JP2012500902A - A method of separating iron from iron ore containing high-concentration zinc and extracting iron and valuable materials - Google Patents

Abstract

  The present invention relates to an improved process for treating high zinc content iron ore to produce steel in an iron oxide having an average particle size of 35-70 μm, a carbonaceous material having an average particle size of 25-60 μm, and an average particle size. To produce an agglomerate comprising a mixture with a flux of 45 to 85 μm to form an agglomerate having a particle size of 8 to 15 mm using a combination of an organic binder and an inorganic binder and moisture, A step of dezincing and metallizing the agglomerates in a furnace; melting the reduced agglomerates under hot / cold charging conditions to form hot metal in the furnace And, as a result, producing crude steel; the method comprising: recovering zinc valuables from the furnace waste gas stream by performing a conventional zinc extraction process.

Description

  The present invention relates to a two-stage process for removing zinc, reducing iron ore and producing liquid metal using process dust and iron ore containing high concentrations of zinc. The invention further relates to selecting the furnace temperature profile and agglomerate binder by continuous adjustment of porosity that facilitates the removal of zinc vapor at elevated temperatures during the reduction reaction. In the first stage, a non-shaft furnace is used to remove zinc and reduce iron ore and dust. In the second stage, an electric furnace is used to produce liquid metal, and then the residual zinc is removed from the reduced metal by using innovative slag chemistry.

  The blast furnace process is used worldwide to produce hot metal using various iron ores. In the blast furnace process, volatile impurities such as alkali metals, zinc, lead, etc. cause various operational problems. Therefore, the blast furnace process is not a convenient method for processing high zinc content iron ores. Alternative methods using shaft furnaces developed to produce steel are also not suitable for treating these high zinc content ores. The boiling point of zinc metal is about 910 ° C., and under oxidizing conditions, zinc metal forms stable zinc oxide (solid phase). In furnaces where various temperature zones and oxidation conditions exist, zinc is recycled and stored inside the furnace. For example, in a shaft furnace, zinc vapor originating from the hot zone (bottom part) is condensed on the charge wall or furnace wall in the top cold zone (T <900 ° C.). This results in zinc recycling within the system. The zinc recycle increases the coke ratio and causes many operational difficulties. Therefore, high zinc content iron ore is rarely used in the steel industry.

Accordingly, it is an object of the present invention to propose an improved method for dezincing and metallizing high zinc content iron ore by using solid phase reduction in a non-shaft furnace.
Another object of the present invention is to propose a combination of binders in a method of improving the agglomeration process for rapid removal of zinc vapor during the reduction reaction by sequentially adjusting the porosity. is there.
A further object of the present invention is to select an appropriate combination of processes for producing steel using the first stage product, ie directly reduced iron.
A further object of the present invention is to propose a method for recovering zinc valuables from a waste gas stream for extracting Zn metal.

  Accordingly, in an improved method for treating high zinc content iron ore to produce steel, iron oxide having an average particle size of 35-70 μm, carbonaceous material having an average particle size of 25-60 μm, and average particle size, respectively. To produce an agglomerate comprising a mixture with a flux of 45 to 85 μm to form an agglomerate having a particle size of 8 to 15 mm using a combination of an organic binder and an inorganic binder and moisture, The process of achieving the desired characteristics of the process, the process of dezincing and metallizing the agglomerates in a furnace, melting the reduced agglomerates under hot charging / cooling conditions, There is provided a method as described above comprising the steps of forming and consequently producing steel, recovering zinc valuables from the furnace waste gas stream by performing a conventional zinc extraction process.

The present invention will be described in more detail with reference to the accompanying drawings.
FIG. 2 shows a plot of [Free Energy Change] vs. [Temperature] for Zn oxide and Fe oxide reduction reactions used to practice the present invention. FIG. ₄ shows a phase diagram of ZnFe ₂ O ₄ —O ₂ used to control the gas atmosphere of various zones inside the furnace and to separate zinc from the waste gas stream.

