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Page 2 The excess sdullons and sdlds are normally disposed of In an Impoundment. Several potential problems may result from disposal Including contamination of groundwater, exposure of wBdlile and water fowl to elevated cyankfe concentrations, and Impacts on surface water environments fdlowing discharge of treated or untreated effluents. The're' Is a need to mitigate these problems, and to minimize potential adverse environmental Impacts. The conventional approach IrnoNes treatment df mflI tailings or decant sdutlons and lining of Impoundments, whle Ignodng the options assxlated whh•recyde of process sdutlons and reagents. The capital and operating costs of wastewater treatment and tailings disposal are substantial and often dictate the economic viability of a mining project. Treatment costs are Increasing sharply due to more stringent environmental regulations and the need for more sophisticated and advanced techndogies. In conjunction with treatment and solid waste disposal costs, are the rapidly Increasing costs of water and reagents, particularly cyanide. The cost of cyanide has risen sharply due to world-wide demands and shortages. The spot•market price for cyanide In certain Instances Is several times higher than the average price. The cost of cyanide is a primary concern in remote areas where cyanide availability is limited. As a result, every attempt must be made to reduce reagent consumption through recycle anc' recovery to minimize the costs of production and of environmental protection. One excellent approach Invdves recovery and recycle of cyanide from process solutions and slurries. Historically the process, termed acidification, vdatilization, and reneutralization or AVR, has been employed In the recovery of cyanide f•om clarified barren or decant soutions. Although cyanide recovery has been employed In the full-scale recovery of cyanide Irom sclutions, only recently has considerable Interest In the process resurfaced, particularly for application with tailings slurries. This paper describes In detail the history, chemistry, applications, advantages, and costs of various cyanide recovery processes. Emphasis is placed on the development of the Cyanisorb Process for recovery of cyanide from ;slurries. This process has been tested and proven through an extensive pilot plant evaluation for application at Cyprus .. Gdd's proposed Gdden Cross Mine In New Zealand, and would represent the first full-scale application of cyanide recovery from slurries. t.' . . HISTORY OF CYANIDE RECOVERY PROCESSES The recovery of cyanide from mining solutions through acidification, air stripping, and reabs.orption was _ originally known as the M1Ie Crows Process (f}. The process Involved acidifying clamed barren sdution,~~•'_ " • . _ , then strlpping the HCN formed and reabsorbing h from the air stream wkh a caustic or m1k d lime spray. The process was employed at the Flin Flon Mine operated by Hudson Bay Smelting and Mining Company ' from about 1930.1975 (2,3}, The Canadian mining operation Invdved cyanidation of gold bearing talings originating from the flotation of a copper•zinc ore. To condition the barren solution for stripping, the pH was I ~, first adjusted downward to 2.5 with sulfuric acid supplied from the zinc electrdytic plant. The acidified soution was then passed through a series of four strlpping towers packed with w~~oden grids. The towers were constructed of concrete and measured about 5m x 2m x 7.Sm In height. The stripping towers were operated In a series, each connected to one of lour concrete absorption tunnels by means of closed loop recycled air streams. The air and liquid vdumes In each strlpping loop were about 56,000 m'/hr and 1D7 m'/hr, resulting In an air to I(quid ratio of about 525/1. The HCN entrained in the air stream was reabsorbed by ccntacting the j ~ air stream with time slurry sprays and recollected In a central storage tank. The stripping process required