4,101,315 Recovery of silver from cuprous chloride solutions by co-crystallization with sodium chloride

Patent Number/Link:

United States Patent [19]

Peters et al.

[11]

[45]

4,101,315

Jul. 18, 1978

ABSTRACf

A process for recovering silver present in cuprous chloride

solutions as a soluble silver chloride which comprises

saturating the cuprous chloride solution with

sodium chloride, subjecting the saturated solution to

evaporation to co-crystallize the sodium chloride and

silver chloride, separating the solid chlorides from the

liquid, recovering silver from the sodium chloride-silver

chloride crystals and reclaiming the sodium chloride,

adding water to the liquid and cooling it to crystallize

cuprous chloride. The procedure is adaptable to

processes for recovering copper from its ores in which

copper is reduced to cuprous chloride in a leach slurry

followed by cooling the leach slurry to crystallize out

the cuprous chloride from which copper is recovered

by conventional techniques.

13 Claims, 4 Drawing Figures

[57]

OTHER PUBLICATIONS

Mellor, Inorganic and Theoretical Chemistry, vol. 3,

Longmans Green, pp. 162, 163.

Primary Examiner-a. R. Vertiz

Assistant Examiner-Brian E. Hearn

Attorney, Agent, or Firm-Sheridan, Ross, Fields &

McIntosh

. U.S. PATENT DOCUMENTS

5/1976 Rogers 423/24

6/1967 Been 23/302

4/1972 Stenger 23/303

5/1975 Matsamoto 23/305

8/1976 Goens et aI 423/493

176,813

3,323,8753,655,333

3,885,921

3,972,711

[54] RECOVERY OF SILVER FROM CUPROUS

CHLORIDE SOLUTIONS BY

CO·CRYSTALLIZATION WITH SODIUM

CHLORIDE

[75] Inventors: Mark A. Peters, Arvada; Robert K.

Johnson, Lakewood, both of Colo.

[73] Assignee: Cyprus Metallurgical Processes

Corporation, Los Angeles, Calif.

[21] Appl. No.: 759,846

[22] Filed: Jan. 17, 1977

[51] Int. CI.2 C22B 15/12; C22B 11/04;

COlO 5/00

[52] U.S. Cl 75/104; 75/108;

75/117; 75/118 R; 75/109; 423/34; 423/42;

423/493

[58] Field of Search 23/296, 300, 302 R,

23/303, 305 R; 423/34, 38, 42, 197, 491, 493,

499; 75/108, 117, 118, 104, 109

[56] References Cited

CONDENSATE

CRYSTALS

AgCI-NaCI

-_!_-

,-------------------------------\

I I

I NaCI CRYSTALS I

HCI WASH

MAKE-UP

NaCi

WATER

------------ ---------\

III

L ~g~ECO~~ PR~~S ._J

u.s. Patent July 18, 1978 Sheet 1 of 4 4,101,315

SOLUBILITY DATA

SYSTEM: CuCI-NaCI-H~

500

400

FREE ACID =8-11 gil HCI

Cu +2 < 2g/1

300

-.......

CuCI SOLID PHASE

:J u

..200

100

NoCI SOLID PHASE

100 200 300 400

0~iiie::::::::::"'_--l._--_...L_---l....dbd--_--1

NoCI, gil

A,B,C,D INDICATE DOUBLE POINTS

T.J.q:.. 1

u.s. Patent

July 18, 1978 Sheet 2 of 4

SOLUBILITY CURVE FOR THE

SYSTEM: CuCI-NaCI-H20

4,101,315

ua 20

rfl

CuCI SOLID PHASE

% NoCI

\ EVAPORATION /

\ CRYSTALLIZATION

NoCI SOLID PHASE

T.J.q:. 2

c::: •

•00

~e. (D=f""t-

LI QUID-SOLIDS

SEPARATION

Cu ....----_t__

I Ag CEMENT II --I IJ

, I

MAKE-UP ,-------------------------------1

NoCI

EVAPORATION I

CuCI CRYSTALS NoCI CRYSTALS EVAPORATION l-

~-------~--- ----~

-.".J::..

~ -..

Co-4 =-'<-I 00 '"- I \0

I -...I 00 II

I rI.:l ::r'

I til I .t.i.l.

