FIELD OF THE INVENTION

[0001] The invention relates to treated iron sinter or green mix for use in a blast furnace. More particularly, the iron sinter or green mix is coated with a chemical treatment.

BACKGROUND OF THE INVENTION

[0002] In a typical metal production process, including iron or steel production processes, metal ore agglomerates are fed to a blast furnace to heat the ore and thereby reduce metal oxides present in the ore to metal. The metal ore is layered and heated with metallurgical coke that also acts as a reducing agent as it is transformed into carbon monoxide by controlled combustion with air. The metal oxidizes into molten metal as the coke burns. The impurities, typically silica and undesirable metal oxides, in the ore form a layer of liquid slag that may be removed before the molten metal is poured. Binders or fluxes, such as lime and calcium may also be added to aid in slag formation.

[0003] The metal ore agglomerates may be fed to the blast furnace as a "green mix." In iron production, green mix is a term of art used to describe the iron- containing material used to produce iron sinter. Green mix usually comprises a combination of raw iron ore powder, iron sinter, iron fines, iron dust, and recycled iron fines and dust. Other materials may also be included in the green mix, such as coke, fluxes, and binder. Fluxes may include dolomite and binder may include lime. The iron sinter is essentially the green mix comprising raw ore powder, agglomerates and metallurgical waste heated to fuse into a porous mass with little change in the chemical properties of the raw iron ore. The resulting product or "sinter" is generally an irregular nodule of metal frequently referred to as "sinter balls" with a diameter ranging from about 3-12 mm. The sinter may be further processed into larger agglomerates in the form of pellets or briquettes. Sinter improves the efficiency of blast furnaces by reducing the amount of ore powder or dust. Ore dust and powder may hinder CO gas distribution throughout the furnace, increase fuel consumption, lower the production capacity, and lower the quality of the metal product.

[0004] Obviously, to maintain the advantages of reduced dust, the sinter should not be easily friable as it is transported or loaded into the blast furnace. In addition, the sinter is typically the largest weight-bearing layer in a blast furnace, thus it should have a mechanical strength to withstand the weight without disintegrating back into powder. In iron production, low-temperature reduction of iron ore is avoided as it can increase dust formation and reduce the quality of the pig iron. Thus, high quality sinter is not easily friable and resists reduction at temperatures below 550 °C. An important metric in measuring sinter quality is the Reduction Degradation Index ("RDI"). Sinter with a low RDI generally has good mechanical strength and reduces at temperatures above 550 °C.

BRIEF DESCRIPTION OF THE INVENTION

[0005] It was surprisingly discovered that treating iron sinter or green mix with a polyaluminum treatment produced an iron sinter that reduced at temperatures above 550 °C and had good mechanical strength. Accordingly, methods for treating iron sinter or green mix is disclosed. In one embodiment, the method may comprise coating an iron sinter with a polyaluminum treatment to a form treated iron sinter. The polyaluminum treatment may comprise at least one anhydrous and/or hydrous polyaluminum salt.

[0006] In another method embodiment, a method of making iron sinter from a treated green mix is disclosed. The method comprises coating a green mix with a polyaluminum treatment to form a treated green mix. The treated green mix may be heated to form an iron sinter. The polyaluminum treatment may comprise at least one anhydrous and/or hydrous polyaluminum salt. In another method, the green mix may comprise at least one material selected from the group consisting of iron ore, iron fines, iron dust, recycled iron fines, recycled iron dust, and combinations thereof.

[0007] In another embodiment, an iron sinter treated with a polyaluminum treatment is disclosed. The polyaluminum treatment may comprise at least one anhydrous and/or hydrous polyaluminum salt. The treated iron sinter may have an improved Reduction Degradation Index (RDI) as compared to untreated iron sinter. The iron in the iron sinter may chemically reduce above 550 °C.

