Geochemical Behavior of Arsenic in Kelly Lake,Ontario

The objective of this study was to investigate the geochemical behavior of As in Kelly Lake, Ontario. A total of 65 water samples were collected from August 1998 to October 1999. Concentrations of As (total, dissolved and particulate) were determined in each water sample. Thermodynamic models suggest that As interactions with Fe hydroxides could limit As concentrations in Kelly Lake water samples (by adsorption and forming arsenate minerals). It was concluded that Fe(II) arsenates (and not Fe(III) arsenate) formation/dissolution could control As concentrations in Kelly Lake. The activity of As (in terms of HAsO₄ ^2-) in the water samples was calculated from the monitoring data. The calculated activities were superimposed on the thermodynamic model of As minerals. All the calculated activity observations clustered around the Fe₃(AsO₄)₂.8H₂O(c)/Fe₄Fe₂(OH)₁₂. SO₄(c).These observation suggest that the solubility of As in Kelly Lake is controlled by the equilibrium of Fe₃(AsO₄)₂.8H₂O(c)/Fe₄Fe₂(OH)₁₂.SO₄(c), as suggested by thermodynamic solubility isotherms. The As concentration data were limited and spatial trend could not be verified in Kelly Lake water samples, although a decreasing trend in As concentrations at all depths was noticed from June to October 1999.