Method for removing gangue and phosphorus from iron ore, and method for producing iron.

Abstract

To provide a novel and improved removal method of gangue and phosphorus in an iron ore, capable of further reducing a gangue and phosphorus concentration in the iron ore.SOLUTION: A removal method of gangue and phosphorus in an iron ore adds a NaOH aqueous solution with a concentration 3 M to 5 M into an iron ore containing phosphorus by 0.10 mass% to 0.25 mass%, and heats in a closed vessel at 200°C to 300°C for 10 mins or longer. Accordingly, a gangue and phosphorus concentration of the iron ore can further be reduced.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for removing gangue and phosphorus in iron ore and a method for producing iron.

Background Art

[0002] As a method for increasing the grade of iron ore (reducing gangue), beneficiation is known. Examples of beneficiation include magnetic separation, flotation, and gravity separation. Beneficiation is often carried out at the mine site (resource country).

[0003] By the way, in recent years, iron ores with high concentrations of not only gangue but also phosphorus have been produced, and there has been a strong demand for technologies to reduce the gangue and phosphorus concentrations in such iron ores. In response to such problems, an alkali hydrothermal reaction that can proceed with a reaction at a relatively low temperature has been proposed (Non-Patent Document 1). The alkali hydrothermal reaction is generally a technique in which an alkaline aqueous solution is added to iron ore and heated in a sealed container.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to the technique disclosed in Non-Patent Document 1, the gangue and phosphorus concentrations in iron ore can be reduced. However, when the present inventors further studied the technique disclosed in Non-Patent Document 1, it was found that there is room for further improvement.

[0006] The present invention was made to solve the above problems, and its objective is to provide a novel and improved method for removing gangue and phosphorus from iron ore and a method for producing iron, which can further reduce the concentration of gangue and phosphorus in iron ore. [Means for solving the problem]

[0007] To solve the above problems, according to one aspect of the present invention, a method for removing gangue and phosphorus from iron ore is provided, characterized by adding an aqueous NaOH solution with a concentration of 3M to 5M to iron ore containing 0.10% to 0.25% by mass of phosphorus, and heating it in a sealed container at 200°C to 300°C for 10 minutes or more.

[0008] According to another aspect of the present invention, a method for removing gangue and phosphorus from iron ore is provided, characterized by adding an aqueous NaOH solution with a concentration of 3M to 5M and glycerin to iron ore containing 0.10% to 0.25% by mass of phosphorus, and heating it in a sealed container at 200°C to 300°C for 10 minutes or more.

[0009] Here, glycerin may be added to the iron ore in an amount of 40% to 70% by mass.

[0010] According to another aspect of the present invention, a method for producing iron is provided, characterized by producing iron by reducing iron ore from which gangue and phosphorus have been removed by the above-described method for removing gangue and phosphorus from iron ore. [Effects of the Invention]

[0011] According to the above-mentioned problems of the present invention, it is possible to further reduce the gangue and phosphorus concentrations in iron ore. [Brief explanation of the drawing]

[0012] [Figure 1] This graph shows the correlation between phosphorus concentration and dephosphorization rate for each type of iron ore. [Modes for carrying out the invention]

[0013] <1. Study by the inventors> First, we will explain the studies conducted by the present inventors. The present inventors focused on the alkaline hydrothermal reaction disclosed in Non-Patent Document 1. They then investigated under what conditions a large amount of gangue and phosphorus can be removed from iron ore.

[0014] The inventors prepared several types of iron ore having different chemical compositions (Table 1). Powder X-ray diffraction (XRD) analysis revealed that ALY and ALR were α-FeOOH, WAL and A, B, and C were α-FeOOH and Fe2O3, and D and E were Fe2O3.

[0015] [Table 1]

[0016] The concentrations (mass%) of T.Fe, SiO2, Al2O3, SiO2+Al2O3, and P in Table 1 were determined by chemical analysis. T.Fe is the iron component, SiO2 and Al2O3 are gangue components, and P is phosphorus. LOI is the loss on ignition (mass%), indicating the content of crystalline water in the iron ore. Adsorbed P (mass%) is phosphorus present in goethite, and in this study, this phosphorus was considered to be phosphorus chemically adsorbed onto goethite. The concentration of adsorbed phosphorus was quantified by MLA (Mineral Liberation Analysis). The remaining phosphorus exists as phosphate minerals or is dissolved in iron oxide (hematite, etc.). Alkaline hydrothermal reaction mainly removes phosphorus chemically adsorbed onto goethite. The mass% shown in Table 1 represents the mass% relative to the mass of the iron ore. According to Table 1, Ore A to D contain a large amount of phosphorus (0.10 to 0.25 mass%), but most of this is adsorbed phosphorus. In other words, iron ore containing a high amount of phosphorus (0.10-0.25% by mass) tends to contain a large amount of adsorbed phosphorus that can be removed by alkaline hydrothermal reaction. This tendency is particularly pronounced in iron ore from Australia.

