Jennifer Arnold

The physical disturbance of the sulphide bearing rocks of the Meguma Group can lead to oxidation of the sulphides and possibly generate Acid Rock Drainage (ARD). ARD is a well known, and costly problem associated with the Meguma Group in the Halifax region of Nova Scotia, Canada. Finding the ideal site for waste rock disposal is not always easy, and it has been proposed that dumping waste acid generating materials into salt water of the Bedford Basin is a possible solution. This study focuses on the survival and geomicrobiological interactions of Acidithiobacillus ferrooxidans, and the behaviour of the Halifax slates and the Goldenville Halifax transition zone (GHT) in fresh and saline waters.

This study examines pH changes in both rock types in fresh and salt water static tests. Rocks from both the GHT and Halifax slate were crushed into several size fractions for the pH experiments, and one size fraction for the control and cycling experiments. Data collected over a period of 5 weeks indicate that for all size fractions, and for both the fresh and salt water samples, an initial dramatic drop of pH is followed by an apparent levelling off in pH, producing an exponential curve of pH versus time (days). This trend is evident for the Halifax slate with an initial average fresh water pH of 5.6 (range 5.3 6.1), and an average final pH of 3.2 (range 3.1 3.5). The salt water samples of Halifax slate had an average initial pH of 6.71 (range 6.3 B 7.0), and an average final pH of 4.03 (range 3.6 5.5). The trend of the GHT data is similar; however the salt water pH drop is not as dramatic as the drop in pH of the fresh water. The average initial pH of GHT fresh water samples is 7.1 (range 6.9 B 7.4), and an average final pH of 4.7 (range 3.8 B 5.5). The GHT salt water average initial pH is 7.23 (range 7.1 B 7.4), and the average final pH is 6.31 (range 5.4 7.0). The addition of bacteria to samples of both rock types in fresh and salt water did not effect the final pH. The cycling of fresh water resulted in a similar trend in pH: the pH decrease was approximately the same amount at the end of each day before the fresh water change. Microprobe analysis confirms the dominance of pyrrhotite in the GHT and Halifax slates in the Beaverbank area. Acid prediction tests confirm the ability of the rocks to produce ARD. The SEM studies examined un inoculated and inoculated samples of both rock types in salt water to observe possible attachment to the rock surface. SEM confirmed bacterial survival and attachment to the rock surface of both rock types in salt water.

Implications from this study show that although the pH change is somewhat small in salt water, the drop is not insignificant, and indicates the continuing oxidization of sulphide minerals. Care should be taken when disposing of waste acid rock in any aquatic environments. Concentration of biological matter does not effect the rate of ARD production in a sample in both fresh and salt water.

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Pages: 117
Supervisor: Steve Armstrong