Composite Particle For Steel Making and Ore Refining

Abstract

Composite particles are used in combination with ore particles in an ore-refining or purification process, such as in a steel- or iron-making process. The composite particles comprise a core, which may be an aggregate of limestone, dolomite, or another ore particle. The core is surrounded by a coating layer of a metal dust and a binder. The metal dust may be iron oxide dust, which, along with limestone, is prevalent in the iron smelting process anyway. In this way, the composite particles help to recycle otherwise wasted and hazardous iron dust. The binder may be mineral clay such as bentonite, montmorillonite or kaolinite, and may comprise about 2-10% by weight of the particle.

Description

BACKGROUND OF THE INVENTION

The present invention relates to improved methods of making steel or other metals using recycled/recovered waste products to make composite particles that can be re-used in the metal-making and ore refining processes. Suitably-sized waste products may be employed as cores and waste fines or dusts may be employed in coatings of the composite particle.

Steel is an alloy of iron and carbon that is typically produced in a two-stage process. In a first “ore-refining” stage, iron ore is reduced or smelted with coke and limestone in a blast furnace, producing molten iron which may be cast into pig iron or carried to the next stage as molten iron. In the second stage, known as “steelmaking”, impurities such as sulfur, phosphorus, and excess carbon are removed and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the exact steel formulation required. Steel mills then turn molten steel into blooms, ingots, slabs and sheets through casting, hot rolling and/or cold rolling. Other metals and alloys may be made in analogous processes of “ore refining” and “metal making.”

Byproducts of the iron- and steel-making process depend, in part, on the particular process used but generally include various slags, sludge and dust. Dust and sludge are collected in the abatement equipment (filters) attached to the iron- and steel-making processes. Sludge is produced from dust or fines in various steelmaking and rolling processes and has a high moisture content. The dust and sludge removed from the gases consist primarily of iron and iron oxides and can mostly be used again in steelmaking. Iron oxides that cannot be recycled internally can be sold to other industries for various applications, from Portland cement to electric motor cores,

However, iron oxide dust is a hazardous substance when inhaled, and therefore somewhat dangerous to handle in large quantities. For example, the MSDS for iron oxides states: “May cause irritation to the respiratory tract. Symptoms may include coughing and shortness of breath. Long term inhalation exposure to iron has resulted in mottling of the lungs, a condition referred to siderosis,” OHSA has set a legal airborne permissible exposure limit (PEL) of 10 mg/m³ averaged over an 8-hour workshift for iron oxide fumes, and 5 mg/m³ for iron oxide dust or particulates. Consequently, if iron oxides are sold as waste or byproducts, they generally must be treated as a hazardous substance and special precautions are required for transport and storage, adding to disposal costs.

In some steel-making plants, iron fines not suitable for direct use in the blast furnace are recycled in various ways. For example, in WO1992/007964, a process for recycling ore fines is described wherein the dust and sludge from the blast furnace and converters is mixed and the mixture is added to the stream of converter slag when the molten slag is poured into a ladle. The stream force draws the mixture down into the molten slag. The resultant slag is solidified, crushed and reintroduced to the blast furnace. Also, Bluescope steel has described a recycle process in which ore fines are mixed with lime fines and coke to agglomerate the fines, followed by sintering in a flame chamber to fuse the fines and coke agglomerate. See, for example: https://www.bluescopesteel.com/media/10538/Reusing%20the%20By-Products1.pdf.

It would therefore be advantageous to find ways to recycle and reuse iron oxide dust and/or other metal dusts or fines without having to dispose of them offsite, and without having to further process them by molten slag, agglomeration or sintering into usable substances.

SUMMARY OF THE INVENTION

The invention relates to composite particles useful for making metal alloys such as iron and steel, the composite particle comprising a core of an aggregate material and a coating surrounding the core, the coating comprising a metal dust such as a iron oxide dust, and a binder. Composite particles so formed may be used like any ordinary ore particle in an ore refining process. Thus, in a first aspect, the invention relates to a composite particle comprising:

an aggregate core;

a coating around the aggregate core, the coating comprising metal dust and a binder.

