1992-04-05_REVISION - M1988112 (3)

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iii iiiiiiiiiiiuiu MINED LAND RECLAMATION DIVISION Department of Natural Resources 1313 Sherman St.. Room 215 Denver, CO 80203 303 866-3567 FA x. 303 832-8106 STATE~OF COLORADO pF COO w _,. '~9 v~ie'~~ O «,~~?~. ~ X8]6 ~ Roy Romer. Governor Michael B. Long. Division Director DATE: April 5, 1992 T0; Larry D. Oehler FROM: Jim Pendleton RE: "Technical R rt roposal - Cyanide Detoxification at San Luis" Response to 3/31/92 NOPV Preliminary Technical Revision Application Battle Mountain Gold (Permit No: M-88-112) I have reviewed the chemical engineering study referenced above. Briefly, the report discusses five possible remedial actions to be used to reduce the cyanide content within the tailings slurry at the Battle Mountain Gald (BMG> mine near San Luis. The report was prepared for BMG by BEI Engineers / Constructors Inc. (BEI), consultant to BMG. The conclusion of the report is that the preferred method for detoxification of the tailings is thraugh the use of "Cytox" chemicals, which are a proprietary product marketed by BEI. The report presents data which projects relatively rapid reduction of the cyanide within the slurry through the application of the "Cytox" chemicals. "'Cytox' (derived from ~anide detoxification) is a ferrous sulphate compound 'stuffed' with differing levels of zinc." BEI represents "Cytox" to be an improvement over the relatively common Ferrous Sulphate process. The drawback of the Ferrous Su]phate process being that the end product is "highly soluble" in comparison to the "totally stable" end product of the "Cytox" process. Discounting BEI's choice of descriptive language within its proposal / report, the data suggests that the "Cytox" chemicals do result in a more stdbie end product precipitate than the more common Ferrous Sulphate process. However, BEI does include cautions within its report. The data presented was collected under laboratory conditions. BEI also observes that the source of BMG'S problem is probably an excess of Copper, resulting from the unexpecited Copper content of the San Luis ore. BEI projects that methodology could be developed to remove the excess Copper levels from the tailings slurry. Finally, BEI projects that a long term slurry treatment could be implemented to maintain low cyanide and Copper levels in the tailings slurry. In the interest of eliminating the potential hazard represented by the existing elevated cyanide levels in the BMG tailings, I recommend that we approve the use of the proposed "Cytox" process. We must require BMG conduct thorough monitoring of the process to verify the final result. Further, we should caution BMG of their responsibility to solve any environmentdl