System and Method for Forming Spherical Silica-Based Proppant and Pig Iron Utilizing Mining Slag

Abstract

Pig iron and spherical silica-based proppant are extracted and produced through the use of formers, fluxes, reductants, and stabilizers, at predetermined specified weight ratios. The base material utilized in this process is slag, typically derived from the mining industry. The slag is delivered and utilized in a manner that allows the adding and mixing of the various materials such as, but not limited to, carbon, calcium oxide, sodium oxide, aluminum oxide, magnesium oxide, and potassium oxide. The formulated mixture is then heated for a predetermined period of time, based upon weight to a liquid state, wherein the molten pig iron is separated from the molten silica glass. The molten pig iron is then poured into molds, and the molten silica glass is atomized into spherical proppant. The process is particularly well suited to slags produced from copper smelting, but can be extended to slags from other commodities and industries.

Claims

1. A system for forming spherical silica-based proppant and pig iron from mining slag, the system comprising: a conduit for conveying slag; a first furnace positioned for receiving the slag from the conduit, the first furnace defining a first opening in the bottom thereof; a second furnace positioned for receiving material from the first opening, the second furnace defining a second opening in the bottom thereof; at least one mold positioned to receive material passing through the second opening; and a conduit for passing material in an upper portion of the second furnace to an atomization chamber having a spinning disc.

2. A method for forming spherical silica-based proppant and pig iron from mining slag, the method comprising: forming a slag mixture by adding and mixing into slag at least one of carbon, calcium oxide, sodium oxide, aluminum oxide, magnesium oxide, and potassium oxide; heating the slag mixture to a liquid state, wherein the molten pig iron is separated from the molten silica glass; pouring molten pig iron into molds; and atomizing molten silica glass into spherical proppant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:

[0050] FIG. 1 depicts a schematic diagram of a continuous process embodying features of the present invention for converting raw slag and its additives into pig iron and silica-based proppant; and

[0051] FIG. 2 depicts a flow chart illustrating steps of a process employing the system of FIG. 1.

DETAILED DESCRIPTION

[0052] The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. Additionally, as used herein, the term substantially is to be construed as a term of approximation.

[0053] Due to the number of different slag compositions, additives, scenarios, and other factors, certain specific numbers, amounts, flow rates, temperatures, times, and the like are not provided herein, but given any particular of compositions, additives, scenarios, and other factors it is believed that specific numbers, amounts, flow rates, temperatures, times, and the like could be readily determined by a person having ordinary skill in the art without undue experimentation.

[0054] 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, this smelting process is carried out at temperatures higher than the melting point of the metal. Once in a molten 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, for example, in 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.

[0055] 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 of slag directly onto the ground to cool and harden.

[0056] 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.

[0057] Referring to FIG. 1, the reference numeral 100 generally designates a system for converting raw slag and its additives into pig iron and silica-based proppant. Accordingly, a conduit 102 for receiving raw slag and additives in the direction of arrow 103 preferably passes through a preheater 104. In one preferred embodiment, preheater 104 is connected via a line 106 for receiving natural gas from a natural gas supply (not shown), but any source of energy may be used, as well known in the art. Conduit 102 is positioned for delivering its contents, raw slag and additives 108, into an initial melt furnace 110, which is preferably an induction furnace, effective for heating raw slag and additives 108 until it becomes a molten mixture 112. Furnace 110 preferably defines an opening 113 in the bottom thereof through which molten mixture 112 may pass to a separation furnace 116, which is also preferably an induction furnace. Separation furnace 116 is configured for heating the molten mixture 112 further until the molten mixture begins to separate into a separated mixture 118 comprising two layers: (1) an iron (pig iron) layer which sinks to the bottom of the melting chamber of the separation furnace, and (2) a glassy constituent (proppant) layer which rises to the top of the melting chamber of the separation furnace 116.

[0058] Furnaces 110 and 116 are preferably provided with susceptors 111 and 117, respectively, for enhancing the effectiveness of the induction heating. Still further, furnaces 110 and 116 are also preferably provided with heat recovery devices 114 configured for capturing heat from the furnaces and using it for other purposes, such as, by way of example, but not limitation, heating steam to run turbines to run electric generators (not shown).

