Note: Descriptions are shown in the official language in which they were submitted.
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A METHOD TO IMPROVE THE
CLEANER FROTH FLOTATION PROCESS
The present invention provides a method to improve the cleaner froth flotation
process
for the selective separation of ore values including, for example, copper,
zinc, molybdenum,
iron, and mixtures thereof, in existing flotation plants comprising the step
of adding one or
more monocarboxylic acid polymers and/or copolymers at the cleaner flotation
step of the
process. Such polymers may be used in combination with conventional anionic
collectors
such fatty acids, thiocarbamates or xanthates, thiols or mercaptans,
dithiophosphates or
aerofloats, trithiocarbonates, thioureas, sulfates, sulfurs, oxides, alkali
and alkaline earth
hydroxides, and low pH range ammoniacal collector bases such as, for example,
amines and
azepines. The process of the present invention accelerates the flotation
kinetics for sulfide ore
resulting in increases in average from 6% to 9% of total copper recovery and
2% of copper
grade. For some ores molybdenum and iron recoveries and grades are also
increased.
Generally, the physical as well as the chemical properties of minerals are
used in ore
processing, in order to separate them from each other. The flotation method
uses differing
surface properties. In the flotation process, an ore is wet ground to obtain a
pulp. Reagents
are added to the pulp to form a suspension called a "slurry", where the
surface properties of
certain minerals can, in this system, either be activated or deactivated. The
success of a
flotation process for copper, molybdenum, zinc, and iron depends to a great
degree on
reagents called collectors that impart selective hydrophilicity to the mineral
value which is to
be separated from other minerals that may be present in the slurry. In the
flotation process the
activated mineral particles are attached to air bubbles formed, typically by
sparging, in the ore
slurry in an apparatus referred to as a flotation cell, they then rise to the
surface as a foam, and
the foam is skimmed off as concentrate. The concentrate from this initial
flotation step,
referred to as a rough or rougher flotation, is sent as a pulp to a second
flotation cell, referred
to as a cleaner flotation cell, and the flotation process is repeated. The
cleaner concentrate
typically presents a higher grade (e.g. % Cu) concentrate than obtained by
rough flotation
alone. Material left behind in the flotation cells is referred to as tails,
tailings, or gangue.
Tails from the cleaner cells are typically reground and recycled to the rough
cells for further
flotation. In a similar manner, tails from the rougher cells are recycled to
flotation cells
referred to as scavenger cells for a further flotation. As a result, the
flotation process
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encompasses a number of flotation steps in which a concentrate from one cell
is refloated in a
second cell and tails are recycled.
For ongoing processing, collector agents, frothing agents, and modifiers are
added to
the pulp, concentrates, and tails to reactivate or deactivate the mineral
surfaces and thus
selectively float valuable minerals from undesirable gangue portions of the
ore in subsequent
flotation steps. These modifiers are also largely responsible for the success
of flotation
separation of sulfide and other minerals. Modifiers include all reagents whose
principle
function is neither collection nor frothing, but one of modifying the surface
of the mineral so
that a collector either adsorbs to it or does not. Modifying agents may thus
be considered as
depressants, activators, pH regulators, deactivators, or rheology modifiers.
Often, a modifier
may perform several functions simultaneously.
The effectiveness of all classes of flotation agents depends to a large extent
on the
degree of alkalinity or acidity of the ore pulp. As a result, modifiers that
regulate the pH are
of great importance. The most commonly used pH regulators are calcium
hydroxide,
hydrated lime, calcium peroxide, calcium carbonate, soda ash and, to a lesser
extent, caustic
soda. In copper sulfide flotation, which dominates the sulfide flotation
industry, lime is by far
the most extensively used to maintain a pH over 10.5. and as high as 12.0-
12.5. This practice
imparts high processing costs associated with adding lime as well as
deterioration due to
scaling on plant and flotation apparatus. One difficulty in flotation
processes is a result of
very fine particles formed during naturally or during the grinding process,
which is referred to
as slime. While it is often possible to deslime ores prior to froth flotation,
this is not always
possible, or desirable, because in many cases certain components of the gangue
carry with
them recoverable values and in other cases it is often necessary to grind the
feed to such a
very fine size that practically all feed may be considered as a slime. The
addition polymers or
salts was recommended to be added at any convenient point in the ore treatment
to improve
the desliming of the pulp without impact on main floatation results.
