KR101311725B1 - Synthesizing method of cobalt oxide from waste cemented carbide - Google Patents

Abstract

The present invention relates to a method for synthesizing cobalt oxide from waste cemented carbide. According to the present invention, a cobalt oxide precursor can be produced by neutralizing titration with respect to a waste hydrochloric acid solution obtained from a waste cemented carbide, and the cobalt oxide precursor thus produced is oxidized through hydrogen peroxide to have a high purity of 10 to 100 nm. The production of cobalt oxide is possible.
According to the present invention, a high purity cobalt oxide having a size of 10 to 100 nm and excellent in dispersibility and excellent in crystallinity can be obtained. It is possible to recycle resources by using ultra-thin hard alloy, and it is possible to save energy by not sintering at high temperature.

Description

Synthesizing method of cobalt oxide from waste cemented carbide}

The present invention relates to a method for synthesizing Co ₃ O ₄ , and more particularly, to synthesize Co ₃ O ₄ using cobalt as a by-product of the regeneration process of waste cemented carbide containing tungsten (W) and cobalt (Co) as main components. It is about how to.

As cutting tools requiring high hardness, alloys of carbon steel, tungsten steel, chromium, cobalt, and the like have been used since early. In 1923, German chemist Schrotter discovered a method of mixing and sintering tungsten carbide powder and cobalt powder. In 1927, German Krupp developed an ultrahard alloy mainly made of tungsten carbide by this method.

Cemented carbide is a high melting point, high strength alloy material mainly composed of expensive tungsten carbide (WC) and cobalt (Co) due to its low reserves. This cemented carbide is currently WC-Co. Three series alloys of WC-TiC, WC-TiC-Co and WC-TiC-TaC-Co make up the mainstream of cemented carbide tools, and tungsten carbide (WC) particle size is used to produce cemented carbide with high toughness and high strength. Micronization research has been extensive. In order to suppress grain growth of tungsten carbide (WC), chromium (Cr) and vanadium (V) are used as particle growth inhibitors.

According to data from the Cobalt Development Institute (CDI), the battery market accounts for the largest share of the total cobalt market at 18.4%, followed by the hard materials sector including cemented carbides at 18.0% and carbide and diamond tools. The pigments such as 14.4%, glass enamel plastic ceramics, etc. are 11.6%, catalyst 9.5%, and so on. Currently, the cobalt market size is small but must be an important part of the non-ferrous metals industry and plays an essential role in many other industries. According to the CDI data, the cobalt demand in the 1990s was 28,000 tons, 40,000 tons as of 2002, showing an average annual growth of 3.2%. The demand for cobalt has evolved and changed with the times, and cemented carbides were the largest market in the past, and batteries were very small compared to dust. Cemented carbide is still a major source of cobalt, but demand for the chemical industry accounts for 48% of the total demand, making it the most dominant industry in the cobalt market. Among the chemical industry, in particular, the battery and catalyst sectors have been leading the cobalt market growth over the last decade. In a battery using a Cobalt Cobalt is a key component of the lithium ion and lithium polymer batteries, LiCoO ₂ Used in the form of positive electrode active material. The cobalt content of these cells is typically on the order of 15-20%. Cobalt is also used as an additive in nickel-hydrogen and nickel-cadmium batteries. Cobalt demand in these battery materials is expected to continue to increase in the near future when the performance price and reliability of cobalt-based lithium-ion and lithium polymer batteries are well established.

Therefore, research on a method of synthesizing high-purity cobalt oxide by separating cobalt from waste hydrochloric acid solution generated during the process of regenerating tungsten carbide from waste cemented carbide is necessary in terms of resource recycling and environmental aspects.

The problem to be solved by the present invention is to neutralize the waste hydrochloric acid solution generated during the process of regeneration of tungsten carbide from waste cemented carbide to obtain a precursor of cobalt oxide and to provide a method for obtaining high purity cobalt oxide by hydrothermal synthesis method. have.

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The present invention comprises the steps of: (a) placing the spent cemented carbide and zinc in the crucible and heating it to a temperature higher than the melting point of zinc and lower than the boiling point of zinc; and (b) the spent cemented carbide and zinc is higher than the boiling point of zinc and tungsten. Increasing the temperature to a temperature lower than the melting temperature of the carbide to volatilize and remove the zinc component; and (c) pulverizing the tungsten carbide-cobalt ingot obtained by cooling the temperature of the crucible and grinding the tungsten carbide-cobalt powder obtained from the phosphoric acid solution. Acid treatment to remove the remaining zinc (Zn), and (d) dissolving the cobalt (Co) in a hydrochloric acid solution by acid treating the zinc (Zn) -removed tungsten carbide-cobalt powder with a hydrochloric acid solution. phase and, (e) the cobalt phase and, (f), which was added to the alkaline solution titrated to pH 7 - 14 generate the Co (OH) ₂ with respect to a hydrochloric acid solution (Co) is dissolved And dispersing the component by filtering and centrifugal separation from a hydrochloric acid solution Co (OH) phase that year ₂ selectively separating and, (g) the separated Co (OH) ₂ in distilled water, dispersed in (h) the distilled water A method for synthesizing cobalt oxide from waste cemented carbide comprising the step of adding hydrogen peroxide to Co (OH) ₂ and (i) heating the solution to which the hydrogen peroxide is added to a temperature of 120 ~ 500 ℃ to provide.

