Note: Descriptions are shown in the official language in which they were submitted.
D 4
° J~ta
SPEC1F1CATION
Techni~at Field of the Invgntion
The present invention is in the technical field of bulk solids handling,
particularly mined
ores.
ackeround of the invention
Tacky surfaces can be a serious problem for the mining, storage and transport
of bulk
solids, particularly bulk solids such as ores. As used herein, "ore(s)" means
not only a mineral
containing a valuable metal or other constituent for which it is mined and
worked, but also any
catthen material that is mined and from which valuable matter is extracted,
such as crude coal,
and spent ore material, such as tailings. By "metalliferous ore" is meant
herein ore in its more
restricted definition of a valuable metal containing mineral, and includes
gold, silver, copper,
nickel, iron, bauxite (aluminurn~, uranium and like ores. Ore is mined by
removal of the ore
from a pit or excavation in the earth, after which it is subjected to
beneficiation, which is
collective term for physical and mechanical processes that precede the
extraction or removal of
the desired constituent. Btneficiation may include crushing, screening, dry or
wet concentrating,
and the like type of recovery steps. In the coal industry, the beneficiation
steps, that is, the
2
processing steps required to make the coal suitable for most of its uses, are
commonly called
"preparation". The brneficiation mill is routinely located at a separate site
and thus the ore must
be transported from the mine to the beneficiation mill, and in-between to and
from one or more
storage sites. Between various sites, the ore may be transported on large
conveyors or conveyor
belts (transfer belts), which can have segments that are 10 to 20, or even
100, yards long. For
longer distances, or where a continuous conveyor system is not practical, the
ore may be
transported in ships, barges, railroad cars and other shipping vehicles.
Similarly, cpent ores
routinely must be transported away from the beneficiation mills.
Wet ire may become sticky or tacky, and difficult to handle. This tackiness
causes the
arc to adhere to conveyor belts and other handling equipment and to resist
removal from storage
bins and shipping vehicles and the like, An ore may be tacky as mined, or it
may be conveyed
or stored in the open or in an otherwise weather exposed condition and wetted
by rain. 1t may be
subjected to an accidental or intentional water wetting. For example, the ore
may be sprayed
with water to wntrol dusting or for some other purpose, or leakage from a
water source to the
ore heap may cause water wetting. The serious transport problems that arise
when attempting to
transfer tacky bulk solids such as tacky ore from one site to another at
minimum decrease the
efficiency of transport and are inevitably costly.
3
~~~~L~t:~~
a l a7
Ores arc routinely transported on conveyor belts or in shipping vehicles and
stored in large silos or bins. Ores are tumbled or fed onto conveyor belts and
eventually arc
discharged therefrom onto other conveyor belts, or to a storage silo or bin,
or into a shipping
vehicle. At such feeding or discharge (transfer) points, the ore must flow.
Adherence of the ore
solids to each other andlor to the equipment surfaces in contact with it will
interrupt and severely
retard the transport process. For instance, bins commonly consist of two types
of parts, namely,
a hopper and bin. The hopper is a converging section at the bottom. The bin is
the vertical
section above the hopper that provides most of the storage volume. Ore is
typically added to the
bin from overhead, and discharged therefrom through the hopper onto a moving
collecting
conveyor or the like. It is extremely desirable that the discharge of ore
through the hopper be
conducted at a controlled, specified rate. if the ore is tacky, the solids
therein may adhere to
each other and to the sides of the bin or hopper, interrupting or slowing the
discharge therefrom.
When tackiness leads to adherence at a feed or discharge point along the
transport system,
auxiliary means, such as extraordinary mechanical agitation, are generally
required to increase or
recommence flow. A partially restricted area of flow would be extremely
detrimental to mast
transport systems, and a wholly restricted area of course could not be
tolerated.
Accordingly it would be advantageous to provide a method and composition for
detackifying ore and like bulk solids.
4
ai' va. r..1
Disclosure of the lnvcntion
The present invention provides a method for detackifying bulk solids,
particularly ore,
and more particularly uncrvshcd ore, by contacting such bulk solids, or ore,
or unerushed ore,
with an effective amount of a water soluble vinyl addition polymer, as a free-
towing solid or as
a water-in-oil latex. Such water soluble vinyl addition polymer is a
substantially linear, high
molecular weight polymer, which is described in more detail below. In
preferred embodiment,
such bulk solids, or ore, or uncrushed ore, is sufficiently wet to be tacky at
the time it is
contacted with the polymer solids or water-in-oil latex, but the present
invention dots not
exclude a prophylactic treatment of non-tacky bulk solids, or ore, or
uncrushed ore, particularly
when there is a significant possibility such material will be wetted after a
convenient treatment
point. In preferred embodiment, the polymer solids or latex is applied to the
bulk solids, or ore,
or uncrushed ore, at a point when such material is being subjected to
mechanical agitation, such
as at a transfer point. The water-in-oil latex is not subjected to phase
inversion prior to its
application to the bulk solids, or ore, or uncrushed ore.
