1992-06-10_REVISION - M1988112 (2)

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ADa TECHNOLOGIE:. IPIC. TEL=~)--~'a=-`E~=' 1i~r~ r~-~ ~-~- 2~~~0~ D1o.002 P.O~ • o 'There is no indication that the processing of the pond with peroxide will require continued processing of ore through the plant (as was purported with the CYTOX process) and thus I would again raise the suggestion that the processing of ore be stopped while the cyanide levels in the pond are reduced to the target 4 ppm total cyanide by peroxide alone. In introducing this approach at the May public hearing, BMG indicated that the delay in putting peroxide treatment !n place would mitigate against its use as sn alternative to CYTOX, but this delay seems to not be an issue of substance at this point. o The Introduction of peroxide into the pond without some means of mixing certainly raises the probability that uneven treatment will occur a~td that cyanides will escape destruction. Gravity induced mixing and diflYtsion of the reagent are not reliable techniques. Dr. E.A Devuyst, in the paper entitled "G~anide Pollution Control -The Inco Process" distributed at the (BMG sponsored) meeting we ttecently attended to hear detalls of the process notes that: "Hydrogen cyanide is selective for cyanide in solutions, but is an extremely expensive reagent which, la roomy cases decomposes rapidly In the presence of solids. This may lead to high reagent consumption and/or incomplete cyanide destn~clion" (Italics, mine). If peroxide Is used in the San Luls ponds, then it would seem prudent to assure mixing to at least have a chance of maximizing cyaanides decomposition. It~ection of the peroxide et the spigot might move toward accomplishing this but probably at the cost of significantly higher peroxide demand. a AS in much of the work and proposed work which has preceded this latest revision, there is precious little laboratory data with real solutions under conditions that accurately reflect practice at San Luis (for ex mple, simultaneous use of peroxide aad CYTOX) to demonstrate the ab~ity to reach 4 ppm cyanide levels. The AVR system was supposed to work (based on design estimates) end it apparently did not. The decompoeleloa of cyanide in the ponds died not proceed as MODELED and iaadegnate testwork was perform$d to determine whether it should have. Ore characterizations were not all they should have been, and hence the copper "problem" which complicatBs the cyanide destruction chemistry. CYTOX was supposed to reduce cyanides (total cyanides as we were given to understand at the hearing) to 4 ppm but there is no evidence that this Is going to be achieved. All In all, there seems to be too much emphasis to jump on the iWtest "maybe" technical fix and not to test it first In a thorough manner. A L060992DEH1