Method for recovering and preparing ultra-pure water from heavy metal wastewater containing nickel

Abstract

The application provides a method for recovering and preparing ultrapure water from nickel-containing heavy metal wastewater, which comprises the following steps: (1) adjusting the pH of the nickel-containing heavy metal wastewater, and then performing flocculation and precipitation treatment to obtain intermediate wastewater; (2) adjusting the pH of the intermediate wastewater, and then performing fluorine removal and precipitation treatment; performing multi-medium filtration and ultrafiltration treatment on supernatant obtained by the precipitation treatment, and then performing first reverse osmosis treatment to obtain reverse osmosis water and lithium-containing concentrated water; (3) sequentially performing activated carbon filtration treatment and second reverse osmosis treatment on the reverse osmosis water to obtain desalination pure water, and then performing EDI treatment on the desalination pure water to obtain ultrapure water. The method solves the technical problems of high operation cost and low production efficiency in the prior art, and realizes the recycling of nickel, cobalt, manganese, lithium and water resources.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling technology and relates to a method for recovering nickel-containing heavy metal wastewater to produce ultrapure water. Background Technology

[0002] Wastewater generated during the production of cathode materials contains heavy metals such as nickel, cobalt, manganese, and lithium. Current technologies mainly remove nickel, cobalt, and manganese through heavy metal flocculation and precipitation, and recover lithium metal through membrane concentration. However, the wastewater generated during the concentration process is not utilized, and production efficiency is not maximized.

[0003] CN116768343A discloses a resource recovery device for nickel-containing heavy metal wastewater, in which a sedimentation mechanism is embedded inside the main body of the device. When external wastewater enters the main body of the device, the heavy metals are collected after sedimentation through the upper sedimentation seat. However, the device requires shutdown during the heavy metal collection process, making continuous production impossible.

[0004] CN116835825A discloses a resource-based treatment method for heavy metal wastewater. This method utilizes the unique physicochemical properties of biochar to capture heavy metal ions under hydrothermal conditions of 150–200℃, promoting precipitation and adsorbing sedimentation during the reaction. Although it achieves high precipitation and removal rates for heavy metal ions, the need for hydrothermal heating presents certain limitations, resulting in high operating costs.

[0005] CN105461139A describes a wastewater reuse rate of over 90% achieved through the reaction of water with a heavy metal chelating agent, followed by flocculation sedimentation, sand filtration, carbon filtration, ultrafiltration, and reverse osmosis. However, the method described does not specify the intended use of the treated water, thus failing to realize the value of wastewater recycling.

[0006] The above-mentioned solutions have high operating costs, low production efficiency, and cannot maximize resource recycling. Summary of the Invention

[0007] The purpose of this invention is to provide a method for recovering nickel-containing heavy metal wastewater to produce ultrapure water. The method of this invention solves the technical problems of high operating costs and low production efficiency in the prior art, and realizes the recovery and utilization of nickel, cobalt, manganese heavy metals, lithium metal and water resources.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for recovering nickel-containing heavy metal wastewater to produce ultrapure water, the method comprising the following steps:

[0010] (1) After adjusting the nickel-containing heavy metal wastewater to the first pH, flocculation and sedimentation treatment is carried out to obtain intermediate wastewater;

[0011] (2) After adjusting the intermediate wastewater to the second pH, it is subjected to defluorination and precipitation treatment. The supernatant obtained by the precipitation treatment is subjected to multi-media filtration and ultrafiltration treatment, and then subjected to the first reverse osmosis treatment to obtain reverse osmosis permeate and lithium-containing concentrate.

[0012] (3) The reverse osmosis permeate is subjected to activated carbon filtration and a second reverse osmosis treatment in sequence to obtain desalinated pure water; the desalinated pure water is subjected to EDI treatment to obtain ultrapure water.

[0013] The first and second reverse osmosis treatments of the present invention only restrict the order of operation and do not involve the number of operations, and both the first and second reverse osmosis treatments are injected through a high-pressure pump.

[0014] The method described in this invention enables the recovery and production of ultrapure water from nickel-containing heavy metal wastewater, solving the technical problems of high operating costs and low production efficiency in the prior art, and maximizing resource recycling.

[0015] Preferably, the first pH in step (1) is 11 to 13, for example: 11, 11.5, 12, 12.5 or 13, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0016] Preferably, the adjuster used to adjust to the first pH in step (1) includes a sodium hydroxide solution.

