U.S. patent number 3,847,357 [Application Number 05/374,024] was granted by the patent office on 1974-11-12 for separation of copper minerals from pyrite.
Invention is credited to David Weston.
United States Patent |
3,847,357 |
Weston |
November 12, 1974 |
SEPARATION OF COPPER MINERALS FROM PYRITE
Abstract
A process of separating copper minerals from pyrite wherein a
flotation concentrate containing copper minerals and pyrite is
reground in the presence of lime and subsequently conditioned at a
pH of 12.0 or more for a predetermined period sufficient to depress
the pyrite, with optional additions of sulf-hydryl collector,
cyanide and dispersing agent, and the conditioned pulp is subjected
to flotation.
Inventors: |
Weston; David (Toronto,
Ontario, CA) |
Family
ID: |
26813487 |
Appl.
No.: |
05/374,024 |
Filed: |
June 27, 1973 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
115709 |
Feb 16, 1971 |
|
|
|
|
Current U.S.
Class: |
241/20;
241/24.13; 209/3; 209/167 |
Current CPC
Class: |
B03D
1/08 (20130101); B03D 1/06 (20130101) |
Current International
Class: |
B03D
1/00 (20060101); B03D 1/08 (20060101); B03D
1/06 (20060101); B03b 001/04 () |
Field of
Search: |
;209/166,167
;241/20,24,3 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Goudin, Flotation, McGraw-Hill, 1957, pgs. 430-433..
|
Primary Examiner: Halper; Robert
Attorney, Agent or Firm: Depaoli & O'Brien
Parent Case Text
This is a continuation, of application Ser. No. 115,709 now
abandoned, filed Feb. 16, 1971.
Claims
What I claim as my invention is:
1. A process for the separation of copper values from copper ores
containing pyrite by differential flotation comprising; preparing a
copper-pyrite flotation concentrate which is substantially free of
slime host rock materials; grinding said copper-pyrite flotation
concentrate in the presence of calcium hydroxide; agitation
conditioning the thus produced pulp at a pH of at least 12.3 in the
presence of a sulf-hydryl collecting agent for a period of time
sufficient to depress the pyrite; and then subjecting the resulting
pulp to flotation in the presence of a suitable frother to produce
a copper concentrate enriched in copper values and impoverished in
pyrite, and a tailings impoverished in copper values and enriched
in pyrite.
2. A process as defined in claim 1 wherein during said agitation
conditioning of the thus produced pulp at a pH of at least 12.3,
the sulf-hydryl collector is added at a rate, per ton of said
grinding feed, equal to at least 50 percent of the rate, per ton of
original feed of sulf-hydryl collector already used to produce said
flotation concentrate.
3. A process as defined in claim 1 wherein during said agitation
conditioning of the thus produced pulp at a pH of at least 12.3,
the sulf-hydryl collector is added at a rate, per ton of said
gringing feed, equal to at least 50 percent of the rate, per ton of
original feed of sulf-hydryl collector already used to produce said
flotation concentrate and cyanide is added during said agitation
conditioning.
4. A process as defined in claim 1 wherein during said agitation
conditioning of the thus produced pulp at a pH of at least 12.3,
the sulf-hydryl collector is added at a rate, per ton of said
grinding feed, equal to at least 50 percent of the rate, per ton of
original feed of sulf-hydryl collector already used to produce said
flotation concentrate and cyanide is added at a rate equivalent to
at least one pound of sodium cyanide per ton of grinding feed.
5. A process as defined in claim 1 wherein said concentrate is a
cleaner copper-pyrite concentrate derived from a flotation
concentrate which has been refloated at least once in the presence
of a dispersing agent.
6. A process as defined in claim 1 wherein a sulf-hydryl collector
is added at a rate, per ton of said grinding feed, equal to at
least 50 percent of the rate, per ton of original feed of
sulf-hydryl collector already used to produce said copper-pyrite
flotation concentrate.
7. A process as defined in claim 1 wherein a sulf-hydryl collector
is added at a rate, per ton of said grinding feed, equal to at
least 50 percent of the rate, per ton of original feed of
sulf-hydryl collector already added during rougher flotation and a
dispersant is added during conditioning of the thus produced
pulp.
8. A process as defined in claim 1 wherein a sulf-hydryl collector
is added at a rate, per ton of said grinding feed, equal to at
least 50 percent of the rate, per ton of original feed of
sulf-hydryl collector already used to produce said flotation
concentrate and cyanide is added during said agitation conditioning
stages.
9. A process as defined in claim 1 wherein the sulf-hydryl
collector is added during said grinding said copper-pyrite
flotation concentrate.
