Utilization of natural and artificial adsorbents in the mitigation of arsenic leached from hydrothermally altered rock

We have developed the adsorption-layer system for the simple and effective disposal of excavated rocks containing hazardous pollutants like arsenic (As). In this study, adsorption properties of natural and artificial materials including their performance in an actual altered rock-adsorption layer setup were evaluated. The adsorption of As[V] and As[III] onto all adsorbents fitted well with the Langmuir isotherm, indicating monolayer adsorption and progressive saturation of adsorption sites. All adsorbents were capable of As[V] and As[III] sequestration, but As[V] was more strongly adsorbed than As[III] based on the Langmuir isotherm. Also, artificial adsorbents were more efficient per unit weight than the natural adsorbent. Using the Langmuir isotherms and sequential extraction results, appropriate adsorbent dosages were estimated and then applied to an actual altered rock-adsorption layer column setup. The leaching concentration of As was lowered below 10 μg/L throughout the experiment regardless of the kind of adsorbent used. This suggests that the adsorption-layer system is a promising alternative to special landfills in the disposal of excavated rocks enriched with As.