CN109897973B - Method for recovering nickel in nickel-containing wastewater by using ferric salt precipitation - Google Patents
Method for recovering nickel in nickel-containing wastewater by using ferric salt precipitation Download PDFInfo
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Abstract
The application discloses a method for recovering nickel in nickel-containing wastewater by ferric salt precipitation, relates to the technical field of wastewater treatment, and solves the technical problems of difficulty in removing nickel ions in nickel-containing electroplating wastewater and high cost in the prior art. The method for recovering nickel from nickel-containing wastewater utilizes an electro-Fenton reaction and a method for generating ferric salt precipitate to recover nickel in the nickel-containing wastewater. The method is mainly used for removing the nickel ions in the electroplating wastewater.
Description
Technical Field
The application relates to the technical field of wastewater treatment, in particular to a method for recovering nickel in nickel-containing wastewater by using ferric salt precipitation.
Background
The nickel-containing wastewater discharged by the electroplating or electrophoresis industry has the characteristics of high organic matter concentration, low nickel ion concentration and high pH value, and is completely recycled or discharged after reaching the standard after being reasonably treated. Due to the confidentiality limitation of the industry on the components of the nickel-containing electroplating solution, the complexing mechanism of organic components and nickel ions in the nickel-containing wastewater cannot be clearly analyzed, so that the nickel ions in the nickel-containing electroplating wastewater are difficult to remove.
A conventional treatment method for nickel-containing wastewater in the industry is to purchase a medicament, destroy the organic complex form of nickel in electroplating solution, and then add a flocculating agent to generate coprecipitation so as to quickly remove nickel ions in the wastewater. Since the chemical is also one of the products for sale containing nickel plating solution, it is expensive and there is a phenomenon of residual nickel in use. If the wastewater is subjected to decomplexing and coagulation treatment, the concentration of the residual nickel ions is higher than 4 mg/L. This is a phenomenon of incomplete decomplexing, requiring further advanced treatment.
The modern nickel-containing wastewater treatment technology can be simply divided into two types, the first type is to recover nickel ions in high-concentration nickel-containing wastewater, and the principle is based on extraction and ion exchange; the second is to remove nickel ions in the low-concentration nickel-containing wastewater. It can be found that the first method inevitably produces low-concentration nickel-containing wastewater after the high-concentration nickel ions are recovered, and the second method is needed for treatment. The method for treating the waste water containing low-concentration nickel comprises a liquid membrane method, an electrolytic method, a chemical check air floatation method, a reverse osmosis method, a coagulation coprecipitation method and the like. The liquid membrane method, the electrolysis method and the medicament check air floatation method are suitable for treating high-concentration nickel-containing wastewater, and when the method is applied to the treatment of low-concentration nickel-containing wastewater, the defects of large medicament amount, large power consumption, long time and the like exist. The reverse osmosis method is easy to cause membrane blockage in use and has high operation cost. Compared with these methods, the coprecipitation method can adapt to the change of water quantity and water quality, has strong operability and low price of the coagulant, so the application is very wide, but the method needs to be matched with a decomplexation agent for use.
Aluminum salt coagulants are most commonly used in the co-coagulation and co-precipitation method and include polyaluminium chloride, polyaluminium sulfate and the like. According to the principle of nickel removal, nickel is hydrolyzed to generate fine particles under the condition of high pH, and colloid particle aggregation and coprecipitation occur after aluminum-containing colloid hydrolyzed by an aluminum salt coagulant is contacted with fine nickel-containing particles, so that nickel ions in a water phase are transferred into a solid phase, and the nickel ions in the water are efficiently removed. Due to the addition of the coagulant, a large amount of heavy metal waste mud containing aluminum and nickel is generated in the low-nickel wastewater treatment. The waste mud is divided according to environmental protection, belongs to hazardous waste, and needs to be recovered by a special hazardous waste disposal company for safe disposal.
There are two main technical problems in recovering nickel in low concentration nickel-containing wastewater. One of the problems is that the amount of chemicals used is large or the amount of electricity consumed is large in the aforementioned technologies based on extraction or ion exchange, which leads to an excessively high recovery cost. The other is that the generated nickel-containing precipitate contains nickel ions, but the aluminum and nickel are difficult to separate, and an effective aluminum or nickel limit separation method is lacked.
