United States Patent Office 3,736,238
Patented May 29, 1973
1 2
The term metal sulfide as used herein is inclusive of
the complex as well as the simple sulfide minerals which
contain economically recoverable quantities of the specified
metals.
The invention is a pollution-free process for the recovery
of the metals of Groups I-B, II-B, IV-A, V-A, VI-A
and VIII of the Periodic Table, from their sulfide and
mixed sulfide ores or concentrates in which the sulfide is
electrolytically dissociated in an acid aqueous media into
elemental sulfur and metal ions which are then recovered
from solution in the electrolyte media by conventional
pollution-free techniques.
The electrolysis process is characterized by certain critical
process conditions which render it economically feasible,
these being the use of:
(l) An electrolyte comprising: a soluble metal chloride
selected from the group consisting of soluble chlorides
of aluminum, chromium, copper, iron, manganese, nickel,
zinc and rare earth metal chlorides either alone or mixed
in combination with alkali metal and/or alkaline earth
metal chlorides, said electrolyte being at least .5 normal
in chloride ion,
and have created demands for pollution-free processes.
An electrolytic process requiring only economic quantities
of power, in which substantially all the sulfur in the above
metal sulfides related to this invention is converted to ele-
5 mental sulfur is an answer to the pollution problem.
The high degree of concentration required for economic
pyrometallurgical processing results in losses in concentration
and in the loss of potentially valuable co-product
values which are not readily recovered. The presence of colO
product values in the main metal product often results in
economic penalties being assessed against the concentrates.
Thus low grade concentrates which are not amenable to
physical segregation techniques are often considered valueless
or of low value because they cannot be processed
economically by conventional pyrometallurgical processes.
In co-pending application of Ser. No. 113,751, filed
Feb. 8, 1971, by Paul R. Kruesi, now U.S. Pat. No. 3,673,061,
it is disclosed that the use of a basic electrolyte media
for electrolytic dissociation of sulfide ores results in the
sulfide sulfur being converted into sulfate with high current
consumption while the use of an acidic electrolyte
media comprised of alkali metal and/or alkaline
earth metal chlorides under specified conditions results
in the sulfide sulfur being converted to elemental sulfur
with a substantial reduction in required current.
While the use of alkali and alkaline earth metal chlorides
as electrolytes as disclosed in the above cited application
Ser. No. 113,751 results in an economic pollutionfree
process for the processing of sulfide ores and concentrates,
it has been found that certain other metal chlorides
under the conditions herein specified are equally
effective as electrolytes for the same purpose and in certain
cases have unexpected advantages.
Many commercial sulfide concentrates contain substan-
35 tial quantities of iron either as a part of the mineral as
in the case of chalcopyrite or mannatite, or as an impurity
as is the case with pyrrhotite. In the process of this
invention the conversion of this iron to chloride results
in a convenient electrolyte media.
In the past it has been difficult to process galena in a
chloride media because of the limited solubility of lead
chloride. Particularly, it was generally believed that this
low solubility would mitigate against economic plating at
the cathode. It has been found that the solubility of lead
chloride is surprisingly high in aluminum chloride and
that aluminum chloride is a suitable electrolyte media for
the efficient electrolytic dissociation of lead sulfide and
subsequently plating of lead at the cathode. This is clearly
shown in Example 6 below.
STATEMENT OF THE INVENTION
BACKGROUND OF THE INVENTION
There are disclosures in the prior art of processes for the
electrolytic recovery of certain metals from their sulfide
ores under various conditions. These processes cannot be 40
used for the economic recovery of metals of Groups I-B,
II-B, IV-A, V-A, VI-A and VIII of the Pe~iodic Table
from their sulfide and mixed sulfide ores, partlcularly low
"rade ores, for various reasons.
b U.S. Pat. No. 2,839,461 discloses an electrolytic process
for the recovery of nickel from nickel sulfide but it 45
is dependent upon the formation of a highly conductive
nickel sulfide matte anode and is not applicable to low
grade concentrates. Such common sulfide minerals as
galena, sphalerite, chalcopyrite, and chalcocite have resistivities
many times that of the anode used in the proc- 50
esses of Pat. No. 2,839,461 and, therefore, that process
cannot be used with these minerals.
U.S. Pat. No. 3,464,904 relating to the electrolytic recovery
of copper and zinc from their sulfide ores discloses
the use of a hydrochloric acid electrolyte having a con- 55
centration of 5-10%. In the absence of the metal chlorides
used in the electrolytes of co-pending application SeI. No.
113,751 and in the electrolytes of this application, this high
acidity does not lead to economic recovery from their
sulfides of the metals to which the present invention ap- 60
plies as demonstrated in Example 8 which follows.
