2:30 PM - 2:45 PM
[HRE12-04] Utilizing isotopic Fe fractionations to trace the behaviour of dissolved and colloidal Fe in mine drainages
Mining-related water contamination is on the rise, thereby increasing the popularity of passive treatment in mine drainages. Fe, a commonly occurring element in mine drainages significantly affects the behaviour of other elements, therefore, understanding its behaviour would highlight the fate of the co-existing elements. This study utilizes iron isotope fractionations as important tracers of the contamination caused by mining, given that varying Fe sources and phases have varied δ56Fe values.
An investigation was carried out at two mine drainages; circumneutral mine drainage that has Fe2+ input, that oxidizes to Fe3+, resulting in the formation of ferrihydrite colloids, and acidic mine drainage that has a Fe3+input, which, through hydrolysis, forms schwertmannite colloids. The isotopic fractionations were observed in three fractions; the total (0.2 µm + 200 kDa), colloidal (0.2 µm to 200 kDa) and dissolved (< 200 kDa).
In both drainages, the total fractions displayed δ56Fe values representing averaged isotopic fractionation values of the different filtered sizes and that are near continental crust values (0.07 ± 0.03 ‰). However, in the circumneutral system, clear fractionation was observed in the dissolved and colloidal fractions. The colloidal fraction had heavier δ56Fe values compared to the dissolved fraction, which was attributed to the preferential complexation of heavier Fe by hydroxyl groups to form stronger bonds. This trend was not seen in the acidic drainage, thereby strongly showing that the oxidation process is a significant factor for the δ56Fe fractionation. An overall negative fractionation is observed in both colloidal and dissolved fractions towards the downstream. These trends correspond with the Rayleigh fractionation model; however, misfits are observed, particularly in the colloidal fraction. The misfit, Δ56Fecolloid-rayleigh is considered to reflect the Fe colloids transported in the drainage.
Utilizing Fe isotopes, we understand that (i) filtration of samples highlights δ56Fe fractionation behaviours, (ii) a certain amount of Fe in the drainage is transported in colloidal phase to rivers, transporting along the other toxic elements.
An investigation was carried out at two mine drainages; circumneutral mine drainage that has Fe2+ input, that oxidizes to Fe3+, resulting in the formation of ferrihydrite colloids, and acidic mine drainage that has a Fe3+input, which, through hydrolysis, forms schwertmannite colloids. The isotopic fractionations were observed in three fractions; the total (0.2 µm + 200 kDa), colloidal (0.2 µm to 200 kDa) and dissolved (< 200 kDa).
In both drainages, the total fractions displayed δ56Fe values representing averaged isotopic fractionation values of the different filtered sizes and that are near continental crust values (0.07 ± 0.03 ‰). However, in the circumneutral system, clear fractionation was observed in the dissolved and colloidal fractions. The colloidal fraction had heavier δ56Fe values compared to the dissolved fraction, which was attributed to the preferential complexation of heavier Fe by hydroxyl groups to form stronger bonds. This trend was not seen in the acidic drainage, thereby strongly showing that the oxidation process is a significant factor for the δ56Fe fractionation. An overall negative fractionation is observed in both colloidal and dissolved fractions towards the downstream. These trends correspond with the Rayleigh fractionation model; however, misfits are observed, particularly in the colloidal fraction. The misfit, Δ56Fecolloid-rayleigh is considered to reflect the Fe colloids transported in the drainage.
Utilizing Fe isotopes, we understand that (i) filtration of samples highlights δ56Fe fractionation behaviours, (ii) a certain amount of Fe in the drainage is transported in colloidal phase to rivers, transporting along the other toxic elements.