Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/24—Binding; Briquetting ; Granulating
  • C22B1/2413—Binding; Briquetting ; Granulating enduration of pellets
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/24—Binding; Briquetting ; Granulating
  • C22B1/2406—Binding; Briquetting ; Granulating pelletizing
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B1/00—Preliminary treatment of ores or scrap
  • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
  • C22B1/24—Binding; Briquetting ; Granulating
  • C22B1/242—Binding; Briquetting ; Granulating with binders
  • C22B1/244—Binding; Briquetting ; Granulating with binders organic

Definitions

• This invention relates generally to methods for agglomerating or pelletizing mineral ore concentrate. More specifically, this invention relates to methods for agglomerating or pelletizing mineral ore concentrate using water soluble polymer binder systems in either water-in-oil emulsions or as dry powders.
• Mineral ore concentrates can include iron oxides, copper oxides, barytes, lead and zinc sulfides, and nickel sulfides.
• Agglomerates of coal dust and nonmetallic minerals used to make bricks or ceramics are also formed. Agglomerate forms can include pellets, briquettes, and sinters.
• Methods of pelletizing mineral ore concentrate are frequently used in mining operations where the ore is a low grade iron ore.
• low grade iron ores are taconite, hematite, and magnetite. Numerous other low grade ores exist wherein pelletizing of the ground particles is beneficial to the handling and shipment of the mineral ore.
• an ore is passed through a 100 mesh (0.149mm) screen.
• the screened mineral ore is known as a "concentrate".
• taconite mineral ore concentrate after grinding and screening has an average moisture content of between about 6 to about 11 percent.
• the moisture content of the mineral ore concentrate can be selectively altered.
• the moisture content affects the strength of the- pellets that are formed later in the process.
• the mineral ore concentrate is transported on a first conveyor means to a balling drum or another means for pelletizing mineral ore concentrate.
• a binding agent Prior to entering the balling drum, a binding agent is applied or mixed into the mineral ore concentrate. Commingling the binding agent with the mineral ore concentrate occurs both on the conveyor means and in the means for pelletizing. The binding agents hold the mineral ore concentrate together as pellets until after firing.
• Balling drums are apparatuses comprising long cylindrical drums which are inclined and rotated.
• the mineral ore concentrate is simultaneously rotated about the balling drum's circumference and rolled in a downward direction through the drum. In this manner the mineral ore concentrate is rolled and tumbled together to form roughly spherical-shaped pellets.
• the pellets grow in size and weight they travel down the incline of the drum and pass through the exit of the drum at which point they are dropped onto a second conveyor means which transports them to a kiln for firing.
• agglomerates begins with the interfacial forces which have a cohesive effect between particles of mineral ore concentrate. These include capillary forces developed in liquid ridges between the particle surfaces. Numerous particles adhere to one another and form small pellets. The continued rolling of the small pellets within the balling drum causes more particles to come into contact with one another and adhere to each other by the capillary tension and compressive stress. These forces cause the union of particles in small pellets to grow in much the same manner as a snowball grows as it is rolled.
• pellets After the balling drum operation, the pellets are formed, but they are still wet. These pellets are commonly known as "green pellets" though taconite pellets, for example, are usually black in color. Green pellets usually have a density of about 130 Ib/ft 3 in sizes between about 1/2 inch and about 3/8 of an inch. The green pellets are transported to a kiln and heated in stages to an end temperature of approximately 2800°F. After heating, fired pellets are extremely hard and resist cracking upon being dropped and resist crushing when compressed.
• Two standard tests are used to measure the strength of pellets whether the pellets are green pellets or fired pellets. These tests are the "drop" test and the “compression” test.
• the drop test requires dropping a random sampling of pellets a distance, usually about 18 inches or less, a number of times until the pellets crack. The number of drops to crack each pellet is recorded and averaged. Compression strength is measured by compressing or applying pressure to a random sampling of pellets until the pellets crumble. The pounds of force required to crush the pellets is recorded and averaged.
• the drop and compressive test measurements are important because pellets, proceeding through the balling drum and subsequent conveyor belts, experience frequent drops as well as compressive forces from the weight of other pellets travelling on top of them.
• the tumble strength of fired pellets can also be tested.
• the tumble strength test is designed to measure impact abrasion resistance of fired pellets.
• To test tumble strength equal weight samples of a selected size of pellets such as 1/2 inch pellets are rotated in a drum at a standard speed for equal amounts of time. The sample of fired pellets is then removed from the drum and sized on a 1/4 inch screen. The amount of small particles and fines that pass through the screen is compared between samples. High percentages of fines indicate that, during shipment, the pellets can be expected to deteriorate. A high rate of deterioration during shipment results in higher costs in smelting the pellets and poor furnace performance. Tumbled test results are also used to calculate a "Q-index".
• the Q-index was derived by the American Society for Testing and Materials (ASTM) and is described in the ASTM publication E279-65T.
• a high Q-index such as a value of about 94 or greater is an indication that the fired pellets are impact and abrasion resistant.
• Thermal shock resistance is a factor which must be taken into consideration in any process for agglomerating mineral ore concentrate. Increases in a pellet's thermal shock resistance improve that pellet's ability to resist internal pressures created by the sudden evaporation of water when the pellet is heated in a kiln. If the pellet has numerous pores through which the water vapor can escape thermal shock resistance is improved. If the surface of the pellet is smooth and continuous without pores the pellet has an increased tendency to shatter upon rapid heating. This causes a concurrent increase in the amount of "fines" or coarse particles in the pelletized mineral ore. A binder which increases the pores formed in a pellet improves that pellet's ability to resist thermal shock.
