WO2015081399A1 - Process for producing a fluidizing composition that can be used in ferrous metallurgy, fluidizing composition that can be used in ferrous metallurgy and use of said composition - Google Patents

Abstract

The present invention relates to a spent potlining-based fluidizing composition that can be used in secondary metallurgy, particularly as a fluidizing agent for secondary steelmaking, and to the process for producing a fluorite- and alumina-based composition produced by crushing and sieving, to a suitable particle size (up to 30 mm), a mixture of waste from the renewal of electrolytic cells used in primary aluminium smelting, which is considered to include insulating fire bricks (pot lining), as well as components from the electrolysis bath, such as alumina (Al₂O₃), cryolite (Na₃AlF₆), aluminium fluoride (AlF₃), optionally carbon cathode material, fluorides from the electrolytic bath, and which also comprises: a. fluorine compounds; b. aluminium compounds; c. sodium compounds; d. silicon compounds; e. calcium compounds; f. iron compounds; g. compounds of other metals such as: magnesium, chrome, titanium, phosphorus, sulphur, potassium, tungsten, etc.; and h. optionally carbon compounds.

Description

 14 000419

 1

Process for obtaining a fluidizing composition for use in the steel industry, a fluidizing composition for use in the steel industry and the use of such composition

Application field

 The present invention comprises a fluidizing composition obtained from a by-product generated in the production of primary aluminum which comprises a fluorite-alumina-based fluidizing composition for use in secondary metallurgy, particularly in the secondary refining of steel.

State of the art

The aluminum production process begins with the extraction of bauxite (aluminum ore), which contains about 40 to 60% alumina or aluminum oxide (Al ₂ O ₃ ). The aluminum oxide refinery uses the Bayer Process to extract the alumina contained in bauxite, a mineral rich in hydrated alumina (AI2O3.3H2O), which contains impurities such as silica reactive (kaolinite) and non-reactive (quartz), iron oxide, organic, among others.

 The first part of the process known as red area is by a process of digestion of bauxite in caustic soda; the hydrated alumina is solubilized in caustic soda liquor at about 150 ° C and is filtered for purification of the liquor, thereby removing the insoluble impurities. In the second stage, also called the white area, precipitation of dissolved alumina occurs in the liquor and subsequent calcination of the aluminum hydrate, where the final product is called aluminum oxide (Al 2 O 3 J). The aluminum oxide in turn is subjected to the process of electrolytic reduction in furnaces, converting alumina into liquid aluminum.

The Hall-Heroult process is by electrolysis in a molten salt bath, where fluxes, such as aluminum fluoride (AIF3) are added in order to lower the melting point of the electrolytic bath. The process consists of electrolysis at approximately 960 ^and C in electrolytic cells (container surrounded by an iron or steel structure) with carbon electrodes (anodes) immersed in the electrolytic bath. Alumina (Al2O3) main raw material is dissolved in the electrolytic bath generating free ions Α ³ and O ² ions. The cathode (negative pole) corresponds to the cathode blocks (blocks arranged in the steel vessel) where the reduction of aluminum ions in metallic aluminum takes place, since its melting point (660,37 ° C) is below the melting point of the mixture and being its higher density, flows to the bottom of the vessel and is subsequently collected by suction.

In the anodes (positive poles) corresponding to the carbon electrodes occurs oxidation of oxygen anions to oxygen gas, which in turn reacts with the carbon electrode forming carbon dioxide (C0 _2).

Electrolytic cells are metal housings coated with insulating materials, refractories, and carbonaceous materials in the form of monolithic and blocks that serve as the cathode of the electrolytic cell. The anode being formed of carbonaceous material is consumed in the electrolytic process by reaction with oxygen.

The electrolytic bath is composed of about 80% cryolite (Na ₃ AIF _e ), 10% aluminum fluoride (AIF ₃ ), 6% fluorite (CaF ₂ ) and 4% dissolved alumina (Al 2 O 3).

 The attached Figure 1 shows an electrolytic primary aluminum collection vessel, with:

 (1) Refractory Coating

 (2) Carbon Coating

 (3) Carbon Anode

 (4) Anodic Tip

 (5) Bus

 (6) Liquid Aluminum

 (7) Power Output

 In the reaction of electrolytic decomposition of the aluminum, it is observed that the cathode is not consumed in the process, but receives the metallic aluminum. However, at the high temperatures involved (of the order of 960 ° C), the presence of sodium, aluminum and calcium fluorides, in addition to other impurities, causes deterioration and consumption of the cathode, necessitating periodic exchange. One of the objects of this invention is to reduce the generation of waste in a sustainable, technically, economically and environmentally correct manner.