The usual zinc mineral is zinc blende, ZnS. However, zinc is also found in the form of flankite [(Zn, Fe, Mn) [Fe, Mn] ₂ O ₄ ], an oxide mineral. In the magnetite lattice, Zn ²⁺ can be replaced by Fe ²⁺ cations that form a stable (Fe ₃ O ₄ —ZnFe ₂ O ₄ ) solid solution phase. Since Zn ²⁺ cations are smaller in size than Fe ²⁺ , lattice expansion and strain energy are reduced when Fe ²⁺ is replaced by Zn ²⁺ . Therefore, when ZnO in the magnetite melts, thermodynamic stability and structural stability increase. The crystal structure of hematite (HCP) is not favorable for the melting of ZnO, but the structure adapts to partial substitution of Fe ³⁺ by Zn ²⁺ cations by formation of vacancy points and lattice expansion Can do. Thus, high zinc concentrations are detected in hematite minerals (as in the case of Thach Khe oxide ore, Vietnam). It is not possible to remove this lattice of zinc in the iron ore by conventional beneficiation techniques such as magnetic or gravity separation. Accordingly, the present invention provides a method that can remove zinc trapped in a lattice of iron minerals and can be integrated with conventional steel manufacturing processes.

The important reduction reactions of ZnO, Fe ₃ O ₄ and ZnFe ₂ O ₄ with solid carbon and CO gas are described below, and a plot of [free energy] versus [temperature] of these reduction reactions is shown in FIG. Indicated.
ZnO + C → Zn + CO (R1)
ZnO + CO → Zn + CO ₂ (R2)
Fe ₃ O ₄ + 4C → 3Fe + 4CO (R3)
_{Fe 3 O 4 + 4CO → 3Fe} + 4CO 2 ··· (R4)
ZnFe ₂ O ₄ + 4C → Zn + 2Fe + 4CO (R5)
ZnFe ₂ O ₄ + 4CO → Zn + 2Fe + 4CO ₂ (R6)

From FIG. 1, zinc oxide is reduced to zinc metal by solid carbon at temperatures higher than 900 ° C. (reaction R1), whereas the reduction of pure magnetite by carbon (reaction R3) begins at temperatures higher than 710 ° C. I understand that. When zinc oxide is present in the form of zinc ferrite, the thermodynamic activity of zinc oxide changes significantly, so the reduction of zinc ferrite to metallic zinc and metallic iron (reaction R5) is more than 750 ° C. depending on the solid carbon. Can occur at high temperatures (ΔG <0). FIG. 1 confirms that gas reduction of ZnO or ZnFe ₂ O ₄ with carbon monoxide requires a high temperature, ie, a temperature higher than 1200 ° C. A phase diagram of —O ₂ of ZnFe ₂ O ₄ calculated using the FACT-Sage program is shown in FIG. FIG. 2 shows the boundaries for the thermodynamic stability of Zn—Fe—O compounds in various phases (solid phase, liquid phase and gas phase). Thus, solid state reduction at temperatures higher than 750 ° C. and oxygen partial pressures lower than 10 ⁻¹⁶ are critical thermodynamic conditions for removing zinc from the magnetite lattice.

In the magnetite lattice, the Zn ²⁺ and Fe ³⁺ cations have zero octahedral regioselective energy, and thus the cation site occupancy is mainly determined based on the cation radius and charge. As a result, smaller Zn ²⁺ cations and Fe ³⁺ cations occupy both tetrahedral and octahedral positions, whereas larger Fe ²⁺ cations selectively occupy octahedral positions in the magnetite lattice. . In a reducing atmosphere, the chemical potential of the applied oxygen is such that the Fe cation and Zn cation pass through the oxygen anion on the magnetite CCP (cubic close packed structure) lattice toward the reaction interface on the surface of the grain. To spread to The vacancy points generated during this process diffuse inward and then facilitate the diffusion of cations towards the reaction interface. Since Fe ³⁺ and Zn ²⁺ cations have zero octahedral regioselective energy, these cations are transferred from one octahedral position to another octahedral position via an adjacent empty tetrahedral position. Jump over to the position. It is energetically more advantageous that the balanced diffusion path of charge and ions jump directly between two octahedral positions that are separated by anions. At high temperatures, zinc is uniformly distributed in the lattice (T> immiscibility dome), and the zinc removal rate is determined by the diffusion of Zn through the anion lattice. Detailed studies of reaction kinetics and reaction mechanism have also shown that the rate limiting process is the diffusion of cations through the oxygen anion lattice. Thus, the reaction temperature is higher than the thermodynamic conditions for dezincification.

