WO2025178799A1 - System and method for converting waste smelter slag into pig iron and silicia-based products - Google Patents

Abstract

A system for forming spherical silica-based products and pig iron from waste smelter slag. The system includes a furnace having a fill port, a first opening towards a bottom of the furnace, and a second opening towards the bottom of the furnace, the first opening being positioned below the second opening. The furnace is configured to receive a slag mixture via the fill port, heat the slag mixture until the slag mixture becomes molten causing a metallurgical reduction reaction that separates the pig iron from glassy material, remove the pig iron from the furnace using the first opening, and remove the glassy material from the furnace using the second opening.

Description

SYSTEM AND METHOD FOR CONVERTING WASTE SMELTER SLAG INTO PIG IRON AND SILICA-BASED PRODUCTS

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Patent Application No. 63/556,529, filed on February 22, 2024. U.S. Provisional Patent Application No. 63/556,529 is incorporated herein by reference.

BACKGROUND

TECHNICAL FIELD

The invention relates generally to waste slags and, more particularly, but not by way of limitation, to a method of and system for conversion of copper smelting slag into products such as, for example, pig iron and silica-based glass-like products.

HISTORY OF RELATED ART

Copper-rich ore that is mined to produce copper also contains iron. During smelting of the copper-rich ore, copper matte is extracted but iron is not. The iron remains a portion of undesirable impurities that float to top of molten copper matte and are removed and discarded as waste product. For every ton of molten copper matte produced, there is approximately 2.2 tons of waste slag produced. There is approximately 30% elemental iron trapped within the waste slag. There are approximately over 120 copper smelters operating in 21 different countries all over the world. With current copper production rates, the world is producing over 24 million tons of waste slag every year. Trapped within the waste slag is over 7 million tons of elemental iron.

Unprocessed waste slag is used for producing, for example, abrasives, roofing granules, road-base construction, railroad ballast, aggregate fillers in concrete or the like. However, none of these uses has had an impact on reducing the amount of accumulating waste slag that litters the earth. BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of various embodiments of the present invention may be obtained by reference to the following Detailed Description when taken in conjunction with the accompanying Drawings wherein:

FIG. 1 illustrates an exemplary system to convert slag into pig iron and silica-based glasslike products; and

FIG. 2 is a flow diagram of an illustrative process for converting slag into pig iron and silica-based glass-like products.

SUMMARY

A system for forming spherical silica-based products and pig iron from waste smelter slag. The system includes a furnace having a fill port, a first opening towards a bottom of the furnace, and a second opening towards the bottom of the furnace, the first opening being positioned below the second opening. The furnace is configured to receive a slag mixture via the fill port, heat the slag mixture until the slag mixture becomes molten causing a metallurgical reduction reaction that separates the pig iron from glassy material, remove the pig iron from the furnace using the first opening, and remove the glassy material from the furnace using the second opening.

A method for forming spherical silica-based products and pig iron from waste smelter slag. The method includes receiving, via a fill port of a furnace, a slag mixture, heating, in the furnace, the slag mixture until the slag mixture becomes molten causing a metallurgical reduction reaction, and separating the pig iron from glassy material. The method further includes removing, via a first opening of the furnace, the pig iron and removing, via a second opening of the furnace, the glassy material.

A method for forming silica-based products and pig iron from waste smelter slag. The method includes forming a solid slag mixture by adding and mixing into the slag at least one of coal, coke, lime, limestone, and dolomite and heating, in a furnace, the solid slag mixture to a molten state. Prior to cooling, separating, in the furnace, molten pig iron from molten silica glass, pouring the molten pig iron into molds, cooling the molten silica glass, and crushing the molten silica glass to shapes and sizes applicable to end use.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

While the making and using of various embodiments of the present disclosure are discussed in detail below, it should be appreciated that the present disclosure provides many applicable inventive concepts, which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative and do not delimit the scope of the present disclosure. In the interest of clarity, not all features of an actual implementation may be described in the present disclosure. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

