1992-05-04_REVISION - M1988112 (3)

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i Table 1 -Cyanide destruction results -treatment of CIP or CIL tailings or repulped tailings MIM CN,e, Aeaay ImprL) Raapant ueape (pip CN,e,) Bdote Aher SO, Lime CW Colosseum 364 0.4 4.6 0.12 0.04 Keva Rner t50 5.0' 6.0 0 0.30 Equrry t75 2.3 3d D 0.03 Casa Be2mi 150 2.3 3.4 - O.tO Westmin Prewar t50 <0.? 5.8 - 0.72 Goltlen.Beer 205 0.3 2.8 - - 'Compete ryanitle tlestruulion not regwretl 1o meet permit levels. discharge. Relying on secondary vest- ment can also result in pond water bal- ance concern ifthe treatment capacity is exceeded by precipitation inflow rates. An opera[ion runs the risk of temporary plant shutdown during periods of in- clement weather if an unmanageable pond overflow is anticipated. The prob- lem of migratory birds using cyanide contaminated ponds is also of increaz- ing concern az hazbeen demonstrated in NevaQa and other places. All of the above problems arc over- come with destruction of cyanide at the source using the Inco process. A rela- tively small, unlined pond can be used that results in substantial capital cost savings. By using natural degradation az a polishing step, tailings pond levels can be easily managed year round while providing a safe habitat for migratory birds. Other key advantages of slurry vest- ment are the provision of clean solids forunderground backfill operations and of clean recycle water to flotation cir- cuits and grinding mills treating preg- robbing carbonaceous feed. Finally, natural degradation ponds characteristically direct operators to- wards maintaining low cyanide concen- trations in leach solutions. Many ores require high strength cyanide solution for maximum recovery. Slurry treat- ment provides this opportunity without complicating pond conditions. Table 2 -Cyanide destruction results - treat- ment of barren solution on pond waters Mme CN1O, Aaeay (mp/y Raapent ueepa (prp Ctt,e,) Balore Auer SOr Lime CW McKean (oanen) 370 0.2 4.0 4.0 0 LynnpoW(pontl) 106 0.6 7.0 9.0 0.12 M~neml Hill(barten) 350 0.5 6.0 9.0 0 Lac Strom (pontll t0 0.5 5.0 D Cilaoel (banan) 350 5' 4.0 0 St. Antlrew (pond) t 5 1 5.0 - 0.70 'Complete ryanitle destruction rot regWretl to me~r permtl levest. Barren solution, pond water, heap leach rinse sofurion Despite the advantage of treating pulps, mining operations can some[imes take advantage of natural degradation. Plants using the Merrill-Crowe gold recovery process will often only have to treat barren bleed solution to control cyanide levels in holding ponds. In cases where large natural ponds arc available, many companies choose to treat pond water bleed into a polishing pond before discharge to the environ- ment Operations that have chosen the SO/ Air process on barren solution arc loco- Queenston's McBcan (I I m'Po or 3gg cu ft per hour), American Copper & Nickel-Homestake's Mineral Hill (14 m'/h or 494 cu ft per hour) and Citadel (5 m'Po or 176 cu fr per hour). At Mineral Hill, there can be no net discharge to the environment Barren solution is therefore collected in a small, lined pond after treatment The pond waur is used az process waur and to wash tailing solids. Wazhed solids arc impounded on a lined surface from which any seepage is collected and recycled to the cyanide deswction facility. Treatment of pond water into a pol- ishingpond waz implemented on a sea- sonal basis (about six months a year) at Lynngold's MacLellan (100 m'/h or 3531 cu ft per hour), Minova's Lac Shorn (170 m'/h or 6003 cu ft per hour) and St Andrew Goldfl eid's Stock Mine (170 mr/h or 6003 cu ft per hour). Typical plant re- sults for barren or pond treatment are summarized in Table 2. In all of these operations, a single reaction tank is usually used with the same design criteria az used for pulp treatment. Recently, Inco has been involved in applying its process to the rinsing and detoxification of heap leach pads that arc widely pres- ent inthe US. At Sut}shine's Snow Caps operation in Calif¢rnia, the existing barren solution pond waz convened into a S0,/Air reactor w+th minimal capital cost. Treatment is oft 32 LJs 1500 gpm) of return water frog the heap. Cyanide was reduced from I>SO to 4 mg/L in less than five months of'solution rccireula- tion. Process control strategy The process conttol sttaugy for the Inco process is based on measuring feed and effluent cyanideconcentrations and monitoring of process indicators such as oxidation-reduction poundal, free cya- nide probe readings hrrd dissolved oxy- gen readings. Inco has developed an analytical method for cyanide ianalysis that takes only minuus. It earl be used by opera- tors in the plant fonquick response to reagent adjustments) Adequate instru- mentation for conmm¢¢Ming process vari- ables haz greatly reduced reagent con- sumption. Inco is ct~tentiy developing an automatic contm~ package that will further optimiu reagent use. Capital costs Capital costs for~the Inco SO,/Air process depend on the type of treatment required and the sizh of the operation. The main capital itgms are a reaction tank, a mixer with mdtor and support. an air compressor (or blower) with associ- aud piping, an SOt reagent system with associated instrumentation and piping, a copper sulfate delivery sysum (when required) and a lime delivery sysum. For a large instal la 'on (3 kt/d or 3300 stpd)requiring5tol t/d(S.Stollstpd) of S0, and treating pulps for total cya- nide detoxification, ~e principle equip- mentcost is about $ 500.000, or about SCl ~ million installEd. Alternatively. the sl7rtle operation only requiring seazonal pond water treatment can have a cost of SC500.000 installed. In many cases, existing equipment can be used for operations switching to the Typical flowsheet or SO~Air system.