 Electrolytic cells have an average life of 3000 days. After the life of the vessel, it is turned off for refurbishment and all the material that constituted it (refractory, cathodic block, and solidified bath) is removed, giving rise to the residue named by Votorantim Metais - Alucoque Brazilian Aluminum Company, known as SPL ("Spent Pot Lining"), that is to say, the residue from the demolition of primary aluminum production electrolytic vats is a by-product known as environmental class I. They exhibit at least one of the following characteristics: flammability, corrosivity , reactivity, toxicity and pathogenicity. About 30 to 50 kg of Alucoque are generated per ton of liquid aluminum produced.

 Among the possibilities to inert the cyanide, there are treatments at high temperatures (above 900 ° C) where this compound is neutralized becoming volatile / inert. Under such conditions, the cyanides are decomposed, the fluorides take the stable form of fluorite, the carbides and nitrides are oxidized and the sodium forms silicate.

As is well known, the processes considered (metallurgy secondary) are characterized by high temperatures and high levels of CaO, in most cases, close to saturation.

Is known in literature, experiments and industrial practice that secondary steel metallurgy processes are characterized by high temperatures and slag of CaO-Si02-03 ₂ AI system, i.e. CaO saturated. In addition, other fluidizing components are employed in the secondary refining of steel such as fluorite and alumina found in Alucoque.

 The present invention proposes the use of Alucoque in secondary metallurgy based on its physicochemical characteristics, theoretical evaluation, experimental evaluation and industrial tests that prove the efficacy of this by-product as a fluidifier of the slag generated in semi-integrated steelworks furnaces.

 JP 2005322610 relates to a molten steel treatment crucible in which the torpedo converter has baked brick containing magnesium oxide and chromium oxide, alumina and / or iron oxide in the free edge portion of high alumina mortar.

 Document RU 2001133182 relates to the preparation of coating for steel using metallurgical alumina waste, which can be used for industrial enamelling. The aim of the invention is to create a coating for steel with a firing temperature of 820 to 850 ° C and a reduced amount of CaO, NiO, MnO, which are expensive, and have the same adhesion strength and quality.

 Obietivos

 The object of the present invention was:

 - make technical, economic and environmental feasible the use of the by-product generated in the production of primary aluminum;

 - develop a sustainable and commercial alternative for the use of the by-product generated in the demolition of electrolytic cells.

 - to develop a fluidizing composition capable of being used in steel refining metallurgy processes.

 Description of the figures

 The invention will be better understood in the light of the attached figures, given by way of example but not by way of limitation, in which:

 Figure 1 shows a primary process vessel for obtaining aluminum by electrolysis

 - Figure 2 ternary diagram of the type CaO - MgO - S1O2 for the fluidifier in laboratory application;

Figures 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 represent CaO - MgO - S1O2 ternary diagrams for the fluidifier in industrial application.

 Brief description of the invention

The invention relates to a composition based on fluorite and alumina which has been obtained from the crushing and sifting in suitable granulometry (up to 30 mm) of the mixture of residues originating from the reforming process of primary aluminum production electrolytic cells which comprises refractory bricks (Al ₃ O ₃ ), cryolite (Na ₃ AIF ₆ ), aluminum fluoride (AIF ₃ ), optionally carbonaceous material, fluorides of the electrolytic bath and which further comprises:

 (a) Fluorine compounds

 (b) Aluminum compounds

 (c) Sodium compounds

 (d) Silicon compounds

 (e) Calcium compounds

 (f) Iron compounds

 (g) composed of other metals such as: magnesium, chromium, titanium, phosphorus, sulfur, potassium, tungsten, etc.

 (h) optionally carbon compounds

Detailed description of the invention

 Physical - chemical characterization of Alucoque:

 It was developed a methodology to make feasible the use of Alucoque fluidizing composition, from the furnace to electric arc (FEA) leakage to the FP (Furnace Panela), in order to act particularly on secondary steel refining.

 Alucoque is a heterogeneous material, composed of refractory and insulating bricks (luminous silica) of the tubular refractory lining, and carbonaceous fraction, both impregnated with electrolyte fluoride. Sodium from the bath is one of the elements that penetrates the most, making the oven bottom with basic characteristics. During the process, small amounts of carbides and nitrides are formed, as well as fluoride compounds from cryolite and fluorine alumina.