[0017] Preferably, the flocculation and sedimentation treatment in step (1) includes mixing and reacting nickel-containing heavy metal wastewater with flocculant, filtering by pressure to obtain filter cake and intermediate wastewater, and drying the filter cake at high temperature to obtain mixed metal hydroxide.

[0018] Preferably, the flocculant includes polyacrylamide (PAM).

[0019] Preferably, the mass ratio of the flocculant to the nickel-containing heavy metal wastewater is 5-15 mg:1 kg, for example: 5 mg:1 kg, 8 mg:1 kg, 10 mg:1 kg, 12 mg:1 kg or 15 mg:1 kg, etc.

[0020] Preferably, the temperature of the high-temperature drying treatment is 100-180°C, for example: 100°C, 120°C, 150°C, 160°C or 180°C.

[0021] This invention uses sodium hydroxide solution to adjust the pH of the wastewater, causing nickel, cobalt, and manganese oxides in the water to react and form hydroxide precipitates. A flocculant is added to chelate heavy metal ions and form insoluble salts, causing the nickel, cobalt, manganese, and other heavy metals generated in the water to precipitate as hydroxide colloids. The precipitates are then pumped into a filter press for filtration to achieve solid-liquid separation. The filter press is used to press the sludge cake, which is then dried at high temperature to generate metal hydroxides for recycling, achieving a high recovery rate of heavy metals such as nickel, cobalt, and manganese.

[0022] Preferably, in step (2), the second pH is 6 to 9, for example: 6, 6.5, 7, 8 or 9, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0023] Preferably, the defluorinating agent used in step (2) includes any one or a combination of at least two of ferric sulfate, polyferric sulfate, polyaluminum sulfate, formic acid, or calcium chloride.

[0024] Preferably, a bactericide is added to the supernatant before the multi-media filtration in step (2).

[0025] Preferably, the bactericide includes sodium hypochlorite.

[0026] Preferably, the dosage of the bactericide is 2 to 10 ppm, for example: 2 ppm, 4 ppm, 5 ppm, 8 ppm or 10 ppm, etc.

[0027] The addition of a bactericide in this invention can prevent the growth of bacteria in the wastewater system.

[0028] Preferably, step (2) the first reverse osmosis treatment includes a first-stage reverse osmosis treatment and a second-stage reverse osmosis treatment performed sequentially.

[0029] Preferably, the first-stage reverse osmosis treatment yields first-stage permeate and first-stage concentrate, the first-stage concentrate undergoes second-stage reverse osmosis treatment to yield lithium-containing concentrate and second-stage permeate, and the first-stage permeate and second-stage permeate are mixed to obtain reverse osmosis permeate.

[0030] The reverse osmosis membrane used in the first reverse osmosis treatment of this invention has numerous pores, the size of which is comparable to that of water molecules. Since bacteria, viruses, most organic pollutants, and hydrated ions are much larger than water molecules, they cannot pass through the reverse osmosis semi-permeable membrane and are thus separated from the water phase that does pass through. The desalination rate through the reverse osmosis element reaches 98%, and the water production rate is between 70% and 80%. The high-pressure reverse osmosis permeate is used to prepare ultrapure water, and the high-pressure reverse osmosis concentrate is pumped to the lithium hydroxide production workshop.

[0031] Preferably, scale inhibitors and reducing agents are added to the solution obtained by multi-media filtration and ultrafiltration before the first-stage reverse osmosis treatment.

[0032] Preferably, the scale inhibitor comprises polyacrylic acid.

[0033] Preferably, the amount of scale inhibitor added is 2 to 10 ppm, for example: 2 ppm, 4 ppm, 5 ppm, 8 ppm or 10 ppm, etc.

[0034] Preferably, the reducing agent comprises a sodium bisulfite solution with a mass percentage concentration of 8% to 12% (e.g., 8%, 9%, 10%, 11% or 12%).

[0035] Preferably, the dosage of the reducing agent is 0.1–0.5 L / m³. 3 For example: 0.1L / m 3 0.2L / m 3 0.3L / m 3 0.4L / m 3 Or 0.5L / m 3 wait.

[0036] Preferably, the first-stage reverse osmosis treatment yields first-stage permeate and first-stage concentrate.

[0037] Preferably, the lithium-containing concentrated water in step (2) is used to prepare lithium hydroxide.

