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
Ag
CRYSTALS
AgCI-NaCI
Cu
-_!_-
Ag
,-------------------------------\
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
-.......
01
CuCI SOLID PHASE
u
:J u
..200
100
o
D
NoCI SOLID PHASE
100 200 300 400
0~iiie::::::::::"'_--l._--_...L_---l....dbd--_--1
o
NoCI, gil
A,B,C,D INDICATE DOUBLE POINTS
T.J.q:.. 1
u.s. Patent
4
July 18, 1978 Sheet 2 of 4
SOLUBILITY CURVE FOR THE
SYSTEM: CuCI-NaCI-H20
4,101,315
30
ua 20
rfl
CuCI SOLID PHASE
10
% NoCI
20
I
\ EVAPORATION /
\ CRYSTALLIZATION
\
NoCI SOLID PHASE
30
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
r
CuCI CRYSTALS NoCI CRYSTALS EVAPORATION l-
I
~-------~--- ----~
-.".J::..
~o
~ -..
W
~
U1
Co-4 =-'<-I 00 '"- I \0
I -...I 00 II
I rI.:l ::r'
I til I .t.i.l.
I w
- --I .0..., ~
-
Ag
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
~
H2
CuCI
REDUCTION
t
FeCI~ n Cu
I
HYDROLYSIS II
I.J.q=
PRECIPITATE
c•
C/.)
•
"'C a(I) ::s t"'t-
~,::
q00
~'
0
......:a
00
tzl
::r
nl
n....l.
+:o....,
+:-
~ -... .......
o.......
-...
w
.......
til
DESCRIPTION OF THE PREFERRED
EMBODIMENTS
4,101,315
1
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.
2
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
5
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;
(c) recovering silver from the crystallized silver chloride;
45
(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
6
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;
(c) separating the crystallized sodium and silver chlorides
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;
(c) reducing the cuprous chloride crystals to solution;
(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.
• • • • •
65