Disclosure of Invention
The application aims to provide a method for recovering nickel in nickel-containing wastewater by using ferric salt precipitation, which is used for solving the technical problems of difficulty in removing nickel ions in nickel-containing electroplating wastewater and high cost in the prior art.
The method for recovering nickel in nickel-containing wastewater by using ferric salt precipitation comprises the following steps:
(1) adjusting the pH value of the nickel-containing wastewater to 7-9, stirring and uniformly mixing the adjusted nickel-containing wastewater and ferric salt under the electro-Fenton process condition, and continuously stirring to generate a first mixture;
(2) taking supernatant liquid 2cm below the liquid level of the first mixture, performing full spectrum scanning within the wavelength range of 300-360 nm, recording the light absorption value as A, performing dA/d lambda differential calculation, and detecting the inflection point of data by using a counter; adding persulfate when two inflection points are detected, stirring and mixing for 30-1 h, standing for 10-20 min, then carrying out dA/d lambda differential calculation again within the range of 300-360 nm of wavelength lambda, stopping adding persulfate when one inflection point is detected, stopping stirring, finishing the Fenton reaction, collecting a first precipitate generated by the Fenton reaction, and standing the first precipitate for 18-36 h;
(3) mixing part of the first precipitate with nitric acid, wherein the volume ratio of the mixed part of the first precipitate to the nitric acid is 3-5, the stirring speed is 60-180 rpm, and continuously stirring for 0.5-5 h to obtain a second mixture;
(4) continuously adding the first precipitate into the second mixture, wherein the adding amount is 0.5-1.5% of the volume of the second mixture, continuously stirring for 0.5-5 h to obtain a third mixture, and measuring the pH value of the supernatant of the third mixture;
(5) repeating the step (4) until the pH value of the supernatant of the mixture obtained in the step (4) is 0.4-1, stopping adding the first precipitate, continuously stirring for 2-5 h, and collecting the obtained first supernatant for later use;
(6) putting the first supernatant into a closed reaction kettle, heating and keeping constant temperature, performing magnetic separation to obtain a second supernatant and a second precipitate, and detecting the TOC (Total Organic Carbon) value and the iron content of the second supernatant;
(7) in response to the iron content in the second supernatant exceeding 10mg/L, adding sodium citrate into the second supernatant, and repeating the operation of the step (6) on the liquid after the sodium citrate is added to obtain a third supernatant and a third precipitate;
(8) supplementing nitrate into the third supernatant in response to the iron content in the third supernatant exceeding 10mg/L to obtain a fourth supernatant, wherein the fourth supernatant is a final supernatant, and finishing the reaction; in response to that the iron content in the third supernatant is less than 10mg/L, the third supernatant is a final supernatant, and the reaction is ended;
(9) and directly using the final supernatant to prepare an electrophoretic solution or an electroplating solution, or adjusting the pH value of the final supernatant to 10-11 by using alkali, standing and precipitating for 8-12 h, collecting bottom precipitate, and drying at 105 ℃ for 2h to obtain the nickel oxide with the purity of 95.5-99.2%.
Preferably, in the step (1), the anode of the electro-Fenton process is a titanium dioxide electrode plate, the cathode of the electro-Fenton process is a stainless steel electrode plate, and the current intensity is 10mA/cm2～15mA/cm2The stirring speed is 120rpm to 300 rpm.
Preferably, in the step (1), the molar ratio of the added iron salt to the nickel in the solution is 5-20: 1, the iron salt is one of polymeric ferric chloride and polymeric ferric sulfate, or a mixture of the polymeric ferric chloride and the polymeric ferric sulfate.
Preferably, in the step (2), the formula of the addition amount of the persulfate is as follows:
formula (1) where m is α × V/S;
wherein alpha is a constant and takes a value of 1.8 × 10-3(ii) a V is the volume of the first mixture solution in m3(ii) a S is the area of the integral area under the wavelength of 300 nm-360 nm; m is the addition of persulfate in kg. .
Preferably, in the step (6), the first supernatant is placed into a closed reaction kettle according to the filling degree of 60-80%, the temperature is heated to 120-160 ℃, the temperature is kept constant for 5-6 hours, and then magnetic separation is carried out, wherein the magnetic field intensity of the magnetic separation is 300 kA/m-500 kA/m.
