A treatment method for phosphorus resource of electroless nickel plating wastewater

Abstract

The present application relates to a kind of chemical nickel plating wastewater phosphorus resource processing method, comprising the following steps: wastewater is adjusted and pretreated after pH and carries out breakage reaction, again through high-temperature oxidation reaction, nickel capture recovery and ammonia recovery etc., wherein, by accurately controlling reaction conditions, such as pH value, temperature, pressure and air change frequency etc., the efficient recovery of phosphorus resources in wastewater is realized, and the COD and nickel ion load of wastewater are significantly reduced, with the characteristics of complete recovery, recyclable, while avoiding introducing new impurities, reducing processing cost, improving processing efficiency and safety.

Description

Technical Field

[0001] This invention relates to the field of chemical wastewater treatment technology, specifically to a method for the treatment of phosphorus resource recovery from chemical nickel plating wastewater. Background Technology

[0002] The electroless nickel plating process generates a large amount of wastewater containing phosphorus. Traditional wastewater treatment methods have many shortcomings, such as incomplete recovery, leading to a significant waste of phosphorus resources, and the recovered wastewater still containing high concentrations of organic pollutants and nickel ions, placing a heavy burden on the environment.

[0003] In the prior art, patent CN117800521B discloses an oxidation complex-breaking reaction, which maintains the solution pH at 4-6 at the end of the oxidation complex-breaking reaction. However, this method has certain limitations when treating chemical nickel plating wastewater. It cannot efficiently convert hypophosphite into orthophosphate, and its removal effect on COD and nickel ions in wastewater is not ideal, making it difficult to meet increasingly stringent environmental protection requirements and the demand for efficient resource recycling.

[0004] CN114772779A describes a method for treating nickel plating wastewater containing ammonia complexing agents using alkaline stripping chelation precipitation combined with hypophosphite oxidation homogeneous co-precipitation. First, sodium hydroxide is used to adjust the pH of the wastewater to above 12, converting the ammonia into free ammonia. The adjusted wastewater is then aerated to strip the ammonia. After most of the ammonia nitrogen is removed (≤50 mg / L), the wastewater is precipitated to obtain nickel hydroxide precipitate. However, hypophosphite remains, so sodium hypochlorite oxidation is used to oxidize it to orthophosphate. Then, lime and ferrous sulfate, which have strong chelating abilities, are added for coagulation, forming large molecular impurities into effective flocs and achieving good precipitation. The resulting nickel and phosphorus effluent meets discharge standards. However, this method requires a large amount of liquid alkali and involves complex processes, making it difficult to implement industrially.

[0005] This invention addresses the shortcomings of existing technologies by proposing a novel method for recovering phosphorus resources from chemical nickel plating wastewater. Summary of the Invention

[0006] This invention addresses the shortcomings of existing electroless nickel plating wastewater treatment technologies by innovatively developing a highly efficient phosphorus resource recovery method. This method aims to completely recover phosphorus resources while reducing the COD and nickel ion load of the wastewater. Based on the characteristics of pollutants in electroless nickel plating wastewater, this method recovers high-purity, high-value magnesium ammonium phosphate through precise control of the reaction process. The specific treatment process includes: pH adjustment and pretreatment, complex-breaking reaction treatment, high-temperature oxidation reaction treatment, nickel capture and recovery, and ammonia recovery.

[0007] A method for treating phosphorus resources from chemical nickel plating wastewater includes the following steps:

[0008] Step 1, Pretreatment: Adjust the wastewater to weakly acidic, put it into the reaction vessel, and add ferrous sulfate as a complex-breaking agent;

[0009] Step 2, Complex-breaking reaction treatment: After filling the reaction vessel with air to the first pressure, the temperature is raised for the first time to treat the wastewater by complex-breaking reaction. During the reaction, the pressure inside the reaction vessel is controlled at the second pressure and the temperature at the second temperature.

[0010] Step 3, High-Temperature Oxidation Reaction Treatment: This includes two high-temperature oxidation reactions, with two ventilation treatments during the process.

[0011] Step 3.1, the first high-temperature oxidation reaction: after the first air exchange treatment of the reactor, the second heating is carried out to treat the wastewater with the first high-temperature oxidation reaction. During the reaction, the pressure inside the reactor is controlled at the third pressure and the temperature at the third temperature.

[0012] Step 3.2, Second high-temperature oxidation reaction: After the second air exchange treatment of the reactor, the wastewater is treated with a second high-temperature oxidation reaction. During the reaction, the pressure inside the reactor is controlled at the third pressure and the temperature at the third temperature.

[0013] Step 4, Nickel capture and recovery: Add a heavy metal ion capture agent to the wastewater treated by high-temperature oxidation reaction, so that the nickel ions in the wastewater complex with the heavy metal ion capture agent to form a solid and precipitate out. After filtration, the filtrate is obtained.

[0014] Step 5, Phosphorus recovery: Add magnesium sulfate solution and ammonia water to the filtrate in step (4) to adjust the pH to weakly alkaline, precipitate and filter to recover magnesium ammonium phosphate, and the filtered effluent can be directly discharged after evaporation and desalination.

[0015] In step (2), the second pressure is 3.5-4.2 MPa and the second temperature is 230-240℃; in step (3), the third pressure is 4.4-5.8 MPa and the third temperature is 245-260℃.

