JP7583859B2 - Precipitation Mixer - Google Patents

Description

The present invention relates to a method for recovering valuable metal powder contained in waste resist liquid, and an apparatus suitable for said recovery method.

Lithography technology is used to process fine patterns in the manufacturing process of semiconductor devices such as ICs and LSIs. In lithography, a resist pattern is formed using a polymeric resist material such as a photosensitive resin, and then a thin film of the desired metal (hereinafter referred to as a valuable metal thin film) such as gold, silver, palladium, platinum, rhodium, ruthenium, iridium, copper, nickel, cobalt, or chromium is formed on the resist by deposition or plating, and then the resist is removed (lifted off) with a solvent such as a stripping solution. Since valuable metal thin films are contained in waste resist liquid, there has been a demand for the recovery of valuable metals. The recovery of valuable metals from waste resist liquid is also desired in the manufacturing processes of printed wiring boards, semiconductors, and other products.

As a method for removing solids from resist waste liquid, for example, separation and removal in a treatment tank equipped with multiple filters is known (Patent Document 1). However, the valuable metal thin film in the resist waste liquid is partially finely divided by contact in, for example, piping, pumps, or storage tanks during the time it is supplied from the resist waste liquid source to the treatment tank. Therefore, a filter with small mesh size is required to recover the finely divided valuable metals (hereinafter referred to as valuable metal fine particles). However, valuable metals that exist in a relatively large thin film form (hereinafter referred to as valuable metal thin film) also exist, and there is a problem that the valuable metal thin film is prone to clogging the filter due to its large surface area. In addition, since resist waste liquid is highly viscous, if the filter mesh size is made small, clogging will easily occur. Therefore, frequent maintenance of the filter is required, and the cost of recovering valuable metals increases.

Special Publication No. 2001-502847

The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to reduce the concentration of valuable metal powder in the supernatant liquid by precipitating a portion of the valuable metal powder in the waste liquid.

The present invention, which has solved the above problems, has the following configuration.
[1] A method for recovering valuable metal powder from a resist waste liquid containing valuable metal powder, comprising a step of separating the resist waste liquid by sedimentation into a supernatant liquid containing floating valuable metal powder and a sediment containing a precipitate containing valuable metal powder, a step of adding insoluble particles to the supernatant liquid overflowing from the sedimentation step, and a step of filtering the supernatant liquid containing the insoluble particles.

[2] The valuable metal powder recovery method described in [1], in which the filtering step is performed by filtering the supernatant after forming a precoat layer.

[3] A valuable metal powder recovery method according to [1] or [2], in which the valuable metal powder contained in the resist waste liquid has a particle size of 0.1 μm or more.

[4] The valuable metal powder recovery method according to any one of [1] to [3], wherein the valuable metal powder is at least one selected from the group consisting of gold, silver, palladium, platinum, rhodium, ruthenium, iridium, copper, nickel, cobalt, and chromium.

[5] A precipitation mixing device used in the settling separation step and the insoluble particle addition step of the valuable metal powder recovery method described in any one of [1] to [4], the precipitation mixing device having a settling separation tank that separates a resist waste liquid containing valuable metal powder into a buoyant valuable metal powder-containing supernatant liquid and a settleable valuable metal powder-containing precipitate by settling separation, and an addition mixing tank that adds insoluble particles to the supernatant liquid that overflows from the settling separation tank.

[6] A filtration device used in the filtration step of the valuable metal powder recovery method described in any one of [1] to [4], the filtration device having a precoat layer and a filtration membrane.

[7] A valuable metal powder recovery facility equipped with the precipitation mixer described in [5] and the filtration device described in [6].

The present invention makes it possible to separate and recover valuable metal powder from waste resist liquid. The present invention also makes it possible to extend the life of the filtration membranes used in treating waste resist liquid.

FIG. 1 is a schematic diagram illustrating the flow of the valuable metal powder recovery method of the present invention. FIG. 2 is an exploded view of the precipitating mixer of the present invention, in which (A) is a side view, (B) is a view from the settling tank side, and (C) is a view from the mixing tank side. FIG. 3 is an exploded view of the precipitating mixer of FIG. 2, where (D) is a view from the ceiling side and (E) is a view from the bottom side. FIG. 4 is a schematic explanatory diagram of the filtration device, in which (A) is a side view, (B) is a front view, and (C) is a schematic explanatory diagram of the mixed liquid supply means as viewed from the ceiling surface side. FIG. 5 is a graph showing the change in filtration rate in the examples. FIG. 6 is a graph showing the change in filtration rate in the examples.

The inventors have studied a method for recovering valuable metal powder contained in resist waste liquid. The resist waste liquid contains valuable metal fine particles and valuable metal thin films of various sizes, and these must be treated at the same time (hereinafter, valuable metal fine particles and valuable metal thin films are collectively referred to as valuable metal powder). In addition, resist waste liquid has a high viscosity due to the resist, so there is a problem that the filter is easily clogged. The inventors have attempted to recover valuable metal powder in stages by installing multiple filters with different mesh sizes, but the filters became clogged in a short time and had to be replaced frequently. As another valuable metal powder recovery method, for example, recovery by precipitating valuable metal powder in resist waste liquid was also considered, but a large settling tank was required to treat the resist waste liquid discharged from the factory in a short time, and it was difficult to secure the installation space. As such, the conventional valuable metal powder recovery method required frequent maintenance, and in order to ensure a sufficient processing volume, the equipment became large, so installation space was required, and there were practical problems.

After extensive research into valuable metal powder recovery methods, the inventors discovered that by precipitating a portion of the valuable metal powder in the resist waste liquid, and then filtering and separating the valuable metal powder remaining in the supernatant, and adding insoluble particles to the supernatant prior to filtration, valuable metal powder can be recovered in a small space and with a high yield. In particular, the present invention can extend the life of the filtration membrane, greatly reducing the frequency of maintenance.

