Copper sulfate, hydrate of copper sulfate, aqueous copper sulfate solution, plating solution, and method for producing copper sulfate

Abstract

The present invention pertains to copper sulfate that satisfies all of the following characteristics (1) and (2). (1) In an aqueous copper sulfate solution obtained by dissolving copper sulfate in pure water, the number of particles having a particle diameter of 0.5 μm or greater as measured using an in-liquid particle counter is 2,000,000 or less per 1.0 g of Cu. (2) The Fe concentration is 0.700 ppm by mass or less.

Description

Copper sulfate, hydrate of copper sulfate, aqueous solution of copper sulfate, plating solution, and method for producing copper sulfate

[0001] The present invention relates to copper sulfate, a hydrate of copper sulfate, an aqueous solution of copper sulfate, a plating solution, and a method for producing copper sulfate.

[0002] Copper sulfate is known to be used as a raw material for copper plating solutions for printed circuit boards, a raw material for copper plating solutions for semiconductors, a catalyst raw material, a copper fine powder raw material, and the like. Heretofore, copper sulfate with reduced concentration of metal impurities has been proposed.

[0003] In Japanese Unexamined Patent Application Publication No. 2018-172265 (Patent Document 1), among metal impurities contained in commercially available copper sulfate crystals (concentration: 95 to 99.9% by mass), particular attention is paid to Al, and copper sulfate having an Al concentration of 0.08 mass ppm or less is described. Further, in Japanese Unexamined Patent Application Publication No. 2018-188348 (Patent Document 2), among metal impurities contained in commercially available copper sulfate crystals (concentration: 95 to 99.9% by mass), particular attention is paid to Fe, and copper sulfate having an Fe concentration of 0.08 mass ppm or less is described.

[0004] Japanese Unexamined Patent Application Publication No. 2018-172265 Japanese Unexamined Patent Application Publication No. 2018-188348

[0005] In the field of advanced semiconductor technology, copper sulfate used as a raw material for copper plating solutions is required to have metal impurities reduced as much as possible. Copper sulfate contains a relatively large amount of Fe as a metal impurity, and it can be said that reducing the Fe concentration is effective for reducing metal impurities from copper sulfate.

[0006] Further, when copper sulfate is dissolved in water, a large number of insoluble fine particles may be suspended in the resulting aqueous solution. Since these insoluble fine particles are considered to be suspended even in the copper plating solution, it is desirable to reduce the insoluble fine particles in addition to the above metal impurities.

[0007] Therefore, one embodiment of the present invention aims to provide copper sulfate in which at least Fe as a metal impurity is reduced and insoluble fine particles are also reduced, a hydrate and aqueous solution of said copper sulfate, and a plating solution using said copper sulfate. Another embodiment of the present invention aims to provide a method for producing copper sulfate in which at least Fe as a metal impurity is reduced and insoluble fine particles are also reduced.

[0008] Embodiments of the present invention can be described in the following [1] to [7]. [1] Copper sulfate that satisfies all of the following characteristics (1) to (2): (1) In an aqueous solution of copper sulfate obtained by dissolving copper sulfate in pure water, the number of particles with a particle size of 0.5 μm or more, measured using a liquid particle counter, is 2,000,000 or less per 1.0 g of Cu, (2) The Fe concentration is 0.700 ppm by mass or less. [2] Copper sulfate according to [1] that further satisfies the following characteristic (3): (3) The total metal impurity concentration is less than 1.0 ppm by mass, where the total metal impurity concentration is the sum of the concentrations of Na, K, Co, Cr, Ni, Zn, Al, Ca, Mg, Mn, Pb, Sn, Cd, As, Fe, Ag, and Ti. [3] A hydrate of copper sulfate according to [1] or [2]. [4] An aqueous solution of copper sulfate as described in [1] or [2]. [5] A plating solution using copper sulfate as described in [1] or [2]. [6] A method for producing copper sulfate, comprising: preparing an aqueous solution of copper sulfate by dissolving copper sulfate in pure water while heating it; and performing crystallization of copper sulfate by cooling the aqueous solution of copper sulfate at a cooling rate of 0.06°C / min or higher while stirring, provided that the number of particles with a particle size of 0.5 μm or more, as measured using a particle counter in liquid, is 3,000,000 or more per 1.0 g of Cu, provided that the cooling rate is 0.08°C / min or higher. [7] The method for producing copper sulfate as described in [6], wherein the crystallization is performed under conditions where the Reynolds number is 28,000 or higher.

[0009] According to one embodiment of the present invention, it is possible to provide copper sulfate in which at least Fe as a metal impurity is reduced and insoluble fine particles are also reduced, a hydrate and aqueous solution of said copper sulfate, and a plating solution using said copper sulfate. Furthermore, according to another embodiment of the present invention, it is possible to provide a method for producing copper sulfate in which at least Fe as a metal impurity is reduced and insoluble fine particles are also reduced.

[0010] This shows the ratio of the number of copper sulfate particles after crystallization to the number of copper sulfate particles before crystallization.

[0011] The following describes in detail the copper sulfate, copper sulfate hydrate, aqueous solution of copper sulfate, plating solution, and method for producing copper sulfate according to the embodiment of the present invention.

