CA2098543C - Bulk solids detackification - Google Patents

Abstract

Detackification of bulk solids is achieved by contacting the bulk solids with an effective amount of a water soluble vinyl addition polymer, as a free-flowing solid or as a water-in-oil latex. The water soluble vinyl addition is a substantially linear, high molecular weight polymer.

Description

° J~ta 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 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.

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, 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.

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 ,.
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;

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 ~; ~ 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 (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 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 ~~'~~~~~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.

~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.

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.

Claims (14)

CLAIMS:

1. A method for detackifying a bulk solid comprising:
contacting said bulk solid with an effective amount of a water soluble vinyl addition polymer, as a free-flowing solid or as a water-in-oil latex, wherein said water soluble vinyl addition polymer is substantially linear and has a weight average molecular weight of at least 500,000.

2. The method of claim 1, wherein said bulk solid is sufficiently wet to be tacky at the time said bulk solid is contacted with said polymer.

3. The method of claim 1 or 2, wherein said polymer solid or latex is applied to said bulk solid at a transfer point of a bulk solid transport system.

4. The method of any one of claims 1 to 3, wherein said bulk solid is ore.

5. The method of any one of claims 1 to 4, wherein said polymer comprises from about 0 to 100 mole percent of (meth)acrylamide mer units and from about 0 to about 100 mole percent of anionic mer unit.

6. The method of any one of claims 1 to 4, wherein said polymer is comprised of from about 0.1 to about 40 mole percent of mer units of N-sulfoalkyl (meth)acrylamide mer units or (meth)acrylic acid or monovalent salt(s) thereof or combinations thereof, and the remainder of the mer units are substantially (meth)acrylamide.

7. The method of any one of claims 1 to 4, wherein said polymer is comprised of at least 40 mole percent of (meth)acrylamide mer units or N-sulfoalkyl (meth)acrylamide mer units or anionic acrylate mer units or combinations thereof.

8. The method of any one of claims 1 to 4, wherein said polymer is comprised of (meth)acrylamide mer units and cationic mer units of the quaternary ammonium salt type.

9. The method of any one of claims 1 to 4, wherein said polymer is substantially comprised of acrylamide and diallyldimethyl ammonium chloride.

10. The method of any one of claims 1 to 9, wherein said polymer has a weight average molecular weight of at least 1,000,000.

11. The method of any one of claims 1 to 10, wherein said polymer is contacted with said bulk solid as water-in-oil latex with a concentration of the polymer up to about 50 weight percent.

12. The method of any one of claims 1 to 10, wherein said polymer is contacted with said bulk solid as a water-in-oil latex with a concentration of the polymer of from about 25 to about 50 weight percent.

13. The method of any one of claims 1 to 10, wherein said polymer is applied to said bulk solid in an amount to provide from about 0.001 to about 0.3 1b of said polymer per ton of ore.

14. The method of any one of claims 1 to 10, wherein said polymer is applied to said bulk solid as a latex which contains from about 25 to about 50 weight percent of said polymer and said bulk solid is contacted with from about 0.002 to about 1.2 lb of said latex per ton of said bulk solid.