Pig iron is an alloy of iron and carbon and is typically manufactured from iron ore. Pig iron is typically not useful as a direct material but is often intended for remelting and is a principal component of a charge make-up used by high quality steel mills and ferrous foundries to produce, for example, steel, cast iron, wrought iron, or other forms of high purity iron. Pig iron has a lower melting point than scrap steel. A lower melting point combined with a denser charge make-up results in lower energy requirements and faster melting time when compared to that of an all-scrap steel charge make-up. The current annual worldwide production of pig iron is 1.2 billion metric tons. The largest producer of pig iron is China with 60-70% of worldwide total. The United States produces 2-3% of the worldwide total and imports $3B of pig iron annually. Of the pig iron produced in the United States, over 95% is produced at steel mills and transported in molten form to steelmaking furnaces located at the same site.

Metal ores are found throughout the globe in impure states. When unearthed, these metals are usually mixed with other impurities. The smelting process is used to extract the metal from its ore origins and separate it from impurities. In most cases, the smelting process is carried out at temperatures higher than, for example, the melting point of the metal. Once in a molten metal bath, the impurities can be separated and removed from the molten metal based on differences in density and immiscibility. Once removed, these impurities are then categorized as “slag”. The process is used in, for example, copper smelters, iron blast furnaces, and steel recycling facilities. Slags rich in iron are referred to as ferrous slags, and those deficient in iron are referred to as non-ferrous slags.

More specifically, the smelting process is normally carried out in batch-operated converting furnaces where the molten metal sinks to the bottom and the molten slag floats on top. Slag is usually tapped from a smelter furnace at the end of each batch processing period. The slag stream is often water-quenched, the preferred practice, to form granules that can be easily handled after dewatering. A far less frequent practice is pouring the slag directly onto the ground to cool and harden. Slag that has been rapidly cooled, as in quenching, displays an amorphous or glassy microstructure. Slag that has been cooled slowly exhibits a crystalline microstructure. Slag feed material of either amorphous or crystalline microstructure may be used interchangeably in the process described below.

Some uses have been found for unprocessed waste copper slag such as, for example, abrasives, roofing granules, road-base construction, railroad ballast, and aggregate fillers in concrete. However, none of these uses has had an impact on reducing the amount of slag that litters the earth as waste. Until now, there has never been an economical commercial method for separating iron and glass from the smelter slag and making products such as, for example, pig iron and silica-based glass-like products from the slag.

A conventional way to produce pig iron from iron ore includes an extraction process that requires smelting in large furnaces at temperatures in excess of, for example, 2700°F. A fuel such as, for example, coke, carbon, or other sources of carbon and a flux such as, for example, lime, limestone, dolomite, or the like are added to the iron ore. The molten iron is separated and directed into molds known as pigs. This “pig iron,” also known as crude iron, is an intermediate form of iron. The pig iron can be further refined to produce, for example, steel, cast iron, wrought iron, or the like. It takes approximately 1.5 tons of iron ore to produce 1 ton of pig iron. Exemplary embodiments disclose a low-cost process for making products from waste slag. These products are described as metal and glass-like material, namely, (1) pig iron, for use in the foundry and steel industries, and (2) silica-based products such as, for example, glass beads for use in the oil and gas industry, glass beads for use in the up-and-coming enhanced geothermal industry, fine material cement additive, sand and aggregate for concrete production, pavement aggregate, highway anti-skid aggregate, glass beads and crushed glass for the abrasive media market, garnet substitute, or the like. The process is best suited if the slag comes from copper smelting but may be extended to slags from other commodities and industries. For the production of the products described above, slag is used as the base material. In a typical embodiment, the slag is processed in its molten form at active smelters before cooling and solidifying. Processing the slag in molten form reduces energy requirements. Through research and discovery, it has been determined that when suitable fluxes and material additives are introduced, in measured proportions, during the mixing and melting process of the slag, then proper chemical analysis for the pig iron is achieved, and crush strength and chemical resistance of the silica-based products are greatly enhanced.

In a typical embodiment, pig iron may be produced from industrial waste and does not require mining of the earth’s natural resources. The waste copper smelter slag is charged into large furnaces at temperatures in excess of, for example, 2700°F. A fuel such as, for example, coke, carbon, or other sources of carbon and a flux such as, for example, lime, limestone, dolomite, or the like are added to the waste slag. The molten iron is separated and directed into molds known as pigs. It takes approximately 3.3 tons of waste slag to produce 1 ton of pig iron.