The following describes the valuable metal powder recovery method of the present invention and an apparatus suitable for the valuable metal powder recovery method.

The method for recovering valuable metal powder from waste resist liquid of the present invention comprises the following steps.
(1) A process for separating a resist waste liquid containing valuable metal powder into a supernatant liquid containing floating valuable metal powder and a sediment containing sinking valuable metal powder (hereinafter referred to as a sedimentation separation process).
(2) A step of adding insoluble particles to the supernatant liquid overflowing from the sedimentation separation step (hereinafter referred to as the adding step).
(3) A step of filtering the insoluble particle-containing supernatant (hereinafter referred to as the filtering step).
The above recovery method allows valuable metal powder to be recovered from resist waste liquid as precipitates and filtration residues with high yields, and also allows the maintenance interval of the filtration membrane to be significantly extended.

(Waste resist liquid)
The resist waste liquid targeted by the present invention is waste liquid containing various known polymeric resist components such as phenolic resin, various known developers, etching solutions, cleaning solutions, and other resist removers used to remove resist, and valuable metal powder. The resist waste liquid may also contain various additives such as photosensitizers and solvents. The composition of the resist waste liquid varies depending on the source of discharge, but any of them can be treated by the present invention. The resist waste liquid has viscosity due to the resist material, but the viscosity of the resist waste liquid targeted by the present invention is not particularly limited because it varies depending on the source of discharge. The viscosity of the resist waste liquid is, for example, 1.0 cP or more at room temperature.

In the present invention, the valuable metal powder contained in the resist waste liquid is exemplified by gold, silver, palladium, platinum, rhodium, ruthenium, iridium, copper, nickel, cobalt, and chromium. The valuable metal powder to be recovered is preferably at least one selected from the group consisting of gold, silver, palladium, platinum, rhodium, ruthenium, iridium, copper, nickel, cobalt, and chromium, and more preferably gold. Therefore, if the precipitate or filtration residue contains metals other than the target to be recovered, they may be separated by various known methods. The valuable metals to be recovered in the present invention are metals precipitated in the resist waste liquid in the form of fine particles or thin films, and do not include unprecipitated metals.

The concentration of valuable metal powder in the resist waste liquid is not particularly limited, as it varies depending on the amount of valuable metal used, the amount of resist, the amount of resist removal liquid, etc. in various manufacturing processes such as the semiconductor manufacturing process. In the present invention, even if the concentration of valuable metal powder contained in the resist waste liquid is high, problems such as clogging do not occur, and valuable metal powder can be recovered with a high yield. Therefore, the concentration of valuable metal powder contained in the resist waste liquid may be preferably 0.001 g/L or more, more preferably 0.01 g/L or more. There is also no particular upper limit. The method for measuring the concentration of valuable metal powder is to filter the resist waste liquid, dry the residue together with the filter paper, measure its weight, and calculate the solid weight by subtracting the dry weight of the filter paper.

The size of the valuable metal powder contained in the resist waste liquid is preferably 0.1 μm or more in maximum particle diameter. The valuable metal powder in the resist waste liquid is pulverized by collisions during the transfer process, but in the present invention, the pulverization of the valuable metal powder can be suppressed, so a high yield can be achieved by targeting valuable metal powder with a maximum particle diameter of 0.1 μm or more. The upper limit of the maximum particle diameter of the valuable metal powder and the film thickness of the thin film-like valuable metal powder are not limited because they depend on the manufacturing conditions in the semiconductor manufacturing process, etc. The maximum particle diameter of the valuable metal powder in the present invention is measured using a laser diffraction/scattering type particle size distribution measuring device.

The valuable metal powder recovery method of the present invention will be described below with reference to FIG.
Resist waste liquid is supplied to the settling separation process 3 of the present invention from a resist waste liquid generation source 1 such as a semiconductor manufacturing process. The resist waste liquid may be supplied to the settling separation process 3 directly from the resist waste liquid generation source 1, or may be temporarily stored in a resist waste liquid storage tank 2 and then supplied to the settling separation process 3. By providing the resist waste liquid storage tank 2, it is not necessary to stop the manufacturing line of semiconductors or the like even during maintenance of the valuable metal powder recovery process of the present invention. Furthermore, by providing the resist waste liquid storage tank 2, the component composition of the resist waste liquid supplied to the valuable metal powder recovery process of the present invention can be made uniform. Furthermore, the supply amount of the resist waste liquid can be adjusted according to the processing amount of the valuable metal powder recovery process of the present invention. The resist waste liquid may be supplied to the settling separation process 3 continuously, or may be supplied in a constant amount at a time for batch processing. Considering the precipitation efficiency of the valuable metal powder in the settling separation process 3, batch processing is preferable.

(1) Sedimentation separation process The sedimentation separation process 3 of the present invention is a process for separating the resist waste liquid into a supernatant liquid containing floating valuable metal powder and a precipitate containing sedimentary valuable metal powder. The concentration of valuable metal powder in the supernatant liquid can be reduced by precipitating a part of the valuable metal powder in the resist waste liquid. Therefore, clogging of the filtration membrane caused by the valuable metal powder can be suppressed when filtering the supernatant liquid in the filtration process. In the present invention, both floating valuable metal powder and precipitated valuable metal powder are valuable metal powders in the resist waste liquid, but the floating valuable metal powder refers to the valuable metal powder that does not settle within a predetermined time and is floating in the resist waste liquid, and the precipitated valuable metal powder refers to the valuable metal powder that has a large specific gravity and has settled. The supernatant refers to the resist waste liquid supplied from the sedimentation separation process 3 to the addition process 4.