[0012] (Copper Sulfate) The copper sulfate according to one embodiment of the present invention is a copper sulfate that satisfies all of the following characteristics (1) to (2), and more preferably is a copper sulfate that satisfies the following characteristic (3): (1) In an aqueous solution of copper sulfate obtained by dissolving copper sulfate in pure water, the number of particles with a particle size of 0.5 μm or more, measured using a liquid particle counter, is 2,000,000 or less per 1.0 g of Cu. (2) The Fe concentration is 0.700 ppm by mass or less. (3) The total metal impurity concentration is less than 1.0 ppm by mass, where the total metal impurity concentration is the sum of the concentrations of Na, K, Co, Cr, Ni, Zn, Al, Ca, Mg, Mn, Pb, Sn, Cd, As, Fe, Ag, and Ti.

[0013] Characteristic (1): Particle number characteristic (1) is a characteristic relating to insoluble fine particles suspended in an aqueous solution when copper sulfate is dissolved in water. The particles measured by the liquid particle counter correspond to insoluble fine particles. Insoluble fine particles can be substances that may be mixed in during the manufacturing process or storage of copper sulfate, such as substances derived from raw materials, dust, and dirt. By suppressing the number of particles with a particle size of 0.5 μm or more, the number of insoluble fine particles suspended in the aqueous solution can be reduced. This can prevent the lifespan of microfilters installed in solutions such as plating solutions from being shortened, and can also prevent problems that may occur due to the presence of insoluble fine particles in solutions such as plating solutions (for example, deterioration of plating quality). From this viewpoint, it is preferable that the number of particles with a particle size of 0.5 μm or more is 2,000,000 or less per 1.0 g of Cu. Furthermore, there is no particular lower limit, but the number of particles with a particle size of 0.5 μm or more may be 10,000 or more per 1.0 g of Cu. Here, the particle count is calculated by converting the mass of copper sulfate contained in the aqueous solution (in other words, copper sulfate before dissolution) to copper equivalent, and expressing it as the number of particles per 1.0 g of copper. Note that the mass of copper sulfate is the mass assuming that the copper sulfate contains no impurities such as metallic impurities, insoluble fine particles, or organic matter, and that it is composed entirely of copper sulfate. Furthermore, as described later, when copper sulfate is in the form of a hydrate, the mass of copper sulfate hydrate (usually copper sulfate pentahydrate) is the mass assuming that the copper sulfate hydrate contains no impurities such as metallic impurities, insoluble fine particles, or organic matter, and that it is composed entirely of copper sulfate hydrate.

[0014] The particle count can be measured as follows. First, pure water is filtered to remove particles contained in the pure water. For filtration, it is preferable to use a membrane filter with a pore size smaller than the size of the insoluble fine particles to be measured. In the examples described later, a 0.1 μm membrane filter was used for filtration. Next, copper sulfate is dissolved in the filtered pure water to prepare an aqueous copper sulfate solution. Copper sulfate may be in solid form, such as anhydrous copper sulfate or copper sulfate hydrate, or it may already be in the form of an aqueous solution (i.e., an aqueous copper sulfate solution). When measuring the particle count of an aqueous copper sulfate solution that is already in aqueous solution form, the aqueous copper sulfate solution is diluted with filtered pure water to prepare an aqueous copper sulfate solution for measurement. Solid copper sulfate is dissolved in filtered pure water to prepare an aqueous copper sulfate solution for measurement. The copper ion concentration in the aqueous copper sulfate solution for measurement is preferably in the range of 0.3 to 1.0 g / L. In the examples described later, the copper ion concentration was adjusted to approximately 0.75 g / L. The copper ion concentration here is calculated assuming that the copper sulfate solution contains no impurities such as metal impurities, insoluble fine particles, or organic matter, and is composed solely of copper sulfate. Next, a liquid particle counter is used to measure the particle size and number of particles suspended in the copper sulfate aqueous solution. A liquid particle counter is a liquid particle detector that can detect particles suspended in a liquid using a light scattering method and measure their particle size and number. For example, the KS-42C light scattering liquid particle detector manufactured by Rion Co., Ltd. can be used. When performing measurements using the KS-42C light scattering liquid particle detector manufactured by Rion Co., Ltd., a device for introducing the sample into the particle detector (for example, the KZ-31W syringe sampler manufactured by Rion Co., Ltd.) and a device that can control the operation of the particle detector and display the measurement data (for example, the KE-40B1 controller manufactured by Rion Co., Ltd.) can be used in combination. The particle size is the equivalent diameter of light scattering of calibration particles suspended in pure water, and polystyrene latex (PSL) particles (refractive index 1.6 in pure water) are used as calibration particles. Measurement using a liquid particle counter is performed by washing 50 mL of the sample with water at a flow rate of 10 mL / min, and then measuring 10 mL of the sample with water at a flow rate of 10 mL / min.The measurement is performed three times, and the average of the three measured values ​​is taken as the particle count described in characteristic (1). Furthermore, if the particle count concentration in the sample exceeds the maximum particle count concentration measurable by the liquid particle counter (e.g., 1200 particles / ml) during measurement with the liquid particle counter, the particle count concentration in the sample can be adjusted to be below the maximum particle count concentration of the liquid particle counter by increasing the dilution ratio, thereby enabling particle count measurement. When measuring with the liquid particle counter, all instruments used are washed with pure water filtered through a membrane filter with a pore size smaller than the size of the insoluble microparticles to be measured, for example, a 0.1 μm membrane filter. The pure water is also filtered through a membrane filter with a pore size smaller than the size of the insoluble microparticles to be measured, for example, a 0.1 μm membrane filter, as described above. The filtered pure water is pre-checked using a liquid particle counter to confirm that the number of particles with a particle size of 0.5 μm or larger is 1000 or less per 10 mL.

