Behavior of hazardous metal(loid)s release from excavated marine sedimentary rock under atmospheric exposure with drying-wetting cycles

Large amounts of marine sedimentary rock are excavated for the construction of modern high-speed railways and roads, and they pose environmental risk due to the release of hazardous metal(loid)s. It is therefore important understand how hazardous metal(loid)s are released from excavated rock. This study investigated the influences of alteration surface structure of excavated rock induced by atmospheric exposure with drying-wetting cycles on the release of hazardous metal(loid)s. The atmospheric exposure with the drying-wetting cycles caused the particle size reduction, but not carbonation. In addition, it induced the oxidation of framboidal pyrite, resulting in the increase in the sulfate ion release and decrease in the pH in the excavated rock. The amount of amorphous iron content decreased with the increase in the period of atmospheric exposure. The amounts of arsenic, lead, and fluoride ion release were decreased with the increase in the period of atmospheric exposure, while those of selenium was gradually increased. The amount of boron release was stable during the atmospheric exposure. On the basis of these results, this study suggests that the atmospheric exposure with the drying-wetting cycles enhances/suppresses the release of hazardous metal(loid)s from the excavated rock.