In some embodiments, the metal dust is iron oxide dust and the aggregate core is a limestone or dolomite particle, or a taconite particle, which are often used in steelmaking anyway, so they is prevalent in steel mills. The cores may be sized to a standard size number of about 7-10, for example 8 to 9. In some embodiments the binder may comprise mineral clay such as the kaolinite, montmorillonite/smectite/bentonite, palygorskite/attapulgite, vermiculite, and minnesotaite groups. In some embodiments, the binder may comprise from about 2% to about 10% by weight of the composite particle, for example about 5%. Thus, the bulk of the composite particle (e.g. from about 90% to about 98% by weight) is the aggregate and iron dust, which are already components used in steelmaking, In some embodiments the metal (e.g. iron oxide) dust may comprise about 20% to about 60% by weight of the composite particle, such as from about 30% to about 50% by weight. The coating is relatively thin, so that the final composite particle may have standard size number from 6-9 or 6-8, only slightly larger than the aggregate core. The composite particles may be formed in a batch rolling process as is known in the art.

In other embodiments, the core may comprise any other ore particle of suitable size, and the metal dust may comprise fines or dusts of any metal useful in making a desired alloy.

In a second aspect, the invention relates a process for making metals or alloys by (1) smelting composite particles described above with other metal ores; (2) cooling the molten ore-melt; and (3) optionally further processing the metal with carbon or other elements and to remove further impurities, and optionally alloying it with other metals. In a particular embodiment, the invention relates a process for making iron and/or steel by (1) smelting composite particles described above having dolomite or limestone cores and iron oxide dust with other iron ore; (2) cooling the molten pig iron; and (3) optionally further processing the steel with carbon and to remove further impurities, and optionally alloying it with other metals.

Other features and advantages of the invention will be apparent from the detailed description that follows.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to composite particles useful for making iron and steel, the composite particle comprising a core of an aggregate material and a coating surrounding the core, the coating comprising iron oxide dust and a hinder. Composite particles so formed may be used like any ordinary ore particle. They also are a means to recycle iron oxide dust—normally a waste byproduct—within in a steel mill.

Those of ordinary skill in the art will realize that the following detailed description of the embodiments is illustrative only and not intended to be in any way limiting. Other embodiments will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference to an “embodiment,” “aspect,” or “example” herein indicate that the embodiments of the invention so described may include a particular feature, structure, or characteristic, but not every embodiment necessarily includes the particular feature, structure, or characteristic. Further, repeated use of the phrase “in one embodiment” does not necessarily refer to the same embodiment, although it may.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. All references cited herein, including books, journal articles, published U.S. or foreign patent applications, issued U.S. or foreign patents, and any other references, are each incorporated by reference in their entireties, including all data, tables, figures, and text presented in the cited references.

Numerical ranges, measurements and parameters used to characterize the invention—for example, angular degrees, quantities of ingredients, polymer molecular weights, reaction conditions (pH, temperatures, charge levels, etc.), physical dimensions and so forth—are necessarily approximations; and, while reported as precisely as possible, they inherently contain imprecision derived from their respective measurements. Consequently, all numbers expressing ranges of magnitudes as used in the specification and claims are to be understood as being modified in all instances by the term “about.” All numerical ranges are understood to include all possible incremental sub-ranges within the outer boundaries of the range. Thus, a range of 30 to 90 units discloses, for example, 35 to 50 units, 45 to 85 units, and 40 to 80 units, etc. Unless otherwise defined, percentages are wt/wt %.

Composite Particles

Composite particles similar to those of the invention are known and described in the art along with various specific embodiments and/or sediment capping systems containing the same. See for reference U.S. Pat. No. 5,538,787, which issued to Nachtman et al. on Jul. 23, 1996, U.S. Pat. No. 5,897,946, which issued to Nachtman et al. on Apr. 27, 1999, U.S. Pat. No. 6,386,796, which issued to Hull on May 14, 2002, U.S. Pat. No. 6,558,081, which issued to Hull on May 6, 2003, U.S. Pat. No. 7,011,766, which issued to Hull on Mar. 14, 2006, U.S. Pat. No. 7,438,500, which issued to Hull on Oct. 21, 2008, and WO 2012/048215 published Apr. 12, 2012, each of which is incorporated herein by reference in their entirety.