The most common copper-bearing ores are made up of sulfides. Chalcopyrite
(CuFeS2), is the most common copper sulfide mineral and, as such, contributes
to the
majority of the world copper production. There are other copper sulfide
minerals with
significant contribution, such as, for example, bornite (Cu2FeS4), chalcosite
(Cu2S), and
covellite (CuS). These minerals may appear with other natural contaminants
that make up the
gangue minerals.
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The success of a sulfide flotation process depends upon reagents called
collectors that
impart selective hydrophobicity to the value sulfide mineral (copper) that has
to be separated
from other minerals. Conventional sulfide collectors include xanthates (K+ or
Na+ salts of
ROC(S)SH)), dithiophosphates, thiocarbamates, (RORN(H)C(S)OR), and
trithiocarbonates.
In general, xanthates and dithiophosphates are employed as sulfide collectors
in the froth
flotation of base metal sulfide ores. A major problem with such sulfide
collectors is that at
pH's below 11.0, poor rejection of pyrite or pyrhotite is obtained. Use of
modifiers, more
particularly depressants, to depress the non-value sulfide minerals and gangue
minerals so
that they do not float in the presence of collectors, thereby reduces the
levels of non-value
sulfide contaminants found in the concentrate. Sulfide depressants have
generally comprised
highly toxic and difficult to handle inorganic compounds such as sodium
cyanide, (NaCN),
sodium hydro sulfide, (NaSH), and Nokes reagent (P2S5 and NaOH). They cannot
be used
safely over a wide range of pH values, but instead must be used at high pH
values, so that
lime consumption problems are not solved by their use. In addition, in the
case of high
contaminated ores the gangue minerals present a unique problem in that they
exhibit natural
floatability, i.e. they float independent of the value mineral collectors
used. Such gangue
minerals are often siliceous, calcareous or dolomitic. Even if very selective
value mineral
collectors, such as, for example, low pH range collectors based on amine or
azepine use in
combination with current collectors and acrylic polymers in the first stages
of ore treatment,
are used for oxidized ores when the gangues are siliceous, calcareous or
dolomite, non value
minerals the gangue are still not sufficiently differentiated.
U.S. Patent No. 4,162,044 discloses the benefits achieved through
incorporation of
acrylic polymers into the grinding operation for processing of coal or mineral
ores and were
described as increase in particle breakage and production of higher density
(solids) slurries,
leading to a greater throughput of the refined ore in flotation processes. In
other cases,
similar polymers have been introduced into prior conditioning stages or
flotation circuits; see,
for example, U. S. Patent No. 2,740,522.
Unexpectedly, in view of the foregoing, I have discovered that certain
synthetic polymers
and copolymers which contain specific functional groups are very effective
depressants for
sulfide mineral s in general, and, more particularly, for pyrite, pyrrhotite,
and other gangue
sulfide minerals when added to the flotation process at the cleaner flotation
stage. Such
polymers and copolymers overcome the low efficiency of conventional collectors
in the cases
above and increase the throughput to improve the mineral recovery and grade
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Polymers useful in the practice of the method of this invention are
homopolymers or
copolymers which comprise from 40 to 100 mol percent polymerized units of one
or more
monoethylenically unsaturated C3 to C6 monocarboxylic acids, from 0 to 60 mol
percent
polymerized units of one or more monoethylenically unsaturated C4 to C6
dicarboxylic acids,
and from 0 to 40 mol percent polymerized units of one or more lower-alkyl
esters of the one
or more mono- or dicarboxylic acids, or mixtures thereof. In one embodiment of
this
invention, the polymers have a molecular weight of from 2000 to 1200,000
Daltons. In one
embodiment of this invention, the monocarboxylic acid unit is acrylic acid,
methacrylic acid,
or a mixture thereof.