FIG. 1 illustrates an exemplary system 100 used to convert slag into pig iron and silica- based glass-like products. The system 100 includes a furnace 102. In a typical embodiment, the furnace 102 may be, for example, a preheated batch, induction, or continuous arc furnace. In other embodiments, the furnace 102 may be, for example, an efficient melting furnace operated as an all-electric, fossil fuel fired, or alternatively a furnace that uses electric melting and fossil fuel top firing, can be used. An all-electric furnace is preferred.

A fill port 101 is positioned for delivering a mixture 110 of for example, solid slag, flux, and fuel into the furnace 102. Once introduced into the furnace 102, the mixture 110 is heated until the mixture 110 becomes molten and causes a metallurgical reduction reaction that separates elemental iron from glassy material. Due to the density of the iron, iron migrates towards the bottom of the molten mass and allows glassy material to remain on top. The furnace 102 includes a first opening 103 positioned towards a bottom region of the furnace 102 and a second opening 106 that is positioned above the first opening 103. In a typical embodiment, the slag is processed in its molten form at active smelters before cooling and solidifying. Processing the slag in molten form reduces energy requirements. Through research and discovery, it has been determined that when suitable fluxes and material additives are introduced, in measured proportions, during the mixing and melting process of the slag, then proper chemical analysis for the pig iron is achieved, and crush strength and chemical resistance of the silica-based products are greatly enhanced.

In a typical embodiment, iron is removed from the furnace 102 in, for example, a batch or continuous manner using the first opening 103. The iron flows into, for example, pig iron molds 104 that are fixtured to a conveyor-style machine where they cool and eventually drop out and form solid pig-iron product 105. After the iron has been separated from the slag, the leftover material is a unique glass-like material comprising of, for example, silicon dioxide, calcium oxide, iron oxide, and aluminum oxide. Using different amounts and types of fluxes allows the final composition of the glass-like material to be altered. Various embodiments utilize different cooling methods, crushing methods, and other post-processing methods to create products in different forms that can be used in various industrial applications. More particularly, glass-like material is cooled at different rates and further processed by employing additional steps such as, for example, crushing, grinding, sizing and re-heating. Depending on the steps taken, numerous potential products can be produced such as, for example, irregular-shaped and various-sized aggregates, coarse and fine sand, fine powder, smooth spherical beads, or the like. As with the pig iron, in various embodiments, products are produced from waste material rather than mining of the earth’s natural resources.

In a typical embodiment, the glassy material is removed from the furnace 102 in, for example, a batch or continuous manner using the second opening 106. The glassy material is cooled with, for example, water or air and further crushed to shapes and sizes applicable to end use. In particular, the glassy material may be, for example, quenched into water to generate a granular form of material. Additional crushing and sizing generate fine irregular-shaped grains of material that can be sieved to different mesh ranges such as 50/80 mesh and 80/120 mesh. Utilizing a natural -gas-heated upward draft bead furnace, the grains can be transformed from irregular shapes into near perfectly round and spherical beads.

Figure 1 further illustrates the solidified and crushed glass entering an upward draft beadmaking furnace 107, where the crushed glass becomes spherical beads 108. Additionally, Figure 1 depicts the solidified and crushed glass being formed into different sizes of aggregates 109 (a)-109(d). Glass beads can also be used in the abrasive blast media industry. Glass beads that are currently on the market are made from regular recycled soda lime glass. Beads made in accordance with principles disclosed herein have unique chemistry consisting mainly of silicon dioxide, calcium oxide, iron oxide, and aluminum oxide and due to their higher strength, they have been proven to provide 4 times the number of cycles before breaking down compared to industry standard soda-lime glass beads.

