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~ III IIIIIIIIII IIIIII <br />. <br />,~,~ <br /> ~ <br />~~, v__ ;` v~~3~~ <br /> <br />PdiVtD LAND RECLAMATION DIVISION ~~°• <br /> <br />Department of Natural Resources <br />1313 Sherman SI.. Room 215 c, <br />~~~-^~`'.: ~~P~$ <br />m. , <br />~ <br />Denver, C080203 ~. <br />• <br />303 866-3567 `ie ae' <br />RA x: 303 832-8106 <br /> Roy Romer. <br /> Governor <br />DATE: May 1 , 1992 Michael O. Long, <br /> Division D~reotor <br />T0: Bruce Humphries <br />FROM: Harry Posey i~~ <br />RE: Fate of Cyanide in the Battle Mountain, San Luis Project <br />process; M-88-112 <br />Jim Stevens and I met with BMG Consultant Cliff Shutt on Monday, <br />April 27, and had other conversations with BMG mine personnel Ron Zumwalt <br />and Rich Neu and BMG consultant Art Lefler on April 29. A pertinent part <br />of those conversations is reviewed here. <br />NaCN is added to the leach tanks at the rate of about 0.5 gallons per ton <br />of ore. Prior to the use of cytox, the cyanide was to have been <br />recovered from the process as NaCN by adding NaOH to the HCN gas that was <br />liberated from the AVR. However, this process has failed. <br />Between the AVR tank and the first leach tank the mill measures the <br />amount of HCN (gas) from the AVR that is converted to NaCN (liquid) prior <br />to re-entering the leach tanks. Throughout the mine's operation, the <br />amount of NaCN that has been recovered has been approximately 10 gallons <br />every three days. Thus, BMG and their consultants believe that, without <br />cytox, the majority of the cyanide added to the cyanidation process at <br />the beginning of the mill stream has not been recovered. <br />This means that virtually all of the cyanide that went into the tailings <br />stream prior to April S (the date cytox was first added) was vented, by <br />natural processes, to the atmosphere. <br />I contacted MSHA (Dick Durand, Industrial Hygienist; Metals and <br />Non-metals; 303/231-5465), and asked about regulatory or safety limits on <br />free cyanide in tailings ponds and in the air above the tailings. His <br />was not concerned with the air (the molecular weight of air is about 29 <br />whereas that of HCN is 27, so cyanide gas should "float" on air). He <br />said MSHA has no standard for free cyanide in tailings impoundments, but <br />suggested contacting E°A to check on regulatory or danger levels. Their <br />standard deals with NaCN. <br />Whether these quantities are dangerous or just how dangerous they are I <br />believe should be considered prior to approving further milling under <br />these conditions. We should seek assurance from BMG and, perhaps, the <br />hzaith dz~ar=,~~znt or EPA, that thesz level; are non-toxic by breathing. <br />...,.. <br />~95~:F/scg <br />