United States Patent [19]
Coltrinari
[11] Patent Number:
[45] Date of Patent:
4,708,804
Nov. 24, 1987
[75] Inventor:
[73] Assignee:
26 Claims, 2 Drawing Figures
Primary Examiner-Ivars Cintins
Attorney, Agent, or Firm-Sheridan, Ross & McIntosh
Effluents", 13th Annual Meeting of Canadian Mineral
Processors, Ottawa, Ontario, Jan. 20-22, 1981, paper
No. 21, pp. 380-416.
J. C. Ingles and J. S. Scott, "Overview of Cyanide
Treatment Methods" presented at The Cyanide Gold
Mining Seminar, Ottawa, Ontario, Canada 1/22/81.
[57] ABSTRACT
A process is provided for removing cyanide from a
dilute cyanide solution. The solution is passed through a
weak base anion exchange resin to absorb cyanide complexes.
The resin is eluted with a weakly basic Ca(OH)z
solution, to produce a cyanide-rich eluate. Elution is
accomplished by recycling the eluting fluid past a bed
of solid Ca(OH)z, to maintain the eluting fluid in Ca(
OH)2 saturation. Recycling in this manner produces an
eluate with relatively high cyanide concentration using
•economical reagents. The eluate is subjected to an
acidification/volatilization process including acidification,
preferably with H2S04, heating by introduction
of steam and removal of volatilized HCN by an air
sparge. The HCN-rich off-gas and slats produced therefrom
may be recycled in the process. The cyanide-depleted
waste streams may be disposed of in, for example,
tailings ponds.
[56] References Cited
U.S. PATENT DOCUMENTS
2,507,992 5/1950 Payne et al. 127/46
2,900,227 8/1959 Dancy et al. - 23/14.5
3,357,900 12/1967 Snell 203/47
3,391,078 7/1968 Odland 210/670
3,788,983 111974 Fries 210/684
3,869,383 3/1985 Shimamura et al. 210/684
3,909,403 9/1975 Abe et al. 210/684
3,984,314 10/1976 Fries 423/24
4,115,260 9/1978 Avery 210/684
4,267,159 5/1981 Crits 423/367
4,299,922 1111981 Holl et al. 521126
4,321,145 3/1982 Carlson 210/678
4,543,169 9/1985 D'Agostino et al. 423/24
OTHER PUBLICAnONS
Scott, J. S. et aI., "Removal of Cyanide from Gold Mill
Enzo L. Coltrinari, Golden, Colo.
Resource Technology Associates,
Boulder, Colo.
[21] App!. No.: 750,419
[22] Filed: Jun. 28, 1985
[51] Int. Cl.4 : C02F 1/42
[52] U.S. Cl. 210/677; 210/684;
423/371; 521/26
[58] Field of Search 210/670, 684, 677;
423/24, 100, 139, 364, 367, DIG. 14, 236, 371,
372; 521/26
[54] METHOD FOR RECOVERY OF CYANIDE
FROM WASTE STREAMS
CYANIDE __10
SOLUllON
Co(OH)2
27
28
(30
TREATI:O
SOLUllON WASTI: CO(CN)2.
u.s. Paten~ Nov. 24, 1987 Sheet 1 of2
CYANIDE __10
SOLUTION
11
COMPLEXING I Ca(OH)2
4,708,804
H2 S04
I 12 14
ION EXCHANGE REGENERATION
ADSORPTION I----t-~ ELUTION OF ION EXCHANGE
RESIN
L---- 15 Ca(OH)2
17~
H SO I - J
Ca(OH)2 ---I~~ 2 4 ACIDIFICATION/ HCN SCRUBBING
AIR ---. VOLATILIZATION
STREAM )
~16
18
~-27
n /28
_c_a(_O_H)-I2_~ NEUTRALIZATION
~
. (30
TREATED
SOLUTION
FIG.1
.Ir
WASTE Ca(CN)2
~
C/.) •
""C
~
('D=~.
-\0
00
-....J
en ;-
a
N
g,
N
z
~
~
146 --
150
H2O ...~
156
152 .----/
......,J
0
FIG.2
..0. 0
00
~
~120
Ca(OH)~111
!-,----T"'-1-18-- Ca(CN )2~ 113
r=142 ,t. ,t
----130
122
128
I ., HCN
132
148
- - - -
114
154___
116
126
112
110~
CYANIDE
....------S-.O,LUtTION
128
EFFLUENT
OUT
SUMMARY OF THE INVENTION
Cyanide values are efficiently recovered from
streams containing low levels of cyanide by processes of
the present invention wherein the cyanide values are
first concentrated by use of weak base ion exchange
resins selective for complex metal cyanides and capable
of being'eluted and regenerated by hydroxides. HCN is
formed by acidification of the cyanide-enriched resin
eluant and then volatilized for easy recovery as a gas
which can optionally be neutralized to a more conve-
65 nient form, e.g. Ca(CN)z or the like. More particularly,
according to the process of the present invention, a
solution containing cyanide values in the form of simple
or complex ions is concentrated by first passing the
2
Jan. 22, 1981 and in U.S. Pat. Nos. 4,267,159 and
4,321,145, another method for cyanide removal from
waste streams involves use of ion exchange resin beds.
A number of resins, both weak and strong base, are
5 known to be selective for both free and complexed
cyanides. See for example, U.S. Pat. Nos. 3,984,314;
3,788,983; 4,267,159; 4,321,145; and 4,115,260. One
problem associated with the use of strong base resins is
the difficulty in eluting the cyanide once it is absorbed.
10 Certain cyanide complexes, e.g. cyanide complex of Zn
and Cd, are difficult to elute even from commercially
available weak base resins.
U.S. Pat: Nos. 3,391,078 and 2,507,992 each disclose
methods in which Ca(OH)z is used as a regenerant for
certain ion exchange resins from which at least some
cyanides can be eluted with hydroxides. Although lime
or Ca(OH)z is economically preferred over NaOH as a
reagent, its low solubility in water generally makes its
use more difficult than more soluble hydroxides, e.g.
NaOH.
While U.S. Pat. No. 4,321,145 suggests an AVR
method to recover HCN from the cyanide loaded resin
eluate, its teachings are limited to the use of a complex
multi-level resin bed having a strong base anion exchange
resin layer, a weak acid cation exchange resin
and a strong acid cation exchange resin and the concomitant
need for a complex resin regeneration sequence.
Accordingly, it is an object of the present invention
to provide a novel method for recovering rather than
destroying cyanide values from streams initially containing
relatively low levels of cyanide, using weak base
ion exchange resins to concentrate the cyanide before
recovery.
Another object of the present invention is to provide
an improved method of eluting complex cyanides, such
as complexed zinc cyanide, from weak base resins.
Yet another object is to provide a unique system of
concentrating cyanide in the eluant of an ion exchange
resin using calcium hydroxide as the resin regenerant. A
further object is to provide a novel calcium hydroxide
elution circuit which permits full elution of cyanide
values using a predetermined volume of eluant so as to
concentrate the cyanide therein.
Still another object is to provide a method whereby
acidification/volatilization techniques can be used to
recover cyanide from low level cyanide streams due to
effective concentrating of the cyanide values prior to
acidification.
These and other advantages are achieved by practice
of the processes of the present invention as described
hereinbelow.
4,708,804
1
FIELD OF THE INVENTION
METHOD FOR RECOVERY OF CYANIDE FROM
WASTE STREAMS
Hydrogen cyanide, HCN, is a source of valuable
compounds used in many industrial processes, e.g.
KCN, NaCN and Ca(CN)z. When solutions or waste 15
streams contain cyanide compounds other than HCN,
such as metallic complexes, it is often useful to convert
these compounds to the more convenient salts which
can be sold or used directly.
A further benefit of recovery of cyanide values from 20
solution arises from restrictions on the disposal of cyanide
compounds. Processes which produce cyanide
compounds as a waste product must include some
method for disposing of these cyanide compounds in an
environmentally acceptable manner. Alternative solu- 25
tions to the cyanide removal problem as applied to gold
mill effluents are described in Scott and Ingles, "Removal
of Cyanide from Gold Mill Effluents," Paper No.
21 of the Canadian Mineral Processors Thirteenth Annual
Meeting, Ottawa, Ontario Canada, Jan. 20-22, 30
1981.
The cost of disposal can be somewhat offset if the
cyanide values can be recovered for recycle in the process
itself or for sale to another user. However, many of
the most common cyanide removal techniques involve 35
oxidation whereby the cyanide is destroyed. Moreover,
recovery of useful cyanide from waste streams has
proved to be particularly difficult when, as is typically
the case, the cyanide is present in only low concentrations
in the waste stream, e.g. on the order of less than 40
about 0.5 percent by weight. Recovery of cyanide values
is further complicated by the presence of metals in
the waste stream and particularly by the tendency of
cyanide to form complex ions with metals, such as Fe,
Ni, Co, Zn and Cu. 45
One method which has been used to recover HCN
from a cyanide-containing solutions is acidification/volatilization/
reneutralization (AVR). This process
takes advantage of the very volatile nature of hydrogen
cyanide at low pH. In the AVR process, the waste 50
stream is first acidified to dissociate CN- from metal
complexes and to convert it to HCN. The HCN is volatjlized
usually by the introduction of steam, often accompanied
by air sparging. The HCN evolved is then
recovered, for example, in a lime solution and the cya- 55
nide-free wastestream is then reneutralized. A commercialized
AVR method known as Mills-Crowe method is
described in the Scott and Ingles paper. One difficulty
with known AVR processes is that when a solution
contains only low concentrations of cyanide com- 60
pounds, the reagent costs for acidifying the stream and
later neutralizing the waste solutions and/or the energy
costs associated with raising the solution temperature to
achieve volatilization become extremely high compared
to the benefit of recovering the cyanide values.
As discussed in Ingles and Scott, "Overview of Cyanide
Treatment Methods for Presentation at the Cyanide
Cold Mining Seminar," Ottawa, Ontario, Canada,
This invention relates to methods of recovering cyanide
from solutions, such as waste waters, which contain
cyanide compounds and, in particular, to methods
where HCN is formed from the cyanide values and
recovered by volatilization.
