Abstract

Some troubles of arsenic leaching and acid water drainage from natural ground have been reported at mainly terrestrial sediments in volcanic arcs. Arsenic is abundant in volcanic ejecta on the forearc side of the volcanic front. Volcanic terrestrial sediments have accumulated on the marine sediment, and recycling arsenic has been confirmed in the subduction zone. The interaction of arsenic and marine sediment clay particles are also important to understand soil contamination processes on land by arsenic. The sediments in the Kazusa Group, which were well explored stratigraphically volcanic ash stratum as the key bed, were marine sediments from the late Pliocene to the middle Pleistocene. The concentrations of sulfur and some heavy metal elements in these were related to sedimentation depth.

The concentrations of arsenic in leachate and of arsenic and sulfur in rock samples were analyzed, and these maximum concentrations were 0.08 mg/L, 84 mg/kg and 1.8 wt.% respectively. There is a remarkable relationship between stratigraphy and sulfur content, recognizing the geochemical differences between fresh and weathered sediments. The sulfur and arsenic are distributed in framboidal pyrite crossing to pumice particles in the sediments. Pyrites included in the sediments were divided in three types. Framboidal pyrites in open space had highest arsenic concentration. We could confirm the change of arsenic leaching ratio and pH in leachate water from sediments using thermo-dynamic simulator “PRHEEQC”. This result suggests that arsenic leaching and acid water drainage from sediments accrue from dissolution of pyrite. The proposed method could predict the phenomenon caused by dissolution of framboidal pyrite such as arsenic leaching and acid water drainage. The Sustainable Development Goals (SDGs) involve a goal, for efforts to reduce soil pollution, and the importance of effectively utilizing the generated soil as a construction by-product is increasing.

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