My invention is, therefore, a process to improve the recovery of mineral
values from a
cleaner froth flotation process comprising the step of incorporating one or
more
homopolymers, copolymers, or mixtures thereof into the cleaner flotation pulp
prior to or
during the cleaner flotation process, wherein each of the homopolymer,
copolymer, and
mixture thereof independently comprise from 40 to 100 mol percent polymerized
units of one
or more monoethylenically unsaturated C3 to C6 monocarboxylic acids, from 0 to
60 mol
percent polymerized units of one or more monoethylenically unsaturated C4 to
C6
dicarboxylic acids, and from 0 to 40 mol percent polymerized units of one or
more lower-
alkyl esters of the one or more mono- or dicarboxylic acids, and mixtures
thereof.
The term "copolymer" as used herein refers to a polymer of two or more
monomers.
The term "polymerized units" as used herein refers to units which may occur in
the polymer
chain as the result of polymerizing the monoethylenically unsaturated mono- or
dicarboxylic
acids, however one skilled in the art will recognize that identical units may
occur in the
polymer chain as the result of polymerizing the corresponding anhydride, and
therefore the
term refers to polymers containing units derived from polymerizing either the
monoethylenically unsaturated mono- or dicarboxylic acid, or the corresponding
anhydride.
The term "lower alkyl" as used herein refers to a linear or branched alkyl
group
containing from one to eight carbon atoms. The terms "(meth)acrylate" and
"(meth)acrylic"
as used herein mean acrylate, methacrylate or both acrylate and methacrylate;
and acrylic,
methacrylic or both acrylic and methacrylic. The term "unsubstituted" as used
herein with
respect to the lower alkyl group means that the lower alkyl group is not
substituted with a
functional group such as a hydroxyl group; it does not exclude the presence of
a hydrocarbon
branch.
CA 02528651 2005-12-02
In one embodiment of this invention the monoethylenically unsaturated C3 to C6
monocarboxylic acid is one or more of acrylic acid, methacrylic acid, vinyl
acetic acid,
crotonic acid, and acryloxypropionic acid. In another embodiment of this
invention the
monoethylenically unsaturated C4 to C6 dicarboxylic acids is one or more of
maleic acid,
5 itaconic acid, mesaconic acid, fumaric acid, citraconic acid, and the
anydrides of cis
dicarboxylic acids, such as maleic anhydride.
In one embodiment of this invention, the range for the polymerized units of
one or
more monoethylenically unsaturated C4 to C6 dicarboxylic acids is from 5 to 50
mol percent,
and in another embodiment from 15 to 35 mol percent. In one embodiment of this
invention
the range for the polymerized units of one or more lower-alkyl esters of
(meth)acrylic acid is
from 10 to 30 mol percent, in another embodiment from 15 to 25 mol percent.
The combined
dicarboxylic acid units and units of alkyl esters of (meth)acrylic acid total
at most 60 mol
percent of the polymer, as the minimum amount of monoethylenically unsaturated
C3 to C6
monocarboxylic acids is 40 mol percent.
The alcohol component of the lower-alkyl ester of (meth)acrylic acid is
preferably
methanol, ethanol, propanol or butanol, and may be linear or branched, and
further may be a
diol, such as ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol,
1,3-butanediol and
1,4-butanediol, resulting in an ester substituted with a single hydroxyl group
on the alcohol
component. The unsubstituted lower-alkyl ester of (meth)acrylic acid is more
preferably
selected from the group consisting of methyl acrylate, ethyl acrylate, n-
propyl acrylate, sec-
propyl acrylate, n-butyl acrylate, iso-butyl acrylate, 1-methylpropyl acrylate
and 2-
methylpropyl acrylate, and the corresponding methacrylates, and is still more
preferably
selected from the group consisting of methyl acrylate, methyl methacrylate,
ethyl acrylate and
ethyl methacrylate. Examples of the lower-alkyl ester of (meth)acrylic acid
substituted with a
hydroxyl group, which are useful in the present invention, are hydroxyethyl
acrylate and
methacrylate, hydroxypropyl acrylate and methacrylate and hydroxybutyl
acrylate and
methacrylate.