In order to prevent clogging of the filtration membrane in the filtration process 7, it is desirable to precipitate the valuable metal powder in the resist waste liquid as much as possible in the sedimentation separation process 3. The amount of valuable metal powder to be precipitated may be appropriately determined according to the concentration of valuable metal powder in the resist waste liquid and the processing capacity of the filtration process 7. For example, the amount of valuable metal powder in the supernatant liquid supplied from the sedimentation separation process 3 to the addition process 4 relative to the amount of valuable metal powder in the resist waste liquid introduced into the sedimentation separation process 3 (= amount of valuable metal powder in the supernatant liquid (g) / amount of valuable metal powder in the resist waste liquid (g) × 100%) is preferably 30 mass% or less, more preferably 20 mass% or less, even more preferably 10 mass% or less, and even more preferably 5 mass% or less.

The separation processing conditions in the sedimentation separation process 3, particularly the residence time of the resist waste liquid, may be appropriately determined so that the valuable metal powder in the supernatant liquid reaches a predetermined concentration. The precipitated valuable metal powder may be recovered by various known methods. Note that in the present invention, the valuable metal powder is separated by natural sedimentation, and no additives such as flocculants are added.

In the present invention, it is also preferable to remove valuable metal powder floating near the surface of the resist waste liquid from among the valuable metal powder floating in the resist waste liquid in the sedimentation separation process 3. By removing the valuable metal powder floating near the surface of the resist waste liquid, the valuable metal powder concentration in the supernatant liquid supplied to the next process can be further reduced. The valuable metal powder near the surface of the resist waste liquid may be removed by any means, for example, by contacting a nonwoven fabric with the resist waste liquid to cause the valuable metal powder to adhere to the nonwoven fabric, or by using a solid-liquid separation means such as a filter. Alternatively, a plate member such as a blocking plate 16 may be provided to prevent the resist waste liquid from overflowing, as described below.

When resist waste liquid is supplied to the settling separation process 3 in a batchwise manner, the water level of the resist waste liquid rises with the supply of new resist waste liquid. Also, when resist waste liquid is continuously supplied to the settling separation process 3, the water level of the resist waste liquid rises continuously. When the resist waste liquid in the settling separation process 3 exceeds a certain water level, the excess is supplied to the adding process 4 as a supernatant liquid. In the present invention, the resist waste liquid is supplied from the settling separation process 3 to the adding process 4 by overflow. Therefore, compared to when resist waste liquid is transferred by connecting the processes with piping or pumps, it is possible to suppress the fineness of valuable metal powder, and this is effective in suppressing clogging of the filtration membrane.

(2) Addition Step The addition step 4 of the present invention is a step of adding insoluble particles to the supernatant liquid overflowing from the above-mentioned settling separation step 3. The insoluble particles also function as a body feed in the next step, the filtration step 7, and therefore can suppress adhesion of valuable metal powder and resist components to the filtration membrane.

(Insoluble particles)
The insoluble particles used in the present invention are solids that are insoluble in the resist waste liquid. They are preferably organic or inorganic particles that are insoluble in the resist removal liquid contained in the resist waste liquid, and more preferably inorganic particles. In addition, it is preferable that the insoluble particles are porous. The porous insoluble particles adsorb fine valuable metal powders among the valuable metal powders in the supernatant liquid and retain the valuable metal powders in the pores during filtration, so that the adhesion of valuable metal powders to the filtration membrane can be further reduced. In addition, it is preferable that the insoluble particles have a specific gravity that is sufficient to precipitate during filtration.

Examples of insoluble particles include organic adsorbents such as cellulose and carbon, and inorganic adsorbents such as diatomaceous earth, perlite, and glass beads. Among these, porous inorganic adsorbents are preferred, and diatomaceous earth is more preferred. One type of insoluble particle may be used, or two or more types may be used in combination.

The average particle size of the insoluble particles is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 20 μm or more, and is preferably 100 μm or less, more preferably 80 μm or less, and even more preferably 40 μm or less. From the viewpoint of improving the body feed effect, it is preferable that the average particle size of the insoluble particles is large, but if the particle size is too large, the packing density may decrease and the body feed effect may decrease. Furthermore, if the average particle size of the insoluble particles having porosity becomes too large, the amount of adsorption of fine valuable metal powder may decrease due to the reduced surface area.

The amount of insoluble particles added varies depending on the concentration of valuable metal powder in the resist waste liquid and the specific gravity of the insoluble particles added, but is preferably 0.001 g/L or more, more preferably 0.005 g/L or more, even more preferably 0.01 g/L or more in the supernatant liquid, and is preferably 10 g/L or less, more preferably 5 g/L or less, even more preferably 1 g/L or less. The more insoluble particles are added, the better the above effect, but if too much is added, the amount of processing will increase.

It is preferable to mix the added insoluble particles with the supernatant liquid to disperse them uniformly. The insoluble particles may be added to the supernatant liquid as is, or may be added to a solvent such as water to form a liquid (hereinafter referred to as an insoluble particle-containing liquid). In environments where scattering of powder is undesirable, such as clean rooms, an insoluble particle-containing liquid is preferable.

Since the insoluble particles added to the supernatant liquid tend to settle, it is desirable to agitate the supernatant liquid to maintain a uniform dispersion state. The means for agitating the supernatant liquid are not particularly limited. For example, it is preferable to agitate the supernatant liquid using a non-mechanical agitation means. Examples of the non-mechanical agitation means include a jetting means such as a nozzle. For example, a gas such as air; a liquid such as the insoluble particle-containing liquid or the supernatant liquid in the mixing tank is supplied from the jetting means to the supernatant liquid, and agitation by a jet (hereinafter referred to as a non-mechanical means) is preferable. In the present invention, a previously prepared insoluble particle-containing liquid may be stored in an insoluble particle storage tank 5 and supplied from the tank 5 to the supernatant liquid via a jetting means such as a nozzle, or the supernatant liquid in the mixing tank may be extracted and supplied from the jetting means to circulate the supernatant liquid.