[0059] Separation furnace 116 is provided with a conduit 126 for draining the upper layer of glassy constituent (proppant) to an atomization chamber 128 which channels the glassy constituent to a spinning disc 130, also known as a rotating wheel. Disc atomization chamber 128 preferably has an inverted conical shape, with a diameter at the top of about ten feet. Disc 130 preferably spins at a speed (e.g., about 3,000 RPM) optimized for atomizing the molten enhanced glass.

[0060] The bottom of furnace 116 defines an opening 119 through which the heavier iron (pig iron) layer 120 is drawn off to pig iron molds 122 preferably passing on a conveyer belt 124.

[0061] Referring to FIG. 2, the reference numeral 200 generally designates a sequence of steps for one preferred method performed according to the present invention for forming spherical silica-based proppant and pig iron from mining slag. The method for making the pig iron and silica-based proppant is set forth in a three-stage production process.

[0062] The first stage begins at step 202, wherein raw slag material is mitigated of outside agents being unknowingly introduced into the production process. This is accomplished preferably via a large capacity rotary dryer. This drying step is crucial due to the high explosive manner in which water reacts when introduced to extremely high-temperature environments.

[0063] Next the raw slag material is screened and sized for production. The widths (or lengths) of particles of raw slag are preferably set at about or smaller for optimized production melting efficiencies, though larger widths (or lengths) may be set as desired. The raw material is delivered to the screening plant preferably via belt conveyance. Raw material that meets the sizing requirements moves onto the next production stage. Material/particles exceeding about are sent to a vertical impactor for processing. Large particles are crushed so they may meet the measurement requirements. Once processed, crushed particles are sent back to the initial processing pile to be rescreened.

[0064] At step 204, raw slag material is delivered to a blending/mixing station (not shown) preferably via belt conveyance.

[0065] Various additives, such as, but not limited to, calcium oxide, sodium oxide, aluminum oxide, magnesium oxide, and potassium oxide, are introduced into the delivery stream of material entering the blending station in amounts measured based on the volume, weight, and elemental makeup of the raw slag material, that would be effective for limiting the variance in quality in both produced products, that is, in both the pig iron and the spherical silica-based proppant.

[0066] Carbon, graphite, acetylene black, and the like, are introduced into the stream in specified metered amounts, based on weight and volume effective for facilitating the separation in the molten material into two separate layers: (1) an iron (pig iron) layer which sinks to the bottom of the melting chamber of the separation furnace, and (2) a glassy constituent (proppant) layer which rises to the top of the melting chamber of the separation furnace.

[0067] The mixture then enters a large mixing cylinder (not shown) where the delivered material is blended together in a manner that more evenly distributes the various additives throughout the slag base material.

[0068] At step 206, the slag base material is delivered via conduit 102 to a preheat station 104 preferably via belt conveyance (not shown) where the temperature of the raw slag material is preferably raised to a level between about 700 F.-800 F., though lower or higher temperatures may be used as appropriate. The preheat step dramatically reduces the time spent in the melting phase of production.

[0069] The second stage begins at step 208, wherein the blended preheated mixture is delivered to initial melt furnace 110 which heats the mixture at least until it begins to melt. The initial melt furnace 110 is preferably an induction furnace utilizing a susceptor 111 and is positioned in a manner to deliver molten material directly into the main melt chamber of separation furnace 116. Initial melt furnace 110 preferably receives a continuous flow of the preheated mixture to allow the constant continual delivery of molten material to separation furnace 116.

[0070] At step 210, the molten material is transferred to main melting chamber of separation furnace 116, where the temperature of the molten mixture is preferably raised beyond the melting point to a temperature (e.g., within the range of approximately 2200 F.-3000 F.) and for a period of time sufficient to separate the molten material into two separate layers: an iron (pig iron) layer which sinks to the bottom of the melting chamber, and a glassy constituent (proppant) layer which rises to the top of the melting chamber. The process as described herein enhances the conversion of the molten stream into two products with superior qualities, namely, (1) pig iron and (2) spherical silica-based proppant that preferably meets or exceeds upper specification levels, as outlined by ISO and API of Crush Strength (7,000-15,000 lbs psi), Sphericity (Y 0.9/X 0.9 Krumbein's Chart0.9 API), Roundness (0.9 API), Conductivity, and Chemical Resistance, wherein, according to the ISO standards, namely (ISO) 13503-2, Sphericity is a measure of how close a proppant particle approaches the shape of a sphere. Roundness is a measure of the relative sharpness of corners or of curvature.