In addition, the present invention comprises the steps of (a) adding the spent cemented carbide and zinc in the crucible and heating it to a temperature higher than the melting point of zinc and lower than the boiling point of zinc, and (b) boiling the spent cemented carbide and zinc than the boiling point of zinc. Volatilizing and removing the zinc component by raising it to a temperature higher than the melting temperature of tungsten carbide; and (c) tungsten carbide-cobalt powder obtained by pulverizing and grinding the tungsten carbide-cobalt ingot obtained by cooling the temperature of the crucible. Acid treatment with a phosphoric acid solution to remove residual zinc (Zn), and (d) cobalt (Co) is added to the hydrochloric acid solution by acid treatment of the tungsten carbide-cobalt powder from which zinc (Zn) has been removed with hydrochloric acid solution. Dissolving (e) adding an alkali solution to the hydrochloric acid solution in which cobalt (Co) is dissolved, and titrating the pH to 7-14 to produce Co (OH) ₂ ; (f) selectively separating Co (OH) ₂ by filtering and centrifuging the hydrochloric acid solution, and (g) heating at a temperature of 220 to 500 ° C. in an oxidizing atmosphere for separated Co (OH) ₂ . It provides a method for synthesizing cobalt oxide from waste cemented carbide comprising the step of obtaining cobalt oxide.

The alkaline solution may be sodium hydroxide (NaOH) solution.

In the step (a), the spent cemented carbide and zinc are placed in a crucible, and the crucible is covered with a lid to be hermetically sealed, and then charged into a chamber of an electric furnace, and the gas atmosphere in the chamber is made of a non-oxidizing atmosphere. Heating the chamber by raising the temperature of the chamber to a temperature higher than the melting point of zinc and lower than the boiling point of zinc while suppressing evaporation of zinc in the sealed crucible and opening the lid of the crucible and tilting the crucible to form liquid Co- And may be followed by removal of the Zn alloy phase.

When the cobalt contained in the waste cemented carbide reacts with zinc, the weight ratio of the waste cemented carbide and zinc charged in the crucible is in the range of 1: 0.5 to 1: 6 so that the zinc content is not small.

The zinc forms a liquid phase by heating for 10 minutes to 12 hours at a temperature of 420 to 800 ° C., which is higher than the melting point of zinc and lower than the boiling point of zinc.

The temperature higher than the boiling point of zinc and lower than the melting temperature of tungsten carbide is a temperature of 910 to 1200 ° C, and step (b) is performed for 10 minutes to 12 hours at a temperature of 910 to 1200 ° C so that zinc can be volatilized. It is preferable.

In step (h), Co (OH) ₂ and H ₂ O ₂ is preferably added in a ratio of 3: 1 to 1: 1 in molar ratio.

The step of obtaining cobalt oxide by heating at a temperature of 120 ~ 500 ℃ for the solution to which the hydrogen peroxide is added, the step of heating the solution to which the hydrogen peroxide is added to a temperature of 120 ~ 500 ℃, the solution containing the cobalt oxide Selectively separating the cobalt oxide by centrifugation and washing the separated cobalt oxide.

In addition, the present invention is prepared by a method for synthesizing cobalt oxide from the waste cemented carbide, and provides a cobalt oxide having a particle size of 10 ~ 100nm.

According to the method for synthesizing cobalt oxide from the waste cemented carbide according to the present invention, a precursor of cobalt oxide is produced by neutralizing titration with respect to the waste hydrochloric acid solution generated during the process of regenerating tungsten carbide from the waste cemented carbide, and the oxidation produced as such High purity cobalt oxide having a size of 10 to 100 nm can be prepared by oxidizing the precursor of cobalt through hydrogen peroxide.

Cobalt oxide prepared by the present invention, while having a size of 10 ~ 100nm, excellent dispersibility, excellent crystallinity and high purity.

According to the present invention, it is possible to recycle resources by using an ultra-thin hard alloy and to save energy by not sintering at a high temperature. Since the waste hydrochloric acid solution used for the regeneration of cemented carbide is used, it is an efficient process in terms of resource recycling.

1 is a view schematically showing an electric furnace for obtaining tungsten carbide powder.
Figure 2a is a Transmission Electron Microscope (TEM) photograph of Co ₃ O ₄ obtained by hydrothermal synthesis for 1 hour at a temperature of 120 ℃ according to Example 1.
2B is a transmission electron microscope photograph of Co ₃ O ₄ obtained by hydrothermal synthesis for 1 hour at a temperature of 140 ° C. according to Example 1. FIG.
2C is a transmission electron microscope photograph of Co ₃ O ₄ obtained by hydrothermal synthesis for 1 hour at a temperature of 160 ° C. according to Example 1. FIG.
Figure 2d is a transmission electron micrograph of Co ₃ O ₄ obtained by hydrothermal synthesis for 1 hour at a temperature of 180 ℃ according to Example 1 _.
3 is an X-ray diffraction pattern of Co ₃ O ₄ obtained by hydrothermal synthesis at 100 ° C., 120 ° C., 160 ° C., and 180 ° C. for 1 hour according to Co (OH) ₂ and Example 1. FIG.
FIG. 4 is a transmission electron microscope photograph of Co ₃ O ₄ hydrothermally synthesized by heat treatment at 300 ° C. for 10 minutes with respect to Co (OH) ₂ , a cobalt oxide precursor, according to Example 2. FIG.
5 is an X-ray diffraction pattern of Co ₃ O ₄ hydrothermally synthesized at 220 ° C., 300 ° C., and 380 ° C. according to Co (OH) ₂ and Example 2. FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, it should be understood that the following embodiments are provided so that those skilled in the art will be able to fully understand the present invention, and that various modifications may be made without departing from the scope of the present invention. It is not.

First, the Zn process, which is a purification process of obtaining tungsten carbide (WC) from waste cemented carbide, will be described.

Prepare the cemented carbide. The waste cemented carbide may be waste scrap of a cemented carbide tool containing tungsten carbide (WC) and cobalt (Co) as main components. Carbide tools are used to mean all tool products based on tungsten carbide and cobalt, such as scrap, inserts and molds.