(3) Filtration step The filtration step 7 is a step of separating the supernatant liquid (hereinafter referred to as the mixed liquid) to which the insoluble particles have been added into a residue containing valuable metal powder and a waste liquid not containing valuable metal powder. After filtration, the valuable metal powder can be recovered from the residue containing valuable metal powder by a known means. Filtration is preferable to other solid-liquid separation means such as sedimentation, centrifugation, and filter separation because of its excellent recovery rate of valuable metal powder, ease of maintenance, space saving, and processing speed.

The filter membrane used for filtration may be appropriately determined taking into consideration the yield of valuable metal powder, processing efficiency, etc. The smaller the pore size of the filter membrane, the higher the yield of valuable metal powder. On the other hand, if the pore size of the filter membrane is too small, clogging by resist components is likely to occur. In the present invention, since the fineness of valuable metal powder is suppressed in the transfer of the supernatant from the sedimentation separation process 3 to the addition process 4 and in the mixing of the supernatant with insoluble particles, if valuable metal powder with a maximum diameter of 0.1 μm or more can be collected by filtration, a sufficiently high yield, for example, preferably 99% or more, more preferably 99.9% or more of the valuable metal powder contained in the mixed liquid can be recovered. Therefore, according to the present invention, it is possible to ensure a high yield while suppressing clogging for a long period of time.

Specifically, microfiltration (MF) is preferred. Valuable metal powder can also be collected by ultrafiltration (UF) or nanofiltration (NF), but since clogging due to resist components or valuable metal powder can easily occur, microfiltration (MF) is preferred from the viewpoint of maintainability. In the present invention, considering that the target of recovery is valuable metal powder with a maximum particle size of 0.1 μm or more, the pore size of the filtration membrane is preferably 0.01 μm or more, more preferably 0.05 μm or more, and preferably 10 μm or less, more preferably 5 μm or less. In addition, the filtration may be natural filtration, reduced pressure filtration, or pressure filtration, but reduced pressure filtration or pressure filtration is preferred from the viewpoint of improving the filtration speed.

Examples of the material for the filtration membrane include organic membranes such as polyethylene, tetrafluoroethylene, polypropylene, cellulose acetate, polyacrylonitrile, polyimide, polysulfone, polyethersulfone, and pulp, and inorganic membranes such as aluminum oxide, zirconium oxide, titanium oxide, stainless steel, and glass. It is desirable to select the material for the filtration membrane appropriately in consideration of durability and other factors according to the liquid properties of the resist waste liquid (e.g., pH, liquid temperature, organic composition, resist removal components, etc.). In the present invention, paper filters and glass filters are preferred.

Filtration conditions can be determined appropriately taking into account the capacity of the filtration device. For example, the filtration flow rate is 20 L/min and the filtration pressure is -0.07 MPa.

In the present invention, it is preferable to form a precoat layer 6 before filtration. By providing the precoat layer 6, clogging of the filter medium by valuable metal powder and resist components can be further suppressed. The material forming the precoat layer 6 can preferably be one of the materials exemplified as the insoluble particles above. The material used for the precoat layer 6 may be one type, or two or more types may be used in combination. There is no restriction on whether the material used for the precoat layer 6 is the same as the material used for the insoluble particles.

In addition, the insoluble particles contained in the mixed liquid supplied from the addition step 4 to the filtration step 7 are successively deposited on the filtration membrane or on the precoat layer 6 to produce a filter cake. As a result, the outermost surface of the filter cake is successively renewed, making it possible to suppress the increase in cake resistance that accompanies the progress of filtration, and to suppress clogging of the filtration membrane for a long period of time.

As described above, the present invention makes it possible to separate and recover valuable metal powder from waste resist liquid. The present invention also makes it possible to extend the life of the filtration membranes used in treating waste resist liquid.

Below, a valuable metal powder recovery facility suitable for the valuable metal powder recovery method of the present invention will be described with reference to Figures 2 to 4.

Valuable metal powder recovery equipment A valuable metal powder recovery equipment suitable for the above valuable metal powder recovery method of the present invention has at least a precipitation mixer 10 (Figs. 2 and 3) and a filtration device 11 (Fig. 4). The valuable metal powder recovery equipment of the present invention may further have a resist waste liquid storage tank (2 in Fig. 1) and/or an insoluble particle-containing liquid storage tank (5 in Fig. 1). These devices and tanks are connected to each other by piping (8a to 8e in Fig. 1). In addition, the piping is provided with pumps and valves (not shown) as necessary to adjust the supply amount.

Precipitation Mixing Apparatus The precipitation mixing apparatus 10 of the present invention has a configuration including a settling tank 12 for carrying out the settling separation step 3 and a mixing tank 13 for carrying out the addition step 4. The precipitation mixing apparatus 10 is preferably a rectangular parallelepiped or cube, and the interior of the precipitation mixing apparatus 10 is divided into a settling tank 12 and a mixing tank 13 by partitioning with a partition 17. The partition 17 is installed so that a gap is formed between the ceiling surface 22 and the upper end of the partition 17. By providing the gap, when the liquid level of the resist waste liquid in the settling tank 12 exceeds the upper end of the partition 17, it overflows and is supplied to the mixing tank 13. Note that, unlike the illustrated example, when the partition 17 is installed so as to be in contact with the ceiling surface 22, an opening may be provided in the partition 17 so that the supernatant liquid is supplied to the mixing tank 13 from the opening.