The polymeric compositions of the present invention may be made by aqueous
polymerization, solvent polymerization or bulk polymerization. Further, the
polymerization
may be conducted as a batch, co-feed, heel, semi-continuous or continuous
process.
Preferably the polymerization is conducted as a co-feed process. When the
process of the
present invention is conducted as a co-feed process, the initiator and
monomers are preferably
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introduced into the reaction mixture as separate streams and at a constant
rate. If desired, the
streams may be introduced so that addition of one or more of the streams is
completed before
the others. If desired, a portion of the monomers or initiator may be added to
the reactor
before the feeds are begun. The monomers may be fed into the reaction mixture
as individual
streams or combined into one or more streams. Typical processes for the
preparation of the
polymers are disclosed in U.S. Patents No. 5,077,361, 5,244,988, 4,314,044,
4,301,266,
4,704,303.
The molecular weight, as determined by gel permeation chromatography by
comparison with standards of known molecular weight, of the polymeric additive
composition is from 1,000 to 120,000 Daltons. The molecular weight will vary
depending
upon the relative amounts, and the hydrophilicity, of the monomer components
incorporated
into the copolymer. If desired, chain regulators or chain-transfer agents may
be employed
during the polymerization to assist in controlling the molecular weight of the
resulting
polymers. Any conventional water-soluble chain regulators or chain-transfer
agents may be
used such as, for example, mercaptans such as 2-mercaptoethanol and 3-
mercaptopropionic
acid, hypophosphites, isoascorbic acid, alcohols, aldehydes, hydrosulfites and
bisulfites.
Preferred as chain regulators or chain-transfer agents are bisulfites such as
sodium
metabisulfite. End groups of the polymers utilized in the process of this
invention are
determined by the initiator and/or chain transfer agent utilized in the
preparation of the
polymer as well as the process used to prepare the polymers. In another
embodiment of this
invention, the molecular weight is from 2,000 to 70,000 Daltons. In a third
embodiment of
this invention, the molecular weight is from 5,000 to 60,000 Daltons.
I have also discovered a method to incorporate in the cleaner flotation pulps
the
polymers and copolymers. The effect of such incorporation is to optimize the
segregation of
the minerals from the gangue by a one or more of the following mechanisms: a)
changing the
surface chemical characteristics of the mineral particles in the slurry to
improve the
electrostatic repulsive forces between the particles sufficient to prevent
aggregation
decreasing the pulp yield, preventing the sedimentation of the solids in the
cells, and avoiding
scaling, b) promoting control of air bubble size and number to increase their
contact surface
and speed up the flotation kinetics, and/or c) removing the majority of the
lime species from
the surfaces of the metal sulfide particles. Once the insoluble lime species
have been
removed, the underlying mineral surfaces are exposed to collector and or
depressants action.
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A wide variety of conventional collectors are useful in combination with the
polymers
and copolymers of this invention including, for example, fatty acids,
thiocarbamates or
xanthates, thiols or mercaptans, dithiophosphates or aerofloats,
trithiocarbonates, thioureas,
sulfates, sulfurs, oxides and hydroxides of sodium and other alkali and
alkaline earth metals,
other inorganic compounds, and low pH range ammoniacal collector based amines
or
azepines, and or mixture thereof. Hydrocarbon oils and frothers such as, for
example, pine
oil, cresylic acids, higher alcohols, and other frothing., agents may also be
used.
However, I have discovered that the cleaner flotation is the best dosage point
in the
flotation circuit, particularly with adequate conditioning timing, and
optimizing the dosage of
the polymers or copolymers. For operating at 30% standard solids level in the
slurry a dosage
of 100 g/ton to 300 g/ton of polymer or copolymer into a cleaner flotation
cells is preferred.
