Electrokinetic Injection of Ammonium and Sulfate Ions into Sand and Kaolinite Beds

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Abstract
The efficiency of electrokinetic injection of a cation (ammonium) from the anode and an anion (sulfate) from the cathode into a fine-grained sand bed and a kaolinite bed is investigated. Electrodes are placed in chambers across 80 cm of soil beds in a flume. The electrical conductivity of the kaolinite bed was 124.1 ± 6.6 μS/cm approximately an order of magnitude higher than the fine sand bed while the hydraulic conductivity of the same was 2 × 10−7 cm/s about three orders of magnitude lower than the fine-grained sand bed. The electrical gradients of 1 V/cm or less constituted the predominant driving force for transport under constant current densities of 15 μA/cm2 and 123 μA/cm2 in the sand and kaolinite beds, respectively. An electrolyte conditioning scheme where the co-ions (hydroxide ion in the ammonium hydroxide used at the anode and the hydronium ion in the sulfuric acid used at the cathode) depolarized the electrode reactions maintained the pH value across the beds between 6.5 and 7.4. This novel conditioning scheme prevented formation and introduction of species formed by the electrode reactions and avoided unnecessary increase in the electrical conductivity in the electrolytes. Transport rates on the order of 8–20 cm/d were achieved for sulfate and ammonium ions in both the fine-grained sand bed and the kaolinite bed.

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