A method and system for recovering prussian blue wastewater

Abstract

The application provides a recovery method and a recovery system device for prussian blue wastewater. The prussian blue wastewater comprises mother liquor and washing water, and the recovery method comprises the following steps: (1) sequentially performing ion exchange resin adsorption and reverse osmosis membrane separation on the washing water to obtain concentrated water and dilute water; (2) mixing the concentrated water and the mother liquor, and then performing metal ion removal treatment to obtain wastewater after metal ion removal; and (3) sequentially performing evaporation concentration and condensation crystallization on the wastewater after metal ion removal, and separating to obtain sodium sulfate crystals and recovery liquid containing sodium citrate. By using the recovery method, iron ions and manganese ions in the prussian blue wastewater can be fully removed, and sodium citrate in the wastewater can be recovered, so that the production cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and relates to a method and system device for recovering Prussian blue wastewater. Background Technology

[0002] Compared to lithium-ion batteries, sodium-ion batteries have advantages such as abundant raw material resources and low price, and have gradually become a research hotspot in energy storage batteries. In recent years, significant progress has been made in the development of sodium-ion cathode materials such as polyanionic compounds, transition metal oxides, Prussian blue (PB) and its analogues, and fluorides. Among them, Prussian blue materials are considered to be a promising sodium-ion battery cathode material due to their low cost, unique open-frame structure, and suitable insertion / extraction potential, and have attracted widespread attention from researchers.

[0003] The production of Prussian blue materials inevitably generates a large amount of wastewater, which must be treated to meet standards before discharge. Prussian blue cathode material wastewater mainly consists of mother liquor wastewater and washing wastewater. Depending on the material composition and process, the ions contained in the wastewater may include metal ions (such as iron, manganese, and sodium ions), sulfate ions, citrate ions, and ferrocyanide ions. If the Prussian blue wastewater contains large amounts of iron and manganese ions, it will have a significant impact on the subsequent solid waste generated and recycling; therefore, removing iron and manganese ions from the Prussian blue wastewater is crucial. Meanwhile, sodium citrate, as a complexing agent in the Prussian blue synthesis process, remains essentially unchanged in total amount before and after material synthesis. Recovering sodium citrate from the wastewater can significantly reduce the production cost of Prussian blue materials.

[0004] Therefore, there is an urgent need to provide a solution that can remove iron and manganese ions from Prussian blue wastewater and recover sodium citrate from the wastewater, thereby reducing production costs. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method and system for recovering Prussian blue wastewater. The recovery method of this invention can effectively remove iron and manganese ions from Prussian blue wastewater and recover most of the sodium citrate, which can then be reused in the subsequent production of Prussian blue cathode materials, thereby reducing production costs.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for recovering Prussian blue wastewater, wherein the Prussian blue wastewater comprises mother liquor and wash water, and the recovery method includes:

[0008] (1) The wash water is sequentially adsorbed by ion exchange resin and separated by reverse osmosis membrane to obtain concentrated water and fresh water.

[0009] (2) The concentrated water and mother liquor are mixed and then subjected to metal ion removal treatment to obtain wastewater after metal ion removal.

[0010] (3) The wastewater after metal ion removal is evaporated, concentrated and condensed and crystallized in sequence, and sodium sulfate crystals and sodium citrate-containing recovery liquid are obtained after separation.

[0011] This invention removes metal ions (such as iron and manganese ions) from wash water through an ion exchange resin adsorption step, thereby reducing the burden of subsequent metal ion removal. Then, the wash water after metal ion removal is concentrated using a reverse osmosis membrane to obtain concentrated water and desalinated water. The concentrated water is mixed with the mother liquor for further treatment, and the desalinated water is discharged or recycled after meeting the standards.

[0012] The mechanism by which ion exchange resins adsorb and remove metal ions from wash water is as follows: when wash water passes through the ion exchange resin, under the action of Coulomb force, ions carrying the same charge on the resin will be replaced and attached to the ion exchange resin, thereby removing metal ions from the wash water.

