Removal of Arsenic, Boron, and Selenium from Excavated Rocks by Consecutive Washing

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This paper describes the leaching behavior and release mechanisms of arsenic (As), boron (B) and selenium (Se) from excavated rocks using sequential extraction for solid-phase fractionation, batch experiments with pH variation, and consecutive batch experiments with changes in the solid-liquid mixing ratios. Arsenic in the excavated rock was mostly found with the sulfides/organic matter fraction while majority of the leachable B and Se were associated with the exchangeable phases. The leaching of As was strongly pH dependent, Se was pH dependent only around the acidic region, and B was pH independent. Consecutive washing technique with deionized water effectively lowered the B and Se concentrations in the leachate below the drinking water standards of Japan, but was inefficient in the removal of As. Arsenic exhibited non-conservative leaching behavior and its movement was affected by processes like dissolution, precipitation and pyrite oxidation. In contrast, B and Se behaved more conservatively, resulting in their easy removal from the excavated rock by simple washing and dilution.