JP5109012B2 - Solid-liquid separation method and apparatus of solid-liquid mixed material by specific gravity difference separation using supercritical carbon dioxide - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a solid-liquid separation method and apparatus for solid-liquid mixed material, in which solid-liquid mixed material such as slurry waste liquid is solid-liquid separated with high efficiency using supercritical carbon dioxide or liquid carbon dioxide as a specific gravity difference separation solvent. More specifically, by solid-liquid separation of a solid-liquid mixed material such as slurry waste liquid generated in a silicon wafer manufacturing process using supercritical carbon dioxide or liquid carbon dioxide as a specific gravity difference separation solvent. , A new solid-liquid separation method and apparatus using specific gravity difference separation of solid-liquid mixed substances such as slurry waste liquid, which enables separation of solid-liquid with high separation efficiency and recovery of valuable materials and reuse is there.

  In recent years, against the background of global warming and environmental pollution, countries around the world are actively seeking clean energy that can be renewed, and the demand for solar cells and the like has been increasing. It is estimated that it will continue to grow.

  There are various types of solar cells, including silicon crystal systems using single crystal silicon and polycrystalline silicon, amorphous systems formed by CVD, etc., compound systems such as CdTe, etc. About 90% of solar cells are silicon crystal. In addition to solar cells, silicon wafers are also used for ICs, LSIs, and other substrates, and their production volume is increasing as demand for personal computers, mobile phone terminals, and digital home appliances increases.

  While the demand for solar cells, ICs and LSIs is increasing, the amount of waste associated with production is increasing. For example, a silicon wafer is manufactured by thinly cutting a silicon ingot with a wire saw, performing mirror processing, cleaning, etc., and when cutting a silicon ingot with a wire saw, silicon wafers are made into a large number of thin wires running at high speed. The silicon ingot is being cut while the slurry is mixed with abrasive grains and coolant while pressing the ingot.

  There are two types of slurry, water-based using polyethylene glycol and oil-based using mineral oil as the coolant, and SiC is mainly used for abrasive grains. Yes. In any slurry, silicon scrap or iron scrap from the wire accumulates when the silicon ingot is cut, causing them to deteriorate the cutting performance of the wire saw. The remaining slurry is used after being centrifuged and mixed with a new slurry. However, since a part of the slurry is discarded at every cutting, a considerable amount of the slurry waste liquid is discarded.

  The component content ratio of the waste slurry waste is 45 to 60% SiC, 30 to 40% coolant, 10 to 20% silicon scrap, and 5 to 15% iron scrap, most of which are reusable SiC and Coolant. Although some of the discarded slurry waste liquid has been subjected to the life extension of SiC and coolant by centrifugation, the amount of slurry discarded is enormous.

  In addition to silicon scrap, this discarded slurry waste liquid contains iron scrap, reusable coolant and abrasive grains, so that they can be separated and recovered from the discarded slurry waste liquid. Conventionally, various methods have been proposed (see Patent Documents 1 to 6). In recent years, various attempts have been made to develop an efficient separation process for valuable materials from discarded slurry waste liquid in response to a significant increase in demand for semiconductors and solar cells.

  For example, a prior art document discloses a method of recovering abrasive grains (SiC) by diluting an oil-based slurry waste liquid with an extractant such as kerosene, and precipitating and separating with a specific gravity difference (see Patent Document 7). . In addition, in other prior literatures, SiC particles are separated by mixing a slurry waste liquid separated by a filter press or the like with a trapping agent such as sodium alkyl sulfonate and a foaming agent to raise fine bubbles. A method is disclosed (see Patent Document 8). However, these methods require the addition of a dispersant, and have a problem that new waste is generated when useful components of the slurry waste liquid are separated.

  In other prior literature, after extracting and separating organic components using subcritical or supercritical carbon dioxide, the temperature and pressure are lowered to separate carbon dioxide and organic components, and carbon dioxide is recovered. Again, a method of using subcritical or supercritical carbon dioxide as an extractant is disclosed (see Patent Document 9). However, this type of method has a problem that the target extraction substance is limited to a substance that dissolves in supercritical carbon dioxide.

  On the other hand, the inventors of the present invention firstly used supercritical carbon dioxide and / or liquid carbon dioxide as a specific gravity difference separation solvent and / or an extraction separation solvent to convert a solid-liquid mixed material into a specific gravity difference and / or extraction separation. A separation method and apparatus for solid-liquid mixed substances to be separated by use have been developed (see Patent Document 10).

In the prior art document disclosing the above prior art, as a specific method, the specific gravity difference separation and the extraction separation are simultaneously performed in the same system, the solid matter is taken out with a water slurry, and the SiC is recovered with a filter or a cyclone. A basic method and apparatus for separating solid and liquid with high separation efficiency by controlling the density and viscosity of the mixed fluid of CO ₂ and slurry waste liquid by mixing the subsequent CO ₂ with slurry waste liquid and performing specific gravity difference separation Proposed.

  However, after that, while the inventors proceeded with further practical research, this method obtained a good solid-liquid separation result. The amount of coolant is recovered, and this method still has a problem as a solid-liquid complete separation process that enables practical use of a slurry waste liquid separation process.

  Thus, in this technical field, as a method for separating and recovering reusable SiC and coolant from waste slurry, there is no settling of coolant to the lower stage of the specific gravity difference separator, and as a complete solid-liquid separation process. There has been a strong demand to establish a new valuable material recovery technique using supercritical carbon dioxide as a specific gravity difference separation medium that can be put into practical use and has a low load on the human body and the environment.

Japanese Patent No. 3199159 JP 11-48146 A JP 2002-28866 A JP 2003-225700 A JP 2000-254543 A JP-A-11-172237 JP-A-9-109144 JP 2004-223321 A Japanese Patent Laid-Open No. 8-183989 JP 2007-330964 A

  In such a situation, in view of the above-described conventional technology, the present inventors have developed a new valuable resource recovery technology that enables highly efficient separation and recovery of valuable resources from solid-liquid mixed substances such as slurry waste liquid. As a result of intensive research with the goal of developing a solid-liquid mixed material in the middle stage of a specific gravity difference separator using supercritical carbon dioxide or liquid carbon dioxide as a specific gravity difference separation medium. Supply from the material supply port, always supply a constant amount of supercritical carbon dioxide or liquid carbon dioxide from the bottom to the top of the supply port, and further supply the fluid flowing out from the specific gravity difference separator to supply the solid-liquid mixed material Use circulation means to circulate as a circulating fluid in the mouth, mix a solid-liquid mixture such as slurry waste liquid with the circulating fluid in the circulation process, and supply it to the supply port of the solid-liquid mixed material of the specific gravity difference separator Continuous solid-liquid separation By performing, we found that it is possible to achieve the intended purpose, further extensive research, and completed the present invention.

