REP43993

• Permit No: M1988112
• IBM Index Class Name: Report
• Doc Date: 4/16/1992
• Doc Name: FAX COVER
• From: BATTLE MOUNTAIN GOLD CO
• To: MLRD
• Media Type: D
• Archive: No

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J. J. BYERLEY ET AL
An-X-2). The An-X-1 column is sized [u cnllcct virtually all
the residual meta! cyano complexes (Cu, Fe, NI, Co, etc.} as
well as a small perrcntatge of SCN' and unknown amounts of
sulfate and thiosulfate (Snopck, ]986). The Aa-X-2 column
wllects 8D-85% of the SCN' and again unknown amounts of
sulfate and [hiosulfate (Trang,1985), After step four, the main
wastes[rcamwill contain csscntiallyno Cu, Fe, Ni, Co, possibly
a few mg/1 Zn, about 15%a o[ the original SCt~r concentration
and all original ryanide less the amount associated with the
metals removed in Lbc previous steps. Step five shows the
waste stream being recycled after the pH has been raised and
fresh makeup cyanide has bees added For total recycle there
will be a build-up of impurities in the circuit not removed or
controlled by the preceeding steps, thus a bleed of between 2
and 5°l0 of the recycle stream is rcgtfued Step six is an
oxidation step to destroy the SCN- and CN' in the bleed
stream. To accomodate the water balance in the circuit it may
be necessary to upgrade the cyanide recycle stream by a factor
of at least 10 using an anion exchanger- The entire pror^cc u
not wmplete until exhausted columns have been eluted and
re;~enetated. Of particular iatere;t i; thq yluant from the
second anion exchange (An-X-2). This column contains SCN'
with some sulfate and thiosulfatc. The alkaline eluan[ stream
may be oxidized electrochemically to regenerate
approximately60% of the Gl~moietyFrom SCIT and recycled
to the cy'.widation circuit (13yerley and E.nns,1984; lJS Patent
4519880; U5 Patent452666Z).
PRECIPITATION STUDIES.
Copper Cyanide Precipitation
The metal complexspeaes formed when copper interacts with
cyanide in basic solution (pH 1Q-12) have been identified as
Gtit(CN)z-, Glt(CN)3~ and Cu(CN)a3 [Copper and PIat,1966;
Penaeman and Jones,1956; Noblitt (7973)]. 7n the case oFzinq
the cyano com2plexcs aze reported to be Zn(CN)z, Zn(CN)~
and Zn(CN)q ~ (Iza[t et al, 7965). Besides these aqueous
complexes i[ u Found the[ at low pH, solid CuCN i5 formed
No evidence of asimilaz solid zinc cyanide or ZnCN+ has been
reported or found experimentally in this work. The stability
constant data for these and other c}^alt0 complexes of interest
in this Communication arc cpmpilcd in many volumes (Sillen,
1964; SIDety 1971],
Tn view of the above an aqueous solution containing cyanide,
copper and zinc is a complicated system which may be
adequately represented as a solution containing the copper
and zinc cyanide complexes noted above as well as HZQ, H+,
CN", HCN, Cu+, and Zak+. Using this aqueous solution
model two sets of equations can be written to represent the
chemical equilibria before and after the precipitation of
CuCN. This equih~brium model can be used to determine
et7aceatrations of all species at different pH values of the
cyatude solution thereby predicting the precipitation of CuCN
P. 07
i
and the decomposition of zin~ cyanide complexes upon
aGddipti00.
FIGURE 2
DISTRIBUTION OF DIAGRAM FOR COPPER
CYANIDE GOMPLEXES
to
0.8
m
~u O.fi
c
N
C
a
~ O.d
0
0
b 0.2
v,
'•~~ u(Ct•Q4
.`
.~
z-
Cu(CN)3
1
1
1
1
Cu(CN)2 1
L
1 ____ a_t
)
1 A-2
1
1
t
CuCN
0 ,`~
p 4 6 8 t0
pH
I"igute 2 shows the copper cyanide distribution diagrams
calculated using the equilibrium model for two solutions, one
a copper-cyanide solution (A-1) and the other a
capper-zinc-cyanide solution (A-2), (refer Co Table 2 for
solution composition). These diagrams provide an overall
picture of the equilibria of the systtms. A vertical 1'me drawn
at a selected pH divides the distribution curves into segments
which are proportional to molar ratio of the concentration of
a copper containing cyano complex and the total
concentration of copper in solution. For example at pH 3 the
fraction of capper present as CuCM is 0.70 and of Cu(CN)a--'
is D.30. The fractions of Cu(CN)3a-and Cu(CN)a'3 arc quite
small at this pH. As the pH increases the di, tri and tetra cyano
complexes become more predominant as competition o(thc
proton for cyanide ion weakens. 1t is interesting to note that
there is no range of pH where more than two
copper-containing cyano species are present in appreciable
quantity. The distribution diagram also indicates the[ the
distribution of copper cyano complexes is affected only
marginallyby the addition of Zn(II) to [he solution. A similar
distribution diagram can be calculated for the zinc-cyanide
- 333 -
RANDOL GOLD FORUM 88