[0016] The inventors discovered that the main inorganic pollutants in electroless nickel plating wastewater are hypophosphite and nickel ions. To recover phosphorus from the wastewater and utilize it as a resource, the wastewater first needs pH adjustment and pretreatment to convert hypophosphite into orthophosphate. Otherwise, the efficiency of subsequent recovery will be greatly reduced, leading to a decrease in the quality of magnesium ammonium phosphate. Orthophosphate readily combines with magnesium and ammonium ions under weakly alkaline conditions to form magnesium ammonium phosphate precipitate, which is separated after precipitation and filtration. Nickel ions precipitate out in the form of complexes under the action of heavy ion scavenging agents.

[0017] In step 1, to ensure that the hypophosphite in the wastewater can be fully converted into orthophosphate, the pH of the wastewater is adjusted to a slightly acidic state. Too high a pH value will inhibit the generation of hydroxyl radicals and reduce the oxidation efficiency; too low a pH value will be unfavorable for the subsequent combination of orthophosphate with magnesium ions and ammonium ions.

[0018] Preferably, in step 1, the pH of the wastewater is controlled and adjusted to 6.5-7 to disrupt the structure of the complexes in the wastewater. If the pH of the wastewater is higher than 7, it will reduce the reducing and coordination functions of ferrous ions; if the pH of the wastewater is lower than 6.5, it will not only weaken the complex-breaking effect but also lead to a decrease in the quality of subsequent magnesium ammonium phosphate.

[0019] Furthermore, in step 1, to balance the complex-breaking effect and cost, the amount of ferrous sulfate is controlled at 0.3-0.8 wt% of the water volume. If the amount is too small, the complex structure cannot be effectively destroyed; if the amount is too large, the processing cost will increase, and excessive iron ions may be introduced, affecting subsequent processing. In addition, the hydroxyl radicals generated during the reaction have limited oxidation effect on organic matter, mainly focusing on complex breaking, and cannot completely oxidize organic matter.

[0020] Preferably, in step 2, to ensure the complex-breaking reaction proceeds fully, the initial pressure inside the reactor is set to 1 MPa, the wastewater is heated to 230-240°C, and the pressure inside the equipment is increased to 3.5-4.2 MPa. Too low a temperature or pressure will not effectively break down the structure of the complexes in the wastewater, leading to a decrease in hypophosphite conversion rate; too high a temperature or pressure may cause some organic matter to decompose prematurely, affecting the efficiency of subsequent oxidation reactions. Preferably, the reaction time is controlled at 30 minutes to ensure the complex-breaking reaction proceeds fully. If the reaction time is too short, the complex structure will not be completely destroyed, affecting the release of hypophosphite; if the reaction time is too long, it will increase energy consumption and reduce treatment efficiency.

[0021] Preferably, in step 3, the parameters for both high-temperature oxidation reactions are set as follows: the temperature inside the reactor is raised to 245-260℃, and the pressure is raised to 4.4-5.8 MPa. During the first ventilation treatment, the ventilation volume is set to 38.5 L, and the reaction duration is set to 30 min; during the second ventilation treatment, the ventilation volume is 38.5 L, and the reaction time is 30 min. This combination of heating, reaction, and ventilation ensures that hypophosphite is fully oxidized to orthophosphate, while simultaneously promoting the oxidative decomposition of organic matter. Insufficient temperature or pressure may lead to incomplete oxidation of hypophosphite and organic matter, affecting the treatment effect; while excessive temperature or pressure may increase energy consumption and equipment burden, reducing treatment efficiency.

[0022] The inventors discovered that during the high-temperature oxidation reaction in step 3, oxygen oxidizes the COD in the wastewater, producing acid ions and causing the solution to become acidic, thus lowering the pH. Preferably, before adding the heavy metal ion scavenging agent in step 4, the pH of the wastewater should be controlled and adjusted to be greater than 4 to ensure that nickel ions react fully with the heavy metal ion scavenging agent to form a solid precipitate. Preferably, pH=6. If the pH is too low, the scavenging agent is easily decomposed, affecting the removal efficiency of nickel ions; if the pH is too high, other impurity ions may react with the scavenging agent, reducing the purity of the product.

[0023] Preferably, the heavy metal ion scavenging agent mainly consists of dithiocarbamates and their derivatives, including but not limited to sodium dimethyldithiocarbamate; and contains water as a diluent.

[0024] Preferably, in step 4, the heavy metal ion scavenging agent is added to the treated effluent at a slow and uniform rate, with the addition time controlled between 0.5 and 2 hours; the reaction time for the nickel scavenging reaction is controlled between 1 and 3 hours. If the addition time is too short, it will lead to uneven local reactions, affecting the precipitation effect and ultimately reducing the purity of the product; if the reaction time is too short, it will lead to incomplete removal of nickel ions, resulting in low purity of the produced solid product and easy contamination with impurities.

[0025] Preferably, in step 4, the amount of heavy metal ion scavenging agent added is controlled according to a nickel to sulfur molar ratio of 2:1.01~1.05, with a preferred ratio of 2:1.05. If the amount added is insufficient, nickel ions cannot be completely captured, resulting in excessive nickel load in the effluent; if the amount added is excessive, it will not only increase costs but also increase the COD of the wastewater due to residual scavenging agent, affecting the effectiveness of subsequent treatment steps.