  The present invention uses supercritical carbon dioxide or liquid carbon dioxide as a specific gravity difference separation medium, and can reliably prevent liquid components such as coolant from settling. It is an object of the present invention to provide a new method for completely separating a solid-liquid mixed substance, which makes it possible to separate and recover substances with high separation efficiency. The present invention is also a solid-liquid separation method in which a solid-liquid mixed material such as slurry waste liquid is solid-liquid separated in a solid-liquid separator using supercritical carbon dioxide or liquid carbon dioxide as a specific gravity difference separation medium. Establish and provide a solid-liquid complete separation process by specific gravity difference separation, which enables practical use of the slurry waste liquid separation process without the coolant settling in the solids collection tank as in the conventional method It is intended. Furthermore, the present invention provides a new solid-liquid mixed substance separation method and apparatus capable of recovering valuable materials from slurry waste liquid with high separation efficiency by combining a specific gravity difference separation step and a surfactant washing step. It is intended to provide.

The present invention for solving the above-described problems comprises the following technical means.
(1) In a specific gravity difference separation method for a solid-liquid mixed material using supercritical carbon dioxide or liquid carbon dioxide as a specific gravity difference separation solvent, the solid-liquid mixed material is supplied from a middle supply port of the specific gravity difference separator, and the specific gravity difference The liquid and carbon dioxide in the solid-liquid mixed material are discharged from the upper stage of the separator, and the solid matter is settled down and recovered. From the bottom to the upper part of the solid-liquid mixed substance supply port in the middle stage of the specific gravity difference separator Supercritical carbon dioxide or liquid carbon dioxide whose density is equal to or higher than that of the liquid in the solid-liquid mixed substance is quantitatively supplied, and the fluid flowing out of the specific gravity difference separator is used as a circulating fluid to the supply port of the solid-liquid mixed substance. The solid-liquid mixed substance is turbulently mixed in this circulating fluid and supplied to the specific gravity difference separator, so that the liquid in the solid-liquid mixed substance settles below the solid-liquid mixed substance supply port. prevention to be characterized by continuous solid-liquid separation The difference in specific gravity separation method of the solid-liquid substance mixture.
(2) The specific gravity difference separation method according to (1), wherein the solid-liquid mixed material is slurry waste liquid generated in a silicon wafer manufacturing process or polishing / cutting slurry waste liquid.
( 3 ) When the density of supercritical carbon dioxide or liquid carbon dioxide is controlled by changing the temperature and / or pressure, the solid-liquid mixed substance is above the solid-liquid mixed substance supply port of the specific gravity difference separator. In order to obtain a predetermined terminal velocity of the solids, the density of the specific gravity difference separation solvent is reduced by controlling it at a higher temperature than the lower part, and at the lower part, the density of the specific gravity difference separation solvent is controlled at a lower temperature than the upper part. The density of the liquid in the solid-liquid mixed substance and the density of the liquid in the solid-liquid mixed substance and the mixed fluid of carbon dioxide should be higher than the supply port of the solid-liquid mixed substance in the solid-liquid mixed substance. The specific gravity difference separation method according to the above ( 1 ), which prevents sedimentation into the liquid.
( 4 ) The liquid and carbon dioxide in the solid-liquid mixed material flowing out from the specific gravity difference separator are separated by the gas-liquid separator, the separated carbon dioxide is condensed, and the carbon dioxide is supplied to the solid-liquid mixed material supply port. The specific gravity difference separation method according to (1), wherein the separation is performed as supercritical carbon dioxide or liquid carbon dioxide supplied from below to above.
( 5 ) From the above (1) to ( 3 ), the fluid flowing out from the upper discharge port of the specific gravity difference separator through the filter is circulated as a circulating fluid to the solid-liquid mixed material supply port of the specific gravity difference separator. The specific gravity difference separation method according to any one of the above.
( 6 ) In the step of circulating the fluid flowing out from the upper stage of the specific gravity difference separator as a circulating fluid to the solid-liquid mixed substance supply port of the specific gravity difference separator and mixing the solid-liquid mixed substance with this circulating fluid, The specific gravity difference separation method according to any one of (1) to ( 5 ), wherein the circulating fluid and the solid-liquid mixed substance are mixed with a mixer.
( 7 ) In the step of circulating the fluid flowing out from the upper stage of the specific gravity difference separator as a circulating fluid to the solid-liquid mixed substance supply port of the specific gravity difference separator and mixing the solid-liquid mixed substance with this circulating fluid, Controlling the temperature, pressure, and / or flow rate of the fluid and ensuring mixing of the circulating fluid and the solid-liquid mixed material, while mixing the carbon dioxide in the specific gravity difference separator and the liquid and carbon dioxide mixed fluid in the solid-liquid mixed material The specific gravity difference separation method according to any one of (1) to ( 6 ), wherein the flow rate is controlled to be equal to or lower than a predetermined terminal velocity of the solid.
( 8 ) Using supercritical carbon dioxide or liquid carbon dioxide as a specific gravity difference separation solvent, supplying a solid-liquid mixed substance from the middle stage of the specific gravity difference separator, and liquid in the solid-liquid mixed substance from the upper stage of the specific gravity difference separator And a solid-liquid mixed substance specific gravity difference separation device that continuously solid-liquid separates the solid-liquid mixed substance by flowing out and carbon dioxide and collecting the solid by settling down,
Quantitatively supply supercritical carbon dioxide or liquid carbon dioxide whose density is higher than the density of the liquid in the solid-liquid mixed material, from the bottom to the top, at a position below the supply port of the solid-liquid mixed material at the interruption of the specific gravity difference separator A means for circulating the fluid that has flowed out of the specific gravity difference separator as a circulating fluid to the supply port of the solid-liquid mixed material, and a turbulent mixing of the solid-liquid mixed material with the circulating fluid, A means for supplying to the differential separator is provided, and the liquid in the solid-liquid mixed substance is continuously solid-liquid separated by preventing sedimentation below the supply port of the solid-liquid mixed substance. A continuous specific gravity difference separation apparatus for solid-liquid mixed materials.
( 9 ) A gas-liquid separator that separates carbon dioxide from the liquid in the solid-liquid mixed material flowing out from the upper stage of the specific gravity difference separator, means for condensing the separated carbon dioxide, and the specific gravity difference separator for the carbon dioxide The continuous specific gravity difference separation device according to ( 8 ), comprising means for re-supplying and using the same.
( 10 ) having means for adjusting the density of supercritical carbon dioxide or liquid carbon dioxide supplied from below to above the supply port of the solid-liquid mixed material of specific gravity difference separation type by changing temperature and / or pressure; The continuous specific gravity difference separation device according to ( 8 ) above.
( 11 ) The continuous specific gravity difference separation device according to ( 8 ), further including means for controlling the upper part and the lower part of the specific gravity difference separator to have different temperatures from the supply port of the solid-liquid mixed substance.
( 12 ) In a device for circulating a fluid flowing out from a specific gravity difference separator as a circulating fluid to a solid-liquid mixed substance supply port of the specific gravity difference separator and mixing the solid-liquid mixed substance with this circulating fluid, The continuous specific gravity difference separation device according to any one of ( 8 ) to ( 11 ), comprising mixer means for mixing a solid-liquid mixed substance.