Typically, the flotation kinetics stabilize in the first three minutes of
addition of the polymer
or copolymer. The pH of the pulp should be slightly adjusted in flotation
process for recovery
and concentration; not affecting value mineral recovery level given by the use
of existing
collectors.
Examples:
Laboratory rougher and/or cleaner flotation tests were conducted on
copper/molybdenum ore flotation feed slurries obtained from mines in Chile.
Conventional
combinations of xanthates and dithiocarbamates and/or amoniacal collectors
(such amines,
azepines, etc), were utilized in the processes. The following polymers were
evaluated:
Polymer 1 - 70/30 acrylic/maleic acid copolymer, fully neutralized
Molecular weight about 60,000 Daltons
Polymer 2 - acrylic acid homopolymer, fully neutralized
Molecular weight about 8,000 Daltons
Unless otherwise specified, all percentages are percent by weight. The term
"g"
means grams and the term "ton" means metric ton.
Example 1
A copper ore (1.1% grade) containing chalcopyrite, calcocite, covellite,
boetite and
siliceous gangue minerals was wet ground to 22% minus 65 mesh resulting in a
67% solids
pulp. The pulp was conditioned at a rate equivalent to 14 g/ton of
dithiophosphate, 15 g/ton
xanthate, and 40 g/ton of a conventional foamer. The pH was adjusted to 11.5
with lime.
The pulp was floated in a laboratory flotation cell to remove a copper
concentrate. Then,
various dosages from 50 g/ton to 400g/ton of Polymer I were added during
further grinding
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of the concentrate and cleaner flotation cells operating with 23 % and 30%
solids pulps.
After that the effect on sedimentation stage evaluated. For 200 g/ton of
Polymer 1, the results
indicate no major effect was produce on grinding for higher solids pulps 71,7%
or 76,7%, the
particle size distributor was similar to the control grinding pulp standard at
67% solids. No
significant increase of copper recovery or grade were obtained by adding the
copolymer into
the initial grinding stages. An average of 3.5% increase in copper recovery
was obtain when
using 200 g/ton of Polymer 1 into a rougher flotation operated at 40% solids,
after 1 minute
of copolymer conditioning time. An increase to 50% pulp solids resulted in an
increase of
about 0.5% copper recovery.
The best results were obtained by addition of Polymer 1 into cleaner flotation
cells
where with dosages from 100 g/ton to 300g/ton reflected a significant increase
of the copper
recovery. The highest final concentrate was produced from addition of 300
g/ton into a
cleaner flotation which contained 88.84% of copper recovery, 6% higher than
obtained in
control test in which the copolymer was omitted, 82.24%. Improvement of 2%
copper grade
concentrate were also obtain for 200g/ton added into clean flotation with 23%
solids pulp. An
increase to 30% solids pulp did not improve the copper recovery or grade. The
kinetic of
flotation is improved around three minutes of conditioning time.
Further benefits were observed with the addition of Polymer 1 including
increases in the
sedimentation capacity, no damage to the flocculates, and accelerated
filtration rate. The
scavenger recovery of insoluble copper from the gangue decreased from 0.42% in
the control
to 0.22% with Polymer 1 dosage.
Example 2
Example 1 was repeated with a 1.2% copper ore containing chalcopyrite, and
high
contamination gangue composed of siliceous minerals. The ore was ground at 67%
pulp
solids to 20% minus 65 mesh and conditioned with the equivalent of 14 g/ton of
dithiophosphate and 15 g/ton xanthate and 40 g/ton of conventional foamer, and
the pH was
adjust to 11.5 with lime. The pulp was floated to remove a copper concentrate.
In this case
both Polymers 1 and 2 were evaluated.