[0038] Preferably, the preparation of lithium hydroxide includes:

[0039] After adjusting the pH of the lithium-containing concentrate to 4-6 (e.g., 4, 4.5, 5, 5.5 or 6, etc., not limited to the listed values, other unlisted values ​​within this range are also applicable), defluorinate, add bactericide, and after the bacterial count drops to <0.5 CFU / mL, add scale inhibitor and reducing agent. After filtration, reverse osmosis and concentration, add calcium hydroxide and centrifuge to obtain a lithium hydroxide mixed solution.

[0040] Sodium hydroxide is added to the lithium hydroxide mixture for caustic conversion, followed by freeze crystallization to obtain sodium sulfate decahydrate crystals and lithium hydroxide solution. The lithium hydroxide solution is then concentrated and evaporated to obtain lithium hydroxide.

[0041] Preferably, the pH adjuster of the lithium-containing concentrated water includes sulfuric acid.

[0042] The equation for the above reaction is as follows:

[0043] 2LiOH + H₂SO₄ = Li₂SO₄ + 2H₂O;

[0044] Li2SO4+Ca(OH)2=2LiOH+CaSO4↓;

[0045] Li2SO4+2NaOH=2LiOH+Na2SO4.

[0046] Preferably, the defluorinating agent used for defluorination includes any one or a combination of at least two of ferric sulfate, polyferric sulfate, polyaluminum sulfate, formic acid, or calcium chloride.

[0047] Preferably, the bactericide includes sodium hypochlorite.

[0048] Preferably, the dosage of the bactericide is 2 to 10 ppm, for example: 2 ppm, 4 ppm, 5 ppm, 8 ppm or 10 ppm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] Preferably, the scale inhibitor comprises polyacrylic acid.

[0050] Preferably, the amount of scale inhibitor added is 2 to 10 ppm, for example: 2 ppm, 4 ppm, 5 ppm, 8 ppm or 10 ppm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0051] Preferably, the reducing agent comprises a sodium bisulfite solution with a mass percentage concentration of 8% to 12% (e.g., 8%, 9%, 10%, 11% or 12%, etc., not limited to the listed values, other unlisted values ​​within this range are also applicable).

[0052] Preferably, the dosage of the reducing agent is 5 to 10 ppm, for example: 5 ppm, 6 ppm, 7 ppm, 8 ppm or 10 ppm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0053] Preferably, the temperature of the freeze crystallization treatment is -10 to -15°C, for example: -10°C, -11°C, -12°C, -13°C or -15°C, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0054] The caustic conversion solution is subjected to continuous freeze crystallization at -10 to -15°C to precipitate sodium sulfate decahydrate crystals. These crystals are then separated by centrifugation to obtain a lithium hydroxide solution. The lithium hydroxide solution is then evaporated to a certain concentration using a multi-effect evaporator or MVR evaporator, followed by cooling and crystallization to precipitate single-crystal lithium hydroxide crystals. After further centrifugation, the resulting lithium hydroxide monohydrate is dried in a dedicated drying system, and the dried product is then packaged.

[0055] Preferably, the median particle size D50 of the activated carbon used in the activated carbon filtration process in step (3) is 0.8 to 1.8 mm, for example: 0.8 mm, 1 mm, 1.2 mm, 1.5 mm or 1.8 mm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0056] Activated carbon adsorption can remove residual chlorine, chloroform, volatile phenols, and other organic matter, as well as odors and unpleasant smells, from raw water. It also adsorbs some toxic and harmful metal elements and ultimately reduces the turbidity and color of the raw water. The presence of oxidizing substances such as residual chlorine can oxidize ion exchange resins and ion exchange membranes, causing RO membrane breakdown. After treatment, the water quality meets the inlet water quality requirements of ultrapure water reverse osmosis devices: Fe < 0.05 mg / L, Ni < 0.05 mg / L, and turbidity ≤ 1.0 NUT. This invention uses 0.8-1.8 mm activated carbon as the filter media, which has high adsorption efficiency, can treat large volumes of water, greatly reduces the replacement frequency, saves operating costs, and can be repeatedly cleaned and reused.

[0057] Preferably, step (3) the second reverse osmosis treatment includes a three-stage reverse osmosis treatment and a four-stage reverse osmosis treatment.

[0058] After carbon adsorption, the water enters the extremely fine pores on the surface of the semipermeable membrane. A layer of water molecules is selectively adsorbed on the surface of the membrane, while salt solutes are repelled by the membrane. Ions with higher valence states are repelled further away. Under the pressure of reverse osmosis, water molecules around the membrane pores flow out as pure water through the capillary action of the membrane, thus achieving the purpose of desalination.

