1992-04-02_REVISION - M1988112 - Laserfiche WebLink

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:.. 1 1 LJ In eddRion, the Impact of cyanide recovery on'the anticipated chemistry d the tailings seepage was Investigated through a series of laboratory decay experiments conducted by Stuart Miller andiAssociates, located In Sydney, Australia (10).. The expected chemistry Of the fallings liquor end seepage with and without cyanide recovery Is presented In Table 11. The results o} cyanide decay and metals aEtenuatlon In entrained fallings liquor are presented In Table 12. By reducing WAD cyanide In the fallings liquor, the tree metals formed qulcMy precipitated Into the tailings mass. As a result, the potential for elevated cyankle and metals levels In the seepage was slgnlOcanUy reduced. The Improvement In seepage chemistry reduced long-term treatment requirements after mine closure and monftoring requirements, as well as other environmental liabllftles. ' Figure 8 presents the anticipated cyanide decay curves for the decant water end entrained t~llings liquor at the Gdden Cross Mine. By lowering the WAD cyanide levels entering the Impoundment, very low levels of residual metals and cyanide will result, minimizing the Impacts on wildlife and groundwater, while significantly reducing downstream treatment requirements. The expected WAD cyanide levels Will be more than an order of magnftude less than typical values found In decant and pore waters. TABLE 11 EXPECTED CHEMISTRY OF TAILINGS LIQUOR AND SEEPAGE AT THE GOLDEN CROSS MINE Tailing s Liquor Taliin s See a e Without Cyanide With Cyanide Without Cyanide With Cya ide Parametef'! Recovery Recovery Recovery Recovery pH 10.11 9.5-10 9.5-10 8.0-9.5 Hardness (CaCO) 750 2000 --- 2000 Alkalintry (CaC0,3 1000 200 300-500 Sodium 400 400 30000 300-4Q0 Calcium 200-300 800 300~i00 800 Sulfate 1000 2500 iD00-2000 250D Total CN 150-220 25-30 50 25-30 WAD CN 150-220 5-10 20-30 <1.0 Cadmium <1.0 0.1 <0.005 <0.01 Chromium <0.02 <0.02 0.002-0.02 <0.0P Cobalt 0.1 0.3 0.1-0.5 0.25 Copper ------ ---- 5.0-10.0 <0.5.1~.0 Iron 1.0-5.0 5-10 5 8-10i lead 0.001-0.1 <0.1 <0.001 r. ~ <0.1 Mangansese 0.05-0.1 <0.02 0.03-0.OS <0.4 Mercury 0.001-0.009 <0.0005 0.001-0.005 <O.OOb1 Nickel 0.01 0.05 ------ ---- Selenium 0.01-0.4 0.1 <0.05 Zinc 0.5.0 0.01-0.1 2.0.0 0.1 SCN 30-40 30 d0 ------- ----• ~'~ All values in mg/I, unless otherwise stated.