Preferably, in step (7), the second supernatant is supplemented with sodium citrate, and the addition amount is calculated according to the following formula:
m＝(kC2-C1) Formula (2) of x V/2;
wherein, C in the formula1The TOC value of the second supernatant is measured in mg/L; c2The concentration of iron in the second supernatant is measured in mg/L; k is a constant and has a value range of 1.3-1.9; m is the addition amount of sodium citrate in mg.
Preferably, the dosage of nitrate added in step (8) is calculated according to the following formula:
C3＝4.5C4-b×lgC5formula (3);
wherein, C3The dosage of the nitrate is calculated by mol/L; c4The iron concentration in the third supernatant is measured in mol/L; c5The concentration of dissolved oxygen in the solution is shown in mol/L; and b is the filling degree of the reaction kettle.
Optionally, the nitrate is added as one of sodium nitrate and potassium nitrate, or as a mixture of sodium nitrate and potassium nitrate.
Preferably, the second precipitate and the third precipitate are dried at 105 ℃ for 2-5 h, and the content of iron oxide in the product obtained after drying is greater than or equal to 96.7%.
Preferably, in the final supernatant in the step (8), the concentration of nickel is 4855 mg/L-2450 mg/L, the concentration of iron is 3.7 mg/L-10 mg/L, the TOC value of the supernatant is 3.1 mg/L-6.5 mg/L, and the pH value is 1.2-2.3.
The method for recovering nickel in nickel-containing wastewater by using ferric salt precipitation has the following technical effects:
(1) the enrichment and purification of nickel in the nickel-containing wastewater are realized by ferric salt precipitation and separation of iron in the iron-containing precipitation, so that a high-purity nickel-containing solution is obtained, and the high-purity nickel-containing solution can be used for preparing an electrophoretic solution or preparing high-purity nickel oxide, and is simple in method and low in price;
(2) in the process of separating iron, magnetic separation is firstly used, and then sodium citrate is used, so that the use amount of the sodium citrate is greatly saved;
(3) the method can efficiently separate iron from iron and nickel, and the collected precipitate has high purity of iron and can be directly used as iron concentrate powder;
(4) the nickel-containing wastewater treatment method can completely recycle the nickel-containing heavy metal sludge, can save the treatment cost of the heavy metal sludge, can reuse the separated product or prepare a high-value iron or nickel product, and has obvious economic benefit.
The terms used herein have their meanings well known in the art, however for clarity the following definitions are still given.
The term "substantially" does not exclude the meaning of "completely". For example, a component "substantially free" of Y may also be completely free of Y. Where a particular value is defined, it is meant that the particular value has a range that floats above and below the particular value, which may be +/-5%, +/-4%, +/-3%, +/-2%, +/-1%, +/-0.5%, +/-0.2%, +/-0.1%, +/-0.05%, +/-0.01%, etc., of the particular value. If desired, "substantially" or "essentially" may be substituted for or deleted from the definition of the invention with the above floating ranges.
The terms "comprising," "including," "containing," and "having" are intended to be inclusive of the stated elements and to allow for inclusion of additional, undefined elements.
"about," "about," or "approximately," when defining a particular value, means that the particular value has a range that varies from top to bottom based on the particular value, and the range can be +/-5%, +/-4%, +/-3%, +/-2%, +/-1%, +/-0.5%, +/-0.2%, +/-0.1%, +/-0.05%, +/-0.01%, etc., of the particular value.
The numerical ranges used herein for the sake of brevity include not only the endpoints thereof, but also all the subranges thereof and all the individual numerical values within that range. For example, a numerical range of 1 to 6 includes not only sub-ranges, such as 1 to 3, 1 to 4, 1 to 5, 2 to 4, 2 to 6, 3 to 6, etc., but also individual numbers within that range, such as 1, 2, 3, 4, 5, 6.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art according to the drawings.
FIG. 1 is a data plot of wavelength λ and dA/d λ of the present application;
FIG. 2 is a sample X-ray diffraction pattern of a magnetic field separated solid;
FIG. 3 is a scanning electron microscopy analysis of a magnetically separated solid of the present application.
