Albert T. Yeung

A review on techniques to enhance electrochemical remediation of contaminated soils

Electrochemical remediation is a promising remediation technology for soils contaminated with inorganic, organic, and mixed contaminants. A direct-current electric field is imposed on the contaminated soil to extract the contaminants by the combined mechanisms of electroosmosis, electromigration, and/or electrophoresis. The technology is particularly effective in fine-grained soils of low hydraulic conductivity and large specific surface area. However, the effectiveness of the technology may be diminished by sorption of contaminants on soil particle surfaces and various effects induced by the hydrogen ions and hydroxide ions generated at the electrodes. Various enhancement techniques have been developed to tackle these diminishing effects. A comprehensive review of these techniques is given in this paper with a view to providing useful information to researchers and practitioners in this field.

Physicochemical soil-contaminant interactions during electrokinetic extraction

The feasibility of using electrokinetics to extract contaminants from soils has been established by bench-scale laboratory experiments and small-scale field tests. However, the physics and chemistry associated with the innovative remediation technology are not yet fully understood. Many physicochemical reactions occur simultaneously during the process. These reactions may enhance or reduce the cleanup efficiency of the process. They are particularly important in fine-grained soils because the large specific surface area of the soil provides numerous active sites for these reactions. In this paper, several prominent physicochemical soil-contaminant interactions during electrokinetic extraction and their influences on the cleanup efficiency of the technology are discussed. These interactions include: (1) change of zeta potential at the soil particle/pore fluid interface; (2) resistance of the soil-fluid-contaminant system to pH change; and (3) sorption/desorption of reactive contaminants onto or from the soil particle surface and precipitation/dissolution of metallic contaminants in the pore fluid. The effects on these interactions of injecting an enhancement fluid into the contaminated soil are also discussed. In addition, a brief review on the state-of-development of the technology is presented.

Field Pullout Testing and Performance Evaluation of GFRP Soil Nails

Glass fiber–reinforced polymer (GFRP) materials provide practical solutions to corrosion and site-maneuvering problems for civil infrastructures using conventional steel bars as reinforcements. In this study, the feasibility of using GFRP soil nails for slope stabilization is evaluated. The GFRP soil nail system consists of a GFRP pipe installed by the double-grouting technique. Two field-scale pullout tests were performed at a slope site. Fiber Bragg grating (FBG) sensors, strain gauges, linear variable displacement transformers (LVDTs), and a load cell were used to measure axial strain distributions and pullout force-displacement relationships during testing. The pullout test results of steel soil nails at another slope site are also presented for comparison. It is proven that the load transfer mechanisms of GFRP and steel soil nails have certain difference. Based on these test results, a simplified model using a hyperbolic shear stress-strain relationship was developed to describe the pullout performance of the GFRP soil nail. A parametric study was conducted using this model to study some factors affecting the pullout behavior of GFRP soil nails, including nail diameter, shear resistance of soil-grout interface, and ratio of interface shear coefficient to the Young’s modulus of the nail. The results indicate that the GFRP soil nail may exhibit excessive pullout displacement and thus a lower allowable pullout resistance than with the steel soil nail.

Design, Fabrication, and Assembly of an Apparatus for Electrokinetic Remediation Studies

This paper presents the design, fabrication, and assembly of a new geo-environmental engineering apparatus specifically made to experimentally evaluate the viability, feasibility, practicality, and economics of electrokinetic extraction of conservative and reactive contaminants from fine-grained soils and to develop a better understanding of the various complex transport processes, electrochemical reactions, and physicochemical soil-contaminant interactions during the process. The design criteria and details of each component of the new apparatus are presented. The distinct advantages of the apparatus developed are discussed. Typical experimental results obtained by the apparatus are presented to demonstrate its simplicity of operation and versatility of measuring various parameters at different spatial and temporal intervals.

Desorption of cadmium from a natural Shanghai clay using citric acid industrial wastewater.

The sorption/desorption characteristics of heavy metals onto/from soil particle surfaces are the primary factors controlling the success of the remediation of heavy-metal contaminated soils. These characteristics are pH-dependent, chemical-specific, and reversible; and can be modified by enhancement agents such as chelates and surfactants. In this study, batch experiments were conducted to evaluate the feasibility of using citric acid industrial wastewater (CAIW) to desorb cadmium from a natural clay from Shanghai, China at different soil mixture pHs. It can be observed from the results that the proportion of cadmium desorbed from the soil using synthesized CAIW is generally satisfactory, i.e., >60%, when the soil mixture pH is lower than 6. However, the proportion of desorbed cadmium decreases significantly with increase in soil mixture pH. The dominant cadmium desorption mechanism using CAIW is the complexion of cadmium with citric acid and acetic acid in CAIW. It is concluded that CAIW can be a promising enhancement agent for the remediation of cadmium-contaminated natural soils when the environmental conditions are favorable. As a result, CAIW, a waste product itself, can be put into productive use in soil remediation.

