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Pags d coarse bubble diffusers slmplined the process, while maintaining process pedormance. Total cyanide levels were routinely reduced Irom an average of 330 mg/I to less than 2.0 mg/l. Also In the mid-1980's, Investlgatlons were conducted at the Noranda Research Center aimed at designing a cyanide recovery. process employing packed towers and plastic, media Q). Stripping towers slgn~cantly reduced the surface. area required for the~CVR process, as well as the horsepower requirements due to the reduced pressure losses through the system. Employing Information derived In a bench-scale study, a ~,,.~- contlnuous flow pilot plant system was designed and operated. The data obtained In the pilot study was ~" ', util'¢ed In the development of a design for afull-scale stripping system to treat about 2,000 rt'/d of barren 1, ~ ! solution, utilizing an air to Iiguld ratio of 330. 1'- k IZo~ The pilot plant evaluations Indicated the total cyanide levels could be reduced from about 4,000 mg/I to about 720 mg/1, for an overall removal efficiency of 97 percent. The stripped cyanide was reabsorbed In a second packed tower using a counter current caustic sdu[lon. The process empoyed a pH of 2.5 and t~ considerable precipitation of copper thiocyanate and calcium sulfate was realized. It was noted that the precipitated solids would eventually reduce the stripping efficiency, and mechanical cleaning of the media would be necessary and difficult. The study demonstrated that use of modern mass transfer te~:hnology and materials could be employed In the removal and recover of cyanide from clarified barren solutions A full-scale packed tower cyanide recovery system was designed and operated from 7985.1987 by Golconda Engineering and Mining Services at the Beaconsfield Gold Mine In Tasmania (B). The proces~t was termed the C.R.P. or Cyankle Regeneration Process. Initially, a continuous flow pilot plant operation was conducted to establish the appropriate air to liquid ratio, stripping time, and caustic requirements for the absorber. The full-scale facility was-dgs_igned to treat y20Q-_lonr~g$/Q.af~arified barren water using a systen of multiple packed aeration towers. A schematic of the full-scale facility Is presented in Figure t. -~' `,. The plant was designed using the most modern mass transfer technology, plastic media, and cyanide monitoring equipment. The system was designed for maximum safety incorporating an enclosed negative pressure system. Fan exhausts were monitored routinely for HCN with typical values of <7.0 rt,g/m', which were t J70 of the 8-hour 10.0 mg/m' TLV for free cyanide. Cyanide recoveries of nearly 95 percent were reported in the full-scale system. recovery systems. The various laboratory, pilot plant, and IuII-scale cyanide recovery facilities described have demonstrated that application of mass transfer technology coupled with state-of-the-art monitoring equipment and engineering design approaches can be employed In the construction and operation of full-sale cyanide urries and the lack of adeau;it@materlals_and~quipm~r)I. _~ J,ruN-" -ery proces:~can not ba cal properties of lo- w pH._ IfCi~ - Since 7985, an Intensive research effort has been undertaken to expand the capabilities of tha process to slurries, while minimizing the chemical and mechanical problems associated with past systems. The work involved both detailed laboratory and continuous flow pilot plant evaluations conducted for Cyarus Gold of New Zealand, to develop and design the first full-scale commercial cyanide recovery system for tailings slurries to be Installed at the proposed Golden Cross Mine near Walhi, New Zealand. Based on the test results, afull-scale cyanide recovery system utilizing packed towers would be built to treat 200 m'/hr of a 35 percent tailings slurry from a WAD cyanide level of 200 mgt less than to mg/I. The 'i ;~ commercial cyankie recovery process Is known as the Cyanlsorb Process. applications and a patent Is pending