Since the waste cemented carbide is industrial waste that is already used and disposed of, waste cleaning is performed to remove impurities present on the surface of the cemented carbide. The cleaning process may be performed by using a solvent such as ethanol, methanol, acetone to wash the surface of the fecho hard alloy at a temperature of about 10 ~ 40 ℃.

1 is a view schematically showing an electric furnace for obtaining tungsten carbide powder.

Referring to FIG. 1, the electric furnace 100 includes a chamber 110 and a chamber cover 112 covering the chamber 110. The crucible 120 is provided in the chamber 110 and sealed by the crucible lid 125. The crucible 120 is connected to the crucible rotating means 170 through the connecting bar 180, the crucible 120 by the crucible rotating means 170 is provided to be rotated by a predetermined angle. The crucible rotating means 170 is provided with a handle to rotate the handle to rotate the crucible or a driving means such as a motor may be provided to rotate the handle. Although not shown, the crucible cover 125 is connected to a driving means such as a motor and is provided to be opened and closed automatically. The chamber 110 is provided with a heating means 130, the heating means 130 is supplied with power by the power supply means 190 to adjust the temperature in the chamber 110. The chamber 110 is surrounded by the heat insulator 140, and the coolant pipe 116 is provided around the chamber 110 so that the coolant flows. The chamber cover 112 may include a heat insulating material 140 to insulate the inside of the chamber 110 and a metal material 114 larger than the size of the inside of the chamber 110. The chamber cover 112 is provided with a gas discharge pipe 118 that provides a passage through which zinc (Zn) is evaporated, and zinc (Zn) evaporated from a collector (not shown) connected to the gas discharge pipe 118 is collected. The gas discharge pipe 118 may be pumped by a vacuum pump (not shown) to easily collect zinc (Zn) in the collector. The chamber cover 112 may also be provided with a coolant pipe 116 through which coolant flows.

The cleaned cemented carbide and zinc (Zn) are placed in the crucible 120 and the crucible 120 is covered with a crucible lid 125 of a screw cap type to be completely sealed, and then charged into the chamber 110 of the electric furnace 100. do. The crucible 120 is completely sealed with a crucible lid 125 of a screw cap type, thereby increasing the zinc (Zn) vapor pressure in the crucible 120 and suppressing the evaporation amount of zinc (Zn) to perform a zinc distillation process. I can promote it.

It is preferable that the weight ratio of the waste cemented carbide and zinc (Zn) charged to the crucible 120 is about 1: 0.5-1: 6. If the content of the waste cemented carbide is too high, the content of zinc (Zn) reacting with the cobalt (Co) contained in the waste cemented carbide is insufficient, so it may be difficult to sufficiently remove the cobalt (Co) component by subsequent heat treatment. In the case of too much content of Zn, the remaining heat does not react with the cobalt (Co) contained in the waste cemented carbide, resulting in the remaining zinc (Zn), and a large amount of energy is consumed in the subsequent heat treatment process in which the zinc (Zn) is volatilized. It is economical. The crucible 120 is preferably made of a graphite material of the same material as the carbide (C) constituting the waste cemented carbide.

Non-oxidizing gases, such as argon (Ar) and nitrogen (N ₂ ), are injected into the chamber 120 using the gas supply device 160 to control the gas atmosphere in the furnace such as argon (Ar) and nitrogen (N ₂ ). Makes it non-oxidizing gas atmosphere. It is preferable that the supply flow volume of the non-oxidizing atmosphere gas supplied to the chamber 110 is about 0.1-20 L / min.

The temperature of the chamber 110 using the heating means 130 is higher than the melting point (419.6 ° C.) of zinc (Zn) and lower than the boiling point (907 ° C.) of zinc (Zn). For example, it raises to the temperature of 420-800 degreeC. When the temperature of the chamber 110 reaches a temperature higher than the melting point of zinc (Zn) and lower than the boiling point of zinc (Zn) (eg, 420 to 800 ° C.), zinc (Zn) penetrates into the waste cemented carbide and enters the waste cemented carbide. Reaction occurs with the cobalt (Co) contained therein to form a molten metal, Co-Zn alloy, and tungsten carbide (WC), a carbide phase constituting the main component of the waste cemented carbide is settled to the bottom of the crucible (120). Due to the difference in specific gravity, tungsten carbide (WC), which is a solid with a high specific gravity, is allowed to sink while maintaining its original shape, and is separated from a relatively small liquid phase of Co-Zn alloy phase. Since the melting point of the tungsten carbide WC is 2777 ° C., the tungsten carbide WC does not melt even when the temperature of the chamber 110 is increased to 420 to 800 ° C. When zinc (Zn) penetrates into the spent cemented carbide and reacts with cobalt (Co), there is volume expansion and there is a change in the crystal structure of the used cemented carbide.

When the temperature of the chamber 110 reaches a temperature higher than the melting point of zinc (Zn) and lower than the boiling point of zinc (Zn) (eg, 420 to 800 ° C.), cobalt (Co) contained in the waste cemented carbide is zinc (Zn). (Zn) penetrates into the cemented carbide to allow sufficient reaction with cobalt (Co) contained in the cemented carbide. At this time, since the crucible 120 is sealed by the crucible lid 125 having a screw cap type, the zinc (Zn) vapor pressure in the crucible 120 may be increased and the amount of evaporation of the zinc (Zn) may be suppressed. Since the crucible 120 is sealed by the crucible cover 125, the pressure in the crucible 120 may be increased, and cobalt and zinc may react faster than when the crucible cover 125 is not used. have.

The metallurgical reaction of waste cemented carbide and zinc (Zn) is summarized as follows.