When the glass-like material is tapped from the arc furnace, it can be air cooled and formed into larger pieces that can be further broken up and crushed to the size of common rock-based aggregates. In the construction industry, aggregates comprise 60-80% of concrete and over 90% of pavement mix for constructing roads. Aggregates are also used for base material of roads prior to placing concrete or pavement. It is estimated that it takes 38,000 tons of aggregates to create one mile of one lane for an interstate highway. Current aggregates that are used in the construction industry are taken from the earth’s natural resources, namely rock quarries, where material is crushed and screened to various sizes. The black glassy material made in accordance with embodiments disclosed herein performs well in several common national highway standard tests for wear and durability including, for example, the LA Abrasion Test, Micro-Deval Test, and Mg Sulfate Test.

FIG. 2 is a flow diagram illustrating an illustrative process 200 for converting slag into pig iron and silica-based glass-like products. For illustrative purposes, FIG. 2 will be described herein relative to FIG. 1. The process 200 begins at step 202. At step 204, a mixture 110 of, for example, solid slag, flux (e g., lime, limestone, dolomite, or the like), and fuel (e.g., coke, carbon, or other sources of carbon) is introduced into the furnace 102. At step 206, the mixture 110 is heated until the mixture 110 becomes molten causing a metallurgical reduction reaction that separates elemental iron from glassy material at step 208. Due to the density of the iron, iron migrates towards the bottom of the molten mass and allows glassy material to remain on top. In a typical embodiment, the mixture 110 is processed in its molten form at active smelters before cooling and solidifying. Processing the mixture 110 in molten form reduces energy requirements. Through research and discovery, it has been determined that when suitable fluxes and material additives are introduced, in measured proportions, during the mixing and melting process of the mixture 110, then proper chemical analysis for the pig iron is achieved, and crush strength and chemical resistance of the silica-based products are greatly enhanced.

At step 210, iron is removed from the furnace 102 in, for example, a batch or continuous manner using the first opening 103. The iron flows into, for example, pig iron molds 104 that are fixtured to a conveyor-style machine where they cool and eventually drop out and form solid pig- iron product 105 (step 212). At step 214, the glassy material is removed from the furnace 102 in, for example, a batch or continuous manner using the second opening 106. The glassy material is cooled with, for example, water or air and further crushed to shapes and sizes applicable to end use (step 216). From steps 212 and 216, the process 200 ends at step 218.

Using pig iron in the iron and steel industries include various advantages listed below.

High Purity:

- Quality assured

- Lower detrimental residual elements

- Free from extraneous materials

- More useable iron per ton

Lower Ferro Alloy Additions:

- Consistent chemical composition

- Reduced additions of ferrosilicon, ferromanganese, coke, and recarburisers

Energy Savings:

High density charge Lower coke usage in cupolas

- Faster melting in induction furnaces

- Lower melting point than steel

Reduce Storage Space:

- Higher density reduces required storage space

- Reduce handling and charging

Due to the relatively low cost of the slag, the pig iron and silica-based products can be commercially offered for sale at a lower or similar price structure than silica-based products and pig iron on the market today.

An efficient melting furnace operated as an all-electric, fossil fuel fired, or alternatively a furnace that uses electric melting and fossil fuel top firing, can be used. An all-electric furnace is preferred.

Pig iron ingot casting can utilize forms on a conveyer that run directly underneath the furnaces that are in-line with the evacuation channel-a standard methodology utilized in this case. Additionally, zinc oxide may be gathered and processed as a byproduct of the melting process.

The presence of typical contaminant compounds contained in the slag is not generally detrimental to the end product manufacture or specification. For example, smelter slags that are targeted and analyzed for production normally contain small amounts of copper, lead, zinc, cadmium, chromium, sulfur, tellurium, zirconium, arsenic, cobalt, manganese, antimony, nickel, tin, strontium, barium, titanium, germanium, fluorine, chlorine, potassium, sodium, and/or others. Minor contaminants must be controlled in the pig iron product, namely phosphate and sulfur. However, minor contaminants are not detrimental to the glass product. Glass systems have been abundantly shown to be capable of accommodating minor ingredient contaminants without detriment, as is well-known in glass technology. Various embodiments provide a silica-based glass that has been shown to produce a commercially viable product. The formulation has incorporated into it, by design, sufficient glass formers, fluxes, and modifiers to absorb slag chemistry variation.

