Transport and attenuation of metal(loid)s in mine tailings amended with organic carbon: Column experiments

A laboratory-scale column experiment was conducted to evaluate the effect of organic carbon amendments on the mobility of As, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Tl and Zn in mine tailings. Three columns were packed with sulfide- and carbonate-rich tailings, which were amended with a 1:1 (vol.) mixture of peat and spent brewing grain at proportions of 0, 2 and 5 vol. %. A simulated input solution characterized by circumneutral pH and elevated concentrations of SO4 and S2O3 was passed through the columns for 540 days. The input solution contained low concentrations of metal(loid)s during the initial 300 days and elevated concentrations thereafter. Decreases in mass transport of S2O3 were observed in all columns; with increased attenuation observed at 5 vol. % organic carbon content. Removal of Mn, Ni, Cu, Sb and Mo was observed in all columns during the initial 300 days. However, during this time, mobilization of Fe, As, Zn and Pb was observed, with the greatest increases in concentration observed at the higher organic carbon content. During the final 240 days, S2O3 removal was enhanced in columns containing organic carbon, and Fe, Mn, Ni, Tl, As and Sb removal also was observed. This study demonstrates the influence of organic carbon amendments on metal(loid) mobility in mine tailings. Decreases in mass discharge of metal(loid)s may be achieved using this technique; however, site-specific geochemical conditions must be considered before field-scale implementation.

Research highlights
► Examined metal(loid) transport and attenuation in organic carbon amended tailings.
► Initial release of SO4, Zn, Fe, Ni, Pb and As from amended tailings and control.
► Direct relationship between initial Fe and As mobilization and amendment rate.
► Attenuation of S2O3, Mn, Ni, Pb, Cu, Tl and Sb enhanced in amended columns.
► Metal-sulfide formation contributed to metal(loid) attenuation in amended columns.