[0059] Preferably, the EDI treatment in step (3) includes injecting desalinated pure water into the EDI device, applying voltage to the positive and negative electrodes of the EDI device, performing electro-deionization treatment, and obtaining ultrapure water.

[0060] The EDI process is an electro-deionization process.

[0061] After being desalinated by reverse osmosis, the purified water enters the EDI (Electronic Diode Ionization) unit. Inside the unit, a certain DC voltage is applied between two electrodes. Charged ions in the water are pushed towards the electrodes: cations move towards the positive electrode, and anions move towards the negative electrode. In the cation and anion exchange membranes, the cation exchange membrane allows cations to pass through, while the anion exchange membrane allows anions to pass through. Ion exchange resin is filled between the two membranes to achieve selective ion permeation. When ions pass through the ion exchange membrane, they exchange sites with other ions on the resin and move to the concentrate chamber, thus achieving ion removal.

[0062] As a preferred embodiment of the present invention, the method includes the following steps:

[0063] (1) After adjusting the pH of the nickel-containing heavy metal wastewater to 11-13, flocculant is added for flocculation and sedimentation treatment. After pressure filtration, filter cake and intermediate wastewater are obtained. The filter cake is dried at high temperature to obtain mixed metal hydroxide.

[0064] (2) After adjusting the pH of the intermediate wastewater to 6-9, a defluorinating agent is added for defluorination precipitation treatment. A bactericide is added to the supernatant obtained from the precipitation treatment, followed by multi-media filtration and ultrafiltration treatment. A scale inhibitor and a reducing agent are added to the solution obtained from the ultrafiltration treatment. The solution is then subjected to a first-stage reverse osmosis treatment to obtain a first-stage permeate and a first-stage concentrate. The first-stage concentrate is subjected to a second-stage reverse osmosis treatment to obtain a lithium-containing concentrate and a second-stage permeate. The first-stage permeate and the second-stage permeate are mixed to obtain reverse osmosis permeate. The lithium-containing concentrate is used to prepare lithium hydroxide.

[0065] (3) The reverse osmosis permeate is filtered by activated carbon with a median particle size D50 of 0.8 to 1.8 mm, and then subjected to three-stage and four-stage reverse osmosis treatment to obtain desalinated pure water. The desalinated pure water is then subjected to EDI treatment to obtain ultrapure water.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] This invention adjusts the pH to cause nickel, cobalt, and manganese oxides in water to react and form hydroxide precipitates. A flocculant is added to chelate heavy metal ions, forming insoluble salts. This causes the nickel, cobalt, manganese, and other heavy metals in the water to precipitate as hydroxide colloids. These precipitates are then pumped into a filter press for solid-liquid separation. The filter press removes the sludge cake, which is then dried at high temperature to generate metal hydroxides for recycling. This allows for the recovery of heavy metals such as nickel, cobalt, and manganese, as well as lithium and water resources. Reverse osmosis achieves a lithium recovery rate of 95% and a wastewater treatment recovery rate of 90%. A reverse osmosis desalination and EDI system achieves a pure water production rate of 70%. Attached Figure Description

[0068] Figure 1 This is a flowchart of the method for recovering nickel-containing heavy metal wastewater to produce ultrapure water according to an embodiment of the present invention. Detailed Implementation

[0069] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0070] The reverse osmosis membrane elements used in the embodiments and comparative examples of this invention are: the RO membrane for the first stage of reverse osmosis treatment is Dow SW30-4040, the RO membrane for the second stage of reverse osmosis treatment is Dow XUS180804, the RO membrane for the third stage of reverse osmosis treatment is TimeWalton ULP22-8040, and the RO membrane for the fourth stage of reverse osmosis treatment is TimeWalton ULP22-8040.

[0071] Example 1

[0072] This embodiment provides a method for recovering nickel-containing heavy metal wastewater to produce ultrapure water. A schematic flowchart of the method is shown below. Figure 1 As shown, the method includes the following steps:

[0073] (1) After adjusting the pH of the nickel-containing heavy metal wastewater (raw water) to 12, add 10 ppm of flocculant polyacrylamide (i.e., add 10 mg of flocculant per 1 kg of wastewater) for flocculation and sedimentation treatment, and then filter cake and intermediate wastewater are obtained by pressure filtration. The filter cake is dried at 140°C in an oven to obtain mixed metal hydroxide.