[0015] Characteristic (2): Fe concentration characteristic (2) is a characteristic relating to the amount of iron that may be contained as a metallic impurity in copper sulfate. Copper sulfate contains a relatively large amount of Fe as a metallic impurity, and reducing the Fe concentration is effective in reducing metallic impurities from copper sulfate. By reducing the amount of metallic impurities contained in copper sulfate, it is possible to reduce the occurrence of defects in the wiring of semiconductor devices, for example. The Fe concentration of copper sulfate is 0.700 ppm by mass or less, and preferably 0.600 ppm by mass or less. Furthermore, there is no particular limit on the lower limit, but the Fe concentration of copper sulfate may be 0.00001 ppm by mass or more.

[0016] Characteristic (3): The total metal impurity concentration characteristic (3) relates to the total amount of metal impurities that may be contained in copper sulfate. Reducing the amount of metal impurities contained in copper sulfate can reduce defects in semiconductor device wiring, for example. The total metal impurity concentration in characteristic (3) is the sum of the concentrations of Na, K, Co, Cr, Ni, Zn, Al, Ca, Mg, Mn, Pb, Sn, Cd, As, Fe, Ag, and Ti. The "total metal impurity concentration" is sometimes referred to as the "total dissolved metal impurity concentration." The total metal impurity concentration of copper sulfate is preferably less than 1.0 ppm by mass, and more preferably 0.800 ppm by mass or less. There is no particular lower limit, but the total metal impurity concentration of copper sulfate may be 0.00001 ppm by mass or more.

[0017] In one embodiment of the present invention, the copper sulfate preferably has a Na concentration of 0.20 ppm by mass or less. While there is no particular lower limit, the Na concentration may be 0.00001 ppm by mass or more.

[0018] In one embodiment of the present invention, the copper sulfate preferably has a K concentration of 0.20 ppm by mass or less. While there is no particular lower limit, the K concentration may be 0.00001 ppm by mass or more.

[0019] The copper sulfate according to one embodiment of the present invention preferably has a Co concentration of 0.20 ppm by mass or less. While there is no particular lower limit, the Co concentration may be 0.00001 ppm by mass or more.

[0020] The copper sulfate according to one embodiment of the present invention preferably has a Cr concentration of 0.40 ppm by mass or less. While there is no particular lower limit, the Cr concentration may be 0.00001 ppm by mass or more.

[0021] In one embodiment of the present invention, the copper sulfate preferably has a Ni concentration of 0.40 ppm by mass or less. While there is no particular lower limit, the Ni concentration may be 0.00001 ppm by mass or more.

[0022] In one embodiment of the present invention, the copper sulfate preferably has a Zn concentration of 0.20 ppm by mass or less. While there is no particular lower limit, the Zn concentration may be 0.00001 ppm by mass or more.

[0023] The copper sulfate according to one embodiment of the present invention preferably has an Al concentration of 0.20 ppm by mass or less. While there is no particular lower limit, the Al concentration may be 0.00001 ppm by mass or more.

[0024] The copper sulfate according to one embodiment of the present invention preferably has a Ca concentration of 0.20 ppm by mass or less. While there is no particular lower limit, the Ca concentration may be 0.00001 ppm by mass or more.

[0025] In one embodiment of the present invention, the copper sulfate preferably has a Mg concentration of 0.20 ppm by mass or less. While there is no particular lower limit, the Mg concentration may be 0.00001 ppm by mass or more.

[0026] In the copper sulfate according to one embodiment of the present invention, the Mn concentration is preferably 0.20 ppm by mass or less. Furthermore, there is no particular lower limit, although the Mn concentration may be 0.00001 ppm by mass or more.

[0027] The copper sulfate according to one embodiment of the present invention preferably has a Pb concentration of 0.20 ppm by mass or less. While there is no particular lower limit, the Pb concentration may be 0.00001 ppm by mass or more.

[0028] The copper sulfate according to one embodiment of the present invention preferably has a Sn concentration of 0.20 ppm by mass or less. While there is no particular lower limit, the Sn concentration may be 0.00001 ppm by mass or more.

[0029] In one embodiment of the present invention, the copper sulfate preferably has a Cd concentration of 0.20 ppm by mass or less. While there is no particular lower limit, the Cd concentration may be 0.00001 ppm by mass or more.

[0030] In one embodiment of the present invention, the copper sulfate preferably has an As concentration of 0.20 ppm by mass or less. While there is no particular lower limit, the As concentration may be 0.00001 ppm by mass or more.