BACKGROUND OF THE INVENTION
4,708,804
4
with a basic solution. When the basic solution comprises
calcium hydroxide, it is recycled through the resin continuously,
while maintaining the solution at hydroxide
saturation, until the resin has been substantially stripped
of its cyanide load, as indicated, for example, by an
increase in the solution pH to above about 11. The
resulting eluate contains a sjgnificantly higher concentration
of complex cyanide than the initial stream, e.g.
more than about 0.5 wt. % cyanide and preferably from
about 15 to about 25 grams total cyanide per liter. The
concentrated or cyanide-enriched stream then undergoes
acidification and volatilization of the acid in an
efficient manner for recovery of the initial cyanide values.
Cyanide values present as stable cobalto- and ferrocyanide
complexes, which are not susceptible to acidification,
result in a cyanide loss. However, these cyanide
values which are removed from the initial stream,
though not recovered, are placed in concentrated form
more suitable for disposal.
Typical feeds useful for practice of the present invention
are those containing relatively dilute concentrations
of complex and/or free cyanide, for example, less
than about 0.5 wt. % cyanide. Although the process.of
the p'resent invention may be practiced with a variety of
dilute cyanide solutions, the process is particularly useful
for treating industrial waste streams such as those
produced by mining, petrochemical and plating operations.
Metals milling and recovery operations, for example
uranium, copper, silver and particularly gold pro-
30 cessing, produce waste streams containing environmentally
unacceptable amounts of cyanide, typically in a
dilute solution. The various industrial operations typically
provide waste streams in an amount from 10 to
107 gallons per day. Such waste streams may contain
35 from about 1 mgll to over 50 grams per liter of total
cyanide. Many such streams will also contain other
toxic materials such as thiocyanate (CNS) and sulfides
which"may also be beneficially removed by practice of
the present invention. Similarly, such feeds will often
40 contain one or more metal contaminants such as copper,
zinc, iron, nickel, cobalt, chromium, and cadmium, with
which cyanide forms metal complexes. One or more of
such metal complexes are prevalent in the waste streams
emanating from mining and metals recovery processing.
Waste leach solutions from mining operations typically
contain cyanides in concentrations of 10 to 2500 milligrams
per liter. As will be known and understood by
those skilled in the art, various modifications to the
processes described herein will be dictated by the
makeup of the feed stream.
The ion exchange resins useful for practice of the
invention are weak base anion exchange resins. Virtually
any weak base anion exchange resin selective for
metal cyanide complexes and capable ofbeing eluted by
hydroxide can be employed. Preferred resins are those
typically having tertiary amine functionality in a suitable
matrix, such as acrylics or styrene. Exemplary of
such resins are Amberlite IRA-35 and IRA-99, commercially
available from Rohm & Haas Co. Dowex
WGR or MWA-I produced by Dow Chemical Co.,
Duolite A-2 or A-4 produced by Diamond Shamrock
Corp. are suitable for the processes of the present invention
as well.
Suitable anion exchange resins are first placed in acid
form prior to contact with a cyanide-containing feed
stream. The resin is acidified by contact with an acid
such as sulfuric acid according the following reaction:
20
The processes of the present invention provide improved
methods for recovering cyanide values from
waste streams or solutions using acidification/volatilization
techniques. These processes provide a unique 45
overall processing scheme which permits use of weak
base ion exchange resins which are easily eluted under
mild hydroxide conditions to remove substantially all
metal-cyanide complexes as well as most of the thiocyanate
and or sulfide which may be present in the initial 50
feed stream. Thiocyanate removed from the waste
stream or added during elution, if necessary, is used to
aid elution of some metal cyanide complexes, such as
zinc cyanide, when such complexes are present in the
feed stream. In addition, practice of the present inven- 55
tion, permits an overall system wherein inexpensive
sulfuric acid and lime are the primary reagents. In particular,
the novel resin elution/regeneration circuit of
the present invention permits elution using calcium
hydroxide while nevertheless producing a cyanide- 60
enriched eluate suitable as a feed for hydrogen cyanide
recovery by acidification/volatilization.
According to the processes of the present invention,
a complex metal cyanide-containing feed is first passed
through a weak base anion exchange resin in acid form 65
in order to concentrate the complex cyanides from the
solution and remove any thiocyanates which may be
present. T~e cyanides adsorbed on the resin are eluted
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic representation of one embodiment
depicting a method for recovery of cyanide
from a waste solution combining an ion exchange resin
adsorption step with an acid/volatilization step.
FIG. 2 is a schematic flow diagram depicting a Ca(
OHh elution circuit.
DETAILED DESCRIPTION OF THE
.PREFERRED EMBODIMENT
3
solution through a weak base ion exchange resin (acid
form). Free cyanide with any solids present in the feed
stream pass through. The complex cyanide values are
adsorbed on the resin and are eluted by a hydroxide. In
a preferred embodiment, elution is by calcium hydrox- 5
ide, preferably using a novel recycle system described
herein which prevents dilution of the effluent despite
the low solubility of Ca(OHh in water. When complex
zinc cyanide or other similar cyanide complexes are
present in the feed stream, improved elution is achieved 10
by the presence of thiocyanate in the elution circuit.
When thiocyanate is present in the feed, the presence of
thiocyanate during elution is secured by controlling the
resin loading to a low level. Alternatively, thiocyanate
may be advantageously added to the elution circuit. 15
The eluate containing a high concentration of cyanide
compounds is acidified by contact with an acid such as
sulfuric acid. The acidified eluate is then heated, preferably.
by introduction of steam, to volatilize the hydrogen
cyanide which is then recovered.
By means of the ion exchange resin concentration
step, the concentration of cyanide values in the eluate
which is sent to the acid volatilization step is sufficiently
high such that the reagents and the heat supplied to the
acid volatilization step are efficiently utilized. In one 25
embodiment, any free cyanide in the stream is complexed
prior to ion exchange to permit removing all
cyanide from the initial stream, thereby enabling environmentally
acceptable disposal of the cyanide-depleted
solution.
(iii)
6
(RNHhCu(CN)3 + Ca(OHh--->2RN·
+ CaCu(CN)3 + 2H20
Elution according to this reaction leaves the resin in the
free amine form. The resin must therefore be acidified,
as described above, before it is again contacted with the
feed stream to initiate another cycle of partial resin
loading and elution. Regeneration (acidification) of the
fication. Thus, it is preferred, when the feed stream
contains substantial amounts of copper and/or zinc
cyanide compounds to interrupt or otherwise monitor
the resin adsoption or ion exchange in order to assure
5 partial loading at a level less than that at which thiocyanate
breakthrough occurs.
Metal cyanide complexes are desorbed from the
anion exchange resin during the elution step under
mildly basic conditions, e.g. from about pH 9 to about
pH 13. While sodium hydroxide may be used, it is particularly
advantageous from an economic point of view
to use lime or other sources of calcium hydroxide. In
preferred embodiments of the present invention, calcium
hydroxide is used to yield a concentrated solution
of cyanide complexes, leaving the resin in its free amine
form for reuse after regeneration to acid form. Because
of the poor solubility of calcium hydroxide in water, a
single pass of calcium hydroxide hydroxide-saturated
solution will only partially elute the resin. Sustained
one-pass treatment with calcium hydroxide-saturated
solution will eventually elute the resin to a satisfactory
degree, however, the resultant large volume eluate
contains cyanide in an undesirably low concentration
for use as a feed to the acidification/volatilization step.
Thus according to the present invention, a novel calcium
hydroxide elution/regeneration circuit is provided.
A quantity of calcium hydroxide-saturated solution,
typically of a predetermined volume, is repeatedly recycled
through the loaded resin to produce an eluate having
cyanide concentrations high enough to make acidification/
volatilization of the eluate economically attractive.
The adsorbed CN complexes are eluted from the
resin with a weak base such as a saturatedCa(OHh
solution, yielding a concentrated solution of the cyanide
complexes, and leaving the resin in its free amine form
for recycle. In order to maintain the eluting fluid in a
calcium hydroxide-saturated condition, the eluting fluid
is contacted with a bed of solid caicium hydroxide or
other source of calcium hydroxide prior to recycle to
the resin. The eluting fluid is provided in a quantity
sufficient to hold in solution substantially the entire"
cyanide load of the partially loaded resin, but of a volume
small enough that the resulting cyanide concentration
in the eluate may be economically recovered. The
pH of the solution exiting the resin column can act as an
indicator of the completeness of elution. The eluting
fluid is preferably recycled through the resin column
until the exiting fluid attains a pH greater than about 11,
preferably greater than about 12. Elution preferably
occurs at a flow rate of about 0.5 to about 5.0 gpm/ft2,
preferably from about 1 to about 2 gpm/ft2, and at a
temperature of from about 10° to about 60° C., preferably
from about 20° to about 40° C.
The elution of the resin proceeds according to a reaction
such as the following wherein Cu(CN)J= is the
complex cyanide:
(i)
(ii)
10
4,708,804
5
2RN+ H2S04--->(RNHhS04
(RNHhS04+ Cu(CNh- 2--->(RNHhCu(CN)3_
+S04-2
Operation of the ion exchange beds is by conventional
means. However, in some instances lower than
normal resin loading is preferred. In particular, when
the feed stream contains sulfides and/or thiocyanate,
low resin loading (about 0.5 to 3lbs. CNT/ft3resin) with 15
respect to the metal-cyanide complexes will provide
removal of both thiocyanate and sulfides. In general,
when thiocyanate is present in the feed stream, resin
loading will be such to assure only partial loading. Preferably,
the resin is loaded with complex metal cyanides 20
to a point at or below which the thiocyanate is no
longer being totally adsorbed by the resin and thus
"breaks through" to appear in the treated solution or
resin effluent.
As will be known and understood by those skilled in 25
the art, the weak base anion exchange resins used for
practice of·the present invention do not and are not
intended to remove free cyanide which passes through
the resin bed and which is present in the treated solution
or resin effluent. The free cyanide-containing effluent 30
may be recycled for use where the waste producing
operation calls for cyanide leach or the like. Alternatively,
where the resin bed effluent is to be disposed of
and/or a cyanide-free effluent is otherwise desirable,
free cyanide removal is effected by first complexing the 35
free cyanide of the feed stream prior to the ion exchange
step. Such complexing is typically achieved by
addition of a metal salt such as copper sulfate or ferrous
sulfate to the feed stream.