[Reaction Scheme 1]

WC-Co (s) + Zn (l) → WC (s) + Co-Zn (l)

Opening the lid 125 of the crucible 120 and tilting the crucible 120 while maintaining the temperature at which zinc (Zn) maintains the liquid phase (eg, tilted at an inclination of about 95 to 100 °) to the liquid Co-Zn alloy Follow the award. At this time, solid tungsten carbide (WC) remains at the bottom of the crucible 120, and since the melting point of zinc is 419.6 ° C, the liquid phase is maintained even in the temperature range of 420 to 800 ° C. The inclination of the crucible 120 is controlled through the crucible rotating means 170 which is connected to the crucible 120. The crucible rotating means 170 is connected to the crucible 120 by the connecting bar 180, so that the connecting bar 180 is rotated by turning the handle of the crucible rotating means 170 in a clockwise or counterclockwise direction. Accordingly, the crucible 120 connected to the connection bar 180 is also inclined. As such, the inclination of the crucible 120 can be adjusted by controlling the crucible rotating means 170. As described above, the cobalt (Co) component can be easily removed from the waste cemented carbide through the process of pouring out the molten metal, which is a Co-Zn alloy phase present in the crucible.

When some of the cobalt (Co) is removed from the waste cemented carbide, the chamber 110 of the furnace is above 907 ° C, the boiling point of zinc (Zn), and lower than the melting temperature (2777 ° C) of tungsten carbide (WC). For example, it raises to 910-1200 degreeC. When the temperature of the chamber 110 rises above the boiling point of zinc (Zn), the zinc (Zn) component is volatilized and removed. Since the melting temperature of tungsten carbide (WC) is higher than the temperature, it remains in the crucible 120 without any change. When the temperature of the chamber 110 is above the boiling point of zinc (Zn) and reaches a temperature (910-1200 ° C.) lower than the melting temperature of tungsten carbide (WC), zinc (Zn) remaining in the crucible 120 is sufficiently volatilized. Hold for several hours (e.g., 10 minutes to 12 hours). If the temperature of the chamber 110 is too high, a lot of energy must be consumed, and if the temperature of the chamber 110 is too low, zinc (Zn) may not be sufficiently volatilized, so the temperature of the chamber is 910-1200 ° C. It is desirable to keep constant in the range.

Evaporated zinc (Zn) is collected in a collector (not shown) connected to the gas discharge pipe 118 of the chamber cover 112.

During the volatilization of zinc, zinc (Zn) is volatilized even in the molten metal formed of the Co-Zn alloy phase remaining in the crucible 120, and when cooled, the ingot containing tungsten carbide (WC) and cobalt (Co) components ( lump) form. Cobalt (Co), which forms a molten metal by reacting with zinc (Zn) from the waste cemented carbide, serves as a binder to bind tungsten carbide (WC) to obtain a lumped state in which particles are aggregated.

When the temperature of the chamber 110 is cooled, ingots including tungsten carbide (WC) and cobalt (Co) remain. Cooling of the chamber 110 may be cooled to a natural state by cutting off the power of the heating means 130, or may be cooled by setting a temperature drop rate (for example, 10 ° C / min) arbitrarily. Even while the temperature of the chamber 110 is lowered, the gas atmosphere inside the chamber 110 may maintain a non-oxidizing atmosphere.

The grinding process is carried out to obtain a complete powder from the obtained WC-Co ingots. Cobalt (Co) components remain in the WC-Co ingots, which are agglomerated due to the cobalt (Co) binder. Therefore, in order to grind | pulverize and refine | pulverize the obtained WC-Co ingot, the grinding | pulverization process is used. However, since the aggregated WC-Co lump is a high-strength material, it is difficult to obtain it in the form of powder by atomizing by a simple grinding method, and therefore, it is preferable to use the following grinding process.

To micronize the WC-Co ingots, they are charged into a ball milling machine and wet mixed with a solvent such as ethanol. The ball mill is rotated at a constant speed to mechanically grind the WC-Co ingots. Balls used for ball milling use carbide balls made of tungsten carbide to suppress the generation of impurities, and the balls may be all of the same size or may have balls of two or more sizes together. The size of the balls, the milling time, and the rotation speed per minute of the ball miller are adjusted so as to be crushed to the target particle size. For example, in consideration of the particle size, the size of the ball can be set in the range of about 1 mm to 50 mm, and the rotational speed of the ball mill can be set in the range of about 100 to 400 rpm. Ball milling is carried out for 1 to 36 hours in consideration of the target particle size and the like. The cobalt (Co) component that binds tungsten carbide (WC) by ball milling is separated from the tungsten carbide (WC) particles, so that tungsten carbide (WC) is crushed into finely sized particles, resulting in a uniform particle size distribution. Will have

The WC-Co powder obtained by pulverization is removed by using an acid treatment step to remove zinc (Zn). Hereinafter, a process of removing residual zinc (Zn) by acid treatment of tungsten carbide (WC) -cobalt (Co) ingot with phosphoric acid is described.

The ground tungsten carbide (WC) -cobalt (Co) powder is acid treated with a phosphoric acid solution. Acid treatment with a phosphoric acid solution dissolves the remaining zinc (Zn) contained in the WC-Co powder, followed by washing several times (e.g. three times) with a cleaning solution such as ethanol and water after the acid treatment, followed by drying. A WC-Co powder from which residual zinc (Zn) has been removed is obtained. The acid treatment process using the phosphoric acid solution is preferably carried out for 30 minutes to 48 hours at room temperature (for example 15 to 25 ℃). As the phosphoric acid solution, it is preferable to use a solution having a concentration of phosphoric acid higher than 20%.

