Characterization of Zinc Speciation in a Smelter Contaminated Canadian Boreal Forest Landscape: From Micro-XANES, XRF Mapping, and XAFS to Speciation Mapping of the Contaminated Landscape.

The Hudson Bay Mining and Smelting Co., Limited (HBMS) has operated a zinc (Zn) and copper (Cu) processing facility in Flin Flon, MB since the 1930’s. Located in the Boreal Shield, the area surrounding the mine complex has been severely impacted by both natural (forest fires) and the anthropogenic disturbance, which has adversely affected the natural revegetation of the local forest ecosystem. Zinc is one of the most prevalent smelter-derived metals in the soils and has been identified as a key factor limiting the natural revegetation of the landscape. Because metal toxicity is related more to speciation than to total concentration, Zn speciation in soils from the impacted landscape was characterized using XAFS, XRF mapping and micro-XANES. Beginning with speciation at a micro scale and transitioning to bulk we were able to determine Zn speciation and link it to two distinct landform characteristics: (1) soils stabilized by metal tolerant grass species—in which secondary adsorption species of Zn (i.e., sorbed to Mn and Si oxides, and as outer-sphere adsorbed Zn) were found to be more abundant. (2) Eroded sparsely vegetated soils in mid to upper slope positions in the landscape were almost entirely dominated by high temperature produced Zn minerals, specifically franklinite (ZnFe₂O₄) a spinel mineral. Based on these speciation trends, a landscape-scale Zn speciation map of the smelter affected region was developed to facilitate the application/selection of management strategies that will effectively reduce Zn phytotoxicity and promote the revegetation of the affected areas.