RESUMEN
The effect of low frequency pulse current on decreasing the polarization and energy consumption during the process of electrodialytic soil remediation was investigated in the present work. The results indicated that the transportation of cations through the cation exchange membrane was the rate controlling step both in constant and pulse current experiments, thus responsible for the major energy consumption. After 180 h, a decrease in both the initial ohmic resistance in each pulse cycle and the resistance caused by concentration polarization of the anion exchange membrane were seen in the pulse current experiment compared to the constant current experiment. At the cation exchange membrane, only the resistance caused by concentration polarization decreased. In the soil compartment, an average of +60 mV overpotential caused by the polarization of the electric double layer of the clay particles was obtained from the Nernstian behavior simulation of the relaxation process, which was significantly lower than the ohmic voltage drop induced by pore fluid resistance. Therefore, the ohmic polarization was the major contributor to the energy consumption in the soil compartment and diminished by pulse current.
Asunto(s)
Restauración y Remediación Ambiental/métodos , Metales Pesados/química , Contaminantes del Suelo/química , Suelo/química , Electroquímica , Metales Pesados/análisis , Contaminantes del Suelo/análisisRESUMEN
Energy consumption is an important factor influencing the cost of electrodialytic soil remediation (EDR). It has been indicated that the pulse current (in low frequency range) could decrease the energy consumption during EDR. This work is focused on the comparison of energy saving effect at different pulse frequencies. Based on the restoration of equilibrium, the relaxation process of the soil-water system was investigated by chronopotentiometric analysis to find the optimal relaxation time for energy saving. Results showed that the pulse current decreased the energy consumption with different extent depending on the pulse frequency. The experiment with the frequency of 16 cycles per day showed the best restoration of equilibrium and lowest energy consumption. The energy consumption per removed heavy metals was lower in pulse current experiments than constant current and increased with the pulse frequency. It was found that the transportation of cations through the cation exchange membrane was the rate controlling step both in constant and pulse current experiments, thus responsible for the major energy consumption. Substitution of the cation exchange membrane with filter paper resulted in a dramatic decrease in energy consumption, but this change impeded the acidification process and thus the removal of heavy metals decreased significantly.
Asunto(s)
Cadmio/química , Cobre/química , Electroquímica/métodos , Restauración y Remediación Ambiental/métodos , Contaminantes del Suelo/química , Conservación de los Recursos Energéticos , Intercambio IónicoRESUMEN
Electrodialytic remediation (EDR) can be used for removal of heavy metals from suspended soil, which allows for the soil remediation to be a continuous process. The present paper focused on the processing parameters for remediation of a soil polluted with Cu and As from wood preservation. Six electrodialytic treatments lasting from 5 to 22 days with different liquid to solid ratio (L/S) and current intensity were conducted. Among treatments, the highest removal was obtained from the soil fines with 5 mA current at L/S 3.5 after 22 days where 96% of Cu and 64% of As were removed. Comparing the removal from the original soil and the soil fines in experiments with identical charge transportation, higher removal efficiency was observed from the soil fines. Constant current with 5 mA could be maintained at L/S 3.5 for the soil fines while not for the original soil. Doubling current to 10 mA could not be maintained for the soil fines either, and doubling L/S to 7 at 5 mA entailed a very fast acidification which impeded the removal. The results showed that a very delicate balancing of current density and L/S must be maintained to obtain the most efficient removal.