I w

- --I .0..., ~

CONDENSATE

7:J..q=. :3

AgCI-NoCI I CRYSTALS lOr DISSOLUTION LIQUID-SOLIDS I

SEPARATION

PURIFIED CuCI

CRYSTALS

t t

LIQUID-SOLIDS

SEPARATION

MOTHER LIQUOR

DILUTION

CuCI

CRYSTALLIZATION

WATER

1 BLEED

~------------~---------I

III

L --------Ag-RE-CO-VER-Y -PR-OC-ESS-----

FeCI3 LEACH

CuCI

AND

CRYSTALLIZATION

Cu++ REDUCTION

LIQUID -SOLIDS MOTHER LIQUOR

SEPARATION

-I

CuCI CRJSTALS

MOTHER LIQUOR SILVER IMPURITY

RECOVERY REMOVAL

BLEED

CuCI

RECRYSTALLIZATION

CuCI

REDUCTION

FeCI~ n Cu

HYDROLYSIS II

I.J.q=

PRECIPITATE

c•

C/.)

•

"'C a(I) ::s t"'t-

~,::

q00

......:a

tzl

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n....l.

+:o....,

+:-

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o.......

-...

.......

til

DESCRIPTION OF THE PREFERRED

EMBODIMENTS

4,101,315

SUMMARY OF THE INVENTION

The invention is based on the discovery that sodium

chloride and cuprous cWoride can be recovered from 50

solution by selective crystallization and that silver chloride

co-crystallizes with the sodium chloride. Accordingly,

the invention comprises saturating a cuprous

cWoride solution containing silver as silver chloride

with sodium cWoride, co-crystallizing sodium chloride 55

and silver cWoride by evaporative crystallization without

the crystallization of cuprous cWoride, separating

the liquid and solid chlorides, diluting the liquid with

water to change the concentration of the solution from

a region of sodium chloride solid phase to one of cu- 60

prous cWoride solid phase accompanied by cooling to

crystallize cuprous cWoride from which copper is recovered.

The process may be performed continuously

by returning the sodium cWoride, after removal of silver

chloride from which silver is recovered, to the 65

circuit to resaturate the mother liquor and continuously

adding cuprous cWoride at the rate at which it is removed.

Although the invention is applicable to cuprous chlo-

RECOVERY OF SILVER FROM CUPROUS ride from any source, it is particularly adaptable to

CHLORIDE SOLUTIONS BY processes for recovering copper from its sulfide ores

CO.CRYSTALLIZATION WITH SODIUM containing silver in which process the copper is solubi-

CHLORIDE 5 lized as cuprous chloride in a leach slurry followed by

crystallization of the cuprous chloride with recovery of

BACKGROUND OF THE INVENTION copper from the crystals, the invention being to remove

1. Field of the Invention silver from the crystals before copper is recovered from

The invention lies in the field of recovering silver them by reduction or otherwise.

from cuprous chloride. 10 BRIEF DESCRIPTION OF THE DRAWING

2. Description of the Prior Art

In the recovery of copper from its ores, particularly FIG. 1 is a solubility diagram for the system CuCIsulfide

ores, it is well known, as disclosed in U.S. Pat. NaCI-H20;

Nos. 3,785,944, and 3,972,711, in order to avoid the FIG. 2 is a solubility diagram based on the graph of

disadvantages of recovering copper electrolytically, 15 FIG. 1 in which a series ofprocess steps (represented by

pyrometallurgically, and by other methods, to solubi- the dotted lines) for a selected set of conditions of temlize

the copper in the ore as cuprous chloride in a leach perature and co.ncentrations of C~CI and NaCI. have

followed by cooling the solution to crystallize out the been selected to illustrate the operatIon of the process of

cuprous chloride and recover copper from the cuprous the invention;

chloride crystals. A major disadvantage of wet recov- 20 FIG. 3 is a flowsheet of a method of the invention

ery like this technique, is that impurities like silver and showing a circuit for a continuous process, and

iron are carried over during the crystallization into the FIG. 4 is a schematic flow diagram showing the incorporation

of the silver recovery method of the invencuprous

cWoride crystals and end up as impurities in the tion into the flowsheet of a typical process as disclosed

fmal copper product. ~ome of these impurities ar~ dele- 25 in U.S. Pat. No. 3,972,711 for recovering copper from

terious to the propertIes of copper and reduce Its sale its sulfide ores.

