A method for recovering phosphorus and nickel resources in electroless nickel plating wastewater by paired electrolysis and synthesizing high-purity iron phosphate

Abstract

The application belongs to the technical field of industrial wastewater recycling and lithium ion battery cathode material preparation, and relates to a method for recovering phosphorus and nickel resources in electroless nickel plating wastewater by paired electrolysis and synthesizing high-purity iron phosphate. The method comprises the following steps: a double-chamber diaphragm electrolytic cell is used, wherein the diaphragm is an anion exchange membrane, the anode is iron, the cathode is at least one of a metal electrode, an alloy electrode and a graphite electrode, the anode electrolyte is a solution containing sulfate, and the cathode electrolyte is electroless nickel plating wastewater; the method of paired electrolysis is used, the anode recovers phosphorus resources to synthesize high-purity iron phosphate, and the cathode electrodeposits nickel to recover nickel resources. The method for recovering phosphorus and nickel by electrodeposition greatly improves the current efficiency; the method has high recovery rate, low cost and simple process, can be industrialized and mass-produced, and the recovered iron phosphate has high purity and can be used as a precursor raw material for synthesizing lithium ion battery cathode material lithium iron phosphate.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater recycling and lithium-ion battery cathode material preparation technology, and relates to a technology for recovering phosphorus and nickel resources from chemical nickel plating wastewater and synthesizing high-purity lithium iron phosphate. Background Technology

[0002] Electroless nickel plating is a surface treatment technology that does not require an external current. It boasts advantages such as corrosion resistance, uniform plating ability, high hardness, wear resistance, high weldability, a certain degree of electromagnetic shielding, and no limitations on the size and shape of components. Electroless nickel plating is widely used in electronics, aerospace, automotive, and machinery industries. However, with the continuous expansion of the application scope and production scale of electroless nickel plating technology, the resulting environmental problems are becoming increasingly serious. Industrial electroless nickel plating solutions become waste liquid after 8-10 uses, primarily composed of heavy metal nickel and large amounts of phosphates (hypophosphite, phosphite, orthophosphate, and pyrophosphate, etc.). The former poses carcinogenic, teratogenic, and mutagenic risks to humans, while the latter is one of the pollutants contributing to eutrophication of aquatic environments. Treatment technologies for electroless nickel plating waste liquid include oxidation precipitation, ion exchange, and electrodialysis, mainly focusing on the removal of phosphorus or nickel. These methods suffer from problems such as long treatment processes, large amounts of chemical reagents, low product resource utilization, and low added value. Currently, there is limited research on using electroless nickel plating waste liquid for the preparation of lithium-ion battery cathodes.

[0003] In recent years, my country's new energy vehicle sales have grown rapidly. According to the latest data from the China Association of Automobile Manufacturers, in 2023, China's automobile market sales reached 30.094 million units, of which new energy vehicles accounted for 9.495 million units, or 31.6%. Power batteries account for nearly 40% of the total cost of new energy vehicles, with cathode materials accounting for 51% of the battery cost. The cathode materials for new energy vehicle power batteries mainly include four categories: nickel-cobalt-manganese, nickel-cobalt-aluminum ternary cathode materials, lithium iron phosphate (LiFePO4, or LFP) cathode materials, lithium cobalt oxide cathode materials, and lithium manganese oxide cathode materials. Among them, lithium-ion batteries using LFP as the cathode material surpassed ternary material batteries in 2021 and became the dominant type of power battery for new energy vehicles due to their advantages such as high energy density, low cost, abundant resources, and higher safety. Furthermore, LFP is also a key material for the transformation of energy storage batteries from commercialization to large-scale production. Expanding the sources of LFP raw materials and increasing the scale of LFP production are urgent needs for the development of the new energy vehicle and energy storage industries.