According to the present invention, the presence of 40
thiocyanate is particularly advantageous when zinc
cyanide and/or cobalt cyanide complexes (or other
similar metal cyanide complexes which are known to be
more difficult to elute from strong base resins, e.g. quarternary
amines and/or known not to decompose during 45
acidification) have been adsorbed on the resin. It has
been found that the presence of thiocyanate in the elution
circuit aids in eluting such metal cyanides. Similarly,
as described more fully below, it has been found
that the presence of thiocyanate during acification/- 50
volatilization may enhance total cyanide recovery by
complexing some of the copper which would otherwise
form insoluble precipitates with CN and thereby prevent
recovery of that CN. Accordingly, as indicated
hereinabove, when the initial feed stream contains thio- 55
cyanate, resin loading is such that the thiocyanate is
adsorbed on the resin and is thus eluted and present in
the elution circuit for aiding elution of the metal complexes.
Low loading thus has a potential three-fold benefit,
namely, removal of thiocyanate as a contaminant of 60
the waste stream, assuring its presence during elution
and/or assuring its presence during acidification/volatilization.
In instances where no thiocyanate or an
insufficient amount of thiocyanate is present in the original
feed stream, it may be nevertheless advantageous to 65
add it for purposes of aiding elution and/or enhancing
overall CN recovery. Typicl!lly, such addition will be
in the elution circuit and/or to the eluate prior to acidiwhere
RN=resin in free amine form.
During adsorption, there is an exchange of the polyvalent
metal cyanide complexes for sulfate. Adsorption
occurs according to reactions such as the following
with CU(CN)3-2 as the complex:
8
of copper sulfate 32 or other metal salt wherein the
cation is among those metals which complex cyanide.
The treated solution 30 leaving the ion exchange will
have free cyanide where such is present in the feed
stream and not complexed prior to ion exchange. In
such instances, the treated solution 30 is appropriate for
recycle to a cyanide leach step or other process operation
step (not shown) utilizing free cyanide. Of course
caution should be exercised when the pH is low as any
free cyanide present in the treated stream will be in the
form of hydrogen cyanide.
Upon completion of the ion exchange 12, the complex
cyanides adsorbed on the resin undergo elution 14
by contact with hydroxide, preferably calcium hydrox-
IS ide. The eluant 15 is cyanide-enriched and passes to
acidification/volatilization step 16. The eluant is contacted
with an acid such as sulfuric acid to free the
cyanide and form hydrogen cyanide which is then volatilized
by heating and/or air sparging The volatilized
HCN 17 is collected by scrubbing with calcium hydroxide
or the like 18 to form cyanide salts, such as Ca(CN)2
or NaCN. The acidified solution remaining 27 is then
reneutralized with calcium hydroxide and is suitable for
waste disposal.
Referring now to FIG. 2, in which the preferred
embodiment ofthis invention, including a novel calcium
hydroxide elution circuit, is depicted, a weak base resin
110 is packed into a column 112 and contacted with a
cyanide-containing feed solution 114. Partial loading of
the resin 110 is effected. When the desired partial loading
is achieved, the feed stream 114 flow to the column
112 is stopped, leaving a quantity of solution 116 in the
packed column 112. Ca(OHh 111 and Ca(CN)2 113 are
35 added via line 118 to recycle tank 120, which contains
solution from the previous elution cycle as described
hereinafter. The solution of tank 120 will typically be of
a predetermined volume equalling the minimum which
is economically viable to elute the resin in the manner
described herein. The contents of the recycle tank 120
are filtered by filter 122 and introduced to the packed
column 112 by line 124. As the recycle solution from
tank 120 enters the column 112, the solution 116 in the
column is displaced via line 126 to the column feed tank
114. When substantially all of the solution 116 which
was present in the column 112 when flow of feed stream
114 to the column 112 was stopped, has been sent to the
feed tank 114, the recycle solution originally from tank
120 which has been sent through column 112 is directed
back to the recycle tank 120 by line 128. In this fashion,
the solution from the recycle tank 120 is continuously
cycled over a Ca(OH)z bed, through the filter 122 and
packed column 112 and returned to the recycle tank 120
at a predetermined rate. The previously added amount
of Ca(OH)z 111 and Ca(CN)2 113 maintains the recycle
tank solution 120 near Ca(OH)z saturation. The recycle
circuit is continued until the pH of the solution 128
leaving the column 112 is increased from its original
value of between 8 and 9 to a value of between 11 and
12, typically occurring in about 2 hours. As will be
understood in practice the actual time is dependent
upon the flow rate Ca(OH)z-saturated solution through
the resin, i.e. on the amount of OH- passing through
the resin.
The recycle is then terminated and the pregnant resin
eluate is directed to the HCN volatilization head tank
130 by line 132. A saturated Ca(OH)z solution from the
first flush tank 134 is sent to the column 112 by line 136,
(v)
(iv)
4,708,804
4CuCN+ 2CNS- + HZS04--+2CuCNS.CuCN+
2HCN+S04-z
40
The hydrogen cyanide formed by the acidification of
the eluate is volatilized by heating. Preferably the heat
necessary is added by introduction of steam. Air sparging
can be employed to separate the volatilized'HCN.
The rate at which HCN is evolved is dependent on the 45
rate that H2S04 is added, temperature, vacuum, rate of
air sparging, and the specific CN--containing compound.
The CN associated with free CN and the'easily
decomposed complexes is evolved rapidly as HCN on
acidifying. Additional time is required to remove the 50
soluble HCN from solution, and to decompose CuCN
and/or ferrocyanides, cobaltocyanides which may be
present,
The volatilized HCN is then recovered, as for example
by scrubbing with a mild Ca(OH)z solution or with 55
NaOH thereby converting the cyanide to reusable
Ca(CN)2 or NaCN, which can be recycled as a cyanide
reagent or commercially disposed of. Effluent from the
volatilization step may be neutralized 'by contact with,
for example, a lime solution, producing a substantially 60
cyanide-free waste stream suitable for disposal.
Referring now to FIG. 1 which is a block diagram of
the overall process, the cyanide-containing feed stream
10 passes through the ion exchange step 12 wherein the
metal cyanide complexes are adsorbed on the weak base 65
anion exchange resin. Optionally, prior to entering the
ion exchange step, the feed solution 10 may undergo
complexing 11 of any free cyanide present, by addition
7
resin may be preceded by flushing the resin with fresh
water or with a solution having a low cyanide content.
The eluate, now containing from about 5 to about 25
gil of total cyanide, and particularly containing a
higher concentration of cyanide than the initial feed 5
stream, is treated to recover the cyanide values therefrom
by an acidification/volatilization step. The eluate
is first acidified with a reagent, such as H2S04 or S02,
which acts to release the CN from most of the metal
cyanide complex ions present in the eluate and permit 10
formation of HCN. In the preferred embodiment, acidification
is accomplished using H2S04, typically in a
concentration of from about 1.0 to about 40 gil, preferably
about 10 to about 20 gil H2S04 in the acidified
mixture.
Cyanide losses during acidification/volatilization are
generally due to formation ofinsoluble precipitates such
as CU2Fe(CN)6, CuCN, 2CuCNS.CuCN, and
CO(CN)6-4 compounds. Of the metal complexes normally
present in mining waste solutions, uncomplexed 20
CN, and the complexes of Zn, Ni, and Cd decompose
readily on acidification with H2S04, generating HCN
and metal sulfates. The Cu complexes decompose to a
large extent but some insoluble CuCN may be formed.
Though practice ofthe present invention does not result 25
in complete recovery of cyanide from such complexes,
nor from the thiocyanate present, it does result in concentration
of these values in the eluant.
As mentioned hereinabove, in practice of the present
invention it has been found that the presence of thiocya- 30
nate may be beneficial to overall cyanide recovery.
Without intending to be bound by any theory, it is believed
that, for example, when CuCN is present, the
presence of CNS aids in overall CN recovery, the following
replacement reactions may occur:
lprepared with NaCN, CuCN, Zn/Co/NilCdS04, NaCNS, and K.,Fe(CN)6'
2MC solution spiked with Co/Ni/CdS04 and K.,Fe(CN)6'
3MC solution spiked from 0.25 to 0.49 gil Cu with Na2Cu(CN)3.
No.1!
Analysis of Synthetic and
Spiked Solutions Used in Test Work
Assay, gil
CN, total 1.45 1.20 1.10
cm QM QM ~4
Cu 0.24 0.24 0.49
Zn 0.094 0.085 0.090
Fe 0.094 0.089 0.049
Ni 0.098 0.095 0.007
Co 0.10 0.10 0.0008
Cd 0.12 0.11 0.0002
Au 0.1 mgll
S-2 0.01
S203-2 0.1
CNO- 0.1
pH 10.5 10.5 10.6
EXAMPLE 1
Short-term stability tests were run in order to determine
the performance of certain resins during repeated
acidification, adsorption and elution cycles. The tests
were run using two weak base resins, Amberlite IRA-35
and IRA-99 made by Rohm & Haas. Both resins have
polyamine functionality but differ in matrix. Four experiments
were run, testing each of the two resins with
each of the feed solutions shown in Table 1. For each
test, the resin was subjected to nine loading/elution
cycles in a 5 cm diameter column. Test conditions and
results are given in Table 2A. After nine cycles, a 30 cc
portion of the resin was transferred to a 1.5 cm diameter
column and compared to 30 cc fresh, conditioned resin
in the identical column under identical acidification
adsorption elution conditions.
The results of the tests using the synthetic solution
(No.1) to load the resins showed no apparent chemical
problems or physical degradation in ten cycles for both
resins. A comparison of the 2 and 10 cycle results is
presented in Table 2B.
Resin elution processes using a number of eluants
were compared. Tests conditions and results are presented
in Table 2C.
TABLE2A
EXPERIMENTAL
Three different solutions were used in Examples 1-3
which follow. Solution I was synthetic prepared from
reagent grade NaCN, CuCN and sulfate salts. Solutions
2 and 3 were actual barren Merrill-Crowe (Me) solutions
spiked with Na2Cu(CN)3 and sulfate salts to simulate
waste solutions which might be obtained from cyanide
leaching of high-copper and gold ore. Analyses of
Solutions 1-3 are given in Table 1.
