Mud Lake ARUM experiment and biogeochemical barriers in mine waste restoration : an ecological engineering approach : final report 1995

Abstract

Groundwater with a low pH and contaminated with heavy metals is entering Mud Lake. This water body has been identified as the best site to treat this water before it enters Confederation Lake. Biological treatment using ARUM (Acid Reduction Using Microbiology) is the suggested treatment method. A laboratory experiment was carried out to determine whether ARUM can remove Zn and other contaminants from Mud Lake water. A preliminary experiment was carried out to determine what would happen to the groundwater in oxidising conditions. Such conditions will be present in the mixed surface waters of Mud Lake. This experiment sought to determine whether, to what extent and at what rate Fe oxidation and subsequent precipitation of Fe(OH), can occur. This experiment determined that aeration of groundwater entering Mud Lake (GD trap water) at room temperature (similar to summer conditions in the field) results in oxidation, hydrolysis and precipitation of Fe commencing at 88 h. From around 213 h, an equilibrium between Fez' and Fe3' is attained with no further net oxidation or removal of Fe from solution. Oxidation rate was estimated as around 103 mg.m-3.min-' and was little influenced by the presence of a sediment. However, in the presence of sediment approximately 50 % of the Fe and acidity in the water was removed in 27 days. In cold room conditions, where the temperature (1-5OC) is similar to what would be encountered within and just above sediments in the field in winter, oxidation did not occur during the first 27 day period of observations with all Fe remaining in the Fe2+ state. However, within 72 days oxidation had commenced in jars with sediment and pH had declined to <3. As at room temperature, 50 YO of the acidity and Fe was removed by the sediment. ARUM worked very well on groundwater entering Mud Lake (GD trap water). Within 23 days at room temperature, dissolved Zn concentration was reduced from >80 mg.L-' to 4 mg.L-' in reducing condition induced through addition of decomposable organic matter (alfalfa or potato waste). With added alfalfa some of the Zn remained in the suspended solid fraction. This is potentially mobile. With potato waste, the Zn was almost totally removed to the sediment. Therefore, potato waste is the amendment of choice. In cold room conditions, and in the presence of an amendment and Mud Lake sediment, reducing conditions were established in Mud Lake groundwater within 54 days and Zn concentration reduced to 0.334 mg.L-' in the presence of potato waste.