 The chemical composition of Alucoque, originating from the process of obtaining aluminum, is shown below by Table 1:

 Sample F Na Mg Al Si P S K Ca Ti Fe W C

 Eur-lex.europa.eu eur-lex.europa.eu

01 19.09 23.33 0.15 33.56 14.18 0.05 0.36 0.85 4.39 0.66 3.25 0.15 9.69

02 20.03 22.97 0.20 33.52 13.60 0.04 0.35 0.73 4.30 0.63 3.49 0.14 9.83 03 18.34 23.19 0.16 33.51 14.59 0.04 0.38 0.80 4.63 0.62 6.60 0.16 10.1

Average 19.15 23.16 0.17 33.53 14.12 0.04 0.36 0.79 4.44 0.64 4.45 0.15 9.87

 Table 1

 The fluorine compounds (a) increase the fluidity of the slags and reduce their melting point. In the desulfurization, the lime efficiency increases, by the rupture of the CaS layer that is formed around the particles. In the formation of liquid slag, with low oxygen potential, they favor the protection against oxidation and improve the absorption of inclusions of the capture slag. They are potentially aggressive to coating.

The fluorine compounds are present in the composition in a content of about 6 to about 40% (preferably 9 to 29%) by weight relative to the total mass of the composition, comprised in the group of compounds comprising fluorite (CaF ₂ ).

 Aluminum compounds (b), such as alumina, are components of various synthetic slags, scavengers and desulfurizers, where they form low-melting calcium aluminates and low oxygen activity. They are also used in distributor and ingot hedge flows. High concentrations are not recommended for pig iron treatment agents.

 The aluminum compounds (b) are present in the composition at a content of from 15 to about 48% (preferably from 23 to 43%) relative to the total mass of the composition, comprised of the group comprising alumina (Al 2 O 3).

 Sodium compounds (c) act as desulfurizers, dephosphants, fluxes and flowing agents. It is a strong base, contributing to the formation of basic and liquid slags can be aggressive to the coating. They are present in the composition in a content of about 8 to about 43% (preferably 13 to 33%) by weight relative to the total mass of the composition, comprised in the set comprising Na 2 O compounds.

 The silicon compounds (d) are present in the composition in a content of about 1 to about 30% (preferably 4 to 24%) by weight relative to the total mass of the composition, wherein silicon compounds present are comprised in the of compounds encompassing S102, etc.

The calcium compounds (e) are present in the composition in a content of about 0.1 to about 24% (preferably between 0.4 and 14%) by weight relative to the total mass of the composition, with calcium compounds present are comprised of the group of compounds encompassing CaO, Ca ₂ SiO 4, etc. The iron (f) compounds are present in the composition in a content from about 0.1 to about 24% (preferably from 0.4 to 14%) by weight relative to the total mass of the composition, with iron compounds present are included in the set of compounds that comprise FeO, FeSi, FeSiMn, Ρβ2θ ₃ , etc.

The other compounds (g) of magnesium, chromium, titanium, phosphorus, sulfur, potassium, tungsten, manganese and the like are present in the composition in a content of about 0.1 to about 10% (preferably 0.14 to 8%) by weight based on the total weight of the composition, with the participation of other elements is in the range of compounds which comprise the Cr203, ΤΊθ2, Go, Mg ₂ SI0 _4, etc.

 The carbon compounds (h) can act as reducing agents, reducing environment generators and fuels. In the desulfurization operations, combining with the oxygen favors the formation of the sulphides. In coating slags, in pans, distributors or ingots (conventional or continuous casting), they delay the melting of the slag promoting thermal insulation. In the injection processes it acts as a lubricant, facilitating the flowability. They are not desirable in the case of low carbon steels.

 The carbon compounds are present in the composition in a content of about 0 to about 25% (preferably 0 to 18%) by weight relative to the total mass of the composition.

 There are, of course, several other characteristics that should be considered, but which, either by low concentrations or by little influence on the process, do not affect the conclusion as to the feasibility of using Alucoque in the proposed application.

 Among possible applications for the described composition besides the application in iron and steel (secondary metallurgy) we can mention co-processing appendages in cement, ceramics, refractory and mortar industries. But these destinations are costly for the aluminum industries.

 Below are examples of some embodiments of the invention, and these are not to be construed as limiting thereof.

 Exemplol

 A laboratory scale test was performed using an application simulator.