Prior to the present time there has been little incentive
for the development to commercial application of electrolytic
or other pollution-free processes for the recovery
of metals from sulfide ores. Metals are conventionally re- 65
covered from their sulfide ores by pyrometallurgical processes
in which sulfur contained in the ores or concentrates
is oxidized to sulfur dioxide, of which a substantial portion
is released to the atmosphere with consequent damage
to the environment and loss of sulfur values. Recently 70
promulgated pollution standards have made the pyrometallurgical
processes, as presently applied, prohibitive
ABSTRACT OF THE DISCLOSURE
A pollution-free process for the electrolytic dissociation
of sulfide ores of the metals of Groups I-B, IT-B, IV-A, 15
V-A VI-A and VIII of the Periodic Table in aqueous
acidi~ media with the formation of metal ions and elemental
sulfur followed by recovery of the metal ions from
solution in the electrolyte media, the process characterized
by certain process conditions, these being the use ?f: 20
(1) An electrolyte comprising a soluble metal chlo;lde
selected from the group consisting of soluble chlondes
of aluminum, chromium, copper, iron, manganese, nickel,
zinc and rare earth metals alone or mixed or in combination
with alkali metal and/or alkaline earth f!1etal ch.lo- 25
rides, the electrolyte being at least .5 normal III chlonde
ion,
(2) A sulfide feed of average particle size smaller than
about 60 mesh U.S. Standard,
(3) A pH range of up to about 3.9, 30
(4) An electrolyte temperature range between about
50° C.-105° C., and
(5) An anode current density above about 12 ampere/
ft.2•
3,736,238
PROCESS FOR THE RECOVERY OF METALS FROM
SULFIDE ORES THROUGH ELECTROLYTIC DiS·
SOCIATION OF THE SULFIDES
Paul R. Kruesi, Wheatridge, and Duane N. Goens,
Golden Colo., assignors to Cyprus Metallurgical Processes
C~rporation, Los Angeles, Calif.
No Drawing. Filed Apr. 21, 1972, Ser. No. 246,435
Int. Cl. C22d 1/10,1/14,1/16
U.S. Cl. 204-105 R 37 Claims
3,736,238
4
efficiency. Further, it was found that at high current densities
in the presence of sulfate graphite anodes were appreciably
attacked and this type anode is the most satisfactory.
5 The preferred electrolyte media has been set forth
above. Ferrous chloride is particularly effective as an
electrolyte for dissociation of chalcopyrite as this compound
is produced in quantity by the electrolytic dissociation
of chalcopyrite in an acid medium. Aluminum
10 chloride is particularly suited as an electrolyte for the
dissociation of lead sulfide ores and concentrates, leadzinc
and lead-silver concentrates, because of the high
solubilities of lead and silver chloride in aluminum chloride.
This discovery is highly unexpected in view of the
15 insolubility of lead and silver chlorides in most solvents.
Zinc chloride is preferred with zinc ores essentially free
of lead.
Concentrations of chloride ion in excess of .5 normal
to saturation may be used for the process. Voltage across
20 the cell is lower at higher salt concentrations and the
latter are preferred except where low grade feeds are used
and where salt losses would therefore become significant.
It is highly important that a high percentage of the
sulfur in the metal sulfide be recovered as elemental sulfur
both from the standpoint of pollution control and the
electrical efficiency of the process. If sulfur is converted
to sulfate, high current consumption results and the disposal
of the sulfate may create a pollution problem. Every
mole of sulfur which is oxidized beyond the elemental
state requires six Faradays which is equivalent to 2275
ampere hours per pound of sulfur. As chalcopyrite, for
example, contains approximately one pound of sulfur per
pound of copper, any sulfur oxidation of the sulfate represents
a substantial loss of efficiency. As shown by the
examples below, an average of at least 90% of the sulfur
in the sulfides is converted to elemental sulfur in the process
of the invention. The elemental sulfur does not result
in any polarization problems at the reaction temperatures
of the electrolyte media.
The particle size of the feed material is critical as it
directly affects the conversion of 'sulfide sulfur to elemental
sulfur. The elemental sulfur produced is extremely
fine. The anode current attacks the metal sulfide preferentially
to sulfur provided the sulfide has sufficient activity
near the anode. The activity of the sulfide is a
function of its concentration and its exposed surface
area. Therefore, the presence of a high concentration
of fine sulfide near the anode prevents the continuing
oxidation of sulfur and results in higher efficiency and
conseqeuntly lower current consumption. An average
grain size for the feed sulfide smaller than about 60
mesh U.S. Standard is the operable range and is compatible
with other critical parameters.