[0013] This invention treats a mixture of concentrated water and mother liquor to remove metal ions (such as iron and manganese ions). Then, utilizing the different solubilities of sodium citrate and sodium sulfate at low temperatures, sodium sulfate decahydrate crystals precipitate through evaporation, concentration, and condensation crystallization, simultaneously yielding a recovery solution rich in sodium citrate. The recovery solution contains a high concentration of sodium citrate and a very low concentration of sodium sulfate. Therefore, by adding a small amount of sodium citrate to the recovery solution, a reaction substrate can be prepared for reuse in the synthesis of Prussian blue cathode materials, thereby achieving full recovery and utilization of sodium citrate and reducing production costs.

[0014] Preferably, the mass content of iron ions in the mother liquor is 500-2000 ppm, for example, it can be 500 ppm, 800 ppm, 1000 ppm, 1500 ppm, 1800 ppm or 2000 ppm, etc.; the mass content of manganese ions is 500-2000 ppm, for example, it can be 500 ppm, 800 ppm, 1000 ppm, 1500 ppm, 1800 ppm or 2000 ppm, etc., but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0015] Preferably, the concentration of sodium citrate in the mother liquor is 0.1-2 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L, etc., and the concentration of sodium sulfate is 0.1-1 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L or 1 mol / L, etc., but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0016] Preferably, the pH value of the mother liquor is 5-8, for example, it can be 5, 6, 7 or 8, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] Preferably, the iron ion content in the wash water is 100-1000 ppm, for example, it can be 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm or 1000 ppm, etc.; the manganese ion content is 100-1000 ppm, for example, it can be 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm or 1000 ppm, etc., but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0018] Preferably, the pH value of the wash water is 6-8, for example, it can be 6, 7 or 8, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, in step (1), a filtration step is performed before the ion exchange resin adsorption.

[0020] In this invention, the wash water is filtered before the ion exchange resin adsorbs the material to remove residual Prussian blue particles.

[0021] Preferably, the ion exchange resin adsorbs at a temperature of 20-60°C, such as 20°C, 30°C, 40°C, 50°C, or 60°C, and at a flow rate of 3-5 t / h, such as 3 t / h, 4 t / h, or 5 t / h, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0022] In this invention, the effect of removing metal ions is better when the temperature and flow rate of the ion exchange resin are controlled within the above-mentioned preferred range.

[0023] Preferably, the COD content in the fresh water is less than 300 ppm, for example, it can be 290 ppm, 250 ppm, 200 ppm, 100 ppm or 50 ppm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, in step (2), a filtration step is performed before the metal ion removal treatment.

[0025] In this invention, the mixture of concentrated water and mother liquor is filtered before the metal ion removal treatment to remove residual Prussian blue material particles.

[0026] Preferably, the metal ion removal process in step (2) includes: adding an oxidant and an alkaline substance to the mixture obtained by mixing the concentrated water and the mother liquor, carrying out a precipitation reaction, and then performing solid-liquid separation to obtain wastewater after metal ion removal.

[0027] In this invention, during the metal ion removal process, oxidants and alkaline substances are introduced to cause metal ions (such as iron ions and manganese ions) to precipitate in the form of hydroxides and oxides, thereby achieving the effect of removing metal ions.

[0028] Preferably, the oxidant comprises a hydrogen peroxide solution.

[0029] Preferably, the mass concentration of the hydrogen peroxide solution is 20-30%, for example, it can be 20%, 22%, 25%, 28% or 30%, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 30%.

[0030] Preferably, the mass ratio of the oxidant to the mother liquor is ≥0.005, for example, it can be 0.005, 0.0052, 0.0055, 0.006, 0.008, 0.01, 0.05 or 0.1, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] Preferably, the alkaline substance includes sodium hydroxide.

[0032] Preferably, the mass ratio of the alkaline substance to the mother liquor is ≥0.05, for example, it can be 0.05, 0.06, 0.08, 0.1, 0.15, 0.2, 0.5 or 0.8, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] In this invention, the removal effect of metal ions is better when the amounts of oxidant and alkaline substance meet the above conditions.

[0034] Preferably, the solid-liquid separation method includes sedimentation.

[0035] Preferably, after the solid-liquid separation, the pH of the resulting liquid is adjusted.

[0036] Preferably, the pH of the liquid obtained after solid-liquid separation is adjusted using an acidic substance.

[0037] Preferably, the acidic substance includes sulfuric acid.

