Restoration Technique for Heavy Metal Polluted Soil by Use of Hydrothermally-Treated Microargae, Chrollera

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Recently, the heavy metal pollution of soil for the site of chemical factory and metal-refining factory have been frequently in trouble. Also, the landfill of fossil fuel ash and municipal incineration ash have caused the pollution of soil and groundwater. In this study, the leaching removal of heavy metals from polluted soil, coal fly ash, and incineration ash was performed by use of hydrothermally-treated natural products, which are abundantly present but so far unused. Firstly, hydrothermally-treated microalga cell (cellulose) were tested, however the resulting matter did not show good leaching ability. Then, pectin, which has a carboxyl group within a molecule, was hydrothermally-treated at various temperature (130-220℃), and the resulting matter was used for a leaching agent. When the treating temperature was 175℃, the best leaching ability for heavy metals in some reference standards of polluted soil was obtained. Such a biochelating agent also effectively worked for the leaching of arsenic from coal fly ash and municipal incineration ash. A squeeze residue of mandarin orange, which contains a lot of pectin, was hydrothermally-treated, and the resulting matter showed a leaching ability similar to that for the hydrothermally-treated pectin. Further, the selective recovery of arsenic from the leaching waste was attempted. It was found that an aluminium-loaded Shirasu-zeolite, which was prepared from an unused resource, Shirasu, in Kagoshima Prefecture, worked as an effective adsorbent for arsenic.