[0017] Next, an alkaline hydrothermal reaction was carried out using each iron ore shown in Table 1. Specifically, first, approximately 4.0 g of iron ore and 3.5 mL of 5 M NaOH aqueous solution were put into a reactor made of SUS316 (outer diameter 25 mm), and it was connected to a path equipped with a pressure gauge and a valve. Here, the iron ore used was classified to have a particle size of 4.0 mm or less. Specifically, the iron ore was put through a sieve with a mesh size of 4 mm, and the iron ore that fell through the sieve was subjected to an alkaline hydrothermal reaction.

[0018] Thereafter, high-purity He was introduced into the reactor through the valve, and a leak check was performed under a pressurized state. After purging the inside of the reactor sufficiently with He, the inside of the reactor was made into a He atmosphere at normal pressure and the valve was closed. The reactor was placed in a flowing sand bath maintained at 250 °C or 300 °C and held for 30 minutes or more. The change in gauge pressure at this time was in the range of 0 - 4 MPa. After the holding time ended, the reactor was taken out of the flowing sand bath and quenched with water. The solid (solid phase) and liquid inside the reactor were separated and recovered by filtration. The recovered solid phase was repeatedly washed with warm water until the filtrate reached pH 6. Then, the content of each component (iron, gangue, phosphorus) in the solid phase after the alkaline hydrothermal reaction was specified by chemical analysis, and the iron recovery rate (%), gangue removal rate (%), and phosphorus removal rate (%) were determined by the following formulas (1) and (2).

[0019]

Number

[0020]

Number

[0021] In formulas (1) and (2), Wa is the mass of the solid phase after the alkaline hydrothermal reaction, Wb is the mass of the iron ore before the alkaline hydrothermal reaction, Fa is the iron concentration (mass%) in the solid phase after the alkaline hydrothermal reaction, and Fb is the iron concentration (mass%) in the iron ore before the alkaline hydrothermal reaction.

[0022] When calculating the degane rate using formula (2), Pa is the total gangue concentration (mass%) in the solid phase after the alkaline hydrothermal reaction, and Pb is the total gangue concentration (mass%) in the iron ore before the alkaline hydrothermal reaction. When calculating the dephosphorization rate using formula (2), Pa is the phosphorus concentration (mass%) in the solid phase after the alkaline hydrothermal reaction, and Pb is the phosphorus concentration (mass%) in the iron ore before the alkaline hydrothermal reaction. The results are shown in Table 2 and Figure 1. In Figure 1, the horizontal axis represents the phosphorus concentration (mass%) in the iron ore before the alkaline hydrothermal reaction, and the vertical axis represents the dephosphorization rate (%). Point P1 shows the correlation between the phosphorus concentration and dephosphorization rate of ALY, and point P2 shows the correlation between the phosphorus concentration and dephosphorization rate of ALR. Points P3 to P8 show the correlation between the phosphorus concentration and dephosphorization rate of WAL to OreE.

[0023] [Table 2]

[0024] ALY and ALR are highly crystalline water ores with low phosphorus concentrations, and their dephosphorization rates are high. However, since their original phosphorus concentrations are low (<0.10 mass%), there is little incentive to incur the cost of dephosphorization treatment.

[0025] Iron ore with high phosphorus concentrations is abundant, making it highly valuable to dephosphorize and utilize it effectively. Table 2 and Figure 1 show that alkaline hydrothermal treatment can efficiently dephosphorize iron ore with a phosphorus concentration of 0.1 to 0.25 mass%.

[0026] Iron ore with a higher phosphorus concentration exhibits a lower amount of gangue and a higher degailing rate. Alkaline hydrothermal treatment of iron ore with a phosphorus concentration of 0.1% by mass or higher resulted in a high degailing rate of over 60%. The iron recovery rate by alkaline hydrothermal treatment was high, exceeding 80%, regardless of the type of iron ore.