[0038] Preferably, the pH value of the wastewater after metal ion removal is 6-7, for example, it can be 6, 6.2, 6.5, 6.8 or 7, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Preferably, the evaporation and concentration temperature in step (3) is 60-100℃, for example, it can be 60℃, 70℃, 75℃, 80℃, 82℃, 85℃, 90℃, 95℃ or 100℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] Preferably, the evaporation and concentration factor is 2-4 times, for example, it can be 2 times, 2.5 times, 3 times, 3.5 times or 4 times, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] Preferably, the COD mass content of the evaporation condensate produced by the evaporation concentration is less than 300 ppm, for example, it can be 290 ppm, 250 ppm, 200 ppm, 100 ppm or 50 ppm, etc., but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0042] In this invention, the evaporation and concentration step produces concentrated liquid and evaporation condensate. The evaporation condensate is discharged or recycled if it meets the standards, and the concentrated liquid enters the next step for condensation and crystallization.

[0043] Preferably, the condensation and crystallization step includes: cooling the concentrated liquid produced by the evaporation and concentration to T1 to precipitate sodium sulfate crystals.

[0044] Preferably, the range of T1 is 2-16℃, for example, it can be 2℃, 3℃, 4℃, 5℃, 6℃, 7℃, 8℃, 9℃, 10℃, 11℃, 12℃, 13℃, 14℃, 15℃ or 16℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable. Preferably, it is 3-10℃, and more preferably 5-8℃.

[0045] In this invention, when T1 is within the above-mentioned preferred range, sodium sulfate crystals can be fully separated, resulting in a low sodium sulfate content and a high sodium citrate content in the recovered liquid after separation, which is beneficial for the reuse of the recovered liquid.

[0046] Preferably, in the sodium citrate-containing recovery solution, the mass content of iron ions is less than 50 ppm, for example, it can be 48 ppm, 45 ppm, 40 ppm, 30 ppm, 20 ppm or 10 ppm, etc.; the mass content of manganese ions is less than 50 ppm, for example, it can be 48 ppm, 45 ppm, 40 ppm, 30 ppm, 20 ppm or 10 ppm, etc., but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0047] In this invention, by combining the two steps of ion exchange resin adsorption and metal ion removal treatment, iron and manganese ions in the washing water and mother liquor can be effectively removed, thereby greatly reducing the mass content of iron and manganese ions.

[0048] Secondly, the present invention provides a recycling system for Prussian blue wastewater, wherein the recycling method described in the first aspect is performed using the recycling system. The recycling system includes a wash water treatment unit and a mother liquor treatment unit. The wash water treatment unit includes an ion exchange resin adsorption device and a reverse osmosis membrane separation device connected sequentially along the wash water flow direction, and the reverse osmosis membrane separation device has a concentrate outlet and a desalination outlet. The mother liquor treatment unit includes a mother liquor collection device, a metal ion removal device, an evaporation and concentration device, and a condensation and crystallization device connected sequentially along the mother liquor flow direction. The concentrate outlet of the reverse osmosis membrane separation device is connected to the mother liquor collection device.

[0049] Preferably, the washing water treatment unit further includes a first filtration device, wherein the first filtration device, the ion exchange resin adsorption device, and the reverse osmosis membrane separation device are connected in sequence along the washing water flow direction.

[0050] Preferably, the mother liquor treatment unit further includes a second filtration device, which is disposed between the mother liquor collection device and the metal ion removal device.

[0051] Preferably, the metal ion removal device includes a chemical precipitation tank and a sedimentation tank arranged in series along the flow direction of the mother liquor; the inlet of the chemical precipitation tank is connected to the outlet of the second filtration device.

[0052] Preferably, the metal ion removal device further includes a pH adjustment tank, the inlet of which is connected to the outlet of the sedimentation tank, and the outlet of which is connected to the inlet of the evaporation and concentration device.

[0053] In this invention, a precipitation reaction is carried out in a chemical precipitation tank, and the wastewater after the reaction enters a sedimentation tank for natural sedimentation. The supernatant obtained after sedimentation is overflowed into a pH adjustment tank for pH adjustment.

[0054] Preferably, the metal ion removal device further includes a sludge treatment tank for collecting sludge from the chemical precipitation tank and the settling tank.

[0055] In this invention, the sludge in the chemical precipitation tank and settling tank is collected in the sludge treatment tank and then treated by centrifugation and pressure filtration.

[0056] Preferably, both the first filtration device and the second filtration device include a media filter.

[0057] Preferably, the evaporation and concentration apparatus includes an MVR evaporator.