Detailed Description
The technical solutions in the embodiments of the present application are clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Example one
(1) Nickel-containing wastewater
Electroplating nickel-containing wastewater with the total volume of 1m3The pH value is 13.6, the nickel content is 142mg/L, the TOC content is 420mg/L, and the color is light yellow.
Specifically, the pH value of the electroplating nickel-containing wastewater can be between 12 and 14, the nickel content can be between 3.4mg/L and 221mg/L, and the TOC (Total Organic Carbon) value can be between 350mg/L and 790 mg/L.
(2) Selection of electro-Fenton conditions
The titanium dioxide electrode plate is used as an anode plate, the stainless steel electrode plate is used as a cathode plate, and the current intensity is 10mA/cm2。
In one embodiment, the current intensity is 10mA/cm2～15mA/cm2Any value in between, e.g. 11mA/cm2、12mA/cm2、13.5mA/cm2、15mA/cm2(ii) a After the pH value is adjusted, the pH value of the nickel-containing wastewater is any value between 7 and 9, such as 7, 8, 8.5 and 9; the stirring speed is any value between 120rpm and 300rpm, such as 120rpm, 180rpm, 200rpm, 240rpm, 280rpm and 300 rpm; the added ferric salt can also be polymeric ferric sulfate or a mixture of polymeric ferric chloride and polymeric ferric sulfate; adding iron salt to the solutionThe molar ratio of nickel is 5-20: 1, such as 5:1, 9:1, 10: 1. 15:1 and 20: 1.
In this embodiment, after the pH was adjusted to 7.5 with hydrochloric acid, the power was turned on, and poly-ferric chloride was added at a stirring speed of 150 rpm. Wherein the dosage of the polyferric chloride is added according to the molar ratio of iron in the polyferric chloride to nickel ions in the solution being 8: 1. Stirring for 10-30 min to obtain a mixture solution.
After taking the supernatant below the liquid surface and carrying out full spectrum scanning, preferably, taking the supernatant 2cm below the liquid surface, and calculating the area value of an integration area under the wavelength of 300 nm-360 nm to be 1937.558. Fig. 1 is a data graph of wavelength λ and dA/d λ in the present application, and as shown in fig. 1, 2 inflection points are obtained by integrating dA/d λ in an integration region, and it is determined that persulfate is added and that persulfate is potassium persulfate. The addition amount of potassium persulfate is according to the formula
Formula (1) where m is α × V/S;
wherein m is the addition amount of potassium persulfate in kg; alpha is a constant and takes a value of 1.8 multiplied by 10-3(ii) a V is the volume of the mixture solution in m3(ii) a S is the area of the integral area under the wavelength of 300 nm-360 nm.
The amount of the additive was calculated to be 3.49 kg.
After adding potassium persulfate, continuously stirring for 30min, and standing for 10 min. And (3) taking the supernatant, carrying out full-wavelength scanning, detecting the dA/d lambda integral value under 300-360 nm, obtaining 1 inflection point as shown in figure 1, and judging that the addition of the potassium persulfate is stopped.
Specifically, after persulfate is added, the continuous stirring time can be controlled within 30 min-1 h, such as 35min, 40min, 50min and 1 h; the standing time can be controlled within 10 min-20 min, such as 15min and 20 min.
In the process of rescanning, if 2 inflection points are still detected, the amount of persulfate to be added is continuously calculated according to the formula (1), after stirring and standing, full-wavelength scanning is carried out again, dA/d lambda integral values under 300-360 nm are detected until 1 inflection point is obtained, the Fenton reaction is finished, and mixed precipitates containing iron and nickel at the bottom are collected.
And turning off the power supply, stopping stirring, and standing for 2 hours until the concentration of nickel in the supernatant is 0.003 mg/L. The concentration of nickel ions in the supernatant is low, and the supernatant can be discharged or used for preparing an electrophoretic fluid.
(3) Determining a precipitation treatment method
It is to be explained that the standing time of the collected precipitate can be controlled between 18h and 36h, such as 18h, 20h, 26h, 30h and 36 h; the volume ratio of the precipitate to the nitric acid is 3-5, such as 3, 3.5, 4.5 and 5; illustratively, the concentration of nitric acid may be between 35% and 45%; the stirring speed can be controlled between 60rpm and 180rpm, such as 60rpm, 100rpm, 120rpm, 160rpm and 180rpm, and the stirring is continued for 0.5h to 5 h.