[0026] In addition, the inventors discovered through multiple experiments that the nickel content in the wastewater after nickel capture treatment should be controlled below 0.1 mg / L. Nickel content exceeding this concentration will interfere with the chemical precipitation reaction, resulting in a low recovery rate of magnesium ammonium phosphate.

[0027] In step 5, phosphorus recovery, magnesium sulfate and ammonia are selected as additives. These are not only low-cost, but magnesium ions can also more effectively combine with inorganic phosphorus to form a more stable magnesium ammonium phosphate precipitate, improving recovery efficiency. Simultaneously, the use of magnesium ions avoids the formation of byproducts such as calcium carbonate or calcium sulfate that may result from calcium ions, reducing the risk of system scaling and pipe blockage. Furthermore, magnesium ammonium phosphate, as a valuable fertilizer, has higher economic added value, further enhancing the economic benefits and environmental friendliness of wastewater treatment.

[0028] Preferably, in step 5, before adding magnesium sulfate solution and ammonia, the pH of the wastewater is adjusted to a slightly alkaline state, preferably pH = 8-10, more preferably 8.5-9.5, to ensure that inorganic phosphorus combines with magnesium ions and ammonium ions to form magnesium ammonium phosphate precipitate. When pH < 8, phosphorus in the solution mainly exists in the form of hydrogen phosphate ions, resulting in insufficient phosphate ions to reach the solubility product of magnesium ammonium phosphate, thus affecting the precipitation efficiency. Conversely, when pH > 10, the alkalinity is too strong, and magnesium ions react with hydroxide ions to form magnesium hydroxide precipitate, similarly affecting the precipitation efficiency of magnesium ammonium phosphate.

[0029] Preferably, in step 5, the concentration of magnesium sulfate solution is 10-20 wt%, and the concentration of ammonia water is 10-30 wt%, with the amount determined according to the total amount of inorganic phosphorus. If the concentration is too low, the reaction rate will be slow, precipitation will be incomplete, and the recovery rate will be reduced; if the concentration is too high, it will increase costs and may introduce excessive impurities, affecting the purity of magnesium ammonium phosphate. Preferably, the precipitation reaction time is 1 hour.

[0030] In addition, the wastewater treated in step 5 has significantly reduced COD and nickel load. The filtered effluent can be evaporated to remove moisture, achieving further concentration and purification of the wastewater, and can be directly discharged.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] (1) Efficient recovery of phosphorus resources: By precisely controlling the reaction conditions, this invention can efficiently convert hypophosphite in chemical nickel plating wastewater into orthophosphate, and further recover it into high-purity, high-value magnesium ammonium phosphate, which is a thorough recovery and has the characteristics of resource utilization.

[0033] (2) Significantly reduce wastewater load: The chemical oxygen demand (COD) and nickel ion load of the wastewater are significantly reduced during the treatment process, so that the treated wastewater has a lower pollutant content and meets stricter environmental emission standards.

[0034] (3) Low-cost treatment: Ferrous sulfate is selected as the complexing agent, which is inexpensive and readily available, avoiding the introduction of new impurities. Compared with traditional complexing agents, the treatment cost is significantly reduced.

[0035] (4) High safety and stability: By optimizing reaction conditions (such as temperature, pressure, pH value, etc.), the safety and stability of the treatment process are improved, and the risk of side reactions and system scaling is reduced. Attached Figure Description

[0036] Figure 1 This is a process flow diagram of a method for treating phosphorus resources from chemical nickel plating wastewater according to the present invention. Detailed Implementation

[0037] In order to clearly and thoroughly explain the technical solution provided by the present invention, it is necessary to explain the definition of phosphorus in the wastewater before introducing the method for phosphorus resource utilization treatment of chemical nickel plating wastewater of the present invention.

[0038] Total phosphorus in wastewater includes all phosphorus, including dissolved, particulate, organic, hypophosphite, and orthophosphate. The test method is "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method" (GB11893-1989).

[0039] Inorganic phosphorus in wastewater: specifically refers to phosphorus in orthophosphate in wastewater, excluding phosphorus hypochlorite. The test method is the same as in "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method" (GB11893-1989), except that potassium persulfate or other oxides are not used to digest and oxidize the phosphorus in the water sample to orthophosphate.

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] <Example 1>

[0042] The method of this invention was used to treat nickel plating wastewater from a factory production workshop in Chaoyang. The wastewater quality is shown in the table below:

[0043] Table 1. Water quality table of nickel plating wastewater from a factory in Chaoyang.

[0044]

[0045] The specific processing steps are as follows:

[0046] (1) Pretreatment: Take 500ml of raw water sample, adjust the pH value to 6.8, add 0.5wt% ferrous sulfate, stir evenly and put it into the oxidation reactor.

[0047] (2) Complex breaking reaction treatment: Open the air valve of the reactor and purge air until the pressure display shows 1 MPa. After the instrument stabilizes, raise the temperature to 230℃ and the pressure to 3.5 MPa; react fully for 30 minutes.

