Long Term Sulphur Storage

Syncrude Canada Ltd (SCL) commissioned a scientific investigation into long-term sulphur storage options at the sulphur pilot block test site in 2005. Originally constructed to investigate the production of sulphuric acid under the influences of temperature, water and oxygen, the storage options evaluated at the pilot block test site consisted of: (1) control (uncovered) block; (2) insulated block; (3) reclamation block; (4) saturated block (net percolation not monitored); and (5) coletanche block. The majority of the research was led by Dr. Jim Hendry and the University of Saskatchewan. Currently all research programs are complete. Research themes: (1) sulphur block physical characteristics/water migration;( 2) sulphur block geochemistry; (3) in-ground storage and reclamation covers to limit infiltration; and (4) sulphur impacts on clay soils. These themes were explored in numerous thesis, papers and reports.

Because sulphur blocks are hydrophobic fractured porous media, precipitation infiltrates rapidly. Up to 97% of the annual sulphuric acid production occurs in the upper 1m during summer months. Internal acid strength is significantly higher than measured effluent pH, an important predictive design consideration. Sulphuric acid exposure produced pH-related mineral dissolution of clay soils, commonly used for cover and reclamation construction. Sulphur oxidation rates are temperature-sensitive and controlled by autotrophic sulphur-oxidizing microbes. Research suggests that only 0.6% of mean annual precipitation is necessary to sustain these reactions. Therefore, while a soil cover can reduce infiltration into the block, the observed oxidation required so little water to sustain reactions that traditional soil covers will have limited success. Overall, results indicate that acid production is associated with the preferential flow through sulphur fractures, and the selected cover technologies do not appear to serve as effective barriers. Therefore, the technical recommendation from Syncrude R&D is that long term sulphur storage is not a viable option for mine closure. The long term sulphur project was closed in 2012.