[0004] Industrially, lithium iron phosphate (LFP) is mainly prepared using solid-state and hydrothermal methods, both employing iron phosphate as a raw material. These two methods are simple, have high raw material utilization, good reproducibility, and produce highly active cathode materials. Their production technologies are becoming increasingly mature and are currently the mainstream processes for LFP preparation. The performance and cost of LFP prepared using these technologies primarily depend on the purity, morphology, and cost of the iron phosphate precursor. With the booming development of the new energy industry, the profit margins of LFP are constantly being squeezed, creating market demand for new low-cost, high-quality iron phosphate preparation technologies. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of phosphorus and nickel pollution and waste in existing electroless nickel plating wastewater, as well as the problem of low-cost, high-quality lithium iron phosphate preparation technology. This invention provides a method for recovering phosphorus and nickel resources from electroless nickel plating wastewater using a paired electrolysis method and synthesizing high-purity iron phosphate. Compared with existing preparation methods, this method has the following outstanding advantages: (1) it utilizes the resources of electroless nickel plating wastewater; (2) it provides a novel method for synthesizing iron phosphate, a precursor for lithium iron phosphate; (3) this method has lower production costs; and (4) this technology is easily industrialized. Using the iron phosphate obtained by the method of this invention as a precursor, lithium iron phosphate cathode materials are prepared by solid-state method and assembled into lithium-ion batteries, achieving battery performance consistent with commercial lithium iron phosphate.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] A method for recovering phosphorus and nickel resources from electroless nickel plating wastewater and synthesizing high-purity iron phosphate using a paired electrolysis method, the method comprising: employing a dual-chamber diaphragm electrolytic cell, wherein: the diaphragm is an anion exchange membrane, the anode is iron, and the cathode is at least one of a metal, alloy, and graphite electrode; the anode electrolyte is a sulfate-containing solution, and the cathode electrolyte is electroless nickel plating wastewater; employing a paired electrolysis method, the anode recovers phosphorus resources to synthesize high-purity iron phosphate, and the cathode electrodeposits nickel to recover nickel resources.

[0008] Preferably, the cathode is at least one of metals such as iron, nickel, stainless steel, and titanium, as well as alloys such as lead alloys, which can further improve the recovery rate of nickel and phosphorus.

[0009] Preferably, the diaphragm is a quaternary ammonium anion exchange membrane.

[0010] Preferably, the sulfate-containing solution includes at least one of a sulfate solution and a dilute sulfuric acid solution; more preferably, the sulfate includes at least one of ammonium sulfate, lithium sulfate, and sodium sulfate; the ratio of sulfate concentration (g / L) in the sulfate-containing solution to sulfate concentration (g / L) in the electroless nickel plating wastewater is 0.5-4:1, more preferably 1-4:1.

[0011] Preferably, the paired electrolysis is performed using constant current electrolysis, wherein the anode current density is controlled to be 150-450 A / m. 2 The cathode current density is 50-300 A / m 2 The ratio of anode and cathode current densities is controlled by the anode and cathode area ratio method, with an area ratio of 1:1-5. Constant current paired electrolysis recovers the vast majority of nickel, with a recovery rate of not less than 80%. More preferably, the anode current density is 300-450 A / m². 2 More preferably, the constant current electrolysis time is 3-5 hours. The constant current electrolysis is carried out until the phosphorus recovery rate reaches about 55%, or the color of the chemical nickel plating waste liquid in the cathode area is close to colorless (generally within 3-5 hours), which can achieve the recovery of most of the nickel and some of the phosphorus. The constant current electrolysis time can be longer, but it will result in higher energy consumption.

[0012] Preferably, the paired electrolysis employs variable current electrolysis, which includes two constant current electrolysis processes. The method is as follows: the aforementioned constant current electrolysis serves as the first stage, and after electrolysis continues until the phosphorus recovery rate is >55%, or the color of the electroless nickel plating waste liquid in the cathode area is nearly colorless, a small current constant current electrolysis is used as the second stage. The small current in the second stage is less than the current in the first stage. More preferably, the cathode current density is controlled at 30-150 A / m during the second stage of constant current electrolysis. 2 Nickel recovery, anolyte current density 150 A / m 2 Constant current electrolysis recovers most of the phosphorus, with a recovery rate of no less than 60%; a more efficient method is low-current constant current electrolysis for approximately 2 hours. Using variable current electrolysis can further improve the phosphorus recovery rate and reduce energy consumption.