[0031] In one embodiment of the present invention, the copper sulfate preferably has an Ag concentration of 0.20 ppm by mass or less. While there is no particular lower limit, the Ag concentration may be 0.00001 ppm by mass or more.

[0032] In one embodiment of the present invention, the copper sulfate preferably has a Ti concentration of 0.20 ppm by mass or less. While there is no particular lower limit, the Ti concentration may be 0.00001 ppm by mass or more.

[0033] The concentration of metal impurities in copper sulfate can be determined by ICP-MS or ICP-MS / MS. ICP-MS and ICP-MS / MS can quantify each of the metal impurities with high accuracy, even when many types of metal impurities are present in an aqueous solution of copper sulfate. For example, in the analysis of metal impurities by ICP-MS or ICP-MS / MS, it is possible to quantify 17 types of metals at once: Na, K, Co, Cr, Ni, Zn, Al, Ca, Mg, Mn, Pb, Sn, Cd, As, Fe, Ag, and Ti.

[0034] ICP-MS is a term that refers to inductively coupled plasma mass spectrometry. Inductively coupled plasma mass spectrometry is an analytical method that typically involves introducing a sample into a high-temperature argon (Ar) plasma, ionizing the elements in the sample, and measuring the number of ions in m / z (mass-to-charge ratio) using a mass spectrometer to determine the concentration of elements and their isotopes. ICP-MS / MS is a term that refers to an inductively coupled plasma mass spectrometer equipped with two mass spectrometers. It is an improved instrument designed to perform analysis with higher precision than an inductively coupled plasma mass spectrometer equipped with a single mass spectrometer. For example, MS and MS / MS instruments can use quadrupole, double-focusing, or TOF types. Specific examples of such MS and MS / MS instruments include ICP-Q-MS, ICP-QQQ-MS, and ICP-SF-MS.

[0035] Analysis of metal impurities by ICP-MS or ICP-MS / MS can be performed as follows: First, copper sulfate is dissolved in pure water to prepare an aqueous copper sulfate solution. Copper sulfate may be in solid form, such as anhydrous copper sulfate or hydrated copper sulfate, or it may already be in aqueous solution form (i.e., an aqueous copper sulfate solution). If there are particles that do not dissolve in pure water alone, the aqueous copper sulfate solution may be diluted 100-fold with dilute nitric acid as needed to prepare an aqueous copper sulfate solution for measurement. Next, the concentration of metal impurities (Na, K, Co, Cr, Ni, Zn, Al, Ca, Mg, Mn, Pb, Sn, Cd, As, Fe, Ag, Ti) in the aqueous copper sulfate solution is measured using an ICP mass spectrometer such as ICP-MS or ICP-MS / MS. As an ICP mass spectrometer, for example, an Agilent ICP-MS / MS (Agilent 8900 Triple Quadrupole ICP-MS) can be used. Next, the concentration of each metal impurity and the total metal impurity concentration can be determined from the concentration of copper sulfate in the prepared copper sulfate aqueous solution and the mass of metal impurities contained in the copper sulfate aqueous solution.

[0036] In one embodiment of the present invention, the copper sulfate preferably has a total organic carbon (TOC) content of 0.60 ppm by mass or less.

[0037] The TOC concentration of copper sulfate can be measured using a wet ultraviolet oxidation method, for example, with an analytikjena multi N / C UV HS. Specifically, an aqueous solution of copper sulfate is prepared, sodium peroxodisulfate (or an oxidizing agent) is added to the aqueous solution, and the carbon dioxide generated by oxidation is detected by an infrared gas analyzer (NDIR) to measure the TOC concentration.

[0038] The amount of copper in copper sulfate can be determined by the sodium thiosulfate titration method as follows: A predetermined amount of copper sulfate sample is taken and dissolved in ultrapure water to prepare a copper sulfate aqueous solution with a copper sulfate concentration of 255 g / L. A precision balance capable of measuring to four decimal places is used for measuring the mass of the copper sulfate sample. Here, the aforementioned ultrapure water is water with an electrical conductivity of 0.05882 μS / cm or less (electrical resistivity (specific resistivity) of 17.0 MΩ·cm or more). The measured value is used to four decimal places. Then, the following procedure is performed: An excess of potassium iodide is added to the copper sulfate aqueous solution. The following reaction proceeds when potassium iodide is added to the copper sulfate aqueous solution: 2Cu 2+ + 4KI → 2CuI + I2 + 4K + Next, the I2 produced by the reaction of potassium iodide with sodium thiosulfate is titrated. Specifically, the titration is continued until the purple color of iodine disappears and the solution becomes cloudy. The reaction between iodine and sodium thiosulfate is as follows: I2 + 2Na2S2O3 → Na2S4O6 + 2NaI Then, the amount of substance (moles) of sodium thiosulfate used in the titration is calculated, and this calculated amount of substance (moles) is taken as the amount of copper contained in the copper sulfate used to prepare the copper sulfate solution. The amount of copper in the copper sulfate can be determined from the mass of copper sulfate used to prepare the copper sulfate solution and the mass of copper sulfate calculated from the amount of copper determined by titration.

