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<br />MEMO <br /> <br />DA'L'E: June 16, 1992 <br />TO: Dr. Nora Jacques Esq <br />FROM: D.E. Hyatt, Ph.D. <br />RE: Comments on Battle Mountain Gold (BMG) Technical Revision 007 <br />Subsequent to our recent discussions regarding the on-going efforts at the Sa I..uis site of <br />13MG's operation to reduce the cyanide level in the taillngs ponds and holdi g pond to 4 <br />ppm, and in continued response to the comments by Mr. A.J. Douchane of B G regarding <br />the need to continue processing ore while the pond is being treated I offer t e following <br />comments: <br />Continued processing of ore for gold recovery at the San Luis site re utres <br />that cyanide (sodium cyanide) be continuously added to the atcr <br />returning from the tailings pond to the mill's vat leaching circuit. <br />The continuous addition of this cyanide puts an additional strain o the <br />removal systems that are being tried (f;'I'TOX and, now, hyd ogen <br />peroxide) in the pond to attempt to meet the permitted 4 ppm le el of <br />cyanide in the ponds. <br />Since the objective of the current treatment work at San Luis is to <br />demonstrate that the permitted cyanide level can be achieved and t also <br />render the ponds safe at this 4 ppm level, then the continuous additi n of <br />new cyanide to the system appears unnecessary to achieve these ends., <br />__ Mr. Douchane, in his letters of June 11, 1992 and June 12, ]992 re rates <br />-t'i'cs opinion, concurred with by both Degttssa and FMC (supplie s of <br />hydrogen peroxide), that the mixing and solids deposition in the pon are <br />integral for best cyanide removal. This is opinion only at this point inee, <br />to my knowledge, no testwork to compare cyanide removal rates wit and <br />without circulation, in the actual pond, has been completed. <br />However, even if circWation is 6enellclal, the option exists to mai rain <br />this circulation (and even to maintain the solids content of the s urry <br />entering the pond from the mill if solids are intrinsically bane cial) <br />without the addition o[ cyanide in the mill. That is, recirculation f the <br />pond water, through the mill and back to the pond, with on-going se of <br />CYTOX and peroxide, should demonstrate the ability of the pro osed <br />systems to meet the permitted 4 ppm cyanide level in the pond i the <br />shortest possible time. <br />M061692DEH1 ~x~`~ <br />