[0008] In another embodiment, a method of smelting iron is disclosed. The method may comprise using an iron sinter treated with a polyaluminum treatment. In another embodiment, the smelting method may further comprise using a green mix treated with a polyaluminum treatment. The polyaluminum treatment may comprise at least one anhydrous and/or hydrous polyaluminum salt.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Fig. 1 shows the RDI of iron sinter at varied dosages of PACH.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0010] It was surprisingly discovered that coating iron sinter with a polyaluminum treatment produced an iron sinter that reduced at temperatures above 550 °C had good mechanical strength. Accordingly, methods for treating iron sinter or green mix is disclosed. In one embodiment, the method may comprise coating an iron sinter with a polyaluminum treatment to form a treated iron sinter. The polyaluminum treatment may comprise at least one anhydrous and/or hydrous polyaluminum salt. Suitable polyaluminum salts include, but are not limited to basic salts with one or more hydroxyl groups. An exemplary basic salt is polyaluminum chlorohydrate with the formula A1 ₂ C1(0H) ₅ (anhydrous) or A1 ₂ C1(0H) ₅ 2H ₂ 0 (hydrous). Suitable polyaluminum salts may also include double or complex salts wherein more than one type of anion is present. Exemplary complex salts include hydrated aluminum chlorosulfate (AlS04Cl6'7H ₂ 0) and the basic complex salt, polyaluminum

hydroxy chlorosulafte ( Al 13 OH ₂₈ C I S0 ₄ ) .

[0011] In another embodiment, the polyaluminum salt may have a formula:

Al„X(3n-2G+k)-m)(Y _j +Y'k)(OH) _m

wherein n may range from 1 to 20; m may range from 0 to 15; j may range from 0 to 5; k may range from 0 to 5; X may be a monovalent ion such as NO3 ^" or a halide such as F ^" , CI ^" , Br, L; Y, if present, may be SO4 ^2" ; and Y', if present, may be S1O3 ^2" .

[0012] Suitable polyaluminum salts include, but are not limited to, polyaluminum chloride (PAC), polyaluminum chlorohydrate (PACH), polyaluminum chlorosulfate (PACS), polyaluminum sulfate (PAS), polyaluminum silicate sulfate (PASS), polyaluminum silicate chloride (PASC), polyaluminum nitrate (PAN), polyaluminum bromide (PAB), polyaluminum fluoride (PAF), and polyaluminum iodide (PAI).

[0013] In another method embodiment, at least one polyaluminum salt may be selected from the group consisting of polyaluminum chloride (PAC), polyaluminum chlorohydrate (PACH), polyaluminum chlorosulfate (PACS), polyaluminum sulfate (PAS), polyaluminum nitrate (PAN), and combinations thereof.

[0014] In another embodiment, the polyaluminum salt may be anhydrous and/or hydrous polyaluminum chhlorohydrate (PACH) with a formula Al _n Cl(3n- m)(OH)m, wherein m may range from 1 to 7 and n may range from 1 to 12. In yet another embodiment, the polyaluminum salt may be polyaluminum chlorohydrate PACH dihydrate with a formula A1 ₂ C1(0H) ₅ -2H ₂ 0.

[0015] The polyaluminum treatment may be an aqueous solution comprising a polyaluminum salt as described above. The concentration of the polyaluminum salt in the aqueous solution may range from about 10 wt% to about 90 wt % of the polyaluminum salt based on a total weight of the polyaluminum treatment. The balance may comprise water. In one embodiment, the polyaluminum treatment may comprise 50 wt% polyaluminum salt and 50 wt% water. In yet another embodiment, the concentration of polyaluminum salt in the aqueous solution may range from about 0.01 to about 500 grams per liter (g/1).

[0016] In one embodiment, the concentration of the polyaluminum treatment to the iron sinter may range from about 1 gram to about 200 grams per metric ton (g/ton). In another embodiment, a concentration of the polyaluminum treatment to the iron sinter may range from about 10 to about 100 grams per metric ton. In yet another embodiment, the concentration may range from about 50 to about 90 grams per metric ton (g/ton).

[0017] The polyaluminum treatment is particularly useful in preparing iron sinter, but may also be useful in preparing metal sinter from other types of metal ore. The iron sinter produced using the polyaluminum treatment has an improved

Reduction Degradation Index (RDI) as compared to iron sinter produced without the polyaluminum treatment. The iron sinter produced using the polyaluminum treatment may chemically reduce at temperatures above about 550 °C and/or have an RDI of less than about 30.