[0039] Copper sulfate according to one embodiment of the present invention can be suitably used for applications such as copper plating solution raw materials for printed circuit boards, copper plating solution raw materials for semiconductors, catalyst raw materials, and copper fine powder raw materials. In particular, copper sulfate according to one embodiment of the present invention is suitable as a raw material for copper plating solutions for semiconductors because at least Fe as a metallic impurity is reduced and insoluble fine particles are also reduced.

[0040] Copper sulfate according to one embodiment of the present invention can be obtained by the method for producing copper sulfate according to one embodiment of the present invention described later.

[0041] (Copper sulfate hydrate) The copper sulfate hydrate according to one embodiment of the present invention is the copper sulfate hydrate according to one embodiment of the present invention described above. Copper sulfate obtained by the method for producing copper sulfate according to one embodiment of the present invention described below is normally in the form of a hydrate. Copper sulfate hydrates include monohydrate and trihydrate, but normally take the form of copper sulfate pentahydrate. At normal temperature, copper sulfate hydrate takes the form of copper sulfate pentahydrate and is a stable substance.

[0042] (Plating solution) The plating solution according to one embodiment of the present invention is a plating solution using the copper sulfate according to one embodiment of the present invention described above, the copper sulfate hydrate according to one embodiment of the present invention, or an aqueous solution of copper sulfate according to one embodiment of the present invention. In the present specification, a plating solution using copper sulfate can also be expressed as a plating solution containing copper sulfate. However, since a plating solution normally uses water or the like as a solvent, copper sulfate is ionized in the plating solution and separated into copper ions and sulfate ions. Similarly, a plating solution using copper sulfate hydrate and a plating solution using an aqueous copper sulfate solution can also be expressed as a plating solution containing copper sulfate hydrate and a plating solution containing an aqueous copper sulfate solution, respectively.

[0043] The copper ion concentration and sulfate ion concentration in the plating solution are not particularly limited, and can be appropriately adjusted according to the application. Further, the plating solution may contain additional components, and examples of such additional components include ions such as chloride ions and various additives.

[0044] (Aqueous copper sulfate solution) The aqueous copper sulfate solution according to one embodiment of the present invention is an aqueous solution obtained by dissolving the copper sulfate according to one embodiment of the present invention or the copper sulfate hydrate according to one embodiment of the present invention described above in water (preferably pure water).

[0045] (Method for producing copper sulfate) The method for producing copper sulfate according to one embodiment of the present invention is a method for producing copper sulfate comprising the following steps (1) to (2): (1) Prepare an aqueous copper sulfate solution by dissolving copper sulfate in pure water while heating. (2) Crystallize copper sulfate by cooling the aqueous copper sulfate solution at a cooling rate of 0.06°C / min or more while stirring. However, when the number of particles having a particle diameter of 0.5 µm or more measured using an in-liquid particle counter in the aqueous copper sulfate solution obtained by dissolving the copper sulfate used in step (1) in pure water is 3,000,000 or more per 1.0 g of Cu, the cooling rate shall be 0.08°C / min or more.

[0046] Step (1): Step for preparing aqueous copper sulfate solution Commercially available copper sulfate can be used as the copper sulfate used in step (1). Hereinafter, the copper sulfate used in step (1) may also be referred to as copper sulfate (raw material). As the copper sulfate (raw material), anhydrous copper sulfate can be used, but it is preferable to use a copper sulfate hydrate or an aqueous copper sulfate solution, and it is more preferable to use a copper sulfate hydrate, particularly copper sulfate pentahydrate. In addition, a copper sulfate hydrate and an aqueous copper sulfate solution may be used in combination.

[0047] For the copper sulfate (raw material), in an aqueous copper sulfate solution obtained by dissolving the copper sulfate in pure water, the number of particles having a particle diameter of 0.5 µm or more measured using an in-liquid particle counter is preferably 4,000,000 or less per 1.0 g of Cu. The lower limit is not particularly limited, but the number of particles having a particle diameter of 0.5 µm or more may exceed 2,000,000 per 1.0 g of Cu.

[0048] The copper sulfate (raw material) preferably has an Fe concentration of 2.500 ppm by mass or less. The lower limit is not particularly limited, but the Fe concentration of the copper sulfate (raw material) may exceed 0.700 ppm by mass.

[0049] The copper sulfate (raw material) preferably has a total metal impurity concentration of 4.0 ppm by mass or less. While there is no particular lower limit, the total metal impurity concentration of the copper sulfate (raw material) may be 1.0 ppm by mass or more.

[0050] The number of particles, Fe concentration, and total metal impurity concentration of copper sulfate (raw material) can be determined by a method similar to that described in the description of copper sulfate according to one embodiment of the present invention.

[0051] The pure water used in step (1) can be commercially available pure water, but it is preferable to use water of very high purity, such as that classified as ultrapure water. In this specification, ultrapure water refers to water with an electrical conductivity of 0.05882 μS / cm or less (in other words, an electrical resistivity (specific resistivity) of 17.0 MΩ・cm or more). The electrical conductivity of water can be measured in accordance with JIS K0552:1994 "Test method for electrical conductivity of ultrapure water". Furthermore, ultrapure water can be produced using commercially available ultrapure water production equipment, such as the RFU400 series ultrapure water production equipment manufactured by Advantec Toyo Co., Ltd.