A pH range for the electrolytic media up to about 3.9
is prderred. Current efficiency is reduced at pH's above
3.9 and at very high acidities (low pH values) in the
absence of substantial concentrations of the specified
metal chlorides. In certain cases such as that of aluminum
chloride which hydrolyzes at about pH 2.0, chromic
chloride which hydrolyzes at about pH 3.0, and rare
earth metal chlorides which hydrolyze at about pH 4.0,
the acidity must be strong enough to prevent this hydlOlysis.
The preferred pH range is 0.3-0.8. The pH of
the electrolyte is conveniently adjusted with hydrochloric
acid.
The reaction temperature of the electrolyte is critical
and high process efficiency is not obtainable at low temperature.
The preferential attack on the sulfide over elemental
sulfur is accentuated at high temperatures and,
indeed, at temperatures below 50° C. a substantial portion
of the sulfide is converted to undesirable sulfate. The
operable range is about 50° C.-105° C. when used in
conjunction with the other critical factors. A temperature
of 80° C. is most preferred.
3
(2) A sulfide feed of average particle size smalIer than
about 60 mesh U.S. Standard,
(3) A pH range up to about 3.9,
(4) An electrolyte temperature range between about
50° C.-105° C., and
(5) An anode current density of above about 12 amperes/
ft.2• The temperature and pH ranges are the most
critical of the above parameters. Within the above process
parameters the chloride electrolytes of this invention
are substantial equivalents for electrolytic dissociation of
the metal sulfides of metals of Groups I-B, II-B, IV-A,
V-A, VI-A and VIII of the Periodic Table.
The other soluble halide salts, including the bromides,
iodides and fluorides, of aluminum, chromium, copper,
iron, manganese, nickel, zinc, and rare earth metals, are
operative for the purpose of the invention; however, they
are not as economically attractive as the chlorides of these
metals. Soluble halide metal salts in general are operative
as electrolytes for recovering metals from their sulfides
in accordance with the process of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The economic feasibility of the process is dependent
upon the current required to produce a given quantity of
metal. It is expressed herein as the ampere hours of cur- 25
rent required to release a pound of metal. The current
requirement will vary for each metal and economic viability
will depend somewhat on the cost per pound at
which that metal can be produced by present processes.
This statement does not take into consideration recently 30
promulgated air pollution standards which may completely
eliminate or drastically limit the economic competition
of present air polluting processes.
The process parameters which have been found to control
the current requirements for the process are elec- 35
trolyte composition, feed particle size, operating pH range,
operation temperature, and anode current density. As the
examples which follow show, these factors are mutually
interactin¥ and dependent as respects their effect on cur- 40
rent reqUIrements.
It has been found that sulfide ores and concentrates
of metals of Groups I-B, II-B,IV-A, V-A, VI-A and
VIII of the Periodic Table are characterized by certain
similar properties related to the electrolytic dissociation
to elemental sulfur and metal ions therefrom by the proc- 45
ess of this invention. For example, their sulfides all have
relatively low conductivities. While certain nickel sulfides
are relatively good conductors, others are not. Further,
the metal ions of these sulfides are most favorably produced
by electrolysis in aqueous acidic electrolytes of 50
soluble chlorides of aluminum, chromium, copper, iron,
manganese, nickel, zinc, rare earth metals, alkali metals,
and alkaline earth metals, and mixtures thereof, at a pH
range of up to about 3.9 using anode current densities
above about 12 amperes/ft.2 with a sulfide feed particle 55
size smaller than about 60 mesh U.S. Standard, and a
temperature range between about 60° C.-105° C. for the
alkali and alkaline earth metal chlorides and between
about 50° C.-lOS ° C. for the other electrolytes. The examples
which follow illustrate that the power require- 60
ments for the process applied to recover the stated metals
from their sulfides are well within the limits of commercial
feasibility.
The minerals containing the metals which can be recovered
by the process often contain the metals in the 65
form of complex or mixed sulfides.
The electrolytic media for the process must be acidic
as an alkaline electrolyte has proven unsatisfactory for
recovery from their sulfides of the defined metals to which
the invention is related. Elemental sulfur is not stable 70
in an alkaline media because oxidation of the sulfur proceeds
rapidly through thiosulfate, hydrosulfite, sulfide to
sulfate. The presence of sulfate ions is undesirable because
at high sulfate concentrations oxygen is rapidly
evolved at the anode resulting in a decrease in current 75
3,736,238
5
The anode current density is also critical as used with
the other critical parameters with a preferred range being
above about 12 amperes/ft.2 anode current density. In
contrast to the earlier prior art teaching (U.S. Pat. No.