[0013] Preferably, the method for treating the electrolytic products in the anode region is as follows: the turbid liquid in the anode region is removed, filtered, washed with water until the pH is around 7.0, and the filtered product is then dried to obtain high-purity hydrated ferric phosphate, preferably at a drying temperature of 80°C. More preferably, the hydrated ferric phosphate is calcined to obtain ferric phosphate, preferably at a calcination temperature of 650°C.

[0014] Preferably, the method for processing the electrolytic products in the cathode region is as follows: the nickel glass deposited on the cathode electrode is washed with water until the pH is close to 7.0, the filtered product is dried to obtain nickel, and the drying temperature is preferably 80°C.

[0015] Furthermore, the hydrated iron phosphate obtained by electrolysis is high-purity hydrated iron phosphate, which is then calcined to obtain high-purity iron phosphate. Under preferred electrolysis conditions, the iron-to-phosphorus ratio of the product is in the range of 0.96-1.02, which can meet the battery-grade iron phosphate standard (battery-grade iron phosphate "HG / T 4701-2021").

[0016] Preferably, hydrated iron phosphate or calcined iron phosphate obtained from the anode region is used as a precursor for lithium iron phosphate, the cathode material of lithium-ion batteries. Lithium iron phosphate@carbon is synthesized by solid-state method, and lithium-ion batteries are assembled to test the battery performance. The lithium iron phosphate cathode material synthesized from the iron phosphate recovered in this invention meets the quality standards of commercial-grade lithium-ion battery cathode material raw materials.

[0017] Furthermore, the lithium iron phosphate cathode material synthesized from the obtained iron phosphate has good purity. The prepared lithium iron phosphate half-cell exhibits good performance. The initial discharge capacity at 0.1C is 158.1 mAh / g, and the initial coulombic efficiency is 89.98%. After 60 cycles at 0.1C, the discharge capacity retention rate is 98.67%, and after 500 cycles at 1C, the discharge capacity retention rate is 88.95%.

[0018] Compared with existing chemical methods for recovering waste phosphorus and nickel resources, the beneficial effects of the technical solution described in this invention are as follows: (1) This invention uses a paired electrodeposition method to recover phosphorus and nickel, which greatly improves the current efficiency and has a high recovery rate; (2) This invention uses an anion single-diaphragm method, which is simple in process and can obtain high-purity iron phosphate; (3) A new type of anolyte has been developed, which greatly improves the selective permeation of phosphate anions through the anion membrane by adjusting the sulfate ratio in the anode and cathode regions, thereby significantly improving the current efficiency and recovery efficiency; (4) It avoids the consumption of a large amount of hydrogen peroxide in chemical methods; (5) The method described in this invention is low in cost, simple to operate, and suitable for large-scale industrial production. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of the present invention;

[0020] Figure 2 This is a structural diagram of the electrolysis device of the present invention;

[0021] Wherein, 1-anode, 2-anion exchange membrane, 3-cathode, 4-anode chamber, 5-cathode chamber

[0022] Figure 3 Here is a SEM image of the iron phosphate synthesized in Example 1;

[0023] Figure 4 The image shows the XRD pattern of the iron phosphate synthesized in Example 1.

[0024] Figure 5 The image shows the XRD pattern of lithium iron phosphate synthesized in Example 1.

[0025] Figure 6 This is a comparison of the first charge-discharge curves of the lithium iron phosphate half-cell assembled by Example 1 and the chemical precipitation method.

[0026] Figure 7This is a comparison chart of the cycle discharge performance at 0.1C between the lithium iron phosphate half-cell assembled by Example 1 and the one assembled by chemical precipitation method.