  In this innovative method, high zinc content iron ore is mixed with carbonaceous material as the reducing agent and other fluxes. The mixture is then agglomerated in the form of pellets or briquettes. Desirable properties of these agglomerates include wet drop numbers in the range of 6-8, dry drop numbers in the range of 10-15, unfired crush strength of 1.5 kg / pellet, and dry crush strength of 15 kg / pellet. Comprising. The green agglomerates are dried to remove moisture. A non-shaft furnace such as a rotary hearth furnace is used to perform solid-phase reduction and solid-phase dezincification. However, the present invention does not exclude operation with other types of furnaces. In a rotary hearth furnace, the agglomerate feed is continuously charged in layers into a charge that is held at an appropriate height above the hearth. These agglomerates are heated in various zones of the furnace. The heat required for the endothermic reduction reaction is supplied by the combustion products and the radiant energy from the furnace heater / burner. The ratio of furnace burner air to fuel is maintained at an appropriate level in the various zones to maintain the desired reducing conditions in the various zones of the furnace. The carbonaceous material in the agglomerates acts as a reducing agent and maintains a reducing atmosphere in the vicinity of the reaction interface. The ratio of [Ore] to [Carbonaceous Material] is adjusted to provide the C necessary for reduction and to maintain a reducing atmosphere at the reaction interface. The furnace temperature profile is maintained as desired to form the molten slag at the appropriate time and allow fusion of the reduced metal. In the cooling zone, the reduced pellets are cooled to 800 ° C. to 1000 ° C. required for subsequent processes. If necessary, DRI (direct reduced iron) is agglomerated by a high temperature briquetting process. Control the cooling zone and subsequent high temperature process atmosphere to minimize re-oxidation of newly formed metallic iron. In this innovative process, as much as 70-95% of the metallization with 80-95% dezincification can be achieved in a temperature range of 1100-1400 ° C. and a heating cycle of 10-60 minutes. The process also results in DRI with very low silicon content (0.1-0.9%) and carbon content (0.3-1.5%).

  In the present invention, as shown in FIG. 2, it is preferred to maintain the furnace conditions in such a way that the product gas is blown / conveys the zinc vapor exiting the furnace. In a preferred example, the gas flow follows the charge / center movement so that the hot gas does not contact the cold charge and the zinc vapor can accumulate and recirculate / accumulate inside the furnace. Another option used in this innovative process is to recover the gas from the hot zone and then cool to a temperature below 900 ° C. to separate the zinc vapor and then reuse it in the furnace to reduce it. It is to maintain the atmosphere. However, other uses of high temperature top gas (eg, air and fuel preheating) are not excluded in the present invention.

  According to a further advantageous embodiment of the invention, the porosity of the dried carbon composite pellets is adjusted to facilitate zinc evaporation near the reaction interface and rapid transport of Zn vapor to the outlet gas stream. Is preferred. This is achieved by using a combination of composite binder and moisture in agglomeration. The dosage of inorganic binder ranges between 0.5-2%, in which case the organic binder is used at a dosage between 1-5%. The volume ratio of iron ore, coal, binder and moisture is adjusted in an innovative manner that creates porosity within the agglomerates as the reduction and dezincification reactions proceed. The binder evaporation process and the coal utilization process are sequenced in such a way as to compensate for the aggregate shrinkage during the reduction reaction and to achieve the required strength in the reduced pellets. . The composite pellet is dried in a temperature range of 110-300 ° C. to remove moisture and thereby generate porosity (primary gap). In the present invention, the combination of organic binder and inorganic binder is such that the organic binder increases the strength of the dried pellet / briquette, while the inorganic binder is hot inside the furnace during the reduction reaction. Used to provide strength. The organic binder evaporates at the initial stage of the reduction reaction. This increases the pellet / briquette porosity (secondary gap) by 5-10%. These interstitial channels (primary and secondary gaps) generated at low temperatures facilitate rapid transport of Zn vapor formed during solid-phase reduction of the solid solution phase of magnetite and zinc ferrite at temperatures above 800 ° C. To do. As the reduction reaction proceeds, the carbon / reducing agent is consumed, thereby maintaining a gap channel, i.e., a high porosity, for rapidly transporting the gas phase from the reaction interface to the furnace atmosphere.