[0058] The system refers to an equipment system, device system, or production device.

[0059] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0060] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0061] This invention removes metal ions (such as iron and manganese ions) from wash water through an ion exchange resin adsorption step, thereby reducing the burden of subsequent metal ion removal. Then, the wash water after metal ion removal is concentrated using a reverse osmosis membrane to obtain concentrated water and desalinated water. The concentrated water is mixed with the mother liquor for further treatment, and the desalinated water is discharged or recycled after meeting the standards.

[0062] This invention treats a mixture of concentrated water and mother liquor to remove metal ions, effectively removing metal ions (such as iron and manganese ions). Then, utilizing the different solubilities of sodium citrate and sodium sulfate at low temperatures, sodium sulfate decahydrate crystals precipitate through evaporation, concentration, and condensation crystallization, simultaneously yielding a recovery solution rich in sodium citrate. The recovery solution contains a high concentration of sodium citrate and a very low concentration of sodium sulfate. Therefore, by adding a small amount of sodium citrate to the recovery solution, a reaction substrate can be prepared for reuse in the synthesis of Prussian blue cathode materials, thereby achieving full recovery and utilization of sodium citrate and reducing production costs. Attached Figure Description

[0063] Figure 1 A schematic flowchart of the Prussian blue wastewater recovery method provided for embodiments of the present invention. Detailed Implementation

[0064] It should be understood that in the description of this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature.

[0065] It should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0066] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0067] In one embodiment, the present invention provides a recycling system for Prussian blue wastewater, the recycling system comprising a wash water treatment unit and a mother liquor treatment unit.

[0068] The washing water treatment unit includes a first media filter, an ion exchange resin adsorption device, and a reverse osmosis membrane separation device connected in sequence along the washing water flow direction. The reverse osmosis membrane separation device has a concentrated water outlet and a fresh water outlet, and the fresh water outlet is connected to a recycled water tank.

[0069] The mother liquor treatment unit includes a mother liquor collection device, a second media filter, a metal ion removal device, an MVR evaporator, and a condensation crystallization device connected sequentially along the mother liquor flow direction; the concentrate outlet of the reverse osmosis membrane separation device is connected to the mother liquor collection device; a pump is installed on the connecting pipeline between the mother liquor collection device and the second media filter; the metal ion removal device includes a chemical precipitation tank, a sedimentation tank, and a pH adjustment tank connected in series along the mother liquor flow direction, the inlet of the chemical precipitation tank is connected to the outlet of the second filter device, and the outlet of the pH adjustment tank is connected to the inlet of the MVR evaporator; the metal ion removal device also includes a sludge treatment tank for collecting sludge from the chemical precipitation tank and the sedimentation tank; the evaporation condensate outlet of the MVR evaporator is connected to the recycled water tank, and the concentrate outlet of the MVR evaporator is connected to the condensation crystallization device.

[0070] In one embodiment, the present invention provides a method for recovering Prussian blue wastewater, wherein the recovery method is carried out in the recovery system device provided in the above embodiment, and the specific process is as follows: Figure 1 As shown, it includes the following steps:

[0071] (1) Prussian blue wastewater includes mother liquor and wash water; firstly, the wash water is filtered by the first medium filter, and then the filtered wash water is filtered by the ion exchange resin adsorption device to remove iron ions and manganese ions; then the wash water after removing iron ions and manganese ions is filtered by the reverse osmosis membrane separation device to obtain concentrated water and fresh water, and the fresh water enters the recycled water tank.

[0072] (2) The obtained concentrated water is passed into the mother liquor collection device and mixed with the mother liquor, and then passed into the second medium filter for filtration. The step of removing metal ions after filtration is as follows: the filtered wastewater is passed into the chemical precipitation tank, and an oxidant and alkaline substance are added to it to carry out a precipitation reaction, so that iron ions and manganese ions are converted into precipitates. The wastewater after the reaction enters the sedimentation tank for natural sedimentation, and the supernatant overflows into the pH adjustment tank. Dilute sulfuric acid is added to adjust the pH value of the wastewater to obtain the wastewater after metal ion removal.

[0073] (3) The wastewater after metal ion removal is passed into the MVR evaporator for evaporation and concentration to obtain concentrated liquid and evaporation condensate. The evaporation condensate enters the recycled water tank. Then the concentrated liquid is passed into the condensation crystallization device to cool down and condense crystals to precipitate sodium sulfate crystals. Then the liquid is separated to obtain sodium sulfate crystals and recovery liquid. The recovery liquid is rich in sodium citrate.