~~3~~~3
Preferred Embodiments of the Invention
The present invention, in one embodiment, provides a water-in-oil latex of a
vinyl
addition polymer which is applied to the ore to detackify the ore and reduce
adherence of the ore
particles to surfaces. According to an embodiment of the invention, the ore is
contacted with an
amount of such latex effective to reduce ore tackiness. In a preferred
embodiment of the
invention, the latex is applied to the ore in an amount to provide from about
0.001 to about 0.3
1b of vinyl addition polymer actives per ton of ore as is (without factoring
out the moisture
content). In a more preferred embodiment of the invention, the latex is
applied to the ore in an
amount to provide from about 0.015 to about 0.05 1b of vinyl addition polymer
actives per ton
of ore as is.
In a preferred embodiment of the invention, the latex contains from about 25
to about 50
weight percent of the vinyl addition polymer and the ore is contacted with
from about 0.002 to
about 1.2 1b of latex per ton of ore as is (without factoring out the moisture
content). In a more
preferred embodiment of the invention, the latex contains from about 25 to
about 50 weight
percent of the vinyl addition polymer and the ore is contacted with from about
0.0075 to about
0.2 1b of latex per ton of ore as is (without factoring out the moisture
content).
In another preferred embodiment of the invention, the ore is contacted with
from about
0.001/n to about 0.3/n 1b of latex per ton of ore as is (without factoring out
the moisture
6
content), wherein n is the fraction of the latex comprised of vinyl addition
polymer actives,
expressed as a decimal. In a more preferred embodiment of the invention, the
ore is contacted
with from about O.OlS/n to about O.OS/n 1b of latex per ton of ore as is
(without factoring out the
moisture content), wherein n is the fraction of the latex comprised of vinyl
addition polymer
actives, expressed as a decimal.
The present invention, in one embodiment, provides a free flowing powder of a
vinyl
addition polymer which is applied to the ore to detackify the ore and reduce
adherence of the ore
particles to surfaces. According to an embodiment of the invention, the ore is
contacted with an
amount of such powder effective to reduce ore tackiness. In a preferred
embodiment of the
invention, the powder is applied to the ore in an amount to provide from about
0.001 to about
0.3 1b of vinyl addition polymer actives per ton of ore as is (without
factoring out the moisture
content). In a more preferred embodiment of the invention, the powder is
applied to the ore in
an amount to provide from about 4.015 to about 0.05 1b of vinyl addition
polymer actives per
ton of ore as is.
The upper limit of the polymer powder or latex dosage may not merely be an
economic
application level, above which the treatment will be excessively costly. It is
believed that a
performance peak may well exist, beyond which treatment is not only increasing
in cost but also
decreasing in effectiveness, and thus decreasing rapidly in cost-
effectiveness.
7
The dosage of polymer powder or latex that is effective to reduce tackiness
will vary
depending on the nature of, and severity of, the tackiness problem. The
constituents of ores, the
physical and chemical characteristics of ores, and the degree of wetness at
which tackiness is
seen, all vary widely. For instance, tackiness was seen in one bauxite ore at
a moisture content
of 23 percent, but not at a moisture wntent of 18 percent, while another ore
was tacky at a
moisture content of only 10 percent. It is well known that tackiness is not
only a function of
moisture content, but also of the chemical and physical characteristics of the
are. For instance,
an ore of greater porosity typically will hold a greater amount of moistwe
within pores, and for a
given total rnoisture content will have less surface water, and less of a
tendency to become tacky,
than a less porous ore because surface moisture makes a greater contribution
to tackiness than
entrapped (inherent) moisture. ?ackiness of course arises not from water
alone, but from a
combination of water and ore constituents, and some ore constituents, such as
certain clays,
probably promote tackiness more than other ore constituents.