Sedimentation tank The sedimentation tank 12 is a means for allowing the resist waste liquid to remain for a predetermined time to precipitate at least a part of the valuable metal powder. The sedimentation tank 12 has a resist waste liquid supply port 19 and a flow path plate 14. Hereinafter, the space between the flow path plate 14 and the wall surface 20c of the sedimentation tank 12 (i.e., the side where the resist waste liquid supply port 19 is provided) may be referred to as a first sedimentation section 30, and the space between the flow path plate 14 and the partition wall 17 may be referred to as a second sedimentation section 31.

The resist waste liquid supply port 19 is a means for supplying resist waste liquid delivered from a resist waste liquid source to the settling tank 12. The resist waste liquid supply port 19 is connected to a resist waste liquid source such as a semiconductor manufacturing process (not shown) or a resist waste liquid storage tank (not shown). The resist waste liquid supply port 19 is provided on the ceiling surface 22 on the first settling section 30 side. The position of the lower end of the resist waste liquid supply port 19 is not particularly limited. In the illustrated example, it extends to the vicinity of the resist waste liquid receiving section 15.

The flow path plate 14 is a means for controlling the flow of the supplied resist waste liquid. The flow path plate 14 is provided between the wall surface 20c of the settling tank 12 and the partition wall 17. The sides of the flow path plate 14 are fixed to the opposing wall surfaces 20a, 20b of the settling tank 12 as shown in FIG. 3. The upper end of the flow path plate 14 only needs to be higher than the upper end of the partition wall 17, and it does not matter whether it is in contact with the ceiling surface 22 of the settling tank 12. The lower end of the flow path plate 14 is also provided so that there is a gap between it and the bottom surface 21 of the settling tank 12. The resist waste liquid supplied from the first settling section 30 side is supplied to the second settling section 31 side through the gap between the lower end of the flow path plate 14 and the bottom surface 21 of the settling tank 12. It is preferable that the lower end of the flow path plate 14 is lower than the upper end of the partition wall 17, or the opening (hereinafter the same) if an opening is provided in the partition wall 17. If the gap between the lower end of the flow path plate 14 and the bottom surface 21 of the settling tank 12 is too narrow, the flow rate of the resist waste liquid passing through the gap may increase, causing the precipitate to be stirred up. In order to prevent such stirring up, the height of the gap between the lower end of the flow path plate 14 and the bottom surface is preferably about 20% of the height of the settling tank, and more preferably 10% or more. By providing the flow path plate 14, the flow rate of the supplied resist waste liquid can be reduced, and as a result, the settling inhibition of valuable metal powder in the resist waste liquid retained in the second settling section 31 can be suppressed.

An inclined plate 18 may be provided on the bottom surface 21 of the settling tank 12 as necessary. The inclined plate 18 is a means for moving the precipitate from the first settling section 30 side to the second settling section 31 side. The inclined plate 18 is preferably installed so that it lowers from the wall surface 20c side on the first settling section 30 side toward the partition wall 17. Since the resist waste liquid supplied from the resist waste liquid supply port 19 passes through a gap at the lower end of the flow path plate 14, precipitates tend to accumulate near the gap. Therefore, providing the inclined plate 18 can suppress the accumulation of precipitates in the gap. Furthermore, since the precipitates accumulate on the second settling section 31 side, it becomes easier to collect the precipitates.

A blocking plate 16 may be provided in the settling tank 12 as necessary. The blocking plate 16 is a means for preventing valuable metal powder floating on the surface of the resist waste liquid from being supplied to the mixing tank 13 together with the supernatant liquid. The sides of the blocking plate 16 are fixed to the opposing wall surfaces 20a and 20b of the settling tank 12 shown in FIG. 3. The lower end of the blocking plate 16 is installed so as to be lower than the upper end of the partition wall 17. It is also preferable that the lower end surface of the blocking plate 16 is horizontal in the direction of the wall surfaces 20a and 20b. The lower end of the blocking plate 16 may be installed so as to leave a space between it and the bottom surface 21 of the settling tank 12. The lower end of the blocking plate 16 may be installed so as to be preferably 1 cm to 5 cm, more preferably 5 cm to 10 cm lower than the upper end of the partition wall 17. The upper end of the blocking plate 16 should be higher than the upper end of the partition wall 17 so as not to allow the resist waste liquid to overflow, and it does not matter whether or not it comes into contact with the ceiling surface 22 of the settling tank 12. The blocking plate 16 may be installed at an angle to the wall surface 20c of the settling tank 12. In that case, it is preferable to incline the blocking plate 16 so that the partition wall 17 side of the blocking plate 16 is on the upper side and the flow path plate 14 side is on the lower side, as in the illustrated example. When the blocking plate 16 is inclined, the valuable metal powder accumulated on the blocking plate 16 is pushed toward the partition wall 17 (the opposite direction to the liquid surface), so the accumulated valuable metal powder does not return to the waste resist liquid, and the valuable metal powder can be efficiently recovered.

The sedimentation tank 12 may be provided with a resist waste liquid receiving section 15 as necessary. The resist waste liquid receiving section 15 is a means for attenuating the flow rate of the resist waste liquid supplied from the resist waste liquid supply port 19. In the illustrated example, the resist waste liquid receiving section 15 has walls on the bottom and all four sides, the ceiling surface is open, and a plurality of openings 15a are provided on the side of the resist waste liquid receiving section 15 on the wall surface 20c side. As illustrated, the side of the resist waste liquid receiving section 15 is fixed to the walls 20a and 20b of the sedimentation tank 12. A gap 32 is provided between the wall surface 20c and the resist waste liquid receiving section 15. The supplied resist waste liquid is supplied from the openings 15a of the resist waste liquid receiving section 15 through the wall surface 20c to the first sedimentation section 30.