2,761,829) it was found that high copper dissociation in
copper sulfide concentrate in the presence of iron sulfide
(pyrite) was attained at current densities of 240 .amperes/
ft.2• For the mixture of chalcopyrite and pyrite
where chalocpyrite is the predominant mineral, a preferred
current density range is 120--240 amperes/ft.2•
Where pyrite predominates current densities of between
60-120 "amperes/ft.2 are preferred.
Within a fairly broad range current anode density may
6
in the process of the invention as operated within the
critical parameter ranges of temperature, current density,
pH and particle size.
For each test 400 grams of comemrcial copper sulfide
5 concentrate having a particle size of -60 mesh analyzing
by weight 27.7% copper and 28.4% iron was slurried
in 2 liters of electrolyte and subjected to 30 amps./hr.
of current under the conditions shown. For the mixed
electrolytes approximately equal volumes of each were
10 used. Other alkali metal chlorides may be added to the
electrolyte, such as, potassium and lithium cWorides.
Alkaline earth metal chlorides, such as, calcium and
barium chlorides may be added.
Test No 1 2 3 4 5 6
Electrolyte •• • __ ._ 2 M AICh 1 M AI0I3 2 M NaCI; 0.5 M FeCh__ • 2M NaCI; 3 M FeCh.
1 M AlCh. 1M FeCI,.
Temperature (0 C.)---------------------- ••• ---------- 78 • 74 0_ 75 75__; cc 75__•• _•• _. __ ._ 75.
Anode current density (ACD) (amps/ft.')------------- 120 120 •__ 120 • __ • __ 120. ••__ 120._••••• _._._ 120.
pH ••• 004 • __ 0.5 ._ 0.6 •••__• 0.6__ ._•• __ • 0.5_. ._._. __ 0.5.
~~~~nil~·e?~e~r~e§~~~~========================== §g~===========~ ~=~=========~= g8=~==~==~=~~=~ ~~~~=~~~===~~~ ~~~==~~=~==~==~ ~~~.
be adjusted to the situation so long as it is above about
12 amperes/ft.2. With low grade feeds an anode current
density between 40-120 amperes/ft.2 may be used. Often
when metal is being plated at the cathode the necessities 25
of cell geometry will dictate the anode current density.
Thus with copper if copper powder is desired current densities
of 100-200 amperes/ft.2are preferred at the cathode
and this range of current density is suitable for high
grade copper concentrates. When plating lead or zinc at 30
the cathode a current density range of 20--30 amperes/ft.2
is preferred at the cathode and is suitable for the anode.
The following examples with results are illustrative of
the process of the invention but not limiting thereof. The
process is not limited to a specific electrolytic cell design 35
or type of cell. The cells used in the examples, well
known in the art, comprised an anode section containing
a suitable anode such as graphite or coated titanium, provided
with means for agitation and heating, and separated
from the cathode section by a diaphragm. The cathode 40
section consisted of a suitable cathode of stainless steel,
copper, lead or aluminum depending upon the metal being
plated or the cathode reaction desired and was provided
with means for liquid circulation and heating.
In the examples, average grain size is given in U.S. 45
Standard mesh size, anode current density designated as
The high conversion of sulfide sulfur to elemental sulfur
and low current consumption prove the effectiveness
of the electrolytes within the parameter ranges of the
process. As in the examples which follow in which it is
reported the high conversion of sulfide sulfur to elemental
sulfur in the acid electrolyte and low current consumption
is in marked contrast to prior art processes
using basic electrolytes resulting in conversion of the
sulfide sulfur to sulfates with consequent high current
consumption.
EXAMPLE 2
Selection of the following tests was made to demonstrate
the equivalence for the purposes of the invention
of the electrolytes of Example 1 and the electrolytes
nickelous chloride, cupric chloride, chromic chloride,
managanous chloride, and rare earth metal chlorides.
For each test 400 grams of -60 mesh particle size
copper sulfide concentrate analyzing by weight 27.7%
copper and 28.4% iron were slurried in 2 liters of electrolyte
and subjected to 30 ampere hours of current under
the conditions shown. Analysis by weight of the rare earth
metal chloride mixture as oxides was as follows:
La20a-78.7%, Ce20a-11.2%, Pr20a-3.8%, Nd20 a-l%,
Sm20a-2%.
Test No 1 2 3 4 5
Electrolyte • 1 M NiCh 1 M CUCh. 1 M CrCh 1 M MuCh 1 M (rare earth) 013'
Ibr:P(~~/fr,)~~~~================ i~iC=======~=== i~o============== ik============= ik============= i~. pH 0.6 ._ 0.5 •• _ 0.5 • 0.5 0.5.