[0027] Furthermore, if the phosphorus concentration is less than 0.1% by mass, except for the highly crystalline water ore mentioned above, most of the phosphorus exists as phosphate minerals coexisting with Fe2O3, resulting in poor dephosphorization by alkaline hydrothermal reaction. In iron ore with a phosphorus concentration of 0.1% by mass or higher, most of the phosphorus is chemically adsorbed onto goethite. In the alkaline hydrothermal reaction, the reactivity of adsorbed phosphorus is high, and therefore the dephosphorization rate improves when the phosphorus concentration is 0.1% by mass or higher. In addition, gangue components (SiO2, Al2O3) also dissolve in the alkaline aqueous solution, improving the gangue degane rate as well. On the other hand, if the phosphorus concentration exceeds 0.25% by mass, the initial phosphorus content becomes excessive relative to the reactivity of the alkaline hydrothermal reaction, and the dephosphorization rate decreases.

[0028] Therefore, the inventors of the present invention used iron ore with a phosphorus content of 0.1 to 0.25% by mass as the target of dephosphorization and degane removal by alkaline hydrothermal reaction. Furthermore, the reaction temperature of the alkaline hydrothermal reaction was set to 200 to 300°C, and the reaction time was set to 10 minutes or more, preferably 30 minutes or more. This is because a reaction temperature below 200°C is undesirable because the reaction rate of the alkaline hydrothermal reaction is not fast enough, and the alkaline hydrothermal treatment takes a considerable amount of time. A reaction temperature above 300°C is undesirable because although the reaction rate is fast enough, it is not much different from the reaction temperature at 200°C, and a great deal of energy is required for heating. Also, if the reaction time is less than 10 minutes, the alkaline hydrothermal reaction does not proceed sufficiently. There is no particular upper limit to the reaction time, but for example, industrially it may be within 3 hours.

[0029] Next, the inventors investigated the concentration of the NaOH aqueous solution. Specifically, they performed the alkaline hydrothermal reaction described above while varying the concentration of the NaOH aqueous solution from 2 to 6 M. OreA was used as the iron ore. The results are shown in Table 3.

[0030] [Table 3]

[0031] According to Table 3, when the concentration of the NaOH aqueous solution is 3 to 5 M, the degailing rate and dephosphorization rate are 60% or higher. Similar results were obtained for other ore types (B to D). However, when the concentration of the NaOH aqueous solution was less than 3 M, sufficient degailing rate and dephosphorization rate (60% or higher) could not be obtained for any iron ore type. On the other hand, when the concentration of the NaOH aqueous solution exceeds 5 M, more than 0.12% of Na remains in the iron ore (solid phase) after the alkaline hydrothermal reaction, which is undesirable. When sintered ore is produced using such high-Na iron ore, the reductivability (RDI) of the sintered ore deteriorates (40% or higher). RDI is the reductivability index of sintered ore as defined in JIS M 8720. It is expressed as the powder content (2.8 mm or less) after reducing 500 g of sintered ore with CO-30% (N2-70%) gas at 550°C for 30 minutes, cooling, and then performing a predetermined rotary pulverization treatment. While there are methods to reduce residual Na by intensifying the cleaning process, this is undesirable because it significantly reduces the productivity of sintered ore.

[0032] Next, the inventors investigated substances to be added to the alkaline hydrothermal reaction. As a result, the inventors found that a high reduction rate can be obtained by adding glycerin to iron ore in the alkaline hydrothermal reaction described above. The preferred concentration of glycerin is 40 to 70% by mass. In this case, in addition to a high reduction rate, a high dephosphorization rate and degane rate can be obtained. The concentration of glycerin is the mass ratio to the total mass of glycerin, iron ore, and NaOH.

[0033] The inventors believe the reason for these results is as follows: First, glycerin and NaOH react to produce H2 and H2O (Chemical Formula 1). Furthermore, excess glycerin decomposes to produce H2 (Chemical Formula 2). The H2 produced by these reactions reduces the coexisting iron ore (Chemical Formula 3). C3H5(OH)3+NaOH=CH3CH(OH)COONa+H2+H2O (Formula 1) C3H5(OH)3= CH3CH(OH)COOH+H2 (chemical formula 2) Fe2O3+3H2=2Fe+3H2O (chemical formula 3)

[0034] Table 4 shows the results of an alkaline hydrothermal reaction carried out by adding 65% by mass of glycerin to a 5M NaOH aqueous solution. In Table 4, the reduction rate was determined by measuring the amount of reduced oxygen obtained from the chemical analysis of T.Fe, M.Fe, and FeO in the sample before the alkaline hydrothermal reaction and the amount of residual oxygen obtained from the chemical analysis of T.Fe, M.Fe, and FeO in the sample after the alkaline hydrothermal reaction, and calculating the ratio of the amount of oxygen removed to the amount of oxygen reduced.

