Leaching behavior of heavy metals and metalloids from geomaterials under reducing conditions

- Feasibility of chemical and biological treatments -

Abstract

To establish an evaluation method for the leaching behavior of heavy metals and metalloids from geomaterials exposed to a reducing environment, we simulated a reducing environment by adding 0.01 mol/L sodium ascorbate (chemical method) and 0.17 – 0.34 mol/L organic carbon (biological method), and examined changes in Eh, pH and the leaching concentration of heavy metals. In the excavated rock, the average Eh was −50 mV in the chemical method and −154 mV in the biological method, which was lower than non-additive system (249 mV). Under these conditions, significant increase in leaching concentration of arsenic was not observed. Coal ash mixed material and concrete exhibited Eh values lower than 0 mV with the chemical method, but did not necessarily fall below 0 mV with the biological method regardless of conditions. Since the leaching behavior of heavy metals and metalloids are affected by pH and bacterial activity as well as Eh, these chemical indexes should be carefully evaluated under simulated reducing conditions.