Effects of Dolomitic Limestone Application on Zinc Speciation in Boreal Forest Smelter-Contaminated Soils

Anthropogenic activities at the HudBay Minerals, Inc., Flin Flon (Manitoba, Canada) mining and processing facility have severely affected the surrounding boreal forest ecosystem. Soil contamination occurred via a combination of metal and sulfuric acid deposition and has resulted in forest dieback and ineffective natural recovery. A community-led effort to revegetate areas of the landscape through the application of a dolomitic limestone has been met with varied success. Zinc (Zn) speciation has shown to be closely linked to the presence or absence of an invasive metal-tolerant grass species, with soils being broadly classed into two revegetation response groups. Group I, characterized by the absence of metal-tolerant grasses, and group II, characterized by the presence of metal-tolerant grasses. The systematic approach used to lime areas of the landscape produced a liming chronosequence for each group. This study used a combination of X-ray absorption spectroscopy, X-ray fluorescence mapping, and X-ray diffraction techniques to determine the effect of liming on Zn speciation in these chronosequences. Liming group I soils resulted in the formation of a neo-phase Zn-Al-hydroxy interlayer coprecipitate and subsequent rapid boreal forest revegetation. The effect of liming on Zn speciation on the group II soils resulted in a gradual transition of increasingly stable adsorption species, culminating with a stable Zn-Al-layered double hydroxide precipitate. Boreal forest vegetation has failed to recolonize group II soils during the study. However, the formation of the layered double hydroxide species resulted in a significant reduction in CaCl-extractable Zn. Further research is required to determine how to promote the revegetation of these soils.