TABLE 1
10
Alternatively, scrubbing step 18 may be conducted
with a reagent such as sodium hydroxide to form reusable
NaCN.
The following examples are provided by way of illustration
and not by way of limitation.
4,708,804
9
displaces the pregnant resin eluate leaving the column
112. An amount of the pregnant resin eluate equal to the
quantity of solution 116 in packed column 112 when
feed flow 114 to column 112 is first stopped, with
makeup from the first flush tank 134 if necessary, is 5
directed to the HCN volatilization head tank 130. After
that amount of eluate has been directed to the HCN
volatilization head tank 130, the solution 148 leaving the
resin column is directed to the recycle tank 120 by line
128, with displacement fluid for the column 112 com- 10
ing, first, from the first flush tank 134 and, when that is
depleted, from the second flush tank 138 via line 140.
An amount of solution equal to the column volume of
resin is directed to the recycle tank 120 in this fashion,
and when this amount has been accumulated in the 15
recycle tank 120, the solution leaving the resin column
148 is directed to the first flush tank 134 via line 142
with the displacement fluid for the column 112 coming,
first, from the second flush tank 138 and then from the
third flush tank 144 via line 150 which contains a barren 20
solution to which Ca(OHh has been added by line 146
to form a solution saturated with Ca(OHh. After the
column volume of solution has accumulated in the first
flush tank 134, the solution 148 leaving the resin column
112 is directed, in tum, to the second flush tank 138 and 25
the third flush tank 144, with the replacement fluid
coming, first, from the third flush tank 144 and then
from a fresh water supply 152. This procedure is continued
until the column of volume of fluid has accumulated
in each of the second flush tank 138 and the third 30
flush tank 144. Fresh water flush of the resin is then
continued until most of the entrained CN in resin column
112 is displaced, with the effluent being directed to
the column feed tank 114 by line 126. The system is now
in the condition it was at the beginning of the elution 35
cycle, except that the resin 110 is stripped ofthe cyanide
load and has been converted to the free amine form.
The resin is acid-treated and the cyanide feed 114 is
again directed to the resin column 112 to partially load
the resin and the process described above is repeated. 40
The filter 122 is cleaned as required and solids removed
therefrom comprising unreacted Ca(OH)z, CaS04.2H20
and minor amounts of metal cyanide insolubles are
disposed of to the tailings area.
A number of modifications of the preferred embodi- 45
ment may be emplQyed to accommodate specific applications.
Since free cyanide is not adsorbed by the ion
exchange resin 110, it will appear in the ion exchange
effluent 154 which may be "recycled back to the operation.
If the effluent 154 is to be discharged, the free 50
cyanide can be complexed with a copper salt or other
suitable metal salt 132 and removed along with the
other complexes.
The greater part of stable ferro- and cobaltocyanide
complex ions are not recovered in the acidification/- 55
volatilization step 156, but appear in concentrated form
in the waste stream.
Amberlite lRA-35/99 Resins, Synthetic Solution Stability Test
I. Acidification Resins,
Column
H2S04 soln
Flow rate
Conditions
Series 2(99) - Amlierlite lRA·99, 20 X 50 mesh; 40 cc
Series 2(35) - Amberlite IRA-35, 35, 20 X 50 mesh; 40 cc
5cm diam
0.10 ~ H2S04, 500 ml (50 meg)
30/40 mllmin
4,708,804
11
TABLE 2A-continued
Amberlite IRA-35/99 Resins, Synthetic Solution Stability Test
12
2. Adsorption
Temperature 22-240 C.
Wash H20, 300 ml
Synthetic solution as shown below: 1500 ml
Assay gil "R",ea",g",e",n,,-t _
Cu
Zn
Fe
Co
Ni
CNS
CNF
Cd
0.25
0.10
0.10
0.10
0.10
0.34
0.20
0.10
Na2Cu(CNh
ZnS04 + 4NaCN
iC4Fe(CN)6·3H20
COS04 + 6NaCN
NiS04 + 4NaCN
NaCNS
NaCN
CdS04 + 4NaCN
Wash
3. Elution Eluant
Wash
H20,IOOml
1.5 gil Ca(OHh + 4.1 gil NaCNS + 1.0 gil NaCN, 1600 ml
H20, 300 ml
3.59 6.49
2.98 3.64
1.98 3.36
4.64 5.62
1.33 2.65
6.35 5.74
20.86 27.51
2.16 4.02 1.99 4.98 6.21 3.86 5.60 3.98 6.34 3.83 6.01
5.18 3.75 3.96 3.70 3.08 2.67 3.45 2.63 3.19 2.40 3.12
1.79 3.14 1.59 3.19 2.91 1.98 3.24 1.82 3.19 1.83 3.01
6.02 4.15 5.07 5.04 5.42 5.78 5.31 5.81 5.14 5.15 5.24
1.49 2.76 1.43 2.28 2.15 1.39 2.25 1.24 2.07 1.17 2.12
9.38 4.38 8.00 4.94 5.02 6.30 5.23 5.95 4.96 5.57 5.06
26.0 22.2 22.2 24.1 24.8 22.0 25.2 21.4 24.9 20.0 24.6
33 23 35 29 29 25
TABLE2B
Comparison of Ten-Cycle and Two-Cycle
Amberlite IRA-35/99 Resins Synthetic Solution (No. I)
Cycle
Resin IRA- 35
Acidification 36.5
H2S04 consumed, meq.
Adsorption
Adsorbed, meg.
Cu
Zn
Ni
Co
Cd
Fe
CNS
Total cations
Elution
Eluted, meg.
Cu
Zn
Ni
Co
Cd
Fe
Total cations
Base consumed, meq.
99
33.3
35
Results: Cycles 1-9
2 __3_
99 35 99
37.5
35
30.6
99
36.6
35
7
99 35
9
99
I. Pre-elution
2. Acidification
3. Adsorption
4. Elution
Resin
Column
Eluant
Flow rate
Temperature
Wash
Feed solution
Wash
Feed solution
Wash
Eluant
Wash
Conditions
IO-cycle - Amberlite lRA-99 from Cycle 9; 30 cc
2-cycle - Fresh Amberlite IRA-99 conditioned I cycled; 30 cc
IO-cycle - Ambeflite lRA·35 from Cycle 9; 30 cc
2-cycle - Fresh Amberlite lRA-35 conditioned I cycle; 30 cc
1.5 cm diam X 17 cm
1.5 gil Ca(OHh and 4.1 gil NaCNS and 1.0 gil NaCN; 300 ml
7 mllmin (= I gpm/ft2)
23 0 C.
H20, 300 ml
0.10 N H2S04; 375 ml (37 meq)
H20;200 ml
Synthetic solution No. I; 1500 ml
H20 ,IOOml.
1.5 gil Ca(OHh + 4.1 gil NaCNS 4- 1.0 gil NaCN; 1500 ml
H20, 200 ml
Results
I. Amberlite IRA-35, adsorption
Volume Effiuent Assay, gil
BV
2 Cycle 10 Cycle
5 6
II 12
19 20
29 29
38 41
44 47
Cu
2 Cycle 10 Cycle
<0.0001 <0.0001
<0.0001 <0.0001
<0.0001 0.0006
0.031 0.14
0.53 0.51
0.45 0.43
Zn
2 Cycle 10 Cycle
0.0002 0.0003
<0.0001 0.0001
<0.0001 <0.0001
0.0002 0.0007
0.0043 0.014
0.0078 0.021
Cd
2 Cycle 10 Cycle
0.0079 oms
0.016 0.024
0.030 0.045
0.046 0.087
0.17 0.15
0.15 0.14
Ni
2 Cycle
<0.0001
<0.0001
<0.0001
0.0070
0.16
0.16
10 Cycle
<0.0001
<0.0001
0.0002
0.036
0.17
0.16
Volume Effiuent Assay, gil
13
4,708,804
14
TABLE 2B-continued
Comparison of Ten-Cycle and Two-Cycle
Amberlite IRA-35/99 Resins Synthetic Solution (No. I)
BV Co Fe CNS
2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle
5 6 <0.0001 <0.0001 0.0002 0.0002 0.002 <0.002
11 12 <0.0001 <0.0001 <0.0001 0.0002 0.011 0.02
19 20 <0.0001 0.0002 <0.0001 <0.0001 0.35 0.43
29 29 0.0054 O.oI8 0.0003 0.0017 0.52 0.58
38 41 0.069 0.081 0.013 0.029 0.30 0.31
44 47 0.079 0.092 0.033 0.51 0.30 0.32
2. Amberlite IRA·35, elution
Volume Eluate Assay, gil
BV Cu Zn Cd Ni
2 cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle
6 7 0.26 0.19 0.053 0.084 0.13 0.13 0.13 0.11
15 16 0.035 O.oI8 0.36 0.35 0.076 0.058 0.040 0.025
24 26 0.002 0.0005 0.088 0.052 0.014 0.0080 0.0017 0.0012
36 39 0.0002 <0.0001 0.0028 0.0017 0.0010 0.0006 0.0002 0.0002
49 53 <0.0001 <0.0001 0.0002 0.0002 0.0Q02 <0.0001 <0.0001 0.0002
Resin <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005
Volume Eluate Assay, gil
BV Co Fe CNS
2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle
6 7 0.10 0.12 0.19 0.23 2.80 2.85
15 16 0.20 0.19 0.21 0.20 2.90 2.86
24 26 0.073 0.029 0.035 0.15 2.80 2.77
36 39 0.0003 0.0002 0.0004 <0.0001 2.81 2.80
49 53 0.0001 <0.0001 <0.0001 <0.0001 2.80 2.79
Resin <0.005 <0.005 <0.005 <0.005
3. Amberlite IRA-99, adsorption
Emuent Assay, gil
Volume Cu Zn Cd Ni
BV 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle
6 <0.0001 <0.0001 0.0012 0.0015 0.0039 0.0046 0.0001 0.0001
12 <0.0001 <0.0001 0.0004 0.0005 0.0017 0.0018 0.0002 0.0002
22 0.0002 0.0010 <0.0001 0.0002 0.0007 0.0002 0.0002 0.0002
31 0.Q38 0.055 <0.0001 0.0002 0.0003 0.0003 0.0045 0.0078
43 0.34 0.34 0.0002 0.0007 0.017 0.021 0.050 0.051
49 0.43 0.43 0.0008 0.0021 0.044 0.051 0.079 0.080
Emuent Assay, gil
Volume Co Fe CNS
BV 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle
6 <0.0001· <0.0001 <0.0001 <0.0001 0.017 0.014
12 <0.0001 <0.0001 <0.0001 <0.0001 0.014 0.011
22 0.0004 0.0011 <0.0001 0.0002 0.056 0.043
31 0.020 0.026 0.013 0.016 0.63 0.58
43 0.10 0.098 0.065 0.066 0.83 0.83
49 0.12 0.12 0.080 0.082 0.51 0.51
4. Amberlite IRA·99, elution
Eluate Assay, gil
Volume Cu Zn Cd Ni
BV 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle
6 0.60 0.61 0.061 0.075 0.31 0.31 0.29 0.28
14 0.091 0.080 0.41 0.39 0.29 0.28 0.46 0.44
23 0.0021 0.0019 0.029 0.028 0.33 0.032 0.0035 0.0030
34 0.0006 0.0005 0.0074 0.0071 0.015 0.014 0.0007 0.0006
46 0.0002 0.0002 0.0032 0.0032 0.0086 0.0081 0.0004 0.0002
Resin wt % <0.005 <0.005 0.022 0.019 0.085 0.073 <0.005 <0.005
Eluate Assay, gil
Volume Co Fe
,
CNS
BV 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle
6 0.21 0.21 0.19 0.20 2.29 2.20
14 0.12 0.11 0.14 0.13 2.74 2.69
23 0.0028 0.0032 0.0029 0.0026 2.65 2.67
34 0.0010 0.0014 0.0006 0.0006 2.75 2.63
46 0.0007 0.0010 0.0005 0.0004 2.76 2.77
Resin wt % 0.13 0.17 0.032 0.031
15
4,708,804
16
TABLE2C
Sample
Resin
Eluants
Contact
Eluant gil
RESIN ELUTION TESTS USING VARIOUS ELUANTS
IRA-99, 6.0 g moist (2.42 g dry), loaded from solution No. I; 5 cc resin/test.