It is preferable to provide a discharge port 38 on the bottom surface 21 of the settling tank 12. The discharge port 38 is a means for discharging the precipitate in the settling tank 12. The resist waste liquid in the settling tank 12 may be discharged from the discharge port 38 together with the precipitate, or an extraction port 36 may be provided as shown in the figure separately from the discharge port 38 to extract the resist waste liquid. The extraction port 36 may be provided at any position of the settling tank 12, preferably near the bottom surface 21, and the precipitate may be collected from within the settling tank 12 after the resist waste liquid is discharged. The discharged resist waste liquid may be returned to a resist waste liquid storage tank and then supplied to the settling tank 12 again. Alternatively, the discharged resist waste liquid may be supplied to a filtration device 11 for solid-liquid separation.

Mixing Tank The mixing tank 13 is a means for adding insoluble particles to the supernatant liquid supplied from the settling tank 12 and stirring and mixing the particles. The mixing tank 13 has an insoluble particle supplying means 34, a stirring and mixing means 35, and a discharge port 33.

The insoluble particle supplying means 34 is a means for supplying insoluble particles to the supernatant liquid supplied to the mixing tank 13. The tip of the insoluble particle supplying means 34 is not particularly limited, and a known supplying means such as a nozzle can be used. The insoluble particle supplying means 34 is connected to an insoluble particle supply source such as an insoluble particle storage tank (not shown), and is configured to be supplied to the mixing tank 13 via a feeding means such as a pump. Powdered insoluble particles may be supplied by a feeder, or the insoluble particles may be mixed with a liquid and supplied by compressed air. Considering the processing in the filtration device, it is also preferable to supply the insoluble particles as a powder rather than mixing them with a liquid. It is desirable to adjust the installation position of the tip of the insoluble particle supplying means 34 so that the supplied insoluble particles do not scatter. For example, when diatomaceous earth is fed as insoluble particles using compressed air, if the tip of the insoluble particle feed means 34 is in contact with the supernatant liquid in the mixing tank, the compressed air will cause the supernatant liquid to bubble, scattering the diatomaceous earth and causing it to become mixed into the settling tank 12. For this reason, it is desirable to install the tip so that it does not come into contact with the liquid surface.

The stirring/mixing means 35 is a means for stirring and mixing the supernatant liquid and the insoluble particles. The stirring/mixing means 35 has a jetting means such as nozzles 37a and 37b at the tip, and the supernatant liquid is made to flow by the liquid or gas jetted from the nozzles 37a and 37b. From the viewpoint of suppressing the fineness of the valuable metal powder during mixing, it is desirable to install the jetting means at the tip of the stirring/mixing means 35 so that the supernatant liquid flows in a spiral shape by the jetting. From the viewpoint of efficiently flowing the supernatant liquid, it is more preferable that the jetting means is located near the bottom surface 21. The number of stirring/mixing means 35 is one or more, and preferably two. In the illustrated example, the nozzles 37a and 37b, which are jetting means, are installed diagonally on a horizontal plane. The stirring/mixing means 35 is connected to the lower part of the mixing tank 13, i.e., the discharge port 33. During operation, the supernatant liquid is extracted from the mixing tank 13 via a pump (not shown) and supplied from the supply port 35a of the stirring/mixing means 35, and is injected into the supernatant liquid from the nozzles 37a and 37b.

The outlet 33 is a means for extracting the supernatant liquid (hereinafter referred to as the mixed liquid) mixed with insoluble particles. The pipe connected to the outlet 33 branches and connects to the supply port 35 and also to the filtration device 11. It is preferable to provide an adjustment means such as a valve on each of the branched pipes. The outlet 33 is provided on the bottom surface of the mixing tank 13, and the mixed liquid is appropriately extracted from the outlet 33 and supplied to the filtration membrane 39 from the mixed liquid supply means 40 of the filtration device 11 through a pipe not shown. For example, an adjustment means such as a valve or a temporary storage tank may be provided to adjust the amount of the supernatant liquid supplied to the filtration device 11.

Filtration device The filtration device used in the present invention can be an industrially used filtration device. Therefore, it is not limited to the illustrated example and can be modified as appropriate. The filtration device 11 is a means for separating the supernatant liquid into a residue containing valuable metal powder and a waste liquid from which the valuable metal powder has been removed (hereinafter referred to as a treated liquid). The filtration device 11 has a filtration membrane 39 and a mixed liquid supplying means 40. A filtration membrane having a desired filtration performance is used as the filtration membrane 39. The peripheral portion of the filtration membrane 39 is preferably fixed by a fixing means such as a protective plate 44. In the illustrated example, the filtration membrane 39 is shown through in order to show it.

The mixed liquid supply means 40 is a means for supplying the mixed liquid delivered from the mixing tank 13 to the filtration membrane 39. The mixed liquid supply means 40 has a supply port 42 for supplying the mixed liquid to the filtration membrane 39. In the illustrated example, the mixed liquid is supplied from the supply port 42 to the filtration membrane 39 via a supply path 43a installed so that the mixed liquid flows vertically and a supply path 43b installed so that the mixed liquid flows horizontally. Specifically, the supply path 43b is formed in a ring shape as shown in FIG. 4(C). The supply port 42 is also installed diagonally downward outside the ring-shaped supply path 43b, preferably so that the mixed liquid hits the protective plate 44. With this configuration, the drop impact of the mixed liquid supplied from the supply port 42 is attenuated by the protective plate 44 before being supplied to the filtration membrane 39. Also, if the distance from the supply port 42 to the protective plate 44 is large, the droplets falling from the supply port 42 may bounce back and damage the filtration membrane 39. Therefore, it is preferable that the distance between the supply port 42 and the protective plate 44 is as close as possible. The specific distance can be set appropriately taking into consideration the size of the droplets, the strength of the filtration membrane, etc. Note that the precoat layer 41 is omitted in FIG. 4(C). The filtrate is temporarily stored in the filtrate tank 46 and then appropriately processed.