• Both the binder agent and pelletizing apparatus used to form pellets from a mineral ore concentrate can affect the pellet size distribution obtained during the pelletizing operation. It is desirable to form pellets having a diameter of approximately 1/2". It is also desirable to have a low variation between the diameter sizes of the pellets formed during a pelletizing operation. Pellets having a diameter of more than about 1/2" are less capable of being reduced in a furnace because of their increased surface area. Pellets having a diameter of about 1/2" are easily reduced in a furnace and result. in-fuel efficiency in the operation of the furnace as compared to reducing pellets of larger diameters. Pellets having a size distribution averaging less than 3/8" have an increased resistance to gas flow within a furnace.
• Desirable permeability of pellets to gas flow within a furnace is obtained when the pellets are large, evenly sized, and have an approximately even distribution of surface area. An even distribution of surface area is obtained with spherical pellets as compared to pellets that vary in their geometrical shapes.
• the optimum pellet size for furnace operations is between about 3/8" and about 1/2" diameter.
• Bentonite (montmorillonite) is used as a binding agent in the pelletizing operations for clay mineral ore concentrate such as taconite ore concentrate. Bentonite produces a high strength pellet having an acceptable drop strength, compressive strength, and thermal shock resistance. Bentonite also provides moisture control in the formation of pellets made from mineral ore concentrate. Moisture control in the formation of pellets is important because the rate of growth of pellets increases with increased moisture. This increase in the rate of growth of the pellets is due to the increased efficiency of the agglomerate coalescence. Commercially available bentonite has a typical layer structure, a high particle surface area, and a specific affinity for water.
• Bentonite's ability to-act as a binding agent in pelletizing operations for mineral ore concentrates is believed to result from the immobilization of water contained in a mineral ore concentrate. Bentonite is believed to immobilize water in the mineral ore concentrate by adsorbing free water into the surface layers of the bentonite clay. The addition of bentonite to a mineral ore concentrate decreases the water available for participating in the pelletization of the mineral ore concentrate which leads to a desirable retardation in the pellet growth process during the ball mill operation.
• Bentonite has the disadvantage of increasing the silica content of the pellets that are formed. Bentonite is converted to silica.when pellets containing bentonite are fired at about 2400°F or higher. Bentonite also imparts a significant concentration of alkalis to the pellets. Silica decreases the efficiency of blast furnace operations used in smelting of the ore. For this reason bentonite requires a higher energy expenditure than do organic binders in the blast furnace.
• silica and alkalis in pellets of mineral ore concentrate impacts the hot metal quality and furnace operating efficiency during steel production. For these reasons rigid specifications exist for the presence of these contaminates in pellets of mineral ore concentrates and it is desirable to keep the presence of these contaminates in pellets as low as possible.
• silica separates from the mineral ore in the cohesive zone to form slag.
• the addition of a 1% concentration of bentonite or 24.4 lbs./tonne provide an undesirable 0.85% silica or silicon dioxide (Si0 2 ) and alumina or aluminum oxide (A1 2 0 3 ). This concentration of silica and alumina decreases the iron content of a pellet about 0.6%.
• the quantity of slag is undesirably higher with this concentration of bentonite.
• An increased quantity of slag within the furnace decreases the productivity and fuel rate consumption of the furnace during the smelting operation.
• the increase in slag during the smelting operation resulting from the presence of bentonite in the mineral ore concentrate pellets also affects hot metal sulfur control.
• Other disadvantages of the presence of bentonite in pellets include an increased shipping expense because of the additional weight added to the pellets by bentonite, and an increase in the requirement for limestone and coke during the smelting operation.
• An increase in the limestone and coke used during the smelting operation reduces the amount of iron ore than can be converted to iron at a constant volume within a blast furnace.
• alkalis which are oxides of sodium, potassium, and zinc. These alkalis are reduced in the stack zone of a blast furnace, descend into the blast furnace and are vaporized and recirculated in the stack zone. The phenomenon occurs with alkalis because of the low boiling points of these metals.
• the presence of alkalis in the blast furnace causes both the pellets and coke to deteriorate and form scabs on the furnace wall which increase the fuel rate consumption and decrease the productivity of the smelting operation.
• the decrease of productivity of the smelting operation results from a decrease in the gas permeability of the pellets.
• binding agents have proven to be better binders than bentonite.
• These agents or "ore binding polymers" include organic binders such as poly(acrylamide), polymethacrylamide, carboxymethyl cellulose, hydroxyethyl cellulose, carboxyhydroxyethyl cellulose, poly(ethylene oxide), guar gum, and others.
• organic binders such as poly(acrylamide), polymethacrylamide, carboxymethyl cellulose, hydroxyethyl cellulose, carboxyhydroxyethyl cellulose, poly(ethylene oxide), guar gum, and others.
• organic binders in mineral ore pelletizing operations is desirable over the use of bentonite because organic binders do not increase the silica content of pellets and they improve the thermal shock resistance of the pellets.
• Organic binders burn during , pellet firing operations and cause an increase in the porosity of the pellets. Firing conditions can be modified to improve the mechanical properties of fired pellets for organic binder systems.