[0052] It is preferable that the pure water be filtered before use to remove any particles that may be present in it. Filtration is preferably performed using a membrane filter with a pore size smaller than the size of the insoluble particles to be measured, for example, a 0.1 μm membrane filter. The filtered pure water is preferably measured using a liquid particle counter to find no more than 1000 particles per 10 mL with a particle size of 0.5 μm or larger.

[0053] It is preferable to dissolve copper sulfate (raw material) in pure water while heating it to, for example, 65 to 80°C, preferably 70 to 75°C. It is also preferable to dissolve copper sulfate (raw material) in pure water while stirring.

[0054] The copper sulfate aqueous solution prepared in step (1) is preferably adjusted so that the concentration of copper sulfate is, for example, 155 to 170 g / L, more preferably 160 to 165 g / L, when converted to copper.

[0055] Step (2): In step (2) of copper sulfate crystallization, the copper sulfate aqueous solution prepared in step (1) is cooled at a cooling rate of 0.06°C / min or higher while being stirred to crystallize the copper sulfate. However, if the copper sulfate (raw material) used in step (1) has a particle size of 0.5 μm or larger measured using a liquid particle counter, and the number of particles is 3,000,000 or more per 1.0 g of Cu, the cooling rate shall be 0.08°C / min or higher. Insoluble fine particles may be mixed into the aqueous solution due to contact between the liquid surface and air during stirring of the copper sulfate aqueous solution. However, the faster the cooling rate, the shorter the time until copper sulfate precipitates, and the shorter the contact time between copper sulfate and air, thereby reducing the number of particles. For this reason, according to the method for producing copper sulfate according to one embodiment of the present invention, metal impurities can be reduced, as can insoluble fine particles. On the other hand, if the cooling rate is too fast, vacuoles may form between crystals, potentially increasing the concentration of metal impurities. Therefore, it is preferable that the cooling rate be 0.250°C / min or less.

[0056] For cooling during crystallization, known methods such as a chiller (cooling water circulation device, e.g., PCU-3310R manufactured by Apiste Co., Ltd.) can be used.

[0057] Cooling during crystallization is preferably carried out to a temperature of, for example, 10 to 25°C, preferably 20°C. Crystallization can be completed once this temperature is reached.

[0058] Stirring during crystallization can be carried out, for example, using a stirrer. The stirring speed during crystallization is preferably 50 to 500 rpm, and more preferably 50 to 400 rpm.

[0059] Crystallization is preferably carried out under conditions where the Reynolds number is 28,000 or higher. The Reynolds number is a dimensionless number that represents the ratio of viscous force to inertial force in a flow. When viscous force is dominant, the Reynolds number is low and the flow is laminar, while when inertial force is dominant, the Reynolds number is high and the flow is turbulent. In a method for producing copper sulfate according to one embodiment of the present invention, it has been found that performing crystallization under conditions where the Reynolds number is 28,000 or higher enhances the effect of reducing metal impurities contained in copper sulfate. In the crystallization of copper sulfate, the crystals are recovered with an aqueous copper sulfate solution contained between the precipitated crystals, and it is thought that metal impurities dissolved in the aqueous copper sulfate solution are trapped between the copper sulfate crystals. However, if the Reynolds number is 28,000 or higher, it is thought that bonding between crystals can be suppressed and the amount of aqueous copper sulfate solution trapped between crystals can be reduced. There is no particular upper limit to the Reynolds number.

[0060] Furthermore, if crystallization is performed under conditions where the Reynolds number is 28,000 or higher at the cooling rate described above, the number of copper sulfate particles before crystallization can be significantly reduced. For example, the ratio of the number of copper sulfate particles after crystallization to the number of copper sulfate particles before crystallization, which can be calculated using the following formula, can be reduced to 50% or less, preferably 40% or less. Formula: Number of copper sulfate particles after crystallization / Number of copper sulfate particles before crystallization × 100 Here, the number of particles is the number of particles with a particle size of 0.5 μm or more, measured using a liquid particle counter in an aqueous solution of copper sulfate obtained by dissolving copper sulfate in pure water.

[0061] The Reynolds number can be calculated using the following formula: Reynolds number = (rotational speed × stirring blade diameter × stirring blade diameter × solution density) / viscosity, where rotational speed is the speed at which the stirring blade rotates per second (s -1 The stirring blade diameter is the diameter (m) of the circle traced by the rotation of the stirring blade. The stirring blade is a general term for the rotating component attached to the agitator, and is sometimes called a stirring vane. If there are two or more stirring blades, the average value is used as the stirring blade diameter in the formula. The solution density is the density of the copper sulfate aqueous solution (kg / m³). 3) The density of the copper sulfate aqueous solution changes from the start to the end of cooling; therefore, in this specification, the average value of the density at the temperature at the start of cooling and the density at the temperature at the end of cooling is used as the solution density in the formula. If crystals have precipitated, the density of the copper sulfate aqueous solution containing the crystals is used. Viscosity is the viscosity (Pa·s) of the copper sulfate aqueous solution. The viscosity of the copper sulfate aqueous solution changes from the start to the end of cooling; therefore, in this specification, the average value of the viscosity at the temperature at the start of cooling and the viscosity at the temperature at the end of cooling is used as the viscosity in the formula. If crystals have precipitated, the viscosity of the copper sulfate aqueous solution containing the crystals is used. The viscosity of the copper sulfate aqueous solution is measured using a Brookfield-type viscometer, which is a rotational viscometer. For example, it is measured using a VIS-COMETER manufactured by Toki Sangyo Co., Ltd.