1.5 gil Ca(OHh plus NaCNS, NaCI, NaCNS + NaCI; 500 mlltest.
Stirred in 800 ml beaker, '22/24' c., I hr.
Assay, % % Eluted
Zn Ni Co Fe Cu Zn Ni Co Fe Cu
8.1 NaCNS
32 NaCNS
12 NaCI
59 NaCI
4.1 NaCNS + 12 NaCl
Loaded resin
Treated resin
Treated resin
Treated resin
Treated resin
Treated resin
0.85 0.71 0.77
0.22 0.036 0.18
0.22 0.017 0.18
0.30 0.48 0.31
0.26 0.39 0.25
0.22 0.081 0.25
0.19 0.65
0.12 0.016 74 95 77 37 98
0.14 0.012 74 98 77 26 98
0.13 0.17 65 32 60 32 74
0.12 0.10 69 45 68 37 85
0.14 0.026 74 89 68 26 96
15 resin. No marked differences were found for the IRA99
resin between the fresh and recycled resins. However,
less than 5% of the ten cycle IRA-99 beads appeared
to have changed somewhat in appearance, suggesting
some physical degradation occurred. Comparisons
of the 2-cycle and lO-cycle tests are presented in
Table 3B.
TABLE3A
EXAMPLE 2
Comparative data for resin loading of the IRA-35 and
IRA-99 with feed solution No.2 are shown in Table 3A.
There was no significant difference in the fresh and ten
cycle IRA-35 resins in loading or eluting characteris- 20
tics, indicating no short-term degradation of the IRA-35
Ten-Cycle Amberlite IRA-35/99 Resins - Solution No.2 Stability Test
Conditions
I. Acidification Resins
Column
• H2S04s01n
Flow rate
Temp
Wash
2. Adsorption Adsorption feed solution
Amberlite IRA-35 and IRA-99, 20 X 50
mesh, 40 cc
5 em diam.
0.10 N H2S04, 500 ml
30 cc/min for Cycle 5, all others at 40
cc/min
22_24' C.
H20, 300 ml
spiked barren solution
Assay, gil
As Received Spiked to Reagent
Cu
Zn
Fe
Co
Ni
CNS
CNF
Cd
0.24
0.085
0.05
0.001
0.006
0.34
0.20
0.001
0.089
0.10
0.Q95
0.11
~Fe(CN)6·3H20
COS04 + 6NaCN
NiS04 + 4NaCN
CdS04 + 4NaCN
3. Elution Eluant 1.5 gil Ca(OHh + 4.1 gil NaCNS +
1.0 gil NaCN, 1600 ml
Wash H20, 300 ml
Resin elution processes using a number of eluants
were compared. Test conditions and results are presented in Table 3C.
Results: Cycles 1-9
Cycle 1 2 5 7 9
Resin IRA- 35 99 35 99 35 99 35 99 35 99 35 99
Acidification 41.1 32.2 37.2 29.5 (27) 37.5 38.3 33.1 34.7 36.7 37.4 34.0
H2S04 consumed, meq.
Adsorption
Adsorbed, meg.
Cu 6.55 6.34
Zn 3.21 2.81
Ni 3.28 2.97
Co 6.93 5.53
Cd 2.03 2.25
Fe 6.90 5.38
CNS 0.92 1.7
Total cations ~8.9 25.3
Elution
Eluted, meg.
Cu 6.64 6.76 6.58 6.13 6.63 5.88 6.51 6.43 6.19 5.93 5.74 6.08
Zn 2.91 2.29 3.30 2.59 3.26 2.92 3.54 3.10 2.95 2.76 3.21 3.09
Ni 3.05 3.76 3.21 2.84 2.96 2.69 3.20 2.88 2.91 2.65 2.91 2.82
Co 6.76 5.08 7.33 4.69 5.87 4.10 6.61 4.72 6.24 4.47 5.87 4.28
Cd 1.56 1.42 1.64 1.68 1.70 1.82 1.85 1.95 1.67 1.76 1.71 1.92
Fe 6.12 4.61 6.88 4.40 (6.4) (4.6) 7.15 5.59 6.35 4.89 6.82 5.40
Total cations 27.0 22.9 29.0 22.3 27 22 28.9 24.7 26.3 22.5 26.3 23.6
17
4,708,804
TABLE 3A-continued
18
Ten-Cycle Amber1ite IRA·35/99 Resins· Solution No.2 Stability Test
Base consumed, meg. 34 26 34 31 30 28
10
15
20
25
30
35
40
45
50
55
60
65
36 29
TABLE3B
Volume Cu Zn Cd Ni Co Fe CNS pH
BV 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle 2 Cycle 10 Cycle
Comparison of Ten-Cycle to Two-Cycle Amberlite-35 Resin, Adsorption Data
Resin Amberlite IRA-35, 20 X 50 mesh Acidified with O.I.!"! H2S04; 30 cc Flow rate 7 mllmin
Feed soln No.2 Temperature 23° C.
Effluent assays, gil
6 <0.0001 <0.0001 0.0005 0.0004 0.011 0.012 0.0001 0.0001 <0.0001 <0.0001 <0.0001 <0.0001 0.0026 <0.002
12 <0.0001 <O.O(JOI 0.0002 0.0003 0.021 0.022 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 0.026 0.032
21 <0.0001 <0.0001 0.0003 0.0003 0.027 0.022 <0.0001 <0.0001 <0.0001 <0.0001 0.0001 0.0002 0.46 0.48
29 0.054 0.051 0.0002 0.0003 0.060 0.061 0.0095 0.0080 0.013 0.013 0.0002 0.0002 0.52 0.54 I-'
41 0.56 0.57 0.0004 0.0004 0.13 0.13 0.15 0.15 0.10 0.10 0.0040 0.0015 0.34 0.33 \e
47 0.50 0.50 0.0008 0.0007 0.14 0.14 0.17 0.18 0.099 0.98 0.049 0.025 0.33 0.34
Comparison of Ten-Cycle to Two-Cycle Amberlite IRA-99 Resin, Elution Data
Resin Amberlite IRA-99, 20 X 50 mesh, loaded with feed solution No.2 Flow rate 7 mllmin
Eluant 1.5 gil Ca(OH)z + 4.1 gil NaCNS + 1.0 gil NaCN Temperature 23° C.
Eluate assays, gil
6 0.75 0.69 0.021 0.038 0.20 0.23 0.25 0.27 0.17 0.16 0.24 0.23 2.30 2.42 8.4 8.3
15 0.19 0.15 0.35 0.35 0.37 0.36 0.20 0.16 0.13 0.12 0.18 0.18 2.93 2.93 11.2 11.5
24 0.010 0.0075 0.13 0.074 0.077 0.054 0.019 0.0097 0.023 0.014 0.029 0.021 2.68 2.53 12.5 12.6
36 0.0009 0.0009 0.0086 0.0050 0.014 0.011 0.0008 0.0006 0.0021 0.0022 0.0012 0.0014 2.85 2.82 12.6 12.6
48 0.0005 0.0005 0.0031 0.0016 0.0084 0.0055 0.0002 0.0002 0.0013 0.0014 0.0006 0.0012 2.82 2.81 12.6 12.6
Resin wt % 0.005 0.005 O.oI5 0.004 0.076 0.069 0.005 0.005 0.14 0.18 0.037 0.051 ~.f:>.
Comparison of Ten-Cycle to Two-Cycle Amberlite IRA-99 Resin, Adsorption Data -.I
0
Resin Amberlite IRA-99, 20 X 50 mesh Acidified with 0.1 ~ H2S04; 30 cc Flow rate 7 mllmin ,?O
Feed soln No.2 Temperature 23° C. 00
Effluent assays, gil 0
6 <0.0001 <0.0001 0.0005 0.0013 0.0039 0.0042 <0.0001 <0.0001 <0.0001 <0.0001 0.0002 0.0002 0.256 0.127 .f:>.
