Utilization of pyritic tailings to mitigate arsenic mobilization in groundwater

The ability of arsenic in solution to coprecipitate with iron and manganese oxyhydroxides is fundamental to arsenic removal or stabilization at various waste water treatment facilities. Arsenic can be problematic in certain mine/mill tailings and at smelter sites as arsenic trioxide associated with flue dust. Research was conducted at a Superfund site where arsenic trioxide from flue dust left residues in soils and a shallow alluvial aquifer. Arsenic manifestation in the alluvial aquifer ceased upon interception of pyritic mine tailings down-gradient of the flue dust. Investigations were conducted to determine the effect of tailings stabilization for arsenic plume migration. Results of column testing on core containing pyritic and oxidized mine tailings show a significant adsorption of arsenic when spiked from solution originating from the up-gradient, flue dust. Source effluent was generated by leaching arsenic enriched soils and flushing columns containing pyritic-derived iron-oxyhydroxides. Evidence supports that iron-rich tailings provide a suitable host medium for arsenic stabilization and that desorption may not be a concern under normal conditions of pH and Eh. Several States have established stricter standards for arsenic effluent discharges from mine sites than municipal water treatment facilities. Many base and precious metals deposits have local arsenic-enriched zonation that can be problematic for mine operators due to these more restrictive regulations. Acid Rock Drainage (ARD) mitigation in such areas may result in temporary stabilization of arsenic as calcium arsenate complexes. These arsenates are relatively unstable under saturated, neutral pH conditions. Selective staging of pyritic tailings to intercept arsenic effluent will result in a stable assemblage of arsenic mineral complexes.