Amp-hrs./lb Cn recovered 586 745_. 799 601. __ • 565.
Percent S as elemental S • 87 • __ 85. 94 • • 85.
EXAMPLE 3
In order to define the critical temperature range for the
process utilizing other conditions within the process
parameter ranges the following tests were performed.
For each test 400 grams of -60 mesh particle size com.
mercial copper sulfide concentrate analyzing by weight
The results of the example in terms of large conversion
of sulfide sulfur to elemental sulfur with low current consumption
demonstrates the effectiveness of the electrolytes
under the conditions for a representative metal sulfide. In
the case of all the electrolytes used in the tests except
60 cupric chloride and chromic chloride the copper was recovered
essentially as cuprous copper resulting in very
high electrical efficiency. The copper recovered using
cupric cWoride and chromic chloride electrolytes was essentially
cupric copper, this accounting for the somewhat
65 higher current consumptions. The higher valent forms of
copper and chromium are preferred because the lower
valent forms have limited solubility. However, cuprous
chloride may be used as the electrolyte instead of cupric
chloride.
EXAMPLE 1
The following tests were selected to illustrate the operativeness
of aluminum chloride and ferrous chloride
alone and with an alkali metal chloride as electrolytes 75
ACD is given in amperes/ft.2, current requirement is 55
reported in terms of ampere hours/pound of metal dissociated,
and recovered. The percent sulfur converted to
elemental sulfur is computed by dividing the amount converted
to elemental sulfur by the total amount of sulfur
converted from sulfide sulfur and is expressed in percent.
The metal dissolved in the electrolyte can be finally
recovered by conventional methods such as, electrolysis,
precipitation, cementation, etc., depending on the metal
being recovered. In certain cases the metal can be plated
out on the cathode during the dissociation process and
recovered in this manner.
Elemental sulfur is readily recovered from the electrolyte
media by the process disclosed in co-pending application
Ser. No. 233,352, filed in the U.S. Patent Office on
Mar. 9, 1972, William G. Kazel, entitled "Sulfur Re· 70
covery Process."
3,736,238
7
27.7% copper and 28.49% iron were slurried in 2 liters
of electrolyte and subjected to 30 ampere hours of current
under the conditions recorded.
8
lyte were separated to enhance plating of lead and zinc of
high purity. The electrolyte media was subjected to 38.3
ampere hours of current before analysis for results at an
Test No 1 2 3 4 5 6
Electrolyte 2 M AlCh 2 M AICh 2 M AlCla 3 M FeCb 3 M FeCb 3 M FeCI,.
~~~l~~~~:~mm:m~~~~~im~:::~:~~:-~~~:~:m:~~~~~:~:~~~~:~~:~~~j:::~::~:~m::~:m~~:mm~~~.
The results show striking increase in current consumption
and decrease in cOIiversion of sulfide sulfur to elemental
sulfur at temperatures below about 50° C. with
current consumption as high as 2193 amp./lb. Cu recovered
and sulfur conversion as low as 54%. The results
illustrate that the lower limit of the critical temperature
range is somewhere between about 44-50° C.
EXAMPLE 4
The following tests are incuded to demonstrate the operativeness
of the process at high acidities.
For each test 400 grams of-60 mesh commercial
copper sulfide concentrate assaying by weight 27.7% copper
and 28.4% iron were slurried in 2 liters of electrolyte
and subjected to 30 ampere hours of current under the
conditions indicated with the following results.
anolyte pH of 0.5, a temperature of 80° C., and a cur15
rent density of 30 amps/f1.2 on both the anode and cathode.
The following results were obtained.
MetaL__________________________________ Lead Zinc Iron Silver
Dissolved metal (gms.) _________________ 76.0 33.8 10.3 .044
20
Pereentage recovery ofmetals___________ 97.7 27.3 31. 9 69.8
133 grams of lead were plated at the cathode indicating
90% cathode current efficiency.
The electrolysis was continued for an additional 65.6
25 ampere hours with the same anolyte pH and temperature
using anode and cathode current densities of 30-60 amps!
f1.2 • Zinc chloride dissolved in aluminum chloride was
used as the catholyte. The following results were obtained.
Test No .!,, 1 2 3 4 5 6 7
Cd
.059
93.7
Silve·r
Fe
17.1
52.8
Iron
Ag
98.4
79.5
Zinc
Zn
79. 2 126.7 . 09 39.5 .07
9696..28 93.2 95.7 74.7 82.0_
95 _
Dissolved metal (gms.) _
Percentage recovery of metal _
Sulfur reeovered, gms _
Pereent S as elemental S _
The high percentage recovery of lead, zinc, silver and
cadmium demonstrates the suitability of ferrous chloride
as an electrolyte for recovery of the metals from their
MetaL__________________________ Pb
70 grams of zinc were plated at the cathode indicating
a cathode current efficiency of 91 %.