Next, the present invention will be described in more detail.
In the specific gravity difference separation method of the solid-liquid mixed material using supercritical carbon dioxide or liquid carbon dioxide as the specific gravity difference separation solvent, the present invention supplies the solid-liquid mixed material from the middle supply port of the vertically long specific gravity difference separator, The liquid and carbon dioxide in the solid-liquid mixed substance are discharged from the upper stage of the specific gravity difference separator, and the solid matter is settled down and recovered, and is lower than the supply port of the solid-liquid mixed substance in the middle stage of the specific gravity difference separator. The supercritical carbon dioxide or liquid carbon dioxide is constantly supplied from above to the top, and the fluid flowing out of the specific gravity difference separator is circulated as a circulating fluid to the supply port of the solid-liquid mixed material. A mixed substance is supplied, and solid-liquid separation is performed continuously by supplying the mixed substance to a specific gravity difference separator.

  In addition, the present invention uses supercritical carbon dioxide or liquid carbon dioxide as a specific gravity difference separation solvent to supply a solid-liquid mixed substance from the middle stage of a vertically long specific gravity difference separator, and from the upper stage of the specific gravity difference separator, This is a solid-liquid mixed material specific gravity difference separation device that continuously separates solid-liquid mixed material by letting the liquid and carbon dioxide in the mixed material flow out, and the solid matter is settled down and recovered. At the position below the solid-liquid mixed substance supply port of the separator, there is a supply means for quantitatively supplying supercritical carbon dioxide or liquid carbon dioxide from the bottom to the top, and the fluid flowing out from the specific gravity difference separator is circulated. The fluid includes means for circulating to the solid-liquid mixed substance supply port, and means for mixing the solid-liquid mixed substance with the circulating fluid and supplying the mixed liquid to the specific gravity separator. is there.

  In the present invention, for example, a vertically long cylindrical specific gravity difference separator is preferably used, but its specific form can be appropriately designed. In the present invention, supercritical carbon dioxide or liquid carbon dioxide having a temperature of 31.17 ° C. or higher and a pressure of 7.386 MPa or higher is used as the specific gravity difference separation solvent. The density of the supercritical fluid is close to that of the liquid, and the diffusion coefficient is significantly higher than that of the liquid. It has the action of dissolving nonpolar, weakly polar oils and fats, and its density and its dissolving power change the temperature and / or pressure. It changes with that. Carbon dioxide can be reused by vaporization, removal and liquefaction only under pressure conditions. In the present invention, the carbon dioxide is used as a specific gravity difference separation solvent, so that the specific gravity difference separation process of the present invention can be constructed. It is possible.

  In the present invention, examples of the solid-liquid mixed material include slurry waste liquid such as general polishing / cutting slurry waste liquid and silicon slurry waste liquid generated in the process of manufacturing a silicon wafer. These slurry waste liquids contain abrasive grains, coolants, and the like used as abrasives, abrasives, and the like.

  Examples of the abrasive grains include fine alumina, colloidal silica, silicon carbide, cerium oxide, silicon oxide, boron carbide, boron nitride, zirconium oxide, fine diamond, and fine sapphire. Examples of the coolant include oil-based coolants such as mineral oil, water-based coolants such as poly water-soluble glycols and amines, and lubricants. Moreover, although a surfactant, water, a solvent, etc. may be contained in coolant, the coolant containing these is also the object of this invention.

  In general, for abrasives and abrasives, the abrasive grains are usually dispersed in a coolant and a lubricant. These slurry waste liquids contain solids such as the above-mentioned abrasive grains, chips such as silicon, polishing scraps, iron scraps derived from wire saws, and fragments of crushed abrasive grains. The present invention is not limited to the above-described slurry waste liquid, and can be applied as a means for separating all kinds of solid-liquid mixed substances having properties and compositions equivalent or similar to those.

  However, in the present invention, in order to make the description of the present invention simple and easy, a case of slurry waste liquid will be described as an example. As a composition of slurry waste liquid, for example, in the case of slurry waste liquid generated in a silicon wafer manufacturing process, the slurry waste liquid is generally 48 to 55 w% of SiC abrasive grains, 30 to 35 wt% of coolant, and 9 of silicon scrap. It consists of a ratio of iron scraps as -10% and others.

  When supercritical carbon dioxide and / or liquid carbon dioxide is used as a specific gravity difference separation solvent, when solid-liquid mixed substances are separated into solid and liquid, supercritical carbon dioxide and / or liquid carbon dioxide are separated by specific gravity difference. Supply from the supply port of the solid-liquid mixed substance located in the middle stage of the vessel, perform solid-liquid separation using the specific gravity difference, discharge oil system components from the upper stage of the specific gravity difference separator, The solid substance is settled and separated below. For example, in the case of silicon slurry waste liquid using mineral oil as the coolant, the coolant flows out and separates from the upper stage of the specific gravity difference separator, and the solid matter settles and separates below.

  After discharging the settled and separated solids to the outside, for example, an aqueous solution containing a surfactant is added to the collected solids, mixed, and allowed to stand, so that silicon chips and iron scraps are formed as a supernatant. Also, SiC separates as a precipitate. If necessary, iron scraps can be efficiently recovered by irradiating ultrasonic waves during mixing, putting a magnet in the supernatant, or the like. By repeating the above operation, SiC can be refined and made into a state where it can be reused as abrasive grains.

  In the present invention, in the specific gravity difference separation, the density and / or the pressure of the specific gravity difference separation solvent can be changed by changing the temperature and / or pressure of the supercritical carbon dioxide and / or liquid carbon dioxide that is the specific gravity difference separation solvent. By adjusting the flow rate, the solid-liquid separation efficiency can be increased. In the present invention, in addition to the above basic configuration of the present invention, the pressure, temperature, and / or flow rate conditions of the specific gravity difference separation solvent are important basic factors for performing the solid-liquid separation operation of the solid-liquid separation mixed material of the present invention. Positioned as a factor.

For example, when the liquid component (low density ρ _L ) and the solid component (high density ρ _H ) constituting the solid-liquid mixed substance are separated, these density and density ρ _CO2 of the specific gravity difference separation solvent are ρ _L <ρ _CO2. <is required to be in the relationship of ρ _H. In the present invention, high separation efficiency can be achieved by adjusting the density of the specific gravity difference separation solvent. For example, in the case of silicon slurry waste liquid, the density of the liquid component coolant is about 800 kg / m ³ and the solid main component SiC density is about 3000 kg / m ³ , the density of the specific gravity separation solvent is It is required to be 800 kg / m ³ or more and 3000 kg / m ³ or less.

If the density of the separation solvent is 800 kg / m ³ or more, the coolant can be separated into the upper part, and if it is 3000 kg / m ³ or less, SiC can be separated into the lower part. However, since the density of carbon dioxide does not exceed 3000 kg / m ³ , it should be substantially 800 kg / m ³ or more (even with solid carbon dioxide dry ice, about 1500 kg / m ³ ).

