varying degrees. However, results are obscure for several reasons. For example, it is known that calciumtype bentonite has lower swelling potential than sodiumtype bentonite under the same testing conditions (Azam et al. 2000). However, the comparison of maximum swelling pressures shown in Fig. 6 indicates that the maximum swelling potential of calcium-type bentonite yields a larger swelling pressure than sodium-type bentonite. Furthermore, even though the other sodium-type bentonites (B, D, E) are affected by artificial seawater, bentonite A is not affected. These results from Fig. 6 are also in apparent contradiction with Figs. 9 and 12. For example, the maximum swelling strain difference between distilled water and artificial seawater is negligible for bentonite C. On the other hand, there are appreciable strain differences in bentonite A. We wonder if the presented maximum swelling pressures of the bentonites are merely a function of the water content of the samples. To this end, we plotted the maximum swelling pressure of bentonites as a function of their average water content (Fig. D1). We also plotted the maximum swelling pressure as a function of the montmorillonite content of bentonites (Fig. D2). As seen from Fig. D1, the swelling pressure of bentonites increases linearly with average water content, implying that the reported maximum swelling pressures are also a function of moisture content. In conclusion, the results show that the maximum swelling pressure of bentonites appears to increase concomitant with montmorillonite and water contents (Fig. D2). This should be expected as the listed average water content is a function of the montmorillonite content (Fig. D3). We believe that the reported swelling pressures of bentonites are a coupled function of their water and the montmorillonite content. Thus, from the presented data it is hard to reach the conclusion that the ‘‘influence of artificial seawater on the swelling characteristics of sodium-type and artificial sodium-type bentonites is low’’ and ‘‘the influence of artificial seawater on swelling characteristics of calcium-type bentonite is more slight than sodium-type and artificial sodium-type bentonites.’’ Further evidence of the above statements is the variation of maximum swelling pressures with liquid limit. As seen from Fig. D4, the swelling pressure decreases with an increase in the liquid limit of bentonites. This appears to contradict previous research that documents swelling pressures that increase (not decrease) with an increase in liquid limit of soils (Vijayvergiya and Ghazzaly 1973; Chen 1988; Issa 1997). Additional evidence of the above stated statement comes from the authors’ own data. For example, if we take the maximum swelling strain differences between distilled water and artificial seawater at 1.4 Mg/m3 of initial density under 10 kPa vertical pressure and plot them as a function of the liquid limit of bentonites, the maximum swelling differences increase with an increase in liquid limit (Fig. D5). We chose the initial dry density of 1.4 Mg/m3 as this density is the only initial density in all tested samples. We validate our observations by plotting the observed maximum swelling strains presented in Fig. 9 as a function of the liquid limit of samples at 1.65 Mg/m3. As seen from Fig. D6, the observed maximum swelling strain is a function of liquid limit. We would appreciate the authors’ comments on our interpretation of the reported results.