[0074] (2) After adjusting the pH of the intermediate wastewater to 6, calcium chloride is added as a defluorinating agent for precipitation. The supernatant obtained from the precipitation is then treated with 6 ppm sodium hypochlorite as a bactericide, followed by multi-media filtration and ultrafiltration. The solution obtained from the ultrafiltration is then treated with 6 ppm polyacrylic acid as a scale inhibitor and 0.2 L / m³ of [unspecified substance]. 3 A reducing agent (10% sodium bisulfite solution by mass) is added at 0.2 L per cubic meter of solution. This solution undergoes a first-stage reverse osmosis treatment to obtain first-stage permeate and first-stage concentrate. The first-stage concentrate is then subjected to a second-stage reverse osmosis treatment to obtain lithium-containing concentrate and second-stage permeate. The first-stage and second-stage permeate are mixed to obtain reverse osmosis permeate. Specifically, the lithium-containing concentrate is used to prepare lithium hydroxide by: adjusting the pH of the lithium-containing concentrate to 6 with sulfuric acid, adding calcium chloride as a fluoride precipitant to remove fluoride, adding a bactericide to reduce the bacterial count to <0.5 CFU / mL, and then adding 6 ppm of polyacrylic acid as a scale inhibitor and 0.2 L / m³ of... 3 A reducing agent (sodium bisulfite solution with a mass percentage concentration of 10%) is filtered, reverse osmosised, and concentrated, and then calcium hydroxide is added for centrifugation to obtain a lithium hydroxide mixed solution. Sodium hydroxide is added to the lithium hydroxide mixed solution for caustic conversion. The solution is then subjected to freeze crystallization at -12°C to obtain sodium sulfate decahydrate crystals and a lithium hydroxide solution. The lithium hydroxide solution is then concentrated and evaporated to obtain lithium hydroxide.

[0075] (3) After the reverse osmosis permeate is treated by activated carbon filtration with activated carbon of median particle size D50 of 1.5 mm, it is subjected to three-stage reverse osmosis treatment and four-stage reverse osmosis treatment to obtain desalinated pure water. The desalinated pure water is then subjected to EDI treatment to obtain ultrapure water.

[0076] The concentrations of various ions in the material, as well as the solution pH, suspended solids (SS), and conductivity obtained from each step of the method are shown in Table 1.

[0077] Table 1

[0078]

[0079]

[0080] In this embodiment, the lithium recovery rate is 95%, the wastewater treatment recovery rate is 90%, the reverse osmosis desalination rate is ≥95%, and the pure water production rate is 70% through the EDI system. The resulting ultrapure water has a conductivity of 0.08 μs / cm and does not contain metal ions.

[0081] The wastewater treatment recovery rate described in this invention is equal to the amount of usable water recovered divided by the total amount of wastewater.

[0082] The pure water production rate described in this invention is equal to the hourly water production rate of EDI divided by the feed water volume of the fourth-stage reverse osmosis system.

[0083] Example 2

[0084] This embodiment provides a method for recovering nickel-containing heavy metal wastewater to produce ultrapure water. A schematic flowchart of the method is shown below. Figure 1 As shown, the method includes the following steps:

[0085] (1) After adjusting the pH of the nickel-containing heavy metal wastewater to 11, 5 ppm of polyacrylamide was added for flocculation and sedimentation treatment. After pressure filtration, filter cake and intermediate wastewater were obtained. The filter cake was dried at 100°C in a hot air oven to obtain mixed metal hydroxide.

[0086] (2) After adjusting the pH of the intermediate wastewater to 6.3, calcium chloride, a defluorinating agent, is added for defluorination and precipitation treatment. 2 ppm of sodium hypochlorite, a bactericide, is added to the supernatant obtained from the precipitation treatment, followed by multi-media filtration and ultrafiltration. 2 ppm of polyacrylic acid, a scale inhibitor, and 0.1 L / m³ of [unspecified substance] are added to the solution obtained from the ultrafiltration treatment. 3 A reducing agent (10% sodium bisulfite solution by mass) is added at 0.1 L per cubic meter of solution. This solution undergoes a first-stage reverse osmosis treatment to obtain first-stage permeate and first-stage concentrate. The first-stage concentrate is then subjected to a second-stage reverse osmosis treatment to obtain lithium-containing concentrate and second-stage permeate. The first-stage and second-stage permeate are mixed to obtain reverse osmosis permeate. Specifically, the lithium-containing concentrate is used to prepare lithium hydroxide by: adjusting the pH of the lithium-containing concentrate to 4 with sulfuric acid; adding calcium chloride as a fluoride precipitant to remove fluoride; adding a bactericide; reducing the bacterial count to <0.5 CFU / mL; and then adding 2 ppm of polyacrylic acid as a scale inhibitor and 0.5 L / m³ of [unspecified substance]. 3 A reducing agent (sodium bisulfite solution with a mass percentage concentration of 10%) is filtered, reverse osmosised, and concentrated, and then calcium hydroxide is added for centrifugation to obtain a lithium hydroxide mixed solution. Sodium hydroxide is added to the lithium hydroxide mixed solution for caustic conversion. The solution is then subjected to freeze crystallization at -10°C to obtain sodium sulfate decahydrate crystals and a lithium hydroxide solution. The lithium hydroxide solution is then concentrated and evaporated to obtain lithium hydroxide.