  This condition is achieved, for example, in the case of saturated liquid carbon dioxide at a saturation temperature of 17 ° C. (saturation pressure at that time 5.3 MPa) or less, and in the case of pressurized liquid carbon dioxide or supercritical carbon dioxide, at 20 MPa. 47 ° C. or lower, 30 MPa, and 67 ° C. or lower.

On the other hand, the sedimentation property of solid particles is generally evaluated by a critical flow velocity (= terminal velocity) calculated from the Stokes equation: (ρ ₁ −ρ ₂ ) g · d ² / 18μ, and the rise of the separation solvent is smaller than this value. The flow rate is determined so as to be the speed. For example, assuming that the particle size of SiC is 10 μm and supercritical carbon dioxide (density 840 kg / m ³ ) at 40 ° C. and 20 MPa is used as a separation solvent, the critical flow rate, that is, the end velocity is calculated as 5.4 m / h. Therefore, it is preferable to adjust the flow rate so that the rising speed of the supercritical carbon dioxide becomes a numerical value sufficiently smaller than this.

In the case of an aqueous slurry, since the liquid component is water and the density is 1000 kg / m ³ , a larger numerical value is required for the density of the specific gravity difference separation solvent. This condition is achieved in the case of saturated liquid carbon dioxide at a saturation temperature of −14 ° C. (saturation pressure at that time: 2.4 MPa) or less, and in the case of pressurized liquid carbon dioxide, at 5 MPa or less at 20 MPa, In the case of 30 MPa, it is achieved at 15 ° C. or lower, and in the case of supercritical carbon dioxide, it is achieved at 36 MPa or lower at 50 MPa.

  The solid-liquid separation operation of the present invention enables dehydration and drying at a low temperature. In any case, when the solid-liquid separation operation is completed, the solvent, liquid component, and solid substance can be reused. Possible valuable materials can be separated, recovered and reused. In the present invention, the density of supercritical carbon dioxide or liquid carbon dioxide supplied from below to above the supply port of the solid-liquid mixed substance in the middle stage of the specific gravity difference separator is controlled by changing the temperature and / or pressure. Preventing the sedimentation of the liquid component in the solid-liquid mixed material by making the density equal to or higher than the liquid density in the solid-liquid mixed material and the density of the mixed fluid of the liquid and carbon dioxide in the solid-liquid mixed material. Is possible.

  In the present invention, the upper part and lower part of the solid-liquid mixed substance supply port in the middle stage of the specific gravity difference separator are adjusted to different temperatures, the density of the specific gravity difference separation solvent is controlled, and in the upper part, the solid substance of the solid-liquid mixed substance In order to obtain a predetermined terminal velocity, the density of the specific gravity difference separation solvent is reduced by controlling it at a higher temperature than the lower part, and the density of the specific gravity difference separation solvent is controlled at a lower temperature than that of the upper part. It is preferable to prevent sedimentation of the liquid component of the solid-liquid mixed material so as to be equal to or higher than the liquid density of the liquid-mixed material and the density of the liquid of the solid-liquid mixed material and the mixed fluid of carbon dioxide.

  Further, in the present invention, the liquid and carbon dioxide in the solid-liquid mixed substance flowing out from the upper stage of the specific gravity difference separator are separated by the gas-liquid separator, and the separated carbon dioxide is condensed, and this is separated into the solid-liquid mixed substance. It can be recycled as supercritical carbon dioxide or liquid carbon dioxide supplied from below to above the supply port. Further, in the present invention, a filter is installed at the upper outlet of the specific gravity difference separator, and the fluid flowing out of the filter is used as a circulating fluid via a circulation / mixing line, and the solid liquid in the middle of the specific gravity difference separator. The solid-liquid mixed material is circulated through the supply port of the mixed material, and in this process, the solid-liquid mixed material is mixed with this circulating fluid and supplied to the solid-liquid mixed material supply port of the specific gravity difference separator. It can be performed.

  In the method of the present invention, the fluid flowing out from the upper stage of the specific gravity difference separator is circulated as a circulating fluid to the solid-liquid mixed substance supply port in the middle stage of the specific gravity difference separator, and the solid-liquid mixed substance is supplied to this circulating fluid. In the step of mixing, the circulating fluid and the solid-liquid mixed substance are mixed with a mixer and then supplied to the specific gravity difference separator. In the step of mixing the circulating fluid and the solid-liquid mixed substance with the mixer, a turbulent mixing mixer is used. It is preferable to mix using.

  Further, in the method of the present invention, the fluid flowing out from the upper stage of the specific gravity difference separator is circulated to the supply port of the solid-liquid mixed substance in the middle stage of the specific gravity difference separator, and the solid-liquid mixed substance is supplied to this circulating fluid. The flow rate of carbon dioxide in the specific gravity separator is set to a predetermined level of solids while controlling the temperature, pressure, and / or flow rate of the circulating fluid and ensuring a good mixing state of the circulating fluid and the solid-liquid mixed material. It is preferable to separate the solid-liquid mixed material by controlling it so that the terminal speed is less than or equal to the above.

  Further, the apparatus of the present invention has a gas-liquid separator that separates carbon dioxide from the liquid in the solid-liquid mixed material flowing out from the upper stage of the specific gravity difference separator, and means for condensing the separated carbon dioxide, the carbon dioxide Means for re-feeding to the lower stage of the specific gravity difference separator, the density of supercritical carbon dioxide or liquid carbon dioxide fed from the bottom to the top of the solid-liquid mixed substance feed port, the temperature and / or the pressure. It is preferable to have means for controlling by changing, and to have means for controlling the temperature above and below the supply port of the solid-liquid mixed substance in the middle stage of the specific gravity difference separator to different temperatures.

  Here, the background of the development of the present invention will be described. The present inventors have previously developed a solid-liquid separation method for performing solid-liquid separation of a slurry using the experimental apparatus shown in FIG. 1 as a prior art. . In this method, as shown in FIG. 2, a good solid-liquid separation result was obtained, but a small amount of coolant (6.4%) was recovered from the solid recovery tank, and the solid recovery tank was verified by verification. It was found that the coolant that settled in the slurry was settled when the slurry waste liquid was supplied. Therefore, the present inventors have determined a new separation process and specific separation conditions by improving the separation process and examining separation conditions in order to prevent coolant settling and enable solid-liquid complete separation. So, we succeeded in building a new solid-liquid separation process that enables complete solid-liquid separation.

The new separation process constructed as the solid-liquid separation method of the present invention and the results of solid-liquid separation are shown in FIGS. In the solid-liquid separation process of the present invention, 1) a constant amount of CO ₂ is always supplied from below the slurry supply port, and 2) a circulation / mixing line is provided between the discharge port of the specific gravity difference separator and the slurry waste solution supply port. The basic configuration is that the fluid flowing out from the specific gravity difference separator is circulated as a circulating fluid, and the slurry waste liquid is mixed and supplied to the circulating fluid. As the separation conditions, the relationship between the density of CO ₂ supplied from the bottom to the top of the slurry waste liquid supply port, the density of the coolant, and the density of the mixed fluid of the coolant + CO ₂ is expressed as (coolant density) <(CO ₂ density). ), (Density of coolant + CO ₂ mixed fluid) <(CO ₂ density).