Variable slag chemistries can be processed by balancing the additive ingredients, such as coal, coke, or other sources of carbon, lime, limestone, dolomite or the like.

The additives for the proposed production of pig iron and spherical silica-based products may be purchased as raw material, which is readily available as granular or powdered products. For example, raw material in mesh sizes of and smaller have been found to be beneficial. Smaller particle sizes are preferred and will be sought out for the advantages of higher reactivity than the larger sizes. This higher reactivity provides lower energy input as well as shorter processing times.

Conditional language used herein, such as, among others, "can," "might," "may," “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment.

While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the devices or algorithms illustrated can be made without departing from the spirit of the disclosure. As will be recognized, the processes described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others. The scope of protection is defined by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. Although various embodiments have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth herein.

Claims

Claims:

1. A system for forming spherical silica-based products and pig iron from waste smelter slag, the system comprising: a furnace comprising a fill port, a first opening towards a bottom of the furnace, and a second opening towards the bottom of the furnace; wherein the first opening is positioned below the second opening; wherein the furnace is configured to: receive a slag mixture via the fill port; heat the slag mixture until the slag mixture becomes molten causing a metallurgical reduction reaction that separates the pig iron from glassy material; remove the pig iron from the furnace using the first opening; and remove the glassy material from the furnace using the second opening.

2. The system of claim 1, wherein the furnace comprises at least one of a preheated batch, induction and continuous arc furnace.

3. The system of claim 1, wherein the furnace comprises an all-electric furnace.

4. The system of claim 1, wherein the slag is processed in a molten form.

5. The system of claim 1, wherein the slag is processed before at least one of cooling and solidifying.

6. The system of claim 1, wherein the spherical silica-based products comprise glass beads.

7. The system of claim 1, wherein the slag mixture comprises at least one of solid slag, flux, and fuel.

8. The system of claim 7, wherein the flux comprises at least one of lime, limestone, and dolomite.

9. The system of claim 7, wherein the fuel comprises at least one of coke and carbon.

10. The system of claim 1, wherein the pig iron and the glassy material are removed from the molten slag mixture based on differences in density and immiscibility.

11. The system of claim 10, wherein the pig iron migrates towards the bottom of the molten slag and the glassy material remains on top.

12. A method for forming spherical silica-based products and pig iron from waste smelter slag, the method comprising: receiving, via a fill port of a furnace, a slag mixture; heating, in the furnace, the slag mixture until the slag mixture becomes molten causing a metallurgical reduction reaction; separating the pig iron from glassy material; removing, via a first opening of the furnace, the pig iron; and removing, via a second opening of the furnace, the glassy material.

13. The method of claim 12, wherein the furnace comprises at least one of a preheated batch, induction and continuous arc furnace.

14. The method of claim 12, wherein the furnace comprises an all-electric furnace.

15. The method of claim 12, wherein the slag is processed in a molten form.

16. The method of claim 12, wherein the slag is processed before at least one of cooling and solidifying.

17. The method of claim 12, wherein the spherical silica-based products comprise glass beads.

18. The method of claim 12, wherein the slag mixture comprises at least one of solid slag, flux, and fuel.

19. The method of claim 18, wherein the flux comprises at least one of lime, limestone, and dolomite.

20. The method of claim 18, wherein the fuel comprises at least one of coke and carbon.

21. The method of claim 12, wherein the pig iron and the glassy material are removed from the molten slag mixture based on differences in density and immiscibility.

22. The method of claim 21, wherein the pig iron migrates towards the bottom of the molten slag and the glassy material remains on top.

23. The method of claim 12, wherein the first and second openings are located towards a bottom of the furnace.

24. The method of claim 12, wherein the first opening is positioned below the second opening.

25. A method for forming silica-based products and pig iron from waste smelter slag, the method comprising: forming a solid slag mixture by adding and mixing into the slag at least one of coal, coke, , lime, limestone, and dolomite; heating, in a furnace, the solid slag mixture to a molten state; prior to cooling, separating, in the furnace, molten pig iron from molten silica glass; pouring the molten pig iron into molds; cooling the molten silica glass; and crushing the molten silica glass to shapes and sizes applicable to end use.