[0027] Figure 8 This is a comparison chart of the 1C cycle discharge performance of the lithium iron phosphate half-cell assembled by Example 1 and the chemical precipitation method. Detailed Implementation

[0028] To better clarify and understand the objectives, process solutions, and advantages of this invention, the technical solutions and implementation methods of this invention will be further described clearly, completely, and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described in this invention are implemented under the premise of the technical solutions of this invention, providing detailed implementation methods and specific operating procedures, but are only some embodiments of this invention, not all embodiments. The specific implementation methods described are limited to illustrating and explaining this invention and do not limit this invention. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0029] Unless otherwise specified, the experimental methods and conditions used in the following examples are conventional methods and conditions. The materials, reagents, and instruments used in the examples, unless otherwise specified, can be obtained commercially or prepared by conventional methods. The reaction conditions described in the invention can all achieve the reactions and obtain the desired products. Due to space limitations, some examples are listed below to further illustrate the advantages of the technical solution of the present invention.

[0030] Example 1:

[0031] The process flow diagram for this experiment is as follows: Figure 1 .

[0032] S1. Electrolyte pretreatment. A chemical nickel plating waste liquid from a certain enterprise, with a pH of approximately 4, was taken. The main components of the waste liquid were obtained using ICP testing, as shown in Table 1.

[0033] Table 1 Main Components of Chemical Nickel Plating Waste Liquid

[0034]

[0035] The electroless nickel plating waste liquid was filtered using a filtration device. The waste liquid (phosphorus content 60 g / L, nickel content 6 g / L, sulfur content 30 g / L) was diluted 5 times (phosphorus content 12 g / L, nickel content 1.2 g / L, sulfur content 6 g / L) and used as the cathode electrolyte. A 0.12 mol / L (NH4)2SO4 solution was prepared as the anolyte (sulfate concentration approximately 12 g / L, sulfate content ratio of anolyte to cathode electrolyte approximately 2:1).

[0036] S2, Electrolysis experiment. For example... Figure 2 As shown, using Figure 2 A dual-chamber electrolytic cell is used, with an anion exchange membrane (2) as the diaphragm. The above-mentioned cathode electrolyte is injected into the cathode chamber (5), and the anolyte is injected into the anode chamber (4). A DT4C type anode iron plate (1) and a 304 type cathode stainless steel plate (2) are placed in each chamber respectively. 铁板 :S 不锈钢板 =1:3.

[0037] One stage of constant current electrolysis: Adjusting the anode current density to 300 A / m 2 The cathode current density is 100 A / m 2 The electrolyte temperature is room temperature (15-40℃, preferably 25℃). During electrolysis, the temperature rises naturally, and an appropriate amount of water is added to maintain a relatively constant electrolyte volume in both the cathode and anode areas. During electrolysis, hypophosphite and sulfate anions in the electroless nickel plating wastewater pass through the anion exchange membrane into the anode chamber under the influence of the electric field, forming a phosphorus concentrate. Simultaneously, hypophosphite ions react with ferrous ions dissolved from the iron anode in the presence of oxygen to form ferric phosphate, resulting in a pale yellow suspension in the anode area. Nickel ions are reduced to nickel at the cathode and deposited on the stainless steel plate. When the cathode wastewater solution is nearly colorless, the phosphorus and nickel content in the cathode wastewater before and after the reaction is determined by ICP. The results show a nickel recovery rate of 96% for paired electrodeposited cathodes, a phosphorus recovery rate of 56% for anodes, a cathode current efficiency of 30%, and an anode current efficiency of 84%.

[0038] The nickel and phosphorus recovery rates and current efficiency are calculated as follows:

[0039]

[0040] C0 — Ni and P concentrations on the cathode side measured by ICP before the reaction;

[0041] C1—Ni and P concentrations on the cathode side measured by ICP after the reaction;

[0042] V0 — Volume of cathode electrolyte before reaction;

[0043] V1 — Volume of cathode electrolyte after reaction.

