EXPERIMENTAL INVESTIGATION OF COLLOID-INFLUENCED METAL TRANSPORT IN WETLAND SEDIMENT

While metal mining operations provide crucial materials for society, the impacts of these operations are often widespread and long-lasting. Mineral weathering of mine waste releases toxic heavy metals and the subsurface transport of these metals can lead to widespread contamination. In particular, colloids (small, mobile particles) can keep contaminants stable in suspension, leading to increased transport distances for contaminants that would otherwise be expected to strongly sorb to sediments and be immobilized close to mine workings. This research investigated the role of colloids on the transport of metal contaminants in saturated wetland sediment that has received metal rich drainage from an abandoned waste-rock pile for almost a century. Experimental, laboratory column tests that utilized sediment collected at the abandoned Ore Chimney mine near Kaladar, Ontario, Canada, were used to study the effect of various solution parameters, including metal composition and pH, on the mobility of metals when natural colloids were also present in solution. It was determined that small (<0.01 μm) colloids, most likely humic substances, substantially altered the mobility of metals, increasing their ability to transport through the sediment. Competitive adsorption was found to operate to increase the mobility of zinc when multiple metals were present in solution, and a decrease in pH increased overall metal mobility but decreased the influence of colloids. The study indicates that humic colloids are involved in metal mobility in wetland sediment, but changing solution conditions that could be expected to occur with aging waste-rock piles, will alter the influence of colloids.