[0062] In a method for producing copper sulfate according to one embodiment of the present invention, after step (2), crystals precipitated from the aqueous copper sulfate solution by crystallization can be recovered. These crystals are composed of copper sulfate hydrate, particularly copper sulfate pentahydrate.

[0063] One method for recovering crystals from an aqueous copper sulfate solution is to filter the solution to separate the crystals from the aqueous solution. Filtration methods include suction filtration.

[0064] In a method for producing copper sulfate according to one embodiment of the present invention, the crystals can be washed after being recovered from an aqueous copper sulfate solution. A means of washing the crystals is to immerse them in pure water. After washing, the crystals can be recovered by means of recovery, such as suction filtration.

[0065] It is preferable that the pure water be filtered before use to remove any particles that may be present in it. The filtration of the pure water is preferably carried out using a membrane filter with a pore size smaller than the size of the insoluble particles to be measured, for example, a 0.1 μm membrane filter. The filtered pure water is preferably measured by a liquid particle counter to show that the number of particles with a particle size of 0.5 μm or larger is 1000 or less per 10 mL.

[0066] In a method for producing copper sulfate according to one embodiment of the present invention, the recovered crystals can be dried.

[0067] In a method for producing copper sulfate according to one embodiment of the present invention, it is preferable to wash all the instruments used, especially the copper sulfate aqueous solution and any instruments that may come into contact with copper sulfate, with pure water filtered through a membrane filter with a pore size smaller than the size of the insoluble particles to be measured, for example, a 0.1 μm membrane filter.

[0068] According to the method for producing copper sulfate according to one embodiment of the present invention, it is possible to produce copper sulfate in which at least Fe as a metal impurity is reduced and insoluble fine particles are also reduced, and in particular, it is possible to produce copper sulfate according to one embodiment of the present invention. The method for producing copper sulfate according to one embodiment of the present invention can produce copper sulfate in which at least Fe as a metal impurity is reduced and insoluble fine particles are also reduced, even in a general environment that does not use a clean room where particle control is performed.

[0069] One embodiment of the present invention will be described in more detail below with reference to examples, but the copper sulfate, copper sulfate hydrate, aqueous solution of copper sulfate, and method for producing copper sulfate according to the embodiment of the present invention are not intended to be limited to the following examples.

[0070] <Example 1 and Comparative Examples 1-3> 1. Preparation of copper sulfate aqueous solution Using a SUS316L stainless steel container manufactured by MONOVATE Co., Ltd., 3750 g of copper sulfate pentahydrate was dissolved in 4.5 L of pure water while heating to 70°C to prepare a copper sulfate aqueous solution. The copper sulfate concentration of the copper sulfate aqueous solution was approximately 160 g / L in terms of copper.

[0071] (1) Copper sulfate (raw material) In all of the examples of Example 1 and Comparative Examples 1 to 3, JX Metals Corporation's Yupinog (crystalline product) was used.

[0072] The particle count, Fe concentration, and total metal impurity concentration of copper sulfate (raw material) were determined by the method described above. The results are shown in Table 1.

[0073] (2) Pure water The pure water was filtered using a 0.1 μm membrane filter manufactured by ADVANTEC before use.

[0074] 2. Crystallization of Copper Sulfate A copper sulfate aqueous solution at 70°C was cooled to 20°C while stirring under the cooling rates and Reynolds numbers shown in Table 1 to crystallize copper sulfate. The apparatus used for the crystallization of copper sulfate was the same as the apparatus used for the preparation of the copper sulfate aqueous solution.

[0075] 3. Filtration and Washing: To recover the precipitated crystals (copper sulfate pentahydrate), suction filtration was performed in an aqueous copper sulfate solution. The recovered crystals were washed by immersing them in pure water at a mass equal to 0.4 times their mass. The pure water was filtered using a 0.1 μm membrane filter before use. Subsequently, suction filtration was performed again to recover the crystals.

[0076] 4. The dried and recovered crystals were placed in a clean dryer (ALP SB-120HG) and dried at 30°C for 17 hours.

[0077] The particle count, Fe concentration, Al concentration, Sn concentration, Ag concentration, total metal impurity concentration, and TOC of the dried copper sulfate were determined by the method described above. The results are shown in Table 1.

[0078]

[0079] In Table 1, the data for copper sulfate (raw material) is shown under "Raw Material / Before Crystallization," and the data for copper sulfate dried in "4. Drying" is shown under "After Crystallization." In the table, "Total Concentration" refers to the total concentration of metal impurities, and "Number of Particles" refers to the number of particles with a particle size of 0.5 μm or larger.

[0080] As can be seen from Table 1, the copper sulfate recovered after crystallization in Example 1 is copper sulfate with reduced levels of metallic impurities and insoluble fine particles compared to Comparative Examples 1 to 3.

