Controls and Rates of Acid Production in Commercial-Scale Sulfur Blocks

Acidic drainage (pH 0 4-1 0) from oxidizing elemental sulfur (S-0) blocks is an environmental concern in regions where S-0 is stockpiled In this snide, the locations, controls and rates of H2SO4 production in commercial-scale S-0 blocks (similar to 1-2 x 10(6) m(2)) in northern Alberta. Canada, were estimated. In situ modeling of O-2 concentrations ([O-2]) suggest that 70 to >97% or the annual H2SO4 production occurs in the upper 1 m of the blocks where temperatures increase to >15 degrees C during the till miner Laboratory experiments show that S-0 oxidation rates are sensitive to temperature (Q(10) = 4 3) and dependent on the activity of autotrophic S-0-oxidizing microbes The annual efflux of SO4 in drainage water from a S-0 block (5 5 x 10(5) kg) was within the estimated range of SO4 production within the block (2 7 x 10(5) to 1 2 x 10(6) 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 S-0 oxidation was an important factor in maintaining elevated temperatures (mean, 11 1 degrees C) within the block The implications of this research arc relevant globally because construction methods and the physical properties of S-0 blocks are similar worldwide