• Some organic binders used in mineral ore pelletizing operations are dissolved in an aqueous solution which is sprayed onto the mineral ore concentrate prior to entering the balling drums. This application of an aqueous solution increases the moisture content above the natural or inherent moisture content of the mineral ore concentrate which requires a greater energy expenditure during the firing operation of the pellets. This increased moisture content also causes an increased likelihood of shattering due to inadequate thermal shock resistance during firing.
• Pellet formation is improved with the use of organic binders, but the drop strength and compression strength of the pellet are frequently below that desired or achieved with bentonite.
• binders commonly used for agglomerating mineral ore concentrate include a mixture of bentonite, clay and a soap, Portland cement, sodium silicate, and a mixture of an alkali salt of carboxymethylcellulose and an alkali metal salt.
• the agglomerates made from these binding agents frequently encounter the problems described above of insufficient pellet strength or insufficient porosity for the rapid release of steam during induration with heat.
• these binding agents are usually applied to a mineral ore concentrate in aqueous carrier solutions or as dry powders.
• Aqueous carrier solutions increase the amount of energy required to fire the pellets and increase the incidence of pellet shattering due to inadequate thermal shock resistance.
• U.S. Patent Number 3,893,847 to Derrick discloses a binder and method for agglomerating mineral ore concentrate.
• the binder used is a high molecular weight, substantially straight chain water soluble polymer. This polymer is used in an aqueous solution.
• the polymers disclosed as useful with the Derrick invention include copolymers of acrylamide as well as other polymers.
• the Derrick invention claims the use of polymers in an "aqueous" solution.
• the use of water as a carrier solution for the binding agents increases the moisture of the agglomerates or pellets that are formed. The higher moisture content increases the energy required to fire the pellets and can increase the rate of destruction of the pellets during induration due to the rapid release of steam through the agglomerate.
• organic polymers regardless of the molecular weight of the organic polymer or the form in which it is applied to a mineral ore concentrate can result in formation of pellets having dissimilar geometric shapes.
• the formation of non-uniform, non-spherical pellets results in a greater variation in the surface area of the pellets which results in uneven reduction of the pellets in the furnace during the smelting operation and undesirably higher levels of fines being generated.
• Organic polymers have been used as bentonite extenders wherein the polymers themselves do not significantly add to the strength of the resulting pellets. Additionally, various synthetic and natural resins and modified resins have been used in conjunction - with bentonite to pelletize mineral ores. As disclosed in an article by Das Gupta et al., "Additives To Increase Bentonite Effectiveness In Iron Ore Pelletizing", Society of Mining Engineers of AIME, preprint 78-B-97 at page 1 the use of polymers with bentonite has resulted in less than desirable pellet (1) formation or (2) reducibility and behavior in a blast furnace. Additionally, this article reports undesirable economic factors resulting from high concentration of the resins required to effectively pelletize a mineral ore concentrate.
• the industry is lacking a method for agglomerating mineral ore concentrate utilizing a two component low water polymer binder system, wherein moisture control is provided during pellet formation and wherein the pellets formed from the mineral ore concentrate have high mechanical strength properties.
• This invention is a method for agglomerating a particulate material such as a mineral ore concentrate comprising the commingling of the particulate material with two essential components.
• the two essential components include a first component and a second component of a binder system.
• the first component of the binder system is a binding amount of water soluble, ore binding polymers.
• the polymers are adapted to be selectively usable in at least one of either of two conditions of use. In a first condition of use the polymers are applied to the particulate material as a dry powder. In a second condition of use the polymers are applied to the mineral ore concentrate in a water-in-oil emulsion.
• the second component of the binder system is a clay. The clay is applied to the particulate material to obtain a concentration of up to about 10 pounds per tonne.
• This invention is a method for agglomerating particulate material such as a mineral ore concentrate with a two component binder system.
• the first component of the binder system is one or more water soluble, ore binding polymers in an amount sufficient to bind the particulate material.
• the polymers are applied to the particulate material in at least one of either a water-in-oil emulsion system or a dry powder system.
• the second component of the binder system is a clay which is desirably bentonite.
• the clay or bentonite is applied to the particulate material as a powder to obtain a concentration in the particulate material of up. to about 10 pounds per tonne.
• the commingled polymers, clay, and particulate material composition can be in any sequence.
• the commingled composition then enters a standard means for pelletizing or a balling drum.
• the means for pelletizing further commingles the ingredients and forms wet or "green" pellets.
• the pellets are then transferred or conveyed to a furnace or kiln where they are indurated by heat at temperatures above about 1800°F and more preferably at about 2800°F. After induration, the pellets are ready for shipping or further processing in a smelting operation such as a blast furnace.
• Suitable polymers useful as the first component of the binder system of this invention can include water soluble homopolymers, copolymers, terpolymers, and tetrapolymers.
• the selected polymer is produced by polymerizing its monomeric water-in-oil emulsion precursor.
• Suitable polymers can be anionic, amphoteric, or nonionic.
• synthetic and natural polymers of high or low molecular weights, as characterized by their intrinsic viscosities, can be used. This invention is not limited to polymers of a particular intrinsic viscosity.
• polysaccharides the most desirable of which are members selected from the group consisting of carboxymethyl cellulose, guar gum, hydroxyethyl cellulose and mixtures of these.
