Electrokinetic Remediation Modeling Incorporating Geochemical Effects

Abstract

Electrokinetic remediation technology is one of the developing technologies that offers great promise for the cleanup of soils contaminated with heavy metals. However, the performance of an electrokinetic remediation system depends on the interaction of a complex set of interrelated system variables and parameters. Many of these interactions were addressed in this study by incorporating geochemical reactions into electrokinetic remediation modeling. A one-dimensional transport model was developed to predict the transport and speciation of heavy metals ͑chromium, nickel, and cadmium͒ in soil during electrokinetic remediation as a function of time and space. The model incorporates: ͑1͒ pH-dependent adsorption of contaminants to the soil surface; ͑2͒ sensitivity of soil surface potential and electroosmotic flow to the pore water properties; and ͑3͒ synergistic effects of multiple chemical species on electrokinetic remediation. The model considers that: ͑1͒ Electrical potential in the soil is constant with time; ͑2͒ surface complexation reactions are applicable in the highly concentrated clay suspensions; ͑3͒ the effect of temperature is negligible; and ͑4͒ dissolution of soil constituents is negligible. The predicted pH profiles, electroosmotic flow, and transport of chromium, nickel, and cadmium in kaolin soil during electrokinetic remediation were found to reasonably agree with the bench-scale electrokinetic experimental results. The predicted contaminant speciation and distribution ͑aqueous, adsorbed, and precipitated͒ allow for an understanding of the transport processes and chemical reactions that control electrokinetic remediation.

Electrokinetic Remediation of Zinc and Copper Contaminated Soil: A Simulation-based Study

“…The experimental measurement was not available to validate pH prediction, yet our prediction is consistent with the pH profile in the soil under unenhanced EKR tests reported by others [12,13,23]. In the unenhanced test, pH of a soil near the anode compartment decreased to 2, and near the cathode compartment increased to values around 11 [12,13,18] which is in agreement with pH predicted by our model. Furthermore, as Figure 3.…”

“…Al-Hamdan and Reddy developed a one-dimensional transport model incorporated with geochemical reactions in order to predict the transport of heavy metals in the soil during the unenhanced EKR. They reported good agreement between the simulation results and the experimental measurements [18]. Paz-Garcia et al introduced a finite element numerical implementation based on Petrov-Galerkin scheme for Nernst-Planck-Poisson system of equations for the EKR.…”

“…2) through the tortuosity factor [29]. In the present study the electric field was assumed to be constant during the simulation [18,23].…”

“…We utilized an implicit finite difference, because most of the proposed Electrokinetic models have used finite element methods or explicit finite difference methods. In addition; proposed EKR models based on implicit finite difference used restrictive simplification assumption such as implementing Dirichlet and Neumann boundary conditions without considering flux or electrolysis reactions at the boundaries which do not reflect the reality of the EKR process [18,16]. Thus, in the present study, the realistic boundary conditions with considering the impact of flux and electrolysis reactions were employed.…”

Computing multi-species chemical equilibrium with an algorithm based on the reaction extents

“…(Al-Hamdan & Reddy, 2008;Javadi & Al-Najjar, 2007;Rubin, 1983;Vereda-Alonso et al, 2007). Rate-controlled equilibrium models, which are considered more realistic, include a set of feasible reactions capable to reach the equilibrium in the time scale of the transport process and a parallel solution of the kinetic equations for the slow and/or the irreversible reactions (Koukkari & Pajarre, 2006;Ribeiro et al, 2005;Steyer et al, 2005).…”