If necessary, a precoat layer 41 may be provided on the filtration membrane. The various known precoat materials already exemplified can be used for the precoat layer 41. It is also possible to use the insoluble particles of the present invention.

The following describes a method for recovering valuable metal powder from resist waste liquid using the above-mentioned device of the present invention.

The resist waste liquid is supplied to the settling tank 12 from the resist waste liquid supply port 19 in a batch or continuous manner. The resist waste liquid is supplied to the first settling section 30 through the wall surface 20c from the opening 15a provided in the resist waste liquid receiving section 15, and is further supplied to the second settling section 31 through the gap between the lower end of the flow path plate 14 and the bottom surface 21. When the liquid level of the resist waste liquid in the second settling section 31 becomes higher than the upper end of the partition wall 17, it overflows and is supplied to the mixing tank 13. A precipitate containing valuable metal powder accumulates at the bottom of the settling tank 12. In addition, some of the valuable metal powder floating on the liquid surface of the resist waste liquid accumulates on the blocking plate 16. Insoluble particles are supplied to the supernatant liquid introduced into the mixing tank 13 from the insoluble particle supply means 34. The supernatant liquid extracted from the discharge port 33 is sprayed into the supernatant liquid from the nozzles 37a and 37b. The supernatant liquid flows in a spiral shape due to the ejection, and the supernatant liquid and the insoluble particles are mixed. After mixing for a predetermined time, the mixed liquid is extracted from the discharge port 33 and supplied to the mixed liquid supply means of the filtration device 11. The mixed liquid is supplied to the filtration membrane 39 from the supply port 42 via the supply paths 43a and 43b. The filtration membrane 39 separates the mixed liquid into a solid containing valuable metal powder and a treated liquid from which the valuable metal powder has been removed, and the treated liquid passes through the filtration membrane 39 and is discharged to the filtrate tank 46. The valuable metal powder is collected from the settling tank 12 as a precipitate and an accumulation on the blocking plate 16, and from the filtration device 11 as a filtration residue.

The present invention will be explained in more detail below with reference to examples. However, the present invention is not limited to the following examples, and it is of course possible to carry out the invention with appropriate modifications within the scope of the above and below-mentioned aims, and all such modifications are included in the technical scope of the present invention.

Experiment 1
The lifespan of the filter membrane used to recover gold powder from waste resist liquid under the following conditions was investigated. The lifespan of the filter membrane was determined to have been reached when the supply rate of the waste resist liquid to the filter membrane was equal to or greater than the filtration rate. Specifically, the filter membrane was determined to have reached the end of its lifespan when the filtration rate became less than 0.043 mL/sec·4.9 ^cm2 . The results of each experiment are shown in Table 1, and the relationship between the amount of the filter membrane processed and the filtration rate is shown in Figure 5.

The service life of the filtration membrane was calculated by filtering 200 ml of 4 L of supernatant liquid at a time and plotting the data over time. The amount of liquid passing when the filtration rate reached the allowable lower limit (0.043 ml/sec·4.9 ^cm2 ) was calculated from the function of the graph, and the number of days was calculated from the average amount of resist waste (L/day) discharged from the factory where the membrane is expected to be installed.

Comparative Example 1
Resist waste liquid (52 L) containing resist components, resist stripping solution, and gold powder (0.04 g/L) discharged from a semiconductor manufacturing factory was fed into a settling tank (width 320 mm x depth 460 mm x height 500 mm) to separate the valuable metal powder by settling. After 50 minutes, the supernatant liquid (10 L) was extracted and subjected to suction filtration (filtration pressure: -0.07 MPa). 1 μm glass filter paper (filtration area: 4.9 ^cm2 ) was used, and neither body feeding nor precoating was performed.

Comparative Example 2
Filtration was carried out in the same manner as in Comparative Example 1, except that a precoat layer of diatomaceous earth (0.2 g: Radiolite (registered trademark) #800 manufactured by Showa Chemical Industry Co., Ltd.) was formed during filtration. Filtration area: 0.2 g of diatomaceous earth was precoated per 4.9 ^cm2 .

Example 1
In the same manner as in Comparative Example 1, the resist waste liquid was supplied to a settling tank and the gold powder was allowed to settle and separated. After settling and separation, the supernatant liquid (10 L) was transferred to another beaker and 0.5 g of diatomaceous earth powder was added as insoluble particles, after which the supernatant liquid and diatomaceous earth were mixed by stirring with a glass rod for about 10 seconds. The resulting mixture was suction filtered (filtration pressure: -0.07 MPa). 1 μm glass filter paper (filtration area: 4.9 ^cm2 ) was used.

Example 2
Filtration was carried out in the same manner as in Example 1, except that a precoat layer of diatomaceous earth (0.2 g) was formed to a thickness of about 2 mm on the filtration membrane.

The following can be seen from Table 1 and FIG.
It can be seen that the life of the filtration membrane was significantly extended by adding insoluble particles to the supernatant in Examples 1 and 2. Furthermore, it can be seen that the life of the filtration membrane was further extended by providing a precoat layer.

On the other hand, in Comparative Examples 1 and 2, in which insoluble particles were not added, the filtration membrane had a significantly shorter lifespan, regardless of the presence or absence of a precoat layer. Compared to Comparative Example 1, the filtration membrane lifespan in Example 1 was more than three times longer, and in Example 2 it was more than four times longer.

The gold powder concentration in the treated liquid after filtration in Examples 1 and 2 and Comparative Examples 1 and 2 was examined, but no gold powder was found in any of them. This result was achieved by the filtration performance of the filtration membrane, but as mentioned above, the lifespan of the filtration membrane differs depending on the treatment method. Therefore, when considering the filtration lifespan, Examples 1 and 2 have a superior effect compared to Comparative Examples 1 and 2.