Description
This invention relates to the separation of copper minerals from
pyrite.
Copper minerals frequently occur in association with pyrite. When
such ores are concentrated by froth flotation the normal tendency
is for the pyrite to report in the copper concentrate. The presence
of the pyrite in the copper concentrate lowers the grade thereof
and it has been the practice to attempt to eliminate as much as
possible of the pyrite through the use of pyrite depressing agents
during the rougher flotation.
Unfortunately the use of pyrite depressing agents such as cyanide
during the rougher flotation has, in the past, been only partly
effective and has succeeded to the extent that it has, only at the
expense of lower recovery of the copper minerals. This has made
necessary a compromise between pyrite elimination and copper
recovery which results in the presence of a considerable amount of
pyrite in copper concentrates delivered to the smelter. In the case
of many ore bodies the principal sulphur containing ingredient in
concentrates delivered to the smelter is pyrite. While pyrite may
be tolerated in copper concentrates in the sense that such
concentrates are capable of being smelted, its presence adds to the
expense of the smelting operation both in terms of operating costs
and in the capital cost of smelter installation per pound of copper
produced.
Perhaps more important than the economic disadvantages brought
about by the presence of pyrite in copper concentrates is the air
pollution which results from the noxious gases, mainly sulphur
dioxide, which are released during smelting. Consequently there has
been, and is, considerable demand for a means of eliminating, to
the maximum possible extent, the presence of pyrite in copper
flotation concentrates.
GENERAL DESCRIPTION OF INVENTION
I have discovered that it is possible to separate pyrite from
copper concentrates to a very effective extent without significant
losses of copper values. According to my invention a flotation
concentrate is produced which contains the copper minerals and such
of the pyrite as will normally float therewith. Surprisingly, even
though the pyrite may be essentially free of being combined with
any of the copper minerals, with my invention it is necessary to
regrind, in a wet regrind mill, at least part of the copper pyrite
concentrate. For instance, if the regrinding circuit is in closed
circuit with a classifier, the concentrate may be fed first to the
classifier, with the finely ground portion of the concentrate going
directly from the classifier to the conditioning circuit and the
coarse fraction going to the head of the regrind mill. Although
this circuit may be used, I generally prefer to feed all of the
concentrate to the head of the regrind mill with all of the product
having at least one pass through the regrind mill. I have found
that the reagent control to the regrind mill is of the utmost
importance. If the copper minerals have been heavily activated in
the previous float or flotation circuits, little or no sulf-hydryl
collector need necessarily be added to the regrind circuit. If,
however, this is not the case, then I have found it necessary to
add comparatively large quantities of the sulf-hydryl collector to
the regrind unit. The amount can vary in the range of 50 to 500
percent per ton of feed to the regrind unit as compared to the
amount of sulf-hydryl collector used per ton of feed in the rougher
flotation circuit. Normally, I have found that in following my
invention, lime alone may be used effectively as the depressant for
the pyrite, but only after the copper minerals together with the
pyrite have been floated at least once to form a copper pyrite
concentrate. In addition, if the ore contains an appreciable host
rock slime content, a dispersant such as sodium silicate should be
present in at least one stage of flotation in the production of the
flotation concentrate. Where a rougher flotation concentrate is fed
to the regrind circuit the dispersant will be added to a
conditioning stage preferably ahead of the rougher flotation
circuit. Where the flotation concentrate is either a concentrate
produced from a first or second cleaner, the dispersant may be
added either prior or during the rougher float, prior to the first
cleaner float, or prior to the second cleaner float, in all three
cases or alternately to only one or two points in the system such
as in the conditioning stage before the first cleaner and in a
conditioning stage prior to the second cleaner. The time of
conditioning with a dispersant is normally a maximum of 3 minutes
and in plant practice no specific conditioning equipment need be
used other than, let us say, during the pumping time taken in
pumping the rougher concentrate to the first cleaner circuit. In
this circuit, in addition to the high pH required, the addition of
a sulf-hydryl collector to the grinding unit may be of major
importance.
Where I use cyanide in conjunction with lime as the pyrite
depresssant, I have found it most important to add at least the
majority of the cyanide in the conditioning stage following the
regrind mill and just prior to the cleaner flotation circuit
following the regrind circuit. If the bulk of the cyanide is added
to the regrind mill itself, serious copper losses may ensue in the
following cleaner flotation step or steps.
Although in some conditions a single stage of conditioning and
refloating after the regrind mill is satisfactory, I have found it
preferable to use two stages of conditioning and two stages of
floating following the regrind mill. Where I use cyanide in
conjunction with the lime, the optimum addition point of the
cyanide is to either one or both of the conditioning steps ahead of
the flotation circuits following the regrind mill.
