Abstract
Electrokinetic remediation is a useful technique for the removal of ionic contaminants in soils, sediments, sludges, and other solid porous matrixes. The efficiency of metal removal and the electricity consumption in the electrokinetic treatment of soils largely depend on electric and physicochemical conditions. This study analyzes the electrokinetic treatment of Mn contaminated kaolinite clay specimen and the influence of voltage, current intensity, moisture content, pH, and facilitating agents on metal removal and energy consumption. The objective of this study is to identify the influence of the typical variables used in electrokinetic remediation. The results showed that the operation at constant voltage or constant current intensity were equivalent in terms of metal removal and energy consumption, as long as the electric field intensity was kept low to minimize the consumption in parallel electrochemical reactions, especially the electrolysis of water. The moisture content had a significant influence on the Mn removal. Moisture content higher that 50 percent resulted in very effective Mn removal as compared with kaolinite specimens with lower moisture. The control of pH in the electrolyte solutions and the addition of facilitating agents (organic acids) enhanced the removal of Mn but increased the electric energy cost. Overall, the best conditions for Mn removal involved low to moderate electric potential difference (10 to 30 V), the use of citric acid as the facilitating agent, and the pH control in the cathode at a slightly acid pH. The electrokinetic treatment of a sludge from a water treatment plant contaminated with Mn was effective when pH control on the cathode was used. Mn and various metals (66% of Mn, 30% of Cu, 56% of Zn, 21% Sr, and 21% of Fe) were removed with moderate electricity and acid consumption.
Highlights
Electrokinetic remediation is a soil decontamination technology extensively studied from the 1990s in the twentieth century
The electromigration of Mn in contaminated kaolinite specimen was firstly tested at a constant electric potential gradient of 30 V. This value was selected based on previous electrokinetic tests with metal contaminated kaolinite [8,28] where it was found that 3 DcV/cm was an appropriate voltage gradient for effective removal of metals
The electrokinetic removal of Mn from model kaolinite samples and real industrial sludge is effective under the following selected operating conditions:
Summary
Electrokinetic remediation is a soil decontamination technology extensively studied from the 1990s in the twentieth century. The electrokinetic treatment of contaminated soils is based on the application of a low intensity electric field directly to the soil with two main electrodes, i.e., anode and cathode. The contaminants are removed by two main mechanisms, electromigration (the transport of ions towards the electrode of opposite charge) and electroosmosis (a net flux of water and interstitial fluid induced by the electric field, the interstitial fluid, flows towards the cathode in electronegatively charged soils). The main reactions induced by the electric field are the electrolysis of water that generates H+ ions in the anode and OH− ions in the cathode.
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