[0018] In another method embodiment, a method of making an iron sinter from a treated green mix is disclosed. The method comprises coating a green mix with a polyaluminum treatment to form a treated green mix. The polyaluminum treatment may comprise at least one anhydrous and/or hydrous polyaluminum salt as described above. The treated green mix may then be heated to form an iron sinter. In one embodiment, the concentration of the polyaluminum treatment to the green mix may range from about 1 gram to about 200 grams per metric ton (g/ton). In another method, the green mix may comprise at least one material selected from the group consisting of iron ore, iron fines, iron dust, recycled iron fines, recycled iron dust, and combinations thereof.

[0019] The green mix treated by coating it with a polyaluminum treatment may be used in any iron sintering process anticipated by those of ordinary skill in the art and is not limited to the specific sintering methods disclosed herein. The treated green mix may produce an improved iron sinter as described above. In one embodiment, the polyaluminum treatment may be an aqueous solution supplied from a continuously stirred storage tank equipped with pipes, one or more spray nozzles, and a pump. The green mix may be on a conveyor belt that passes in close proximity to the spray nozzles such that as the green mix passes past the nozzles, it is coated with the polyaluminum treatment sprayed out of the nozzles.

[0020] The coated green mix may then be charged into a sinter machine. The sinter machine may comprise an ignition zone and a soaking zone. The coated green mix may be fed to the ignition zone and heated at temperatures ranging from about 1150 to about 1,250 °C and then be transferred to the soaking zone and heat soaked at temperatures ranging from about 800 °C to about 1,000 °C thereby producing an iron sinter.

[0021] In another embodiment, the polyaluminum treatment may be added to the mixing process used to produce the green mix. The polyaluminum treatment may be in solution as described above, or it may be added to the green mix in dry or powdered form. The polyaluminum treatment may be added to the mixing process similarly in manner to other additives added at the mixing stage or in any manner anticipated by those of ordinary skill in the art.

[0022] In yet another embodiment, iron sinter may be treated by simply spraying already prepared iron sinter with a polyaluminum treatment. The

polyaluminum treatment may be sprayed onto the iron sinter as described above. Iron sinter treated using this method is suitable for use in smelting iron without further processing.

[0023] In another embodiment, an iron sinter treated with a polyaluminum treatment is disclosed. The polyaluminum treatment may comprise at least one anhydrous and/or hydrous polyaluminum salt as described above.

[0024] In another embodiment, at least one polyaluminum salt may be selected from the group consisting of polyaluminum chloride (PAC), polyaluminum chlorohydrate (PACH), polyaluminum chlorosulfate (PACS), polyaluminum sulfate (PAS), polyaluminum nitrate (PAN), and combinations thereof. In yet another embodiment, the polyaluminum salt may be anhydrous and/or hydrous polyaluminum chlorohydrate (PACH) with a formula Al _n Cl( _3n -m)(OH)m, wherein m may range from 1 to 7 and n may range from 1 to 12.

[0025] In another embodiment, the concentration of the polyaluminum treatment to the iron sinter may range from about 1 gram to about 200 grams per metric ton (g/ton). In another embodiment, a concentration of the polyaluminum treatment to the iron sinter may range from about 10 to about 100 grams per metric ton. In yet another embodiment, the concentration may range from about 50 to about 90 grams per metric ton (g/ton).

[0026] The treated iron sinter may have an improved Reduction Degradation Index (RDI) as compared to untreated iron sinter. The iron in the iron sinter may chemically reduce above 550 °C and/or have an RDI of less than about 30.

[0027] In another embodiment, a method of smelting iron is disclosed. In one embodiment, the iron sinter used may be treated with a polyaluminum treatment as it is fed to the smelter. The iron sinter may be treated using the methods described above. For example, if the iron sinter is fed to the smelter using a conveyor, the iron sinter may be sprayed and coated with the polyaluminum treatment as the sinter passes past nozzles located in close proximity to the conveyor. Optionally, the iron sinter may have been spray coated upstream of the smelter feed conveyor, for example as the sinter left the sintering process or as the sinter was being transferred for storage or transport. In yet another embodiment, the iron sinter used may have been prepared from iron ore or green mix that was treated with the polyaluminum treatment prior to sintering as described above.