12 <0.0001 <0.0001 <0.0001 <0.0001 0.0009 0.0008 <0.0001 <0.0001 <0.0001 <0.0001 0.0002 0.0002 0.180 0.116
21 0.0002 <0.0010 <0.0001 <0.0001 0.0013 0.0008 <0.0001 <0.0001 0.0002 0.0009 0.0002 0.0005 0.039 0.047
29 0.014 0.024 <0.0002 <0.0002 0.0015 0.0006 0.0042 0.0076 0.028 0.50 0.0059 0.0095 0.500 0.47
41 0.23 0.29 0.0004 0.0004 0.0079 0.0043 0.032 0.046 0.23 0.28 0.032 0.039 1.03 0.85
47 0.36 0.38 0.0004 0.0004 0.012 0.0094 0.057 0.073 0.36 0.39 0.049 0.050 0.66 0.564
Comparison of Ten-Cycle to Two-Cycle Amberlite IRA-99 Resin, Adsorption Data
Resin' Amberlite IRA-99, 20 X 50 mesh Acidified with 0.1 ~ H2S04; 30 cc Flow rate 7 mllmin
Feed soln No.2 Temperature 23° C.
Effluent assays, gil
6 <0.0001 <0.0001 0.0005 0.0013 0.0039 0.0042 <0.0001 <0.0001 <0.0001 <0.0001 0.0002 0.0002 0.256 0.127
12 <0.0001 <0.0001 <0.0001 <0.0001 0.0009 0.0008 <0.0001 <0.0001 <0.0001 <0.0001 0.0002 0.0002 0.180 0.116 N
21 0.0002 <0.0010 <0.0001 <0.0001 0.0013 0.0008 <0.0001 <0.0001 0.0002 0.0009 0.0002 0.0005 0.039 0.047 0
29 0.014 0.024 <0.0002 <0.0002 0.0015 0.0006 0.0042 0.0076 0.028 0.50 0.0059 0.0095 0.500 0.47
41 0.23 0.29 0.0004 0.0004 0.0079 0.0043 0.032 0.046 0.23 0.28 0.032 0.039 1.03 0.85
47 0.36 0.38 0.0004 0.0004 0.012 0.0094 0.057 0.073 0.36 0.39 0.049 0.050 0.66 0.564
Comparison of Ten-Cycle to Two-Cycle Amberlite IRA-99 Resin Elution Data
Resin Amberlite IRA-99, 20 X 50 mesh, loaded with feed solution No.2 Flow rate 7 mllmin
Eluant 1.5 gil Ca(0H)2 + 4.1 gil NaCNS + 1.0 gil NaCN Temperature 23° C.
Eluate assays, gil
6 0.75 0.69 0.021 0.038 0.20 0.23 0.25 0.27 0.17 0.16 0.24 0.23 2.30 2.42 8.4 8.3
15 0.19 0.15 0.35 0.35 0.37 0.36 0.20 0.16 0.13 0.12 0.18 0.18 2.93 2.93 11.2 11.5
24 0.010 0.0075 0.13 0.074 0.077 0.054 0.019 0.0097 0.023 0.014 0.029 0.021 2.68 2.53 12.5 12.6
36 0.0009 0.0009 0.0086 0.0050 0.014 0.011 0.0008 0.0006 0.0021 0.0022 0.0012 0.0014 2.85 2.82 12.6 12.6
48 0.0005 0.0005 0.0031 0.0016 0.0084 0.0055 0.0002 0.0002 0.0013 0.0014 0.0006 0.0012 2.82 2.81 12.6 12.6
Resin wt % <0.005 <0.005 0.015 0.004 0.076 0.069 <0.005 <0.005 0.14 0.18 0.037 0.051
21
TABLE3C
4,708,804
22
Resin
Eluants
Contact
RESIN ELUTION USING VARIOUS ELUANTS
IRA-99, 12 g moist (4.7 g dry), loaded from solution No.2, 10 cc resin/test
1.5 gil Ca(OHh plus NaCNS, NaCNS + NaCN
First stirred with 1.0 L eluant in beaker for 30 min at 23' C., then transferred resin to
~" column and eluted with 150-250 ml eluant until effluent assayed 0.01 gil Zn.
Assay, % % Eluted
Test Eluant gil Sample Zn Ni Co Fe Cu Zn Ni Co Fe Cu
Loaded resin 0.85 0.71 0.77 0.19 0.65
I 8.1 NaCNS Treated resin 0.070 0.004 0.20 0.13 0.005 92 99+ 74 32 99+
2 8.1 NaCNS + 5.0 NaCN Treated resin 0.016 0.006 0.17 0.080 0.002 98 99+ 87 58 99+
EXAMPLE 3
A test was performed to produce a concentrated
eluate by recycling a saturated Ca(OHh solution
through the resin. 200 cc of IRA-35 resin in a 2.6 cm
diameter column was acidified with H2S04, loaded
with solution No.3 and then eluted by recycling a saturated
Ca(OHh solution containing NaCN through the
15 resin. This cycle was repeated twice. Process conditions
and results are presented in Table 4A.
Resin elution processes using a number of eluants
were compared. Test conditions and results are presented
in Table 4B.
TABLE4A
I. Acidification
2. Adsorption
Assays
Sample
Feed Solution
Effluent
I
2
3
4
Adsorbed,
g
meq
gil
1b/ft3
Adsorption and Elution Data for Amberlite IRA-35 Resin
Cycle I
Resin Amberlite IRA-35, 20 X 50 mesh, 200 cc WSR
Column 2.6 cm diam X 37 cm
H2S04 soln 19.3 gil H2S04, 490 ml (193 meq)
Flow rate 20 mllmin
H2S04 adsorbed 9.46 g, 193 meq
Temperature 23' C.
Feed solution No.3
Flow rate 22 mllmin (6.6 BV!hr, 1.0 gpm/ft2), downflow
Volume (cum) Assay, gil
ml BV CNT CNF CNS Cu Zn Fe Ni pH
4000 1.05 0.56 0.34 0.49 0.091 0.046 0.0064 10.5
910 4.6 0.26 0.002 <0.0002 0.0002 0.0003 <0.0002 9.2
2165 10.8 0.24 0.013 <0.0002 0.0002 0.0003 <0.0002 9.0
3375 16.9 0.24 0.43 <0.0002 0.0002 <0.0003 <0.0002 8.9
3840 19.2 0.24 0.57 <0.0002 0.0002 <0.0003 <0.0002 8.9
3.24 -0.78 1.95 0.364 0.18 0.026
-13 61.5 11.1 13.0 0.8 (Total = 99)
3.9 9.75 1.82 0.90 • 0.13
1.01 0.24 0.61 0.11 0.056 0.0081
3. Elution Eluant, recycle
flush
Temperature
130 ml HP + 8.0 g Ca(OHh + 2.32 g NaCN (contained in 200 ml
beaker, and equipped with 2 glass frits through which
solution was filtered), solution recycled through resin at 22
mllmin until pH - 12.
Saturated Ca(OHh + 5.7 gil NaCn, 1000 ml used to flush
pregnant eluate from' column at 22 mllmin
28/30' C.
Assays Volume Assay, gil
Sample ml BV (Cum) pH CNT CNF CNS Cu Zn Fe Ni
Eluate
I 140 0.7 12+ 16.5 7.7 2.08 6.75 0.30 0.64 0.039
2 100 1.2 12.2 13.2 8.2 1.96 6.82 0.29 0.62 0.035
3 100 1.7 12.2 6.4 5.6 2.02 2.11 0.38 0.12 0.047
Flush eluate
I 100 2.2 12.3 4.4 4.5 1.31 0.28 0.38 0.019 0.038
2 100 2.7 12.4 3.8 4.1 0.38 0.052 0.33 0.004 0.027
3 100 3.2 12.4 4.1 0.13 0.020 0.32 0.002 0.019
4 100 3.7 12.4 4.1 0.03 0.008 0.31 0.001 0.012
5 100 4.2 12.4 4.1 0.01 0.004 0.28 <0.001 0.007
6 100 4.7 12.4 4.1 0.005 0.001 0.22 <0.001 0.004
7 100 5.2 12.4 0.17
9 100 6.2 0.11
Residual Ca(OHh 3.05 g
Eluted, g 3.8 0.87 1.87 0.36 0.166 0.024
Cycle 2
I. Acidification Same as Cycle 1
H2S04 adsorbed 9.85 g, 201 meq.
23
4,708,804
TABLE 4A-continued
24
Adsorption and Elution Data for Amberlite IRA-35 Resin
2. Adsorption Same as Cycle I
Assays
Volume
(Cum) Assay, gil ppm
ml BV pH CNT CNF CNS Cu Zn Fe Ni CNO S" Au
4000 10.6 1.10 0.51 0.35 0.488 0.089 0.047 0.0065 0.063 0.01 0.09
Sample
Feed soln
Effluent
I
2
3
4
Adsorbed,
g
Ib/ft3
913 4.6 9.6
2217 ILl 9.2
3434 17.2 9.2
3852 19.3 9.1
0.21 0.004 <0.0002 0.0003 <0.0002 <0.0002
0.24 0.024 <0.0002 0.0002 <0.0002 <0.0002 0.0441 <0.01 1 <0.0021
0.24 0.22 <0.0002 <0.0002 <0.0002 <0.0002
0.25 0.57 <0.0002 <0.0002 <0.0002 <0.0002
3.24 1.05 1.95 0.356 0.188 0.026
1.01 0.327 0.608 0.111 0.059 0.0081
IComposite of effiuent I, 2, 3, 4.
3. Elution, recycle Solution in resin displaced with Cycle 1 pregnant eluates (330 ml) + 8.0 g Ca(OH)z recycled for
2! hours until pH = 11.5 plus! hour longer at 22 mllmin.
Temperature = 25-28· C.
flush Saturated C~(OH12 (200 ml) + H20 (100 ml) at 22 mllmin, 23· C.
Assays
Sample
Eluant recycle
Eluate
I
2
3
4
Resin
Residual
Ca(OH)z
Vol Assay, gil or %4
inl CNT CNC3 Cu Zn Fe Ni CNS Ca(OH)z Ca Co Au S0 4
230 14.9 6.65 0.300 0.617 0.038 2.03
145 22.0 17.4 11.0 0.51 1.07 0.051 2.72
100 22.0 17.0 10.8 0.50 1.02 0.049 2.71 0.0002
100 8.3 8.2 5.25 0.62 0.23 0.055 2.54
100 3.3 2.9 1.42 0.61 0.040 0.047 1.66
42 g 0.32 0.031 0.40 <0.003 0.016 «0.5) 0.017
3.98 g 3.4 2.3 0.26 0.32 <0.01 32 29.5 28
3CNC = eN calculated as metal complexes.