[0048] (3) High-temperature oxidation reaction treatment: After the reaction in step 2 is completed, a gas exchange operation is performed. After opening the exhaust gas valve and releasing 38.5L of gas to 1MPa, air is then introduced to 1MPa to complete the gas exchange. After the pressure gauge stabilizes, the temperature is raised again to 250℃ and the pressure is 5.2MPa to start the oxidation of phosphorus hypochlorite for 30 minutes. After the reaction is completed, a gas exchange is performed again. During the reaction, the temperature is maintained at 250℃ and the pressure at 5.2MPa. After 30 minutes, other small molecule organic matter in the wastewater is oxidized, and the COD is significantly reduced.

[0049] (4) Nickel capture and recovery: After the effluent from the tertiary treatment is cooled to room temperature, the pH of the wastewater is adjusted to 6; sodium dimethyl dithiocarbamate solution, a heavy metal capture agent, is added, and the molar ratio of nickel to sulfur is controlled to be 2:1.01 to form a nickel solid precipitate. After the reaction is complete, the effluent is filtered.

[0050] (5) Phosphorus recovery: Add 532 ml of 20 wt% magnesium sulfate solution and 18 ml of 27% ammonia water to the filtrate, and adjust the pH value to 9. After stirring and reacting for 60 min, a white solid with magnesium ammonium phosphate as the main component is obtained. After filtration, the inorganic phosphorus and COD content of the effluent is detected. After evaporation and desalination, it can be directly discharged.

[0051] The quality of magnesium ammonium phosphate prepared in the above examples and the inorganic phosphorus and COD content of each stage of effluent were tested, and the results are shown in Tables 2 and 3.

[0052] Table 2. Report on Inorganic Phosphorus and COD Tests in Effluent

[0053]

[0054] Table 3 Report Form for Magnesium Ammonium Phosphate

[0055]

[0056] As can be seen from the table, the treatment using this embodiment significantly reduced the chemical oxygen demand (COD) and nickel ion load in the wastewater, achieved a high conversion rate of inorganic phosphorus (i.e., orthophosphate) in the wastewater, and recovered magnesium ammonium phosphate with high purity.

[0057] <Example 2>

[0058] Wastewater quality is the same as in Example 1

[0059] The specific processing steps are as follows:

[0060] (1) Pretreatment: Take 500ml of raw water sample, adjust the pH value to 7, add 0.3wt% ferrous sulfate, stir evenly and put it into the oxidation reactor.

[0061] (2) Complex breaking reaction treatment: Open the air valve of the reactor and purge air until the pressure display shows 1MPa. After the instrument stabilizes, raise the temperature to 240℃ and the pressure to 4.2MPa; react fully for 30min.

[0062] (3) High-temperature oxidation reaction treatment: After the reaction in step 2 is completed, a gas exchange operation is performed. After opening the exhaust gas valve and releasing 38.5L of gas to 1MPa, air is then introduced to 1MPa to complete the gas exchange. After the pressure gauge stabilizes, the temperature is raised again to 260℃ and the pressure is 5.8MPa to start the oxidation of phosphorus hypochlorite for 30 minutes. After the reaction is completed, another gas exchange is performed. During the reaction, the temperature is maintained at 260℃ and the pressure at 5.8MPa. After 30 minutes, other small molecule organic matter in the wastewater is oxidized, and the COD is significantly reduced.

[0063] (4) Nickel capture and recovery: After the effluent from the tertiary treatment is cooled to room temperature, the pH of the wastewater is adjusted to 6; sodium dimethyl dithiocarbamate solution, a heavy metal capture agent, is added, and the molar ratio of nickel to sulfur is controlled to be 2:1.05 to form a nickel solid precipitate. After the reaction is complete, the effluent is filtered.

[0064] (5) Phosphorus recovery: Add 1000ml of 10wt% magnesium sulfate solution and 54ml of 10wt% ammonia water to the filtrate, adjust the pH value to 8, stir thoroughly and react for 60min to obtain a white solid with magnesium ammonium phosphate as the main component. After filtration, the inorganic phosphorus and COD content of the effluent is detected. After evaporation and desalination, it can be directly discharged.

[0065] The quality of magnesium ammonium phosphate prepared in the above examples and the inorganic phosphorus and COD content of each stage of effluent were tested, and the results are shown in Tables 4 and 5.

[0066] Table 4. Report on Inorganic Phosphorus and COD Tests in Effluent

[0067]

[0068] Table 5 Report Form for Magnesium Ammonium Phosphate

[0069]

[0070] As can be seen from the table, the treatment using this embodiment significantly reduced the chemical oxygen demand (COD) and nickel ion load in the wastewater, achieved a high conversion rate of inorganic phosphorus (i.e., orthophosphate) in the wastewater, and recovered magnesium ammonium phosphate with high purity.

[0071] <Example 3>

[0072] Wastewater quality is the same as in Example 1

[0073] The specific processing steps are as follows:

[0074] (1) Pretreatment: Take 500ml of raw water sample, adjust the pH value to 6.5, add 0.8wt% ferrous sulfate, stir evenly and put it into the oxidation reactor.

[0075] (2) Complex breaking reaction treatment: Open the air valve of the reactor and purge air until the pressure display shows 1MPa. After the instrument stabilizes, raise the temperature to 235℃ and the pressure to 3.6MPa; react fully for 30min.

