Determination of the Optimal Enhancement Concentration for Contaminant Removal from Carbonated Kaolinite in Electrokinetic Remediation

نوع: Type: Thesis

مقطع: Segment: masters

عنوان: Title: Determination of the Optimal Enhancement Concentration for Contaminant Removal from Carbonated Kaolinite in Electrokinetic Remediation

ارائه دهنده: Provider: Sajad Gohari

اساتید راهنما: Supervisors: Vahidreza Ouhadi

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: dr Abas ghadimi - dr mohamad maleki

زمان و تاریخ ارائه: Time and date of presentation: 2025

مکان ارائه: Place of presentation: 45

چکیده: Abstract: Abstract: Electrokinetic technology is an emerging method with significant potential for in-situ and ex-situ remediation of fine-grained soils, whose effectiveness depends on the level of contamination and soil properties. Among the various soil-remediation methods for heavy metal contamination, electrokinetic remediation has emerged as a practical option due to its efficiency in low-permeability soils. Most research in this field has focused on enhancing efficiency and pollutant separation by applying different voltage gradients, adjusting the pH of electrolytes, or injecting chemical agents into the anode and cathode reservoirs. However, studies involving the use of enhancement agents often lack the presentation of an optimized enhancement pattern with the appropriate concentration of these agents—so that while reducing the concentration of enhancement agents, suitable efficiency and uniformity in pollutant removal are still maintained. Additionally, the influence of key parameters such as carbonate content and initial contaminant concentration on the performance of proposed patterns—both in terms of removal efficiency and uniformity—has received less attention. Furthermore, the compatibility of microstructural test results with the main electrokinetic test outcomes has not been thoroughly investigated. Based on this, the general objectives of this research are as follows: • To present an optimized enhancement pattern for the removal of heavy metal contaminants in the electrokinetic method, ensuring that while reducing the concentration of enhancement agents, appropriate efficiency and uniformity of pollutant removal are preserved. • To determine the impact of variations in the concentration of enhancement agents in the cathode reservoir, carbonate removal, and reduction of the initial contaminant concentration on the overall efficiency and uniformity of pollutant removal during the electrokinetic remediation process. To achieve these objectives, the first step of the study involved designing enhancement patterns aimed at optimizing the concentration of enhancement agents (acetic acid and EDTA) along the sample, based on the enhancement patterns introduced in recent research (Farahpour, 2024) and theoretical foundations. In the next step, electrokinetic experiments were conducted to determine the influence of key parameters (carbonate content, initial contaminant concentration, and concentration of enhancement agents in the cathode reservoir) on the overall efficiency and uniformity of contaminant removal along the sample, and to comprehensively evaluate the proposed enhancement patterns under these conditions. Moreover, to assess the compatibility of microstructural test results with the main electrokinetic experiments in terms of contaminant retention phases and the effects of enhancement agents and the electrokinetic process, soil samples after electrokinetic remediation were prepared for Sequential Extraction (SSE) tests. The results from the first phase of the study showed that in certain enhancement patterns, such as aligning the directions of electroosmotic flow, ion migration, and reverse ion migration, it is possible to improve the uniformity coefficient (i.e., more uniform contaminant removal) while approximately maintaining maximum efficiency, by using an optimized concentration of acetic acid to reinforce the acidic front. Additionally, results from combined patterns indicated that by eliminating acid near the cathode (thus reducing chemical consumption), the overall removal efficiency and the uniformity coefficient changed from 55% to 51.3% and from 0.64 to 0.68, respectively. This suggests that to reduce project costs in the electrokinetic method, lower concentrations of acid can be used near the cathode without significantly compromising efficiency and uniformity. Carbonate removal from kaolinite soil significantly improved contaminant removal efficiency. The study showed that reducing carbonate content from 2% to 0% and completely decarbonating the soil sample increased the contaminant removal efficiency by approximately 67% under the baseline condition (without using enhancement agents) and by about 15% when applying the optimized enhancement pattern in the electrokinetic tests. Additionally, the Sequential Extraction experiments demonstrated that the use of the optimized enhancement pattern in electrokinetic tests improved the contaminant removal efficiency by transferring the lead ions retained in the carbonate phase to the exchangeable phase through the use of EDTA as an enhancement agent. Overall, the results of this research not only confirm the proposed patterns in Farahpour's dissertation (2024) but also indicate that by conducting microstructural experiments based on fundamental theories—such as zeta potential, functional groups, contaminant retention phases, and enhancement agents—it is possible to achieve optimized enhancement patterns for kaolinite samples with varying carbonate contents and contaminant concentrations.