• Still other polymers suitable for use in this invention include poly(ethylene oxide) and poly(acrylic acid). These polymers and others act as binders or binding polymers for particulate materials and especially mineral ore concentrates. The concentrations of these polymers that are sufficient to bind particulate materials vary between the polymers.
• Polymers suitable for use with this invention must provide a binding activity to a particulate material and be capable of being used in at least one of two delivery systems.
• the delivery systems are either a water-in-oil emulsion system or a dry powder system.
• Binding polymers suitable for use in this invention are particularly desirable when they are of a high molecular weight. The particular molecular weight of a polymer is not limiting upon this invention.
• Useful measurements of a polymer's average molecular weight are determined by either the polymer's intrinsic viscosity or reduced viscosity.
• polymers of high intrinsic viscosity or high reduced viscosity have a high molecular weight.
• An intrinsic viscosity is a more accurate determination of a. polymer's average molecular weight than is a reduced viscosity measurement.
• a polymer's ability to form pellets of mineral ore concentrate is increased as the polymer's intrinsic viscosity or reduced viscosity is increased.
• the most desirable polymers used in the process of this invention have an intrinsic viscosity of from about 0.5 to about 40, preferably from about 2 to about 35 and most preferably from about 4 to about 30 dl/g as measured in a one normal (N) aqueous sodium chloride solution at 25°C.
• Water soluble polymers include, among others, poly(acrylamide) based polymers and those polymers which polymerize upon addition of vinyl or acrylic monomers in solution with a free radical. Typically, such polymers have ionic functional groups such as carboxyl, sulfamide, or quaternary ammonium groups. Suitable polymers can be derived from ethylenically unsaturated monomers including acrylamide, acrylic acid, and methylacrylamide. Alkali metal or ammonium salts of these polymers can also be useful.
• Desirable polymers for use in this invention are preferably of the following general formula: wherein R, R 1 and R 3 are independently hydrogen or methyl, R 2 + is an alkali metal ion, such as Na+ or K+, R 4 is either
• the alkoxy or acyloxy groups in the polymer can be partially hydrolyzed to the corresponding alcohol group and yield a tetrapolymer of the following general formula: wherein R, R 1 , R 2 +, R 3 , a, b, and d are as previously defined, R 4 is -OR 5 or wherein R 5 and R 7 are as defined previously, c is from about 0.2 to about 20 percent, and e is from about 0.1 to less than about 20 percent.
• the preferred copolymers are of the following formula: wherein R 2 + is an alkali metal ion, such as Na+ or K+, and f is from 5 to about 90, preferably from about 30 to about 60 percent, g is from 5 to about 90, preferably from about 30 to about 60 percent with the proviso that (f)+(g) equal 100 percent, and (d) is an integer of from about 1,000 to about 500,000.
• R 2 + is an alkali metal ion, such as Na+ or K+
• f is from 5 to about 90, preferably from about 30 to about 60 percent
• g is from 5 to about 90, preferably from about 30 to about 60 percent with the proviso that (f)+(g) equal 100 percent
• (d) is an integer of from about 1,000 to about 500,000.
• the preferred terpolymers are of the following formula: wherein R 2 + is Na+ or K+, R 7 is methyl, ethyl, or butyl and f is from about 5 to about 90, preferably from about 30 to about 60 percent, g is from about 5 to 90, preferably from about 30 to 60 percent, h is from about 0.2 to about 20, with the proviso that (f)+(g)+(h) equal 100 percent and d is as previously defined.
• the preferred tetrapolymers are of the following formula: wherein R 1 , R 2 +, R 3 , R 7 , f, g, h, d, and e are as previously defined.
• water soluble polymers for use with this invention include those derived from homopolymerization and interpolymerization of one or more of the following water soluble monomers: acrylic and methacrylic acid; acrylic and methacrylic acid salts of the formula wherein R 8 is a hydrogen atom or a methyl group and R 9 is a hydrogen atom, an alkali metal atom (e.g., sodium, potassium), an ammonium group, an organoammonium group of the formula (R 10 )(R 11 )(R 12 ) NH+ (where R 10 , R 11 and R 12 are independently selected from a hydrogen atom, and an alkyl group having from 1 to 18 carbon atoms (it may be necessary to control the number and length of long-chain alkyl groups to assure that the monomer is water soluble), such as 1 to 3 carbon atoms, an aryl group, such as a benzyl group, or a hydroxyalkyl group having from 1 to 3 carbon atoms, such as triethanolamine,
• X is a monovalent cation such as a hydrogen atom, an alkali metal atom (e.g., sodium or potassium), an ammonium group, an organoammonium group of the formula ( R 17 ) ( R 18 ) ( R 19 ) NH+ wherein R 17 , R 18 , R 19 are independently selected from a hydrogen atom, an alkyl group having from 1 to 18 carbon atoms (it may be necessary to control the number and length of long-chain alkyl groups to assure that the monomer is water soluble) such as 1 to 3 carbon atoms, an aryl group such as a phenyl or benzyl group, or a hydroxyalkyl group having from 1 to 3 carbon atoms such as triethanolamine, or mixtures thereof, and the like.
• R 17 , R 18 , R 19 are independently selected from a hydrogen atom, an alkyl group having from 1 to 18 carbon atoms (it may be necessary to control the number and length of long-chain alkyl groups to
• water-soluble monomers which can be homopolymerized or interpolymerized and useful in the process of this invention are acrylamido- and methacrylamido- sulfonic acids and sulfonates such as 2-acrylamido-2-methylpropanesulfonic acid (available from the Lubrizol Corporation under its trade name, and hereinafter referred to as, AMPS), sodium AMPS, ammonium AMPS, organoammonium AMPS.
