1990-01-09_REVISION - M1988112 ‎(6)‎

• Permit No: M1988112
• IBM Index Class Name: Revision
• Doc Date: 1/9/1990
• Doc Name: FAX COVER
• From: STEFFEN ROBERTSON & KIRSTEN
• To: MLRD
• Type & Sequence: AM1
• Media Type: D
• Archive: No

'90 C+r. 99 1&:1; $ 30i 955 394; SF:k DEN~~E F' 0
BATTLE MOUNTAIN RESOURCES, SAN LUIS PROJECT
CMLRD ADEQUACY LETTER RCSPONSCS
Page I of 28
EXHIBIT D, MINING PLAN
1. On page D-14, reference to a "dilute cyanide solution" is made in
discussing the carbon-in-)each method of ore processfng. What is the
expected concentration of cyanide in this process solution?
RE5°Oh;SE: The expected concentration of cyanide in the carbon-in-leach process
solution is 0.5 to 0.75 lbs per ton of ore. The solutions are
expected to have total cyanide levels of approxlmatel:~ I75 ppm and
free cyanide levels of approximately 60 ppm. As described on page
D-16, these solutions are contained in sealed tanks only.
Additionally, the mill design inclines internal curbing and a
solution collection system to further ensure containme7t within the
mill in the unlikely event of a tank .eak (see response to question
5).
?. On page D-16, referenca is made to use of sulfuric, acid in treating
the tai]Ings slurry prior to disposal. An equilibrium diagram is
provided tc indicate that 70% of the cyanide wi)J be volatilized at
pH 9. What is the expected concentration of free cyanide 1n the
treated slurry solution?
R~SiCh?SF: Laboratory test methods currently available do not al~..Y an
accura':e and consistent determination of free cyanide. Frer _ya,~•'a
is unstal,le at the pH of the slurry and difficult to metsur~ ::rd the
test method is subject to interference from other elenents. T,tal
and weak acid dissociabie cyanide tests provide a mere reliable
indication of cyanide present 1n a solution. i3MR performed laboratory
testing to evaluate total, weak acid dissociabie and Free cyanide
present in the slurry solution. The data shows total cyanide values
of ".,4 ppm and weak acid dissociabie cyanide values of 3.8 ppm. The
iota also indicated free cyanide values of 52.0 ppm, well in excess
n~ the total and weak acid dissociabie values and, therefore,
~~sically impossible. In this case, we believe that thiocyanate is
~~~~sing interference in the testing. The more reliable tctat and weak
acid dissociabie cyanide tests indicate that actual free cyanide
levels in the tailings slurry are below 4.4 ppm. The 1ab~oratory test
data is included as Attachment 1 and will be added to Appendix F of
the permit amendment application. Humidity cell testing is ongoing,
however, preliminary test results as well as test resu',ts from the
approved permit indicate that the San Luis ore is not <:cidic.