[0076] (3) High-temperature oxidation reaction treatment: After the reaction in step 2 is completed, a gas exchange operation is performed. 38.5L of gas is released to 1 MPa by opening the exhaust valve, and then air is introduced to 1 MPa to complete the gas exchange. After the pressure gauge stabilizes, the temperature is raised again to 245℃ and the pressure is 4.4 MPa to start the oxidation of phosphorus hypochlorite for 30 minutes. After the reaction is completed, another gas exchange is performed. During the reaction, the temperature is maintained at 245℃ and the pressure at 4.4 MPa. After 30 minutes, other small molecule organic matter in the wastewater is oxidized, and the COD is significantly reduced.

[0077] (4) Nickel capture and recovery: After the effluent from the tertiary treatment is cooled to room temperature, the pH of the wastewater is adjusted to 6; sodium dimethyl dithiocarbamate solution, a heavy metal capture agent, is added, and the molar ratio of nickel to sulfur is controlled to be 2:1.01 to form a nickel solid precipitate. After the reaction is complete, the effluent is filtered.

[0078] (5) Phosphorus recovery: Add 521 ml of 20 wt% magnesium sulfate solution and 17 ml of 20 wt% ammonia water to the filtrate, adjust the pH value to 10, stir thoroughly and react for 60 min to obtain a white solid with magnesium ammonium phosphate as the main component. After filtration, the inorganic phosphorus and COD content of the effluent is detected. After evaporation and desalination, it can be directly discharged.

[0079] The quality of magnesium ammonium phosphate prepared in the above examples and the inorganic phosphorus and COD content of each stage of effluent were tested, and the results are shown in Tables 6 and 7.

[0080] Table 6. Report on Inorganic Phosphorus and COD Tests in Effluent

[0081]

[0082] Table 7 Report Form for Magnesium Ammonium Phosphate

[0083]

[0084] As can be seen from the table, the treatment using this embodiment significantly reduced the chemical oxygen demand (COD) and nickel ion load in the wastewater, achieved a high conversion rate of inorganic phosphorus (i.e., orthophosphate) in the wastewater, and recovered magnesium ammonium phosphate with high purity.

[0085] <Example 4>

[0086] The wastewater quality is as in Example 1. The difference from Example 1 is that in step (1) pretreatment, the pH value is adjusted to 6.

[0087] The mass of magnesium ammonium phosphate prepared in Example 4 and the inorganic phosphorus and COD contents of the effluent from each treatment stage are shown in Tables 8 and 9, respectively.

[0088] Table 8. Report on Inorganic Phosphorus and COD Tests in Effluent

[0089]

[0090] Table 9 Report Form for Magnesium Ammonium Phosphate

[0091]

[0092] As can be seen from the table, compared to the inorganic phosphorus content of 60996 mg / L (i.e., orthophosphate, converted from phosphorus hyposulfite) and COD of 11027 mg / L in step 3 of Example 1, the inorganic phosphorus content converted in step 3 of Example 4 is 54223 mg / L and COD is 15434 mg / L. The inorganic phosphorus conversion value is lower, and some phosphorus hyposulfite in the wastewater is not completely oxidized to orthophosphate. Moreover, the COD content is higher than that in Example 1. The reason for this is that after adjusting the pH to 6 during the complex-breaking reaction, this pH has a certain inhibitory effect on the generation of hydroxyl radicals in the wastewater, resulting in a low oxidant content. Some pollutants cannot be oxidized, resulting in a higher COD and lower inorganic phosphorus content in the effluent.

[0093] <Example 5>

[0094] The wastewater quality is as in Example 1. The difference from Example 1 is that 0.1 wt% of ferrous sulfate is added in step (1) of the pretreatment.

[0095] The mass of magnesium ammonium phosphate prepared in Example 5 and the inorganic phosphorus and COD contents of the effluent from each treatment stage are shown in Tables 10 and 11, respectively.

[0096] Table 10. Report on Inorganic Phosphorus and COD Tests in Effluent

[0097]

[0098] Table 11 Report Form for Magnesium Ammonium Phosphate

[0099]

[0100] As can be seen from the table, compared to the inorganic phosphorus content of 60996 mg / L and COD of 11027 mg / L in step 3 of Example 1, the inorganic phosphorus content of 41226 mg / L and COD of 14123 mg / L in step 3 of Example 5 are lower. This indicates that some hypophosphite in the wastewater was not completely oxidized to orthophosphate, and the COD content is higher than that in Example 1. Analysis shows that the reason is that the amount of ferrous sulfate added is less than that in Example 1, which means that the ferrous ions did not separate hypophosphite from the organic matter during the complex-breaking reaction. As a result, a certain amount of hypophosphite remained with the organic matter, which means that the orthophosphate content after subsequent oxidation is lower and the COD of the effluent is higher.

[0101] <Example 6>

[0102] The wastewater quality is as in Example 1. The difference from Example 1 is that in step (2), the time for the complex breaking reaction is 25 minutes.

[0103] The mass of magnesium ammonium phosphate prepared in Example 6 and the inorganic phosphorus and COD contents of the effluent from each stage of treatment are shown in Tables 12 and 13.