• AMPS 2-acrylamido-2-methylpropanesulfonic acid
• sodium AMPS sodium AMPS
• ammonium AMPS ammonium AMPS
• organoammonium AMPS organoammonium AMPS.
• water soluble monomers can be interpolymerized with a minor amount (i.e., less than about 20 mole percent, preferably less than about 10 mole percent, based on the total monomers fed to the reaction) of one or more hydrophobic vinyl monomers.
• R 25 is an alkyl group, an aryl group or an aralkyl group having from 1 to 18 carbon atoms
• R 22 is an alkyl group having from-1 to 8 carbon atoms
• suitable copolymerizable hydrophobic vinyl monomers are alkyl esters of acrylic and methacrylic acids such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, isobutyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, etc.; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, etc.; vinylbenzenes such as styrene, alpha-methyl styrene, vinyl toluene; vinyl ethers such as propyl vinyl ether, butyl vinyl ether, isobutyl vinyl ether, methyl vinyl ether, ethyl vinyl ether, etc.; vinyl halides such as vinyl chloride, vinylidene chloride, etc.; and the like.
• the preferred water soluble monomers of these water soluble polymers are acrylamide, AMPS and sodium AMPS, sodium acrylate, and ammonium acrylate.
• the preferred hydrophobic monomers are vinyl acetate, ethyl acrylate, styrene and methyl methacrylate.
• Examples of suitable polymers for use with this invention in water-in-oil emulsions are listed in Table 1. This table provides a representative listing of suitable polymers for use in the water-in-oil emulsions, but does not encompass every suitable polymer or limit the polymers that can be used with this invention.
• a second class of polymers includes those polymers used with this invention in dry powder form. These polymers must be water soluble, but do not necessarily lend themselves to the formation of water-in-oil emulsions. Typically, polymers which form water-in-oil emulsions are also useful with the invented method as dry powder.
• Tables 2 and 3 represents listings of polymers which are desirable for use with this invention- in powder delivery systems. The powders listed in Table 2 and 3 do not encompass all polymers which can be used as powders in this invention.
• the second component of the binder system of this invention is a material that can be mixed with the particulate material prior to agglomeration which partially dries the resulting green pellets by adsorbing and stabilizing free water or moisture present in the particulate material.
• the second component of the binder system of this invention is a clay. Suitable clays include Wisconsin Clay and most desirably' Bentonite Clay. When the second component of the binder system of this invention is clay it is most desirable to use a pure clay. With the increasing scarcity of high quality moisture absorbing clays such as bentonite, clay compositions wherein, for example, bentonite and an extender or other additive is present can be effective for use as the second component in the binder system of this invention:
• the invertible water-in-oil emulsion system is a suspension of droplets comprised of both water soluble, high molecular weight polymers and water in a hydrophobic substance.
• suitable emulsion systems and methods to form suitable emulsions are-found in U.S. Patent Number 4,485,209 to Fan et al., U.S. Patent Number 4,452,940 to Rosen et al., and the parent application U.S. Serial Number 736,237 of this invention each of which are herein incorporated by reference.
• Desirable hydrophobic liquids used in these emulsion systems are isoparaffinic hydrocarbons.
• a suitable isoparaffinic hydrocarbon is that sold by the e Exxon Corporation known as Isopar M.
• Other suitable hydrophobic liquids for use as the external phase in an emulsion system include benzene, xylene, toluene, mineral oils, kerosenes, petroleum, paraffinic hydrocarbons, and mixtures of these.
• two surfactants are used to form the emulsion.
• a first surfactant is used to form the water-in-oil emulsion system.
• a second surfactant is added.
• the second surfactant is a water soluble inverting surfactant which, is believed, permits the inversion of the water-in-oil emulsion to an oil-in-water emulsion upon contact with the inherent or added moisture present in the mineral ore concentrate.
• the surfactants suitable for use in forming emulsions of this invention are usually oil-soluble having a Hydrophile-Lipophile Balance (HLB) value of from about 1 to about 10 and preferably from about 2 to about 6. These surfactants are normally referred to as water-in-oil type surfactants.
• HLB Hydrophile-Lipophile Balance
• Suitable surfactants include the acid esters such as sorbitan monolaurate, sorbitan monostearate, sorbitan monooleate, sorbitan trioleate, mono and diglycerides, such as mono and diglycerides obtained from the glycerolysis of edible fats, polyoxyethylenated fatty acid esters, such as polyoxyethylenated (4) sorbitan monosterate, polyoxyethylenated linear alcohol, such as Tergitol 15-S-3 and Tergitol-25-L-3 supplied by the Union Carbide Corporation, polyoxyethylene sorbitol esters, such as polyoxyethylene sorbital beeswax derivative, polyoxyethylenated alcohols such as polyoxyethylenated (2) cetyl ether, and the like.
