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Fe ITASCK <br /> Denver, Inc. <br /> minerals present in waste rock. As shown in Equation 3.1, the oxidation of 1 mole of pyrite to a <br /> mole of iron oxide and 2 moles of dissolved sulfate generates 4 moles of acidity. <br /> FeS2+ 15/402 + 7/21­12O-> Fe(OH)3+ 2SO42-+4H+ (3.1) <br /> The AGP of a sample is typically calculated based on the sulfur content of the sample and the <br /> stoichiometry of pyrite oxidation, as shown in Equation 3.1. <br /> Different forms of sulfur may be quantified during ABA analysis, including sulfide-sulfur, soluble <br /> sulfate-sulfur, and insoluble sulfate-sulfur. In the Nevada Modified Sobek method, the sulfur <br /> speciation is conducted through a series of wet-chemical-leach sulfur analyses. The procedure <br /> consists of analysis of total sulfur by combustion-infrared spectrophotometer (i.e., a LECOT^° <br /> furnace or similar) followed by analysis of sample duplicates after partial decomposition by <br /> chemical digestion. The chemical digestions (and calculated speciation) include the following: <br /> 1. Hot-water-extractable sulfur (total sulfur from untreated sample minus total sulfur after <br /> extraction with hot water) is attributed to water-soluble sulfates, including acid-forming <br /> sulfates, such as hydrous ferrous sulfates, and non-acid-forming sulfates, such as gypsum <br /> and epsomite (Li et al. 2007). <br /> 2. HCI-extractable sulfur (total sulfur from untreated sample minus hot-water-extractable <br /> sulfur minus total sulfur after extraction with HCI) is attributed to less soluble sulfates, <br /> including jarosite and alunite, and acid-dissociable sulfides, such as chalcopyrite, <br /> pyrrhotite, and sphalerite (NDEP 2015). <br /> 3. HNO3-extractable sulfur(total sulfur after sulfate extraction [HCI or hot water] minus total <br /> sulfur after extraction with 14% HNO3) is attributed to pyritic sulfide-sulfur. <br /> 4. Non-extractable sulfur (total sulfur after HNO3 extraction) is attributed to organic sulfur. <br /> The Nevada Modified Sobek method uses the sum of sulfide-sulfur and soluble-sulfate sulfur for <br /> the calculation of AGP (NDEP 2015). The sulfur content in weight percent is converted to AGP in <br /> units of kilograms of calcium carbonate per ton (kg CaCO3/t) by multiplying by the conversion <br /> factor 31.25 based on the stoichiometry shown in Equation 3.1. <br /> 11 <br />