Theoretical and Experimental Modeling of Removing Contaminants From Soils by an Electric Field.

A mathematical model is formulated for multicomponent transport of reactive species under an electric field. A set on differential and algebraic equations is developed for transport of fluid, charge, and species in a saturated soil under coupled hydraulic, electric, and chemical potential gradients. An iterative scheme is chosen in solution of a system of differential and algebraic equations. Six differential equations and four algebraic equations are used to model transport of Pb\sp{2+}, H\sp+, OH\sp-, NO3\sp-, the associated chemical reactions, electric potential and the hydraulic head across the electrodes. Finite Element Method is used in space discretization. Finite difference technique is used in time discretization. Three unenhanced pilot-scale tests, using about one ton soil specimens, are conducted to investigate the effect of up-scaling bench-scale tests, to evaluate the feasibility and cost efficiency of electrokinetic soil remediation at dimensions representative of field conditions, and to assess the hypothesized principles of multicomponent species transport under an electric field. Two of these tests are conducted on kaolinite specimens spiked with lead nitrate solution at lead concentrations of 856 $\mu g/g$ and 1,533 $\mu g/g$. The third test is conducted on kaolinite/sand mixture loaded with lead at a concentration of 5,322 $\mu g/g$. A direct current density of 133 \mu A/cm\sp2 is maintained across the soil in all pilot-scale tests. Pilot-scale tests demonstrate significant lead removal from soil, up to 98% except the soil zone in direct contact with the cathode. Energy expenditure in these tests is within the range of 300 to 700 kWh/m\sp3. The results demonstrate the feasibility of using electrokinetics for full-scale in-situ remediation of heavy metals from soil. Model predictions show very good agreement with the pilot-scale test results. This agreement demonstrates the validity of the formalisms offered for multicomponent transport of reactive species under an electric field and reinforces the validity of the hypothesized principles of electrokinetic remediation

Cross-Well Radar I: Experimental Simulation of Cross-Well Tomography and Validation

This paper explains and evaluates the potential and limitations of conducting Cross-Well Radar (CWR) in sandy soils. Implementing the experiment and data collection in the absence of any scattering object, and in the presence of an acrylic plate (a representative of dielectric objects, such as DNAPL (dense non-aqueous phase liquid) pools, etc.), as a contrasting object in a water-saturated soil is also studied. To be able to image the signature of any object, more than one pair of receiving and transmitting antennas are required. The paper describes a method to achieve repeatable, reliable, and reproducible laboratory results for different transmitter-receiver combinations. Different practical methods were evaluated for collecting multiple-depth data. Similarity of the corresponding results and problems involved in each method are studied and presented. The data show that the frequency response of a saturated coarse-grained soil is smooth due to the continuous and dominant nature of water in saturated soils. The repeatability and potential symmetry of patterns across some borehole axes provide a valuable tool for validation of experimental results. The potential asymmetry across other borehole axes is used as a tool to evaluate the strength of the perturbation on the electromagnetic field due to hidden objects and to evaluate the feasibility of detecting dielectric objects (such as DNAPL pools, etc.) using CWR. The experimental simulation designed for this paper models a real-life problem in a smaller scale, in a controlled laboratory environment, and within homogenous soils uniformly dry or fully water-saturated, with a uniform dielectric property contrast between the inclusion and background. The soil in the field will not be as homogenous and uniform. The scaling process takes into consideration that as the size is scaled down; the frequency needs to be scaled up. It is noteworthy that this scaling process needs to be extensively studied and validated for future extension of the models to real field applications. For example, to extend the outcome of this work to the real field, the geometry (antennas size, their separation and inclusion size) needs to be scaled up back to the field size, while soil grains will not scale up. Therefore, soil, water and air coupling effects and interactions observed at the laboratory scale do not scale up in the field, and may have different unforeseen effects that require extensive study

Electromagnetic Waves in Contaminated Soils

Soil is a complex, potentially heterogeneous, lossy, and dispersive medium. Modeling the propagation and scattering of electromagnetic (EM) waves in soil is, hence, more challenging than in air or in other less complex media. This chapter will explain fundamentals of the numerical modeling of EM wave propagation and scattering in soil through solving Maxwell’s equations using a finite difference time domain (FDTD) method. The chapter will explain how: (i) the lossy and dispersive soil medium (in both dry and fully water-saturated conditions), (ii) a fourth phase (anomaly), (iii) two different types of transmitting antennae (a monopole and a dipole), and (iv) required absorbing boundary conditions can numerically be modeled. This is described through two examples that simulate the detection of DNAPL (dense nonaqueous-phase liquid) contamination in soil using Cross-well radar (CWR). CWR —otherwise known as cross-borehole GPR (ground penetrating radar)—modality was selected to eliminate the need for simulation of the roughness of the soil-air interface. The two examples demonstrate the scattering effect of a dielectric anomaly (representing a DNAPL pool) on the EM wave propagation through soil. The objective behind selecting these two examples is twofold: (i) explanation of the details and challenges of numerical modeling of EM wave propagation and scattering through soil for an actual problem (in this case, DNAPL detection), and (ii) demonstration of the feasibility of using EM waves for this actual detection problem

Cross-Well Radar II: Comparison and Experimental Validation of Modeling Channel Transfer Function

