JP7216393B2 - Graphite refiner - Google Patents

Description

TECHNICAL FIELD The present invention relates to a graphite refining apparatus configured to recover highly purified granular graphite by removing impurities from granular graphite.

Graphite has been widely used as a negative electrode material for lithium ion secondary batteries. In order to increase the capacity of the lithium ion secondary battery, it is necessary to increase the purity of the graphite used. For this reason, conventionally, a technique has been developed in which the high melting point of graphite is used to sublimate impurities by heating graphite, thereby realizing high-purity graphite.

However, when the graphite is highly purified by heat treatment, it is necessary to heat the graphite to a temperature of 2000° C. or higher, which requires a huge amount of energy. In addition, since equipment that can withstand such high temperatures is required, there is a disadvantage that equipment costs increase.

Therefore, among the conventional techniques, there is a technique for increasing the purity of granular graphite by heating granular graphite using electromagnetic waves (see, for example, Patent Document 1).

U.S. Publication No. 2017/0312730

However, the above-described prior art requires equipment for generating electromagnetic waves and a reactor with sufficient heat resistance to accommodate the graphite heated by the electromagnetic waves. Therefore, even if the time required to heat the graphite can be shortened, expensive and complicated equipment is still required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a graphite refiner capable of achieving cost reduction and simplification of equipment.

The graphite refining apparatus according to the present invention is configured to recover highly purified granular graphite by removing impurities from the granular graphite. Granular graphite is highly purified to 99.80% or more, more preferably 99.95% or more. This graphite refining apparatus includes an electrolytic cell, a graphite container, a first electrode section, a second electrode section, and power supply means.

The electrolytic cell is configured to be able to contain an electrolytic solution. Considering the possibility of using an acidic or alkaline solution as the electrolytic solution, it is preferable to use a chemical-resistant material such as polyvinyl chloride, polytetrafluoroethylene, or polyolefin resin for the electrolytic cell.

The graphite containing portion is composed of a basket-shaped mesh body that is immersed in the electrolytic solution of the electrolytic cell. For example, a material such as a carbon mesh or a chemical-resistant metal mesh is preferable as the mesh body.

The first electrode portion is arranged around the graphite containing portion. Considering that the first electrode may be immersed in an acidic or alkaline electrolyte, it is preferable to use a chemical-resistant conductive member such as carbon for the first electrode.

The second electrode portion is configured to energize the granular graphite in the graphite containing portion. As the second electrode portion, a conductive member that is in direct contact with the granular graphite and conducts electricity, or a member that conducts electricity through the granular graphite through an electrolytic solution is used. A member for stirring the electrolytic solution may be used as the second electrode portion, or a graphite mass inserted into the granular graphite may be used as the second electrode portion.

The power supply means is configured to pass current necessary for electrolysis treatment between the first electrode portion and the second electrode portion. The power supply means applies a voltage of a value set to the first electrode portion and the second electrode portion so that a current of about 30 A to 180 A flows through the granular graphite to be treated. The power supply means is usually controlled to energize the granular graphite to be treated for a period of about 30 to 120 minutes.

The opening of the mesh body forming the graphite containing portion is configured to have a size that does not allow the granular graphite to be treated to pass through. Granular graphite to be treated is often scaly powder (flakes) with a size of about 100 μm to 200 μm.

By adopting the above-described configuration, it becomes possible to highly purify the granular graphite in the graphite container by electrolysis treatment. In particular, since the granular graphite is highly purified while being accommodated in the graphite container made of the mesh body, the granular graphite can be easily recovered. In addition, since the treatment can be performed with simple equipment similar to equipment such as an electrolytic polishing apparatus, the cost of the equipment can be reduced and the equipment can be simplified as compared with the equipment required for conventional heat treatment.

In the above configuration, it is preferable that the electrolytic solution contained in the electrolytic cell is an aqueous solution containing sodium chloride. By adopting such a configuration, it becomes possible to perform electrolysis treatment on granular graphite at low cost without requiring an expensive electrolytic solution.

Further, it is preferable that the electrolysis tank is constructed so as to be connectable to the glass etching apparatus, and the used etching liquid used in the glass etching apparatus can be introduced into the electrolysis tank. When granular graphite contains silica (silicon dioxide), it may be necessary to add hydrofluoric acid, hydrosilicofluoric acid, or the like to the electrolyte. Since the used etchant used in the glass etching device contains hydrofluoric acid, hydrosilicofluoric acid, etc., silica (silicon dioxide) can be removed from granular graphite at low cost without procuring unused hydrofluoric acid. it becomes possible to

Glass etching equipment is roughly classified into a dip type etching equipment in which glass is immersed in an etchant, and a spray type etching equipment in which an etching solution is sprayed onto continuously conveyed glass. It is preferably connected to an etching device.