[0044]

[0045] Two-stage constant current electrolysis: When the wastewater solution in the cathode region becomes nearly colorless, most of the nickel has been recovered. Simultaneously, as the phosphorus content in the solution decreases, the rate of iron phosphate synthesis in the anode region and the anode current efficiency decrease. At this point, the anode current density is adjusted to 150 A / m³. 2 The cathode current density is 50 A / m 2S 铁板 :S 不锈钢板 The electrolyte ratio was 1:3, the electrolyte temperature was room temperature, and it naturally heated up during electrolysis. Appropriate amounts of water were added to maintain a relatively constant electrolyte volume in both the cathode and anode areas. Constant current electrolysis was continued using a small current to reduce energy consumption and increase product yield. The electrolysis time was approximately 2 hours. The cathode current efficiency in the second stage of electrolysis was 0%, and the anode current efficiency was 42%. After one and two stages of constant current electrolysis, the total nickel recovery rate was 98%, and the total phosphorus recovery rate was 70%.

[0046] S3. Product Processing. The suspension was removed from the anode chamber, filtered, washed with water, and dried at 80°C to obtain nano-sized hydrated iron phosphate. Figure 3 The image shown is a SEM image of the iron phosphate synthesized in Example 1. ICP testing showed that the Fe / P ratio of the hydrated iron phosphate was 0.97, which is within the standard range for battery-grade iron phosphate. The hydrated iron phosphate was calcined in air at 650°C to obtain anhydrous iron phosphate. Figure 4 (XRD pattern of iron phosphate synthesized in Example 1); scrape off the deposit on the cathode stainless steel plate, wash and dry to obtain nickel metal.

[0047] S4. Synthesis of Lithium Iron Phosphate Cathode Material. Lithium hydroxide and the above-mentioned hydrated or anhydrous iron phosphate were mixed in a ratio of 1.02:1, and an appropriate amount of glucose was added as a carbon source. After ball milling for 12 hours, the mixture was heated to 380°C at a rate of 10°C / min and held for 1 hour under an inert atmosphere, then heated to 650°C at a rate of 10°C / min and held for 6 hours to obtain lithium iron phosphate (LiFePO4). Figure 5 The above-mentioned lithium iron phosphate, PVDF, and SP were added to NMP solvent in a ratio of 8:1:1 and stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was then coated onto an aluminum sheet with a coating amount of 1.1 mg / cm². 2 The sample was dried in an oven at 60°C for 2 hours, and then kept at 110°C in a vacuum oven for 12 hours to obtain the lithium iron phosphate positive electrode sheet.

[0048] S5. Battery Assembly. Assemble half-cells inside an argon atmosphere glove box. The assembly sequence is: positive electrode shell, positive electrode plate, battery separator, negative lithium plate, gasket, spring contact, and battery negative electrode shell.

[0049] S6. Battery Testing. The electrochemical performance of the battery was tested using a Newway tester. The initial discharge capacity at 0.1C was 158.1 mAh / g, and the initial coulombic efficiency was 89.98%. Figure 6 After 60 cycles at 0.1C, the discharge capacity retention rate was 98.67%. Figure 7 After 500 cycles at 1C, the discharge capacity retention rate was 88.95%. Figure 8 It exhibits battery performance consistent with commercial lithium iron phosphate batteries.

[0050] Examples 2-6

[0051] Similar to the method in Example 1, the cathode in S2 was replaced with iron (DT4C), nickel (N6), and titanium (TA1), and the graphite electrode (SHCM-7) and lead alloy (PbSb2) were used. Nickel and iron phosphate were recovered through single-stage and two-stage electrolysis, and lithium iron phosphate cathode material was prepared. The experimental results are shown in Table 2.

[0052] Table 2 Experimental results of different cathode materials

[0053]

[0054] The results in Table 2 show that different cathode materials have a significant impact on the recovery rate of nickel phosphorus, which may be due to the influence of the conductivity and hydrogen evolution potential of different electrode materials on the electrochemical reaction process.