[0074] Example 1

[0075] This embodiment provides a method for recovering Prussian blue wastewater. The recovery method is carried out in the recovery system device provided in the above embodiment. The Prussian blue wastewater includes mother liquor and wash water. The mother liquor has a pH value of 7.10, and the mass content of iron ions is 798.09 ppm, the mass content of manganese ions is 709.59 ppm, the concentration of sodium citrate is 0.84 mol / L, and the concentration of sodium sulfate is 0.35 mol / L. The amount of mother liquor to be treated is 45 t. The wash water has a pH value of 6.58, and the mass content of iron ions is 145.34 ppm, the mass content of manganese ions is 137.89 ppm. The amount of wash water to be treated is 100 t.

[0076] The method for recovering Prussian blue wastewater specifically includes the following steps:

[0077] (1) The wash water is filtered through the first medium filter, and then the filtered wash water is passed through the ion exchange resin adsorption device to remove iron and manganese ions. The ion exchange resin is styrene resin spherical particles with a particle size D50 of 1.2 mm. The adsorption temperature is 30℃ and the flow rate is 5 t / h. After removing iron and manganese ions, the wash water is passed through the reverse osmosis membrane separation device to separate concentrated water and fresh water. The concentrated water enters the next step, and the COD mass content of the fresh water is less than 300 ppm and enters the recycled water tank.

[0078] (2) The concentrated water is fed into the mother liquor collection device and mixed with the mother liquor. Then, it is pumped into the second medium filter for filtration. The step of removing metal ions after filtration is as follows: The filtered wastewater is fed into the chemical precipitation tank, and 250 kg of hydrogen peroxide solution with a mass concentration of 30% and 2.5 t of sodium hydroxide are added to it to carry out the precipitation reaction so that iron ions and manganese ions are converted into precipitates. The wastewater after the reaction enters the sedimentation tank for natural sedimentation. The supernatant overflows into the pH adjustment tank, and the pH value of the wastewater is adjusted to 6.5 by adding dilute sulfuric acid to obtain the wastewater after metal ion removal.

[0079] (3) The wastewater after metal ion removal is fed into the MVR evaporator and concentrated at 85°C with a concentration factor of 3 times to obtain concentrated liquid and evaporation condensate. The COD mass content of the evaporation condensate is less than 300ppm and enters the recycled water pool. Then the concentrated liquid is fed into the condensation crystallization device to cool down to 8°C for condensation crystallization, so that sodium sulfate crystals precipitate out. Then the liquid is separated to obtain sodium sulfate crystals and recovery liquid containing sodium citrate.

[0080] Example 2

[0081] This embodiment provides a method for recovering Prussian blue wastewater. The recovery method is carried out in the recovery system device provided in the above embodiment. The Prussian blue wastewater includes mother liquor and wash water. The mother liquor has a pH value of 7.21, and the mass content of iron ions is 638.30 ppm, the mass content of manganese ions is 582.23 ppm, the concentration of sodium citrate is 0.79 mol / L, and the concentration of sodium sulfate is 0.32 mol / L. The amount of mother liquor to be treated is 45 t. The wash water has a pH value of 6.74, and the mass content of iron ions is 121.94 ppm, the mass content of manganese ions is 125.95 ppm. The amount of wash water to be treated is 100 t.

[0082] The method for recovering Prussian blue wastewater specifically includes the following steps:

[0083] (1) The wash water is filtered through the first medium filter, and then the filtered wash water is passed through the ion exchange resin adsorption device to remove iron and manganese ions. The ion exchange resin is styrene resin spherical particles with a particle size D50 of 1.2 mm. The adsorption temperature is 30℃ and the flow rate is 5 t / h. After removing iron and manganese ions, the wash water is passed through the reverse osmosis membrane separation device to separate concentrated water and fresh water. The concentrated water enters the next step, and the COD mass content of the fresh water is less than 300 ppm and enters the recycled water tank.