According to a further advantageous embodiment of the invention, the required green and dry pellets are adjusted by adjusting the particle size and particle size distribution of the feed materials (iron ore, reducing agent, flux and binder) used for the agglomeration process. A gap channel for rapid delivery of gas products and increase the rate of the reduction reaction (topochemistry). Iron oxide, carbonaceous material and flux are prepared to achieve average particle sizes of 35-70 μm, 25-60 μm, and 45-85 μm, respectively, and form agglomerates with a particle size of 8-15 mm. As a result, high productivity (ton / hour / m ² ) is achieved with this short reduction process (heating and cooling cycle).

  In the present invention, a combination of fluxes is used to form a slag having a desired liquidus. The rate of the reduction reaction is also adjusted with an innovative method that produces the desired amount of FeO in the charge during the reduction reaction to form a molten slag. The flux used in the charge material imparts desirable physicochemical properties to the molten slag and suppresses the loss of Fe in the slag phase. The slag characteristics are adjusted to melt the gangue phase and maintain the desired viscosity so that the molten slag does not block the gap and thereby interfere with the flow of Zn vapor and product gas. At high temperatures, when a desired level of dezincing is achieved, the planned slag chemistry forms a flowable slag that promotes coalescence of reduced metal particles and better separation of the slag and metal. Thus, in the present invention, rapid dezincing and better slag-metal separation is achieved by innovative flux chemistry and heating cycle / heating rate.

  In the present invention, a higher degree of metallization and dezincification was also achieved by using an appropriate grade of iron ore concentrate. By increasing the Fe content of the iron ore, the degree of metallization is increased and the removal of the gangue component helps to reduce the flux requirements. However, the higher the rate of metallization and the lower the slag content, the reduced cold crush strength of the reduced pellets. Thus, the heating cycle, porosity, feed particle size, and slag chemistry are adjusted to achieve the desired properties of the reduced pellet / briquette.

The process described in connection with the present invention was used to treat iron ore containing about 0.07% zinc. Agglomerates were prepared using anthracite, iron ore fines, and flux using the combination of binders described in connection with the present invention. The agglomerates were reduced in the furnace using the desired heating profile in the temperature range of 1100-1400 ° C. DRI (direct reduced iron) metalized in the range of 70-95% and containing less than 0.01% zinc was produced by this process. Using the DRI, a liquid metal was produced in an electric furnace.
In the second step of the process of the present invention, the high temperature DRI is melted directly in an electric furnace and (a) by adjusting the concentration of C, Si, S, P, it can be used for the production of BOF steel. Or (b) forming the steel directly by performing two slag runs. The choice of manufacturing process will be determined by regional economics.

  One embodiment of the present invention is zinc recovery. Zinc evaporated during reduction in the furnace is carried away by the waste gas stream. The zinc vapor is concentrated by lowering the temperature below 900 ° C. and, if necessary, by re-adjusting the oxygen partial pressure of the waste gas stream. The waste gas stream from the electric furnace used to produce steel is also treated in a similar manner to recover valuable zinc. Zinc oxide condensed in the condenser is recovered. Since coal is used as a reducing agent, the zinc oxide dust also contains many impurities that need to be removed. If the zinc concentration in the dust is> 40%, the dust is used directly to extract zinc. In the present invention, carbo-thermic reduction of zinc oxide is performed to extract metallic zinc. The metallic zinc is then purified by conventional electrolysis methods. On the other hand, dust with a zinc concentration of less than 40% is reduced in another way to separate iron and produce high zinc content dust. Another method used to obtain zinc-enriched dust is to melt the furnace dust in an arc furnace, thereby producing high zinc content dust. The high zinc content dust can then be treated by conventional methods.