4So1utions as gil. solids as %.
Material balance:
Amount, g
Zn Fe
Input,
resin
eluant
total
Output eluant
Ca(OH)z
Resin
Total
% eluted
3.24
3.42
6.66
6.55
0.13
0.13
6.81
98.1
Cu
1.95 0.356
1.53 0.069
3.48 0.425
3.34 0.247
0.092 0.010
0.013 0.168
3.45 0.425
99.6 60
0.188
0.142
0.330
0.284
0.013
<0.001
0.297
99+
Ni CNS
0.026 1.05
0.0086 0.47
0.035 1.52
0.022 1.08
<0.001 NA
0.007 <0.2
0.029
76 >82
Ca(OH)z consumption Feed 8.00 g X 95% = 7.60 g Ca(OH)z
Excess = 1.27
Soluble - 0.5 L X 1.5 gil = 0.75
Consumed 5.58(= 151 meg)
TABLE4B
Resin
Eluant
Assay (in gil)
Volume
Flow Rate
Temperature
Samples,
eluate
resin
RESIN ELUTION TESTS USING VARIOUS ELUANTS
IRA-35, from 2nd cycle elution
Assay (in %, dry) = 0.44 Zn, 0.031 Cu, 0.016 Ni, 0.017 Co, 0.001 Fe (filtered, H20 washed)
Amount/test = 20 cc WSR (4.1 g dry)
Test 1 8.1 NaCNS + 4.0 NaOH
2 8.1 NaCNS + 12 NaOH
3 8'.1 NaCNS + 4.9 NaCNS + 4.0 NaOH
4 4.1 NaCNS + 4.0 NaOH
5 1.0 NaCNS + 4.0 NaOH
6 8.4 NaHC03 (after H20 flush)
7 8.4 NaHC03 + 0.9 NaCN (after H20 flush)
200 mlltest
2 mllmin
22124· C.
20 ml fractions
Final resin filtered and dried for assay
4,708,804
25 26
TABLE 4B-continued
RESIN ELUTION TESTS USING VARIOUS ELUANTS
Test No. 2 3 4 5 6 7
8.1 NaCNS 8.1 NaCNS 8.1 NaCNS 4.1 NaCNS 1.0 NaCNS 8.4 NaHC03 8.4 NaHC03
4.0 NaOH 12 NaOH 4.9 NaCN 4.0 NaOH 4.0 NaOH 0.9 NaCN
4.0 NaOH
Eluate
I, mg/L Zn 78 153 73 123 61 33 43
2, mg/L Zn 189 207 131 198 258 25 24
3, mg/L Zn 36 19 93 50 50 18 8.9
4, mg/L Zn 4.5 4.5 49 7.3 6.0 14 2.4
5, mg/L Zn 1.2 1.8 ·22 2.1 1.7 10 1.9
Resin, % Zn <0.01 <0.01 <0.01 <0.01 <0.01 0.03 0.11
'Zn eluted,
mg 6.17 7.71 7.36 7.61 7.52 2.02 1.59
% 98+ 98+ 98+ 98+ 98+ 95 75
EXAMPLE 4 EXAMPLE 5
Acidification/volatilization tests were run on eluates
from a weak base ion exchange process. The resin was
eluted with Ca(OH)2. The feed solutions for these tests
have the assays shown in Table 8. Feed Solution I is a
synthetic feed prepared with NaCN, CuCN, ZnS04and
K.4Fe(CN)6. Feed solutions 2 and 3 are ion exchange
eluates from the elution of Amberlite IRA-99 with Ca-
(OHh and NaCN spiked with NaCNS, K4Fe(CN)6 and
ZnS04+4NaCN. Feed solutions 4 and 5 are synthetic
solutions prepared with NaCN, CuCN, NaCNS,
K4Fe(CN)6, and ZnS04+4NaCN. Feed Solutions 6-13
are synthetic solutions simulating ion exchange resin
eluates obtainable from the elution of weak base resins
with calcium hydroxide.
In Tests 1-7, 200 grams per liter H2S04 was added
gradually to the feed solution contained in a 250 ml
distillation flask under 4 to 5 inches mercury vacuum
with 70 to 90 cc/min air sparge. Tests 8 and 9 were
identical except that the feed solution was added gradually
to 200 grams per liter H2S04 in the distillation flask.
In Tests 10-17 100 ml of synthetic solution was added
at I mllmin to 30 to 54 ml of 200 grams per liter H2S04
(plus 5 grams CaS04 to H20) contained in a 250 ml
distillation flask. Air was sparged into the slurry at
about 80 cc/min.
Cyanide recoveries of 75-87% were obtained in two
hours at 55°-60° C., 5 in. Hg vacuum, and 30-40 gil
H2S04 acidity. Increasing the temperature to 89° C.
increased cyanide recovery to 90%.
Results for Tests I and 2 are presented in Table 9.
50 Results for Tests 3-9 are presented in Table 10. Results
for Tests 10-17 are presented in Table 11.
TABLE5A 30
Resin Stability Test
Solution, gil Vol,ml
4.8 H2SO4 500
H2O 300 35
Feed solution 2600
1.5 Ca(OHh + 1.0 NaCN 1600
H2O 200
I 2 3 4 5 Total
0.59 0.48 0.48 0.56 0.58 40
1.28 1.04 1.06 1.09 1.12 5.59
1.06 1.01 1.02 1.01 1.10 5.20
1.06 1.17 1.13
45
1.03 1.02 0.93
0.93 0.93 0.93
1.55
0.20 0.20
28 g Cull, 34 g CNTII (2.1 lb CNTlft3)
(0.88 meqll)
Acidification
Flush
Adsorption
Elution
Flush
2.
3.
1.
H2S04
Ca(OHh
Final resin,
% Cu
g Cu
Resin loading
Data summary
Cycle
A synthetic feed solution prepared from Na2. 20
Cu(CNh having 0.5 to 0.6 grams per liter Cu at pH 10.2
was downflowed through a 5 cm diameter by 2 cm resin
bed at 30 to 40 ml per minute and 22° to 24° C. The resin
used was XE-299 (Amberlite IRA-99 equivalent),
15xMesh, 40 cc WSR (capacity equal 1.2 meq/L). Pro- 25
cedures and results are presented in Table 5A.
Resin elution processes using a number of eluants
were compared. Test conditions and results are presented
in Table 5B.
Feed solution,
"gil Cu
Cu adsorbed, g
Cu eluted,;,
Ratio, CN ICu!
Acidlbase consumed,
meg/ml
'Ratio of g NET CNTin e!uate/g Cu in eluate (MR 3CN/Cu = 1.23).
TABLE5B
Weak-base Resin Elution Scoping Tests
Resin IRA-99, 4.4 g moist, loaded using barren MC solution and eluted with
saturated Ca(OHh + 5 gil CN, then 20 gil NaOH
Eluants NaCNS + NaOH, N140H, NaOH + NaCI, NaCN + NaOH
Contact Percolated eluants (100 ml) through resins in gooch crucibles at 1-3
mllmin in 10·20 ml portions.
Assay, % % Eluted
Test Eluant gil Sample Zn' Fe Cu Zn Fe Cu
Feed resin 0.40 0.20 0.040
I 81 NaCNS + 4 NaOH Treated resin 0.030 0.17 0.014 93 IS 65
2 3.5 ~N140H Treated resin 0.34 0.20 0.040 IS <10 <10
3 40 NaOH + 58 NaCI Treated resin 0.020 0.17 0.030 95 IS 25
4 49 NaCN + 40 NaOH Treated resin 0.38 0.20 0.019 <1O <10 53
4,708,804
27 28
TABLE 8 TABLE 9-continued
Feed Solution Assays Summary of HCN Volatilization Tests
Feed solution 2 4 6 7 Test 2
Feed solution assay, 5 Time, min
gil H2S04 addn. 99
CNT 30.5 33.6 31.6 33.6 34.5 33.8 33.6 Total 99 81
CNS 5.6 6.6 13.0 17.0 5.1 5.2 5.3 % evolved,
Cu 15.8 16.3 16.5 15.9 17.1 15.3 14.5 CN 77 92
Zn 2,21 2.94 2.98 3.42 3.60 3.57 3.45 CNS I <5
Fe 0.84 1.56 1.55 1.58 1.64 1.82 1.75 10 Precipitate assay, %
Feed Solution 8 9 10 11 12 13 CNT 20 15.4
CNS 14 31.0
Feed solution assay, Cu 49.1 43.8
gil Fe 3.58 4.95
CNT 36.5 38.1 38.1 33.6 33.6 33.6 Zn 2.38 0.11
CNS 5.2 6.1 10.4 5.1 5.3 9.8 15 Solution assay, gil
Cu 6.90 6.70 7.35 14.5 15.0 14.8 CNT 0.27 0.11
Zn 10.3 5.10 5.50 3.62 3.63 3.57 CNS <0.01 0.02
Fe 1.93 5.49 5.13 1.79 1.93 1.92 Cu 0.046 7.25
Fe 0.026 11.1
Zn 0.76 1.76
TABLE 9 20 H2SO4 29 24
Summary ofHCN Volatilization Tests
% precipitated
CNT 22 7
Test I 2 CNS 99 98
Feed solution I I Cu 99+ 45
H2S04 added, gig CNT 2.7 Fe 96
Additive Fe2(S04h! 25 Zn 52
gig CNT 1.8 ITested the effect of adding Fe2(S04h to residual acid slurry after initial HeN was
Temperature, °c. 65 52 evolved.