[0084] (2) The concentrated water is fed into the mother liquor collection device and mixed with the mother liquor. Then, it is pumped into the second medium filter for filtration. The step of removing metal ions after filtration is as follows: The filtered wastewater is fed into the chemical precipitation tank, and 250 kg of hydrogen peroxide solution with a mass concentration of 30% and 2.5 t of sodium hydroxide are added to it to carry out the precipitation reaction so that iron ions and manganese ions are converted into precipitates. The wastewater after the reaction enters the sedimentation tank for natural sedimentation. The supernatant overflows into the pH adjustment tank. The pH value of the wastewater is adjusted to 6 by adding dilute sulfuric acid to obtain the wastewater after metal ion removal.

[0085] (3) The wastewater after metal ion removal is fed into an MVR evaporator and concentrated at 60°C with a concentration factor of 2 times to obtain concentrated liquid and evaporation condensate. The COD mass content of the evaporation condensate is less than 300 ppm and enters the recycled water pool. Then the concentrated liquid is fed into a condensation crystallization device to cool down to 5°C for condensation crystallization, so that sodium sulfate crystals precipitate out. Then the crystals are separated to obtain sodium sulfate crystals and a recovery liquid containing sodium citrate.

[0086] Example 3

[0087] This embodiment provides a method for recovering Prussian blue wastewater. The recovery method is carried out in the recovery system device provided in the above embodiment. The Prussian blue wastewater includes mother liquor and wash water. The mother liquor has a pH value of 7.09, and the mass content of iron ions is 693.75 ppm, the mass content of manganese ions is 632.37 ppm, the concentration of sodium citrate is 0.85 mol / L, and the concentration of sodium sulfate is 0.37 mol / L. The amount of mother liquor to be treated is 45 t. The wash water has a pH value of 6.89, and the mass content of iron ions is 127.54 ppm, the mass content of manganese ions is 135.18 ppm. The amount of wash water to be treated is 100 t.

[0088] The method for recovering Prussian blue wastewater specifically includes the following steps:

[0089] (1) The wash water is filtered through the first medium filter, and then the filtered wash water is passed through the ion exchange resin adsorption device to remove iron and manganese ions. The ion exchange resin is styrene resin spherical particles with a particle size D50 of 1.2 mm. The adsorption temperature is 30℃ and the flow rate is 5 t / h. After removing iron and manganese ions, the wash water is passed through the reverse osmosis membrane separation device to separate concentrated water and fresh water. The concentrated water enters the next step, and the COD mass content of the fresh water is less than 300 ppm and enters the recycled water tank.

[0090] (2) The concentrated water is fed into the mother liquor collection device and mixed with the mother liquor. Then it is pumped into the second medium filter for filtration. The step of removing metal ions after filtration is as follows: The filtered wastewater is fed into the chemical precipitation tank, and 250 kg of hydrogen peroxide solution with a mass concentration of 30% and 2.5 t of sodium hydroxide are added to it to carry out the precipitation reaction so that iron ions and manganese ions are converted into precipitates. The wastewater after the reaction enters the sedimentation tank for natural sedimentation. The supernatant overflows into the pH adjustment tank. The pH value of the wastewater is adjusted to 7 by adding dilute sulfuric acid to obtain the wastewater after metal ion removal.

[0091] (3) The wastewater after metal ion removal is fed into an MVR evaporator and concentrated at 100°C with a concentration factor of 2.5 times to obtain concentrated liquid and evaporation condensate. The COD mass content of the evaporation condensate is less than 300 ppm and enters the recycled water pool. Then the concentrated liquid is fed into a condensation crystallization device to cool down to 3°C for condensation crystallization, so that sodium sulfate crystals precipitate out. Then the crystals are separated to obtain sodium sulfate crystals and a recovery liquid containing sodium citrate.

[0092] Example 4

[0093] The difference between this embodiment and embodiment 1 is that the amount of hydrogen peroxide solution added in step (2) is 300 kg and the amount of sodium hydroxide is 2 t.

[0094] The remaining parameters are the same as in Example 1.

[0095] Example 5

[0096] The difference between this embodiment and embodiment 1 is that the amount of hydrogen peroxide solution added in step (2) is 100 kg and the amount of sodium hydroxide is 3 t.

[0097] The remaining parameters are the same as in Example 1.

[0098] Example 6

[0099] The difference between this embodiment and Embodiment 1 is that the flow rate of ion exchange adsorption is 8t / h.

[0100] The remaining parameters are the same as in Example 1.