The reason for this is that dip-type etching equipment often discharges the etching solution after the concentration of the etching solution has decreased to the limit, whereas spray-type etching equipment often discharges a relatively high-concentration etching solution. It is from. However, even if the concentration of the used etching solution is low, it is possible to remove silica (silicon dioxide) from the granular graphite over time. is feasible.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to implement|achieve cost reduction and simplification of the installation for graphite refining.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows schematic structure of the graphite refiner|purifier which concerns on one Embodiment of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows schematic structure of the graphite refiner|purifier which concerns on one Embodiment of this invention. It is a figure which shows schematic structure of the graphite refiner|purifier which concerns on other embodiment of this invention.

1 and 2 show a schematic configuration of a graphite refiner 10 according to one embodiment of the present invention. The graphite refiner 10 includes an electrolytic processing unit 12 , a control unit 14 and a liquid circulation unit 16 . The electrolysis processing unit 12 is configured to recover high-purity (98.00% or higher) granular graphite by removing impurities from the granular graphite.

The control unit 14 includes a power supply section 142 and a control section 144 . The power supply unit 142 is configured to apply current required for electrolysis treatment between the electrode plate 24 (first electrode unit) and the second electrode unit (stirrer 26), which will be described later. The control unit 144 is configured to perform overall control such as applied voltage control and electrolytic solution temperature control in the graphite refining apparatus 10 .

The liquid circulation unit 16 is configured to circulate the electrolytic solution used in the electrolysis treatment unit 12 by means of a circulation pump 162 . As a method of liquid circulation, in addition to the structure of the liquid circulation unit 16, it is also possible to use a method such as providing a bubbling unit in the electrolysis treatment unit 12 to generate a liquid flow containing microbubbles.

The electrolysis treatment unit 12 includes an electrolysis tank 20 , a graphite container 22 , an electrode plate 24 and a stirrer 26 . The electrolytic bath 20 is made of a material having chemical resistance such as heat-resistant polyvinyl chloride, and is configured to be able to contain an electrolytic solution. In this embodiment, the electrolytic solution 32 uses an aqueous solution containing 10% by weight of sodium chloride. Examples of the electrolytic solution include an aqueous sodium chloride solution (approximately 5 to 15% by weight), an aqueous solution or mixed solution containing at least one of sulfuric acid and phosphoric acid in an amount of approximately 5 to 15% by weight. In some cases, a component such as hydrofluoric acid or hydrosilicofluoric acid capable of dissolving silica (silicon dioxide) may be appropriately added.

A heater 28 is provided inside the electrolytic bath 20 . In this embodiment, the heater 28 heats the electrolytic solution 32 to a temperature of about 60 to 70.degree.

The graphite containing portion 22 is composed of a basket-shaped mesh body capable of containing the granular graphite 30 to be purified. When the granular graphite 30 is refined, the graphite containing portion 22 is suspended from above and immersed in the electrolytic solution 32 of the electrolytic bath 20 . Although a carbon mesh basket is used as the graphite containing portion 22 in this embodiment, it is possible to adopt a configuration other than this. In principle, the graphite containing portion 22 is entirely composed of a conductive member, but in order to prevent damage due to electric current, a portion thereof is composed of an insulator (polyvinyl chloride, etc.) or is subjected to an insulation treatment. is also possible.

The electrode plate 24 corresponds to the first electrode portion according to the present invention, and is arranged around the graphite containing portion 22 . In this embodiment, the electrode plate 24 has a cylindrical shape with a plurality of openings. The electrode plate 24 is preferably made of acid-resistant punching metal. For example, precious metals such as silver, platinum, and gold can be used as materials, and carbon can be used.

However, the configuration of the electrode plate 24 is not limited to this, and may be a bottomed cylinder or a polygonal cylinder other than a circle. Further, in this embodiment, the electrode plate 24 is arranged concentrically with the graphite containing portion 22 . By adopting such an arrangement, the gap between the anode and the cathode becomes uniform everywhere, so that it is possible to prevent the occurrence of unevenness in the electrolysis treatment.

The stirrer 26 is connected to the motor via a drive transmission system such as a coupling, and is configured to stir the electrolytic solution 32 in the electrolytic bath 20 . Moreover, in this embodiment, the stirrer 26 is made of a conductive member such as carbon or noble metal. In this embodiment, the agitator 26 constitutes a second electrode section configured to energize the granular graphite 30 within the graphite container 22 .

In the configuration of the graphite refining apparatus 10 described above, the opening of the mesh member forming the graphite storage unit 22 is configured to have a size that does not allow the granular graphite 30 to be treated to pass through. The grain size of the granular graphite 30 generally processed in the graphite refiner 10 is about 100 μm to 200 μm. For this reason, it is preferable that the opening of the mesh member forming the graphite containing portion 22 has a size of about 50 μm to 100 μm.

