ENVIRONMENTAL EARTH SCIENCES

The purpose of this study was to determine the effects of pH, ion type (salt and metal cations), ionic strength, cation valence, hydrated ionic radius, and solid concentration on the zeta potential of kaolinite and quartz powder in the presence of NaCl, KCl, CaCl2, CuCl2, BaCl2, and AlCl3 solutions. The kaolinite and quartz powder have no isoelectric point (iep) within the entire pH range (3 < pH < 11). In the presence of hydrolysable metal ions, kaolinite and quartz powder have two ieps. As the cationic valence increases, the zeta potential of kaolinite and quartz powder becomes less negative. Monovalent cation, K+, yields more negative zeta potential values than the divalent cation Ba2+. As concentration of solid increases, the zeta potential of the minerals becomes more positive under acidic conditions; however, under alkaline conditions as solid concentration increases the zeta potential becomes more negative. Hydrated ionic radius also affects the zeta potential; the larger the ion, the thicker the layer and the more negative zeta potential for both kaolinite and quartz powder

JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING

Contamination of soils by polychlorobiphenyls (PCBs) is of environmental concern because of their toxicity, persistence, hydrophobic nature, and slow biodegradation potential. Among the PCB remedial technologies, direct oxidation by persulfate is considered to have great potential to be both simple and rapid. However, to produce faster reaction rates, persulfate is often activated using heat, metal chelates, hydrogen peroxide, or high pH. Furthermore, delivery of persulfate in low permeability clayey soils is difficult. Integrating electrokinetic remediation with persulfate has the potential to overcome such difficulties because the applied electric potential can facilitate the delivery of persulfate in low permeability soils as well as activate oxidizing radicals and simultaneously induce oxidative/reductive reactions directly in the soil. This study investigates the potential for in situ oxidation of PCBs in low permeability soils using persulfate as an oxidant and also evaluates the benefits of integrating oxidation with electrokinetic remediation. Several series of laboratory batch and bench-scale electrokinetic experiments were conducted using kaolin, a representative clayey soil, spiked with 50 mg/kg of 2,2',3,5' tetrachlorobiphenyl (PCB 44), a representative PCB. Persulfate oxidation activators [elevated temperature (45 degrees C) and high pH (at the cathode)] were investigated to maximize the PCB degradation. In addition, the effect of oxidant dosage on PCB degradation was investigated. The electrokinetically enhanced temperature-only activated persulfate oxidation test resulted in better PCB 44 remediation (77.9%) than the temperature and high-pH activated persulfate oxidation (76.2%) in a 7-day period. The optimal dosage for effective remediation was 30% Na-persulfate (76.2%) because a 20% concentration of the oxidant yielded a lower rate of degradation (55.2%) of PCB 44. The results are encouraging for the use of electrokinetically enhanced persulfate oxidation for the effective remediation of PCBs in soils. DOI: 10.1061/(ASCE)GT.1943-5606.0000744. (C) 2013 American Society of Civil Engineers

ENVIRONMENTAL GEOLOGY

In this study, the zeta potential of montmorillonite in the presence of different chemical solutions was modeled by means of artificial neural networks (ANNs). Zeta potential of the montmorillonite was measured in the presence of salt cations, Na+, Li+ and Ca2+ and metals Zn2+, Pb2+, Cu2+, and Al3+ at different pH values, and observed values pointed to a different behavior for this mineral in the presence of salt and heavy metal cations. Artificial neural networks were successfully developed for the prediction of the zeta potential of montmorillonite in the presence of salt and heavy metal cations at different pH values and ionic strengths. Resulting zeta potential of montmorillonite shows different behavior in the presence of salt and heavy metal cations, and two ANN models were developed in order to be compared with experimental results. The ANNs results were found to be close to experimentally measured zeta potential values. The performance indices such as coefficient of determination, root mean square error, mean absolute error, and variance account for were used to control the performance of the prediction capacity of the models developed in this study. These indices obtained make it clear that the predictive models constructed are quite powerful. The constructed ANN models exhibited a high performance according to the performance indices. This performance has also shown that the ANNs seem to be a useful tool to minimize the uncertainties encountered during the soil engineering projects. For this reason, the use of ANNs may provide new approaches and methodologies

APPLIED CLAY SCIENCE

It is postulated that the behavior of fine-grained soils may be explained by the relationship between surface area and other geotechnical properties. To this end, there are several studies correlating geotechnical indexes with specific surface area (SSA). However, there is no universally accepted specific surface area determining method as several methods are available. Depending on the method employed, the measured specific surface area may show variations for a given soil. This is because the predictive power of each method depends on the type of minerals and organic matter that are present in the soil. Thus, different SSA determination methods yield widely different estimates of index properties and regression equations. To examine the role of method on SSA of soils, the SSAs of 32 soils with different mineralogies were determined using BET-N-2, EGME, MB-titration, and MB-spot test methods. The measured SSA of soils was correlated with their respective geotechnical index properties. Further, the data obtained in this study and those reported by previous researchers were compared. The results suggest that correlations between geotechnical index properties and SSA using different methods may not be comparable. Accurate prediction, however, is provided only if the relationship is calibrated using soils having similar physical and chemical characters. (c) 2010 Elsevier B.V. All rights reserved