In the embodiment, after the precipitate is collected, the precipitate is kept stand for 24h, the bottom precipitate is taken, nitric acid is added according to the volume ratio of the precipitate to the nitric acid of 4, the stirring speed is controlled to be 80rpm, the stirring is continued for 1h, and the measured pH value is 0.32, so that a mixture solution is obtained.
The bottom precipitate was further added in a proportion of 1% by volume based on the total volume of the mixture solution, and after stirring for 0.5h, the pH was measured to be 0.37. The bottom precipitate was added repeatedly 4 times according to this method. The pH was measured to be 0.6, the addition of the precipitate was stopped and after stirring for a further 3h a yellow solution was obtained.
It should be noted that, when the precipitation addition is finished, the pH of the solution needs to be between 0.4 and 1, such as 0.4, 0.5, 0.6, 0.8 and 1. And when the addition of the precipitate is stopped, continuously stirring for 2-5 h to obtain a yellow solution.
(4) Conditions for separating iron in precipitate
In one embodiment, a yellow solution, such as 65%, 70%, 75%, 80%, is filled in a closed reaction vessel at a fill level of 60% to 80%; heating to 120-160 deg.C, such as 120 deg.C, 130 deg.C, 140 deg.C, 160 deg.C; keeping the temperature for 5-6 h, such as 5.5h and 6h, and carrying out magnetic separation; the magnetic field strength of the magnetic separation is 300kA/m to 500kA/m, such as 350kA/m, 380kA/m, 420kA/m, 460kA/m and 500 kA/m.
In the embodiment, 600mL of yellow solution is taken and placed into a closed reaction kettle with the total volume of 1L according to the filling degree of 60 percent, the temperature is heated to 150 ℃, the temperature is kept for 5 hours, and then the yellow solution is naturally cooled to the room temperature. And (3) taking out the mixed liquid in the reaction kettle, putting the mixed liquid into a magnetic field with the magnetic field intensity of 320kA/m, and after the brick red precipitate at the bottom is magnetically separated, the iron concentration in the supernatant is 1372mg/L, the nickel ion concentration is 4921mg/L, and the TOC value is 27.7 mg/L.
Adding sodium citrate into the supernatant according to the formula
m＝(kC2-C1) Formula (2) of x V/2;
wherein, C in the formula1The TOC value of the supernatant is measured in mg/L; c2The iron concentration in the supernatant is measured in mg/L; k is a constant and has a value range of 1.3-1.9; m is the addition amount of sodium citrate in mg.
k is 1.5, and the dosage of the added sodium citrate is calculated to be 1692 mg.
Adding sodium citrate, transferring the solution into a reaction kettle, keeping the temperature at 150 ℃ for 5 hours, taking out the mixed solution in the reaction kettle, putting the mixed solution into a magnetic field with the magnetic field intensity of 320kA/m, naturally cooling to room temperature, and collecting bottom precipitate under the magnetic field to obtain the solution containing nickel ions.
It should be explained that sodium citrate with a dose of 23.3g can also be directly added into the yellow solution obtained at the end of the step (3), the temperature is kept at 150 ℃ for 5h, the mixed solution in the reaction kettle is taken out, the mixed solution is placed into a magnetic field with the magnetic field intensity of 320kA/m, after natural cooling to the room temperature, a solution containing nickel ions is obtained, a red precipitate is generated at the bottom, and the iron concentration in the supernatant is 9.14 mg/L.
(5) Determination of reaction end-Point
And (3) judging that the reaction end point is reached when the iron content in the supernatant obtained in the step (4) is less than 10 mg/L.
And (4) detecting the solution finally obtained in the step (4), wherein the concentration of nickel ions is 4902mg/L, and the concentration of iron is 8.2mg/L, and considering that the reaction end point is reached.