The size of the composite particle can range from a small pebble to a large size rock or even larger. Preferably, the composite particle is generally spherical in form, but it can also be other shapes such as oval, egg, oblong, or irregular giving rise to at least one major axis and at least one minor axis. Particles may he sized by reference to their major dimension, which generally gives rise to an average size. Alternatively and more conveniently, particles may be sized by reference to the sieve or mesh size which allows them to pass through, thus generating a maximum size parameter. The AASHTO uses this latter method and attributes a standard “size number” to aggregate or particles that have a particular size distribution as set forth in their Table 1, partially reproduced below. The larger the “size number” the smaller the particle. For example, aggregate particles of standard size number 8 will have a size distribution such that all will pass a 12.5 mm sieve, most (85-100%) will pass a 9.5 mm sieve, only 10-30% will pass a 4.75 mm sieve, etc.

TABLE 1
adapted from AASHTO Standard Sizes of Processed Aggregate
	Aggregate size distributions, given as Percent (mass)
	that passes through each standard laboratory sieve
		19.0	12.5	9.5	4.75	2.36	1.18
AASHTO	25.0	mm	mm	mm	mm	mm	mm
“Size	mm	(¾	(½	(⅜	(No.	(No.	(No.
Number”	(1 in.)	in.)	in.)	in.)	4)	8)	16)
5	90-100	20-55	0-10	0-5	—	—	—
6	100	90-100	20-55	0-15	0-5	—	—
7	—	100	90-100	40-70	0-15	0-5	—
8	—	—	100	85-100	10-30	0-10	0-5
9	—	—	—	100	85-100	10-40	0-10
10	—	—	—	100	85-100	—	—

Composite particles of the invention generally have a major axis dimension of from about ¼ inch to 1 inch or more; more typically from about ⅜ inch to about ½ inch. Alternatively, composite particles of the invention may be sized as are aggregates by the AASHTO standard sizes, and particles having a standard size number from 6 to 9, or from 6 to 8 should be suitable.

Cores

The core of the composite particle may be formed of nearly any material, may comprise from about 10 to about 80% of the major axis dimension and from about 30 to 80% of the total weight of the composite particle. Cores may also be sized as are aggregates by the AASHTO standard sizes, and size numbers 7 to 10 or from 8 to 9 may be used, corresponding generally to major dimensions of about 3/16 to about ½ inch, or from ¼ to about ⅜ inch. Cores may comprise a solid stone or rock core such as a fine aggregate and/or coarse aggregate. Fine aggregate includes small particles such as sand and other sand-sized materials. Coarse aggregate includes larger particles such as gravel, crushed stone, recycled aggregates (from construction, demolition and excavation waste), and manufactured aggregates (for example, furnace slag and bottom ash).

A particularly useful core material in steel making plants is appropriately sized limestone or dolomite aggregates. Other useful core materials—particularly for steel-making—include iron ore or taconite nuggets or pellets. Taconite is a form of low-grade iron ore and it may be mined from various locations including the Mesabi Iron Range, near Hibbing, Minn. To make these pellets, the hard taconite ore is blasted and then ground down with water to a fine powder. The fine iron-rich particles, mostly of magnetite are extracted from the powder by use of magnetism. The wet taconite powder is rolled with clay inside large rotating cylinders. The cylinders cause the powder to roll into marble-sized halls. The balls are then dried and heated until they are white hot. The balls become hard as they cool. The finished product is taconite pellets. Other iron-related minerals that may also be suitable as cores include, for example, Grunerite/Cummingtonite (Mg,Fe)₇Si₈O₂₂(OH)₂; Actinolite Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂; Minnesotaite (Fe,Mg)₃Si₄O₁₀(OH)₂; Greenalite (Fe)_2-3Si₂O₅(OH)₄; and Stilpnomelane K(Fe,Mg)₈(Si,Al)₁₂(O,OH)₂₇.n(H₂O).