[0087] (3) After the reverse osmosis permeate is treated by activated carbon filtration with activated carbon of median particle size D50 of 0.8 mm, low saline water is obtained. The low saline water is then treated by three-stage and four-stage reverse osmosis to obtain desalinated pure water. The desalinated pure water is then treated by EDI to obtain ultrapure water.

[0088] The concentrations of various ions in the material, as well as the solution pH, suspended solids (SS), and conductivity obtained from each step of the method are shown in Table 2.

[0089] Table 2

[0090]

[0091] In this embodiment, the lithium recovery rate is 95%, the wastewater treatment recovery rate is 88%, the pure water production rate is 67% after reverse osmosis desalination rate ≥95% and EDI system, and the ultrapure water obtained has a conductivity of 0.08 μs / cm and does not contain metal ions.

[0092] Compared with Example 1, the content of metal ions and suspended solids (SS) in this embodiment slightly increased during the treatment process, resulting in a decrease in wastewater treatment recovery rate and pure water production rate of EDI system.

[0093] Example 3

[0094] This embodiment provides a method for recovering nickel-containing heavy metal wastewater to produce ultrapure water. A schematic flowchart of the method is shown below. Figure 1 As shown, the method includes the following steps:

[0095] (1) After adjusting the pH of the nickel-containing heavy metal wastewater to 13, add 10 ppm of flocculant polyacrylamide for flocculation and sedimentation treatment, and then filter cake and intermediate wastewater are obtained by pressure filtration. The filter cake is dried at 180°C in an oven to obtain mixed metal hydroxide.

[0096] (2) After adjusting the pH of the intermediate wastewater to 6.3, calcium chloride, a defluorinating agent, is added for precipitation treatment. 10 ppm sodium hypochlorite, a bactericide, is added to the supernatant obtained from the precipitation treatment, followed by multi-media filtration and ultrafiltration. 8 ppm polyacrylic acid, a scale inhibitor, and 0.5 L / m³ of [unspecified substance] are added to the solution obtained from the ultrafiltration treatment. 3A reducing agent (10% sodium bisulfite solution by mass) is added at 0.5 L per cubic meter of solution. This solution undergoes a first-stage reverse osmosis treatment to obtain first-stage permeate and first-stage concentrate. The first-stage concentrate is then subjected to a second-stage reverse osmosis treatment to obtain lithium-containing concentrate and second-stage permeate. The first-stage and second-stage permeate are mixed to obtain reverse osmosis permeate. Specifically, the lithium-containing concentrate is used to prepare lithium hydroxide by: adjusting the pH of the lithium-containing concentrate to 5 with sulfuric acid, adding a defluorinating agent to precipitate and remove fluoride, adding a bactericide until the bacterial count is reduced to <0.5 CFU / mL, and then adding 5 ppm of scale inhibitor and polyacrylic acid, along with 0.4 L / m³ of [unspecified substance]. 3 A reducing agent (sodium bisulfite solution with a mass percentage concentration of 10%) is filtered, reverse osmosised, and concentrated, and then calcium hydroxide is added for centrifugation to obtain a lithium hydroxide mixed solution. Sodium hydroxide is added to the lithium hydroxide mixed solution for caustic conversion. The solution is then subjected to freeze crystallization at -15°C to obtain sodium sulfate decahydrate crystals and a lithium hydroxide solution. The lithium hydroxide solution is then concentrated and evaporated to obtain lithium hydroxide.

[0097] (3) The reverse osmosis permeate is filtered by activated carbon with a median particle size D50 of 1.8 mm, and then subjected to three-stage and four-stage reverse osmosis treatment to obtain desalinated pure water. The desalinated pure water is then subjected to EDI treatment to obtain ultrapure water.