It is preferable to perform a phosphoric acid treatment process to remove zinc (Zn) after the grinding process, but may also perform a pulverization process after first performing a phosphoric acid treatment process to remove zinc (Zn). .

The tungsten carbide (WC) -cobalt (Co) powder thus obtained may be sold as a product, and may be sold as a product after removing cobalt (Co) by performing an acid treatment process using a hydrochloric acid (HCl) solution as described below.

Tungsten carbide (WC) -cobalt (Co) powder acid treated with phosphoric acid solution is acid treated with hydrochloric acid (HCl) solution. Acid treatment with hydrochloric acid (HCl) solution dissolves cobalt (Co), which coats or binds tungsten carbide (WC), and washes several times (eg, three times) with a cleaning solution such as ethanol or water after the acid treatment. Drying yields a complete tungsten carbide (WC) powder. By the acid treatment process using the hydrochloric acid (HCl) solution, impurities such as V, Cr, Ti, Fe, etc. contained in the tungsten carbide (WC) -cobalt (Co) powder are also removed. The acid treatment process using the hydrochloric acid (HCl) solution is preferably carried out for 30 minutes to 48 hours at room temperature (eg, 10 ~ 30 ℃). As the hydrochloric acid solution, it is preferable to use a solution having a concentration of hydrochloric acid (HCl) higher than 20%. This is because the type and amount of impurities removed may vary depending on the concentration of hydrochloric acid. For example, when the concentration of hydrochloric acid is high, cobalt (Co) component is dissolved, but when the concentration of hydrochloric acid is low, cobalt (Co) component is not dissolved and only impurities such as iron (Fe) may be dissolved.

Impurities such as cobalt (Co) and iron are obtained by hydrochloric acid treatment, and titration of such waste hydrochloric acid solution is necessary. When the waste hydrochloric acid solution is titrated to pH 7-14 using an alkaline solution such as NaOH, Co (OH) ₂ is generated in the waste hydrochloric acid solution.

Separation of Co (OH) ₂ requires filtering and centrifugation of the spent hydrochloric acid solution. After filtering and centrifugation, Co (OH) ₂ can be obtained. Cobalt (Co) dissolved in hydrochloric acid is titrated with sodium hydroxide (NaOH) to produce Co (OH) ₂ , an amorphous precursor, and filtered and centrifuged with a solution of waste hydrochloric acid titrated with sodium hydroxide. Co (OH) ₂ is obtained. The separated Co (OH) ₂ is in the form of a gel and is an amorphous precursor.

For the amorphous precursor, it is possible to prepare Co ₃ O ₄ having a nanometer (nm) size by a hydrothermal synthesis process. There is a need for a process that can produce uniform and fine Co ₃ O ₄ particles using such an amorphous precursor. Here, nanometer size is used to mean a size in the range of 1nm to 1㎛.

In the present invention, a fine powder is prepared without calcination, the yield is high, and the hydrothermal synthesis method capable of synthesizing Co ₃ O ₄ powder by washing with water after the reaction is used. The hydrothermal synthesis method is described below.

The amorphous precursor is dispersed in distilled water. Hydrogen peroxide (H ₂ O ₂ ) is slowly added while stirring the amorphous precursor dispersed in distilled water. At this time, Co (OH) ₂ , which is a cobalt oxide precursor, and hydrogen peroxide (H ₂ O ₂ ) are preferably added to react in a molar ratio of 3: 1 to 1: 1. Such a method is a method of supplying oxygen to Co (OH) ₂ , which is an amorphous precursor, and has the advantage of preparing cobalt oxide (Co ₃ O ₄ ) nanoparticles. In addition, there is an advantage that can be synthesized cobalt oxide at a relatively low temperature by adding hydrogen peroxide.

The reaction using this hydrogen peroxide is according to the following reaction formula 2.

[Reaction Scheme 2]

3Co (OH) ₂ + H ₂ O ₂ → Co ₃ O ₄ + ₄ H ₂ O

The reaction according to Scheme 2 is preferably made at 120 ~ 500 ℃.

In addition, even if hydrogen peroxide (H ₂ O ₂ ) is not added by one method, it is possible to produce Co ₃ O ₄ by heating in an oxidizing atmosphere by the following reaction formula.

Scheme 3

3Co (OH) ₂ + 0.5O ₂ → Co ₃ O ₄ + 3H ₂ O

The reaction according to Scheme 3 is preferably made at 220 ~ 500 ℃. By such a high temperature heating method there is an advantage that can be synthesized cobalt oxide in a relatively short time.

Reaction according to Scheme 3 also uses Co (OH) ₂ , an amorphous precursor that is a reaction product of a waste hydrochloric acid solution and sodium hydroxide, and is a kind of hydrothermal reaction.

Therefore, it includes all the advantages of hydrothermal synthesis. In the case of the hydrothermal reaction, unlike the conventional calcination reaction, since it is made at a low temperature, no particle growth occurs. When it exceeds 500 ° C, grain growth of Co ₃ O ₄ occurs, so that Co ₃ O ₄ having a size of about 10 to 100 nm is difficult to obtain. However, in the hydrothermal synthesis method according to the present invention, since the synthesis temperature of Co ₃ O ₄ is low, the finally obtained Co ₃ O ₄ exhibits excellent dispersibility while having a size of about 10 to 100 nm.

Hereinafter, examples of the method for synthesizing cobalt oxide from the waste cemented carbide according to the present invention are described in more detail, and the present invention is not limited to the following examples.