[0055] Examples 7-9

[0056] Similar to the method in Example 1, the anolyte in S1 was replaced with lithium sulfate, sodium sulfate, and dilute sulfuric acid solutions, respectively. Nickel and iron phosphate were recovered using single-stage and two-stage electrolysis, and lithium iron phosphate cathode materials were prepared. The experimental results are shown in Table 3.

[0057] Table 3 Experimental results for different anolytes

[0058]

[0059] Table 3 shows that the type of sulfate in the anolyte has little effect on the recovery rate of phosphorus and nickel.

[0060] Examples 10-12

[0061] Using the same method as in Example 1, the ratio of sulfate concentration (g / L) in the anolyte solution and the sulfate concentration (g / L) in the cathode region in S1 was changed to 0.5:1, 1:1, and 4:1, respectively. The experimental results of current efficiency and recovery rate of the first-stage and second-stage electrolysis are shown in Table 4.

[0062] Table 4. Experimental results of different sulfate concentration ratios in different anode and cathode electrolytes.

[0063]

[0064] Table 4 shows that the concentration ratio of sulfate in different anolytes and catholytes has a significant impact on phosphorus recovery but little effect on nickel recovery. This may be because when the sulfate concentration in the anolyte is low, the ion concentration difference and electrodynamic driving force cause sulfate ions in the catholyte to preferentially pass through the anion exchange membrane compared to hypophosphite ions, generating impurities such as ferric sulfate (soluble in water), increasing the amount of precipitate washing water used, and reducing the yield and efficiency of ferric phosphate synthesis. This effect weakens when the sulfate concentration in the anolyte is high and reaches a certain proportion. When the sulfate concentration in the anolyte is too high, the excessively high ion concentration may reduce the driving force of ion migration.

[0065] Examples 13-15

[0066] Similar to the method in Example 1, in S1, the cathode electrolyte was treated by undiluted, diluted 2 times with deionized water, and diluted 10 times with deionized water respectively (the purpose was to adjust the phosphorus and nickel concentration in the waste liquid). The experimental results of current efficiency and recovery rate of the first-stage electrolysis and the second-stage electrolysis are shown in Table 5.

[0067] Table 5. Experimental results of waste liquid treatment at different dilution ratios.

[0068]

[0069]

[0070] Table 5 shows that within a certain range, the recovery rate of nickel phosphate increases with increasing dilution factor. This may be because excessively high ion concentrations can clog the pores of the anion exchange membrane, reducing conductivity. However, excessively high dilution factors will increase water consumption and reduce ferric phosphate production.

[0071] Examples 16-17

[0072] Similar to the method in Example 1, in the constant current electrolysis stage S2, the anode current density was adjusted to 150 and 450 A / m, respectively. 2 In the two-stage constant current electrolysis, the anode current density is maintained at 150 A / m. 2 The current efficiency and recovery rate of the first-stage and second-stage electrolysis remain unchanged, as shown in Table 6.

[0073] Table 6. Experimental results of constant current electrolysis at different current densities.

[0074]

[0075] The results in Table 6 show that during a single-stage constant current electrolysis, a higher current density leads to a higher recovery rate of phosphorus and nickel, but a decrease in current efficiency and an increase in energy consumption.

[0076] Examples 18-19

[0077] Similar to the method in Example 1, in S2, the ratio of anode to cathode area (S) is controlled. 铁板 :S 不锈钢板 The method involves adjusting the ratio of cathode and anode current densities to 1:1 and 1:5, respectively. In one stage of constant current electrolysis, the anode current density is kept constant at 300 A / m. 2 The anode current density in the two-stage constant current electrolysis is constant at 150 A / m. 2 The experimental results of current efficiency and recovery rate for single-stage and two-stage electrolysis are shown in Table 7.

[0078] Table 7. Experimental results for different anode and cathode area ratios.

[0079]

[0080] Table 7 shows that adjusting the anode-cathode area ratio did not significantly change the phosphorus and nickel recovery rate, but it did affect the phosphorus and nickel recovery current efficiency.

[0081] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications may be made without departing from the technical solutions described in the claims.

