Rates of elemental sulphur oxidation and associated oxygen and sulphur isotope fractionation

• Main Author: Smith, Laura Ann
• Other Authors: Hendry, Jim
• Format: Others
• Language: en
• Published: University of Saskatchewan 2009
• Subjects: sulphuric acid; storage blocks; oil sands; sour gas
• Online Access: http://library.usask.ca/theses/available/etd-08292009-180320/

Elemental sulphur (S⁰) is removed from sour gas deposits (high H₂S) during refinement. The resulting S⁰ is often stored onsite when the costs of shipping S⁰ to market exceeds the costs of storing it in large above ground blocks. With the aid of acidiphilic bacteria, atmospheric air and water oxidize S⁰ to sulphate (SO₄^2-). Long term storage is under consideration; however, oxidation rates and the role of each oxygen source (O_2(g) and H₂O) is not clear. S⁰ oxidation experiments were conducted over a range of temperatures (6-32¡ãC) to investigate reaction rates and isotopic fractionation of O and S isotopes during oxidation. The experiments also investigated the effect of integrating S⁰ oxidizing microorganisms and available nutrients on both the reaction rates and isotope fractionation. Results indicated > 95% of total SO₄^2- generated can be attributed to autotrophic microbial activity. Experiments conducted in a nutrient rich mineral solution showed rates increase with temperature from 0.16 (6¡ãC) to 0.98 (32¡ãC) ¦Ìg S⁰ cm^-2 d^-1 (Q₁₀ ¡Ö 1.7 - 1.9). Experiments conducted in a nutrient poor solution (deionized water) showed oxidation rates did not increase with temperature (0.06 to 0.08 ¦Ìg S⁰ cm^-2 d^-1) between 12 and 32¡ãC. Oxygen isotope analysis of the generated SO₄^2- indicated essentially all oxygen incorporated into the SO₄^2- originated from H₂O. In addition, effluent samples obtained from S⁰ block effluent at SCL indicated ¦Ä¹⁸O_(SO4) generally reflected the ¦Ä¹⁸O_(H2O) in the system at the time of oxidation. While covering the S⁰ blocks with an impermeable cover would undoubtedly minimize total SO₄^2- accumulation in block effluent, the results of this study suggest ¦Ä¹⁸O_(SO4) can also be used to track water movement through the block.