≪ Example 1 >

A waste cemented carbide composed of waste scrap of a cemented carbide tool composed mainly of tungsten carbide (WC) and cobalt (Co) was prepared. In order to remove impurities present on the surface of the spent cemented carbide, the surface of the cemented carbide was washed with ethanol at a temperature of about 20 ° C. The washed cemented carbide and zinc (Zn) were placed in a graphite crucible, the crucible was covered with a lid, and then charged into a chamber of an electric furnace. The weight ratio of spent cemented carbide and zinc (Zn) in the crucible was about 1: 4. The crucible was made of graphite, which is the same material as the carbide (C) constituting the waste cemented carbide.

Argon (Ar) gas was injected into the chamber to make the gas atmosphere in the chamber non-oxidizing gas atmosphere. The supply flow rate of the argon (Ar) gas supplied to an electric furnace was about 5 L / min. The temperature of the chamber was raised to a temperature of 650 ° C., which is above the melting point of zinc (Zn) and below the boiling point of zinc (Zn). When the temperature of the chamber 110 reaches 650 ° C, cobalt (Co) contained in the waste cemented carbide is maintained for 2 hours and 30 minutes to sufficiently react with zinc (Zn), so that zinc (Zn) penetrates into the waste cemented carbide. The reaction was sufficiently performed with cobalt (Co) contained in the waste cemented carbide.

The voltage supplied to the furnace was 380V and the current was 75A. When the temperature of the chamber 110 reaches 650 ° C., which is higher than the melting point of zinc (Zn) and lower than the boiling point of zinc (Zn), zinc (Zn) penetrates into the waste cemented carbide and cobalt (Co) contained in the waste cemented carbide is coated. ), A molten metal, which is a Co-Zn alloy, is formed, and tungsten carbide (WC), a carbide phase that forms the main component of the waste cemented carbide, sinks to the bottom of the crucible. Due to the difference in specific gravity, tungsten carbide (WC), a solid phase having a high specific gravity, was settled and separated from a relatively small liquid phase Co-Zn alloy phase.

The lid of the crucible was opened and the crucible was tilted about 100 ° to pour out the liquid Co-Zn alloy phase. At this time, solid tungsten carbide (WC) remains on the bottom of the crucible. The inclination of the crucible was adjusted through the crucible rotating means connected with the crucible. The crucible rotating means is connected to the crucible by a connecting bar, and as the handle of the crucible rotating means is turned counterclockwise, the connecting bar is rotated and thus the crucible connected to the connecting bar is tilted. As described above, the cobalt (Co) component could be easily removed from the waste cemented carbide by decanting the molten metal, which is Co-Zn alloy present in the crucible.

When cobalt (Co) is removed from the waste cemented carbide, the chamber of the furnace is raised to 1000 ° C., which is at least 907 ° C., the boiling point of zinc (Zn) and lower than the melting temperature of tungsten carbide (WC), and 1 hour at a temperature of 1000 ° C. For a while. When the temperature of the chamber is raised to 1000 ° C, the zinc (Zn) component is volatilized and removed. The evaporated zinc was allowed to collect in a collector connected to the chamber. Since the melting temperature of tungsten carbide (WC) is higher than the temperature, it remains in the crucible without any change.

The temperature of the chamber was cooled to room temperature to obtain tungsten carbide (WC) -cobalt (Co) ingots. The cooling of the chamber was to cut off the power of the heating means to cool in a natural state, and the gas atmosphere inside the chamber maintained a non-oxidizing atmosphere while the chamber temperature was lowered.

Cobalt (Co) component still remains in the tungsten carbide (WC) -cobalt (Co) ingot and is agglomerated due to the cobalt (Co) binder. Therefore, a ball mill grinding process was performed to micronize the obtained tungsten carbide (WC) -cobalt (Co) ingots. The tungsten carbide (WC) powder was charged to a ball milling machine in order to micronize and wet mixed with ethanol. The tungsten carbide (WC) powder was mechanically milled by rotating the ball mill at a constant speed. The ball used for ball milling was used a carbide ball made of tungsten carbide, the ball size was 10mm, 20mm, 30mm, the rotation speed of the ball mill was set to about 300rpm, ball milling was carried out for 24 hours. .

The tungsten carbide (WC) -cobalt (Co) powder formed by pulverization was acid treated with a phosphoric acid solution to remove zinc (Zn) that remained finely. The acid treatment process using the phosphoric acid solution was carried out at room temperature. As the phosphoric acid solution, a solution having a phosphoric acid concentration of 35.5% was used. After the acid treatment, washed three times with ethanol and dried.

The zinc-depleted tungsten carbide (WC) -cobalt (Co) powder was acid treated with hydrochloric acid (HCl) solution to remove cobalt (Co) using a phosphoric acid solution. The acid treatment process using the hydrochloric acid (HCl) solution was carried out at room temperature. As the hydrochloric acid solution, a solution having a concentration of hydrochloric acid (HCl) of 35.5% was used. When acid treated with hydrochloric acid (HCl) solution, it was found that cobalt (Co) was extracted by melting dark blue.

After the acid treatment step washed three times with ethanol and dried to obtain a tungsten carbide (WC) powder. The drying was carried out in a constant temperature dryer at 80 ℃ for 1 hour.

Since cobalt (Co) is dissolved in the hydrochloric acid (HCl) solution used in the acid treatment, cobalt oxide (Co) was extracted from the waste hydrochloric acid solution to synthesize cobalt oxide (Co ₃ O ₄ ).

The waste hydrochloric acid solution was titrated to 7 ~ 14 using sodium hydroxide (NaOH). Through this titration process, Co (OH) ₂ , a cobalt oxide precursor, is produced in the waste hydrochloric acid solution. However, since impurities other than cobalt (Co) are also formed in the waste hydrochloric acid solution, it is necessary to remove such impurities.

Accordingly, Co (OH) ₂ was separated out by filtering and centrifugation in waste hydrochloric acid solution. The centrifugation was performed at a speed of 10,000 rpm. This filtering and centrifugation resulted in Co (OH) ₂ gel.