The example illustrates that lead, zinc, and silver can
be recovered from their sulfides by the process of the
invention using a representative chloride electrolyte for
the process of this invention and that the process is particularly
effective for these metals with an aluminum
chloride electrolyte.
The process is equally effective for the recovery of O'old
germanium and tin from their sulfides. 0 ,
EXAMPLE 7
Dissolved metal (gms.) 77.5
Percentage reeovery of metals________ 99.6
MetaL________ Lead
The following test is included to show the suitability of
ferrous chloride electrolyte for recovering lead, zinc,
silver and cadmium from their sulfides.
470 grams of -60 mesh particle size sulfide ore concentrate
assaying by weight 31.9% zinc, 17.1% lead,
12.6% iron, .0219% silver, and .018% cadmium were
slurried in 2 liters of electrolyte and fed to the anode
side of a diaphragm cell. The anolyte, 2 molar ferrous
chloride, was subjected to 157.5 ampere hours of current
65 at 80° c., pH 0.5 at an anode current density of 60 amps!
£t.2• The results obtained are shown below.
Cn-2.0
41.5 , " _
5429.85 ------------------------------_ 60
The low current consumption and high sulfur conversion
obtained illustrate the effectiveness of the process for
the recovery of nickel and cobalt from their sulfides.
EXAMPLE 6
The following example is included to show the effectiveness
of the process for the recovery in chloride electrolyte
of additional metals from their sulfides, particularly lead.
500 grams of a -60 mesh particle size commercial sul- 70
fide ore concentrate assaying by weight 25.6% lead,
24.8% zinc, and .013% silver were processed in a diaphragm
cell. The concentrate was slurried in 2 liters of 2
M AICla which served as anolyte. Lead chloride dissolved
in 2 M AlCla served as catholyte. The anolyte and catho- 75
Wt. of metal dissolved (gms.) Fe-46 Ni-1.7 Co--O.2
Gms. snlfur recovered _
Amp-hrs./lb. of combined
metals reeovered _
Percent S as elemental S .i
The results demonstrate the effectiveness of the process
at acidities as high as pH 0.01. The economically feasible 40
maximum pH is about 3.9.
EXAMPLE 5
The following test is included to show the effectiveness
of the process utilizing a representative electrolyte on the 45
sulfides of nickel and cobalt.
For each test 400 grams of a -60 mesh particle size
low grade sulfide ore concentrate assaying by weight
8.33% nickel, 0.337% colbalt, 5.16% copper and 37.8%
iron were slurried in 2 liters of electrolyte and subjected 50
to 60 ampere hours of current under the conditions shown.
Using a 4 M FeC12 electrolyte at a temperature of 80°
C., pH of 0.5 and an anode current density of 120 amps!
ft.2 the following results were obtained from analysis of
the electrolyte media at the end of the test. 55
3,736,238
9
sulfides by the process. Commercially feasible current
consumptions were noted.
EXAMPLE 8
The following tests were run to compare the efficiency
of aluminum chloride and ferrous chloride electrolytes
with that of hydrochloric acid electrolyte.
For each of the tests a commercial -60 mesh particle
size copper sulfide concentrate assaying by weight 27.7%
copper and 28.4% iron was used. 100 grams were used
for Test No. 1 and 400 grams were used for Tests No. 2
and No.3. The concentrate was slurried in 2 liters of
electrolyte and subjected to 30 ampere hours current
under the conditions shown in a diaphragm cell with the
following results.
HCI (5%) 2 M AlCb 3 M FeCI,.
80 78 75.
0.01 (5% HCI)_ 0.01 (5% HCl)_ 0.01 (5%
HCl);
120 ;'c 120"_~_"_;_"_C_ 120.
1,566 "_ 463 558.
73 c =-.' 95 c_"_._C" 88.
Test No "_~_" • 1
Electrolyte • _
pTHemperature (0 C.) __
ACD (amps/it.') "_" __
Amp-hrs./lb. Cn recovered.
Percent S as elemental S_
2 3
10
EXAMPLE 11
The following tests were performed to determine the
effectiveness of the process of the invention in recovering
arsenic, cadmium, antimony and selenium from their
5 sulfides.