value. While the latter may not be necessarily true of

silver, the failure to recover the high priced silver so

that it is not sold along with the copper at the price of

copper, detracts from the economic feasibility of the 30 Reference is now made to FIGS. 1 and 2 for a deoverall

process. Impurities, such as iron, can be re- scription of the physical phenomena upon which the

moved from the recovered copper by fire refining in the operation of the invention is based, the graphs being

presence of oxygen but this procedure results in the based on experimental results. The graph of FIG. 1

fmished product containing oxygen which adversely shows the existence of double points for each temperaaffects

its conductivity. 35 ture studied where both solid phases (CuCI and NaCI)

Accordingly, it is an object of this invention to pro- co-exist. All data points to the left of a line connecting

vide an effective process for recovering silver and re- the double points were determined with the cuprous

moving iron from cuprous chloride. chloride solid phase present and to the right of the line

It is another object of this invention to provide an with the sodium cWoride solid phase present. The curve

improvement in the process for recovering copper from 40 shows, for example, that if 300 gil sodium chloride

its ores in which the copper is solubilized as cuprous solution saturated in cuprous cWoride at 75° C is cooled

cWoride, the cuprous cWoride crystallized out and the to 5° C, a crop of 130 gil cuprous cWoride should cryscopper

recovered from the cuprous chloride crystals, tallize. If a 180 gil CuCI solution saturated in NaCI at

the improvement being a procedure for recovering 75° C is cooled to 5° C, a crop of 20 gil NaCI should

silver from the cuprous chloride crystals before copper 45 crystallize.

is recovered from them. Referring to FIG. 2, paths 4 to 5 and 5 to I represent

additions of sodium cWoride and cuprous chloride to

the circuit in amounts equal to those removed from the

circuit. Evaporative crystallization is represented by

path I and 2. After crystallization of sodium chloride

high in silver chloride, a liquid-solids separation is performed.

Paths 2 to 3 and 3 to 4 represent dilution with

water to change the concentrations from a region of

sodium cWoride solid phase to one of cuprous chloride

solid phase accompanied by cooling to recover a crop

of cuprous chloride crystals. For illustrative purposes,

the conditions shown in FIG. 2 resulted in about 80%

removal of silver. Obviously, the amount of silver removed

depends upon experimental conditions, such as

concentration of sodium cWoride or cuprous chloride

or temperature.

The invention will now be described in more detail

with reference to FIG. 3.

Cuprous chloride is shown at the beginning of the

process as being introduced to the dissolution step in the

form of crystals. The cuprous chloride feed contains

silver and iron as impurities which are to be removed.

In the dissolution step, the cuprous chloride is solubi4,101,315

3 4

lized and the solution saturated with sodium chloride rates of cooling are variable, ambient cooling and rapid

which is shown as being added as crystals and in mother cooling being used. The cooled crystals were then filliquor.

The sodium chloride saturated cuprous chloride tered and subjected to variable washing cycles and

solution is evaporated to crystallize sodium and silver reslurry procedures. The recovered cuprous chloride

chlorides. This step is followed by a liquid-solids sepa- 5 crystals are dried with acetone.

TABLE 1

Recovery of Ag From NaCI-CuCI Solutions

(Temperature 80· C)

Product (NaCl)

Volume % of Added

Supernatant Analyses Reduction NaCI

Ag Cu(Total) Cu++ Fe++ NaCI of Slurry Crystal- Ag Fe NaCI Cu

Test No. gil gil gil gil gil % Iized ppm ppm % % % Ag Removed

0.049 183 0 I 404 O-feed 0 0

0.036 216 12.5 15 38

0.029 254 381 25 29.0 220 3.98 58

2 0.054 127 4.5 371 O-feed

0.02 284 14 399 46 54 210 320 100 0.56 82

3 0.024 122 0 1.2 348 O-feed

0.010 286 4 1.3 398 46 53 100 340 96.3 0.046 80

4 0.154 122 0 1.2 353 O-feed

0.051 282 6 1.3 386 46 53 630 460 96.3 0.24 80

0.050 122 0 10.6 338 O-feed

0.014 304 9 13.9 358 46 61 210 600 98.3 0.14 94

6 0.054 135 13 1.2 350 O-feed

0.018 322 25 1.3 386 46 59 200 410 95 0.25 79

7 0.054 152 30 1.2 350 O-feed

0.016 324 48 1.3 376 46 59 220 330 95.8 0.10 86

8 0.051 122 0 I.2 354 O-feed

0.045 124 0 1.2 353 1.6 900 0.052 II

ration with the silver chloride-sodium chloride crystals

going to a dissolution step and the mother liquor containing

the cuprous chloride, after dilution, passes on to

the cuprous chloride crystallizer where the temperature 30

is reduced to crystallize the cuprous chloride crystals

which are separated from the mother liquor and copper

recovered from them.