Effects of Chelating Agents on Zeta Potential of Cadmium-Contaminated Natural Clay

Abstract The effects of pH, ionic strength, cadmium concentration, and chelating agents on the zeta potential of a natural clay of high acid/base buffer capacity from Shanghai, China were investigated in this study, with a view to enhancing the efficiency of electrokinetic remediation of the cadmium-contaminated clay. An increase in the ionic strength of the background solution or cadmium concentration increases the zeta potential on soil particle surfaces, i.e., less negative. CAIW increases the zeta potential slightly but the effects are not pronounced. EDTA and phosphonates decrease the zeta potentials of soil particle surfaces, thus enhancing forward electroosmotic flow.

Fundamental aspects of prolonged electrokinetic flows in kaolinites

Electrokinetic flows include the migration of fluid, chemicals, fine particles, bacteria, and electrons through a soil–fluid–chemical system driven by an externally applied direct-current (d.c.) electric field. The promising potential of electrokinetic remediation of contaminated fine-grained soils has stimulated recent interest in the study of electrokinetic flow processes, in particular the impact of a prolonged application of a d.c. electric field on fine-grained soils. The results of a bench-scale laboratory experimental investigation on some of the fundamental aspects of prolonged electrokinetic flows in kaolinites, including gas generation rates at power electrodes, electrochemical behaviour of the soil–fluid–chemical system, time variation of electric current intensity flowing through the soil, pH gradient development in the soil, effects of reservoir chemistry on electro-osmotic fluid volume flow rate and flow direction through the soil, time variation of electro-osmotic volume flow rate, and energy requirements per unit volume of fluid transported, are presented in this paper. Effects of soil type and pore fluid chemistry on these aspects were also studied.

Remediation Technologies for Contaminated Sites

Contaminated sites can pose a significant risk to public health and the environment. Many different insitu or ex-situ remediation technologies have been developed throughout the years to mitigate the risk imposed by soil contamination. These technologies may be contaminant and site specific. Remediation can be achieved by contaminated soil removal, contaminant removal, containment, stabilization/solidification, transformation, or different combinations of these mechanisms. It may also be necessary to apply these technologies in combination to achieve remediation goals, in particular, for cases of contamination by multiple contaminants. Some of the remediation technologies currently available are presented in this invited lecture, in particular, the theory, state of development, applicability, limitations, remediation efficiency, cost effectiveness, and potential side effects of the remediation technologies are presented. Details of performance monitoring are described, criteria on selection of the appropriate remediation technology are given, and remediation cost estimate procedure is outlined. As innovative remediation technologies are being developed continuingly to satisfy various needs, the technologies presented in this invited lecture are by no means exhaustive. Nonetheless, a comprehensive list of references is given for readers interested in particular technologies to conduct their further exploration.

A New Apparatus for the Evaluation of Electro-Kinetic Processes in Hazardous Waste Management

Possible uses of electro-kinetics for hazardous waste site remediation are being investigated. This paper describes a new apparatus which has been specifically designed, fabricated, and assembled to evaluate the viability, feasibility, practicality, and potential costs of these conceivable techniques experimentally. Results of studies on the existence of electro-osmotic flow in compacted clay and the electro-kinetic barrier to contaminant transport are used to illustrate the types of information that can be obtained by the apparatus.

A New Laboratory Apparatus for Grout Injection Studies

The design, fabrication, and assembly of a new laboratory apparatus for the investigation of fundamental behavior of compaction grouting and fracture grouting are presented in this paper. Clayey soil specimens of different overconsolidation ratios can be prepared to study the grout deformation pattern, fracture pattern, and consolidation behavior of soil induced by grout injection as a function of operating parameters. Ideal compacting grouting is replicated by expanding a latex balloon placed within the soil specimen and fracture grouting by injecting epoxy resin or high water content cement bentonite grout into the soil specimen. Moreover, the apparatus can accommodate multiple-point grout injection experiments to examine the behavior of grout interactions. Illustrative results are also presented in the paper.