Close agreement between theory and experiment is critical for adequate understanding and implementation of the Cross-Well Radar (CWR, otherwise known as Cross-Borehole Ground Penetrating Radar) technique, mentioned in a previous paper by the authors. Comparison of experimental results to simulation using a half-space dyadic Green’s function in the frequency domain requires development of transfer functions to transform the experimental data into a compatible form. A Channel Transfer Function (CTF) was developed to avoid having to model the transmitting and receiving characteristics of the antennas. The CTF considers electromagnetic (EM) wave propagation through the intervening media only (soil in this case), and hence corresponds to the simulation results that assume ideal sources and receivers. The CTF is based on assuming the transmitting antenna, soil, and receiving antenna as a cascade of three two-port microwave junctions between the input and output ports of the Vector Network Analyzer (VNA) used in the experimental measurements. Experimentally determined CTF results are then compared with computational model simulations for cases of relatively dry and saturated sandy soil backgrounds. The results demonstrate a reasonable agreement, supporting both the model and CTF formulation

Ultrasound-assisted electrodialytic separation of cobalt from tungsten carbide scrap powder

Funding Information: Fundação para a Ciência e a Tecnologia is also acknowledged for P. Guedes Contract established under Individual Call to Scientific Employment Stimulus (CEECIND/01969/2020). The US Strategic Environmental Research and Development Program (project ER19-1130); the Superfund Research Program of the National Institute of Environmental Health Sciences (NIEHS, National Institutes of Health) (NIH; grant number P42ES017198). João P. Veiga from CENIMAT/I3N at FCT NOVA is also acknowledged for the XRF analysis. This research is anchored at RESOLUTION LAB, an infrastructure at NOVA School of Science and Technology. Publisher Copyright: © 2024 The AuthorsRecycling of tungsten carbide-cobalt (WC–Co) will considerably grow in the future. Thus, efficient and greener methods for the recovery of the critical raw materials, Co and W, will be necessary. In this work, we evaluate the separation of Co from WC using an electrodialytic (ED) process alone and coupled with ultrasound-assisted extraction (UAE). The WC-Co powder was suspended in different leaching agents, and the effects of UAE amplitude (probe system), pulse periods, and treatment time were evaluated. The Co extraction was mainly dependent on the leaching agent when only UAE was applied, being more efficient under acidic pH. The ED process, alone and coupled to UAE, was then applied using a reactor with two compartments separated by a cation exchange membrane with nitric acid as anolyte; and the effect of DC intensity was tested for Co separation from WC. Between 24 % and 58 % of Co were solubilized when ED was applied alone, but these values increased up to 96 % through the combination with UAE. The ED process was also applied without the use of nitric acid, taking advantage of the acid generated through water electrolysis, aiming for a more environmentally friendly process. The best Co selective recovery was achieved when ED-UAE was used, reaching 99 % of Co solubilization and 90 % of the total Co electromigration to the cathode compartment, leaving behind the WC residue at the anode. The ED-UAE process presents as a greener process for Co separation from WC residues, with further tests needed to include W recovery.publishersversionpublishe

Experimental Validation of a Numerical Forward Model for Tunnel Detection Using Cross-Borehole Radar

The goal of this research is to develop an experimentally validated twodimensional (2D) finite difference frequency domain (FDFD) numerical forward model to study the potential of radar-based tunnel detection. Tunnel detection has become a subject of interest to the nation due to the use of tunnels by illegal immigrants, smugglers, prisoners, assailants, and terrorists. These concerns call for research to nondestructively detect, localize, and monitor tunnels. Nondestructive detection requires robust image reconstruction and inverse models, which in turn need robust forward models. Cross-Well Radar (CWR) modality is used for experimentation to avoid soil-air interface roughness. CWR is not a versatile field technology for political boundaries but is still applicable to monitoring the perimeter of buildings or secure sites. Multiple-depth wideband frequency-response measurements are experimentally collected in fully water-saturated sand, across PVC-cased ferrite-bead-jacketed borehole monopole antennae at a pilot scale facility (referred to as SoilBED). The experimental results are then compared with the 2D-FDFD model. The agreement between the results of the numerical and experimental simulations is then evaluated. Results of this work provide key diagnostic tools that can help to develop the algorithms needed for the detection of underground tunnels using radar-based methods

Equivalent porous media (EPM) simulation of groundwater hydraulics and contaminant transport in Karst aquifers

Karst aquifers have a high degree of heterogeneity and anisotropy in their geologic and hydrogeologic properties which makes predicting their behavior difficult. This paper evaluates the application of the Equivalent Porous Media (EPM) approach to simulate groundwater hydraulics and contaminant transport in karst aquifers using an example from the North Coast limestone aquifer system in Puerto Rico. The goal is to evaluate if the EPM approach, which approximates the karst features with a conceptualized, equivalent continuous medium, is feasible for an actual project, based on available data and the study scale and purpose. Existing National Oceanic Atmospheric Administration (NOAA) data and previous hydrogeological U. S. Geological Survey (USGS) studies were used to define the model input parameters. Hydraulic conductivity and specific yield were estimated using measured groundwater heads over the study area and further calibrated against continuous water level data of three USGS observation wells. The water-table fluctuation results indicate that the model can practically reflect the steady-state groundwater hydraulics (normalized RMSE of 12.4%) and long-term variability (normalized RMSE of 3.0%) at regional and intermediate scales and can be applied to predict future water table behavior under different hydrogeological conditions. The application of the EPM approach to simulate transport is limited because it does not directly consider possible irregular conduit flow pathways. However, the results fromthe present study suggest that the EPM approach is capable to reproduce the spreading of a TCE plume at intermediate scales with sufficient accuracy (normalized RMSE of 8.45%) for groundwater resources management and the planning of contamination mitigation strategies