232 grams of a -60 mesh grain size commercial low
grade chalcopyrite concentrate analyzing by weight 4.0%
lead, 9.2% zinc, 24.0% copper, 25.5% iron, 0.5% arsenic,
0.018% cadmium, 0.025% antimony and 0.36% selenium
10 wertl slurried in 2 liters of 3 M ferrous chloride electrolyte
and subjected to 30 ampere hours of current at 75° C.,
pH 1.5, and an anode current density of ,60 amps/ft.2
with the following results.
Percent metal
15 Metal: dissolved
Copper ' ----------- 9.4
Zinc 36.4
Lead 87.4
Arsenic 97.0
20 Cadmium ------ 42.9
Antimony 52.0
Selenium 28.9
40
As demonstrated with a representative electrolyte the
25 process is effective for the electrolyte recovery of the
metals arsenic, cadmium, antimony and selenium from
their sulfide ores. The process is equally effective for the
recovery of bismuth and tellurium from their sulfides.
The current requirements set forth in the examples are
30 well within commercial feasibility ranges for large scale
production of the metals from their sulfide and mixed sulfide
ores. The cost of the recovery of the metals from
the electrolyte after electrolysis by conventional techniques
is comparatively small. The process permits the
35 recovery in significant yields of metals present in trace
quantities. The high percentage recovery of sulfur from
the sulfides as elemental sulfur substantially reduces the
pollution problems associated with prior art processes
and enhances the economic attractiveness of the process.
Accordingly, the invention provides a process for recovery
of the metals from their sulfide and mixed sulfide
ores which has the advantages of being commercially
feasible and pollution free.
What is claimed is:
1. A process for the recovery of metals of Groups I-B,
II-B, IV-A, V-A, VI-A and VTII of the Periodic Table
from their sulfides and mixed sulfides, and mixtures thereof,
by electrolysis with the formation of elemental sulfur
and metal ions, which process comprises:
(a) providing an electrolyte in an electrolytic cell including
at least an anode and a cathode, the electrolyte
comprising an acidic aqueous solution of at
least one chloride salt selected from the group consisting
of chlorides of aluminum, chromium, cop·
per, iron, manganese, nickel, zinc, and rare earth
metals, and mixtures thereof, the solution having a
concentration from about .5 N to saturation;
50
2
EXAMPLE 10
Test No • 1
The example shows that, somewhat contrary to the 45
teaching of U.S. Pat. 2,761,829', copper dissolves readily
at the high current densities shown under the process
conditions of the invention.
The following tests were performed to demonstrate
the effectiveness of zinc chloride as an electrolyte.
For each test 400 grams of a -60 mesh grain size commercial
zinc sulfide concentrate assaying by weight 57.2%
zinc was slurried in 2 liters of electrolyte and subjected 55
to 30 ampere hours of current under the conditions indicated
with the following results.
Electrolyte 3 M FeCb 3 M FeCb
Temperature (0 C.) " 75 75.
pH " 0.5 ~ 0.5.
ACD (amps/it.') C " ;'_ 120 240.
Amp-hrs./lb. Cu recovered 558 617.
Percent S as elemental S c_ 88 86.
The results demonstrate the superiority of aluminum
chloride and ferrous chloride acidified with hydrochloric
acid over hydrochloric acid alone as electrolytes.
EXAMPLE 9
The test 'below is included to demonstrate the effectiveness
of the process at high current densities.
400 grams of a-60 mesh gram size chalcopyrite concentrate
assaying by weight 27.7% copper and 28.4%
iron (mineralogical examination showed the sample material
to be about 80% chalcopyrite and 8% pyrite) was
slurried in 2 liters of electrolyte and subjected to 30
ampere hours of current under the conditions shown with
the following results.
Test No 1 2 3 4
Electrolyte c_ 3 M ZnCb 1.5 M ZuCh 3 M ZnCb 3 M ZnCh.
r~~-:::s~i~;)~=~====================:==~~~::=::::=:::::~:~~:::::::::::::~:E:::=:::=::::~l. Amp-hrs./lb. Zn recovered 386 313 372 381.
Sulfur recovered (gms.) 13.2 16.8 12.7 9.7.
Percent S as elemental S.. "" 85 89 83 71.
The tests illustrate that zinc chloride is as effective as
an electrolyte as the other chloride electrolytes of the
invention. Test No.4 was performed at a 3.5 pH which
is near the top of the critical pH range of 3.9 and this
test shows the adverse effect of low acidity on conversion
of sulfide sulfur to elemental sulfur. 75
(b) mixing with the electrolyte a solid feed sulfide of
the metal having an average particle size smaller
than about 60 mesh U.S. Standard;
(c) maintaining the temperature of the electrolyte
media at about 50° C. to 105° C., and the pH of
the electrolyte media below about 3.9 while intro3,736,238
3,673,061
3,464,909
12
27. The process of claim 24 in which the metal is
copper.
