US 2894851 A
Description (OCR text may contain errors)
METHOD OF FORMING A PROTECTIVE COATING N CY ANIDATION TAILINGS AND THE RE- SULTING PRODUCT No Drawing. Application June 2, 1953 Serial No. 359,206
Claims priority, application Great Britain December 15, 1952 3 Claims. (Cl. 117-6) This invention relates to a method of preventing the dissemination of mineral fines into the atmosphere.
The dust problem in many industrial operations such as in mineral dressing, mining, foundry operations and the like is quite acute. Mineral dusts created in the handling or processing of rock, ores, minerals, quarry products, etc., constitute an extreme nuisance and in many instances create a health hazard if not properly controlled.
For example, a serious problem which faces the mining industry is the blowing away of finely-divided ores, mineral concentrates, mineral fines, flotation tailings, cyanidation tailings, etc. One phase of this problem is presented by tailing piles, which in locations where high winds are encountered, results in a considerable tendency for the finely-divided mineral matters to blow across the countryside. A slightly different aspect of the same problem is presented by flotation concentrates. Flotation concentrates are difficult to ship in open-top railroad cars because of windage loss of the concentrates. The shipment and hauling of mineral products containing fines presents a similar problem.
Another serious dust problem is presented in drilling operations. The mineral particles created and disseminated into the atmosphere as a result of such drilling operations frequently constitute a very serious health problem.
In addition, siliceous sand is widely used under the wheels of mine locomotives to prevent slipping and to provide traction for the locomotive on haulageways. The sand is ground to dust and the passage of trains over sections where sand is being or has been used causes the dust to be disseminated into the atmosphere of the underground area and is inhaled by those working there. The inhalation of this dust is an extreme health hazard since the continued breathing of air laden with silicabearing dust causes silicosis.
Another serious dust problem is presented in the mining and handling of coal. Because coal is relatively friable, the mining and handling thereof breaks part of it into dust that is readily carried by currents of air. When such coal dust is present in the mine in small quantities it creates a health hazard, and of more importance it creates an explosive mixture of coal dust and air which inthe past has been a major cause of mine disasters.
Mineral dusts are also created and dispersed into the atmosphere in the grinding of metals, in the making'of moulds for use in casting metals in foundries, in the recovery of foundry sands after moulding operations, as Well as in sand blasting operations. Additionally, mineral Patent O or 7 1C dusts from haulageways and highways present serious problems. All such mineral dusts, unless permanently immobilized, tend to be industrial nuisances and may constitute health hazards.
Attempts have been made to prevent windage losses of flotation concentrates and other mineral products and to prevent blowing of tailing piles by frequent wetting thereof. This has not been satisfactory, however, because as soon as the finely-divided mineral particles dry out they blow just as readily as before.
Attempts have been made to control coal dust in mines and to allay siliceous dust in haulageways by spraying with water. This treatment likewise is not elfective and, when the coal or siliceous sand is dried out, it is as dusty or more dusty than before.
It has also been proposed to use Wetting agents in conjunction with water. While this treatment results in a lessening of the amount of water used and the wetting agents temporarily aid in Wetting the material, they do not aid materially in making the finely-divided materials permanently dustless.
Calcium chloride as solutions has also been suggested as a spray for application to the surface of coal. While this reduces this dust problem for a time, it is not lasting as water Washes off the treatment, but a more serious objection to this treatment is the corrosive nature of calcium chloride which causes the iron or steel equipment in the vicinity of the sprays to corrode rapidly.
Also, it has been proposed to render coal dustless by spraying with oil and other petroleum products. While this treatment is relatively permanent in that the oil sticks to the coal surface and is not washed oif by Water to any appreciable extent, this treatment possesses the distinct advantage of flammability of the atomized oils and the resulting fire hazard is an extremely serious problem.
It has been found that the foregoing problems are solved by the application to finely-divided ores, mineral concentrates, mineral fines, flotation tailing piles, coal, siliceous dusts, foundry and metallurgical dusts and the like, and which will be referred to generally hereinafter as finely-divided mineral matters, of a small amount of water-soluble, ionic, linear, addition polymers of a monoethylenically unsaturated compound and water-soluble salts thereof, having an average molecular weight of at least 10,000.