A series of tests were conducted using a fixed polymer dosage distributed into
different floatation stages to evaluate the best dosage point as follows: a)
200 g/ton was
added to first grinding, b) 100 g/ton was added to the first grinding and 100
g/ton at rough
flotation, and, finally, 200 g/ton was added to cleaner flotation. In all,
30%, 40%, and 45%%
solids pulps were floated. Additional tests were conducted with 50 g/ton and
100 g/ton. The
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results confirmed that the more effective copper recovery and grade increase
occurs when
total polymer dosages of 200 g/ton are added directly into the cleaner
flotation. In general,
Polymer 2 surpassed the performance of Polymer 1. In general, the 30 % solids
pulps in the
presence of either polymer provided better flotation results than higher %
solids pulp. For
40% or 45% solids pulp selectivity of process apparently was harmed by higher
viscosities of
pulp that inhibited the foam dispersion. The highest final concentrate was
produced from
addition of 200 g/ton into a cleaner flotation which delivered 82.17% of
copper recovery, 9%
higher than control test in which the copolymer was omitted, 73.02%. In both
cases the same
12% copper grade concentrate was produced. Molybdenium recovery and iron
depress were
also increase about 5% and 6% from control test. The grades were similar for
both minerals
also. Further benefits similar to those of Example 1 were observed.
Example 3
A copper ore (1.2% grade) obtained from a mine in Chile containing
chalcopyrite,
chalcocite, covellite, and gangue minerals was ground to minus 65 mesh. The
pulp was
conditioned with 6 g/ton of dithiophosphate, 24 g/ton xanthate, and 28 g/ton
of conventional
foamer. The pH was adjust 10.5. The pulp was floated to remove a copper
concentrate. The
addition of 200 g/ton of Polymer 1 to rougher flotation allowed an increase of
solids pulp
from 36% to 50% without harm to the flotation dynamic and delivered additional
2% copper
and 2 % molybdenium recovery in the resulting concentrate. The rheology of
pulps was
improved as well as the flotation kinetics are also improved around 3 minutes
of
conditioning.
Example 4
A low grade copper ore (less than 1.0%) containing chacopyrite, calcocite,
covellite,
and gangue minerals was ground to 30% minus 65 mesh. The resulting 68% pulp
was
conditioned with 8 g/ton of dithiophosphate, 25 g/ton xanthate, and 20 g/ton
of conventional
foamer. The pH was adjusted to 10.8. The pulp was floated to remove a copper
concentrate.
Different dosages of 100 g/ton, 200 g/ton, and 300 g/ton of Polymer l were
added to
the grinding mill resulting in pulps at 34% and 50% solids. The pulps were
then floated in a
cleaner floatation. The results confirmed that the copper recovery is higher
with higher solids
as in Example 3. In this Example the best recovery was obtained with 100 g/ton
at high
solids pulp of 50%, where the copper or molybdenium recoveries were less than
2% for the
same mineral grades. The weak flotation results confirms that the grinding
mill was not the
best point of polymer addition.
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Other results observed in this Example included: a) improved copper grade from
2 %
to 5% and 2% to 5% in molybdenium grade in the concentrates, b) improvement of
6% to
10% in copper recovery and 5% in molybdenum recovery, c) depressed iron
recovery, and d)
faster cleaner flotation kinetics.
5 The improvements of the grade of copper or molybdenum and/or with improved
recovery percentage obtained from the method of this invention will have a
high savings
impact in the economics of the value mineral flotation cost.
It is also an advantage of the present invention that it is applicable to
gangue slimes of
the most varied types of ores such as siliceous gangue present in metallic or
sulfide ores, for
10 example, lead, zinc, copper, pyrite, lead- zinc ores, precious metal ores,
etc. It is also
applicable to the various gangues present in non-metallic ores such as, for
example, those of
tungsten, manganese, barite, fluorspar, limestone and phosphate rock. talcs,
micas, clays,
sericites, limonites, fine carbon and fine calcite are examples of gangues
which interfere with
flotation especially when these are present as slimes, and other minerals when
in the form of
slimes frequently are harmful.