• acid esters such as sorbitan monolaurate, sorbitan monostearate, sorbitan monooleate, sorbitan trioleate, mono and diglycer
• Water-soluble inverting surfactants which can be used include polyoxyethylene alkyl phenol, polyoxyethylene (10 mole) cetyl ether, polyoxyethylene alkyl-aryl ether, quaternary ammonium derivatives, potassium oleate, N-cetyl N-ethyl morpholinium ethosulfate, sodium lauryl sulfate, condensation products of higher fatty alcohols with ethylene oxide, such as the reaction product of oleyl alcohol with 10 ethylene oxide units; condensation products of alkylphenols and ethylene oxide, such as the reaction products of isooctylphenol with 12 ethylene oxide units; condensation products of higher fatty acid amines with five, or more, ethylene oxide units; ethylene oxide condensation products of polyhydric alcohol partial higher fatty esters, and their inner anhydrides (mannitol-anhydride, called Mannitan, and sorbitol-anhydride, called Sorbitan).
• the preferred surfactants are ethoxylated nonyl
• the inverting surfactant is used in amounts of from about 0.1 to about 20, preferably from about 1 to about 10 parts per one hundred parts of the polymer.
• the mixture of both the aqueous phase and the oil phase of the emulsions used in this invention can contain about 20 to about 50 and preferably from about 22 to about 42 percent weight of the hydrophobic liquid and the hydrophobic monomers, based upon the total weight of the composition.
• the aqueous solution used to form the emulsion systems of this invention can contain a mixture of water soluble monomers.
• These monomers have a water solubility of at least 5 weight percent and include acrylamide, methacrylamide, acrylic acid, methacrylic acid, and their alkali metal salts, aminoalkyl acrylate, aminoalkyl methacrylate, dialkylaminoalkyl acrylate, dialkylamino methacrylate and their quaternized salts with dimethyl sulfate or methyl chloride, vinyl benzyl dimethyl ammonium chloride, alkali metal and ammonium salts of 2-sulfoethylacrylate, alkali metal and ammonium salts of vinyl benzyl sulfonates, maleic anhydride, 2-acrylamide-2-methylpropanesulfonic acid, and the like.
• the preferred monomers are acrylamide, acrylic acid, and sodium salt of 2-acrylamido-2-methylpropanesulfonic acid.
• acrylic acid is used as a monomer it is reacted with a base, preferably with an equivalent amount of base, such as sodium hydroxide, so that the sodium acrylate solution has a pH of from about 5.0 to about 10.0, preferably from about 6.5 to about 8.5, depending on the type and amount of base employed.
• a base preferably with an equivalent amount of base, such as sodium hydroxide
• This solution is combined with another water soluble monomer, such as acrylamide, and then with water to form the aqueous phase.
• Hydrophobic monomers which can be useful in forming the emulsion systems of this invention include one or more of vinyl esters such as vinyl acetate, alkyl acrylates such as ethylacrylate, alkyl methacrylates such as methacrylate, vinyl ethers such as butylvinyl ether, acrylonitrile, styrene and its derivatives such as alpha-methylstryrene, N-vinyl carbazole, and the like.
• reactors and catalysts are also used with this invention. These compounds can vary. Examples of suitable reactors and catalysts can be found in the Fan and Rosen patents identified above.
• Emulsions used in this invention are made by any suitable method.
• a desirable method for making emulsions is disclosed in U.S. Patent Number 4,485,209 to Fan. This invention is not limited to a particular emulsion or method for producing an emulsion.
• An advantage to the use of water-in-oil emulsions in the formation of pellets is that the amount of water added to the mineral ore concentrate is greatly reduced from that required to deliver polymers in aqueous solutions, thus resulting in an energy savings upon firing of the pellets. Also, the hydrophobic liquid or oil in the inverted water-in-oil emulsion system is consumed during the firing operation. The burn out of the oil droplets from the interior of the pellets increases the porosity of the pellets in much the same manner as does the burning of the organic binder or polymer from the interior of the pellets. This increase in porosity is believed to improve the release of water vapor from the pellets and decrease the occurrence of thermal shock upon firing of the pellets.
• An additional benefit realized by the use of a water-in-oil emulsion system to deliver a polymer binder to mineral ore concentrate in pelletizing operations is a decrease in the amount of contact time required for sufficient commingling of the polymer binder with the mineral ore concentrate.
• the contact time of a polymer after the emulsion is sprayed onto the mineral ore concentrate need only be sufficient to allow activation of the polymer on the surface of the mineral ore concentrate.
• the amount of time can vary depending upon the emulsion system used and the concentration of the polymer binder within the emulsion system as well as the total amount of polymer binder sprayed upon the mineral ore concentrate.
• sufficient time for commingling of the polymer binder system into the mineral ore concentrate occur by spraying the water-in-oil emulsion onto the mineral ore concentrate just upstream of where the concentrate enters the balling drum.
• Application of a water-in-oil emulsion at the mineral ore concentrate treatment site can be accomplished by applying the emulsion to the mineral ore concentrate through any conventional spraying apparatus.
• the clay is sprinkled from a vibrating hopper or other dispersing means onto the mineral ore concentrate and the composition is conveyed towards the balling drum.
• the activation of the polymers onto the surface of the mineral ore concentrate is rapid, and because the polymers are evenly spread or commingled throughout the mineral ore concentrate, the time required for sufficient commingling to initiate pellet formation is about one minute or less.
• This invention also includes the application of binding polymer systems to mineral ore concentrate that are dry powders.
• the dry powdered polymers are mixed together with the powdered clay or added separately.
• the resulting powder composition is sprinkled onto the mineral ore concentrate as the concentrate is conveyed towards the balling drum.
• the vibration of the conveyor means and the action of the balling drum commingles the powders into the mineral ore concentrate.