The function of the ionic, linear, addition polymer is not fully understood and, therefore, it is not desired to limit the invention to any particular theory of action. It is believed, however, that the action of the polymer is to produce a relatively hard, firm crust or layer over the surface of the mineral particles. This surface layer is frequently very thin and accordingly often filmlike in character. The layer is such that finely-divided ores, tailings, mineral fines, concentrates, siliceous dust, metallurgical dusts, coal dust and the like are immobilized with the result that these materials are much less readily blown about or disseminated into the atmosphere. This phenomenon is all the more surprising because the over-all result is exactly the contrary to that which is observed when similar polymers are used as soil conditioners. In such latter cases, the soil is formed into loose agglomerates' that are easily air-borne rather than a continuous surface resistant to air currents and abrasion as is true with the mineral matters treated in accordance with the present invention. Consequently, for all practical purposes, the finely-divided mineral matters of the present invention are rendered almost permanently immobilized due to the formation of a continuous firm layer on the surface thereof with the result that the dissemination of the mineral fines into the atmosphere is prevented.
The polymers or salts may be applied to the finelydivided mineral particles by spraying a Water solution of the polymer thereon. When mineral concentrates, mineral fines, flotation concentrates and the like are to be treated this may be simply accomplished by spraying a suitable solution of the polymer over the material at any time during the handling or loading thereof. Or if desired, the polymer may be applied to the ores or flotation concentrates at some appropriate earlier stage in the processing thereof.
For example, in discharging suspensions of mineral products and tailings or rejects from processing or beneficiation plants, the polymers may be added to the discharge or at points in the flow to the areas where such products are to be stored. Special conditioning equipment such as tanks provided with agitators may be used but generally are not required. In collecting mineral fines and mineral dusts, it is common practice to draw such materials through water or to Wet such dusts with water sprays; the polymers may be added to the Waters used for such purposes. In all such cases the polymer conditions the surface of the mineral particles so that the particles after discharging and drying are immobilized and rendered less susceptible to movement by air currents.
When tailing piles in place are to be treated, this likewise may be easily effected by spraying the piles with the required amount of a solution of the polymer.
It is not necessary that the polymer be applied to these finely-divided mineral matters in the form of a solution. For example, the polymers may be applied as a mixture with a portion of dry or partially dry fines which is then spread over the main bulk Without appreciable disturbance of the surface and the Whole then wet down with water, or in some cases simply allowed to take up water from the main bulk or pile itself or from the atmosphere. By either method, however, a thin film or layer is produced on these mineral particles which dries to a firm surface and which is extremely resistant to Wind erosion and abrasion.
The linear, addition polymers may be applied to control the silica dust created by drilling or by the passage of railway cars in mine haulageways as described hereinbefore.
The polymers may be applied to reduce dust in coal mining and handling at any suitable point in the mining or hauling thereof and also in the processing and beneficiation of coal Where the dissemination of coal dust is a nuisance. For example, a solution may be sprayed on the face during the coal cutting operation so as to reduce coal dust at its principal source, or it may be sprayed on the mine cars at a loading point or during haulage thereof. In the processing or beneficiation of coal the polymers may be used at convenient points to prevent the dissemination of coal fines into the atmosphere.
The application of the polymers of the present inven tion reduces the dust problem in coal mining operations appreciably. The dust nuisance is abated and since the polymers are generally non-toxic, no deleterious effects are produced on the workers in the mines. When the polymers are applied to the siliceous dust in enclosed haulageways, the fine particles are permanently immobilized and thus the hazard of contracting silicosis from breathing silica-bearing dust is eliminated.
The polymers may be applied to immobilize dusts from grinding operations which produce mixtures of finelydivided metallic particles and mineral grit from the grinding wheel. The polymers are also useful in the treatment of dusts and fines from foundry operations which are mixtures of fine silica, metals, metallic oxides, and decomposition products of the materials used in binders in the sand moulds. The polymers are also applicable in drilling and sand blasting operations for preventing the dissemination of the siliceous minerals into the atmosphere.
Examples of water-soluble, ionic, linear, addition polymers of a monoethylenically unsaturated compound are polymers of unsaturated aliphatic monocarboxylic acids, such as acrylic acid, methacrylic acid, vinyl acetic acid, etc., and water-soluble salts thereof. These polymers may be obtained by polymerizing the acid itself or by polymerizing derivatives having groups which are bydrolyzable to acids, such as, for example, acrylonitrile, acrylamide, esters of acrylic and methacrylic acid, etc. The unsaturated monocarboxylic acids may be polymerized by themselves to form homopolymers or they may be copolymerized with compounds, such as vinyl pyridine, vinyl acetate, styrene, vinyl ethers, vinyl halides, or even unsaturated hydrocarbons such as isobutylene. Polymers of polybasic unsaturated acids are also included, although here it is diificult to obtain a homopolymer. For example, maleic anhydride itself will not polymerize, but it copolymerizes readily with such materials as styrene, vinyl acetate, acrylates and the like.