After dissolution of silver chloride-sodium chloride

crystals the solution is sent to copper cementation for 35

silver recovery. The filtrate is evaporated to recover

sodium chloride which is advanced to the cuprous chloride

dissolution step.

If the silver removal process is to be incorporated

into a typical process for the recovery of copper from a 40

copper sulfide feed as shown in FIG. 4, the silver removal

procedure shown in FIG. 3 will be incorporated

into the flowsheet as shown, prior to the recrystallization

of cuprous chloride crystals. In the flowsheet of

FIG. 4 mother liquor is shown schematically as being 45

bled from the silver removal step to the hydrolysis step

where it may be used to supply sodium to precipitate

sodium jarosite.

The invention is illustrated by the results of eight

examples set forth in Table 1 below, example 8 being a 50

comparative example in which sodium chloride and

silver chloride were co-crystallized from a sodium chloride

saturated solution by cooling from 80°-25° C rather

than by evaporation used in the other seven examples.

The feed solution used for the examples was a syn- 55

thetic solution made by adding the required amount of

cuprous chloride, silver chloride and ferrous chloride to

a water solution saturated at 80° C with sodium chloride

at pH 1. In some exampls cupric copper was added to

determine its effect on the efficiency of silver removal. 60

This feed solution was maintained in the acid range.

The removal of sodium chloride crystals and co-crystallized

silver chloride was accomplished by evaporating

the feed liquor to the point where a portion of the

dissolved sodium chloride crystallizes. The slurry was 65

filtered to recover the silver chloride-rich sodium chloride

crystals. The filtrate was diluted with hot water

and cooled with agitation to recover CuCl crystals. The

It will be noted from the above Table 1 that up to

94% of silver was removed from starting solutions containing

from 0.024 - 0.165 gil of silver. Good silver

recovery was obtained from solutions containing as

much as 30 gil of cupric copper showing that this impurity

does not affect the recovery of silver. Likewise,

ferrous iron present in amounts up to about 10.6 gil

does not affect recovery of silver.

Example 8 is a comparative example in which crystallization

was accomplished by cooling from 80°-25° C

rather than by evaporation, and it will be noted that

only 11% of the silver was removed. If a greater percentage

of silver is to be removed from the solution,

more NaCl must be crystallized and this illustrates the

need for an evaporative crystallization procedure. Another

comparative example not listed in Table 1 of crystallization

by cooling is described below.

If the cooling is conducted in the presence of a high

ferrous iron solution saturated in sodium chloride a

larger percentage of silver will be co-crystallized with

the sodium chloride. For example, if a 152 gil sodium

chloride, 186 gil Fe+ + and 0.036 gil silver solution is

cooled from 85°-25° C; 58% of the silver is co-crystallized

with the sodium chloride. The subsequent production

of cuprous chloride crystals will however produce

a cuprous chloride crop contaminated with iron. This

illustrates the importance of utilizing a sodium chloride

solution low in ferrous iron for crystallization.

It was found that the recrystallization of cuprous

chlorides as carried out in this process (Le., in a NaCl

system) reduced the iron content of the cuprous chloride

from typically 220 ppm to 10 ppm. Accordingly, it

is an advantage of the invention that the silver removal

process additionally results in a reduction in the iron

content of the final cuprous chloride crystals.

Various changes were made in the experimental procedure

without. appreciable change in results. These

included the addition of powdered sodium chloride,

ferrous iron and cupric iron; NaCl crystallization in

three evaporation stages; slow evaporation and fast

evaporation. It was also found that regardless of the

amount of silver present, the percentage of silver re4,101,315

moved is in direct proportion to the amount of sodium

chloride which is crystallized.

