Yalcin B. Acar

Electrokinetic remediation: Basics and technology status

Abstract Electrokinetic remediation, variably named as electrochemical soil processing, electromigration, electrokinetic decontamination or electroreclamation uses electric currents to extract radionuclides, heavy metals, certain organic compounds, or mixed inorganic species and some organic wastes from soils and slurries. An overview of the principals of the electrokinetic remediation technique in soils is presented. The types of waste and media in which the technology could potentially be applicable are outlined and some envisioned environmental uses of conduction phenomena in soils under electric fields are presented. The current status of the electrokinetic remediation technique and its limitations are discussed through a review of the bench-scale and pilot-scale tests. The recent findings of research on different techniques that may improve the technologys effectiveness are mentioned and the status of ongoing efforts in wide-scale implementation and commercialization of the technique in the USA are described.

ENHANCED ELECTROKINETIC REMEDIATION OF HIGH SORPTION CAPACITY SOIL

Abstract In unenhanced electrokinetic remediation of metals, electrolysis reactions at the cathode generate a high pH medium that results in metal precipitation and immobilization in the soil. Different enhancement procedures could be utilized at the electrodes to prevent or hinder the generation and transport of this alkaline medium into the soil. This study investigates the feasibility of enhanced extraction of metals from high sorption capacity soils by the use of acetic acid to neutralize the cathode electrolysis reaction and also the use of an ion selective (Nafion TM ) membrane to prevent back-transport of the OH − generated at the cathode. Synthetic soil samples spiked with lead were used in the testing. Synthetic soils were a mixture of 40% illite, 8% kaolinite, 5% Na-montmorillonite and 47% fine sand representing an illitic deposit. The results demonstrate the feasibility of extracting lead from the deposit. Acetic acid and Nafion enhancement resulted in better removal efficiencies and lead electrodepositions at the cathode compared to unenhanced tests. However, higher energy expenditure and longer processing periods were required when compared to enhanced extraction of lead from kaolinite. Acetic acid tests required less energy than membrane tests.

Removal of contaminants from soils by electrokinetics: A theoretical treatise

Abstract Feasibility and cost‐effectiveness of electrokinetic soil processing in the remediation of contaminated clayey soils has been demonstrated by bench‐scale studies and limited pilot‐scale studies. A review of the fundamentals controlling the process demonstrates that contaminant transport and removal by electrokinetics are dependent on several factors including electrode reactions, pH and surface chemistry of the soil, equilibrium chemistry of the aqueous system, electrochemical properties of the contaminants and hydrological properties of the soil medium. Chemical, hydraulic and electrical fluxes in electrokinetic processing are formalized. A theoretical model describing reactive solute transport is developed in a coupled system of differential/algebraic equations. Considerations for solutions are discussed. An important factor in the removal of contaminants is the transport of the acid front developed by the anode reaction. The basic equation describing the pH distribution resulting from electrod...

Fundamentals of extracting species from soils by electrokinetics

Abstract Bench-scale and pilot-scale studies demonstrate that ionic contaminant species, some organic contaminants, and certain radionuclides can be removed efficiently from fine-grained deposits by application of electrical currents across a soil mass, through electrodes that allow gress and ingress of a pore fluid. This technique (electrokinetic remediation or electrochemical soil processing) results in soil acidification, contaminant desorption, transport, accumulation, and removal. A review of the fundamentals of the process and the theoretical development, together with a review of considerations and limitations for full-scale application of the technique for site remediation, are presented.

Pull-out resistance of geogrid reinforcements

Abstract Testing equipment, specimen preparation and testing procedures are presented for load-controlled and displacement-rate-controlled pull-out tests for geosynthetic reinforcements in granular soils. The influence of the test type, confining pressure, soil density, boundary conditions, and geotextile characteristics on pull-out load-displacement response of selected geogrids embedded in sand are evaluated. Implications for testing procedure and analysis are discussed.

Electrochemical processing of soils: Theory of pH gradient development by diffusion, migration, and linear convection

Abstract A theory, based on the Nernst‐Planck equations, is presented for pH gradient development during the electrochemical processing of soils. Its premises and consequences are discussed in terms of using electrochemical techniques for the decontamination of polluted media. Formation of an acidic front at the anode from water electrolysis and the induced electro‐osmotic flow of pore fluid contribute to facilitate removal of contaminants. The model provides a first‐order, mathematical framework to examine the flow patterns and chemistry generated in electro‐osmosis. Analytical solutions are compared with the numerical results obtained by the finite element method (FEM) and with some preliminary experimental results. Upstream‐downstream effects are included but consolidation effects, neutralization, and ion exchange reactions need to be quantified and incorporated into the model. The physical basis of electro‐osmosis phenomenon needs to be better established. Modelling approaches of this type should assi...