• the polymers are adsorbed onto the surface of the concentrate. Suitable contact time can be essentially instantaneous, but often is between about 1 minute to 3 hours or more. Further commingling occurs in the mixing within the balling drum.
• the use of the dry powder polymer embodiments of this invention eliminates the need for emulsion spraying equipment.
• the useful range of the concentration of the polymer on an active basis is between about 0.001 percent to about 0.3 percent based on weight of bone dry concentrate.
• a desirable range is between about 0.001 percent and about 0.1 percent. These ranges are applicable for both dry and emulsified applications of polymer binder systems.
• the most desirable concentration of the polymer when applied to a wet mineral ore concentrate is between about 0.01 and about 2.0 pounds of polymer per tonne of mineral ore concentrate.
• a wet mineral or concentrate has between about 8 and about 11 percent water.
• taconite pelletizing consists of a two step procedure. Initially, seed balls are prepared from the taconite ore using bentonite clay as a binder. These seed balls are passed through screens to obtain seed balls of a size that pass through a #4 U.S. mesh screen having a 0.187 Inch opening, but not through a #6 U.S. mesh screen having a 0.132 inch opening. The seed balls are then used with additional concentrate and the binder of interest to prepare the larger green pellets. Finished green pellets are sieved to be in a size range between 13.2mm to 12.5mm. This can be accomplished by using USA Sieve Series ASTM-E-11-70. Following sieving, the green pellets are tested for wet crushing strength and wet dropping strength. Additional green pellets are dried (not fired) and tested for both dry crushing and dry dropping strength. For the examples cited, all testing was done with either wet or dry green pellets.
• Seed ball formation in these examples is begun with a sample of 900 grams (bone dry weight) of taconite concentrate containing between 8 to 11% moisture.
• the concentrate is sieved through a 9, 10, or 12 mesh screen and spread evenly over an oil cloth.
• 7.0 grams of bentonite clay is spread evenly over the top of the concentrate and mixed until homogenous.
• the mixture is incrementally added to a revolving rubber drum having approximately a 16 inch diameter and a 6 inch cross section. The drum is rotated at 64 revolutions per minute. Humidity is not controlled in these examples.
• the inside of the drum is wet with water from a spray bottle. While rolling, several handfulls of the bentonite-concentrate mixture is added to the drum.
• Distilled water is added when the forming agglomerates begin to develop a dull appearance.
• seed pellets are formed, they are screened to separate and obtain pellets which pass through a #4 U.S. mesh screen, but not through a #6 U.S. mesh screen. Captured fines are re-added to the balling drum and oversized seeds are rejected. The procedure of readding captured fines is repeated several times until sufficient seed pellets of the desired size have been produced. The seed pellets are then rolled for one minute to finish the surface. Formed seed pellets can be placed in a sealed container containing a damp cloth so as to retard dehydration of the pellets.
• Green pellet formation in these examples is begun with a sample of 1800 grams (bone dry weight) of mineral ore containing between 8 to 11% moisture.
• the concentrate is added into a 12 inch diameter Cincinnati Muller and mixed for 1.0 minute. Thereafter, an amount of binder to be used in the example is uniformly distributed over the surface of the concentrate.
• the emulsified polymers are uniformly delivered dropwise from a syringe.
• the powder is dry blended with the clay or added separately and the resulting mixture is then uniformly sprinkled over the concentrate in the muller. The muller is then turned on for three minutes to mix the binder with the concentrate. The uniform mixture is then screened through an #8 U.S. mesh screen.
• Compression testing in these examples is performed by using a Chatillon Spring Tester of a 25 pound range (Model LTCM - Serial No. 567). Twenty green pellets are crushed in the tester within 30 minutes of pellet completion at a loading rate of 0.1 inches per second. The pounds of force required to crush each pellet is averaged for the twenty pellets and is herein called the wet crush strength. An additional twenty pellets are dried for one hour at 350°F. While these pellets are still warm to the touch, the crushing procedure is repeated to obtain the dry crush strength average measured in pounds per square inch (psi).
• Drop testing in these examples is performed with twenty green pellets which are tested within 30 minutes of their formation. These pellets are dropped one at a time from a height of 18 inches onto a steel plate. The number of drops to obtain pellet failure is recorded. Pellet failure is determined when a crack in a pellet of approximately a 0.7 mm or greater occurs. The average for twenty wet pellet drops is reported. Twenty additional green pellets are dried by the procedure set out for the compression test and then each is dropped from a 3 inch height. The average number of drops to obtain pellet failure for twenty pellets is determined and recorded.
• the tumble test measures impact and abrasion resistance of fired pellets. In this test twenty-five pounds of +1/2 inch pellets are rotated in a drum at twenty-five revolutions per minute for eight minutes. This sample of pellets is then removed and sized at 1/4 inch. A high percentage of fines after screening indicates that the pellets will experience undesirably high frequencies of deterioration during shipment. The results of the tumble test are used to calculate the Q-index.
• Desirable pellets have an 18 inch green drop test value at a minimum of about 7 plus or minus about 1. Desirable pellets are also spherical and have a moist or dry surface. Undesirable pellets have a wet surface. Surface appearance descriptors are shown below.