Moreover, the problems ensuing from a surface tackiness, namely interrupted or
decreased flow due to the solids adhering to various surfaces, is dependent on
the size or weight
of the solids. Some solids, for instance of boulder size, would have little to
no tendency to
adhere to surfaces even if their surfaces were considered very tacky, but
solids of such size and
weight arc rarely processed in mined eras. Uncrushed ores, particularly
metalliferous ores,
8
seldom are wholly fines. (Fines are herein, and generally, defined as
particles that pass through
a 100 mesh screen.) Instead they more often contain no more than 80 weight
percent fines, and
commonly no more than about 50, or 60, weight percent fines, the remainder of
the material
being of course coarser solids. Therefore given the weight dependency of flow
problem, which
is also a particle size dependency for ores , which have reasonably uniform
solids densities, the
solids coarser than fines will better resist adhering to surfaces. The
corollary is that when
uncrushed ore, which typically has a significant percentage of coarse solids,
becomes so tacky
that flow is interrupted or decreased , the performance required for
detackification is of a
different order than that required for merely fines.
In other words, a sufficient reduction of tackiness for purposes of the
present invention is
not measured by merely the adhesiveness of the solids surfaces, and in fact
may not require that
the surfaces of the solids be rendered completely tack-free. Detackification
of the ore is a
restoration of flow properties, and the sufficiency of detackification is
generally determined by
the flow properties.
9
The vinyl addition polymer of the polymer powder or latex employed in the
process of
the present invention may be nonionic, anionic, cationic or amphoteric.
In one embodiment of the present invention, the polymer preferably is
comprised of from
about 0 to 100 mole percent of (meth)acrylamide mer units, which are nonionic,
but polar, mer
units, and from about 0 to about 100 mole percent of anionic mer units. The
anionic mer units
may contain pendant carboxyl radical type, such as (meth)acrylic acid,
itaconic acid, malefic
acid, crotonic acid and the like, and salts thereof with monovalent cations
("monovalent salts
thereof), particularly sodium salts thereof, and preferably such anionic mer
units are in a
monovalent salt form. The anionic mer units may be N-sulfoalkyl
(meth)acrylamide mer units,
which provide a pendant sulfonate radical.
In a preferred embodiment, the vinyl addition polymer is substantially a
homopolymer of
(meth)acrylamide. In another preferred embodiment, the vinyl addition polymer
is substantially
a homopolymer of (meth)acrylic acid or monovalent salts) thereof. In another
preferred
embodiment, the vinyl addition polymer is substantially a homopolymer of N-
sulfoalkyl
(meth)acrylamide.
In another preferred embodiment the vinyl addition polymer is comprised of
from about
0.1 to about 40 mole percent of aforesaid N-sulfoalkyl (meth)acrylamide mer
units or
(meth)acrylic acid or monovalent salts) thereof mer units or combinations
thereof, and in more
~. preferred embodiment from about 1 to about 25 mole percent of such anionic
mer units, while
CA 02098543 2005-04-05
66530-596
,.
the remainder of the mer units are substantially
(meth)acrylamide. In another preferred embodiment, the
vinyl addition polymer is comprised of from about 5 to about
15 mole percent of aforesaid anioic mer units, and the
remainder of the mer units are substantially
(meth)acrylamide.
In another preferred embodiment, the acrylamide
polymer is comprised of at least 40, or 50, mole percent of
(meth)acrylamide mer units or N-sulfoalkyl (meth)acrylamide
mer units or anionic acrylate mer units or combinations
thereof.
U.S. Patent No. 4,678,840 (Fong et al.) issued
July 7, 1987, describes a method for the preparation of
acrylamide polymers having ionizable phosphonate groups.
Phosphonate-containing acrylamide polymers that meet the
preferred molecular weight ranges may possibly be as active
in the present process as other preferred anionic acrylamide
polymers described above.
In another embodiment, the vinyl addition polymer
is comprised of (meth)acrylamide mer units and cationic mer
units, preferably of the quaternary ammonium salt type, such
as the quaternized salts of mer units of N-alkylsubstituted
aminoalkyl esters of acrylic acid and others, including, for
example:
1. the quaterized salts of reaction products of a polyamine
and an acrylate type compound prepared, for example, from
methyl acrylate and ethylenediamine;
2. (methacryloyloxyethyl)trimethyl ammmonium chloride;
11
3. diallylmethyl(beta-propionamido)ammonium chloride,
(beta-methacryloyloxyethyl)trimethylammoniwn methyl sulfate, and the like;
4. quaternized vinyllactam;
5. the quaternized salt of vinylbenzyltrialkylamines such as, for example,
vinylbenzyltrimethylammonium chloride;
6. quaternized salt of vinyl-heterocyclic monomers having a ring nitrogen,
such as
(1,2-dimethyl-5-vinylpyridinium methyl sulfate), (2-vinyl-2-imidazolinium
chloride) and
the like;
7. dialkyldiallylammonium salt including diallyldimethyl ammonium chloride
("DADMAC");
8. methacrylamidopropyltrimethylammonium chloride ("MAPTAC");
In preferred embodiment, the vinyl addition polymer contains up to 50 mole
percent of
such cationic mer units, and in more preferred embodiment up to about 30, or
40, mole percent
thereof. A preferred cationic mer unit is DADMAC. A preferred cationic polymer
is
substantially comprised of acrylamide and DADMAC.