[0028] The polyaluminum treatment may comprise at least one anhydrous and/or hydrous polyaluminum salt as described above. In another embodiment, at least one polyaluminum salt may be selected from the group consisting of

polyaluminum chloride (PAC), polyaluminum chlorohydrate (PACH), polyaluminum chlorosulfate (PACS), polyaluminum sulfate (PAS), polyaluminum nitrate (PAN), and combinations thereof. In yet another embodiment, the polyaluminum salt may be anhydrous and/or hydrous polyaluminum chlorohydrate (PACH) with a formula Al _n Cl(3n-m)(OH)m, wherein m may range from 1 to 7 and n may range from 1 to 12.

[0029] In another method, the concentration of the polyaluminum treatment to the iron sinter may range from about 1 gram to about 200 grams per metric ton (g/ton). In another embodiment, a concentration of the polyaluminum treatment to the iron sinter may range from about 10 to about 100 grams per metric ton. In yet another embodiment, the concentration may range from about 50 to about 90 grams per metric ton (g/ton).

[0030] In another embodiment, the smelting method may further comprise using a green mix treated with a polyaluminum treatment. The polyaluminum treatment may comprise at least one anhydrous and/or hydrous polyaluminum salt as described above. In another embodiment, at least one polyaluminum salt may be selected from the group consisting of polyaluminum chloride (PAC), polyaluminum chlorohydrate (PACH), polyaluminum chlorosulfate (PACS), polyaluminum sulfate (PAS), polyaluminum nitrate (PAN), and combinations thereof. In yet another embodiment, the polyaluminum salt may be anhydrous and/or hydrous polyaluminum chlorohydrate (PACH) with a formula Al _n Cl( _3n -m)(OH)m, wherein m may range from 1 to 7 and n may range from 1 to 12. EXAMPLES

[0031] Sintering experiments were performed to test the efficacy of the polyaluminum treatment on the Reduction Degradation Index ("RDI") on iron sinter. First, a fixed quantity of iron sinter balls ("sinter") was placed in an alumina boat and weighed. The sinter was coated by spraying it with a solution of polyaluminum chlorohydrate (PACH) dihydrate having the formula AbCl(OFi)5-2Fi20. The solution was an aqueous solution comprising 50 wt% PACH. The alumina boat with the coated sinter was weighed again and the PACH dosage (g/ton) was calculated. The alumina boat with sprayed sinter was transferred to an autoclave, or tube furnace. The tube furnace was purged with an argon-hydrogen gas mixture for 10 minutes. The argon- hydrogen gas flowrate was then maintained at about 1-2 L/min. The coated sinter was then heated at a ramp rate of 600 °C/2 hours, and then maintained at 600 °C for 30 minutes. The treated sinter was then removed from the furnace and allowed to cool to room temperature.

[0032] After the sinter cooled to room temperature, the sinter was weighed again to obtain a first weight (mi). The sinter was then shaken with a mechanical shaker for 15 minutes and then placed on a 6.33 mm sieve. The weight of the sinter was measured to obtain a second weight {mi). The RDI at 6.33 mm was then calculated according to the formula:

(m ₁ - m ₂ )

RDl6.33mm = 100

m ₁

where (wij— m ₂ ) was the weight of sinter that passed through the 6.33 mm sieve and wij was the first weight of the sinter. The experiments were repeated at different dosages of PACH solution. The results are shown in FIG. 1.

[0033] In one aspect of the invention, a method of preparing a treated iron sinter using a polyaluminum treatment comprising at least one anhydrous and/or hydrous polyaluminum salt is disclosed. The method may comprise A) treating a green mix with the polyaluminum treatment to form a treated green mix and heating the treated green mix to form the treated iron sinter or B) treating an iron sinter with a polyaluminum treatment to form the treated iron sinter.

