The distinction between ore processing and post-depositional transformation on the speciation of arsenic and antimony in mine waste and sediment

Roasting of As and Sb-associated gold ore at the Giant mine, Yellowknife, Canada, resulted in complex solid–gas phase reactions between As, Sb, and roaster-derived Fe-oxides. Antimony, As, and their respective hosting in two roaster waste streams and mine-impacted sediment were characterized using EPMA, μXRD, μXRF, bulk and μXANES. The roaster oxides in mine waste and sediment host As and Sb in multiple oxidation states. In the cyanided roaster dust (ESP residue — composed of fine-grained particles mobilized during roasting, and sublimated phases), 3+ is the dominant As and Sb oxidation state in the bulk sample and in the roaster-generated iron oxides that host these elements. Conversely, 5+ is the dominant As and Sb oxidation state in the bulk calcine (oxidized and cyanided material collected from the roaster bed), and in the roaster Fe-oxide grains therein. These results have important implications for predicting the fate of As and Sb in the environment, and for distinguishing between anthropogenically-influenced speciation and speciation resulting from post-depositional transformations. Arsenic and Sb-bearing roaster iron oxides and other As and Sb-bearing phases in mine-impacted sediment collected from the surficial zone (0 to − 1 cm) and relatively reducing zone (− 16 cm) are also described. Arsenic and Sb associated with roaster oxides in the relatively reducing sediment have undergone post-depositional transformation and 10–20% of As and Sb are attenuated via precipitation as sulfide or sorption to sulfide surfaces. The attenuation of Sb is more efficient than As, and Sb is only mobile at the micron scale. In the relatively reducing sediment, where most of the As is reduced to As3+, a Sb5+ bound to oxygen phase persists and represents 58% of the total Sb.