Investigating environmental effects of long-term sulphur storage from oil sands mining

摘要

Annual sulphur (S~0) production from bitumen upgrading at Canadian oil sands mining operations in northeastern Alberta, Canada, was 1.5 Mt in 2007 and is expected to increase to 5.3 Mt by 2017. Sale of S~0 produced at the oil sands mines has typically been uneconomical over the past 20 years because of low S~0 prices and relatively high transportation costs. The long-term forecast is for a continued global S~0 surplus and low S~0 prices, therefore long-term storage of S~0 at oil sands mines has become a consideration. However, long-term storage of S~0 blocks poses a potential for contamination of groundwater and surface water as the oxidation of S~0 to H2SO4 creates drainage waters with low pH and elevated SO4 concentrations. Syncrude has initiated studies to investigate options for acceptable long-term in-ground storage of sulphur by following a multi-track approach of utilizing existing cover and liner technologies and to develop the understanding of the environmental loadings of sulphur blocks. Five S~0 pilot blocks were constructed at the Syncrude Canada Ltd. (SCL) Mildred Lake oil sands mine site to evaluate the effect of various cover designs on the H2SO4 production associated with the blocks. Water balance, S~0 block temperature, gas concentrations in the covers and blocks, and drainage water chemistry data measured from 2006-2008 were interpreted. The analysis of S~0 pilot block data indicates estimated rates and locations of H2SO4 production were similar to Syncrude’s Phase 1 block. The [O2] depth profiles indicated that the majority of acid production in the pilot blocks was limited to the upper 1 m. Temperature was an important control on acid production rates in the pilot blocks. The Insulated and Reclamation cover designs are marginally effective at reducing H2SO4 production by minimizing O2 availability. The Coletanche cover appears to be an effective barrier to gas and water transport. However, measurement of drainage flow rates with time is needed to provide a direct measurement of net percolation (or lack of percolation) through the Coletanche cover.