Among the various polymers and water-soluble salts thereof useful in the practice of the present invention are hydrolyzed polyacr'ylonitrile, polyacrylamide, polyacrylic acid, /2 calcium salt of hydrolyzed 1:1 copolymer of vinyl acetate-maleic anhydride, hydrolyzed styrenemaleic anhydride copolymer, ammonium polyacrylate, sodium polyacrylate, ammonium polymethacrylate, sodium polymethacrylate, diethanol ammonium polyacrylate, guanidinium polyacrylate, dimethylaminoethyl polymethacrylate, acrylamide-acrylonitrile copolymer, methacrylic acid-dimethylaminoethyl methacrylate copolymer, sodium polyacrylate-vinyl alcohol copolymer, hydrolyzed methacrylic acid-acrylonitrile copolymer, vinyl acetate maleic anhydride copolymer, vinyl formate-maleic anhydride copolymer, vinyl methyl ether-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, ethyl acrylate-maleic anhydride copolymer, vinyl chloride-maleic anhydride copolymer, hydrolyzed acrylonitrile-vinyl acetate copolymer, hydrolyzed acrylonitrile-methacrylonitrile copolymer, hydrolyzed acrylonitrile-methacrylonitrile-vinyl acetate terpolymer, hydrolyzed acrylonitrile-methacrylic acid copolymer, vinyl pyridine-acrylonitrile copolymer, etc. Polymers containing cation-active groups are useful. Suitable compounds are, for example, copolymers of acrylamide, ethyl acrylate and acrylamidopropylbenzyldimethyl ammonium chloride, copolymers of methylolacrylamide and acrylamidopropylbenzyldimethyl ammonium chloride, copolymers of butadiene and 2-vinyl pyridine, and certain quaternary compounds such as polydimethylaminostyrene quaternized with benzyl chloride, allyl chloride, etc. and quaternized copolymers of vinyl alcohol and morpholinylethylvinylether and the like.
Among the highly effective polymers are those which are obtained by hydrolyzing polymeric material containing polyacrylonitrile. These compounds are cheap and give excellent results. Here again, the polymer may be a homopolymer or the acrylonitrile may be copolymerized with small amounts of other materials, such as vinyl pyridine, acrylic esters and the like. It should be noted that the products obtained by hydrolyzing polymers such as polyacrylonitriles are not completely identical with the corresponding polymers obtained by polymerizing acrylic acid. Both types are, however, useful in the present invention.
It is an advantage of the present invention that the preferred type of linear polymer, namely, hydrolyzed polyacrylonitriles, may be of very low grade. It is thus possible to use polyacrylonitriles which have insufiicient purity for other uses, such as fibers, to prepare the polyacrylic acid of the present invention. The possibility of using these normally discarded, off-grade products makes a source of very cheap material available for use in the present invention. Where the amount of byproduct, off-grade material is not sufiicient to supply the demand and the linear polymers must be made directly, it is usually found that the homopolymer of acrylonitrile is somewhat cheaper to make than the copolymers.
For optimum beneficial effect, the molecular weight of the linear, addition polymers is of some importance in preventing the dissemination of mineral fines into the atmosphere as hereinbefore described. It appears that the molecular weight should be at least about 10,000 in order to secure the desired results. The upper molecular weight limit does not appear to be at all critical and is set only by the practical diificulty of making extremely highly polymerized polymers. Polymers having molecular weights ranging upwards to about 500,000 appear to be quite satisfactory in the practice of the present invention. Those polymers having molecular weights much in excess of 50,000 are diflicult to get into solution or to form dispersions thereof in water. Thus, the insoluble or nondispersible polymers are not included herein. However, so long as the polymer is water-soluble 'or water-dispersi-ble it is operable in carrying out the present invention.