Claims (18)

In an improved method for treating high zinc content iron ore to produce steel,
An agglomerate comprising a mixture of an iron oxide having an average particle size of 35 to 70 μm, a carbonaceous material having an average particle size of 25 to 60 μm, and a flux having an average particle size of 45 to 85 μm is generated, and an organic binder and an inorganic bond are produced. Forming agglomerates with a particle size of 8-15 mm using the combination with the material and moisture to achieve the desired properties of the agglomerates;
Dezincing and metallizing the agglomerates in a furnace;
Melting the reduced agglomerates under hot charging conditions and cold charging conditions to form hot metal, and producing crude steel;
Recovering valuable zinc from the waste gas stream of the furnace by performing a conventional zinc extraction process;
Comprising the above method.   The desired properties of the agglomerates include wet drop number in the range of 6-8, dry drop number in the range of 10-15, unfired crush strength of 1.5 kg / pellet, and dry crush of 15 kg / pellet. The method of claim 1, comprising: strength. The steps of dezincing and metallization are as follows:
A step of continuously adjusting the porosity of the agglomerates (primary gap) during the water evaporation at a temperature of 80 ° C. to 150 ° C .;
Evaporating the organic binder at a temperature between 130 ° C. and 300 ° C. to create a second gap;
Depleting the carbonaceous material in a reduced state at a temperature between 500 ° C. and 1200 ° C. to create a tertiary gap;
The method of claim 1 comprising: The steps of dezincing and metallization are as follows:
4. The method of claim 1, further comprising providing a gap channel for rapid delivery of a gas product by selecting an average particle size of the components that form the agglomerate. The method according to item. The steps of dezincing and metallization are as follows:
Controlling the viscosity of the formed slag by the combination of fluxes so as to avoid clogging of the gap channel, allowing the gas product to be released smoothly. The method of claim 1, further comprising:   The method of claim 1, wherein the furnace is selected from the types of rotary hearth furnaces, non-shaft furnaces and multi-hearth furnaces.   The iron oxide is iron ore containing a high zinc concentration in the range of 0.01 to 1% derived from iron ore, electric arc furnace dust, factory waste, and combinations thereof. the method of.   The method of claim 1, wherein the carbonaceous material comprises anthracite, bituminous coal, caking coal, petcoal, coke breeze, other carbonaceous materials, and combinations thereof.   The binder includes an inorganic binder, an organic binder, and a combination thereof, and the inorganic binder is used at a dose of 0.5 to 2%. The method of claim 1, wherein the method is used at a dose between ˜5%.   10. The organic binder of any one of claims 1 to 9, wherein the organic binder comprises dextrin, cellulose, starch, flour, and combinations thereof, monoacrylates, polyacrylates, and acrylamides, and combinations thereof, gums such as guar gum. The method according to item.   The method according to any one of claims 1 to 9, wherein the inorganic binder comprises bentonite, colloidal silica, swollen clay, and combinations thereof, cement, sodium, silicate. The step of generating the agglomerates includes
Preparing feed materials (iron ore, coal, binder and flux) to achieve the required particle size and particle size distribution, including surface area;
Formulating and mixing said feed fines, pre-wetting to achieve the necessary mixing for agglomeration;
Preparing the agglomerates in a dish and drum granulator or briquette maker having the desired moisture level and process parameters to achieve the desired properties and quality of the agglomerates;
Drying the agglomerates in a temperature range of 110 to 300 ° C. to remove the moisture and forming a primary gap;
The method of claim 1 comprising:   The dezincification and metallization is performed in a furnace where different temperatures are maintained in different zones, thereby removing the organic binder in the initial stage to form interconnected gap channels. And then reducing and evaporating the zinc at a higher temperature.   The method of any one of claims 1-5, wherein the flux minimizes the loss of the Fe in the slag. The flux, CaO, oxides of MgO and SiO _2, as well, comprises those compounds, method of any one of claims 1, 12 and 14. The zinc valuables are separated from the waste gas stream of the furnace by lowering the temperature of the waste gas below 900 ° C. and adjusting the CO / CO ₂ ratio of the waste gas with the introduced air. The method of claim 1, wherein:   The separated zinc valuables are treated in a furnace to increase the zinc concentration in the product recovered from the waste gas stream, and the compound recovered from the waste gas stream is 40 17. A method according to claim 16, having a zinc content greater than% and being adapted to extract zinc by conventional processes.   An improved method for processing high zinc content iron ore for manufacturing steel, substantially as described and exemplified herein with reference to the accompanying drawings.

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