I have found that the lime addition necessary to control the pH in
the regrind circuit is of minor importance compared to the normally
higher pH that is required in the one or two conditioning stages
following the regrind circuit. If a single stage of conditioning is
used the pH in the conditioning stage must be in excess of a pH of
12 and preferably in the range of 12.3 to 12.5. If two stages of
conditioning are used the pH in the first conditioning stage may be
below a pH of 12 with the second stage being at a pH in excess of
12 and preferably in the range of 12.3 to 12.5.
If the flotation concentrate fed to the regrind circuit is high in
insol, comparatively large amounts of dispersant may be used, such
as sodium silicate, tetra-sodium pyrophosphate or the lignen family
of dispersants. Where such heavy concentrations of dispersant are
used, for instance, in excess of 5 pounds of sodium silicate per
ton of concentrate, I have found it necessary to use comparatively
large concentrations of sulf-hydryl collector to prevent undue
copper losses. In the majority of cases in the use of two stages of
conditioning following the regrind circuit with at least one pH in
excess of 12.0, I have found that no cyanide is required for
acceptable pyrite depression.
EXAMPLES OF THE INVENTION
The following examples are illustrative of the process of the
invention:
Example I
A composite sample of daily concentrator feed of a major copper
producer in the United States had the following analysis:
Cu (Total) 1.09% Cu(Acid-Soluble) 0.36% Fe 7.55% S 3.23%
The sample was ground in the laboratory mill with the addition of
0.625 pounds per ton of soda ash to produce a pH of 7.55. The
resulting pulp was conditioned for two minutes with 8.5 lbs. per
ton of lime which produced a pH of 11.75. The pulp was then
subjected to a second conditioning cycle for 19 minutes with 0.255
lbs. per ton of potassium amyl xanthate (Z6) added in stages. The
pH at the end of the conditioning was 11.6. The pulp was then
subjected to a third conditioning cycle for 5 minutes with the
addition of 6.25 lbs. per ton of sodium silicate with 3 drops of
pine oil for the last 2 minutes. The sodium silicate caused the pH
to drop to 11.4.
The pulp was then subjected to flotation, the rougher float
requiring 7 minutes with the addition of 0.025 lbs. per ton of Z6
and one drop of pine oil. Following the first cleaner the cleaner
concentrate was filtered and reground with sufficient lime to
produce a pH of 12.15.
Following regrind the pulp was placed in a 250 gram Denver cell and
conditioned with 1.25 lbs. of NaCN per ton of regrind feed and 7.7
lbs. per ton of Na.sub.2 SiO.sub.3.
In the third cleaner the pH was raised to 12.35 with lime and 1.9
lbs. of NaCN per ton of feed was added and the pulp was conditioned
before floating.
The results were as follows:
Produce % Wt. Analysis % Cu % cu Distribution
______________________________________ Concentrate 2.5 35.7 83.5
No. 3 Clnr. Tlg. 2.7 2.1 5.3 No. 2 Clnr. Tlg. 2.8 1.5 3.9 No. 1
Clnr. Tlg. 12.6 0.19 2.3 Rougher Tlg. 79.4 0.067 5.0 100.0 100.0
______________________________________
In the foregoing test the heavy activation brought about by the
conditioning prior to the rougher float caused virtually all of the
pyrite to report in the first cleaner concentrate. In the case of
the copper minerals the activation was so heavy that in the second
and third cleaners the use of a pH much higher than the usual
optimum for copper flotation resulted in only low drops in copper
values in the cleaner tailings, which consisted principally of
pyrite.
It will be noted that in the case of this ore which contained a
high clay fraction, a large concentration of sodium silicate was
used to reject the insol in the second cleaner tailing.
Concentrations of cyanide in excess of one pound per ton were used
which in a normal circuit would be considered impossible, as the
copper losses would have been unacceptably high. It will further be
noted that 9.2 percent of the total copper is in the second and
third cleaner tailings. On the closed circuiting of these tailings
the calculated recovery would be 80 or approximately 7 percent of
the total copper, resulting in an overall recovery of slightly in
excess of 90 percent of the original copper values and at a grade
of concentrate of 35 percent. In the conventional circuit the grade
of concentrate produced was approximately 16 percent copper at a
recovery of less than 80 percent.