Claims

1. A method for recovering phosphorus and nickel resources from chemical nickel plating wastewater and synthesizing high-purity iron phosphate using paired electrolysis, characterized in that, The method includes: using a dual-chamber diaphragm electrolytic cell, wherein: the diaphragm is an anion exchange membrane, the anode is iron, the cathode is at least one of metal or graphite electrodes, the anode electrolyte is a sulfate-containing solution, the cathode electrolyte is electroless nickel plating wastewater, and a paired electrolysis method is used to recover phosphorus resources at the anode and nickel resources at the cathode; wherein the ratio of sulfate concentration (g / L) in the sulfate-containing solution to the sulfate concentration (g / L) in the electroless nickel plating wastewater is 0.5-4:

1.

2. The method for recovering phosphorus and nickel resources from chemical nickel plating wastewater and synthesizing high-purity iron phosphate using paired electrolysis according to claim 1, characterized in that, The cathode is at least one of iron, nickel, stainless steel, titanium, and lead alloy.

3. The method for recovering phosphorus and nickel resources from chemical nickel plating wastewater and synthesizing high-purity iron phosphate using paired electrolysis according to claim 1, characterized in that, The diaphragm is a quaternary ammonium anion exchange membrane.

4. The method for recovering phosphorus and nickel resources from chemical nickel plating wastewater and synthesizing high-purity iron phosphate by paired electrolysis according to claim 1, characterized in that, The sulfate-containing solution includes at least one of a sulfate solution and a dilute sulfuric acid solution.

5. The method for recovering phosphorus and nickel resources from chemical nickel plating wastewater and synthesizing high-purity iron phosphate by paired electrolysis according to claim 1, characterized in that, The ratio of sulfate concentration (g / L) in the sulfate-containing solution to that in the electroless nickel plating wastewater is 1-4:

1.

6. The method for recovering phosphorus and nickel resources from chemical nickel plating wastewater and synthesizing high-purity iron phosphate by paired electrolysis according to claim 1, characterized in that, The paired electrolysis described herein employs constant current electrolysis, wherein the anode current density is controlled at 150-450 A / m. 2 The cathode current density is 50-300 A / m 2 The ratio of anode and cathode current density is controlled by the anode and cathode area ratio method, with an area ratio of 1:1-5.

7. The method for recovering phosphorus and nickel resources from chemical nickel plating wastewater and synthesizing high-purity iron phosphate by paired electrolysis according to claim 6, characterized in that, Anode current density is 300-450 A / m 2 .

8. The method for recovering phosphorus and nickel resources from chemical nickel plating wastewater by paired electrolysis and synthesizing high-purity iron phosphate according to claim 6 or 7, characterized in that, The paired electrolysis is a variable current electrolysis, which includes two constant current electrolysis processes: the constant current electrolysis of claim 6 or 7 is used as the first stage of constant current electrolysis; when the phosphorus recovery rate is >55%, or when the color of the chemical nickel plating waste liquid in the cathode area is close to colorless, a small current constant current electrolysis is used as the second stage of constant current electrolysis; the current of the second stage of constant current electrolysis is less than the current of the first stage of constant current electrolysis.

9. The method for recovering phosphorus and nickel resources from chemical nickel plating wastewater and synthesizing high-purity iron phosphate by paired electrolysis according to claim 8, characterized in that, The two-stage constant current electrolysis controls the cathode current density to be 30-150 A / m. 2 The anode current density is 150 A / m 2 .

10. The method for recovering phosphorus and nickel resources from chemical nickel plating wastewater by paired electrolysis and synthesizing high-purity iron phosphate according to claim 1, characterized in that, The method for treating the electrolytic products in the anode area is as follows: the turbid liquid in the anode area is taken out, filtered, washed with water, and the filtered product is dried to obtain hydrated ferric phosphate. The method for processing the electrolytic products in the cathode region is as follows: the nickel deposited on the cathode electrode is stripped off, washed with water, filtered, and dried to obtain nickel.

Images