1992-04-07_REVISION - M1988112

• Permit No: M1988112
• IBM Index Class Name: Revision
• Doc Date: 4/7/1992
• From: D J PENDLETON
• To: BATTLE MOUNTAIN GOLD
• Type & Sequence: TR3
• Media Type: D
• Archive: No

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APPENDIX I
GENERAL CDMMENTS
• F' .
It may be beneficial for all of us to discuss now, certain future considerations
that the state must address to help prepare the way. There is no particular
order to these Comments.
1. Cyanide Definitions
Definitions within the mining, chemical and medical industry about "Cyanide" are
quite varied. In the gold processing industry we talk about 3 cydnide "types,"
namely Free, MAD and Total. We at BEI agree with the generally held definitions
of the industry, as follows:
Free - Limited to only 2 species: (CN)~ and HCN. (CN)~ is highly soluble
in water but it exists exclusively only at pH > 11.0. HCN exists,
exclusively, at pH < 7.5. At pH's tretween 7.5 and 71.0 both species
mutually exist in proportion to the pH, see attached fig. 1.
The only exact way to be certain of free-cyanide content is to adjust the
pH to 11.0 or greater and analyze for {CN) once all HCN i5 converted to
(CN)~, by ion chromatography. The silver nitrate technique is
inappropriate as an analytical method because of interference from WAD's
end other chemicals present within the tailings.
WAD - "Weak Acid Dissociable Complexes" are those metal-cyanide complexes
which can, under certain acidic conditions, liberate (CN)_ to the "free"
state but which, under typical analytical conditions are often not
revealed. At a pH of 4.5 all WAD will release cyanide. Attached as table
1 are these complexes in order of their strength (resistance to
breakdown). WAD analysis is first accomplished by distillation and
therefore WAD inevitably also includes all the free-cyanide component of
the solution.
Hence WAD cyanide analyses must show a greater cyanide level than a free-
cyanide analysis.
Total - A total cyanide analysis is composed of all the free-cyanide, all
the WAO cyanide, and all other compounds normally not broken down when
analyzing for WAD. Thus, compounds Such as Zn2Fe(CN)6 also then "give-up"
their (CN) to the total analysis.
The writer considers the key components to be Free and WAD since immutable
compounds present no hazard.
2. Cyanide Concentrations at San_Luis1Doc. No. 2382F). Point (1)
BMG has been restricted to "must attain total cyanide levels of less than 4.4 ppm
or less, and the weak-acid-dissociable levels of less than 3.8 ppm."
With respect, these are unattainable anywhere in the world in any ~o1d extraction
process. Before further discussion, however, two points of clarification are
offered.