ELECTROKINETIC SOIL PROCESSING COMPLICATING FEATURES OF ELECTROKINETIC REMEDIATION OF SOILS AND SLURRIES: SATURATION EFFECTS AND THE ROLE OF THE CATHODE ELECTROLYSIS.

Abstract Electrokinetic soil processing is an emerging technology for decontamination of certain radionuclides, heavy metals, or organic species from soils or slurries. Tests reveal that the process efficiencies in partially saturated kaolinite samples (without contaminants) are high, since water supplied at the anode eventually flushed across the specimens and saturated the deposits. Consolidation settlements are expected in the vicinity of anodes in fine-grained soils, even when both electrodes allow ingess or egress of the water. Uranyl ion at 1000 pCi/g could be effectively removed from kaolinite but the removal efficiency decreased close to the cathode due to the high pH in this region. A yellow uranium hydroxide precipitate was collected at the cathode. Thorium ion, even at 300 pCi/g, could not be efficiently removed throughout the cell because of its high adsorptive capacity, facile hydrolysis, and the precipitation of insoluble hydroxide. Methods are required to prevent hydroxide ion formation by ...

Surfactant Enhanced Desorption of TNT from Soil

Surfactant enhanced desorption of 2,4,6-trinitrotoluene (TNT) from contaminated soils at a military site was investigated. Anionic (SDS and DOWFAX 8390), cationic (CTAC and CTAB), and nonionic (Tween 80 and Brij 35) surfactants were first tested at concentrations ranging from 0.1 to 1%. The anionic and nonionic surfactants were further tested at concentrations of up to 10%. Anionic surfactants, particularly SDS, provided the best desorption of TNT from the soil. There was not any increase in TNT desorption for both the nonionics and cationics at concentrations ranging between 0.1 to 1% and the extent of desorption was found to be lower than the TNT desorption only by water. The competition of the negatively charged soil surfaces for the positively charged cationics and the neutral nonionic surfactants may constitute the underlying reason. TNT was significantly desorbed when the concentrations of Tween 80, DOWFAX 80 and SDS were increased up to 10%.

Low strain dynamic shear modulus of cemented sand from cone penetration test results

Low strain dynamic shear modulus property is generally used to subclassify soil strata, determine elastic settlements under geotechnical structures, and characterize the dynamic nature of soils. Several methods to interpret the dynamic shear modulus of sands from in situ friction cone test results have been developed. These methods used calibration chamber test data of clean sands. Therefore, these methods are not valid for interpreting the shear modulus of cemented sands. Introduced here is an interpretation method to estimate the shear modulus of cemented sand. Thirty-seven friction cone penetration tests (CPTs) were conducted on artificially cemented sand specimens of relative densities ranging from 45 percent to 85 percent and confining pressures ranging from 100 to 300 kPa in a laboratory stress-straincontrolled calibration chamber. Cementation levels of 1 and 2 percent were used in preparing cemented specimens. Resonant column tests were also conducted on the same sand with identical cementation lev...

Calibration of a Dynamic Penetrometer for Compaction Quality Control of Boiler Slag

A dynamic penetrometer was designed for the purpose of evaluating compaction quality in fills constructed with boiler slag. Laboratory and field calibration tests were conducted to study the effect of densification on dynamic penetration resistance. The effects of specimen preparation method (pluviation and impact compaction) and saturation on dynamic penetration resistance were investigated in the laboratory. A 0.91-m (3-ft)-deep test fill with dimensions of 6.1 m (20 ft) by 30.5 m (100 ft) was prepared in the field. Dynamic penetration resistance and in situ densities were recorded in this slag fill after 0, 2, 4, 6, 10, and 16 passes of a smooth drum vibratory roller of 5.6 tons (11.2 kips). The field-resistance values were compared with laboratory values. Charts are provided to aid both in selecting the lift thickness/number of roller passes and also for field assessment of densification in boiler slag using the dynamic penetrometer.