0.35 g of Co (OH) ₂ in a gel state was dispersed and sufficiently dispersed in 10 ml of distilled water. 10 ml of hydrogen peroxide was added very slowly while stirring distilled water in which Co (OH) ₂ was dispersed.

The solution to which Co (OH) ₂ , distilled water and hydrogen peroxide were added was reacted at 100 ° C., 120 ° C., 140 ° C., 160 ° C. and 180 ° C. for about 1 hour, thereby performing hydrothermal synthesis. After hydrothermal synthesis, centrifugation at 10,000 rpm was carried out, and the resultant was washed five times with water to obtain cobalt oxide (Co ₃ O ₄ ).

<Example 2>

The process of obtaining Co (OH) ₂ , a cobalt oxide precursor, from the waste hydrochloric acid solution was performed through the same process as in Example 1 above.

Co (OH) ₂ was separated out by filtering and centrifugation in waste hydrochloric acid solution. This filtering and centrifugation resulted in Co (OH) ₂ gel.

The gel was hydrothermally synthesized for 10 minutes at 220 ° C., 300 ° C., and 380 ° C. in an oxidation atmosphere of Co (OH) ₂ .

FIG. 2A is a transmission electron microscope (TEM) photograph of Co ₃ O ₄ hydrothermally synthesized by reacting Co (OH) ₂ , distilled water, and hydrogen peroxide added solution at 120 ° C. for 1 hour according to Example 1; .

Referring to FIG. 2A, it can be seen that Co ₃ O ₄ having several tens of nanometers is generated. The amount of Co ₃ O ₄ does not appear to be high because it is synthesized at a relatively low temperature of 120 ° C.

FIG. 2B is a transmission electron microscope photograph of Co ₃ O ₄ obtained by hydrothermally synthesizing a solution to which Co (OH) ₂ , distilled water, and hydrogen peroxide were added at 140 ° C. for 1 hour according to Example 1. FIG.

Referring to FIG. 2B, Co ₃ O ₄ having several tens of nanometer sizes was generated as in FIG. 2A. The generated Co ₃ O ₄ is expected to much compared to Co ₃ O ₄ are relatively generated at 120 ℃.

FIG. 2C is a transmission electron micrograph of Co ₃ O ₄ obtained by hydrothermally synthesizing a solution to which Co (OH) ₂ , distilled water, and hydrogen peroxide were added at 160 ° C. for 1 hour according to Example 1. FIG.

Referring to FIG. 2C, Co ₃ O ₄ having a tens of nanometer size was formed. The frequency of occurrence does not seem to be so different from FIG. 2B.

FIG. 2D is a transmission electron micrograph of Co ₃ O ₄ obtained by hydrothermally synthesizing a solution to which Co (OH) ₂ , distilled water and hydrogen peroxide are added at 180 ° C. for 1 hour according to Example 1;

Referring to Figure 2d, a very large amount of Co ₃ O ₄ particles was generated, similar to the grain size of Co ₃ O ₄ particles size of Figure 2a of Figure 2b, Co ₃ O ₄ that can be seen in Figure 2c . Therefore, in order to activate the synthesis of Co ₃ O ₄ when hydrogen peroxide (H ₂ O ₂ ) is used, it is determined that about 180 ° C is appropriate.

3 is an X-ray diffraction pattern of Co ₃ O ₄ obtained by hydrothermal synthesis at 100 ° C., 120 ° C., 160 ° C., and 180 ° C. for 1 hour according to Co (OH) ₂ and Example 1. FIG. In FIG. 3, (a) is for Co (OH) ₂ , (b) is for Co ₃ O ₄ hydrothermally synthesized at 100 ° C., and (c) is for Co ₃ O ₄ hydrothermally synthesized at 120 ° C. (D) is for Co ₃ O ₄ hydrothermally synthesized at 160 ° C., and (e) is X-ray diffraction pattern for Co ₃ O ₄ hydrothermally synthesized at 180 ° C. FIG.

Referring to FIG. 3, since Co (OH) ₂ is amorphous, it does not show a specific crystal phase, but shows a flat X-ray diffraction pattern. Crystallization was weak when hydrothermal synthesis for 1 hour at 100 ℃. However, at 120 ° C., 160 ° C., and 180 ° C., the Co ₃ O ₄ phase appeared strongly. In particular, when hydrogen peroxide (H ₂ O ₂ ) was used, it was confirmed that the crystallinity of Co ₃ O ₄ became strong.

From this, cobalt oxide precursors could be made in the synthesis of cobalt oxide using waste cemented carbide, and hydrogen peroxide could be used to oxidize nanoparticles with good crystallinity and good dispersibility even at low temperature hydrothermal synthesis. It could be confirmed that the acquisition of cobalt.

4 is a transmission electron micrograph of Co ₃ O ₄ synthesized by heat-treating the cobalt oxide precursor Co (OH) ₂ at 300 ° C. for 10 minutes according to Example 2. FIG.

Referring to Figure 4, it was confirmed that the synthesis of Co ₃ O ₄ is less than the method of supplying oxygen by adding hydrogen peroxide (H ₂ O ₂ ). However, when compared with Example 1 using hydrogen peroxide (H ₂ O ₂ ), the particle size of the resulting Co ₃ O ₄ was similar.

5 is an X-ray diffraction pattern of Co ₃ O ₄ hydrothermally synthesized at 220 ° C., 300 ° C., and 380 ° C. according to Co (OH) ₂ and Example 2. FIG. In FIG. 5, (a) is for Co (OH) ₂ , (b) is for Co ₃ O ₄ hydrothermally synthesized at 220 ° C. according to Example 2, and (c) is Co for hydrothermal synthesis at 300 ° C. ₃ O ₄ , (d) is an X-ray diffraction pattern for Co ₃ O ₄ hydrothermally synthesized at 380 ° C. FIG.