The polymers as described above may be added to or sprayed onto the finely-divided ores, mineral concentrates, mineral fines, flotation or cyanidation failings, coal dust, siliceous dusts, foundry and metallurgical dusts and the like to prevent the dissemination of mineral fines in the atmosphere in amounts ranging from about 0.2 to 15 pounds per 100 square feet of surface area.
The surfaces of certain mineral materials frequently exhibit water-repellency either naturally or because of treatment with chemicals, for example, flotation concentrates which have been treated with hydrocarbons,
fatty acids, and the like to impart water-repellency in.
flotation operations. Such surfaces are frequently diificult to wet and the use of various surface active agents has been found to be of assistance in wetting such materials. Surface active agents of various classes such as those of the anionic, cationic, and nonionic classes are useful for this purpose and may be used in small amounts in conjunction with the polymers hereindescribed. Typical examples of such wetting agents are sulfonated hydrocarbons and sulfated alcohols, acetates and hydrochlorides of long chain amines, and various poly glycol derivatives. Dioctyl sodium sulfosuccinate is a particularly good wetting agent for coal dusts and other mineral dusts.
The surface active agents may be sprayed upon the surfaces of the mineral matters followed by subsequent spraying of the polymer on the surface or by treatment with the polymer in solid form as described above. If desired, the polymer and surface active agent may be added in the same solution. It is to be noted that the surface active agent plays no role in the formation of an impervious layer on the'surface of the mineral matters and which is formed solely by-the action of the hereindescribed polymers; the function of the surface active agent being solely to assist in the wetting, and hence degree of permanency of the disclosed treatment, of difi'iculty wettable mineral matters. 1 1
The invention will be described in further detail in conjunction with the following specific examples, in which the parts are by weight unless otherwise specified.
EXAMPLE 1 Tailings from the cyanidation of a South African gold ore were dried in enamel plates to produce a sample about 9 inches in diameter and 11.5 inches deep. The surfaces of the samples were sprayed with the sodium salt of hydrolyzed polyacrylonitrile as 1% solutions and allowed to dry. The samples were then placed under a laboratory stirrer equipped with a round stiff brush 4" in diameter) under a 450 gram load. The stirrer was revolved at approximately 1000 rpm. and a determination was made of the time required for the revolvingbrush to penetrate $4" of surface. The results are shown in the following table:
Table I Average time (min.) to Penelb. of Pol er er 100 sq. ft.
m p trate 56 inch EXAMPLE 2 Following the procedure of the preceding example, another tailing sample was sprayed with various ionic, linear, addition polymers and salts as specified below as 1% solutions. The polymeric materials used and the abrasion results are shown in the following table. In all tests except the control, the polymer or salt was used in the amount of 1.01 lb./100 sq. ft.
A third sample of tailings was treated with cation-active polymers in the amounts of 1.01 lb./ 100 sq. ft. The polymers were used as 1% solutions and were sprayed on the tailings which after a two-day drying period, were subjected to abrasion tests as described above. The test results are shown in the following table:
Table III Penetration Polymer Used Time (minutes) None-control test 0. 36 Gfplymer of 50:50 methylolacrylemide and Compound 1 20 Polymer of 50:25:25 methylolacrylamide, ethyl acrylate and Compound A 1 10.00 Polymer of 45:45:10 ethyl acrylate, acrylamide and Compound A 10. 00 Quaternized copolymer of vinyl alcohol and morpholinylethylvin ether 1. 67 Oopolymer of 89:11 butadiene and 2-vinyl pyridine 0. 94 Oopolymer of butadiene-2-vinyl pyridine-acrylic acid (approx. :10:10) 0.92 Polydimethylaminostyrene quaternized with benzyl ohlnrirlo 0. 70 Polydimethylaminostyrene quatemized with allyl ohloririe 0. 56
1 O om p oun d A acrylamidopropylbenzyldimethyl am 111 on ium chloride.
EXAMPLE 4 A sample of lead-zinc flotation concentrates was sprayed with a 1% solution of the sodium salt of hydrolyzed polyacrylonitrile. The polymer was used in amounts of 1.01 lb./ sq. ft. of concentrate surface. A similar test was run as a control in which an equal volume of water (no polymer present) was sprayed upon the concentrate surface. The results of abrasion tests conducted, as described above, on the two samples of concentrate Time (min.) Sample to pene trate No polymer 0. 25 Polymer treated 0. 76
EXAMPLE 5 A flotation tailing was treated with 1.01/100 sq. ft. of the sodium salt of hydrolyzed polyacrylonitrile and allowed to air dry. The dried tailing product presented a firm surface resistant to pressure and to abrasion and was immobile to air currents. This tailing without the above treatment was blown readily by air currents.
