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t . <br />1 <br />:... <br />,... ., <br />. -... <br />• <br />r .... _ . <br />Page 9 <br />The results from the various laboratory, pilot plant, and full-scale systems demonstrate the effectiveness of <br />' the processes for the recovery and reuse of cyanide from dadHed barren and decant soutions. In addHlon, <br />the resuts demonstrate the reliability In predicting lull-scale operation based upon data obtained from <br />laboratory or plot plant Investigations. The reabsorptlon of cyanide ldlowing stripping is a well documented <br />end proven process capable of recovering between 95 to 99 percent of the stdpped cyanide. <br />.. ..~: <br />However, h Is still widely believed that the approaches and equipment utilized in the treatmentof sdutlons <br />are not suitable for the recovery of cyanide from slurries. In order to expand the appllcabilhy of cyanide <br />' recovery Irom sdutlons to slurries, extensive laboratory and pilot plant investigations have beeniundertaken <br />on behaff of Cyprus Gdd of New Zealand since 1986 to the present (Madder, unpublished rl3sults). The <br />Investigations have proven the effectiveness of recovering cyankle from fallings slurries. The thext section <br />' of the paper details the Investigations and the results of those studies. <br />RECOVERY OF CYANIDE FROM SLURRIES <br />' Introduction <br />' Although recovery of cyanide from solutions is desirable, recovery of cyanide Irom slurries Is gptimal for a <br />variety of reasons Including: <br />' 1. Elimination of sedimentation or clarification prior to treatment of the barren solution, thereby <br />reducing both metallurgical capftai and operating costs. <br />2. Recovery of an expensive reagent Is realized, which significantly reduces operating costs and the <br />' hazards associated with the manufacture, transport, and storage of cyanide. <br />3. Reduction of the total and WAD cyanide content entering the tailings Impoundment, thereby <br />' minimizing the toxicity effects of cyanide on wildlHe, and significantly reducing the (potential for <br />generation of leachate containing unacceptable levels of metals and cyanide. <br />4. Elimination of a lining requirement In many applications. <br />5. Reduction of total cyanide in mine backiill to acceptable levels, thereby eliminating the need for <br />wash plants In certain Instances. <br />~J <br /> <br /> <br /> <br />LJ <br />6. Reduction of total cyanide and metals concentrations In the decant water and associated cyande <br />containing wastewaters, slgn'rficantly decreases the costs, while Increasing the retiabllity and <br />perfomtance of downstream treatment processes. <br />t. ; <br />7. Minimizing generation of undesirable treatment by-products such as ammonia and cy~nate which <br />exhlbh their own Inherent toxicity and may require significant capital outlays for treatrttent. <br />The need for development of treatment processes for recovery of cyanide Is essential to the isuccess of <br />current and future mining operations. The requirement stems from concerns over the volatil8y~of the gdd <br />price end the realization that more stringent environmental regulations will be developed restricting the <br />concentrations of cyanide discharged Into fallings Impoundments and remaining In solid wastes. <br />The best application of cyanide recovery Is as apre-treatment process prior to discharge of talllhgs Into an <br />Impoundment. The operational problems and costs associated with achieving high treatment efficiency <br />under low pH conditions minimize Its value es a primary treatment alternative. It Is best salted for reduction <br />1 <br />