  As can be seen from the results of the solid-liquid separation shown in FIG. 4, in the solid-liquid separation process of the present invention, the coolant is not recovered from the solid material recovery tank (recovery rate: 0.0%), that is, the specific gravity difference separation. It has been found that coolant settling in the lower stage of the vessel can be completely prevented. As a result, the present invention provides a process that separates the slurry waste liquid for each substance constituting the slurry waste liquid by specific gravity difference separation, for example, a solid that makes it possible to reuse a large amount of SiC and coolant contained in the slurry waste liquid. It has been demonstrated that a complete liquid separation process can be established.

In the above prior art, as a result of verification by the present inventors about the cause of the coolant settling in the solid matter collection tank, the solid matter containing the coolant is present in the upper part of the solid matter collection tank. The mixed layer composed of the fluid mixture of the coolant and CO ₂ gradually settles and comes into contact with the solid matter in the solid matter collecting tank, and as a result, the coolant remains in the solid matter at the top of the solid matter collecting tank. It was considered a thing.

In the present invention, the rising speed of the relationship between the terminal velocity and CO ₂ solids supplied to the difference in specific gravity separator, the terminal velocity of the rising speed <solids CO ₂ that is, also, the difference in specific gravity separator It is important as a basic principle of the solid-liquid separation process of the present invention that the relationship between the density of the supplied coolant and the density of CO _{2 is} the density of the mixed fluid of coolant + CO ₂ <CO ₂ density. When the density of CO ₂ is smaller than the density of the coolant, the coolant settles in the solid matter collection tank. On the other hand, when the density of CO ₂ is too large, the mixed state of CO ₂ and the slurry waste liquid becomes poor, and the slurry waste liquid cannot be effectively dispersed.

  With regard to the apparatus of the present invention, in the present invention, the separation solvent is recovered as a gas by an appropriate evaporation means for separating the separation solvent and the liquid component, and is recycled as liquid carbon dioxide via the cooling and condensation means. Further, it is possible to appropriately install a circulation means for the separation solvent. In addition, a means for continuously discharging the collected solid substance can be installed at the lower part of the specific gravity difference separator. This continuous discharge eliminates the need to store a solid substance in the specific gravity separator, and thus the specific gravity separator can be miniaturized. In the present invention, the specific configuration of each means constituting the apparatus of the present invention is not particularly limited, and can be arbitrarily designed according to the type of solid-liquid mixed material, the purpose of use of the apparatus, etc. it can.

  Furthermore, in the present invention, mixing the solid-liquid mixed material with supercritical carbon dioxide and / or liquid carbon dioxide, controlling the density and viscosity of the fluid after mixing, and adjusting the density and viscosity as appropriate. It is possible to mix a solid-liquid mixed material and supercritical carbon dioxide and / or liquid carbon dioxide in advance, and supply the mixture to specific gravity separation as appropriate while controlling the density and viscosity of the fluid. It is.

  Conventionally, various methods for recovering and reusing usable SiC and coolant contained in a large amount in a slurry waste liquid generated in a silicon wafer manufacturing process have been proposed. However, each method requires the use of a large amount of organic solvent, strong acid / strong alkali, dilute alkaline aqueous solution, surfactant, etc., or special treatment such as ultrasonic irradiation. In actuality, a waste liquid treatment process is required, and in fact, the recovery of valuable materials from slurry waste liquid and the like has hardly been performed.

  In addition, as a method to replace the existing extraction method with an organic solvent, a method of solid-liquid separation in a slurry waste liquid and recovery of valuable materials using supercritical carbon dioxide as an extraction solvent has been proposed. In order to achieve high separation efficiency alone, a large amount of extraction solvent is required, and there are significant restrictions on downsizing the apparatus and improving the extraction efficiency and the recovery rate of valuable materials. In addition, in the conventional specific gravity difference separation method, a centrifuge or the like was used. However, in this type of method, the separation efficiency is poor and complete solid-liquid separation cannot be performed, and in order to improve the separation efficiency. Since the dilution solvent is added, there are problems such as separation of the dilution solvent from the target substance after the separation operation, and post-treatment of the dilution solvent.

  On the other hand, in the present invention, carbon dioxide, which is a gas at normal temperature and normal pressure, is used as the specific gravity difference separation solvent, so that the solvent does not remain in the separated substance and there is no need for post-treatment. In addition, the present invention makes it possible to completely separate a solid-liquid mixed material using supercritical carbon dioxide and / or liquid carbon dioxide as a specific gravity difference separation solvent. In particular, the density of supercritical carbon dioxide can be easily and easily changed by changing the temperature and pressure, and it is overwhelmed by water, alcohol, organic solvents, and other separation solvents used in conventional density difference separation. Since the viscosity is low, a high separation efficiency can be obtained with a very small addition amount compared to these solvents.

  By using supercritical carbon dioxide and / or liquid carbon dioxide as a specific gravity difference separation solvent, the present invention achieves a significant reduction in the amount of solvent used, a reduction in the size of the apparatus, and an improvement in the separation efficiency of valuable materials at the same time. It is possible to do that. The present invention provides a high-efficiency separation method and apparatus for separating a specific gravity difference in a solid-liquid mixture using supercritical carbon dioxide and / or liquid carbon dioxide as a specific gravity difference separation solvent. Useful as.

The present invention has the following effects.
(1) By using supercritical carbon dioxide and / or liquid carbon dioxide as the specific gravity difference separation solvent, there is no sedimentation of the liquid component in the solid-liquid mixed material to the lower stage of the specific gravity difference separator, and the solid-liquid separation is completely achieved. Can do.
(2) Reusable valuable components can be separated and recovered with high efficiency by solid-liquid separation by specific gravity difference separation from slurry waste liquid.
(3) According to the present invention, for example, a recycling process of silicon slurry waste liquid can be established.
(4) By the method and apparatus of the present invention, valuable components can be separated and recovered with higher efficiency compared to the conventional solid-liquid separation method by SC-CO ₂ extraction.
(5) Since carbon dioxide, which is a gas at normal temperature and normal pressure, is used as the separation solvent for specific gravity difference, there is an advantage that the solvent does not remain in the separated substance and no post-treatment is required. It is done.
(6) The density of the supercritical carbon dioxide can be easily and easily changed by changing the temperature and / or pressure, so that the specific gravity difference separation conditions correspond to the density of the substance to be treated. Can be set arbitrarily.
(7) Supercritical carbon dioxide, which is a specific gravity difference separation solvent, has an extremely low viscosity compared to water and organic solvents, and therefore, a significantly higher separation efficiency can be obtained with a very small amount of solvent addition than conventional methods. It is done.
(8) By changing the temperature and / or pressure of carbon dioxide, which is a specific gravity difference separation solvent, and changing its density and viscosity, it is possible to arbitrarily set up a separation process and set separation conditions according to the solid-liquid mixed material to be treated. Can be.
(9) Since the operation at low temperature (about 35 ° C.) is possible, it is possible to separate the material to be treated without thermal denaturation.
(10) Since carbon dioxide is used for the specific gravity difference separation solvent, it is harmless to the environment and the human body.