Also useful as cores are any “steel slag” pellets or fines as that term is used in the industry. During steelmaking (particularly, the open-hearth method), the addition of limestone or dolomite (calcium compounds) forms complexes with aluminum, silicon and phosphorus to form “slag”—a waste product of steelmaking. Slag floats to the top of the melt, is poured off and placed in piles for disposal. The slag cools so quickly, in fact, that it solidifies as an amorphous, glass-like solid ranging from fine sand particles to large blocks, both of which can be extremely hard. Much of the metallic fraction (the discarded steel products in the pile) is removed with large magnets and sold as steel scrap. The resulting nonmetallic grades have applications in construction and in the present invention. The finest fractions (about No. 8 or smaller) are referred to as “slag fines”. But properly sized slag may serve as cores for the invention.

Cores useful for making other metals or alloys include the cores mentioned above, and also ore particles of any ore used in making the desired metal or alloy.

The core may be more dense, less dense or equally as dense as the coating layer. In an exemplary embodiment, the core has a relatively greater density as compared to that of the coating layer.

Coating Layer

The coating layer of the composite particles may partially or completely encapsulate the core. The coating is made of at least two components: metal dust and a binder. The metal dust is preferably the dust of a metal to be incorporated into the metal or alloy, such as iron oxide dust can be incorporated into the making of steel or iron.

In many embodiments, the binder material is a clay mineral or a mixture of clay minerals that, while not hardening, does generate cohesive strength by the hydration process. Clay is common name for a wide variety of weathered mineral or igneous rock. Various classification schemes, such as the Nickel-Strunz classification, divide up mineral clays according to composition and/or structure. Suitable clays may be found in the kaolinite group, the smectite or montmorillonite group, the attapulgite group and the zeolite group. Generally, these groups contain sheets or layers formed of specific tetrahedral and/or octahedral structures of aluminum and silicon oxides. The layers or platelets are held together by ionic bonds with charged ions (usually cations) located between the layers. The Nickel-Strunz classification (version 10) divides silicates (group 9) into nine different subcategories, the most useful being Phyllosilicates (group 9E) and the Tektosllicates with and without Zeolitic H₂O (groups 9G and GF, respectively). Phyllosilicates (group 9E) are divided into nine subcategories, the most useful being group 9EC (with mica sheets), group 9ED (with kaolin layers), and group 9EE (single tetrahedral nets of six-membered rings). Exemplary days from these groups include kaolinite, montmorilionite (also called smectite and bentonite), talc, mondorite, nontronite, palygorskite or attapulgite, muscovite, vermiculite, saponite, hectorite, rectorite, and minnesotaite. Bentonite is a useful impure clay largely containing montmorillonite.

It is the layers or “platelets” of phyllosilicates that give them many of their properties, including the plasticity for use as pottery. When the layers are of thickness dimensions in the few nanometer range, they are often referred to as nanoclays. An example is the NANOLIN DK series of nanoclays available from Zhejiang Fenghong Clay Chemicals Co., LTD., which are made from highly purified smectite that exhibits ultra-fine phase dimensions. The size of these nanoclays is typically in the range of 1-100 nm; the average fully dispersed thickness of platelets is around 25 nm; the aspect ratio ranges from 100 to 1000.

Modified clays are formed when various processes are used to separate and expand the layers or platelets. Intercalation, exfoliation, and fuming are processes that modify the layered structure. Intercalation inserts a polymer or other molecule between the platelet layers to isolate them, but without much physical separation. Exfoliation, on the other hand, inserts a polymer or molecule and expands the space between layers by 10-20 fold. Fuming is a flaming process that introduces hydroxyl groups onto the surface of the silica structures.

A clay-sized material can also be used, such as gypsum, flyash, cement, or other materials, having an average particle size of less than about 10 microns. The binder material may also include other clay-sized or quasi clay-sized materials such as organophilic bentonite, zeolites, and inorganic oxides of aluminum, iron, and/or manganese.

The binder may be present in the composite particle in amounts from about 2% to about 10% by weight, for example, from about 3% to about 7%, or about 5% by weight.

The second component of the coating layer is the metal dust, of which one embodiment is iron oxide dust. According to the steel industry, iron ore is typically crushed to a size of about 7 mm to about 25 mm for use in the blast furnaces, corresponding roughly to a size number of about 5 to about 8. Particulates smaller than about 6 or 7 mm in size are considered “fines” and are either not used or are re cycled as described in the background. In contrast, “dust” refers to particles that are smaller still, having a particle size in the range of about no more than about a hundred microns; or a size such that essentially 100% passes through a standard No. 150 mesh.

