Suppression of arsenic leaching from excavated soil and the contribution of soluble and insoluble components in steel slag on arsenic immobilization

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Abstract
A huge amount of soil is excavated by tunnel and road construction projects in urban, coastal, and mountainous regions. These projects enable the effective use of underground spaces, and generally, the excavated soil is expected to be reused after treatment, which is required due to the potential release of geogenic arsenic from the soil. The present study investigated the level of water-soluble arsenic and arsenic phases in excavated soil in order to identify how arsenic is immobilized by soluble calcium and insoluble components in steel slag. The soluble calcium was found to suppress the level of water-soluble arsenic as well as arsenic in fraction 1 (nonspecifically bound) identified by sequential extraction from the soil but increased the level of fraction 2: specifically bound arsenic. The insoluble component did not suppress the level of water-soluble arsenic, but decreased and increased the arsenic levels in fractions 2 and 3 (amorphous iron/aluminum oxide bound), respectively. A column percolation test demonstrated that the arsenic that was inhibited from leaching by the addition of steel slag was the fractions 1 and 2 arsenic. The amounts of arsenic released in the serial batch leaching test were comparable with levels leached regardless of the addition of steel slag. These results indicate that both soluble calcium and insoluble components of steel slag have different roles in suppressing arsenic leaching from excavated soil. Based on these results, it is suggested that steel slag could be utilized to suppress arsenic release, thus enabling the reuse of excavated soil.

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