  EXAMPLES Next, although this invention is demonstrated concretely based on an Example, this invention is not limited at all by the following Examples.

  In this example, solid-liquid separation was performed using a slurry waste liquid generated in a silicon ingot slicing step as a solid-liquid mixed substance. FIG. 5 shows a separation process of slurry waste liquid constructed according to the present invention and tried in the present example. As shown in the figure, the separation process includes a solid-liquid separation step and a SiC recovery step.

In the solid-liquid separation process, a separation method by SC-CO ₂ specific gravity separation using supercritical carbon dioxide (SC-CO ₂ ) as a specific gravity difference separation solvent is performed to recover the coolant, and in the SiC recovery process, a surfactant is used. A cleaning method by cleaning is performed to collect SiC. In this example, the valuable material recovery process with low environmental impact of the present invention was implemented by combining these two steps.

  With respect to the type of slurry waste liquid, in this example, solid-liquid separation operation was performed using an oil-based slurry waste liquid that is difficult to separate as compared with an aqueous slurry waste liquid as a target. FIG. 6 shows a photograph of the slurry waste liquid used in this example. Although the solid contained in the slurry waste liquid has a high density, the coolant is highly viscous, so the terminal speed is low, and the solid liquid is turbid because it is retained in the coolant. In this example, the coolant in which supercritical carbon dioxide, which is a low-viscosity solvent, is dissolved in the coolant contained in the slurry waste liquid is reduced in viscosity, and the solids (SiC, silicon scrap, iron scrap) and the coolant have a specific gravity difference. Attempts were made to separate by separation.

Usually, the abrasive grains (SiC) in the slurry waste liquid are 45 to 60 wt%, the coolant (mineral oil) is 30 to 40 wt%, the Si scrap is 15 to 10 wt%, and the Fe scrap is 15 to 5 wt%. In this embodiment, the slurry waste liquid is in a condition of total supply amount: 560 g, the coolant is in a supply amount of 165 g, density: 810 kg / m ³ , viscosity: 55 cp, solid matter (SiC, silicon scrap, iron scrap) The experiment was conducted under the conditions of supply amount: 395 g and density: 2550 kg / m ³ . FIG. 7 shows the density and viscosity of SC-CO ₂ under each experimental condition.

(Experimental device)
In the present example, an experiment was performed using an apparatus similar to the experimental apparatus shown in FIG. This experimental apparatus has a configuration in which a supply system, a discharge system, and a circulation / mixing line are arranged around a longitudinal and cylindrical specific gravity difference separator (inner diameter 50 mm, height 1000 mm, capacity 1963 ml, manufactured by SUS316). is doing. Among these configurations, the slurry waste liquid supply system is provided with a piping line from the slurry storage tank to the middle stage of the specific gravity difference separator through the slurry pump, and the discharge system is the upper stage of the specific gravity difference separator. To a high pressure filter, a back pressure valve, and a gas-liquid separator.

  The circulation / mixing line is connected from the upper stage of the specific gravity difference separator to the supply port of the solid-liquid mixed material in the middle stage of the specific gravity difference separator through the high pressure filter, environmental pump, and the pipe where slurry waste liquid is supplied and mixed. A line is provided. A P-2 pump, a V-4 valve, and a V-3 valve are installed in the circulation / supply line.

  The carbon dioxide supply system is provided with a piping line from a liquefied carbon dioxide cylinder containing carbon dioxide used as a separation solvent to the lower stage of the specific gravity difference separator through a precooler and a preheater. Yes. Further, on the side of the specific gravity difference separator, a hot water circulation means is installed in the upper half for heating or temperature adjustment, a heater is installed in the lower half, and the gas-liquid separator has a storage tank for recovered coolant and A scale is installed to measure the amount of coolant.

(experimental method)
The slurry waste liquid is supplied from the slurry storage tank to the high-pressure circulation / mixing line via the slurry pump, mixed with supercritical carbon dioxide (SC-CO ₂ ) in the high-pressure pipe, and then the middle stage of the specific gravity difference separator. To the supply port of the solid-liquid mixed substance located in By setting the ascending flow rate of SC-CO ₂ in the specific gravity difference separator to be equal to or lower than the terminal velocity of the solids contained in the slurry waste liquid, the solids settle in the solids collection tank below the specific gravity difference separator, The coolant was accompanied by SC-CO ₂ , passed through a back pressure valve, and recovered with a gas-liquid separator.

As experimental conditions, the temperature was kept constant at 35 ° C., and the pressure was 10, 15, and 29 MPa, and the pressure dependence of the separation characteristics was examined. SC-CO ₂ was always supplied in a fixed amount from the bottom to the top of the slurry waste liquid supply port of the specific gravity difference separator. The experiment begins by opening both V-1 and V-2 valves, using both P-1 and P-2 pumps, and from the feed port located at the bottom of the specific gravity separator, SC-CO ₂ was supplied, the pressure was increased to the experimental pressure, and at the same time, heating was performed to the experimental temperature with a preheater, a heater, and hot water.

After reaching the experimental conditions, the SC-CO ₂ flow rate of the P-1 pump was set to 5 g / min, and the P-2 pump was temporarily stopped. Next, the V-1 and V-2 valves were closed and the V-3 and V-4 valves were opened, and then the flow rate of the P-2 pump was set to 12 g / min, and the circulation / mixing line was operated.

Next, the supply of the slurry waste liquid adjusted to a flow rate of 5 g / min was started, and after mixing the slurry waste liquid and SC-CO ₂ , the slurry was supplied to the solid-liquid mixed substance supply port in the middle stage of the specific gravity difference separator. By supplying the slurry waste liquid to the circulation / mixing line, it was mixed with the carbon dioxide solvent and the carbon dioxide solvent + coolant (mixed fluid) to reduce the viscosity of the coolant. When the supply time of the slurry waste liquid was 1.8 hr and the total supply amount was 560 g, the supply of the slurry waste liquid was finished. FIG. 8 shows the experimental conditions of Cases 1 and 2 and the evaluation of the mass balance of the solids and coolant collected at each point of the solids collection tank, high-pressure filter, and gas-liquid separator. The mass balance at each point was defined as recovery rate of each component × 100 / total supply amount of each component.

Although the continuous supply experiment of slurry waste liquid has been completed by the above-described operation by continuous operation, supply of slurry waste liquid is performed here in order to carry out a post-processing step of collecting all components of the slurry waste liquid supplied to the circulation / mixing line. After completion, once stop the P-2 pump, switch the V-3 and V-4 valves and the V-1 and V-2 valves again, and use both the P-1 and P-2 pumps. Then, SC-CO ₂ was supplied for 1.5 hr from the lowest supply port of the specific gravity difference separator, and the fluid in the specific gravity difference separator was extracted. Subsequently, after the supply of SC-CO ₂ was stopped and the pressure was reduced, the mass balance of the solid and the coolant recovered in the solid recovery tank and the gas-liquid separator was evaluated.

