Note: Descriptions are shown in the official language in which they were submitted.
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BACKGRO~IND OF THE INVENT ON
Field o~ the In~ention
This invention relates to the hydrometallurgical.
- recovery of copper from chalcopyrite by means of a copper
:~ sul~ate leaching process.
The Prior Art
- Processes have long been disclosed describing the
reco~ery o copper from its sulfide and mixed sulfide forms.
Most of the economic copper recovery processes are classified
:as pyrometallurgical, with the ore being smelted to oxidize
the sul~ide to sulfur dioxide. This sulfur dioxide is now
o~ course recognized as a major air pollutant, and means
must be used in conjunction with pyrometallurgical plants to
eliminate this contaminant. As a result considerable
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development is now being undertaken to formulate hydro-
metallurgical processes in order to circumvent the production
of the byproauct sulfur dio~ide. Much of the hydrometallurgical
development centers around chloride and ammoniacal leaching
processes, some of which may prove to ultimately be beneficial.
Copper sulfate leaching agents have ~een proposed
to be used in conjunction with a number of metal sulfides,
including zinc sulfide. U.S. Patent 3,655,538 to Renken
discloses such a process whereby the zinc sulfide is leached
with copper sulfate in order to produce copper sulfide and a
zinc sulfate solution, the zinc sulfate solution being
easily separated for the ultimate recovery of zinc. Another
similar process discloses the utilization of a copper sulfake
leach to recover nickel from a nickel-copper matte, this
process being set forth by Llanos et al in a paper presented
at the Third Annual Meeting of the Hydrometallurgical Section
of the Metallurgical Society of C.I.N., Edmonton, October 19,
1973.
Heretofore the value of leaching chalcopyrite with
copper sul~ate has not been recognized, and it has commonly
been believed that chalcopyrite does not react with copper
.~ - ,
sulfate. This is borne out by the Renken patent, cited
above, which specifically sets forth at column 3 that chalcopyrite
does not react with copper sulfate.
It has now been recognized that under the proper
processing conditions, as hereinafter set forth, copper
sulfate can be used as a beneficial leaching agent for
chalcopyrite, and such a process results in a number of
advantages including providing an effecti~e means for sepa~at-
ing coppe- sulfide from many other metal sulfides and other
impurities, as well as greatly facilitating any secondary
leaching o~ the copper sulfides.
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SUMMARY OF THE INVENTIO~I
~ pollution-free hydrometallurgical copper recovery
process rcsults from the leaching of chalcopyrite with
copper sulfate .in o.rder to form insoluble copper sul~ides, a
soluble iron sulfate solution and sulfuric acid. The copper
sulfides can then be separated from the product mixture and
further treated in order to recover the copper v~lues.
Also, the products from the initial leach may be immediately
- subjected to a secondary oxidation leach reaction wherein
the copper sulfides are converted to a soluble copper sulfate
solution and the iron is converted to an insoluble state
such that the copper sulfate solution is easily separated
from the residual insoluble iron cons.~ituents along with any
other insoluble impurities~ The copper may then be conventionally
recovered from the isolated copper sulate solution, and if
, desired a portion of the copper sulfate solution may be
recycled for reaction and conversion with fresh chalcopyrite
feed.
. DESCRIPTION OF THE PREFERRED EMBODIMæNTS
The basic chemical reaction with which this process
:. is concerned is as follows: -
3CuFeS2 ~ 6CuS04 ~ 4H20 ~ Cugss + 3FeSO~ + 4H2S04
Along with the digenité (CugS5) some chalcocite (Cu2S) and
covellite (CuS) in minor amounts may also be produced.
. In addition to chalcopyrite the starting materials
may contain other copper sulfides, such as chalcocite and
covelli~e, and also may contain sul~ides of other metals.
For example, copper may be recovered from mixed sulfides
containing chalcopyrite and zinc sulfide according to the
above set forth reaction since the zinc will go into solution
as zinc sulfate, permitting the insoluble digenite to be
easily separated from the solution cont~ining zinc sulfate,
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iron sul~ate and sulfuric acid. Examples of okher metal sulfides
which would similarly react in the presence of chalcopyrite
includo nickel and co~alt.
