Controls and Rates of Acid Production in Commercial-Scale Sulfur Blocks
- T. K. Birkham *a,
- M. J. Hendrya,
- S. L. Barbourb and
- J. R. Lawrencec
- a Dep. of Geological Sciences, Univ. of Saskatchewan, 114 Science Place, Saskatoon, SK, Canada S7N 5E2
b Dep. of Civil and Geological Engineering, Univ. of Saskatchewan, 57 Campus Drive, Saskatoon, SK, Canada S7N 5A9
c National Hydrology Research Centre, 11 Innovation Boulevard, Saskatoon, SK, Canada S7N 3H5
Acidic drainage (pH 0.4–1.0) from oxidizing elemental sulfur (S0) blocks is an environmental concern in regions where S0 is stockpiled. In this study, the locations, controls, and rates of H2SO4 production in commercial-scale S0 blocks (∼1–2 × 106 m3) in northern Alberta, Canada, were estimated. In situ modeling of O2 concentrations ([O2]) suggest that 70 to >97% of the annual H2SO4 production occurs in the upper 1 m of the blocks where temperatures increase to >15°C during the summer. Laboratory experiments show that S0 oxidation rates are sensitive to temperature (Q10 = 4.3) and dependent on the activity of autotrophic S0–oxidizing microbes. The annual efflux of SO4 in drainage water from a S0 block (5.5 × 105 kg) was within the estimated range of SO4 production within the block (2.7 × 105 to 1.2 × 106 kg), suggesting that H2SO4 production and removal rates were approximately equal during the study period. The low mean relative humidity within the block (68%; SD = 17%; n = 21) was attributed to osmotic suction from elevated H2SO4 concentrations and suggests a mean in situ pH of approximately −2.1. The low pH of drainage waters was attributed to the mixing of fresh infiltrating water and low-pH in situ water. Heat generation during S0 oxidation was an important factor in maintaining elevated temperatures (mean, 11.1°C) within the block. The implications of this research are relevant globally because construction methods and the physical properties of S0 blocks are similar worldwide.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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