Experiment 2
The amount of insoluble particles added in Example 1 was changed as shown in Table 2, and the service life of the filtration membrane was similarly investigated. The gold powder content of the resist waste liquid used was the same (0.04 g/L), but since it was resist waste liquid containing the stripping liquid before renewal, the concentration of resist components was higher and the viscosity was higher than in Experiment 1. The results of each experiment are shown in Table 2, and the relationship between the throughput of the filtration membrane and the filtration speed is shown in Figure 6.

As can be seen from Table 2, the higher the concentration of insoluble particles added to the supernatant, the longer the filter life.

Experiment 3
No. 3-1
The experiment was carried out in the same manner as in Example 1, except that the resist waste liquid used in Experiment 2 was used.
No. 3-2
The experiment was carried out in the same manner as in Example 2, except that the resist waste liquid used in Experiment 2 was used.
The results are shown in Table 3.

As shown in Table 3, forming a precoat layer extended the life of the filtration membrane. Also, taking into account the results of Examples 1 and 2, forming a precoat layer extends the life of the filtration membrane regardless of the properties of the resist waste liquid, and reduces the frequency of maintenance.

Experiment 4
The gold powder concentration before and after sedimentation was examined. Specifically, the resist waste liquid (5 L) used in experiment 1 was supplied to a sedimentation tank (width 320 mm x depth 57.5 mm x height 500 mm) at the flow rate shown in Table 4, and the gold powder concentration in the resist waste liquid before treatment and the gold powder concentration in the resist waste liquid after treatment were measured, respectively, to examine the gold powder removal rate by sedimentation. Note that the same conditions were used except for the flow rate. The gold powder concentration in the resist waste liquid before sedimentation was 0.3045 g/L in each run. The results of examining the gold powder concentration in the resist waste liquid after sedimentation are shown in Table 4. The same resist waste liquid was used to perform the experiment four times. The results are shown in Table 4.

From the results in Table 4, the gold powder concentration in the resist waste liquid after settling separation was high in the fourth experiment, in which the flow rate was high. Therefore, it can be seen that the gold powder concentration in the resist waste liquid after settling separation can be reduced by appropriately controlling the flow rate. Note that the particle size distribution of the gold powder was not constant for each test, so the passing rate etc. fluctuated, but the results were generally good.

1 Resist waste liquid generation source 2 Resist waste liquid storage tank 3 Sedimentation separation process 4 Addition process 5 Insoluble particle storage tank 6 Precoat layer 7 Filtration process 8a to 8e Pipe 10 Sedimentation mixing device 11 Filtration device 12 Sedimentation tank 13 Mixing tank 14 Flow path plate 15 Resist waste liquid receiving section 15a Opening 16 Blocking plate 17 Partition wall 18 Inclined plate 19 Resist waste liquid supply port 20a, 20b, 20c Wall surface 21 Bottom surface 22 Ceiling surface 30 First sedimentation section 31 Second sedimentation section 32 Space 33 Discharge port 34 Insoluble particle supply means 35 Stirring/mixing means 35a Supply port 36 Extraction port 37a, 37b Nozzle 38 Discharge port 39 Filtration membrane 40 Mixed liquid supply means 41 Precoat layer 42 Supply port 43a 43b Supply path 44 Protective plate 46 Filtrate tank

Claims (8)

1. A precipitation mixer comprising:
The precipitation mixer is
The apparatus includes a settling tank separated by a partition wall for settling at least a portion of valuable metal powder , and a mixing tank for adding insoluble particles to a supernatant liquid supplied from the settling tank and mixing the insoluble particles therein ,
The settling tank comprises:
a first settling section and a second settling section separated by a flow path plate, the first settling section and the second settling section being connected by a gap provided between a lower end of the flow path plate and a bottom surface of the settling tank,
the mixing tank and the second settling section are connected through an opening provided in the partition wall,
The first settling section is provided with a liquid supply port for supplying a waste liquid containing valuable metal powder ,
the mixing tank is provided with an insoluble particle supplying means for supplying insoluble particles that adsorb valuable metal powder, and a liquid outlet for discharging a mixture of the supernatant liquid and the insoluble particles ;
a blocking plate is provided between the flow path plate and the partition wall in the second settling portion,
A precipitation mixer, wherein the lower end of the baffle plate is installed lower than the upper end of the partition wall, and the upper end of the baffle plate is installed higher than the upper end of the partition wall. The precipitation mixer according to claim 1, wherein the bottom surface of the settling tank is provided with an inclined plate that is inclined so as to become lower from the wall side of the first settling section toward the partition wall side. The sedimentation mixer according to claim 1, wherein a sediment discharge outlet is provided near the bottom surface of the second sedimentation section. 2. The precipitation mixer according to claim 1, wherein said mixing tank is provided with a means for stirring and mixing the insoluble particles and the supernatant liquid . A precipitation mixing apparatus according to claim 1 , and a filtration device connected to the liquid outlet of the mixing tank,
The filtering device has a filtering membrane and a means for supplying liquid from the liquid outlet to the filtering membrane. The valuable metal powder recovery equipment of claim 5, wherein the means for supplying the liquid has a supply path arranged so that the liquid flows horizontally, and a supply port arranged on the supply path for supplying the liquid to the filtration membrane. 7. The valuable metal powder recovery equipment according to claim 6, wherein a protective plate is provided between the supply port and the filtration membrane, and the protective plate is installed so that the liquid supplied from the supply port hits the protective plate. The filtration device comprises:
6. The valuable metal powder recovery equipment according to claim 5, further comprising a precoat layer on the filtration membrane.

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