[0098] The concentrations of various ions in the material, as well as the solution pH, suspended solids (SS), and conductivity obtained from each step of the method are shown in Table 3.

[0099] Table 3

[0100]

[0101] In this embodiment, the lithium recovery rate is 95%, the wastewater treatment recovery rate is 85%, the pure water production rate is 61% after reverse osmosis desalination rate ≥95% and EDI system, and the resulting ultrapure water has a conductivity of 0.08 μs / cm and does not contain metal ions.

[0102] Compared to Example 1, this embodiment showed a slight increase in the content of metal ions and suspended solids (SS) during the treatment process, and the conductivity of the permeate from the third and fourth stage reverse osmosis was higher. This resulted in a decrease in both the wastewater treatment recovery rate and the pure water production rate of the EDI system.

[0103] Comparative Example 1

[0104] The only difference between this comparative example and Example 1 is that activated carbon filtration is not performed; all other conditions and parameters are exactly the same as in Example 1.

[0105] In Example 1, the lithium recovery rate was 95%, the wastewater treatment recovery rate was 90%, the pure water production rate was 70% after reverse osmosis desalination rate ≥95% and EDI system, and the resulting ultrapure water had a conductivity of 0.08 μs / cm and did not contain metal ions.

[0106] In this comparative example, the lithium recovery rate was 95%, the wastewater treatment recovery rate was 90%, and the pure water production rate after reverse osmosis desalination (≥90%) and EDI system was 63%, yielding ultrapure water with a conductivity of 0.5 μS / cm. Because this comparative example did not undergo activated carbon filtration, the presence of residual chlorine severely impacts the lifespan of the reverse osmosis membrane and water quality. Residual chlorine easily penetrates the reverse osmosis membrane, carrying chloride ions from the water into the system, causing chemical reactions and degradation on the membrane surface, thus reducing the lifespan of the reverse osmosis membrane. Furthermore, chlorine also exerts a photocatalytic effect on the reverse osmosis membrane surface, accelerating membrane degradation and leading to decreased membrane performance. This can cause RO membrane breakdown, resulting in a shortened RO membrane lifespan and a decrease in water quality and pure water production rate.

[0107] Compared with Example 1, this comparative example shows that the activated carbon filtration treatment of the present invention can effectively remove residual chlorine and other oxidizing substances from water. The removal of residual chlorine significantly improves the EDI pure water production rate, and the conductivity of ultrapure water decreases significantly, while also eliminating the presence of metal ions.

[0108] Comparative Example 2

[0109] The only difference between this comparative example and Example 1 is that the second reverse osmosis treatment is not performed; all other conditions and parameters are exactly the same as in Example 1.

[0110] In this comparative example, the lithium recovery rate was 95%, the wastewater treatment recovery rate was 90%, and the low-salt water production rate was 85% after primary and secondary reverse osmosis desalination, resulting in a low-salt water with a conductivity of 180 μS / cm. Without a second reverse osmosis treatment, ultrapure water could not be obtained in this comparative example.

[0111] As can be seen from the comparison of this comparative example and Example 1, the water after carbon adsorption of the present invention enters the extremely fine membrane pores that are distributed on the surface of the semi-permeable membrane. A layer of water molecules is selectively adsorbed on the surface of the membrane, while salt solutes are repelled by the membrane. The higher the valence state of the ions, the farther they are repelled. Under the push of reverse osmosis pressure, the water molecules around the membrane pores flow out pure water through the capillary action of the membrane, thereby achieving the purpose of desalination.

[0112] Comparative Example 3

[0113] The only difference between this comparative example and Example 1 is that the EDI treatment is replaced with reverse osmosis treatment; all other conditions and parameters are exactly the same as in Example 1.

[0114] In this comparative example, the lithium recovery rate was 95%, the wastewater treatment recovery rate was 90%, and the pure water production rate achieved by the reverse osmosis desalination system was 77%, with the conductivity of the pure water being 1 μS / cm.

[0115] As can be seen from the comparison of this comparative example and Example 1, the present invention can better remove ions from the solution through EDI treatment. The operation is simple and the ultrapure water recovery rate is slightly reduced, but the reduction is small. The conductivity of ultrapure water is significantly reduced and it does not contain metal ions.