In preferred embodiment, the vinyl addition polymer has a weight average
molecular
weight of at least , 500,000, and in more preferred embodiment at least about
1,000,000, and
even more preferably 4,000,000, or 5,000,000. The polymer has no standard
molecular weight
r ceiling for the purposes of the present invention, and some vinyl addition
polymers having
12
~; ~ a
'~~~~~° 3
molecular weights of 15,000,000 or higher are believed highly useful for the
present invention.
The vinyl addition polymer employed in the presrnt invention is water soluble.
The
water solubility characteristic preferably is defined in terms of fluidity of
aqueous solutions of
the polymer although the polymer is not applied to the bulk solids as an
aqueous solution. By
"water soluble vinyl addition polymer" is meant herein, and generally, that an
aqueous solution
of the polymer, at a polymer actives concentration no lower than about 0.5 or
1 weight percent,
is reasonably fluid, and preferably has a viscosity of no more than about
5,000 to 20,000 cps
Brookfield, at ambient room temperature (from about 23 to about 26 'C.). Such
water solubility
characteristic generally does not create a molecular weight ceiling because
even acrylamide
homopolymers, substantially free of any electrolytic baoups, meet such a
standard at the high
molecular weights that can now be provided by conventional synthesis
techniques, provided the
polymer is substantially linear.
Vinyl addition polymers comprised of (meth)acrylamide mer units, anionic
acrylate mer
units and N-sulfoalkyl (meth)acrylamide mer uniu may be directly synthesized
from the
corresponding monomers by known techniques, for instance using as the
sulfonate-containing
monomer the 2-(meth)acrylamido-2-methylpropane sulfonic acid, or the
methacrylamide version
thereof. N-sulfoalkyl (meth)acrylamide mer units can also be incorporated into
an existing
polymer by post~polyrnerization derivatization, for instance by one of the
methods described in
U.S. Patent No. 4,762,894 (Fong et al.) issued Aubrost 9, 1988, U.S. Patent
No. 4,680,339
13
CA 02098543 2005-04-05
66530-596
(Fong) issued July 14, 1987,1U.S. Patent No. 4,795,789
(Fong) issued January 3, 1989, and U.S. Patent No. 4,604,431
(Fong et al.) issued August 5, 1986. The sulfonated mer
units of such post-polymerization derivatized polymers are
generally of the sulfonate N-alkyl substituted
(meth)acrylamide type.
High molecular weight vinyl addition polymers are
commonly synthesized and commercially supplied in the form
of water-in-oil latices. Such latex form is a common
commercial form because it permits the polymer to be
prepared and shipped at reasonably high concentrations (and
the polymer therein is readily dispersible in water upon
inversion of such emulsion by known techniques, which is
desirable for many use applications). The vinyl addition
polymers may also be formed by other synthesis techniques
and incorporated into a water-in-oil latex after
polymerization by known techniques. Water-in-oil latices of
vinyl addition polymers are well known and are described,
for instance, in U.S. Patent No. 3,284,393, Vanderhoff, and
U.S. Patent No. Re. 28,474, Anderson-Frisque. The use a
such a water-in-oil latex, as commercially supplied, or as
diluted as discussed below, is a preferred embodiment of the
invention.
The present invention does not, however, exclude
the use of high molecular water soluble vinyl addition
polymers supplied in dry powder form. The dry powder form
of such a polymer is generally commercially available with
no more than a 5 weight percent or less
14
moisture content. Such powder should, of course, be free flowing for
reasonable ease of
distribution within the bulk solids.
The vinyl addition polymer is substantially linear and substantially free of
pendant
hydrophobic radicals or hydrophobic polymer backbone segments, but the present
invention
does not exclude the use of polymers having some branching or cross-linking,
or some
hydrophobic moieties, provided the polymer retains its water solubility and
detackification
activity. An amphoteric vinyl addition polymer also is not excluded for use in
the present
process.
