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BMRI -San Luis Pit Backf~HCT Tests • <br />Sample A: BMRII-Ol + BMRII-OS + BMRII-03 <br />Sample B: BMRII-02 + BMRII-09 <br />Sample C: BMRII-10 + BMRII-7 + BMRII-06 + BMRII-04 + BMRII-08 <br />This compositing process and its rationale were described in the July, 1995 test plan <br />memorandum. <br />The three samples were tested at Core Laboratories (Aurora, Colorado) using the EPA <br />methodology for HCTs. All three samples were tested for 28 weeks. <br />4.0 RESULTS <br />All HCT data are attached to this memorandum as received from Core Laboratories. <br />Table 2 presents key results from the humidity-cell testing. <br />Table 2 Humidity Cell Tests -San Luis-West Pit Gneiss <br />Sample pH <br />(su) Net Alk. <br />(mg/1 CaC03eq) Sulfate <br />(mg/I) Iron <br />(mg/I) <br /> Week <br />l Week <br />5 Week <br />28 Week <br />1 Week <br />5 Week <br />28 Week <br />1 Week <br />5 Week <br />28 eek <br />l Week <br />5 Week <br />28 <br />A 4.36 5.63 4.86 -38 <-10 -14 46 34 < 10 6.73 <0.03 <0.03 <br />I; 7.36 7.49 6.27 +23 +17 +l6 68 58 <10 X0.03 <0.03 <0.03 <br />C 7.18 7.26 6.18 +13 +12 +10 15 17 <10 0.03 <0.03 <0.03 <br />Net Alk.: net alkalinity =alkalinity -acidity <br />5.0 DISCUSSION <br />5.1 ACID-GENERATING POTENTIAL BASED ON IKNETIC TESTING <br />The fundamental geochemical weathering processes affecting mine wastes that are <br />placed in the vadose zone or in another variably saturated environment are (a)oxidation <br />of sulfide phases and (b) neutralization of acids by the titratable bases in the gangue <br />and country rock. Because pyrite is the predominant sulfide, the acid-generating <br />reactions can be generalized as the classic stoichiometric oxidation reactions; <br />(l) FeS2jij + 7/2 02 + H2O = _ _ > Fe2+ I„~ + 2 SO4 2 ts) + 2 H' cea~ <br />(2) Fe2+ csw + 1 /4 02 + H ~ I,a~ < _ _ _ > Fe3 ~ ),~ + I /2 H2O <br />(3) Fe's I,y + 3 H 0 =__ <br />e ~ > Fe(OH)~t,l + 3 H aq1 <br />d' <br />2- <br />~ <br />(4) FeSZpt + l4 F <br />cw~ + 8 H2O = _ _ > I S Fe <br />t,qt + 2 SOQ <br />t,~) + 16 H <br />t,v <br />Geochimica, Inc. 4 95021/1-Feb-96 <br />