[0116] The applicant declares that 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 ultra-pure water from heavy metal wastewater containing nickel, characterized by, The method includes the following steps: (1) After adjusting the nickel-containing heavy metal wastewater to the first pH, flocculation and sedimentation treatment is carried out to obtain intermediate wastewater; (2) After adjusting the intermediate wastewater to the second pH, defluorination and precipitation are carried out. The supernatant obtained from the precipitation is subjected to multi-media filtration and ultrafiltration, and then subjected to the first reverse osmosis treatment to obtain reverse osmosis permeate and lithium-containing concentrate. (3) The reverse osmosis permeate is subjected to activated carbon filtration and a second reverse osmosis treatment in sequence to obtain desalinated pure water. The desalinated pure water is then subjected to electro-deionization treatment to obtain ultrapure water. Step (1) The first pH is 11~13, the regulator to adjust to the first pH includes sodium hydroxide solution, the flocculation and precipitation treatment includes mixing and reacting nickel-containing heavy metal wastewater with flocculant, obtaining filter cake and intermediate wastewater after pressure filtration, the filter cake is dried at high temperature to obtain mixed metal hydroxide, and the mass ratio of flocculant to nickel-containing heavy metal wastewater is 5~15mg:1kg; The lithium-containing concentrated water in step (2) is used to prepare lithium hydroxide, and the steps for preparing lithium hydroxide include: After adjusting the pH of the lithium-containing concentrate to 4-6 and removing fluoride, a bactericide is added. Once the bacterial count is reduced to <0.5 CFU / mL, a scale inhibitor and a reducing agent are added. After filtration, reverse osmosis, and concentration, calcium hydroxide is added and centrifuged to obtain a lithium hydroxide mixed solution. Sodium hydroxide is added to the lithium hydroxide mixed solution for caustic conversion, followed by freeze crystallization to obtain sodium sulfate decahydrate crystals and lithium hydroxide solution. The lithium hydroxide solution is then concentrated and evaporated to obtain lithium hydroxide.

2. The method as described in claim 1, characterized in that, The flocculant includes polyacrylamide.

3. The method as described in claim 1, characterized in that, The high-temperature drying treatment is performed at a temperature of 100~180℃.

4. The method as described in claim 1, characterized in that, Step (2) The second pH is 6~9.

5. The method as described in claim 1, characterized in that, The defluorinating agent used in step (2) includes any one or a combination of at least two of the following: ferric sulfate, polyferric sulfate, polyaluminum sulfate, formic acid, or calcium chloride.

6. The method as described in claim 1, characterized in that, In step (2), a bactericide is added to the supernatant before multi-media filtration.

7. The method as described in claim 1, characterized in that, Step (2) The first reverse osmosis treatment includes a first-stage reverse osmosis treatment and a second-stage reverse osmosis treatment performed sequentially.

8. The method as described in claim 7, characterized in that, The first-stage reverse osmosis treatment yields first-stage permeate and first-stage concentrate. The first-stage concentrate undergoes second-stage reverse osmosis treatment to yield lithium-containing concentrate and second-stage permeate. The first-stage permeate and second-stage permeate are then mixed to obtain reverse osmosis permeate.

9. The method as described in claim 7, characterized in that, Before the first-stage reverse osmosis treatment, scale inhibitors and reducing agents are added to the solution obtained through multi-media filtration and ultrafiltration.

10. The method as described in claim 1, characterized in that, The pH adjuster for the lithium-containing concentrate includes sulfuric acid.

11. The method as described in claim 1, characterized in that, The bactericide includes sodium hypochlorite.

12. The method as described in claim 1, characterized in that, The dosage of the bactericide is 2-10 ppm.

13. The method as described in claim 1, characterized in that, The scale inhibitor includes polyacrylic acid.

14. The method as described in claim 1, characterized in that, The scale inhibitor is added at a concentration of 2-10 ppm.

15. The method as described in claim 1, characterized in that, The reducing agent comprises a sodium bisulfite solution with a mass percentage concentration of 8% to 12%.

16. The method as described in claim 1, characterized in that, The dosage of the reducing agent is 5-10 ppm.

17. The method as described in claim 1, characterized in that, The temperature for the freeze-crystallization process is -10 to -15°C.

18. The method as described in claim 1, characterized in that, The median particle size D50 of the activated carbon used in the activated carbon filtration process in step (3) is 0.8~1.8 mm.

19. The method as described in claim 1, characterized in that, Step (3) The second reverse osmosis treatment includes three-stage reverse osmosis treatment and four-stage reverse osmosis treatment.

20. The method as described in claim 1, characterized in that, Step (3) includes injecting desalinated pure water into an electro-deionization device, applying voltage to the positive and negative electrodes of the electro-deionization device, and performing electro-deionization to obtain ultrapure water.

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