EXAMPLE 6 The sodium salt of hydrolyzed polyacrylonitrile was applied in water solution as a fine spray to the surface of an airdried cyanidation tailing. Several sprayings were made to different portions of this tailing and the quantity of the polymer used was varied. 0.20 to 15.0/ 100 sq. ft. of exposed surface were applied in this manner and in all cases a firm surface layer resulted.
EXAMPLE 7 A fine dust, mainly silica, was treated with a solution of the sodium salt of hydrolyzed polyacrylonitrile in amoimts of 1.01 lb./100 sq. ft. The surface on drying showed no tendency towards blowing.
A second lot of this silica dust was similarly treated with a solution of the one-half calcium salt of a hydrolyzed 1:1 copolymer of vinyl acetate-maleic anhydride in amounts of 1.01 lb./100 sq. ft. Generally similar results were obtained.
EXAMPLE 8 The surface of a coal dust was wet down with water containing a small percentage of dioctyl sodium sulfosuccinate and then sprayed with a water solution of the sodium salt of hydrolyzed polyacrylonitrile in amounts of 0.75, 1.0, and 1.25 lb./100 sq. ft. of dust surface. A firm surface layer resulted which was not disturbed when a current of air was blown over the three separate test areas.
EXAMPLE 9 EXAMPLE 10 A sample of the dust obtained in grinding steel, a mixture of finely-divided metal particles, iron oxides, wheel grit and binder was treated with a 1% solution of the sodium salt of hydrolyzed polyacrylonitrile in, amounts of 0.006 lb. of polymer per square foot. A firm surface resulted which was resistant to movement by currents of air.
EXAMPLE 11 A sample of dust from a steel foundry, containing fine silica, metallic particles, metallic oxides, mineral fillers, and charred decomposition products of the cereal flours, oils, resins, plumbago, etc. used as mould binders, was treated with a 1% solution of the sodium salt of hydrolyzed polyacrylonitrile. The polymer was used as a 1% solution in water and was employed in amounts of 0.015 lb./sq. ft. of surface. The treated dust was allowed to dry and formed a firm, hard surface which resisted movement by air currents.
1. The combination with a mass of cyanidation tailings of a thin layer of said cyanidation tailings and a compound selected fromthe group consisting of watersoluble, ionic, linear addition polymers of polymen'zable monoethylenically unsaturated compounds having an average molecular weight of at least 10,000, and salts thereof, in amounts of from 0.2 to 15 pounds per square feet of surface area, said layer forming a protective crust on the surface of said cyanidation tailings.
2. The method of preventing the dissemination of cyanidation tailings into the atmosphere which comprises contacting the surface of finely-divided cyanidation tail ings in the presence of moisture and without substantial disturbance of the surface thereof with a water-soluble, ionic, linear, addition polymer of acrylic acid having an average molecular weight of at least about 10,000, in amounts of from about 0.2 to 15 pounds per 100 square feet of surface area thereby forming a protective crust on the surface of the cyanidation tailings.
3. The method of preventing the dissemination of cyanidation tailings into the atmosphere which comprises contacting the surface of finely-divided cyanidation tailings in the presence of moisture and without substantial disturbance of the surface thereof with the sodium salt of a hydrolyzed polymer of acrylonitrile having an average molecular weight of at least 10,000 in amounts of from about 0.2 to 15 pounds per 100 square feet of surface area thereby forming a protective crust on the surface of the cyanidation tailings.
References Cited in the file of this patent UNITED STATES PATENTS 705,698 Ofiicer et al July 29, 1902 1,995,598 Archibald Mar. 26, 1935 2,204,781 Wattles June 18, 1940 2,234,140 Falconer et al Mar. 4, 1941 2,329,694 Bodman Sept. 21, 1943 2,448,605 Kleinicke Sept. 7, 1948 2,625,529 Hedrick et al Jan. 13, 1953 2,651,883 Hedrick et al. Sept. 15, 1953 2,651,885 Hedrick et al. Sept. 15, 1953 OTHER REFERENCES Kingery: Some Preliminary Data on Methods For Allaying Coal Dust in Tipples and Cleaning Plants, LC. 7248, August 1943, PP. 5 and 6.