Referring to FIG. 5, Co (OH) ₂ , a cobalt oxide precursor, exhibits an amorphous state, but as the temperature increases, Co ₃ O ₄ phases appear for (b), (c), and (d). You can see that.

From this, cobalt oxide precursors could be made through neutralization titration in the synthesis of cobalt oxide using waste cemented carbide, and it was confirmed that cobalt oxide having tens of nanoscales could be synthesized only by heating at a high temperature of about 300 ° C.

As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment, A various deformation | transformation by a person of ordinary skill in the art within the scope of the technical idea of this invention is carried out. This is possible.

Claims (10)

(a) placing the spent cemented carbide and zinc in a crucible and heating it to a temperature above the melting point of zinc and below the boiling point of zinc;
(b) volatilizing and removing the zinc component by raising the waste cemented carbide and zinc to a temperature higher than the boiling point of zinc and lower than the melting temperature of tungsten carbide;
(c) pulverizing the tungsten carbide-cobalt ingot obtained by cooling the temperature of the crucible and acidifying the tungsten carbide-cobalt powder obtained by pulverization with a phosphoric acid solution to remove residual zinc (Zn);
(d) dissolving cobalt (Co) in a hydrochloric acid solution by acid treating the zinc (Zn) -removed tungsten carbide-cobalt powder with a hydrochloric acid solution;
(e) adding an alkaline solution to the hydrochloric acid solution in which cobalt (Co) is dissolved to titrate the pH to 7-14 to produce Co (OH) ₂ ;
(f) selectively separating Co (OH) ₂ by filtering and centrifuging the hydrochloric acid solution;
(g) dispersing the separated Co (OH) ₂ in distilled water;
(h) adding hydrogen peroxide to Co (OH) ₂ dispersed in the distilled water; And
(i) a method of synthesizing cobalt oxide from waste cemented carbide comprising the step of heating the solution to which the hydrogen peroxide is added to a temperature of 120 ~ 500 ℃ to obtain cobalt oxide.
(a) placing the spent cemented carbide and zinc in a crucible and heating it to a temperature above the melting point of zinc and below the boiling point of zinc;
(b) volatilizing and removing the zinc component by raising the waste cemented carbide and zinc to a temperature higher than the boiling point of zinc and lower than the melting temperature of tungsten carbide;
(c) pulverizing the tungsten carbide-cobalt ingot obtained by cooling the temperature of the crucible and acidifying the tungsten carbide-cobalt powder obtained by pulverization with a phosphoric acid solution to remove residual zinc (Zn);
(d) dissolving cobalt (Co) in a hydrochloric acid solution by acid treating the zinc (Zn) -removed tungsten carbide-cobalt powder with a hydrochloric acid solution;
(e) adding an alkaline solution to the hydrochloric acid solution in which cobalt (Co) is dissolved to titrate the pH to 7-14 to produce Co (OH) ₂ ;
(f) selectively separating Co (OH) ₂ by filtering and centrifuging the hydrochloric acid solution; And
(g) A method for synthesizing cobalt oxide from spent cemented carbide comprising the step of heating the separated Co (OH) ₂ in an oxidation atmosphere at a temperature of 220 ~ 500 ℃.
The method according to claim 1 or 2, wherein the alkaline solution is sodium hydroxide (NaOH) solution.
The method of claim 1 or 2, wherein step (a) comprises:
Placing the spent cemented carbide and zinc in a crucible and covering the crucible with a lid, and then charging the crucible into a chamber of an electric furnace;
The gas atmosphere in the chamber is made into a non-oxidizing atmosphere, and the temperature of the chamber is raised to a temperature higher than the melting point of zinc and lower than the boiling point of zinc while suppressing evaporation of zinc in the crucible closed by the crucible cover. step; And
Opening the lid of the crucible and tilting the crucible to remove the cobalt oxide from the waste cemented carbide comprising the step of removing the liquid phase Co-Zn alloy phase.
According to claim 1 or 2, wherein the weight ratio of the cemented carbide to the crucible is 1: 0.5 to 1: 6 so that when the cobalt contained in the waste cemented carbide reacts with zinc, the content of zinc is not small. A method for synthesizing cobalt oxide from spent cemented carbides.
The method of claim 1 or 2, wherein the zinc is formed by heating for 10 minutes to 12 hours at a temperature of 420 ~ 800 ℃ higher than the melting point of zinc and lower than the boiling point of zinc, characterized in that A method for synthesizing cobalt oxide from waste cemented carbide.
The method according to claim 1 or 2, wherein the temperature higher than the boiling point of zinc and lower than the melting temperature of tungsten carbide is a temperature of 910 to 1200 ° C, and the step (b) is performed at 910 to 1200 ° C so that zinc can be volatilized. A method for synthesizing cobalt oxide from spent cemented carbide, which is maintained at a temperature for 10 minutes to 12 hours.
The method of claim 1, wherein in step (h),
Co (OH) ₂ and H ₂ O ₂ are added in a ratio of 3: 1 to 1: 1 in molar ratio.
The method of claim 1, wherein the step of obtaining cobalt oxide by heating at a temperature of 120 ~ 500 ℃ to the solution to which hydrogen peroxide is added,
Heating the solution to which the hydrogen peroxide is added to a temperature of 120 to 500 ° C .;
Selectively separating cobalt oxide by centrifuging the solution containing cobalt oxide; And
A method of synthesizing cobalt oxide from spent cemented carbide comprising the step of washing the separated cobalt oxide.
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