A water-in-oil latex of a vinyl addition polymer can be provided with a
concentration of
polymer actives as high as about 70 weight percent, although it is believed
that latex preferably
should have a polymer actives concentration of no more than about 40, or 50,
weight percent. At
such lower concentration levels a latex is generally more fluid and such
fluidity contributes to
the ease of distributing the latex in the ore. A water-in-oil latex of a vinyl
addition polymer is
often commercially supplied with a concentration of polymer actives of from
about 25 to about
50 weight percent, and use of the latex in this concentration range is
believed very effective for
the purposes of the present invention, and is a preferred embodiment hereof. A
water-in-oil
latex may also be supplied and used, or diluted and used, at polymer actives
concentrations as
low as about 5, or 10, weight percent. By latex dilution is meant herein a
dilution of the
continuous (external) oil phase without any substantially destabilization of
the latex or phase
IS
inversion. Therefore any diluent used must be compatible with the latex, and
preferably should
be a water immiscible diluent that is compatible with the oil phase of the
latex.
There is no need generally for the inclusion of any conventional surface
active agent,
such as a surfactant, dispersant, or detergent, in the treatment of the
present invention, other than
that present in a water-in-oil latex for purposes of forming and retaining the
latex form. No such
agent would generally be added unless required for stabilization of the water-
in-oil latex upon
dilution, and such dilution/stabilization is an unpreferred embodiment of the
present invention.
The terminology "conventional surface active agent" as used herein, and
generally, means
chemical species that have distinct hydrophilic and hydrophobic sections. Such
agents are
generally not polymeric except for sections thereof that have repeating
alkoxylated units, such as
ethylene oxide or propylene oxide sections. While a very broad definition of
surface active
agent may in some instances include polymers such as the vinyl addition
polymers of the present
invention, the terminology of conventional surface active agent does not
include such polymers.
As a generality, one can distinguish such species by molecular weight, and
conventional surface
active agents would not have molecular weight approaching 500,000, and even a
molecular
weight ceiling of 100,000, or 50,000, would be excessively high to define such
agents. In
preferred embodiment the latex used in the present invention does not include
any surface active
agent of less than 50,000 molecular weight other than the amount of water-in-
oil emulsifier
required to form and maintain the water-in-oil latex form.
s
16
~~'~~~~~3
In Examples I and 2 below, a vinyl addition polymer latex designated Latex 1
was
employed. This composition contained from about 28 to 29 weight percent
polymer actives, in
the form of a water-in-oil latex. The polymer was 30/70 mole ratio sodium
acrylate/acrylamide
copolymer having a reduced specific viscosity within the range of from about
30 to 36, which
represents a weight average molecular weight of about 10,000,000.
Ex~ple 1
Equal weight samples of tacky bauxite ore, as mined, having about 23 weight
percent
total moisture, were placed into three jars, designated Jar 1 to Jar 3. The
ore sample in Jar 1 was
left untreated. The ore sample in Jar 2 was treated with Latex 1, at a dosage
of 0.1 Ib per ton of
ore (as is) by lightly mixing the latex into the ore. The ore sample in Jar 3
was treated with Latex
1, at a dosage of 0.4 1b per ton of ore (as is) by lightly stirring the latex
into the ore. Then each
of the jars was closed and shaken by hand for 15 seconds, and the contents
observed. In Jar 1,
the ore fines were clearly seen to be adhering to the sides of the jar. In Jar
2, some amount of
ore fines were seen to be adhering to the sides of the jar, but the amount of
fines so adhering
were clearly less than in Jar 1. In Jar 3, the sides of the jar were
substantially free of adhering
fines and the ore contents of the jar had settled to the bottom of the jar
when the shaking
stopped.
17
~xamrle Z
Four oqual weight samples of a tacky, wet copper ore having about 50/50 weight
ratio of
fines/coarser solids, were subjected to a pipe test as follows. The ore
sample, after treatment, or
as is for the blank, was placed in a 4 inch diameter metal pipe equipped with
a bottom knife
valve, and held therein in a vertical position for 30 minutes. At the end of
such holding time, the
knife valve was opened and the amount of ore that fell out of the pipe within
a set time period
following the valve opening (on the order of a few minutes) was measured. The
treated ore
samples were lightly mixed with Latex 1 immediately prior to placement in the
pipe. The
dosages of Latex 1 used, and the test results in terms of the percent of the
ore sample that fall out
of the pipe ("Fallout Percentage"), are set forth below in Table 1.
18
f~
~~'~~51~3
Table 1
~,pc Test - Latex 1 Treatment
Latex Dosage (1b latex ner ton of orel ~,allout Percentage
None 2.4%
0.05 38.9%
0.11 45.2%
0.18 31.7%
As a water-in-oil latex, the vinyl addition polymer may be applied to the bulk
solids by
spraying, if the viscosity of the latex permits, or by dribbling or like
methods. As a free flowing
solid, the polymer may be contacted applied by dusting or like methods.
~dustrial Anulicabilitv of the Invention
The present invention is applicable particularly to the mining industries.
19
