定電流密度条件下での動電学的手法による土壌からのカドミウムの浄化

Abstract

Restoration of contaminated soils to an environmentally acceptable condition is important. One of the newer techniques in soil remediation is a method based on electrokinetic phenomena in soils. The technology uses electricity to affect chemical concentrations and water flow through the pores of soils. An important advantage of electrokinetic soil remediation over other in-situ processes such as soil flushing is the capability of control over the movement of the contaminants. Because the migration of the contaminants is confined by the electric field, there is little dispersion outside the treatment zone. Furthermore, the process is effective for soils with low and variable permeability.In the present study, the distributions of cadmium concentration, pH and the electrical potential in the electrokinetic processing of kaolinite under the condition of constant current density are investigated. The results obtained in this study are summarized as follows:Cadmium accumulates near the cathode without reducing the diffusion of hydroxide ions into the soil. The electrical potential across the soil column increases with an increase in the processing time, particularly at the time between 96 and 144 hr in this study. However, the electrical potential remains nearly constant thereafter. The increase in electrical potential across the soil column is due to the formation of cadmium hydroxide near the cathode. In keeping the catholyte pH at neutrality, cadmium migrates toward the cathode without any accumulation of cadmium near the cathode and is successfully removed at the cathode reservoir. The electrical potential across the soil decreases with the increase of the processing time and the velocity of cadmium ion decreases. It was also found that the progress of electrokinetic processing of cadmium could be grasped to a certain extent by monitoring the local voltage.