Ecological Engineering: Biological and Geochemical Aspects Phase I Experiments

Abstract

Perpetual operation of acid mine drainage treatment facilities after mine closure imposes economic burdens and environmental liabilities which are difficult to overcome. The main goal of ecological engineering research is the development of methods which facilitate the establishment of vegetation cover types to serve as self-maintaining acid drainage treatment systems. Summarized below are the objectives and results of experiments on tailings and in the laboratory for five aspects relevant to the development of close-out scenarios for acid-generating tailings sites in temperate climates.

• 1. On dry surface areas with sparse vegetation covers, terrestrial moss covers curtail infiltration of precipitation. Vascular plant covers investigated had no amelioration effect on the underlaying tailings. Introduction and promotion of terrestrial mosses require further research.

• 2. Wetlands established in waterlogged, submerged sections and seepages reduce water infiltration and acid generation, as well as removing metals. Hand-transplanted cattails showed a 200% increase in number after 1 year. Hydroponic methods tested to date indicated little promise. Seed germination of some wetland plants was reported on neutralized pyrrhotite. Iron removal in seepages was found to be catalyzed by the surface provided by organic matter. Two species of aquatic mosses can serve as biological polishing agents where flow rates are low.

• 3. The precipitates in settling and polishing ponds from treatment plant operation have to be maintained in an alkaline state. Some species of Charophytes, attached macroscopic algae, have been tested extensively for these conditions and appear to be suitable.

• 4. Relative abundance values for ¹⁸O in sulfate produced at one tailings site indicate that a major proportion of the sulfate oxygen is derived from water molecules rather than from molecular oxygen, suggesting that the oxidation process proceeds partly under anaerobic, water-saturated conditions. The water is slowly moving through the tailings. It is likely that the oxidation of sulfides in the tailings can be stopped only if the tailings are permanently submerged in completely stagnant water.

• 5. Data from freezing gauges and a thermistor cable installed in the tailings indicate that frost penetration in the tailings is minimal, suggesting that the rate of sulfide oxidation may not be reduced significantly during the winter.