After the silver is removed as silver chloride by evaporative

crystallization of sodium chloride, the flltrate is

diluted with water at 80· C to move to the cuprous S

chloride solid-phase region. As an example, the filtrate

was diluted with water until cuprous chloride began to

crystallize at 80· C. The solution (0.017 gil silver, 335

gil sodium chloride, 360 gil cuprous chloride, 80· C)

was cooled to 25· C and the resultant cuprous chloride 10

crop contained 15 ppm silver, less than 10 ppm iron and

140 ppm sodium.

If the silver is not removed from these solutions of a

typical flowsheet (FIG. 4), for example, it will eventually

all be removed by the cuprous chloride. The physi- 15

cal phenomena responsible for this has been determined

experimentally. A portion of the dissolved Ag co-crystallized

with the CuCl and a linear relationship was

found between the concentration of silver in the hot

feed soluton and the silver in the resulting cuprous 20

chloride crystals. This relationship was maintained for a

variety of feed solutions: CuClz, HCI, NaCI, FeClz.

Therefore, recrystallization of cuprous chloride from

any of these systems did nqt offer a silver recovery 25

route and illustrates the need for a silver removal

scheme.

It is thus seen from the above description that a process

has been provided for removing silver impurity

from cuprous chloride, the process being applicable to 30

processes for recovering copper from its ores in which

the copper is reduced to cuprous chloride in a leach

slurry, the cuprous chloride crystallized out and copper

recovered from the cuprous chloride crystals.

What is claimed is: 35

1. A process for recovering silver chloride and cuprous

chloride from solution which comprises:

(a) adding sodium chloride to the solution;

(b) heating the solution to drive off water to co-crystallize

sodium chloride and silver chloride fol- 40

lowed by a liquids-solids separation to separate the

crystallized sodium and silver chlorides from the

cuprous chloride solution;

(d) adding water to the cuprous chloride solution to

change the concentration from a region of sodium

chloride solid phase to one of cuprous chloride

solid phase accompanied by cooling the solution to

crystallize cuprous chloride. 50

2. The process of claim 1 in which the cuprous chloride

solution is that resulting from the reduction of

cupric ion with copper sulfide ore.

3. The process of claim 2 in which the copper sulfide

ore is chalcopyrite. S5

4. The process of claim 1 in which prior to co-crystallization

the concentrations of sodium chloride and

cuprous chloride are adjusted to lie on any point of the

solubility curve in the sodium choloride solid phase

region. 60

5. In the process for recovering copper from its ores

containing iron and silver in which the copper is reduced

to the cuprous form in a leach liquor and recovered

as cuprous chloride by crystallization, the improvement

of recovering silver from the leach liquor

and producing cuprous chloride crystals substantially

free of iron and silver which comprises:

(a) adding sodium chloride to the leach liquor;

(b) evaporating the leach liquor to co-crystallize sodium

chloride and silver chloride;

from the leach liquor;

(d) adding water to the leach liquor to change the

conditions of temperature and concentration from

a region of sodium chloride solid phase to one of

cuprous chloride solid phase, and

(d) cooling the leach liquor to crystallize cuprous

chloride substantially free ofiron and silver impurities.

6. The process of claim 5 in which silver is recovered

from the recovered silver chloride.

7. The process of claim 5 in which the ore is a copper

sulfide ore.

8. The process of claim 7 in which the copper ore is

chalcopyrite.

9. The process of claim 8 in which the copper is reduced

to the cuprous form by leaching the chalcopyrite

with cupric chloride.

10. A process for recovering substantially silver and

iron free copper from copper ores containing silver and

iron which comprises:

(a) reducing the copper in the ore to the cuprous form

by leaching the ore with ferric chloride and cupric

chloride to form a leach liquor containing the cuprous

chloride;

(b) crystallizing the cuprous chloride from the leach

liquor and recovering the formed crystals of cuprous

chloride;

(d) adding sodium chloride to the cuprous chloride

solution;

(e) evaporating the cuprous chloride solution to cocrystallize

the silver and sodium chlorides;

(t) separating the solution from the precipitated chlorides;

(g) adding water to the cuprous chloride solution to

change the concentration of the solution from a

region of sodium chloride solid phase to a region of

cuprous chloride solid phase accompanied by cooling

said cuprous chloride solution to crystallize

said cuprous chloride, and

(h) recovering copper from said cuprous chloride

crystals.

11. The process of claim 10 in which silver is recovered

from the recovered silver chloride.

12. The process of claim 10 in which the ore is a

sulfide ore.

13. The process of claim 12 in which the ore is chalcopyrite.

• • • • •