An Implicit Finite Difference Model for Electrokinetic Remediation of Cd-Spiked Kaolinite Under Acid-Enhanced and Unenhanced Conditions

A numerical model based on an implicit finite difference method is presented to describe multi-species transport in cadmium-contaminated kaolin under electrokinetic remediation process. A set of algebra and partial differential equations were used to mathematically describe the reactive transport of the target species. We considered different coupled transport phenomena such as diffusion, electroosmotic flow, and ionic migration. Geochemical and electrochemical reactions including precipitation/dissolution, adsorption/desorption, water auto ionization, and electrolysis in anode and cathode cells were included in the model. Simulation results were compared with the available experimental data for electrokinetic remediation of cadmium-contaminated kaolinite. The coefficient of determination (R²) and index of agreement (IA) were calculated to indicate the model accuracy and to compare the present model with the existing explicit finite difference model in the literature. The R² and IA calculation described that the present model had a good capability of simulating the experimental measurement. In addition, it illustrated that the presented implicit finite difference model had a better simulation result than the explicit model. The sensitivity analysis was conducted to understand the impact of tortuosity and retardation factors on the model output. Sensitivity analysis indicated that instead of the acid-enhanced test, the retardation factor had more impact on the unenhanced test. In addition, the sensitivity analysis of tortuosity factor revealed that this parameter had more significant effect on the cadmium concentration rather than pH profile.