[0101] Example 7

[0102] The difference between this embodiment and embodiment 1 is that in step (3), the temperature is lowered to 16°C for condensation and crystallization.

[0103] The remaining parameters are the same as in Example 1.

[0104] Example 8

[0105] The difference between this embodiment and Embodiment 1 is that the concentration factor in step (3) is 4 times.

[0106] The remaining parameters are the same as in Example 1.

[0107] Example 9

[0108] The difference between this embodiment and embodiment 1 is that the amount of hydrogen peroxide solution added in step (2) is 150 kg.

[0109] The remaining parameters are the same as in Example 1.

[0110] Example 10

[0111] The difference between this embodiment and embodiment 1 is that the amount of sodium hydroxide added in step (2) is 2t.

[0112] The remaining parameters are the same as in Example 1.

[0113] Comparative Example 1

[0114] The difference between this comparative example and Example 1 is that the step of ion exchange resin adsorption is omitted in step (1), that is, the filtered wash water is directly separated by reverse osmosis membrane.

[0115] The remaining parameters are the same as in Example 1.

[0116] test

[0117] The mass content of iron and manganese ions in the recovery solutions provided in the above examples and comparative examples was detected by inductively coupled plasma atomic emission spectrometry (ICP).

[0118] The mass contents of sodium sulfate and sodium citrate in the mother liquor and recovered liquor provided in the above examples and comparative examples were detected by IC ion chromatography, and the units were expressed as ppm. Sodium sulfate recovery rate = (mass content of sodium sulfate in recovered liquor / mass content of sodium sulfate in mother liquor) * 100%; Sodium citrate recovery rate = (mass content of sodium citrate in recovered liquor / mass content of sodium citrate in mother liquor) * 100%; The sodium sulfate recovery rate and sodium citrate recovery rate were calculated using the above two formulas.

[0119] The test results are shown in Table 1.

[0120] Table 1

[0121]

[0122]

[0123] analyze:

[0124] As demonstrated in Examples 1-3, the recovery method of this invention, through the synergistic effect of ion exchange resin adsorption and metal ion removal steps, can effectively remove iron and manganese ions from the wash water and mother liquor, avoiding the influence of metal ions on the recovered products. The recovery method of this invention can produce sodium sulfate crystal byproducts and a recovery solution rich in sodium citrate. By adding a small amount of sodium citrate to this recovery solution, a reaction base solution can be prepared and reused in the synthesis of Prussian blue cathode materials, achieving the recycling and reuse of sodium citrate and reducing production costs. Furthermore, the effluent from the recovery process of this invention meets all standards and can be recycled.

[0125] As can be seen from Examples 1, 4-5, and 9-10, Examples 4 and 5, by appropriately adjusting the amounts of hydrogen peroxide solution and sodium hydroxide, can also achieve good iron and manganese removal effects, although slightly lower than in Example 1. However, in Examples 9 and 10, the amounts of hydrogen peroxide solution or sodium hydroxide added were relatively small, resulting in higher iron and manganese ion content in the recovered liquid and poorer iron and manganese removal effects.

[0126] As can be seen from Examples 1 and 6, if the flow rate of ion exchange adsorption is too high, it will lead to a higher content of iron and manganese ions in the recovered liquid.

[0127] As shown in Examples 1 and 7, a higher condensation and crystallization temperature results in higher recovery rates of both sodium sulfate and sodium citrate. If the sodium sulfate content in the recovered solution is high, it will significantly exceed the sodium sulfate content requirement of the base solution.

[0128] As can be seen from Examples 1 and 8, if the concentration factor is too high, the recovery rate of sodium citrate will be low, and a large amount of sodium citrate needs to be added in the later process of synthesizing Prussian blue, resulting in high cost.

[0129] As can be seen from Example 1 and Comparative Example 1, if the step of adsorption by ion exchange resin is omitted, the content of iron and manganese ions in the recovered liquid is relatively high.

[0130] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for recovering Prussian blue wastewater, wherein the Prussian blue wastewater comprises mother liquor and wash water, characterized in that, The recycling method includes: (1) The wash water is sequentially subjected to ion exchange resin adsorption and reverse osmosis membrane separation to obtain concentrated water and fresh water; (2) Mix the concentrated water and the mother liquor, and then perform metal ion removal treatment to obtain wastewater after metal ion removal; (3) The wastewater after metal ion removal is evaporated, concentrated and condensed and crystallized in sequence, and sodium sulfate crystals and sodium citrate-containing recovery liquid are obtained after separation.

