Soil, Water and Environmental Science
Abandoned mine sites are of environmental concern worldwide for their potential to contaminate water resources. The Iron King Mine Dewey-Humboldt Smelter Superfund (IKMDHSS) site in Central Arizona is a 163 hectare historic mine waste site. Arsenic concentrations IKMDHSS tailings exceed 3000 ppm, well above EPA standards for human health. Arsenic has the potential to mobilize from tailings into aqueous systems, a concern because it is known to be toxic at low concentrations. The mobility of arsenic is controlled by pH, dissolved oxygen, dissolved organic matter (DOM), iron (Fe) minerals and surfaces, and microbial activity. The role of DOM on the mobilization of As has been studied in the context of natural aquifer systems (e.g., mass poisoning in SE Asia), but less is known about mining-impacted environments. Efforts have been initiated at IKMDHSS to employ compost-assisted phytostabilization as a means to reduce the dispersion of metal-rich dust into nearby communities (Gil-Loaiza et al., 2016). While this strategy has successfully decreased dust emissions (Saez, 2016), it has created conditions known to be favorable to As mobilization. Heterotrophic microbial respiration under O2 limited conditions can cause the reduction of Fe3+ to Fe2+, enhancing desorption or dissolution of As from Fe containing minerals. Additionally, DOM competes with As for sorption sites at mineral surfaces. In this study, batch experiments were used to investigate the mechanisms of sequestration and release of As in compost amended mine tailings. Mine tailings were reacted in triplicate in the presence and absence of DOM, and under biotic or heterotrophic-respiration suppressed (with NaN3) conditions at timescales from ranging from 24 to 800 hours. Highest arsenic dissolution occurred in the presence of DOM and microbial activity after 24 hours. The release of arsenic was lowest in the control treatment with no DOM added to tailings. To further understand the kinetics of sequestration and release of As from tailing material under conditions matching batch experiments, mini-column flow-through experiments with fractionation collection equipment will be conducted at minutes to month time-scales. We aim to describe the impact of DOM on the mobilization of As from mine tailings. This work will help determine if As may be released to groundwater due to remediation strategies.