Effect of ammonia as a complexing agent on electrokinetic remediation of copper-contaminated soil

Ammonium acetate was used as anolytes in the electrokinetic removal of copper from soil. The electrokinetic experiments were conducted using a rectangular reactor 7.5 cm in width, 10 cm in height, and 11 cm in length. Granular graphite was used as the electrode material. All experiments were conducted under constant current conditions (10 mA). The results show that a high concentration of ammonium acetate (>0.1 M) was needed to sustain electroosmotic flow. The apparent electrical conductivity of the system was dominated by a thin layer of soil (1 cm) close to the cathode. When the ammonium acetate concentration was less than 0.1 M, the apparent electrical conductivity of this soil layer decreased to less than 0.001 S/m and caused large voltage loss. The electroosmotic conductivity of the soil was increased and sustained at 1 × 10−4 cm2/V-s by a high concentration of ammonium acetate, whereas it decreased to less than 1 × 10−6 cm2/V-s when the concentration of ammonium acetate was low. The efficiency of copper removal increased with the concentration of ammonium acetate, reaching 36% after 1 wk of treatment. Most of the un-removed copper was concentrated in the soil close to the cathode. For the 0.5 M ammonium acetate experiment, the volume of copper containing soil was less than 10% of the original soil after treatment. Therefore, a remediation strategy can be developed to first treat the contaminated soil by electrokinetics and then, focus on removing copper from the soil close to the cathode.

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► It increases the fraction of copper removed from the soil.
► Apparent electrical conductivity is increased, which reduces the voltage loss in the soil column.
► Electroosmotic flow was sustained, meaning the process can be applied for long period of time.
► Soil EO conductivity was increased leading to high current/voltage ratio and current efficiency.
► Sustained EO flow can be achieved and used to concentrate contaminants to soil close to the cathode.