[0071] Steps 212-218 constitute the third and final stage of the process. Accordingly, at step 212, once the molten mixture has separated into layers, the pig iron is directed to pig iron molds. The temperature of the remaining molten glass is optionally raised to a temperature (e.g., within the range of approximately 2750 F.-3300 F.) and for a period of time sufficient to reduce the viscosity of the molten glass for proper atomization.

[0072] At step 214, the adjusted molten glass is preferably transferred via heated channels to disc atomizing chamber 128. This step allows the molten glass to be metered at a flow rate and controlled at a temperature optimized for atomization.

[0073] At step 216, disc atomization is preferably achieved by channeling the molten enhanced glass onto spinning disc 130 in a disc atomization chamber 128.

[0074] At step 218, once the molten glass strikes spinning disc 130, it is flung off the edge of the disc into the air allowing it to form into spherical beads. The beads travel about half the diameter of chamber 128 (e.g., about five feet) in the air and then hit the edge of a catch basin, such as a large conical shaped catch basin having substantially the diameter of atomization chamber 128 at the top and conically-shaped downwardly so that solidified beads can funnel downwardly and be easily collected, for example, in a pile 132.

[0075] Precise calculations are preferred to achieve optimal quality output and product field performance. These calculations account for the distance (or the strike distance) between the channeling spout 127 and the atomizing disc, the size of the disc, the rate at which the disc spins, the distance in which the molten beads travel after coming into contact with the disc, the cooling temperature, and the cooling method used. These calculations and measurements provide the quality and sizing of proppant that are required in the marketplace. Due to the number of different slag compositions, additives, scenarios, factors, and the like, specific numbers are not provided herein, but it is believed that they could be readily determined by a person having ordinary skill in the art without undue experimentation.

[0076] Due to the low cost of the slag, the pig iron and spherical silica-based proppant can be commercially offered for sale at a lower or similar price structure than lower quality and lower performing proppants and pig iron on the market today.

[0077] 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.

[0078] Pig iron ingot casting can utilize forms on a conveyer that run directly underneath the furnaces that are in-line with the evacuation channela standard methodology utilized in this case.

[0079] Proppant forming techniques involve atomization processes which are efficient and hence inexpensive to operate because the molten stream for proppant development is provided by the same furnace utilized in the melting and development of the pig iron.

[0080] Additionally, zinc oxide may be gathered and processed as a byproduct of the melting process. The production and management of the zinc oxide are preferably arranged and managed adjacent to the atomization process.

[0081] The presence of typical contaminant compounds contained in 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, as shown by way of example, but not limitation, in the Table below. 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.

[0082] The present invention provides 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.

TABLE-US-00001 TABLE Chemical Analysis of Typical Pig Iron (in weight-percents) CCarbon SiSilicon MnManganese (min-max) (min-max) (min-max) SSulfur PPhosphorus FeIron 3.5-4.5 1.5-3.5 0.5-1.0 0.05 max 0.15 max Balance

[0083] Variable slag chemistries can be processed by balancing the additive ingredients, such as carbon, calcium oxide, sodium oxide, aluminum oxide, magnesium oxide, and potassium oxide.

[0084] The additives for the proposed production of pig iron and spherical silica-based proppant 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.

[0085] It is understood that the present invention may take many forms and embodiments. Accordingly, several variations may be made in the foregoing without departing from the spirit or the scope of the invention. For example, the process of the invention may be performed as a batch process in a manner that would be apparent to a person having ordinary skill in the art based upon a reading of the present disclosure.

[0086] Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claim be construed broadly and in a manner consistent with the scope of the invention.