[0081] Table 2 also shows the concentrations of metal impurities other than Fe in copper sulfate before and after crystallization in Example 1, specifically the concentrations of Na, K, Co, Cr, Ni, Zn, Al, Ca, Mg, Mn, Pb, Sn, Cd, As, Ag, and Ti.

[0082]

[0083] In Table 2, the data for copper sulfate (raw material) is shown under "Raw Material / Before Crystallization," and the data for copper sulfate dried in "4. Drying" is shown under "After Crystallization."

[0084] <Examples 2-4> To further verify the effects of the copper sulfate production method according to one embodiment of the present invention, copper sulfate having the properties shown in Table 2 was prepared. The prepared copper sulfate was prepared according to the copper sulfate production method according to one embodiment of the present invention, and all were in the form of copper sulfate pentahydrate.

[0085] The prepared copper sulfate (before crystallization) was subjected to the same procedures as described in <Example 1 and Comparative Examples 1-3> above: preparation of an aqueous copper sulfate solution, crystallization of copper sulfate, filtration and washing, and drying. The cooling rate and Reynolds number conditions during copper sulfate crystallization are shown in Table 3. The particle number, Fe concentration, total metal impurity concentration, and TOC of the dried copper sulfate were determined by the method described above. The results are shown in Table 3.

[0086]

[0087] In Table 3, the data for the prepared copper sulfate (before crystallization) is shown under "Before Crystallization," and the data for the copper sulfate after crystallization, filtration, washing, and drying is shown under "After Crystallization." In the table, "Total Concentration" refers to the total concentration of metal impurities, and "Number of Particles" refers to the number of particles with a particle size of 0.5 μm or larger.

[0088] As can be seen from Table 3, the copper sulfate recovered after crystallization in Examples 2 to 4 shows a reduction in metal impurities and insoluble fine particles compared to before crystallization. From this, it is recognized that metal impurities and insoluble fine particles can be further reduced by applying the copper sulfate production method according to one embodiment of the present invention to the copper sulfate according to one embodiment of the present invention.

[0089] Table 4 also shows the concentrations of metal impurities other than Fe in copper sulfate before and after crystallization in Examples 2 to 4, specifically the concentrations of Na, K, Co, Cr, Ni, Zn, Al, Ca, Mg, Mn, Pb, Sn, Cd, As, Ag, and Ti.

[0090]

[0091] In Table 4, the data for the prepared copper sulfate (before crystallization) is shown under "Before Crystallization," and the data for the copper sulfate that was filtered, washed, and dried after crystallization is shown under "After Crystallization."

[0092] Furthermore, Table 5 and Figure 1 show the ratio of the number of particles in copper sulfate after crystallization to the number of particles in copper sulfate before crystallization, based on the results obtained in Examples 1 to 4 and Comparative Examples 1 to 3. As can be seen from Table 5 and Figure 1, when the Reynolds number is 28,000 or higher at the cooling rate according to the method for producing copper sulfate according to one embodiment of the present invention, the number of particles in copper sulfate after crystallization is significantly reduced compared to the number of particles in copper sulfate before crystallization.

[0093]

[0094] (Potential Contribution to SDGs) According to one embodiment of the present invention, copper sulfate with reduced metal impurities and insoluble fine particles can be obtained, which may improve product yield. Improved product yield leads to a stable supply of products and a reduction in the loss of raw materials, which are limited resources. For this reason, one embodiment of the present invention may contribute to Goal 12 of the United Nations-led Sustainable Development Goals (SDGs), "Ensure sustainable consumption and production patterns."

Claims

1. Copper sulfate that satisfies all of the following characteristics (1) and (2): (1) In an aqueous solution of copper sulfate obtained by dissolving copper sulfate in pure water, the number of particles with a particle size of 0.5 μm or larger, as measured using a liquid particle counter, is 2,000,000 or less per 1.0 g of Cu; (2) The Fe concentration is 0.700 ppm by mass or less.

2. Furthermore, the copper sulfate according to claim 1 satisfies the following characteristic (3): (3) The total metal impurity concentration is less than 1.0 ppm by mass, where the total metal impurity concentration is the sum of the concentrations of Na, K, Co, Cr, Ni, Zn, Al, Ca, Mg, Mn, Pb, Sn, Cd, As, Fe, Ag, and Ti.

3. The copper sulfate hydrate according to claim 1 or 2.

4. An aqueous solution of copper sulfate according to claim 1 or 2.

5. A plating solution using copper sulfate according to claim 1 or 2.

6. A method for producing copper sulfate, comprising: dissolving copper sulfate in pure water while heating to prepare an aqueous solution of copper sulfate; and crystallizing the aqueous solution of copper sulfate by cooling it at a cooling rate of 0.06°C / min or higher while stirring, provided that the number of particles with a particle size of 0.5 μm or larger measured using a liquid particle counter in the aqueous solution of copper sulfate obtained by dissolving the copper sulfate in pure water is 3,000,000 or more per 1.0 g of Cu, in which case the cooling rate is 0.08°C / min or higher.

7. The method for producing copper sulfate according to claim 6, wherein the crystallization is carried out under conditions where the Reynolds number is 28,000 or higher.

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