In the structure described above, the granular graphite 30 to be highly purified is placed in the graphite container 22 and immersed in the electrolytic solution 32 . After the electrolysis treatment is ready, the control unit 144 starts energization from the power supply unit 142 . As shown in FIG. 2, the granular graphite 30 is used as the anode (+ side), and a direct current is passed through the electrolytic solution 32 between the cathode (- side), which is the counter electrode, to cause a reaction similar to electrolytic polishing. occurs. If the stirrer 26 on the anode (+) side and the graphite container 22 are severely damaged by the electric current, a period for reversing the polarity by applying an alternating current may be provided as necessary.

Generally, a current of about 30 A to 180 A is applied to granular graphite for a period of about 30 minutes to 120 minutes. As a result, the impurity metal is eluted as metal ions from the granular graphite 30 in the electrolytic solution 32 . Since the highly purified granular graphite after impurities are removed remains in the graphite containing portion 22 as it is, it is easily recovered.

When a sodium chloride aqueous solution is used as the electrolytic solution 32, chlorine is generated from the anode and hydrogen is generated from the cathode. Since the component of the aqueous sodium hydroxide solution generated increases in the electrolytic solution near the cathode, it is preferable to adjust the pH as necessary. More specifically, sodium chloride dissolved in water ionizes into sodium ions and chloride ions. Since chlorine ions are anions and are attracted to the anode, chlorine molecules are generated at the anode. Since sodium ions are cations, they are attracted to the cathode. If the electrode plate 24 serving as the cathode is made of carbon or the like, hydrogen ions produced by slight ionization of water stick to the electrode plate 24 to generate hydrogen. Sodium hydroxide is generated as a result of sodium ions and hydroxide ions remaining in the electrolyte.

When sodium chloride is used as the electrolytic solution 32, a technique similar to neutral salt electrolytic etching is used. Also, if necessary, a technique similar to electrolytic etching using an inorganic acid or an alkaline solution may be used.

The granular graphite 30 is a tortoise shell-like layered substance, and there is a high possibility that impurities remain between the layers. Therefore, it is important to permeate the electrolyte between the layers, and it is preferable to use ultrasonic vibration, a surfactant, bubbling (microbubbles), etc. together as necessary.

Examples of impurities remaining in granular graphite include SiO ₂ (silicon dioxide: silica) and Al ₂ O ₃ (aluminum oxide: alumina). In particular, silicon dioxide is likely to be difficult to remove only by the above treatment. In such a case, it is preferable to add hydrofluoric acid or hydrosilicofluoric acid in an amount of 1 to 10% by weight to the electrolytic solution. In this case, from the viewpoint of shortening the treatment time, it is preferable to use hydrochloric acid in combination as necessary.

FIG. 3 schematically shows a state in which the graphite refining apparatus 10 is connected to a spray type glass etching apparatus 50. As shown in FIG. The spray-type glass etching apparatus 50 is configured to spray an etchant containing hydrofluoric acid onto glass substrates that are continuously transported. In the processing chamber of the spray type glass etching apparatus 50, the glass substrate is etched by contacting the etching solution with the glass substrate.

The etchant used in the spray type glass etching apparatus 50 still contains enough hydrofluoric acid or hydrosilicofluoric acid to remove silicon dioxide from the granular graphite 30 . Therefore, in this embodiment, the discharge port 42 of the spray type glass etching apparatus 50 and the introduction port 44 of the electrolysis bath 20 are connected via a polyvinyl chloride pipe 40 that is resistant to the etchant containing hydrofluoric acid. Connected. By adopting such a configuration, the used etching liquid in the spray type glass etching apparatus 50 can be introduced into the electrolytic bath 20 and reused as a chemical liquid to be added to the electrolyte.

The description of the above-described embodiments should be considered illustrative in all respects and not restrictive. The scope of the invention is indicated by the claims rather than the above-described embodiments. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and range of equivalents of the claims.

10-Graphite refining device 12-Electrolysis treatment unit 14-Control unit 16-Liquid circulation unit 20-Electrolysis tank 22-Graphite storage part 24-Electrode plate 26-Agitator 32-Electrolyte solution 50-Spray type glass etching device

Claims (1)

A refining apparatus for silicon dioxide-containing graphite configured to recover highly purified granular graphite by removing impurities containing silicon dioxide from the silicon dioxide-containing granular graphite to be purified, comprising:
an electrolytic cell capable of containing an electrolytic solution;
a graphite containing portion made of a basket-shaped mesh body immersed in the electrolytic solution of the electrolytic bath;
a first electrode portion arranged around the graphite containing portion;
a second electrode portion configured to conduct electricity to the granular graphite in the graphite containing portion;
power supply means configured to pass current required for electrolysis treatment between the first electrode portion and the second electrode portion;
with
The opening of the mesh body constituting the graphite containing portion is configured to have a size that does not allow the granular graphite to be treated to pass through, and the electrolytic bath is configured to be connectable to a glass etching apparatus, The used etchant used in the glass etching apparatus can be introduced into the electrolytic bath, and
A graphite refining apparatus, wherein the electrolytic solution contained in the electrolytic bath contains the used etching solution.

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