[0104] Table 12 Effluent Inorganic Phosphorus and COD Test Report

[0105]

[0106] Table 13 Report Form for Magnesium Ammonium Phosphate

[0107]

[0108] As can be seen from the table, compared to the inorganic phosphorus content of 60996 mg / L and COD of 11027 mg / L in step 3 of Example 1, the inorganic phosphorus content converted in step 3 of Example 6 is 58524 mg / L and COD is 13125 mg / L. The inorganic phosphorus conversion value is slightly lower, and a very small amount of hypophosphite in the wastewater is not completely oxidized to orthophosphate. Moreover, the COD content is higher than that in Example 1. After analysis, the reason is that the complex-breaking reaction in step 2 is short, which causes the complex-breaking reaction to not be fully carried out, resulting in a small amount of hypophosphite not being de-complexed and unable to be oxidized to orthophosphate.

[0109] <Example 7>

[0110] The wastewater quality is as in Example 1. The difference from Example 1 is that in the high-temperature oxidation reaction of step (3), the reaction time after the first and second air exchanges is 25 min.

[0111] The mass of magnesium ammonium phosphate prepared in Example 7 and the inorganic phosphorus and COD contents of the effluent from each stage of treatment are shown in Tables 14 and 15, respectively.

[0112] Table 14. Report on Inorganic Phosphorus and COD Tests in Effluent

[0113]

[0114] Table 15 Report Form for Magnesium Ammonium Phosphate

[0115]

[0116] As can be seen from the table, the COD value of the effluent treated in step 5 increased. The content of inorganic phosphorus converted from hypophosphite in step 3 was lower than in Example 1. Finally, the magnesium ammonium phosphate formed in step 5 contained some organic matter, resulting in a slight decrease in the purity of magnesium ammonium phosphate. Analysis revealed that this was because, with the shorter oxidation time, a small portion of hypophosphite was not completely oxidized to orthophosphate, and the COD in the water was not completely oxidized to carbon dioxide and water.

[0117] <Example 8>

[0118] The wastewater quality is as in Example 1. The difference from Example 1 is that in step (4), the pH value of the wastewater was not adjusted after the third-stage effluent and before the addition of the heavy metal scavenging agent.

[0119] The mass of magnesium ammonium phosphate prepared in Example 8 and the inorganic phosphorus and COD contents of the effluent from each treatment stage are shown in Tables 16 and 17.

[0120] Table 16. Report on Inorganic Phosphorus and COD Tests in Effluent

[0121]

[0122] Table 17 Report Form for Magnesium Ammonium Phosphate

[0123]

[0124] As can be seen from the table, the nickel content in the effluent from step 5 did not decrease significantly. Analysis revealed that the reason was that the pH of the wastewater was not adjusted to be greater than 4 before the heavy metal ion scavenger was added in step 4. During the high-temperature oxidation reaction in step 3, oxygen oxidized the COD in the wastewater, which produced acid ions, causing the solution pH to decrease. In the low-pH acidic solution, the heavy metal scavenger was easily decomposed and ineffective, and could not form a precipitate with nickel ions, so the nickel ions were not removed.

[0125] <Example 9>

[0126] The wastewater quality is similar to that of Example 1, except that in step (4), the molar ratio of nickel to sulfur is controlled to be 2:0.5.

[0127] The mass of magnesium ammonium phosphate prepared in Example 9 and the inorganic phosphorus and COD contents of the effluent from each treatment stage are shown in Tables 18 and 19.

[0128] Table 18. Report on Inorganic Phosphorus and COD Tests in Effluent

[0129]

[0130] Table 19 Report Form for Magnesium Ammonium Phosphate

[0131]

[0132] As can be seen from the table, compared to the nickel content of 0.001 mg / L in the effluent treated in step 4 of Example 1, the nickel content in the effluent treated in step 4 of this example is 5 mg / L, which is slightly higher than the data in Example 1. Analysis revealed that the reason is that the amount of heavy metal chelating agent added was reduced, resulting in some nickel not being complexed and remaining in the wastewater.

[0133] <Example 10>

[0134] The wastewater quality is as in Example 1, except that in step (5), the pH value is adjusted to 11.

[0135] The mass of magnesium ammonium phosphate prepared in Example 10 and the inorganic phosphorus and COD contents of the effluent from each treatment stage are shown in Tables 20 and 21.

[0136] Table 20. Report on Inorganic Phosphorus and COD Tests in Effluent

[0137]

[0138] Table 21 Report Form for Magnesium Ammonium Phosphate

[0139]

[0140] As can be seen from the table, compared to the inorganic phosphorus concentration of 1.2 mg / L in the effluent treated in step 5 of Example 1, the concentration in this example is 4386 mg / L, which is much higher than that in Example 1. The reason for this is that when the pH is adjusted to 11 during phosphorus recovery, phosphate and magnesium in the wastewater will form magnesium phosphate precipitate, and some magnesium ions will form magnesium hydroxide precipitate, so some phosphate remains.

[0141] <Comparative Example 1>

[0142] The wastewater quality is as in Example 1: Unlike Example 1, the wastewater first underwent (1) nickel capture and recovery treatment: 500 ml of raw water sample was taken and the pH of the wastewater was adjusted to 6; sodium dimethyl dithiocarbamate solution was added as a heavy metal capture agent, and the molar ratio of nickel to sulfur was controlled to be 2:1.05 to form a nickel solid precipitate. After the reaction was complete, the precipitate was filtered.