2. The recycling method according to claim 1, characterized in that, The mother liquor contains 500-2000 ppm of iron ions and 500-2000 ppm of manganese ions. Preferably, the concentration of sodium citrate in the mother liquor is 0.1-2 mol / L, and the concentration of sodium sulfate is 0.1-1 mol / L. Preferably, the pH value of the mother liquor is 5-8; Preferably, the wash water contains 100-1000 ppm of iron ions and 100-1000 ppm of manganese ions. Preferably, the pH value of the wash water is 6-8.

3. The recycling method according to claim 1 or 2, characterized in that, In step (1), a filtration step is performed before the ion exchange resin adsorption; Preferably, the ion exchange resin adsorbs at a temperature of 20-60℃ and a flow rate of 3-5 t / h; Preferably, the COD content in the fresh water is less than 300 ppm.

4. The recycling method according to any one of claims 1-3, characterized in that, In step (2), a filtration step is performed before the metal ion removal treatment.

5. The recycling method according to any one of claims 1-4, characterized in that, Step (2) of the metal ion removal treatment includes: An oxidant and an alkaline substance are added to the mixture obtained by mixing the concentrated water and the mother liquor to carry out a precipitation reaction, followed by solid-liquid separation to obtain wastewater after metal ions are removed. Preferably, the oxidant comprises a hydrogen peroxide solution; Preferably, the mass ratio of the oxidant to the mother liquor is ≥0.005; Preferably, the alkaline substance includes sodium hydroxide; Preferably, the mass ratio of the alkaline substance to the mother liquor is ≥0.05; Preferably, after the solid-liquid separation, the pH of the resulting liquid is adjusted. Preferably, the pH value of the wastewater after metal ion removal is 6-7.

6. The recycling method according to any one of claims 1-5, characterized in that, The evaporation and concentration temperature in step (3) is 60-100℃; Preferably, the evaporation and concentration factor is 2-4 times; Preferably, the COD content in the evaporation condensate produced by the evaporation concentration is less than 300 ppm.

7. The recycling method according to any one of claims 1-6, characterized in that, The condensation and crystallization step includes: cooling the concentrated liquid produced by the evaporation and concentration to T1 to precipitate sodium sulfate crystals; Preferably, the range of T1 is 2-16℃, more preferably 3-10℃, and even more preferably 5-8℃; Preferably, in the sodium citrate-containing recovery solution, the mass content of iron ions is less than 50 ppm and the mass content of manganese ions is less than 50 ppm.

8. A system for recovering Prussian blue wastewater, characterized in that, The recycling method according to any one of claims 1-7 is carried out using the recycling system apparatus; The recycling system includes a wash water treatment unit and a mother liquor treatment unit; The washing water treatment unit includes an ion exchange resin adsorption device and a reverse osmosis membrane separation device connected in sequence along the washing water flow direction. The reverse osmosis membrane separation device has a concentrated water outlet and a desalination water outlet. The mother liquor treatment unit includes a mother liquor collection device, a metal ion removal device, an evaporation and concentration device, and a condensation and crystallization device connected in sequence along the mother liquor flow direction; the concentrated water outlet of the reverse osmosis membrane separation device is connected to the mother liquor collection device.

9. The Prussian blue wastewater recovery system apparatus according to claim 8, characterized in that, The washing water treatment unit also includes a first filtration device, and the first filtration device, the ion exchange resin adsorption device, and the reverse osmosis membrane separation device are connected in sequence along the washing water flow direction.

10. The Prussian blue wastewater recovery system apparatus according to claim 8 or 9, characterized in that, The mother liquor treatment unit further includes a second filtration device, which is disposed between the mother liquor collection device and the metal ion removal device; Preferably, the metal ion removal device includes a chemical precipitation tank and a sedimentation tank arranged in series along the flow direction of the mother liquor; the inlet of the chemical precipitation tank is connected to the outlet of the second filtration device. Preferably, the metal ion removal device further includes a pH adjustment tank, the inlet of which is connected to the outlet of the sedimentation tank, and the outlet of which is connected to the inlet of the evaporation and concentration device. Preferably, the metal ion removal device further includes a sludge treatment tank for collecting sludge from the chemical precipitation tank and the settling tank.

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