4,708,804 Method for recovery of cyanide from waste streams

Patent Number/Link:

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

(30

TREATI:O

SOLUllON WASTI: CO(CN)2.

u.s. Paten~ Nov. 24, 1987 Sheet 1 of2

CYANIDE __10

SOLUTION

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

~-27

n /28

_c_a(_O_H)-I2_~ NEUTRALIZATION

. (30

TREATED

SOLUTION

FIG.1

.Ir

WASTE Ca(CN)2

C/.) •

""C

('D=~.

-\0

-....J

en ;-

146 --

150

H2O ...~

156

152 .----/

......,J

FIG.2

..0. 0

~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

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

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

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:

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

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)

(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)

4,708,804

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:

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

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

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

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

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

TABLE 2A-continued

Amberlite IRA-35/99 Resins, Synthetic Solution Stability Test

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 _

CNS

CNF

0.25

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.

CNS

Total cations

Elution

Eluted, meg.

Total cations

Base consumed, meq.

33.3

Results: Cycles 1-9

2 __3_

99 35 99

37.5

30.6

36.6

99 35

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

2 Cycle 10 Cycle

5 6

II 12

19 20

29 29

38 41

44 47

2 Cycle 10 Cycle

<0.0001 <0.0001

<0.0001 0.0006

0.031 0.14

0.53 0.51

0.45 0.43

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

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

2 Cycle

<0.0001

0.0070

0.16

10 Cycle

<0.0001

0.0002

0.036

0.17

0.16

Volume Effiuent Assay, gil

4,708,804

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

4,708,804

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

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

CNS

CNF

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

4,708,804

TABLE 3A-continued

Ten-Cycle Amber1ite IRA·35/99 Resins· Solution No.2 Stability Test

Base consumed, meg. 34 26 34 31 30 28

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

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

TABLE3C

4,708,804

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

Adsorbed,

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.

4,708,804

TABLE 4A-continued

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

Adsorbed,

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

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

6.81

98.1

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

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

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

4,708,804

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%.

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.

2\.6

93+

95+

0.4

78.0

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

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.

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;

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.

* * * * *

4,708,804

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.