[0143] The subsequent (2) pretreatment, (3) complex breaking reaction treatment, (4) high-temperature oxidation reaction treatment, and (5) phosphorus recovery are the same as in Example 1.

[0144] The mass of magnesium ammonium phosphate prepared in Comparative Example 1 and the inorganic phosphorus and COD contents of the effluent from each treatment stage are shown in Tables 22 and 23.

[0145] Table 22 Effluent Inorganic Phosphorus and COD Test Report

[0146]

[0147] Table 23 Report Form for Magnesium Ammonium Phosphate

[0148]

[0149] As can be seen from the table, although the inorganic phosphorus and nickel content in the effluent from step 5 is not high, the purity of magnesium ammonium phosphate is low and the COD of the effluent is high. Analysis revealed that in the reaction sequence of Example 1, after the oxidation reaction, the heavy metal scavenger reacts with nickel to form a precipitate, which adsorbs a small amount of small-molecule organic matter, thus reducing the COD of the effluent. However, in Comparative Example 1, nickel removal is carried out at the front end. Although this process at the front end reduces the COD of the effluent from step 1 to some extent, the precipitation only removes a small portion of the small-molecule organic matter. A large amount of large-molecule organic matter remains in the wastewater, resulting in only a slight change in COD content. Therefore, the higher COD of the effluent from step 4 also leads to the presence of a large amount of organic matter in the magnesium ammonium phosphate precipitate, resulting in low purity.

[0150] <Comparative Example 2>

[0151] Wastewater quality is as described in Example 1.

[0152] The specific processing steps are as follows:

[0153] (1) Pretreatment: Take 500ml of raw water sample, adjust the pH value to 6.8, add 0.5wt% ferrous sulfate and 1wt% hydrogen peroxide, stir evenly and put into oxidation reactor.

[0154] (2) Complex breaking reaction: Open the air valve of the reactor and purge air until the pressure display shows 1MPa. After the instrument stabilizes, raise the temperature to 80℃ and react fully for 30min.

[0155] (3) High-temperature oxidation reaction: After the reaction in step 2 is completed, a gas exchange operation is performed. The exhaust gas valve is opened to release gas at 1 MPa, and then air is introduced at 1 MPa to complete the gas exchange. After the pressure gauge stabilizes, the temperature is raised to 90℃ again to start the oxidation of phosphorus hypochlorite. The reaction is carried out for 30 minutes. After the reaction is completed, another gas exchange is performed. During the reaction, the temperature is maintained at 90℃. After 30 minutes, other small molecule organic matter in the wastewater is oxidized, and the COD decreases.

[0156] (4) Nickel capture and recovery, (5) Phosphorus recovery and treatment are the same as in Example 1.

[0157] The mass of magnesium ammonium phosphate prepared in Comparative Example 2 and the inorganic phosphorus and COD contents of the effluent from each treatment stage are shown in Tables 24 and 25.

[0158] Table 24 Effluent Inorganic Phosphorus and COD Test Report

[0159]

[0160] Table 25 Report Form for Magnesium Ammonium Phosphate

[0161]

[0162] As can be seen from the table, due to the low temperatures of the complex-breaking reaction and high-temperature oxidation reaction, the organic matter in the wastewater could not be completely oxidized, and the hypophosphite could not be complexed and separated for oxidation. This resulted in a high hypophosphite content in the treated effluent, and the wastewater contained a large amount of organic matter due to incomplete oxidation. During the precipitation process of magnesium ammonium phosphate, a certain amount of organic matter would be wrapped around it, resulting in very poor purity of magnesium ammonium phosphate.

[0163] <Comparative Example 3>

[0164] The wastewater quality is the same as in Example 1. The difference from Example 1 is that the complex breaking reaction temperature in step (2) is 250°C.

[0165] The mass of magnesium ammonium phosphate prepared in Comparative Example 3 and the inorganic phosphorus and COD contents of the effluent from each treatment stage are shown in Tables 26 and 27.

[0166] Table 26. Report on the Testing of Inorganic Phosphorus and COD in Effluent

[0167]

[0168] Table 27 Report Form for Magnesium Ammonium Phosphate

[0169]

[0170] As can be seen from the table, the high temperature of the complex-breaking reaction accelerated the oxidation process of organic matter in the wastewater, but caused some phosphorus nitrite to fail to be complexed and oxidized into inorganic phosphorus, resulting in the inorganic phosphorus content in the wastewater being lower than that in Example 1.

[0171] <Comparative Example 4>

[0172] The wastewater quality is the same as in Example 1. The difference from Example 1 is that the complex breaking reaction temperature in step (2) is 220°C.

[0173] The quality of magnesium ammonium phosphate prepared in Comparative Example 4 and the inorganic phosphorus and COD contents of the effluent from each treatment stage are shown in Tables 28 and 29.

[0174] Table 28. Report on the Testing of Inorganic Phosphorus and COD in Effluent

[0175]

[0176] Table 29 Report Form for Magnesium Ammonium Phosphate

[0177]

[0178] As can be seen from the table, lowering the complex-breaking reaction temperature will affect the efficiency of the conversion of hypophosphite to orthophosphate during the complex-breaking reaction, resulting in the inability to completely remove phosphorus elements from the wastewater through precipitation reaction. This leads to the content of inorganic phosphorus in step 3 being lower than that in Example 1.