(Experimental result)
Table 1 shows the pressure, temperature, density of SC-CO ₂ , viscosity and maximum ascending flow rate, final terminal velocity of SiC, Reynolds number of the mixing part immediately after mixing SC-CO ₂ and slurry waste liquid in each experiment (Case 1 to 3). , Indicate.

  Table 2 shows the solid recovery rate in the solid recovery tank, the coolant sedimentation rate, and the coolant recovery rate in the gas-liquid separator. In addition, FIG. 9 shows the test conditions of Case 3, and the evaluation of the mass balance of the solid matter and coolant collected at each point of the solid matter collection tank, the high-pressure filter, and the gas-liquid separator. The mass balance at each point was defined as recovery rate of each component × 100 / total supply amount of each component.

The best results were obtained under the condition of 15 MPa (CO ₂ density: 815 kg / m ³ ). Under these conditions, it was found that solid and liquid could be completely separated. Even under the conditions of 10 MPa (CO ₂ density: 713 kg / m ³ ) and 29 MPa (CO ₂ density: 924 kg / m ³ ), good separation results were obtained, but with the solids, a slight amount of coolant was recovered, It was found that the coolant settled into the solid-liquid recovery tank.

This is because the Reynolds number of the mixing part was small under the condition of 29 MPa compared with the condition of 15 MPa, the mixing of SC-CO ₂ and the slurry waste liquid was insufficient, and the flow rate of SC-CO ₂ It is thought that this is caused by the fact that the terminal velocity of the solid matter was not sufficiently obtained. Under the condition of 10 MPa, it is considered that the coolant has settled because the coolant density is larger than the CO ₂ density.

The coolant, together with carbon dioxide, passes through the discharge system from the upper part of the specific gravity separator and is recovered by the gas-liquid separator. In order to prevent the coolant from settling in the solids recovery tank, the specific gravity separator is used. SC-CO ₂ is always quantitatively supplied from the bottom to the top of the slurry waste liquid supply port, and the density of CO ₂ supplied from the bottom to the top is greater than the density of the coolant, and the pressure in the solid-liquid separator It was found that it is about 15 MPa at 35 ° C.

(experimental method)
In this example, using the same experimental apparatus as in Example 1, the temperature conditions in the specific gravity difference separator were changed at the upper and lower portions of the slurry waste liquid supply port in the middle stage of the specific gravity difference separator, thereby solidifying the slurry waste liquid. Liquid separation was performed. As the slurry waste liquid, the same one as in Example 1 was used.

Based on the result of Example 1, in order to increase the Reynolds number in the mixing part of the mixed fluid of SC-CO ₂ and slurry waste liquid, the supply pressure of SC-CO ₂ to the specific gravity difference separator is 10 MPa. The experimental conditions were set such that the portion heated by the heater at the bottom of the specific gravity difference separator was 25 ° C. and the top of the specific gravity difference separator was 35 ° C. The conditions were the same as in Example 1 except for these conditions.

(Experimental result)
Table 3 shows the solid recovery rate and coolant recovery rate in the solid recovery tank and the gas-liquid separator. It was found that at 35 ° C., the pressure was higher than 10 MPa and lower than 29 MPa, and about 15 MPa was preferable. In addition, if the temperature condition is changed, the pressure condition also changes. For example, in order to operate at a low pressure (10 MPa), only the lower part of the specific gravity difference separator is set to a low temperature (35 ° C. or lower) in order to suppress the settling of the coolant. It has also been found that it is effective to set the coolant density ≦ CO ₂ density.

  Even at a low pressure (10 MPa), the upper part of the specific gravity difference separator is set to 35 ° C., the lower part is set to a low temperature (25 ° C. or less), and the temperature conditions are changed. It was also found that the settling of the coolant into the solid matter collection tank can be suppressed.

(SiC recovery)
In the present example, SiC was recovered from the solid collected in the solid collection tank. In the experiment, a solid was put into a 1% nonionic surfactant aqueous solution and then irradiated with ultrasonic waves for about 5 minutes. While the solid was sufficiently dispersed in the liquid, it was allowed to stand for about 5 minutes, and a magnet was brought into contact with the liquid surface to collect Fe scraps. After standing, the turbid liquid of the surfactant aqueous solution and Si waste was discharged, and the precipitated SiC was recovered. In order to increase the purity of SiC, the surfactant was again added to the precipitated SiC, and washing and discharging of the turbid liquid were repeated three times. FIG. 10 shows a SiC recovery process, a photograph of the recovered SiC, and an SEM image.

(Experimental result)
The particle size distribution of the recovered SiC is shown in FIG. The average particle diameter of the recovered SiC was 10 μm and had a sharp distribution. Reusable SiC with the exposed surface was recovered. FIG. 12 shows an overall view of the separation process for recovering valuable materials from the silicon cutting slurry waste liquid.

From the above experimental results of the embodiment of the present invention, the SC-CO ₂ was circulated through the fluid after solid-liquid separation while quantitatively supplying SC-CO ₂ from the lowest supply port of the specific gravity difference separator, and passed through the circulation / mixing line. , By supplying the solid-liquid mixed substance supply port in the middle stage of the specific gravity difference separator and using the specific gravity difference separation, the solid-liquid separation operation of the slurry waste liquid is continuously performed, thereby suppressing the settling of the coolant. It was found that solid-liquid separation can be performed. By adopting the separation process of the present invention, there is no settling of coolant, the recovery rate of coolant and SiC is extremely high, and the recovered SiC also has a sharp distribution with an average particle diameter of 10 μm, It proves useful as an available recovered SiC.

To summarize the results of this example, when using a turbulent mixing type mixer, from the viewpoint of mixing, low pressure is effective under the same temperature conditions in order to increase the Reynolds number of the mixing section, and solids separation In view of the above, a low pressure is effective under the same temperature condition in order to increase the difference between the solid end velocity and the SC-CO ₂ ascending flow rate. However, from the viewpoint of coolant separation, in order to prevent the coolant from settling in the solids collection tank, it is necessary to have a density of carbon dioxide that is higher than the density of the coolant, and it is important to balance these conditions. I understand.

As described above in detail, the present invention relates to a solid-liquid separation method of solid-liquid mixed material by specific gravity difference separation using supercritical carbon dioxide or liquid carbon dioxide as a separation solvent, and an apparatus therefor. By using supercritical carbon dioxide and / or liquid carbon dioxide as the specific gravity difference separation solvent, the liquid component in the solid-liquid mixed material does not settle to the lower stage of the specific gravity difference separator and can be completely solid-liquid separated. . By the method and apparatus of the present invention, valuable components can be separated and recovered with high efficiency compared to the conventional solid-liquid separation method by SC-CO ₂ extraction. In the present invention, for example, a complete solid-liquid separation process such as slurry waste liquid generated in a silicon wafer manufacturing process is established, and a solid-liquid mixture such as slurry waste liquid is completely solid-liquid separated, and its valuables are efficiently collected. The present invention is useful for providing a solid-liquid separation technique for a new solid-liquid mixture that can be recovered.

