2010-08-02_REVISION - M1977300 (28)

Home Browse Search

Environmental Protection Plan, Schwartzwalder Mine 14-8 • composition (Ca, SO4, HCOO of the deep mine water is controlled by precipitation and dissolution reactions involving carbonate minerals and gypsum. Ferrihydrite, a mineral that commonly limits iron concentrations in oxidized waters was also calculated as being oversaturated in solution. This result, however, is a statistical artifact of the high detection limit for iron (<0.03 mg/L) that was used to calculate the input value. All uranium and molybdenum minerals evaluated by the model were undersaturated in the deep mine water. Table 146. Controlling Mineral Phases in Deep Mine Water Mineral Composition Saturation Index' Calcite CaC03 0.87 Alunite KA13(SO4)2(OH 6 -0.35 Chrome Hydroxide (am) Cr OH)3 0.46 Ferrih drite Fe OH)3 1.71 Gypsum CaSO4.2H2O 0.78 MgCr204 MgCr204 -0.34 Magnesite MgCO3 0.31 Jarosite K KFe3(SO4)2(OH)6 0.36 Otavite CdC03 -0.89 Rhodochrosite MDC03 -0.74 Positive values are oversaturated; negative values are undersaturated (iii). 1.3 Reflooded Mine Water Speciation Speciation runs were performed for four samples collected from the flooded mine. The modeled samples • included, water from a depth of 221 feet collected on May 21, 2001, water from a depth of 465 feet collected on April 18, 2002, water from a depth of 291 feet collected on May 20, 2003, and water from just below the surface on June 27, 2007. The modeled water chemistries had acceptable charge balance errors ranging from -2.46% to 2.52 %. The model calculations for the 2001, 2002, and 2003 samples were performed for oxidizing conditions at an Eh of 178 mV similar to values observed in the flooded mine during that period. The calculations for 2007 were performed using an Eh of 23 mV as was observed during measurements in November 2007. Results of the analysis indicate that calcite and gypsum are near equilibrium for all of the samples and that they are the probable mineral controls of calcium, sulfate and bicarbonate in solution. Amorphous aluminum hydroxide, magnesite, and rhodocrosite were also calculated to be near equilibrium. C02 gas is oversaturated in the mine water as compared to equilibrium with atmospheric pressure (atmospheric equilibrium for C02 gas occurs at saturation indices between -3.2 and -3.5). Ferrihydrite saturation ranges from near equilibrium to oversaturated, but the model results are impacted by the relatively high detection limit for iron (<0.03 mg/L) that was used to calculate the input value. The precipitation of ferrihydrite typically limits iron concentrations in oxidized waters at neutral pH, and is the most probable control limiting iron concentrations in mine water. All of the uranium and molybdenum minerals evaluated by the model were undersaturated in solution. Saturation Indices for the probable controlling phases are presented in Table 14-7. 4109C.100731 Whetstone Associates