[0034] In another embodiment, at least one polyaluminum salt may be selected from the group consisting of polyaluminum chloride (PAC), polyaluminum chlorohydrate (PACH), polyaluminum chlorosulfate (PACS), polyaluminum sulfate (PAS), polyaluminum nitrate (PAN), and combinations thereof. In another embodiment, the polyaluminum salt may be anhydrous and/or hydrous polyaluminum chlorohydrate PACH with a formula Al _n Cl( _3n -m)(OH)m, wherein m ranges from 1 to 7 and n ranges from 1 to 12.

[0035] In yet another embodiment, the concentration of the polyaluminum treatment to the green mix or iron sinter may range from about 1 gram to about 200 grams per metric ton (g/ton).

[0036] In another method, the method may comprise A) treating a green mix with the polyaluminum treatment to form a treated green mix and heating the treated green mix to form the treated iron sinter. Alternatively, the method may comprise B) treating an iron sinter with a polyaluminum treatment to form the treated iron sinter. Optionally, the method may comprise both A) and B).

[0037] In another embodiment, the green mix may comprise at least one member selected from the group consisting of iron ore, iron fines, iron dust, recycled iron fines, recycled iron dust, and combinations thereof.

[0038] In another embodiment, an iron sinter treated with a polyaluminum treatment is disclosed. The polyaluminum treatment may comprise at least one anhydrous and/or hydrous polyaluminum salt. The polyaluminum salt may be selected from the group consisting of polyaluminum chloride (PAC), polyaluminum chlorohydrate (PACH), polyaluminum chlorosulfate (PACS), polyaluminum sulfate (PAS), polyaluminum nitrate (PAN), and combinations thereof. In another embodiment, the polyaluminum salt may be anhydrous and/or hydrous polyaluminum chlorohydrate PACH with a formula Al _n Cl( _3n -m)(OH)m, wherein m ranges from 1 to 7 and n ranges from 1 to 12.

[0039] In another embodiment, the iron sinter may have been treated using a method wherein the concentration of the polyaluminum treatment to the iron sinter may range from about 1 gram to about 200 grams per metric ton (g/ton).

[0040] The treated iron sinter may have an improved Reduction Degradation Index (RDI) as compared to untreated iron sinter. Alternatively, the iron in the treated iron sinter may chemically reduce above 550 °C. In yet another embodiment the treated iron sinter may have an improved RDI as compared to untreated iron sinter and the iron in the treated iron sinter may chemically reduce above 550 °C.

[0041] In another aspect of the invention, a method of smelting iron using a treated iron sinter is disclosed. The treated iron sinter may be treated with a polyaluminum treatment comprising at least one anhydrous and/or hydrous polyaluminum salt. In one embodiment, the polyaluminum treatment may have the formula:

Al„X(3n-2G ₊ k)-m)(Y _j +Y'k)(OH) _m

wherein n may range from 1 to 20; m may range from 0 to 15; j may range from 0 to 5; k may range from 0 to 5; X may be a monovalent ion such as NO3 ^" or a halide such as F ^" , CI ^" , Br, Γ; Y, if present, may be SO4 ^2" ; and Y', if present, may be S1O3 ^2" .

[0042] In yet another embodiment, at least one polyaluminum salt may be selected from the group consisting of polyaluminum chloride (PAC), polyaluminum chlorohydrate (PACH), polyaluminum chlorosulfate (PACS), polyaluminum sulfate (PAS), polyaluminum nitrate (PAN), and combinations thereof. Alternatively, the polyaluminum salt may be anhydrous and/or hydrous polyaluminum chlorohydrate PACH with a formula Al _n Cl(3n-m)(OH) _m , wherein m ranges from 1 to 7 and n ranges from 1 to 12. In another method, the concentration of the polyaluminum treatment to the iron sinter ranges from about 1 gram to about 200 grams per metric ton (g/ton).

[0043] In yet another method, the method may further comprise using a green mix treated with the polyaluminum treatment to prepare the treated iron sinter. In another method, the method may further comprise forming an iron sinter and subsequently treating the iron sinter with the polyaluminum treatment to form the treated iron sinter. Alternatively, the method may comprise using both a green mix and iron sinter that have been treated with the polyaluminum treatment.

[0044] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal langi of the claims.

[0045] What is claimed is: