Phosphoric acid-based waste liquid purification method

Abstract

Provided is a method that can remove dissolved divalent metal ions from a high-concentration phosphoric acid-based waste liquid.　This phosphoric acid-based waste liquid purification method for removing dissolved divalent metal ions from a high-concentration phosphoric acid-based waste liquid comprises a metal removal step in which the phosphoric acid-based waste liquid is passed through a column filled with a strongly acidic cation exchange resin, in an upflow manner, to remove the metal ions, wherein the space velocity SV of the liquid passage during the metal removal step is 0.01 / h to 0.8 / h.

Description

Method for Purifying Phosphoric Acid-based Waste Liquid

[0001] The present invention relates to a method for purifying phosphoric acid-based waste liquid, which removes dissolved metal ions from phosphoric acid-based waste liquid discharged from liquid crystal manufacturing processes, semiconductor manufacturing processes and the like.

[0002] Waste acid and waste mixed acid containing various metal ions are discharged from etching processes and the like in semiconductor manufacturing. These are treated as industrial waste, and some are effectively utilized as they are. On the other hand, some are effectively utilized after undergoing treatments such as concentration adjustment and separation of unnecessary acid components from mixed acid.

[0003] However, among acids and mixed acids used in etching processes, high-concentration acids with a phosphoric acid concentration of 40 to 88% are used in phosphoric acid-based processes. No technology for removing metal ions from high-concentration acids has been industrially realized, and the acid has been provided to destinations that can use it while containing various metal ions, and has been effectively utilized.

[0004] On the other hand, depending on the type of metal ion contained in the phosphoric acid liquid, the acid may be colored in appearance or fall under the category of harmful metal, which becomes a factor inhibiting the effective utilization of phosphoric acid, a valuable resource.

[0005] As methods for removing metal ion species from such phosphoric acid-based waste liquid, the methods described in Patent Documents 1 to 3 below have been proposed.

[0006] Patent Document 1 describes a method in which the phosphoric acid concentration is diluted to 40% or less, and metals are removed by a solvent extraction method.

[0007] Patent Document 2 describes a method in which a general-purpose ion exchange resin is used to purify phosphoric acid in a concentrated state without diluting it.

[0008] Patent Document 3 describes a technology for purifying concentrated phosphoric acid liquid (new liquid) to a grade for electronic materials by using an ion exchange resin that is a specific chelate resin.

[0009] Japanese Patent No. 5275767, Japanese Unexamined Patent Publication No. Hei 7-44373, Japanese Patent No. 6132878

[0010] However, the method described in Patent Document 1 requires a considerable increase in liquid volume to dilute the concentrated phosphoric acid, and it needs to be concentrated again to 75-85% for effective use. Therefore, there is room for improvement from the standpoint of economic efficiency and carbon neutrality.

[0011] The method described in Patent Document 2 has a broad scope of application and does not describe specific methods for applying ion exchange resin. In fact, when we supplied a liquid simulating the waste acid to a column packed with ion exchange resin as described in Patent Document 2, the metal ions in the resulting treated liquid remained at a similar level to those in the supplied liquid, and we were unable to remove the metal ions.

[0012] As is clear from the examples, the technology described in Patent Document 3 is optimized for the removal of Al, Fe, and Sb at ppb levels from phosphoric acid. However, the concentration of metal ion species in waste acid and waste mixed acid discharged from semiconductor etching processes ranges from a few ppm to several thousand ppm. In fact, we created a simulated solution that mimicked waste acid and waste mixed acid and applied the technology described in Patent Document 3, but the concentration of metal ion species in the recovered solution did not change significantly before and after treatment.

[0013] This invention has been made in view of the above-mentioned problems, and aims to provide a method for purifying phosphate-based wastewater that can remove dissolved metal ions from high-concentration phosphate-based wastewater.

[0014] To solve the above problems, the present invention comprises the following means.

[0015] [1] A method for purifying phosphate-based waste liquid, comprising a metal removal step in which the phosphate-based waste liquid is passed upflow through a column packed with a strongly acidic cation exchange resin to remove the metal ions, wherein the space velocity SV of the flow in the metal removal step is 0.01 / h to 0.8 / h.

[0016] [2] The method for purifying phosphoric acid-based waste liquid according to paragraph 1, wherein the concentration of phosphoric acid in the phosphoric acid-based waste liquid is 32% by weight to 88% by weight.

[0017] [3] The method for purifying phosphate-based waste liquid according to item 1 or 2 above, wherein the concentration of the metal ions in the phosphate-based waste liquid is 1 mg / L to 2000 mg / L.

[0018] [4] A method for purifying phosphoric acid-based waste liquid according to any one of paragraphs 1 to 3 above, wherein the metal ion contains a cobalt ion.

[0019] According to the method of invention [1], since a highly concentrated phosphoric acid-based waste liquid with a specific gravity greater than that of the strongly acidic cation exchange resin is passed through in an upflow manner, the strongly acidic cation exchange resin floats in the column and is placed in the upward flow, becoming aligned from the outlet side at the top of the column. In this state, by passing the liquid through at a slow space velocity SV of 0.01 / h to less than 0.8 / h, divalent metal ions can be removed from the highly concentrated phosphoric acid-based waste liquid.

[0020] According to the method of invention [2], the state of the strongly acidic cation exchange resin can be stabilized in the column, and divalent metal ions can be removed from high-concentration phosphoric acid-based waste liquid.

[0021] According to the method of invention [3], the metal ion concentration can be efficiently reduced, and the lifespan of the ion exchange resin until regeneration is extended, thereby ensuring high productivity.

[0022] According to the method of invention [4], high purification efficiency can be obtained.

[0023] This is a schematic diagram of the ion exchange apparatus used in the embodiment. This is a graph showing the change in cobalt ion concentration of the treated solution when simulated waste liquid is passed through at an appropriate space velocity. This is a graph showing the change in cobalt ion concentration of the treated solution when simulated waste liquid is passed through at an excessive space velocity. This is a graph showing the change in cobalt ion concentration of the treated solution when simulated waste liquid is passed through at an appropriate space velocity. This is a graph comparing the amount of Co ions adsorbed with respect to the space velocity SV. This is a graph comparing the leakage start point and breakthrough point with respect to the space velocity SV.

[0024] This invention describes one embodiment of a method for purifying phosphate-based wastewater by removing dissolved metal ions from high-concentration phosphate-based wastewater.

[0025] The purification method of this embodiment includes a metal removal step in which a high-concentration phosphate-based waste liquid is passed upflow through a column (packed bed) filled with a strongly acidic cation exchange resin to remove metal ions.

[0026] Upflow refers to a flow direction in which the liquid to be treated is injected through the inlet at the bottom of the column and discharged through the outlet at the top of the column.

[0027] Figure 1 is a schematic diagram of the ion exchange apparatus used in the purification method of this embodiment.

[0028] In this ion exchange apparatus, a strongly acidic cation exchange resin (ion exchange resin) is packed into the column 10. The liquid to be treated is stored in the tank 20 and injected into the column 10 by the pump 30 from the liquid inlet 11 at the bottom of the column. Metal ions are removed within the column 10 and then discharged from the liquid outlet 12 at the top of the column.

[0029] The strongly acidic cation exchange resin can be a general-purpose SO3-type cation exchange resin. The resin type can be styrene-based or acrylic-based, and the structure can be gel-type or macroporous-type. The shape is not particularly limited, but a typical example is a perfectly spherical bead shape with a diameter of about 0.3 mm to 1.2 mm. The density (density at 20°C, the same applies below) of such a strongly acidic cation-based ion exchange resin is generally 1.2 to 1.3 g / mL.

[0030] The liquid to be treated is a highly concentrated phosphoric acid-based waste liquid discharged from processes such as the etching process in semiconductor manufacturing. Highly concentrated phosphoric acid-based waste liquid is an acid waste liquid in which phosphoric acid is the main component, and it may be a waste liquid containing only phosphoric acid as the acid, or a mixed acid containing other acids such as nitric acid or acetic acid. Highly concentrated phosphoric acid-based waste liquid has a higher density than strongly acidic cationic ion exchange resins.

[0031] Because the resin beads of the strongly acidic cation exchange resin have a lower specific gravity than the high-concentration phosphate-based waste liquid, they float in the column. Furthermore, by passing the phosphate-based waste liquid upflow through the column, the resin beads align from the outlet side so that they accumulate towards the outlet side at the top of the column. Maintaining this alignment while passing the liquid through the column helps to suppress the leakage of metal ions adsorbed on the ion exchange resin from the ion exchange resin.

[0032] The phosphoric acid concentration in the phosphoric acid waste liquid is preferably 32% to 88% (by weight, the same applies hereinafter). If the phosphoric acid concentration falls below 32%, the density will be less than 1.2, causing the density of the strongly acidic cation exchange resin and the phosphoric acid to reverse, resulting in the movement of the ion exchange resin beads during liquid flow and leakage of metal ions. If the phosphoric acid concentration exceeds 88%, the viscosity becomes too high, raising concerns that contact with the strongly acidic cation exchange resin will not occur efficiently.

[0033] When the phosphoric acid concentration is between 32% and 45%, the density becomes similar to that of the strongly acidic cation exchange resin. As a result, the strongly acidic cation exchange resin will float in the phosphoric acid solution within the column depending on the liquid flow during startup and shutdown. Consequently, there is a concern that the alignment of the strongly acidic cation exchange resin beads in the packed bed may be disrupted, potentially accelerating the onset of adsorbed metal ions. However, during continuous supply, the liquid flow will push the beads towards the packed bed outlet, allowing for purification as intended by this technology.

[0034] When the phosphoric acid concentration is 45% or higher, the density of phosphoric acid always exceeds that of the strongly acidic cation exchange resin. Therefore, regardless of whether the system is in operation, starting, or stopped, the packed bed of the strongly acidic cation exchange resin can be kept stable with minimal disruption.

[0035] At phosphoric acid concentrations of 80% to 88%, the melting point of phosphoric acid is between 0°C and approximately 30°C, raising concerns that phosphoric acid may freeze in the column of a strongly acidic cation exchange resin outside of the summer months.

[0036] When the phosphoric acid concentration is 80% or less, the melting point is always below 0°C, which reduces the risk of freezing even in winter and makes it easy to maintain fluidity.

[0037] Therefore, the phosphoric acid concentration is preferably 32% to 88%, more preferably 45% to 80%, and most preferably 60% to 80%.

[0038] The metal ions dissolved and removed in the phosphoric acid-based waste liquid are preferably divalent metal ions. The main types of removed metal ions include cobalt ions (Co), nickel ions (Ni), and copper ions, and cobalt ions are particularly preferred.

[0039] In the phosphoric acid purification method according to this embodiment, divalent metal ions, particularly cobalt ions, can be efficiently removed.

[0040] It is generally said that metal ions with higher valences are more easily adsorbed by ion exchange resins. However, in the purification method of the present embodiment targeting high-concentration phosphoric acid-based waste liquid, trivalent metal ions such as iron and aluminum, and metal ions that form large complexes such as molybdenum, tend to be difficult to remove.

[0041] The reasons for this are considered to be as follows.

[0042] Coagulants for wastewater treatment such as polyiron sulfate and aluminum sulfate have been commercialized for trivalent iron and aluminum. It is considered that these metal ions are polymerized (form crosslinks) in solution, and if they take the same form in phosphoric acid, they are bulkier than divalent metal ions existing as individual ions, and diffusion to ion exchange sites is rate-limiting, so they are considered to be very difficult to adsorb.

[0043] In addition, since iron and aluminum ions have extremely high affinity with trivalent phosphate ions, even if they are adsorbed on the ion exchange resin, they are immediately desorbed and regenerated by the large amount of phosphate ions present in the surrounding environment, which is also considered to be the reason why they are difficult to remove.

[0044] Molybdenum also has extremely high affinity with phosphate ions. Even if molybdenum ions, which are the core of the complex, are temporarily adsorbed on the ion exchange resin, it is considered that they are immediately desorbed and regenerated by the surrounding phosphoric acid and return to the original phosphomolybdenum complex. Furthermore, it is also considered that the phosphomolybdenum complex is bulky, leading to diffusion limitation and making it difficult to approach the ion exchange sites.

[0045] Preferably, the concentration of metal ions dissolved in the phosphoric acid-based waste liquid is 1 mg / L to 2000 mg / L.

[0046] According to the method of the present embodiment, when reducing the concentration of divalent metal ions in a high-concentration phosphoric acid solution to a predetermined concentration (for example, 1 / 10 or less of the concentration contained in the solution before treatment), if the metal ion concentration of the solution before treatment is 1 mg / L or higher, the metal ion concentration can be reduced more efficiently than when the concentration is lower than this value. If the metal ion concentration is 2000 mg / L or lower, a longer service life before the ion exchange resin needs regeneration and high productivity can be ensured compared with the case where the concentration is higher than this value.

[0047] In the metal removal step, it is preferable that the space velocity SV of the phosphoric acid-based waste liquid passed through is 0.01 / h to 0.8 / h.

[0048] The space velocity SV is a value obtained by dividing the feed rate of the liquid to be treated by the volume of the packed bed of strongly acidic cation exchange resin.

[0049] In the metal removal step, it is preferable that the linear velocity of the phosphoric acid-based waste liquid passed through is 0.002 m / h to 0.19 m / h.

[0050] The linear velocity is a value obtained by dividing the feed rate of the liquid to be treated by the cross-sectional area of the packed bed of strongly acidic cation exchange resin.

[0051] Figure 2 is a graph showing changes in cobalt ion concentration in a treated liquid when a simulated waste liquid containing cobalt ions is treated by passing it through at an appropriate space velocity (SV 0.1 / h).

[0052] The horizontal axis represents the liquid flow rate, which is indicated by the BV value representing how many times the cumulative volume of the supplied simulated waste liquid is relative to the packed volume of the ion exchange resin.

[0053] As shown in this figure, in the purification method according to the present embodiment, when operated at an appropriate space velocity SV, a state with no cobalt ion leakage continues for a certain period from the initial stage of operation, and phosphoric acid with a sufficiently low cobalt ion content can be obtained.

[0054] Figure 3 is a graph showing the change in cobalt ion concentration in the treated solution when a simulated waste liquid containing cobalt ions is treated by passing it through at an excessively high space velocity (SV 1.0 / h).

[0055] As shown in this figure, when operated at an excessively high space velocity (SV), cobalt ion leakage occurs from the beginning of operation, and the wastewater cannot be properly purified.

[0056] In high concentrations of phosphoric acid, the ion exchange rate of metal ions in strongly acidic cation exchange resins is slow.

[0057] Therefore, if the space velocity SV of the liquid flow exceeds 0.8 / h, metal ion leakage occurs from the very beginning of the liquid flow, making it difficult to remove metal ions sufficiently and purify the phosphoric acid to a level where it can be reused.

[0058] Figure 4 is a graph showing the change in the cobalt ion concentration of the treated solution when a simulated waste liquid with a Co ion (cobalt ion) concentration of 1399 mg / L (ppm) is treated by passing it through at an appropriate space velocity (SV 0.1 / h).

[0059] In the purification of phosphate using ion exchange resin, the point at which the metal ions to be treated begin to leak from the column outlet is called the leak start point. In this example, the leak begins at 3.2 BV.

[0060] In the purification of phosphoric acid using ion exchange resin, the breakthrough point is defined as the point at which the metal ion concentration at the column outlet reaches 10% of the metal ion concentration of the treatment solution (before purification). In this example, at 4.8 BV, the cobalt concentration at the column outlet reaches 140 mh / L, which is 10% of the metal ion concentration of the treatment solution (1399 mg / h), thus reaching the breakthrough point.

[0061] The breakthrough point adsorption equilibrium value is a numerical value expressed as the amount of Co ions adsorbed per liter of strong cation exchange resin at the breakthrough point (mg / L) / the Co ion concentration in the feed solution (mg / L). A larger value indicates that the conditions are more favorable for adsorption onto the ion exchange resin.

[0062] The amount of Co ions adsorbed per liter of strong cation exchange resin at the breakthrough point (mg / L) is shown by the area enclosed by the dashed line in the graph to the left of the breakthrough point in Figure 4.

[0063] The total amount of Co ions supplied, P, is given by P (mg) = [BV value of the breakthrough point] × [Filling volume of strongly acidic cation exchange resin (L)] × [Co ion concentration in the supply solution (mg / L)].

[0064] The total amount of Co ions leaked, Q, is approximated by the following formula: Q (mg) = ([BV value at breakthrough point] - [BV value at the start of Co ion leakage]) × [Filling volume of strongly acidic cation exchange resin (L)] × [Co ion concentration in the feed solution (mg / L)] × (1 / 10) × (1 / 2).

[0065] The amount of Co ions adsorbed at the breakthrough point is P - Q (mg), and the value obtained by dividing this by the packed bed volume (L) of the ion exchange resin used is the amount of Co ions adsorbed (mg / L).

[0066] The leak initiation point and breakthrough point become later (the BV value increases) as the space velocity SV decreases.

[0067] Furthermore, the amount of metal ions adsorbed by the ion exchange resin before reaching these leakage initiation points or breakthrough points increases exponentially as the space velocity SV decreases.

[0068] The greater the amount of metal ions adsorbed by the ion exchange resin, the more efficient it is in that it extends the lifespan of the ion exchange resin before it needs to be regenerated.

[0069] From this viewpoint, a smaller space velocity SV is preferable, specifically 0.5 / h or less, and more preferably 0.1 / h or less.

[0070] On the other hand, if the space velocity SV of the liquid flow is small, it requires a long processing time and an extremely large processing device (ion exchange resin column) relative to the volume of liquid being processed, which leads to production efficiency problems.

[0071] From this perspective, it is practical for the spatial velocity SV to have a certain magnitude, and specifically, it is preferable that it be 0.01 / h or greater.

[0072] In this embodiment, the purification method involves a metal removal step followed by a regeneration step in which the metal ion species adsorbed on the ion exchange resin are desorbed from the ion exchange resin, similar to a general method for regenerating ion exchange resins.

[0073] This regeneration process, unlike the metal removal process, is carried out by passing acid through the column in a downward flow from the top to the bottom.

[0074] The acid used in the desorption operation during the regeneration process is generally not limited to any acid that can regenerate strongly acidic cation exchange resins.

[0075] Specifically, it is a strong acidic aqueous solution of about 1-2 N, and any of nitric acid, sulfuric acid, or hydrochloric acid can be used as the acid component.

[0076] The space velocity SV through which the acid flows during the regeneration process can be a general space velocity SV, rather than the slow space velocity SV used in the metal removal process.

[0077] Next, specific embodiments of this invention will be described, but the present invention is not particularly limited to those embodiments.

[0078] First, as preliminary examples and comparative examples, batch-type adsorption tests were conducted to investigate the metal ion removal performance of various adsorbents in the treated liquid.

[0079] <Preliminary Example 1> As a simulated waste liquid to mimic phosphoric acid-based waste liquid, a solution was prepared consisting of 75% phosphoric acid (by weight, the same applies hereafter), 2% nitric acid, 10% acetic acid, and 419 mg / L (ppm) of Co ions (cobalt ions) as the dissolving metal ions.

[0080] As an adsorbent, we used C100, a gel-type styrene-based strong acid cation exchange resin manufactured by Purolite Co., Ltd.

[0081] To 10 g of simulated waste liquid, 1 g of adsorbent was added, and after 3 hours of agitation contact using a shaker at room temperature, the recovered liquid was collected by filtration, and the cobalt concentration after contact treatment was measured using an atomic absorption spectrophotometer.

[0082] <Preliminary Example 2> The same conditions as in Preliminary Example 1 were used, except that the amount of Co ions dissolved in the simulated waste liquid was 739 mg / L (ppm), and macroporous styrene-based C160, a strongly acidic cation exchange resin manufactured by Purolite Co., Ltd., was used as the adsorbent.

[0083] <Preliminary Example 3> The same conditions as in Preliminary Example 1 were used, except that the amount of Co ions dissolved in the simulated waste liquid was 650 mg / L (ppm), and the adsorbent used was C150, a macroporous styrene-based strong acid cation exchange resin manufactured by Purolite Co., Ltd.

[0084] <Preliminary Comparative Example 1> The procedure was carried out under the same conditions as in Preliminary Example 1, except that C104F, a porous acrylic weak acid cation exchange resin manufactured by Purolite Co., Ltd., was used as the adsorbent.

[0085] <Preliminary Comparative Example 2> The procedure was carried out under the same conditions as in Preliminary Example 1, except that macroporous styrene-based chelate resin S985 manufactured by Purolite Co., Ltd. was used as the adsorbent. This chelate resin was selected from those used in the wet refining process in cobalt recovery.

[0086] <Preliminary Comparative Examples 3-5> These were carried out under the same conditions as in Preliminary Example 1, except that Shirasagi WP-H, Shirasagi ANOX-1, and Shirasagi ANOX-2 activated carbons manufactured by Osaka Gas Chemical Co., Ltd. were used as adsorbents. These activated carbons were selected for their suitability in removing metal components used in wet refining.

[0087] The results, along with the test conditions for the above preliminary examples and comparative examples, are shown in Table 1.

[0088]

[0089] It can be seen that only the strongly acidic cation exchange resins used in Examples 1 to 3 have the ability to remove Co ions from simulated wastewater.

[0090] The negative yield is presumed to be due to the elution of Co ions from the activated carbon itself.

[0091] Next, as examples and comparative examples, continuous adsorption tests were conducted using strongly acidic cation exchange resins.

[0092] <Example 4> As a simulated waste liquid to mimic phosphate-based waste liquid, a solution was prepared consisting of 70% phosphoric acid (by weight, the same applies hereafter), a trace amount of nitric acid, and 63 mg / L (ppm) of Co ions (cobalt ions) as the dissolved metal ions.

[0093] As an adsorbent, we used C150, a macroporous styrene-based strong acid cation exchange resin manufactured by Purolite Co., Ltd.

[0094] A glass column with a packed volume of 75 mL, an inner diameter of 20 mm, and a packed bed height of 239 mm was used as the column.

[0095] The sample (simulated waste liquid) set in a hot water bath was supplied from the bottom of a column packed with strongly acidic ion exchange resin using an Iwaki EHN series electromagnetic metering pump (maximum discharge rate 38 mL / min), and the treated liquid was collected from the top of the column (upflow).

[0096] The supply rate was set to 37.5 mL / h, and the space velocity SV was set to 0.5 / h.

[0097] The treated solution was collected in fractions, and quantitative analysis of various metal ions was performed on each fraction using an ICP-OES analyzer to determine the leak initiation point and breakthrough point, and the amount of Co ion adsorbed was calculated.

[0098] The room temperature was 20°C.

[0099] <Example 5> The same conditions as in Example 4 were used, except that the supply rate was set to 7.5 mL / h and the space velocity to 0.1 / h.

[0100] <Example 6> The same conditions as in Examples 4 and 5 were used, except that the supply rate was set to 7.5 mL / h and the column packing volume to 150 mL, resulting in a space velocity of 0.02 mL.

[0101] <Example 7> The same conditions as in Example 5, with a space velocity of 0.1 / h, were used, except that the concentration of Co ions (cobalt ions) in the simulated waste liquid was set to 444 mg / L.

[0102] <Example 8> This example was carried out under the same conditions as Examples 5 and 7, with a space velocity of 0.1 / h, except that the Co ion (cobalt ion) concentration of the simulated waste liquid was set to 2140 mg / L.

[0103] <Comparative Example 6> The procedure was carried out under the same conditions as in Examples 4, 5, and 6, except that the supply rate was set to 75 mL / h and the space velocity to 1.0 / h.

[0104] <Comparative Example 7> The Co ion (cobalt ion) concentration of the simulated waste liquid was set to 650 mg / L, the column packing volume to 100 mL, the supply rate to 10 mL / h, and the space velocity to 0.1 / h. The simulation was performed by flowing the simulated waste liquid in a downflow manner.

[0105] <Comparative Example 8> The simulated waste liquid was prepared with a Co ion (cobalt ion) concentration of 650 mg / L, a column packing volume of 100 mL, a supply rate of 200 mL / h, and a space velocity of 2 / h. The simulated waste liquid was then flowed in a downflow manner, similar to Comparative Example 8.

[0106] The results, along with the test conditions for the above examples and comparative examples, are shown in Table 2.

[0107]

[0108] Examples 4, 5, and 6 and Comparative Example 6 have the same conditions except for the spatial velocity SV, allowing us to confirm the effect of differences in spatial velocity SV.

[0109] Figure 5 is a graph comparing the amount of Co ions adsorbed with respect to the space velocity SV.

[0110] Figure 6 is a graph comparing the leakage initiation point and breakthrough point with respect to the spatial velocity SV.

[0111] Comparing these data, it can be seen that as the space velocity SV decreases, the onset of Co ion leakage is delayed, and the BV value of the breakthrough point also increases, indicating that the amount of Co ions adsorbed when supplied up to the breakthrough point increases exponentially.

[0112] In Comparative Example 6, where the space velocity SV is 1.0 / h, Co ion leakage begins before a liquid volume equivalent to the filling volume of the ion exchange resin is supplied (leakage initiation point BV 0.5). The breakthrough point BV value is above 1.0, so it is at the borderline where it can be said that Co ion removal is barely achieved. In contrast, in Example 4, where the space velocity SV is 0.5 / h, the leak initiation point BV is 1.7, which is above 1, and the breakthrough point BV is 2.9. Based on these findings, it is estimated that 0.8 / h, between 1.0 / h and 0.5 / h, is a feasible upper limit for the space velocity SV.

[0113] When the space velocity SV is between 1.0 / h and 0.5 / h, the range of change in the amount of Co ions adsorbed per liter of ion exchange resin is small, whereas in the region where the space velocity SV is 0.5 / h or less, the range of change increases linearly. Therefore, a smaller space velocity SV is more efficient in that it extends the lifespan of the ion exchange resin until regeneration. From this viewpoint, a space velocity SV of 0.5 / h or less is preferred, and more preferably 0.1 / h or less.

[0114] In comparative examples 7 and 8, where the liquid was passed through in a downflow manner, Co ion leakage occurred immediately after the start of operation. This is thought to be because, due to the downflow, a downward force acts on the cation exchange resin due to the flow, and at the same time, the density of the cation exchange resin (density at 20°C 1.25 g / ml) is considerably lower than that of the supply liquid (density at 20°C 1.53 g / mL), causing it to float due to buoyancy. As a result, the beads become unstable, and a stable contact state like that shown in Examples 4 to 8 could not be achieved.

[0115] In Example 8, where the Co ion concentration was 2140 mg / L, the Co ion leakage initiation point was small at 3.2 BV, suggesting that the exchange sites of the ion exchange resin were approaching saturation. If the point were any smaller, the adsorption / desorption cycle of the ion exchange resin would accelerate too much, leading to loss of phosphate due to removal during the switching between the adsorption and regeneration processes, and the generation of desorption / regeneration waste liquid due to an increased number of regeneration cycles per phosphate treated, which is undesirable in practical operation. For this reason, the upper limit of the suitable concentration of metal ions is considered to be 2000 mg / L or less (2000 ppm or less).

[0116] <Example 10> This example was carried out under the same conditions as Example 5, with a space velocity SV of 0.1 / h, except that the metal ions dissolved in the simulated waste liquid were replaced with Cu ions (copper ions) at a concentration of 112 mg / L instead of Co ions (cobalt ions).

[0117] <Example 11> This example was carried out under the same conditions as Example 5, with a space velocity SV of 0.1 / h, except that the metal ions dissolved in the simulated waste liquid were replaced with Ni ions (nickel ions) at a concentration of 72 mg / L instead of Co ions (cobalt ions).