 Application Simulation - SlagBal V3-5

The analysis was performed using the SlagBal V3-5 program, considering the manufacture of a 1008 steel, with the following additions during casting (kg) indicated in table 2 below: FeSi FeSiMn Cal Calcium Aluminum Fluorite

 150 500 600 40 100

 Table 2

 Besides that:

It was assumed in the simulation the passage of 300 kg slag from the kiln to the pan, with the following composition (%), indicated in table 3 below:

 Table 3

 Considering that:

 - Filling sand is basically olivine and that 100 kg are added in each run.

 - Si yield of 50%.

 - 0i of the pan of 2.7 m.

 - Bow length in the oven pan is 100-mm

- Slag density of 2460 kg / m ³ for a R203 = 3% a mass of approximately 1465 kg of slag is needed to protect the refractory from the slag line of the arc radiation.

 Example 2

 The SlagBal V3-5 application simulator was still used, but now on an industrial scale.

 According to this test the slag was carried in a region of the liquid line of the ternary diagram where it is just saturated with CaO and MgO at 1600 ° C. This point is approximately the point O, as shown in figure 2 in the appendix, where the Fluorite Substitution Ternary Diagram is indicated by Alucoque. The diagram represents an isothermal section at 1600 ° C (2,912 ° F).

For the effects of mass balance, Alucoque alkalis (Na ₂ O and K ₂ O) were considered to have similar influence to CaF ₂ . This mass balance is merely illustrative to show how much fluorite can be replaced by Alucoque.

 Industrial scale tests

 For the analysis, the following

Compound CaO MgO SiO ₂ S Fe ₂ 0 ₃ CaF ₂

 Cal 94.67 1.18 0.72 0.03

Doloma 63.76 32.68 1.66 0.05 EBT blend 87.2 3.7 1, 9

 Fluorite 4.22 77.1

 You are saddle 4

 It was considered that 300 kg of slag were passed from the furnace to the pan during the casting and that 120 kg of the EBT mixture was used per run. With the addition information of FeSi & FeSiMn, as well as the initial% Si in the pan, the yields for each of the 12 runs were calculated. The mass balance results for all races are shown below in Tables 5 and 6:

 Table 5

 Table 6

The slag mass is around 1200 kg, which translates to a thickness of the same of 96-mm, considering a 0i of the 2.58-m pan. That would be enough to cover the electric arc. The outlet slag must be within the region of coaching, as can be seen from figure 3 attached, which is a ternary diagram of the Cao - MgO - S1O2 type, where:

 C = CaO

 M = MgO

S = SiO ₂

 In the ternary diagrams presented in the annex (Figures 4 to 11) are the ternary diagrams with the results of the industrial tests where we can observe that the input and output slag of the panela furnace are in the hachurada region (gray), indicated interval where the presence of Alucoque in the secondary refining of the steel does not have an impact on the pot life of the ladle (refractory), presenting fluidizing functions similar to or equal to fluorite.

Conclusion

 Alucoque is a possible substitute for fluorite as a thinner in secondary steel refining and has all the necessary characteristics for this application. Laboratory and industrial scale tests were performed validating the invention, we suggest that Alucoque additions be made to the cast.

 Requirements such as steel deoxidation, removal of impurities, reheating of metal (and slag), homogenization (temperature and composition), among others were evaluated and successfully met.

 In the industrial test, the inlet and outlet slag of the panela oven were analyzed, where it was observed that both were within the region favorable to the refractory protection (coating). In the casting there was no clogging, no rupture during the rolling of the rebar produced with the steel. The final product showed no change in physical, mechanical and visual properties.

 Such an invention requires a green patent because of its environmental benefits, where it will reduce the consumption of fluorite (scarce mineral) and promote reduction and / or disposal of landfills for storing primary aluminum reduction electrolytic cell waste. The proposal is technically, economically and environmentally feasible.

Claims

Claims

A process for obtaining a fluidizing composition for use in the steel industry characterized by the fact that it is based on fluorite and alumina which was obtained from the crushing and sifting in a suitable granulometry of the mixture of residues originated from the process of reforming the electrolytic production tanks of (alumina) (Al ₂ O ₃ ), cryolite (Na ₃ AIF ₆ ), aluminum fluoride (AIF ₃ ) and aluminum (Al ₃ O ₃ ) , impregnated with fluorides of the electrolytic bath and further comprising:

 The. fluorine compounds;

 B. aluminum compounds;

 W. sodium compounds;

 d. Silicon compounds;

 and. calcium compounds;

 f. iron compounds;

 g. compounds of other metals such as: magnesium, chromium, titanium, phosphorus, sulfur, potassium, tungsten, etc .;

 H. optionally carbon compounds.

 Process for obtaining a fluidizing composition for use in the steel industry according to claim 1, characterized in that the fluorine compounds (a) are present in the composition in a content of from about 6 to about 40%, preferably from 9 to 29%, in mass relative to the total mass of the composition.