28. The process of claim. 23 in which the metal is
copper.
29. The process of claim 22 in which the metal is
copper.
30. The process of claim 31 in which the metal is
copper.
31. The process of claim 21 in which the metal is selected
from the group consisting of antimony, arsenic,
cadmium, cobalt, copper, iron, lead, nickel, selenium, and
zinc.
32. The process of claim 20 in which the metal is
copper.
33. The process of claim 19 in which the metal is
copper.
34. The process of claim 35 in which the metal is
selected from the group consisting of lead, silver and
zinc.
35. The process of claim 18 in which the metal is selected
from the group consisting of silver, copper, iron,
lead and zinc.
_ 36. The process of claim 2 in which the alkali metal
chloride is sodium chloride.
37. A process for the recovery of metals of Groups I-B,
II-B, IV-A, V-A, VI-A and VIII of the Periodic Ta:ble
from their sulfides: and mixed sulfides, and mixtures thereof,
by electrolysis with the formation of elemental sulfur
and metal ions, which process comprises:
(a) providing an electrolyte in an electrolytic cell including
at least an anode and a cathode, the electrolyte
comprising an acidic aqueous solution of at
least one soluble halide salt selected from the group
consisting of soluble halide salts of aluminum, chromium,
copper, iron, manganese, nickel, zinc, and
rare earth metals, and mixtures thereof, the solution
having a concentration from about .5 N to saturation;
(b) mixing with the electrolyte a solid feed sulfide of
the metal having an average particle size smaller
than about 60 mesh U.S. Standard;
(c) maintaining the temperature of the electrolyte
media at about 50· C. to 105· C., and the pH of
the electrolyte media below about 3.9 while introducing
electric current into the electrolytic cell to
provide an anode current density above about 12
amperes per square foot to dissociate the metal sulfide
into metal ions and elemental sulfur; and
(d) recovering metal from the electrolyte.
References Cited
UNITED STATES PATENTS
6/1972 KIue~ 204--107
9/1969 Brace 204--114
U.s. Cl. X.R.
60 204--106, 107, 111, 113, 117, 118, 123,293
55 JOHN H. MACK, Primary Examiner
R. L. ANDREWS, Assistant Examiner
45
35
15
11
ducing electric curemt into the electrolytic cell to
provide an anode current density above about 12
amperes per square foot to dissociate the metal sulfide
into metal ions and elemental sulfur; and
(d) recovering metal from the electrolyte. 5
2. The process of claim 1 in which at least one chloride
salt selected from the group consisting of alkali metal
chlorides and alkaline earth metal chlorides is added to
the electrolyte.
3. The process of claim 1 in which the metal is recov- 10
ered from the sulfide and mixed sulfide in the presence
of iron sulfides.
4. The process of claim 1 including the step of recovering
the metal from solution in the electrolyte by electrodeposition
on the cathode. _
5. The process of claim 1 including the step of recovering
elemental sulfur from the electrolyte.
6. The process of claim 1 in which the metal recovered
is copper.
7. The process of claim 1 in which the metal recov- 20
ered is lead.
8. The process of claim 1 in which the metal recovered
is silver.
9. The process of claim 1 in which the metal recovered
is zinc. 25
10. The process of claim 1 in which the metal recovered
is antimony.
11. The process of claim 1 in which the metal recovered
is arsenic.
12. The process of claim 1 in which the metal recov- 30
ered is cadmium.
13. The process of claim 1 in which the metal recovered
is selenium.
14. The process of claim 1 in which the metal recovered
is nickel.
15. The process of claim 1 in which the metal recovered
is cobalt.
16. The process of claim 1 in which the metal recovered
is iron.
17. The process of claim 1 in which the metals are 40
selected from the group consisting of antimony, arsenic,
cadmium, copper, cobalt, iron, lead, nickel, selenium,
silver and zinc.
18. The process of claim 1 in which the electrolyte is
aluminum chloride.
19. The process of claim 1 in which the electrolyte is
copper chloride.
20. The process of claim 1 in which the electrolyte is
chromium chloride.
21. The process of claim 1 in which the electrolyte is 50
ferrous ch10ride.
22. The process of claim 1 in which the electrolyte is
manganous chloride.
23. The process of claim 1 in which the electrolyte is
nickelous chloride.
24. The process of claim 1 in which the electrolyte
comprises at least one rare earth metal chloride.
25. The process of claim 1 in which the electrolyte is
zinc chloride.
26. The process of claim 25 in which the metal is zinc.