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~. - - <br />• . <br />.. <br />f: - Paps ~ <br />The results from the vadous laboratory, pilot plant, and full-scale systems demonstrate the effectNeness of <br />the processes for the recovery and reuse of cyanide from darMled barten and decant sdutlons. In addhkxt, <br />the resorts demonstrete the reliabiltry In predicting lull-scale operation based upon data obtained Irom <br />laboretory:or p0ot plant Irnestigatlons. The reabsorption of cyanide fdlowing stdpping LS a well documented <br />and proven process ppable of recovering between 95 to 99 percent of the stripped cyanide. <br />• ~ ~ :~ :: <br />However, h Is st01 widely believed that the approaches and equlpmeM utQlzed In the treatment of adtrilons <br />are not suhable for the recovery of cyanide from slurries. In order to expand the applicability of cyanide <br />recovery from solutions to slurtles, extensive laboratory and pilot plant investigations have been undertaken <br />on behaH d Cyprus Gdd of New Zealand since 1986 to the present (Hodder, unpublished results). The <br />Investigations have proven the eftectNeness of recovering cyenlde from tailings slurries. The next section <br />of the paper detaAs the investlgatlons and the results of those studies. <br />RECOVERY OF CYANIDE FROM SLURRIES <br />introduction <br />Although recovery of cyanide Irom solutions is desirable, recovery of cyanide from slurries Is optimal for a <br />variety of reasons Including: <br />t. Elimination of sedimentation or clarification prior to treatment of the barren solution, thereby <br />reducing both metallurgical captal and operating costs. <br />2. Recovery of an expensNe 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 impoundm?nt, thereby <br />minimizing the toxicity effects of cyanide on wildl'rfe, and significantly reducing the potential for <br />- „ ., _ generation of Ieachate containing unacceptable Ieveis of metals and cyanide. - _ - . _ .. ,.. <br />4. Eliminatlon of a lining requirement In many applications. <br />S. Reductlon of total cyanide In mine backfill to acceptable Ieveis, thereby eliminating the need for <br />wash plants In certain Instances. <br />t° = a _- 6. Reduction of total cyanide and metals concentrations in the decant water and associated cyanide <br />,. <br />` -' ' _~ - containing wastewaters, slgnficantiy decreases the :costs, white increasing the reliability and . _.. -- <br />°._ " - - pertormance of downstream treatment processes. - <br />i~r:... -. --... .. <br />~; <br />7. Minimtzing generation of undesirable treatment by-products such as ammonia and cyanate which <br />exhibit their own Inherent toxicity and may require slgnHicant capital outlays for treatment. <br />The need for development of treatment processes for recovery of cyanide Is essential to the success of <br />current and future mining operations. The requirement stems from concerns over the vdatil2y of the gdd <br />price and the realization that more stringent environmental regulations will be developed re:trlcting the <br />concentrations of cyanide discharged Into tailings Impoundments and remaining In solid wast~as. <br />The best application of cyanide recovery Is as apre-treatment process prior to discharge of fallings Into an <br />Impoundment. The operational problems and costs associated with achieving high treatmeru eNiclency <br />under low pH condftions minimize Its value es a primary treatment alternative. It Is best suited fr~r reduction <br />