 Process for obtaining a fluidizing composition for use in the steel industry according to claims 1 or 2, characterized in that the fluorine compounds present are comprised within the group of compounds comprising CaF 2.

 Process for obtaining a fluidizing composition for use in the steel industry according to claim 1, characterized in that the aluminum compounds (b) are present in the composition in a content of from about 15 to about 48%, preferably from 23 to 43%, in mass relative to the total mass of the composition.

 Process for obtaining a fluidizing composition for use in the steel industry according to claims 1 or 4, characterized in that aluminum compounds present are comprised in the group of compounds comprising AI 2 O 3.

Process for obtaining a fluidizing composition for use in the steel industry according to claim 1, characterized in that the (c) are present in the composition in a content of about 8 to about 43%, preferably between 13 and 33%, by weight relative to the total mass of the composition.

 Process for obtaining a fluidizing composition for use in the steel industry according to claims 1 or 6, characterized in that the carbon compounds present are comprised in the group of compounds comprising Na20.

 Process for obtaining a fluidizing composition for use in the steel industry according to claim 1, characterized in that the silicon compounds (d) are present in the composition in a content of from about 1 to about 30%, preferably from 4 to 24%, in mass relative to the total mass of the composition.

A process for obtaining a fluidizing composition for use in the steel industry according to claims 1 or 8, characterized in that the silicon compounds present are comprised in the group of compounds which it comprises. Si0 ₂ .

 Process for obtaining a fluidizing composition for use in the steel industry according to claim 1, characterized in that the calcium compounds (e) are present in the composition in a content of about 0.1 to about 24%, preferably between 0.4 and 14% by weight relative to the total mass of the composition.

Process for obtaining a fluidizing composition for use in the steel industry according to claims 1 or 10, characterized in that the calcium compounds present are comprised in the group of compounds comprising CaO, Ca ₂ StO 4, etc.

 Process for obtaining a fluidizing composition for use in the steel industry according to claim 1, characterized in that the iron (f) compounds are present in the composition in a content from about 0.1 to about 24%, preferably from 0.4 to 14% by weight relative to the total mass of the composition.

Process for obtaining a fluidizing composition for use in the steel industry according to claims 1 or 12, characterized in that the iron compounds present are comprised in the group of compounds which it comprises. FeO, FeSi, FeSiMn, Fe ₂ 0 _3, etc.

Process for obtaining a fluidizing composition for use in the steel industry according to claim 1, characterized in that the other magnesium, chromium, titanium, phosphorus, sulfur, potassium, tungsten, manganese and the like compounds (g) are present in the composition from about 0.1 to about 10 %, preferably 0.14 to 8%, by weight relative to the total mass of the composition.

A process for obtaining a fluidizing composition for use in the steel industry according to claims 1 or 14, characterized in that the participation of other elements is comprised in the group of compounds comprising: Cr ₂ O ₃ , TiO ₂ MgO, Mg ₂ SiO ₄ , MnO, etc.

 Process for obtaining a fluidizing composition for use in the steel industry according to claim 1, characterized in that the carbon compounds (h) are present in the composition in a content of about 0 to about 25%, preferably between 3 and 18%, in mass relative to the total mass of the composition.

 Process for obtaining a fluidizing composition for use in the steel industry according to claim 1, characterized in that the suitable granulometry is up to 30 mm.

A fluidizing composition for use in the steel industry according to claims 1 to 17, characterized in that it is based on fluorite and alumina which was obtained from the crushing and sifting in suitable granulometry of the mixture of residues originating from the reforming process of eietrolitic tanks primary aluminum production that includes refractory and insulating bricks (tub coating), as well as electrolysis bath components such as alumina (Al2O3), cryolite (Na3AIF _6), optionally carbonaceous material of the cathode, and aluminum fluoride (AlF3) which further comprises:

 The. fluorine compounds;

 B. aluminum compounds;

 W. sodium compounds;

 d. Silicon compounds;

 and. calcium compounds;

 f. iron compounds;

 g. compounds of other metals such as: magnesium, chromium, titanium, phosphorus, sulfur, potassium, tungsten, etc .;

 H. optionally carbon compounds.

 Use of a fluidizing composition according to claim 18 characterized in that the fluidizing composition is based on fluorite and alumina from Alucoque and can be employed in secondary metallurgy, particularly in the secondary refining of steel.