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<br /> <br />Heao Detoxification <br />Recently Inco has been involved in applying its process ro <br />the rinsing and detoxification of heap leach pads which are <br />widely present in the U.S. At Sunshine's Snow Caps operation <br />in California, the existing barren solution pond was conversed <br />into a SO,/Air reactor with minimal capital cost. Troatment is <br />on 500 gallons per minute of return water from the heap and <br />cyanide was reduced from 180 to 1 mg/L in less than five <br />months of solution recirculation. Typical results are shown in <br />Table 4. <br />Table 4: Heav Rinse Treatment Results <br />• Feld (mg/L) 180 CNr <br />(initial) 120 Zn <br />3 Cu <br />• Treated Solution (mg/L) : < 1 CNr <br />0.1 - 0.2 Zn <br />0.1 - 0.2 Cu <br />• Reagents 3 g SOa/g CNT <br />3 g NaOH / g CNT <br />0 - 5 mg/L Cu~* <br />PROCESS CONTROL STRATEGY <br />The process control strategy for the Into process is based on <br />measuring feed and effluent cyanide concenaadons and <br />monitoring of process indicators such as oxidation-reduction <br />potential, free cyanide probe rrzdings and dissolved oxygen <br />readings. <br />Inco has developed an analytical method for cyanide <br />analysis that takes only minutes and can be used by operators in <br />the plant for quick response to reagent adjustments. Adequau <br />instrumentation for controlling process variables has greatly <br />reduced reagent consumption. Inco is currently developing an <br />automatic control package which will further optimize reagent <br />utilization. <br />5 <br />