WATER AIR AND SOIL POLLUTION

The effectiveness of persulfate oxidation for the destruction of tetrachlorobiphenyl a representative polychlorobiphenyl (PCB), in spiked subsurface soils was evaluated in this study. Kaolin and glacial till soils were selected as representative low permeability soils; both soils were spiked with 50 mg PCB per dry kilogram of soil. Activation of persulfate oxidation was necessary to achieve effective destruction of PCBs in soils. As persulfate oxidation activators, temperature and high pH were used in order to maximize PCB destruction. In addition, the effect of oxidant dose and reaction time was investigated. The optimal dose for persulfate was found to be 30% for maximum oxidation. The persulfate activation with temperature of 45A degrees C was superior to persulfate activation with high pH (pH 12), where higher PCB destructions were observed for kaolin and glacial till soils. PCB destruction increased with reaction time, where maximum degradation was achieved after 7 days. The highest PCB destruction was achieved with temperature activation at 45A degrees C using a dosage of 30% persulfate at pH 12 for kaolin and glacial till soils after 7 days

PROCEEDINGS OF THE INSTITUTION OF CIVIL ENGINEERS-GEOTECHNICAL ENGINEERING

In this study, the effect of specific surface area on compressibility and permeability characteristics of remoulded and intact clayey soils was investigated. Fifteen remoulded and 15 intact soils with a wide range of physicochemical properties were tested. The results indicate that specific surface area has a significant effect on compressibility and permeability behaviour of clayey soils. In addition to other soil index properties, specific surface area can be used for estimating these engineering properties. Significantly high correlation coefficient (r = 0.97) between compression index (C-c) and the specific surface area is observed for remoulded clayey soils with only methylene blue-spot specific surface area. There is no significant correlation between the BET-N-2 specific surface area and C-c: The effect of the remoulded water content on proposed specific surface area and C-c relationship is also investigated. The results show that as specific surface area of soils increases, c(v) decreases, indicating the importance of the diffuse double layer on the consolidation process. The results also reveal that permeability is controlled by the specific surface area of soils. In addition, the data obtained in this study indicate that there is a linear correlation between C-c/n(0) and C-c, which indicates the significance of initial void ratio on the compressibility characteristics of soils

PROCEEDINGS OF THE INSTITUTION OF CIVIL ENGINEERS-GEOTECHNICAL ENGINEERING

Some geotechnical index properties, such as the liquid limit, plasticity index, clay content and cation exchange capacity, have been used to predict the swelling potential of soils. However, a literature review indicates that prediction of the swelling potential of soils using these index properties is not completely successful. At the same time, the methods used to determine swelling potential are time-consuming. Thus researchers have been investigating other methods that can predict the swelling potential of soils readily and accurately. To this end, in this study the BET (Brunauer, Emmett and Teller equation)-N-2 adsorption, ethylene glycol monoethyl ether (EGME) and methylene blue (MB) measured specific surface areas (SSA) are correlated with the swell index and modified free swell index of soils. The SSA and swell index of 16 remoulded and 15 undisturbed soils consisting of a wide range of mineralogy were determined. Results indicate that the correlation between the SSA and the swelling behaviour of the clayey soils examined is significant. A linear relationship is observed between the swell index, C-s, and the MB SSA: the swell index of the soils increases as the SSA increases. The correlation coefficient between the SSA and the modified free swell index (MFSI) is 0.93, indicating that the MB SSA does exert a significant influence on the swelling behaviour of clayey soils. Based on the test results obtained, a new swelling potential classification is proposed

APPLIED CLAY SCIENCE

This paper reports the findings of experimental studies on two natural zeolitic soils. Engineering properties (e.g., grain size, specific gravity, compressibility, hydraulic conductivity, swelling behavior and shear strength) were determined in order to assess their suitability for geotechnical and geoenvironmental applications. The two zeolite-rich tuff samples investigated were mainly composed of clinoptilolite. The results show that the cation exchange capacities are 60.5 and 57.2 mEq/100 g, which are below the theoretical reported values. Compression index values obtained reveal that the zeolitic soils are not highly compressible. The modified free swell indexes of the zeolitic samples are around 2.0, suggesting that they have low swelling potential. The drained residual friction angles indicate that the zeolitic soils have relatively high internal friction angles (34 degrees and 36.5 degrees for Z-1 and Z-2, respectively). Based on the results obtained, it was concluded that zeolites are mechanically stable materials that are suitable for embankment materials and landfill liner applications. (C) 2010 Elsevier B.V. All rights reserved