This .ini~ial leach reaction may be opexated in
accoxdcnce with convention~l leaching techniques, with a reaction
tempe-cature preerably maintained at greater than about 100C,
moxc preferably from about 150 to about 250C, and most preferably
from about 180 to about 200C. As is comlmon in leaching operations
the raw ~eed material is crushed and ground to a sufficiently
small particle size in order ~o con~eniently per~orm concentration
operations such as flotation. When leaching mixed sulfides
containing chalcopyrite the copper sulrate concentration is
preferably maintained from about 1 gram per liter of copper to
saturation concentration, more preferably from about 30 to about
100, and most preferably from about 40 to about ~0 grams per
liter. When proce~sing chalcopyrite alone, thi~ concentration
preerably approaches the copper sulfate saturation concen~
tration. The mole ra'cio of copper sul~ate to chalcopyrite is
as shown in the above set forth reaction, i.e., two rnoles of
copper sulfate per mole of chalcopyrite. This i~ of course
; the stoichiome'cric amount required, and an excess amount of
copper sulfate ma~ be maintained.
The reaction time is inversely proportional to
temperature, the amount of time decreasing with increased~
temperatures.
As is conventional in chemical leaching, this
initial leach reaction may be perfoxmed in more than one stage
in order to e~editiously carry out the reaction, and may be
conducted cocurrently or countercurrently.
Following the initial leach reaction the copper
sulfide product may be immediately separated from the soluble
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sul~ates and sulfuric acid Such a separation is accomplished -
by conventional means in the art, as for example by thickening and
filtration. ~ separation at t'nis stage of the process may
be preferred in some instances, however, a further separation
will be necessitated at a later stage of the process since
the gangue material will also be separated with the copper
sulfides. Separation immediately following the initial leach
reaction is therefore dictated by the particular copper
sulfide reaction employed to recover the elemental copper
ln values and also the composition of the initial feed material.
One preferable technique is therefore to subject the
products of the initial leach and conversion reaction directly
to a secondary leach reaction in,conjunction with a jarosite
orming cation to convert the copper sulfides to a copper
sulate solution while precipitating the iron sulfate as
j jarosite. Due to the nature of this reaction it is apparent
that this secondary leach will immediately follow the initial
leac~h in those cases when the sulfides initially fed to ~he
reaction are basically copper or iron s~lfides with only
- 20 relatively small proportions of other metal sulfides. If
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the products of the initial leach include substantial amounts
of metal sulfates other than iron sulfates, it will then
be preferable to separate the copper sulfides prior to the
initiation of this secondary leach.
3 A preferable secondary leach reaction is an oxygen
leach in an acid media in the presence of a jarosite forming
cation. As mentioned the products of this leach reaction
are copper sulfate and jarosite. This oxygen leach is operated
in accordance with known techniques, as for example set forth
in U. S. Pat. 3,642,435. Partial oxygen pressures for such
a reaction are well below the comparable necessary values
required in the absence of the initial copper sulfate leach.
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In performing the secondary oxy~en leach in the
presence of iron sulfates it is preferred to add a su~ficient
amount oE a jarosite-formin~ cation in order that the iron
may be precipitated from the solution. These jarosite-forming
cations are discussed in U. S. Pat. 3,684,490 and are preferably
potassium, sodium and ammonium. The amount added need only
be sufficient to prècipitate the ixon from solution.
Other secondary techniques may also be employed to
recover the copper values from the copper sulfide products
of the primary leach reaction. For example, chloride leaching
techniques as described in U. S. Pat. 3,767,543 may be utilized.
Preferable chloride leaching agents include ferric chloride
and cupric chloride. Also the copper sulfides may be modi-
fied by techniques kn~wn in the art in order to ernploy elec-
trolytic dis~olution processes, as set forth for example in
U. S. Patents 3,673,061 and 3,736,238. Other suitable
secondary leach operations include ammoniacal leaching and
- cyanide leaching. It is therefore understood that while the
following discussion assumes the utilization of a secondary
oxygen leach in an acid media, the artisan can determine
from the present state of the art the necessary modifications
to be made should one of these alternative processes be em-
ployed.
Following the secondary oxidation leach it is
necessary to separate the copper sulfate from the remaining
solids, including the jarosite and the gangue material. This
separation is conveniently made by thickening and filtration
or other means known in the art.
Qnce the copper sulfate is isolated the copper may
be recovered. This recovery is conveniently made by means known
in the art, preferably by electrolysis or cementation. A
portion of the copper sulfate can also be recycled in order
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to treat new chalcopyrire feed matc~ial. The amount of copper
sulfate recycled is dependent upon the fresh sulfide feed
characteristics.