In another embodiment, in the step (4), k is 1.9, when the sodium citrate dosage is calculated to be 2149mg, the temperature is kept at 150 ℃ for 5h, and after the sodium citrate is naturally cooled to room temperature, the concentration of iron ions in the supernatant is 388 mg/L. At this point, further iron removal is required to supplement nitrate. The dosage is according to the formula
C3＝4.5C4-b×lgC5Formula (3);
wherein, C3The dosage of the nitrate is calculated by mol/L; c4The iron concentration in the supernatant is calculated by mol/L; c5The concentration of dissolved oxygen in the solution is shown in mol/L; and b is the filling degree of the reaction kettle.
After calculation, the amount of nitrate added was 0.35 mol/L. And keeping the temperature at 150 ℃ for 5 hours, taking out the mixed liquid in the reaction kettle, putting the mixed liquid into a magnetic field with the magnetic field intensity of 320kA/m, naturally cooling to room temperature, and then obtaining the supernatant with the iron concentration of 6.44mg/L to reach the reaction end point.
Specifically, the added nitrate is one of sodium nitrate and potassium nitrate, or a mixture of sodium nitrate and potassium nitrate.
(6) Product collection
Drying the magnetic field separated solid at 105 deg.C for 3h to obtain red powder, wherein FIG. 2 is X-ray diffraction diagram of sample of the magnetic field separated solid; as shown in fig. 2, the sample composition is characterized as hematite, with a purity of 98.2% and a nickel content of 0.05%, meeting the third-level quality standard for fine iron powder.
FIG. 3 is a scanning electron microscopy analysis of a magnetically separated solid according to the present application, as shown in FIG. 3, showing the EDS spectrum of Fe in the precipitated product obtained by the method of the present application, but no EDS spectrum signal of Ni, indicating that the Ni content in the product is low and cannot be detected.
(7) Supernatant characteristics and uses
In one embodiment, the concentration of nickel in the supernatant of the step (5) is 4855 mg/L-2450 mg/L, the concentration of iron is 3.7 mg/L-10 mg/L, the TOC value of the supernatant is 3.1 mg/L-6.5 mg/L, and the pH is 1.2-2.3; and adjusting the pH value of the final supernatant to 10-11 by using alkali, standing and precipitating for 8-12 h, collecting bottom precipitate, and drying at 105 ℃ for 2h to obtain the nickel oxide with the purity of 95.5-99.2%.
In this embodiment, the supernatant obtained in step (5) contains 4902mg/L nickel ions, 8.2mg/L iron, and 1.25 pH, and can be directly used for preparing electrophoresis solution.
And (3) adjusting the pH value of the supernatant to 10 by using sodium hydroxide, standing and precipitating for 10 hours, collecting bottom precipitates, and drying at 105 ℃ for 2 hours to obtain nickel oxide powder with the purity of 95.7%.
While the preferred embodiments of the present application have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all alterations and modifications as fall within the scope of the application. It will be apparent to those skilled in the art that various changes and modifications may be made in the present application without departing from the spirit and scope of the application. Thus, if such modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include such modifications and variations as well.
Claims (10)
1. A method for recovering nickel in nickel-containing wastewater by using ferric salt precipitation is characterized by comprising the following steps:
(1) adjusting the pH value of the nickel-containing wastewater to 7-9, uniformly stirring and mixing the adjusted nickel-containing wastewater with ferric salt under the electro-Fenton process condition, and continuously stirring to generate a first mixture, wherein the ferric salt is one of polymeric ferric chloride and polymeric ferric sulfate, or the mixture of the polymeric ferric chloride and the polymeric ferric sulfate;
(2) taking supernatant liquid 2cm below the liquid level of the first mixture, performing full spectrum scanning within the wavelength range of 300-360 nm, recording the light absorption value as A, performing dA/d lambda differential calculation, and detecting the inflection point of data by using a counter; adding persulfate when two inflection points are detected, stirring and mixing for 30-1 h, standing for 10-20 min, then carrying out dA/d lambda differential calculation again within the range of 300-360 nm of wavelength lambda, stopping adding persulfate when one inflection point is detected, stopping stirring, finishing the Fenton reaction, collecting a first precipitate generated by the Fenton reaction, and standing the first precipitate for 18-36 h;
