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AUG- J-J5 Wr.L 1 h M CROWN Trc-INULUUY 1-.aX NU. J1 r�45UU6b F. A Nickel, copper and zinc cyanide complexes coprecipitate with ferrocyanlde and can aid in tha precipitation of ferrocyanide and lower minimum achievable cyanide concentrations. While among the most stable of cyanide complexes, ferrocyanide In aqueous solu- tions will decompose In ultraviolet light generating hydrogen cyanide. In tailings slurries, absorption of the ferrocyanide complex by solids provides control (Ingle$-2). Removal of copper cyanide complexes as ferrocyanides can be enhanced by the ad- dition of ferric ions in the form of ferric sulfate. Cuprous ferrocyanide is soluble in cyanide at pH's higher than 9, therefore, pH adjustment can also provide enhanced copper cyanide removal. On contact with acids, ferrocyanide forms the Insoluble hydroferrocyanic acid. Following closure of treated dumps or tailings ponds, the ferrocyanide complex will remain stable in the presence of decomposition products of sulfide minerals. APPLICATIONS Ferrous sulfate can be used to treat cyanide in tailings ponds and heap leach piles forming stable complexes which are nontoxic. If solution is discharged, further treatment will be required in order to comply with discharge regulations. The ferrocyanide complex precipitates and is also absorbed by solids present in tail- ings and heap leach piles. The Complex remains in solid form following water evaporation and is nontoxic. The cyanide content of tailings ponds can be easily controlled to maintain free cyanide levels of less than 50 ppm sodium cyanide. These levels are essentially non- toxic to birds and wildlife. For the treatment of mill tailings, ferrous sulfate can be added either In solid or solu- tlon form directly to the tailings slurry. In treating existing pond solutions, a simple recir- culating pump loop with a break tank which returns solution to the pond can be used. The ferrous sulfate solution is added to the break tank. (See attached application flowsheets.) Reaction kinetics are rapid, the reaction being essentially complete in 10 to 15 minues. Residence times In pump sump boxes and tailings pipelines are generally sufficient to ensure that discharges to the tailings pond contain less than 50 ppm sodium cyanide. — 2 —