TABLE 10
Test 3 4 6 8 9
Feed solution 2 3 4 5 5 5
H2S04 added, gig CNT 2.6 3.1 3.2 3.2 3.2 3.2
Additive 79 gil NaCl
Temperature, 'C. 58 58 58 58 58 58 91
Time, min
H2S04addn. 77 123 93 83 107 (122)
Total 115 19O 152 144 152 204 67
% evolved,
CN 75 83 87 71 73 74 80
CNS <5 <5 <5 <5 <5 <5 <5
H2S04 consumed, gig CN! 1.7 1.8 1.8 1.7 I.7 I.7 1.7
Precipitate assay, %
CNT 10.3 8.0 9.2
CNS (4.4) (5.5) (5.2)
Cu 18.6 21.6 21.8
Fe 1.83 1.92 1.67
Zn 2.46 2.00 0.67
Ca 13.1 14.2 14.4
Feed solution 2 4 5
Solution assay, gil
CNT 0.84 0.12 0.39 0.79 0.39 0.41 0.10
CNS <0.01 <0.01 0.43 <0.01 <0.01 <0.01 <0.01
Cu 0.036 1.89 0.015 0.052 0.13 0.26 0.40
Fe <0.001 0.002 0.003 0.001 0.003 0.005 0.15
Zn 0.42 0.45 0.31 0.85 1.16 1.30 1.91
H2SO4 30 34 36 43 46 42 42
% precipitated
CNS 99+ 99+ 96 98+ 99+ 99+ 99+
Cu 99+ 85 99+ 99+ 98+ 98 97
Fe 99+ 99+ 99+ 99+ 99+ 99+ 86
Zn 79 81 86 62 51 60 85
TABLE 11
Test 1O 11 12 13 14 15 16 17
Feed Solution 6 7 8 9 10 11 12 13
H2S04 added, gig CNT 2.98 3.21 2.95 2.83 2.83 1.79 1.79 2.98
Additive H3P04 Fe2(S04h
gig CNT 0.15 1.0
Temperature, 'C. 58 58 58 58 58 58 89 89
Time, min
soln addn. 100 99 96 90 87 78 87 79
29
4,708,804
30
TABLE II-continued
'Test 10 II 12 13 14 15 16 17
Total 16O 169 172 155 167 158 128 129
% evolved,
CN 73.2 77.6 82.7 55 56 70.3 76.9 89.9
CNS <5 <5 <5 <5 <5 <5 <5 <5
Precipitate assay, %
CNT 9.8 9.2 8.7 15.1 14.7 I\.7 8.7 5.1
CNSl (5.4) (6.6) (5.8) (\.9) (2.8) (5.5) (5.6) (12.0)
Cu 18.0 15.7 9.95 8.40 8.00 17.7 19.2 21.3
Fe 2.22 2.86 2.60 6.05 5.75 2.16 1.90 1.15
Zn \.46 0.021 3.40 5.85 5.95 2.70 1.79 0.34
Ca 14.2 15.1 16.3 13.2 11.3 13.5 1.41 15.8
Solution assay, gil
CNT 0.36 0.32 0.29 0.28 0.25 0.27 0.06 0.07
CNS <0.01 <0.01 2.08 4.60 <0.01 <0.01 <0.01
Cu 0.34 \.89 0.27 <0.001 <0.001 0.052 0.16 0.52
Fe 0.007 3.60 0.003 0.007 0.007 0.002 0.24 0.70
Zn \.52 2.18 5.50 <0.001 <0.001 0.92 1.40 2.20
H2SO4 41 39 35 46 47 11 8.2 30
% precipitated
CNS 97 98 99 36 28 98 98 99
Cu 96.5 79.4 94.2 99.9 99.9+ 99.5 98.6 95.3
Fe 99.4 99.7 99.9 99.8 99.9 83.0 45.2
Zn 33.1 0.4 2\.6 99.9 99.9 64.3 43.7 7.2
leNS assays of precipitates are probably low by 10-20%.
55
tion which is limited only by the scope of the appended
claims.
What is claimed is:
1. A method of treating waste streams containing free
cyanide and cyanide complexes comprising:
concentrating cyanide complexes using weak base ion
exchange resin;
eluting the resin with a recycled saturated lime solution
to form an eluate having a concentration of
cyanide higher than said waste stream;
recovering the cyanide from said eluate by acidification
followed by volatilization.
2. A method according to claim 1 wherein said free
4Q cyanide is complexed prior to said concentrating step.
3. A method according to claim 1 wherein said free
cyanide passes through said ion exchange resin and is
recycled for use.
4. A method according to claim 1 wherein said elut45
ing comprises recycling said lime solution through a
Ca(OHh saturation source and said resin until said resin
is substantially stripped of its cyanide load.
5. A method according to claim 4 wherein said recycling
continues until the effluent pH increases to about
50 11.
6. A method according to claim 1 wherein said waste
stream contains thiocyanate and further comprising:
adsorbing said thiocyanide on said resin during said
concentrating.
7. A method according to claim 6 wherein said con-.
centrating is achieved by partial loading with respect to
metal cyanide complexes.
8. A method according to claim 7 wherein said resin
loading is from about 0.5 to about 3 pounds total cyanide
per cubic foot resin.
9. A method according to claim 1 wherein said acidification
comprises lowering the pH to a level sufficient
to dissociate CN from said complexes by contacting
said eluate with acid, whereby HCN is formed.
10. A method according to claim 9 wherein said acid
is H2S04.
11. A method according to claim 9 wherein said
HCN is volatilized by heating.
35
2\.6
93+
87
5
82
6
95+
0.4
<I
13
95
18
94
<5
78.0
<6
EXAMPLE 7
Although the foregoing invention has been described
in detail and by way of example for purposes of clarity 65
and understanding, as will be known and understood by
those skilled in the art, changes and modifications may
be made without departing from the spirit of the invenlLarge
volumes of NaOH scrub solutions were used. More concentrated solutions 60
can be obtained in actual practice.
2Higher temperatures resulted in excessive frothing.
3precipitate = 6.25 g.
TABLE 12
Assays
Ion-Exchange Scrub Final
Eluate Solnl Soln Precipitate3
gil gil gil gil
CNT 22.0 \.98 0.06 7.75
CNS 2.03 <0.01 <0.01 . 3.3
Cu 10.9 0.96 14.7
Zn 0.60 0.38 0.048
Fe 1.16 0.13 \.46
Ni 0.051 0.032 0.005
Co 0.019 <0.0005 0.028
Ca 12.0 15.9
H2SO4 17.2
Distribution, %
Scrub Final
Soln Soln Precipitate
CNT
CNS
Cu
Zn
Fe
Ni
Co
M.Q.L
added 2.69 gig CNT
consumed \.84 gig CN evolved
Precipitate CaS04.2H20 + probable CU2Fe(CN)6,
composition 2CuCNS.CuCn
An ion exchange eluate prepared by eluting Amberlite
IRA-35 with Ca(OHh/CN was gradually added to 30
50 ml 116 grams per liter H2S04 solution at 700 to 800 C.
Air sparge at about 0.5 cfm/ft3solution was conducted.
The results are presented in Table 12.
32
19. The process of claim 17 further comprising:
separating said volatilized HCN therefrom.
20. The process of claim 17 further comprising recovering
said HCN by contacting with an aqueous solution
of Ca(OHh tQ form Ca(CNh.
21. The process of claim 17 wherein said dilute cyanide
solution contains less than about 0.5 weight percent
cyanide.
22. The process of claim 17 wherein said eluate contains
at least about 0.5 weight percent cyanide.
23. The process of claim 17 wherein said eluting comprises
recycling an eluant comprising Ca(OHh sequentially
through a Ca(OHh saturation source and said
resin until an effluent pH greater than 11 is obtained.
24. The process of claim 17 wherein said solution
comprises free cyanide and further comprising comp1exing
said free cyanide prior to said concentrating.
25. A process for eluting a weak anion-exchange resin
column comprising:
(a) contacting the resin with a complex cyanide containing
feed solution to form a complex cyanideloaded
resin;
(b) discontinuing contact of said feed with the resin;
(c) contacting the complex cyanide-loaded resin with
a calcium hydroxide-saturated aqueous solution;
(d) withdrawing a portion of said solution from the
column;
(e) contacting said withdrawn portion with a solid
bed comprising Ca(OHh to form a calcium hydroxide-
saturated recycled solution;
(f) contacting said recycle solution with a complex
cyanide-loaded resin;
(g) repeating steps (d) through (f) until the pH of said
withdrawn portion is greater than about II; and
(h) recovering cyanide from said withdrawn portion
by acidification followed by volatilization; and
(i) flushing the column with a low-cyanide content
aqueous solution.
26. The process of claim 25 wherein said feed contains
Zn(CN)4-2 and further comprising performing
said discontinuing step when the resin is partially
loaded.
25
35
15
* * * * *
4,708,804
31
12. A method according to claim 11 wherein said
volatilized HCN is neutralized to form cyanide salt.
13. A method of treating waste streams comprising
free cyanide and metal cyanide complexes, wherein said
metal is selected from the group consisting of Zn, Cu, 5
Cd, Fe, Co, and Ni, said method comprising: concentrating
said metal cyanide complexes using weak base
ion exchange resin; and eluting the resin with a recycled
saturated lime solution to which a thiocyanate compound
has been added to form an eluate having a con- 10
centration of cyanide higher than said waste stream.
14. A method of treating waste streams comprising
thiocyanate compounds and metal cyanide complexes
comprising complexes of cyanide with zinc comprising
the steps of:
partially loading weak base ion exchange resin with
metal cyanide complexes and thiocyanate; and
eluting the resin with a recycled saturated lime solution
to form an eluate comprising zinc ions.
15. The method of claim 14 wherein said metal cya- 20
nide complexes comprise complexes of cyanide with
copper and further comprising the steps of:
acidifying said eluate in the presence of an amount of
thiocyanate; and
heating said acidified eluate to volatilize HCN.
16. The method of claim 14 wherein said metal cyanide
complexes further comprise complexes of cyanide
with copper and wherein said waste stream comprises
thiocyanate and further comprising:
recovering the cyanide from said eluate by acidifi- 30
cation followed by volatilization.
17. In a process for recovering HCN from a dilute
complex metal cyanide-containing solution by acidification
followed by volatilization, the improvement
comprising:
concentrating said cyanide in the solution to be acidified
by passing the solution through a weak base
ion exchange resin and eluting said ion exchange
resin by contacting said resin with a saturated solution
of Ca(OHhto produce eluate having a cyanide 40
concentration higher than said dilute solution.
18. The process of claim 17 wherein said acidifying
step comprises contacting said eluate with H2S04.
45
50
55
60
65