(3) mixing part of the first precipitate with nitric acid, wherein the volume ratio of the mixed part of the first precipitate to the nitric acid is 3-5, the stirring speed is 60-180 rpm, and continuously stirring for 0.5-5 h to obtain a second mixture;
(4) continuously adding the first precipitate into the second mixture, wherein the adding amount is 0.5-1.5% of the volume of the second mixture, continuously stirring for 0.5-5 h to obtain a third mixture, and measuring the pH value of the supernatant of the third mixture;
(5) repeating the step (4) until the pH value of the supernatant of the mixture obtained in the step (4) is 0.4-1, stopping adding the first precipitate, continuously stirring for 2-5 h, and collecting the obtained first supernatant for later use;
(6) placing the first supernatant into a closed reaction kettle, heating and keeping the temperature constant, then carrying out magnetic separation to obtain a second supernatant and a second precipitate, and detecting the TOC value and the iron content of the second supernatant;
(7) in response to that the iron content in the second supernatant exceeds 10mg/L, adding sodium citrate into the second supernatant, putting the liquid added with the sodium citrate into a closed reaction kettle, heating and keeping the temperature constant, and then carrying out magnetic separation to obtain a third supernatant and a third precipitate; (8) supplementing nitrate into the third supernatant in response to the iron content in the third supernatant exceeding 10mg/L to obtain a fourth supernatant, wherein the fourth supernatant is a final supernatant, and finishing the reaction; in response to that the iron content in the third supernatant is less than 10mg/L, the third supernatant is a final supernatant, and the reaction is ended;
(9) and directly using the final supernatant to prepare an electrophoretic solution or an electroplating solution, or adjusting the pH value of the final supernatant to 10-11 by using alkali, standing and precipitating for 8-12 h, collecting bottom precipitate, and drying at 105 ℃ for 2h to obtain the nickel oxide with the purity of 95.5-99.2%.
2. The method according to claim 1, wherein in the step (1), the anode of the electro-Fenton process is a titanium dioxide electrode plate, the cathode is a stainless steel electrode plate, and the current intensity is 10mA/cm2～15mA/cm2The stirring speed is 120rpm to 300 rpm.
3. The method of claim 1, wherein in step (1), the molar ratio of the iron salt added to the nickel in the solution is 5-20: 1.
4. The method according to claim 1, wherein in the step (2), the addition amount of the persulfate is represented by the formula:
formula (1) where m is α × V/S;
wherein alpha is constant and takes 1.8 multiplied by 10-3(ii) a V is the volume of the first mixture solution in m3(ii) a S is the area of the integral area under the wavelength of 300 nm-360 nm; m is the addition of persulfate in kg.
5. The method as claimed in claim 1, wherein in the step (6), the first supernatant is placed into a closed reaction kettle according to the filling degree of 60% -80%, the first supernatant is heated to 120-160 ℃, the temperature is kept constant for 5-6 h, and then magnetic separation is carried out, wherein the magnetic field intensity of the magnetic separation is 300 kA/m-500 kA/m.
6. The method of claim 1, wherein the second supernatant is supplemented with sodium citrate in step (7) in an amount calculated according to the following formula:
m＝(kC2-C1) Formula (2) of x V/2;
wherein, C in the formula1The TOC value of the second supernatant is measured in mg/L; c2The concentration of iron in the second supernatant is measured in mg/L; k is a constant and has a value range of 1.3-1.9; m is the addition amount of sodium citrate in mg.
7. The method of claim 1, wherein the dosage of nitrate added in step (8) is calculated according to the following formula:
C3＝4.5C4-b×lgC5formula (3);
wherein, C3The dosage of the nitrate is calculated by mol/L; c4The iron concentration in the third supernatant is measured in mol/L; c5The concentration of dissolved oxygen in the solution is shown in mol/L; and b is the filling degree of the reaction kettle.
8. The method of claim 7, wherein the nitrate is added as one of sodium nitrate, potassium nitrate, or a mixture of sodium nitrate and potassium nitrate.
9. The method of claim 1, wherein the second precipitate and the third precipitate are dried at 105 ℃ for 2 to 5 hours, and the iron oxide content of the product obtained after drying is 96.7% or more.
10. The method of claim 1, wherein the final supernatant in step (8) has a nickel concentration of 4855mg/L to 2450 mg/L, an iron concentration of 3.7mg/L to 10mg/L, a supernatant TOC value of 3.1mg/L to 6.5mg/L, and a pH of 1.2 to 2.3.
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