A study was conducted on biofilm formation on submerged mine tailings with the following primary objectives:
• determine if photosynthetic biofilms are generally present on submerged mine tailings;
• identify the physico-chemical conditions favorable for biofim formation; and,
• clarify the effects of biofilm on metal mobilization, where appropriate.
Five mine sites located across Northern Ontario and Quebec with submerged tailings of different compositions were selected for examination. These include:
1. Tailings impoundment at the closed Louvicourt copper mine in Val d’Or;
2. Small natural pond partially filled with mine tailings at the Nova Scotia silver mine in the historic Cobalt mining camp;
3. Oxidation pond of the Strathcona nickel mine, Onaping Operation northwest of Sudbury;
4. Tailings pond of the historic Hardy nickel mine in Onaping; and,
5. Tailings management area 1 (TMA1) of the former Denison uranium mine in Elliot Lake.
The occurrence of a continuous microbial mat overlying submerged tailings was not observed in any of the five sites examined. At the tailings pond of Louvicourt Mine and the oxidation pond of Strathcona Mine, only loose patches of iron oxyhydroxide of less than 5 mm thickness and colonized with a microbial population were found scattered over the tailings. This contrasted with previous observations made at one of the field test cells studied in 2007 at the Louvicourt Mine, where a biofilm layer up to 5 cm thickness colonized the entire tailings/water interface (Vigneault et al., 2007, MEND Report 2.12.2).
A comparison of the environmental settings between the former Louvicourt field cells and the five sites visited for this study suggests that the requirements for the formation of continuous algal biofilm may include the following:
1. A shallow, oxygenated water cover with sufficient light and heat penetration
2. A relatively quiescent environment, i.e., no active tailings movement
3. A suitable substrate for the microbial population to propagate
Based on the findings of the field and laboratory assessments, the following conclusions can be drawn:
1. Given that microbial mats were not found in any of the study sites, its formation over submerged tailings does not appear to be a common phenomenon.
2. Until further studies reveal the presence of continuous microbial mats over submerged tailings at Canadian mine sites, and the physico-chemical or ecological constraints on the establishment of biofilm are well-defined it is premature to develop new technologies to encourage biofilm formation over submerged tailings despite its beneficial effects.
3. Further research on the influence of microbes on metal mobility under both acidic and neutral conditions is recommended for developing sustainable strategies in managing submerged mine wastes.