[0035] [Table 4]

[0036] According to Table 4, WAL with a phosphorus content of less than 0.1% by mass showed a low reduction rate. On the other hand, ALY and ALR, which are highly crystalline water ores, showed a high reduction rate. Iron ores with a phosphorus content of 0.1% by mass or more showed a high reduction rate. This is thought to be due to the following reason: As mentioned above, iron ores with a high phosphorus content contain a lot of goethite-adsorbed phosphorus, which is easily dephosphorized by alkaline hydrothermal reaction, so less NaOH is consumed for dephosphorization. As a result, it is easier for H2 to be produced by reacting with glycerol, and the reduction proceeds. For this reason, iron ores with a phosphorus content of 0.1% by mass or more are thought to show a high reduction rate. However, if the phosphorus content is excessively high (more than 0.25% by weight), almost all of the NaOH is consumed for dephosphorization, and the amount of H2 produced by reacting with glycerol is limited, so the reduction rate is less than 80%.

[0037] The inventors investigated the preferred concentration of glycerin. Specifically, they performed the alkaline hydrothermal reaction described above with a glycerin addition concentration of 35 to 75% by mass. OreA was used as the iron ore. The results are shown in Table 5.

[0038] [Table 5]

[0039] According to Table 5, high reduction rates were obtained at all glycerin concentrations. In particular, high degailing rates, dephosphorization rates, and reduction rates were obtained when the glycerin concentration was between 40% by mass and 70% by mass. Similar results were obtained for other ore types (B-D). When the glycerin concentration was less than 40% by mass, the amount of H2 generated was insufficient, and the reduction rate decreased to 80% or less. However, a reduction rate of 70% is a practically sufficient value. When the glycerin concentration exceeded 70% by mass, NaOH was preferentially consumed, and the degailing rates and dephosphorization rates decreased to less than 60%. However, the reduction rate was a very high value of 100%.

[0040] As described above, by adding a 3-5 M NaOH aqueous solution to iron ore containing 0.10-0.25% by mass of phosphorus and heating it in a sealed container at 200-300°C for 10 minutes or more, preferably, the concentration of gangue and phosphorus in the iron ore can be further reduced. Specifically, both the dephosphorization rate and the deganeization rate can reach 60% or more. In addition, by further adding glycerin when adding the NaOH aqueous solution to the sealed container, iron with a high reduction rate can be obtained. The concentration of added glycerin is preferably 40-70% by mass. In this case, the reduction rate of the iron ore reaches 80% or more.

[0041] <2. Method for removing gangue and phosphorus from iron ore> Next, a method for removing gangue and phosphorus from iron ore will be described. As described above, the method for removing gangue and phosphorus from iron ore according to this embodiment involves adding a 3-5 M NaOH aqueous solution to iron ore containing 0.10-0.25% by mass of phosphorus, and heating it in a sealed container at 200-300°C for 10 minutes or more, preferably 30 minutes or more. It is preferable to fill the sealed container with an inert gas (such as He). This makes it possible to further reduce the concentration of gangue and phosphorus in the iron ore. In this embodiment, it is preferable to add glycerin when adding the NaOH aqueous solution to the sealed container. This makes it possible to obtain iron with a high reduction rate. The preferred concentration of glycerin to add is 40-70% by mass. If the solid phase after the alkaline hydrothermal reaction is thoroughly washed, no alkaline components will remain in the solid phase, and it can be used in a blast furnace thereafter without problems. Furthermore, the method for removing gangue and phosphorus from iron ore according to this embodiment may be carried out in a batch system or in a flow system in which the NaOH aqueous solution is circulated.

[0042] <3. Iron manufacturing methods> The method for producing iron according to this embodiment involves reducing iron ore from which gangue and phosphorus have been removed by the method for removing gangue and phosphorus from iron ore described above. The method for producing iron is not particularly limited, but for example, iron may be produced by producing sintered ore using iron ore and charging this sintered ore into a blast furnace.

[0043] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention.

Claims

1. To iron ore containing 0.10% to 0.25% by mass of phosphorus, an aqueous NaOH solution with a concentration of 3M to 5M and glycerin are added, and the mixture is heated in a sealed container at 200°C to 300°C for 10 minutes or more. A method for removing gangue and phosphorus from iron ore, characterized by adding glycerin to the iron ore in an amount of 40% by mass or more and 70% by mass or less.

2. A method for producing iron, characterized by reducing iron ore from which gangue and phosphorus have been removed by the method for removing gangue and phosphorus from iron ore described in claim 1 to produce iron.

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