The following examples are illustrati~e of some of
t~e aspects encompassed by this process.
EX~PL~ NO. 1
A commercial copper concentrate assaying 34.5%
C copper, 22.~% iron, 32~ total sulfur, 4.9~ silica di~'d~,
1.7 ounces per ton silver, 0.01 ounces per ton gold, 0.12~
calcium, 0.27~ molybdenum, 0.01% lead and 0.02~ nickel and
being comprised of the approximate mineral percentages of 40%
chalcopyrite, 23~ chalcocite, 23~ pyrite, 3% covellite, 1%
~!,, bornite, less than 1% hematite and 9% gangue was gxound to a
mesh ~ze of -270 and reacted with copper sul~ate in a
r~t~o of 0.84 pounds o~ coppex as copper sulfate per pound of
copp~r ini~ially in the concentrate: The temperaturé was
maintained at 180C and the reaction was permitted to take place
under normal agitatlon for three hours. The initial pulp density
was 192 grams of solids per liter of solution and the c~pper
, . . .
sulfate concentration was 55 grams per liter of copper. The
s~ 20 product analysis indicated that 0.74 pounds o~ copper was
precipitated, mostly as digenite, per pound of copper initially
in the concentrate, representing a substantial conversion o
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chalcopyrite copper to digenite copper. Iron sulfate and
` sulfuric acid were also produced.
!'! EXAMPLE NO. 2
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The process of Example No. 1 was followed in all
respects except that the reaction temperature was maintained
at 210C and the total time o~ the reaction was one hour.
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The results showed 0.8 pounds of copper precipita~ed as
di~enite per pound of cop~r in the initial concentrate.
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FX~PL~ ~IO. 3
Two identical acld pressuxe leaches were performed
on copper concentrates of identical composition as that set
forth in Example 1, one pressure leach being performed
directly on the concentrates ~7hile the other pressure leach
was performed subsequent to a copper sulfate leach reaction.
The concentrate was ground to -325 mesh and a pulp density
C of 4.7% solids was formPd. The leach~ solution contained
13 grams per liter of copper, 33 grams per liter o~ sulfuric
acid, and 11 yrams per liter of sodium sulfate. In both
ca~es the r~action temperature was maintained at 95C, the
vapor and oxygen total pxe~ure at 125 psig and the ~olukion was
agitaked at a turbine tip speed of 525 feet per minute.
Ater an elapsed time of three and one-half hours, th~Q
results showed 82% of the copper was extracted from the
sampLe that was not treated with copper sulfate, ~7hile ~
grams per liter o~ iron remained in solution. On the other
hand, the sample that was initially treated with ~he copper
sulfate leach reaction yielded a 95% copper extraction, with
only 1.3 grams o iron in each liter OL solution, the
remaining iron being precipitated as sodium jarosi~e.
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EXP~LE NO. ~
Ano~her comparative test simil~r to Examp?e No. 3
was performed with two samples or a commercial concentrate
of identical co~position as that set forth in Example No. 1.
One sample was directly leached under ammoniac~l conditions
while the other sample was initially leached with copper
sulfate followed by the ammoniacal leach reaction. The
4 ,~ leache~ solution had a concentration o 80 yrams per liter
1~ of ammonium sulfate and 75 grams per liter of alNmonia as
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ammonium hydroxide. The temperature was maintained at 81C
for both tests, and the oxygen and ammonia total pressure
was kept at 20 psig. After an ~lapsed time of two hour.s, the
sample which had not been treat~d with the copper slllfate
solution showed a 93% coppe~ recovery, while the sample which
had initially been treated showed a 98% copper extraction.
In both Examples 3 and 4 the copper sulfate leach xeaction
was performed in similar fashion to that described in Example 1.
EXAMPI,E NO. 5
A commercial copper concentrate consisting of about 75%
chalcopyrite and assaying 26.1% copper, 27.5% iron and 31.4% total
sulfur was reacted with ~.2 moles of copper as copper sulfate per
mole o copper in the chalcop~rite concentrate at 180C for three
hour~. Th~ product analysi~ indicatea that two moles of copp~r as
copper sul~a te r~acted with one mole of copper in the chalcopyrite
concentrate to yiela three moles o~ copper as digenite, this
analysis being ~erified by Y-ray diffraction. Essentially all
of the iron from the chalcopyrite entered into solution as ferrou~
sulfate.