[0179] <Comparative Example 5>

[0180] The wastewater quality is the same as in Example 1. The difference from Example 1 is that the temperature of the two high-temperature oxidation reactions in step (3) is 230°C.

[0181] The quality of magnesium ammonium phosphate prepared in Comparative Example 5 and the inorganic phosphorus and COD contents of the effluent from each treatment stage are shown in Tables 30 and 31.

[0182] Table 30 Effluent Inorganic Phosphorus and COD Test Report

[0183]

[0184] Table 31 Report Form for Magnesium Ammonium Phosphate

[0185]

[0186] As can be seen from the table, since the oxidation treatment temperature did not reach 245-260℃, the hypophosphite after complex breaking could not be completely oxidized into inorganic phosphorus, resulting in the inorganic phosphorus content in step 3 being lower than that in Example 1, and the COD of the effluent was also higher.

[0187] <Comparative Example 6>

[0188] The wastewater quality is the same as in Example 1. The difference from Example 1 is that the temperature of the two high-temperature oxidation reactions in step (3) is 270°C.

[0189] The quality of magnesium ammonium phosphate prepared in Comparative Example 5 and the inorganic phosphorus and COD contents of the effluent from each treatment stage are shown in Tables 32 and 33.

[0190] Table 32 Effluent Inorganic Phosphorus and COD Test Report

[0191]

[0192] Table 33 Report Form for Magnesium Ammonium Phosphate

[0193]

[0194] Although it is slightly better than Example 1 in terms of complexation and oxidation effects of phosphorus sulfide, raising the temperature in actual process requires more energy, which will increase the cost index and reduce the processing efficiency.

[0195] The above are merely specific embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for treating phosphorus resources from chemical nickel plating wastewater, characterized in that, Includes the following steps: (1) Pretreatment: The wastewater is adjusted to weak acidity and then added to the reactor as a complex-breaking agent, ferrous sulfate. (2) Complex breaking reaction treatment: After air is introduced into the reactor to the first pressure, the temperature is raised for the first time to treat the wastewater by complex breaking reaction. During the reaction, the pressure inside the reactor is controlled to the second pressure and the temperature to the second temperature. (3) High-temperature oxidation reaction treatment, including two high-temperature oxidation reactions, with two air exchange treatments during the process: 3.1) The first high-temperature oxidation reaction: After the first air exchange treatment of the reactor, the second heating is carried out to treat the wastewater with the first high-temperature oxidation reaction. During the reaction, the pressure inside the reactor is controlled at the third pressure and the temperature at the third temperature. 3.2) Second high-temperature oxidation reaction: After the second air exchange treatment of the reactor, the wastewater is treated with a second high-temperature oxidation reaction. During the reaction, the pressure inside the reactor is controlled at the third pressure and the temperature at the third temperature. (4) Nickel capture and recovery: Add a heavy metal ion capture agent to the wastewater treated by high-temperature oxidation reaction, so that the nickel ions in the wastewater complex with the heavy metal ion capture agent to form a solid and precipitate out. After filtration, the filtrate is obtained. (5) Phosphorus recovery: Add magnesium sulfate solution and ammonia water to the filtrate in step (4) to adjust the pH to weakly alkaline, precipitate and filter to recover magnesium ammonium phosphate, and the filtered effluent can be directly discharged after evaporation and desalination. In step (2), the second pressure is 3.5-4.2 MPa and the second temperature is 230-240℃; in step (3), the third pressure is 4.4-5.8 MPa and the third temperature is 245-260℃. In step (1), after adjusting the pH of the wastewater to 6.5-7, a complex-breaking agent is added; In step (2), the first pressure is 1 MPa, and the time for the complex breaking reaction is 30 min; In step (4), the main component of the heavy metal ion scavenger is sodium dimethyl dithiocarbamate.

2. The processing method according to claim 1, characterized in that, In step (1), the amount of the complex-breaking agent ferrous sulfate is 0.3-0.8 wt% of the wastewater volume.

3. The processing method according to claim 1, characterized in that, In step 3.1), the specific air exchange volume for the first air exchange treatment is 38.5L, and the time for the first high-temperature reaction treatment is 30min.

4. The processing method according to claim 1, characterized in that, In step 3.2), the specific air exchange volume for the second air exchange treatment is 38.5L, and the time for the second high-temperature reaction treatment is 30min.

5. The processing method according to claim 1, characterized in that, In step (4), the pH of the wastewater is adjusted to be greater than 4 before adding the heavy metal ion scavenger.

6. The processing method according to claim 1, characterized in that, In step (4), the metal ion scavenging agent is added to the wastewater at a nickel to sulfur molar ratio of 2:1.01~1.

05.

7. The processing method according to claim 1, characterized in that, In step (5), after adding ammonia to the filtrate, the pH is adjusted to 8-10.

8. The processing method according to claim 1, characterized in that, In step (5), the concentration of the magnesium sulfate solution is 10-20 wt%; the concentration of the ammonia solution is 10-30 wt%.

9. The processing method according to claim 1, characterized in that, In step (5), the precipitation reaction time is 1 hour.

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