• Pellets having wet drop numbers above about 7.0 and wet crush numbers above about 3.0 are useful to the industry. Pellets having dry drop numbers greater than about 2.0 and dry crush numbers above about 4 are acceptable to the industry. Comparisons of pellet mechanical properties for different binders need to be made at approximately equal pellet moisture contents. Wet pellet properties are important because wet pellets are transported by conveyors and are dropped from one conveyor to another during their movement. Dry properties are important because in kiln operations pellets can be stacked 6 to 7 inches high or more. The pellets at the bottom of such a pile must be strong enough so as not to be crushed by the weight of the pellets on top of them. Dry pellets are also conveyed and must resist breakage upon dropping.
• water-in-oil emulsion refers to a water-in-oil emulsion containing an inverting surfactant.
• the oil phase is Isopar M.
• the polymer binding agent PAM/NaA/VA. is in a mole ratio of 47.5/47.6/4.9.
• the mineral ore concentrate is a taconite ore concentrate.
• This example illustrates plant trial data wherein bentonite was used alone to form green pellets from taconite ore concentrate.
• the bentonite was used with the taconite ore concentrate at a concentration of 15 pounds per tonne.
• the data of this example is provided for comparative purposes and is the control data for comparison with the examples of the invention.
• the results of this example are presented in Table 4.
• Example 1 demonstrates that the 18 inch green drop test values were equivalent (using a plus or minus 1 for experimental error) to the bentonite control of Example A.
• Example 1 The experimental procedure described for Example 1 was also used to produce the pellets of these examples. The results of these examples are presented in Table 6.
• the value of the green drop test for Example 3 doubled when compared to Example 1. This increase in the green drop test value is the result of increasing the polymer binding agent from 0.6 to 0.8 pounds of emulsion per tonne.
• Example 1 The experimental procedure described for Example 1 was used in this example.
• the dose of the PAM/NaA/VA to the taconite ore concentrate is 0.6 pounds of emulsion per tonne and 4 pounds of bentonite per tonne.
• a full size balling drum was uniformly operated for eight hours to provide the green pellets of this example.
• the results obtained for the green pellets are presented in Table 7.
• the fired pellet data for the eight hour run of the balling drum in this example is not obtainable. This data is not available because the steel sample baskets . melted during the test. Fired pellet data was obtained based on a total plant output (6 balling drums) and comprised pellets made with the PAM/NaA/VA polymer binding agent and bentonite system. Data for a bentonite system is provided for comparative purposes. The data represents results obtained from an 8 hour run using only bentonite followed by a 16 hour run using a polymer binder system of this invention followed by a final 8 hour run using only bentonite.
• Example 1 The experimental procedure described for Example 1 was used to prepare and test the samples of green pellets for this example. This example was conducted using a full size commercial balling drum. The system was allowed to equilibrate for about 30 minutes prior to taking data and making the next incremental change of the bentonite dose.
• the polymer binder agent used in this example was PAM/NaA/VA at a dose of 0.6 pounds per tonne of taconite ore concentrate.
• Test number 1 of this example contained no bentonite and the data is presented for comparative purposes only.
• the data of the green pellets obtained in this example are presented in Table 9.
• This example demonstrates the relative surface drying effect of various low doses of bentonite in green pellets.
• the tests were conducted using 6 pounds of bentonite per tonne of taconite ore concentrate provided the best 18 inch drop test and surface appearance.
• Example 6 The experimental procedure described for Example 6 was used to prepare and test the green pellets of this example.
• the polymer binding agent of this example was a PAM/NaA/VA polymer at a dose of 0.8 pounds per tonne of taconite ore concentrate.
• the results of the green pellets obtained from this example are presented in Table 10.
• This example demonstrates that increasing concentrations of bentonite with a polymer binding agent improve green pellet physical characteristics.
• the green pellets obtained with a bentonite dose of 6 pounds per tonne provided the best results of this example and produced an excellent pellet.
• This example demonstrates the significant increase in green drop test values obtained by increasing the dose of the polymer binding agent in a polymer binder system including small doses of bentonite. Also, of note is that the surface wetness of the green pellets is reduced and eliminated as the concentration of the polymer is increased. Even though increased concentrations of the polymer binding agent provide additional dryness to the resulting green pellets it is less expensive to obtain equivalent degrees of dryness by the addition of bentonite than with the use of additional polymer.
• This example demonstrates that a powdered polymer binding agent is operable in the binder system of this invention. This example also demonstrates that doses of the polymer binding agent as high as 0.6 pound per tonne of to taconite ore concentrate are necessary with this polymer binding agent.
• the laboratory experimental procedure described above was used to prepare and test the samples of green pellet of taconite ore concentrate of this example.
• This example uses polymer binding agents of acrylamide with a bentonite dose of 4 pounds per tonne. In each test the polymer binding agent is applied in a water-in-oil emulsion.
• the acrylamide polymer binding agents of this example comprise either all acrylamide monomers or copolymers of poly(acrylamide) and sodium acrylate.
• the laboratory experimental procedure described above was used to prepare and test the sample green pellets of taconite ore concentrate of this example.
• the polymer binding agents used in this example are copolymers of poly(acrylamide) and dimethyl diallyl ammonium chloride (DMDAC) in a water-in-oil emulsion.
• the polymer binding system of this example contains a bentonite dose of 4 pounds per tonne of taconite ore concentrate.
• the example demonstrates that the two cationic copolymers tested, which were 30% active polymers, did not function within the polymer binder system of this invention at the doses tested.
• starch is not operable as a polymer binding agent in the binding system of this invention at the concentration tested.

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• 1986
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