1 shows a prior art experimental apparatus. The recovered materials and recovery rates at each point of the SiC recovery tank, high-pressure filter, and gas-liquid separator are shown. The flow chart of the continuous solid-liquid separator used in the example is shown. The solid-liquid separation result by this invention is shown. The separation process of the slurry waste liquid which experimented in the present Example is shown. A photograph of the coolant is shown. Experimental conditions, density and viscosity of SC-CO ₂ are shown. The experimental results of Case 1 and 2 and the evaluation of mass balance at each point are shown. The experimental results of Case 3 and the evaluation of mass balance at each point are shown. An SiC recovery process, a photograph of recovered SiC, and an SEM are shown. The particle size distribution of recovered SiC is shown. The whole picture of the separation process of valuables recovery from silicon cutting slurry waste liquid is shown.

Claims (12)

In a specific gravity difference separation method of a solid-liquid mixed material using supercritical carbon dioxide or liquid carbon dioxide as a specific gravity difference separation solvent, the solid-liquid mixed material is supplied from a middle supply port of the specific gravity difference separator, and the specific gravity difference separator The liquid and carbon dioxide in the solid-liquid mixed substance are flowed out from the upper stage, the solid matter is settled down and collected, and the density is fixed from the bottom to the upper side of the solid-liquid mixed substance supply port in the middle stage of the specific gravity difference separator. Supercritical carbon dioxide or liquid carbon dioxide having a density equal to or higher than the density of the liquid in the liquid mixed substance is quantitatively supplied, and the fluid flowing out from the specific gravity difference separator is circulated as a circulating fluid to the supply port of the solid-liquid mixed substance, The solid-liquid mixed substance is turbulently mixed with this circulating fluid and supplied to the specific gravity difference separator to prevent the liquid in the solid-liquid mixed substance from sinking below the supply port of the solid-liquid mixed substance. Solid-liquid separation characterized by continuous solid-liquid separation The difference in specific gravity separation method of case material.   The specific gravity difference separation method according to claim 1, wherein the solid-liquid mixed material is a slurry waste liquid generated in a silicon wafer manufacturing process or a polishing / cutting slurry waste liquid. When the density of supercritical carbon dioxide or liquid carbon dioxide is controlled by changing the temperature and / or pressure, the solid matter of the solid-liquid mixed substance is located above the solid-liquid mixed substance supply port of the specific gravity difference separator. In order to obtain a predetermined terminal velocity, the density of the specific gravity difference separation solvent is reduced by controlling it at a higher temperature than the lower part, and at the lower part, the density of the specific gravity difference separation solvent is controlled at a lower temperature than that of the upper part. Settling of the liquid in the solid-liquid mixed substance below the solid-liquid mixed substance supply port so that the density of the liquid of the substance is equal to or higher than the density of the liquid of the solid-liquid mixed substance and the mixed fluid of carbon dioxide. The specific gravity difference separation method according to claim 1 , wherein   The liquid and carbon dioxide in the solid-liquid mixed material flowing out from the specific gravity separator are separated by a gas-liquid separator, the separated carbon dioxide is condensed, and the carbon dioxide is placed below the solid-liquid mixed material supply port. The specific gravity difference separation method according to claim 1, wherein the separation is carried out as supercritical carbon dioxide or liquid carbon dioxide supplied from above to the top. The fluid that flows out through the filter from the upper outlet of the difference in specific gravity separators, as the circulating fluid, circulating in the feed opening of the solid-liquid substance mixture of a specific gravity difference separation unit, according to any of claims 1 3 Specific gravity difference separation method. In the step of circulating the fluid flowing out from the upper stage of the specific gravity difference separator as a circulating fluid to the solid-liquid mixed substance supply port of the specific gravity difference separator and mixing the solid-liquid mixed substance with this circulating fluid, The specific gravity difference separation method according to any one of claims 1 to 5 , wherein the solid-liquid mixed substance is mixed with a mixer. In the step of circulating the fluid flowing out from the upper stage of the specific gravity difference separator as a circulating fluid to the solid-liquid mixed substance supply port of the specific gravity difference separator, and mixing the solid-liquid mixed substance with this circulating fluid, the temperature of the circulating fluid The flow rate of the mixed fluid of carbon dioxide in the specific gravity difference separator and the liquid and carbon dioxide in the solid-liquid mixed material is controlled while controlling the pressure and / or flow rate and ensuring the mixing of the circulating fluid and the solid-liquid mixed material. The specific gravity difference separation method according to any one of claims 1 to 6 , wherein the separation is controlled so as to be equal to or lower than a predetermined terminal velocity of the solid substance. Using supercritical carbon dioxide or liquid carbon dioxide as the specific gravity difference separation solvent, the solid-liquid mixed substance is supplied from the middle stage of the specific gravity difference separator, and the liquid and carbon dioxide in the solid-liquid mixed substance are supplied from the upper stage of the specific gravity difference separator. A solid-liquid mixed substance specific gravity difference separation device that continuously solid-liquid separates the solid-liquid mixed substance by collecting the solid by settling down and recovering,
Quantitatively supply supercritical carbon dioxide or liquid carbon dioxide whose density is higher than the density of the liquid in the solid-liquid mixed material, from the bottom to the top, at a position below the supply port of the solid-liquid mixed material at the interruption of the specific gravity difference separator A means for circulating the fluid that has flowed out of the specific gravity difference separator as a circulating fluid to the supply port of the solid-liquid mixed material, and a turbulent mixing of the solid-liquid mixed material with the circulating fluid, A means for supplying to the differential separator is provided, and the liquid in the solid-liquid mixed substance is continuously solid-liquid separated by preventing sedimentation below the supply port of the solid-liquid mixed substance. A continuous specific gravity difference separation apparatus for solid-liquid mixed materials. A gas-liquid separator that separates carbon dioxide from the liquid in the solid-liquid mixed material that has flowed out from the upper stage of the specific gravity difference separator, means for condensing the separated carbon dioxide, and re-supplying the carbon dioxide to the specific gravity difference separator The continuous specific gravity difference separation device according to claim 8 , comprising means for use in a continuous manner. The density of the supercritical carbon dioxide or liquid carbon dioxide is supplied from the bottom than the supply port of the gravity difference separation type of the solid-liquid mixed material includes means for adjusting by changing the temperature and / or pressure, according to claim 8 The continuous specific gravity difference separation device described in 1. The continuous specific gravity difference separation device according to claim 8 , further comprising means for controlling the upper part and the lower part of the specific gravity difference separator at different temperatures from the supply port of the solid-liquid mixed material. In the device that circulates the fluid flowing out from the specific gravity difference separator as a circulating fluid to the solid-liquid mixed material supply port of the specific gravity difference separator and mixes the solid-liquid mixed material with this circulating fluid, the circulating fluid and the solid-liquid mixing The continuous specific gravity difference separation device according to any one of claims 8 to 11 , further comprising a mixer means for mixing substances.