Example II
Two samples of ore from an ore body in the Phillipines having a
head assay of 0.64 percent total copper with the sulphide content
consisting mainly of chalcopyrite and pyrite and wherein the copper
minerals were mainly chalcopyrite with small amounts of copper
oxide were ground in the laboratory rod mill and treated by
procedures analogous to those of Example 1 to produce first cleaner
concentrates which were then combined and reground for 3 minutes in
a laboratory ball mill with 37 lbs. of lime per ton of concentrate.
The resulting pulp was then refloated to produce a second cleaner
concentrate having a grade of 24.4 percent copper containing 92.3
percent of the total copper compared to the combined first cleaner
concentrates which contained 95.8 percent of the total copper at a
grade of 18.4 percent.
As it is estimated that 80 percent of the copper in the No. 2
cleaner tailings would be recovered in closed circuiting, the
recovery at the grade of 24 percent copper would be approximately
95 percent. It will be noted that with the extremely high amount of
lime used to the regrind circuit to produce an end pH in excess of
12, the grade of copper was increased by approximately 32 percent
with but a minor drop in copper values. Furthermore, with the large
amount of lime addition to the regrind mill resulting in a final pH
from the regrind mill in excess of 12, it was not necessary to add
any further lime ahead of the second cleaner float.
Example III
Two further samples of the same ore as that used in Example II were
treated in a manner analogous to the procedure of Example I to
produce first cleaner concentrates which were then combined to
produce a combined concentrate analyzing 16.7 percent copper and
containing 95.6 percent of the total copper. The concentrate was
reground in the laboratory rod mill for 3 minutes with 41 lbs. of
lime per ton of concentrate and the resulting pulp was conditioned
and refloated to produce a second cleaner concentrate having a
grade of 25.2 percent copper and containing 91.7 percent of the
total copper.
Example IV
Two further samples of the same ore as that used in Examples II and
III were treated in an analogous manner to produce first cleaner
concentrates which were then combined to produce a cleaner
concentrate having a grade of 18.0 percent copper. The combined
cleaner concentrate was reground in a laboratory rod mill with 43.5
lbs. of lime per ton of concentrate. The resulting pulp was
conditioned with additional lime to bring the pH up to 12.5 for 8
minutes and floated to produce a cleaner concentrate having a grade
of 27.3 percent copper and containing 91.8 percent of the total
copper.
In comparing this example with the previous example it will be
noted that with the higher concentration of lime bringing the pH up
from around 12.1 to 12.5, the concentrate grade was appreciably
increased with no further drop in copper values.
Example V
The combined first cleaner concentrate produced from two further
samples of the same ore as that used in Examples II, III and IV
analyzed 17.4 percent Cu and contained 95.9 percent of the total
copper. The combined cleaner concentrate was reground in the
laboratory ball mill with 41 lbs. of lime per ton and one pound of
potassium amyl xanthate (Z6) per ton of feed. The resulting pulp
was conditioned for 8 minutes and refloated to produce a second
cleaner concentrate, and this concentrate conditioned at pH of 12.5
with CaO to produce the third and final cleaner concentrate
analyzing 28.4 percent Cu and containing 92.2 percent of the total
copper values.
In comparing this test with Example IV it will be noted that with
the addition of the sulf-hydryl collector to the regrind mill, and
using two stages of conditioning and cleaning the final concentrate
grade was not only higher, but also resulted in higher overall
recovery of the copper values in the open circuit.
In either using lime alone as the pyrite depressant or lime in
conjunction with cyanide, I have found that the minimum
conditioning period required for satisfactory pyrite depression is
2 minutes in at least one conditioning stage. Further, with
so-called "clean ores," that is, that produce a minimum amount of
slimes, a rougher concentrate is satisfactory as the feed to the
regrind mill. However, with rougher concentrates that contain
comparatively large amounts of host rock slime I prefer to clean
the rougher concentrate at least once, preconditioning the rougher
concentrate with a dispersant such as sodium silicate or lignen
sulphonate or one of the family of phosphates prior to refloating
to produce a first cleaner concentrate which under such conditions
would be the feed to the regrind circuit.
Where I use the term "regrind" throughout this patent application,
I am referring to a fine grinding wet ball mill circuit as
distinguished from the primary and/or secondary grinding which
normally takes place prior to rougher flotation.
Where I used the term "cyanide" as an added pyrite depressant I am
referring to the common commercial salts of cyanide normally used
in plant practice such as sodium cyanide, potassium cyanide and
calcium cyanide.
The term "sulf-hydryl collector" when used herein is intended to
refer to that class of collectors having an SH group and typified
by the xanthates as classified in "Flotation", A. M Gaudin, McGraw
Book Company, Inc., Toronto, 1957, p. 182.
* * * * *