Zinc Speciation of a Smelter Contaminated Canadian Boreal Forest Soil: Amendment Application Effect On Speciation Using EXAFS, XRF Mapping and µxanes.

The Hudson Bay Mining and Smelting Co., Limited (HBMS) has operated a zinc (Zn) and copper (Cu) processing facility in Flin Flon, Manitoba Canada 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 anthropogenic disturbances, 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. Because metal toxicity is related more to speciation than to total concentration EXAFS, XRF mapping and µXANES where used to study Zn speciation in two soils. Zinc speciation was determined before and after amendment application (bone meal biochar, willow biochar, and zeolite) to determine: a) species of Zn contributing to toxicity and elemental associations, b) whether the amendment application influenced Zn speciation reducing overall bio-availability. In soil A (calcium carbonate un-responsive) the bulk EXAFS indicate secondary Zn species (e.g., Zn-LDH, Zn Sorption to iron (hydr)oxides) were the dominant forms of Zn, and small but distinct changes resulted from amendment application. Soil B (calcium carbonate responsive) contained a much higher percentage of primary Zn (e.g., Franklinite) and was greatly influenced by dolostone application forming Zn Hydroxy Interlayer Material (HIM) with smectite clays. XRF mapping and subsequent µXANES substantiated the bulk EXAFS—providing spatial resolution of Zn in soils A and B. The elemental associations determined though µXANES allowed for the differentiation of individual Zn species, substantiating the standards used in modeling and fitting the bulk EXAFS and XANES.