底質の風乾過程における重金属の挙動

Abstract

Heavy metals in sediment are oxidized under aerobic condition and then changed into other chemical forms in process of airdrying of river sediment. In order to investigate the behavior of heavy metals in the sediment during this process, heavy metals and sulfate ion were extracted from sediment with distilled water and dilute hydrochloric acid. Concentrations of heavy metals and sulfate ion in the extracted solution were determined by atomic absorption spectrometry and colorimetry, respectively. pH and oxidation-reduction (rodox) potential of the sediment were measured and sulfide content was determined by titrimetry. In the airdrying process of the sediment, pH was decreased and rodox potential was increased. According as increasing of rodox potential, sulfide content of sediment was decreased and sulfate was increased. All of ferrous iron was oxidized to ferric before rodox potential reached to +50 mV (Ehsce). Cadmium, zinc and copper were changed from sulfide into sulfate in the airdrying process and it resulted in increasing of their solubilities in water. In the case of cadmium, water-soluble chemical form in the air-dried sediment was more than 17% of the total content. Therefore, on the disposal of dredged sediment containing a large amount of cadmium, cadmium could dissolved from dredged sediment into rain water and the pollution by cadmium is possibly expected.