Collection of iron oxide dust generally already takes place in steel making plants to avoid dispersing the hazardous dust. Collection bags or filters may be used, as well as certain types of scrubbers and separators to isolate the iron oxide dust from other useful components that might he in the process stream (e.g. gases and other particulates).

Other metal dusts that may be useful in the coating include aluminum, copper, nickel, chromium, molybdenum, titanium, zirconium, manganese, magnesium, tungsten, cobalt, zinc, silver, platinum, palladium, gallium, indium, tin, and the like, it will be understood that composite particles containing these other metal dusts may be used in metal-making or alloy-making processes analogous to steelmaking, with the selection of composite particle core and dust component of the coating being dependent on the particular metal or alloy to be made.

The metal particle dust may be included in the composite particles in amounts from about 20% to about 60% by weight of the particle, for example from about 30% to about 50% by weight.

Composite Particle Manufacture and Use

The composite particles of the invention can he manufactured by a batch rolling process, using a roller such as a concrete mixer or pugmill. Typically the binder and iron oxide dust will be combined into a mixture that is applied as a coating to the core which has been prewetted with a water-based emulsified hinder. The prewetted cores and coating materials are added to the mixer, and rotation causes the cores to become coated, and compacting of the coating layer on the core may occur as the aggregates fall and collide against the wall of the roller.

Alternatively, the composite particles can be manufacture using processes analogous to those described in the patent literature cited and incorporated herein in connection with composite particles for sedimentation capping systems.

Composite particles are then used in a blast furnace in the same way an aggregate of ore might be used, to smelt into iron, potentially for the ultimate production of steel. These processes of using ore are well known and need not he described in detail herein. The binder material of the coating layer will often vaporize, leaving only the core aggregate and the iron oxide dust—two of the principal components of smelting.

The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.

Claims

1. A composite particle comprising:

a core comprising an aggregate of limestone, dolomite, or taconite;

a coating on the core, the coating comprising a metal dust and a binder material.

2. The composite particle of claim 1, wherein the binder material is selected from Phyllosilicates.

3. The composite particle of claim 2, wherein the binder material is selected from the kaolinite, montmorillonite/smectite/bentonite, palygorskite/attapulgite, vermiculite, and minnesotaite.

4. The composite particle of claim 1, wherein the binder material is present in an amount from about 2% to about 10% by weight of the composite particle.

5. The composite particle of claim 4, wherein the binder material is present at example about 5%.

6. The composite particle of claim 1, wherein the metal dust comprises iron oxide dust.

7. The composite particle of claim 1, wherein the core aggregate comprises from about 30 to about 90% by weight of the composite particle.

8. The composite particle of claim 1, wherein the core is an aggregate sized to a standard size number from about 7-9.

9. The composite particle of claim 6, wherein the iron oxide dust is present in an amount from about 20% to about 60% by weight of the composite particle.

10. The composite particle of claim 9, wherein the iron oxide dust is present in an amount from about 30% to about 50% by weight.

11. The composite particle of claim 1, wherein the composite particle is sized to a standard size number from about 6-9.

12. An iron composition comprising coke, ore and a plurality of composite particles according to claim 6.

13. A steel manufactured from iron made using composite particles according to claim 6.

14. The composite particle of claim 1, wherein the core is a metal-ore particulate.

15. The composite particle of claim 14, wherein the metal dust comprises a metal of the metal-ore particulate.

16. The method of making iron comprising:

smelting a mixture of iron ore, coke, and a plurality of composite particles according to claim 6; and

cooling the molten iron.

17. A method of recycling iron oxide waste dust from a steel- or iron-making operation, the method comprising:

mixing the iron oxide dust with a mineral clay binder to form a coating;

applying the coating as a layer on a limestone or dolomite aggregate core to form a composite particle; and

re-smelting the composite particle with ore and coke.

18. A method of smelting a metal alloy comprising:

smelting a mixture of at least one metal ore and a plurality of composite particles according to claim 1, the metal dust of the composite particle being a component of the metal alloy; and

cooling the molten metal.