[0118] <Comparative Example 9> The procedure was carried out under the same conditions as in Example 5, with a space velocity SV of 0.1 / h, except that the metal ions dissolved in the simulated waste liquid were replaced with Fe ions (iron ions) at a concentration of 67 mg / L instead of Co ions (cobalt ions).

[0119] <Comparative Example 10> The procedure was carried out under the same conditions as in Example 5, with a space velocity SV of 0.1 / h, except that the metal ions dissolved in the simulated waste liquid were replaced with Al ions (aluminum ions) at a concentration of 103 mg / L instead of Co ions (cobalt ions).

[0120] <Comparative Example 11> The procedure was carried out under the same conditions as in Example 5, with a space velocity SV of 0.1 / h, except that the metal ions dissolved in the simulated waste liquid were replaced with 282 mg / L of Mo ions (molybdenum ions) instead of Co ions (cobalt ions).

[0121] The results, along with the test conditions for the above examples and comparative examples, are shown in Table 3.

[0122]

[0123] Examples 10 and 11 show that divalent copper ions and nickel ions exhibit a metal removal effect similar to that of cobalt ions.

[0124] On the other hand, compared to Example 5, in which cobalt ions were removed at the same space velocity SV 0.1 / h, the leakage initiation point and breakthrough point in Examples 10 and 11 were earlier.

[0125] As seen in Comparative Examples 9, 10, and 11, for iron, aluminum, and molybdenum ions, leakage of each metal ion begins immediately after supply, even under gradual contact conditions such as SV 0.1 / h (passing through the packed bed over 10 hours).

[0126] Iron ions are iron nitrate (the valence of iron is 3:Fe ３＋ The mixture is prepared using the reagent, and the valence of the aluminum ion is 3:Al3+, and the molybdenum ion is H3[P(Mo) in phosphoric acid]. ３ O １０ ) ４ It is thought to have a complex structure of phosphomolybdic acid.

[0127] This shows that metal ions other than divalent metal ions are difficult to remove with this technology.

[0128] Based on the above, this technology is advantageously applicable to the removal of divalent metal ions (Co, Cu, and Ni in the examples) from phosphoric acid, and is particularly suitable for the removal of cobalt ions, achieving high purification efficiency.

[0129] Furthermore, it is thought that the presence of nitric acid increases the oxidation-reduction potential of the solution, causing iron ions to take on a valence of 3. However, in a phosphate system without nitric acid, if the valence of iron ions is 2:Fe2+, it is thought that the same effect as in the cases of Co, Cu, and Ni can be obtained.

[0130] This application is accompanied by a priority claim to Japanese Patent Application No. 2025-031806, filed on February 28, 2025, and the disclosures thereof constitute a part of this application.

[0131] The terms and expressions used herein are for illustrative purposes only and not intended to be restrictive, and should be understood as not excluding any equivalents of the features shown and described herein, and allowing for various modifications within the claimed scope of this invention.

[0132] The phosphoric acid purification method of this invention can remove dissolved metal ions from high-concentration phosphoric acid-based wastewater discharged from liquid crystal manufacturing processes, semiconductor manufacturing processes, etc., and can be used for various applications.

[0133] 10 Column (resin tower) 11 Liquid inlet 12 Liquid outlet 20 Tank of liquid to be treated 30 Pump

Claims

1. A method for purifying phosphate-based waste liquid, comprising a metal removal step of passing the phosphate-based waste liquid in an upflow manner through a column packed with a strongly acidic cation exchange resin to remove the metal ions, wherein the space velocity SV of the flow in the metal removal step is 0.01 / h to 0.8 / h.

2. The method for purifying a phosphate-based waste liquid according to claim 1, wherein the concentration of phosphate in the phosphate-based waste liquid is 32% by weight to 88% by weight.

3. The method for purifying phosphate-based waste liquid according to claim 1 or 2, wherein the concentration of the metal ions in the phosphate-based waste liquid is 1 mg / L to 2000 mg / L.

4. The method for purifying phosphate-based waste liquid according to claim 1 or 2, wherein the metal ion contains a cobalt ion.

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