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Experimental investigation of the impact of pH on colloid-associated metal mobility in mine-impacted wetland sediment

Harper, Colleen1; Amos, Richard1

Published Apr 02, 2026 on Dryad. https://doi.org/10.5061/dryad.tb2rbp0h7

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Abstract

Metal mining operations generate waste rock that is affected by mineral weathering reactions and can produce acidic metal-rich leachate. Leachate pH can have direct impacts on metal mobility by changing metal solubility, and through colloid-facilitated metal transport, potentially increasing metal transport downgradient of the waste rock. This work presents a set of laboratory column experiments that study the effect of colloids on metal mobility in wetland sediment impacted by the drainage from a sulfide-bearing abandoned waste-rock pile. The fully-saturated experiments investigate pH conditions ranging from 2.5 to 7, varying flow rates 45 to 90 m/yr, and measured metal concentrations in leachate filtered at 10 μm, 1 μm, 0.1 μm, and 0.01 μm. Results indicate that metal mobility is higher at lower pHs for Al, Mn, Fe, Cu, Cd, and Zn, but the impact of the smallest colloids studied (i.e., <0.01 μm) is reduced as the pH decreases and metal transport is dominated by the dissolved phase. These findings suggest that colloid-facilitated transport will enhance metal transport in areas receiving mine drainage until the pH of the drainage decreases towards values of approximately pH ~2.5.