ELECTROKINETIC INJECTION OF AMMONIUM AND SULFATE-IONS INTO SAND AND KAOLINITE BEDS

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 i n chambers across 80 cm of soil beds in a flume. The electrical conduc tivity of the kaolinite bed was 124.1 +/- 6.6 mu S/cm approximately an order of magnitude higher than the fine sand bed while the hydraulic conductivity of the same was 2 x 10(-7) cm/s about three orders of mag nitude lower than the fine-grained sand bed. The electrical gradients of 1 V/cm or less constituted the predominant driving force for transp ort under constant current densities of 15 mu A/cm(2) and 123 mu A/cm( 2) in the sand and kaolinite beds, respectively. An electrolyte condit ioning scheme where the co-ions (hydroxide ion in the ammonium hydroxi de used at the anode and the hydronium ion in the sulfuric acid used a t the cathode) depolarized the electrode reactions maintained the pH v alue across the beds between 6.5 and 7.4. This novel conditioning sche me prevented formation and introduction of species formed by the elect rode reactions and avoided unnecessary increase in the electrical cond uctivity 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.