A method for directional recovery of pickling wastewater

Abstract

The application provides a directional recovery method of pickling wastewater. The treatment method of the application uses a complexing agent to cause the complex of fluorine and iron, chromium and nickel to be dissociated into free fluorine, and then uses nanofiltration to realize the separation of free fluorine and iron, chromium and nickel, and adds a fluorine removal agent to the fluorine-rich solution after separation to realize fluorine recovery, thereby solving the problem that the complex state fluorine is difficult to recover. Meanwhile, the treatment method adds a reducing agent to the solution rich in iron, chromium and nickel after separation to cause the trivalent iron ion to be reduced to divalent iron ion, and then uses ion exchange resin to preferentially adsorb chromium and nickel, desorbs the ion exchange resin containing chromium and nickel, and realizes the graded recovery of chromium and nickel through step-by-step pH regulation. Finally, the effluent after the adsorption of the ion exchange resin can also realize iron recovery through pH regulation, thereby solving the problem that iron and chromium are difficult to separate due to the close pH of the precipitation.

Description

Technical Field

[0001] This invention relates to the field of biotechnology, and in particular to a method for the targeted recycling of pickling wastewater. Background Technology

[0002] Pickling is a crucial step in steel production and processing. Its core function is to treat the steel surface with an acid solution to effectively remove the iron oxide scale formed during processes such as annealing, eliminate chromium-depleted areas on the metal surface, and ultimately lay the foundation for the formation of a uniform and stable anti-rust film on the steel surface. In actual production, a mixed acid system of nitric acid (HNO3) and hydrofluoric acid (HF) is commonly used to treat the steel surface during pickling. However, the above pickling process generates a large amount of wastewater with complex composition, the main chemical component of which is hydrogen ions (H+). + ), nitrate ions (NO3) - Hydrofluoric acid (HF), as well as nitrates of metals such as iron, chromium, and nickel (e.g., Fe(NO3)3, Cr(NO3)3, Ni(NO3)2) and fluorides (e.g., FeF3, FeF2) + CrF3, CrF2 + NiF + wait).

[0003] Currently, the steel production industry discharges a huge amount of pickling wastewater annually. This wastewater contains substances such as fluorine (F), iron (Fe), chromium (Cr), and nickel (Ni), which are not only important resources but also pollutants requiring strict control. Currently, the industry primarily uses lime neutralization to treat pickling wastewater. However, this method has significant drawbacks: firstly, lime neutralization generates a large amount of sludge containing chromium and nickel, which can only be disposed of as hazardous waste, significantly increasing the company's hazardous waste disposal costs; secondly, resources with high recovery value, such as F, Fe, Cr, and Ni, contained in the wastewater are not effectively utilized, resulting in serious resource waste. Therefore, there is an urgent need to develop a treatment method for steel pickling wastewater that can both reduce treatment costs and achieve efficient and targeted resource recovery. Summary of the Invention

[0004] This invention provides a method for treating pickling wastewater, comprising the following steps:

[0005] Step 1: Use a de-complexing agent to treat the pickling wastewater to obtain a de-complexing solution;

[0006] Step 2: Perform nanofiltration on the complexation solution to obtain permeate and concentrate;

[0007] Step 3: Mix the produced water and the defluorinating agent to obtain a fluoride-containing product;

[0008] Step 4: Mix the concentrated water and the reducing agent to obtain the reducing solution;

[0009] Step 5: Use ion exchange resin to adsorb chromium and nickel in the reducing solution to obtain ion exchange resin and effluent containing chromium and nickel;

[0010] Step 6: Desorb the ion exchange resin containing chromium and nickel to obtain a resin regeneration solution containing chromium and nickel;

[0011] Step 7: Adjust the pH of the chromium- and nickel-containing resin regeneration solution to 4-6 to obtain the chromium-containing product and the first supernatant;

[0012] Step 8: Adjust the pH of the first supernatant to 9-10 to obtain the nickel-containing product and the second supernatant;

[0013] Step 9: Adjust the pH of the effluent to 9-10 to obtain the iron-containing product and the third supernatant.

[0014] Step 10: Mix the third supernatant with the defluorinating agent to obtain the fluorinated product and the fourth supernatant.

[0015] The treatment method described above, wherein the conditions for the decomposition treatment include: a time of 0.5-1 h, a pH value of 2.5-3.5; and / or,

[0016] Anti-complexing agents include at least one of citric acid and oxalic acid;

[0017] Preferably, when the complex-resolving agent is citric acid, the amount of the complex-resolving agent added is 1-1.5 times the molar amount of the metal element in the pickling wastewater; the molar amount of the metal element is the sum of the molar amounts of iron, chromium, and 2 / 3 of the molar amounts of nickel.

[0018] Preferably, when the anti-complexing agent is oxalic acid, the amount of anti-complexing agent added is 1-1.5 times the molar amount of the metal element in the pickling wastewater; the molar amount of the metal element is the sum of 3 / 2 the molar amount of iron, 3 / 2 the molar amount of chromium, and the molar amount of nickel.

[0019] The processing method described above includes nanofiltration conditions of 20-40°C, 2-6 MPa, molecular weight cutoff of 150-600 Da, and recovery rate of 40-75%.

[0020] In the treatment method described above, the defluorinating agent includes at least one of calcium chloride and lime.

[0021] In the treatment method described above, the reducing agent includes at least one of iron powder, sodium thiosulfate, hydrogen sulfide, sulfide, sulfite, and bisulfite.

[0022] In the treatment method described above, the functional groups of the ion exchange resin include at least one of polyamino and iminodiacetic acid groups; and / or,

[0023] The adsorption conditions include a flow rate of 5-15 m / h and a pH of 3.5-5.

[0024] The processing method described above further includes: filtering the fourth supernatant and adjusting the pH to 1-3 to obtain a complex-dissolving agent.

[0025] The treatment method described above, wherein the filtration treatment comprises sequential ultrafiltration and nanofiltration; the conditions for ultrafiltration include a pH of 6-9, a pressure of 0.1-0.4 MPa, a temperature of 20-40°C, and a recovery rate of 85-95%; the conditions for nanofiltration include a pH of 6-9, a pressure of 2-8 MPa, a temperature of 20-40°C, and a recovery rate of 60-80%; or,

[0026] The filtration process consists of sequential sand filtration and nanofiltration; the nanofiltration conditions include a pH of 6-9, a pressure of 2-8 MPa, a temperature of 20-40℃, and a recovery rate of 60-80%; or,

[0027] The filtration process consists of sequential precision filtration and nanofiltration. The conditions for nanofiltration include a pH of 6-9, a pressure of 2-8 MPa, a temperature of 20-40℃, and a recovery rate of 60-80%.

[0028] This invention provides a treatment system for pickling wastewater, comprising a decomplexing module, a nanofiltration module, a reduction module, an adsorption module, and a desorption module connected in sequence; the nanofiltration module is also connected to a first fluorine recovery module; the desorption module is also connected to a chromium recovery module and a nickel recovery module in sequence; the adsorption module is also connected to an iron recovery module and a second fluorine recovery module in sequence.

[0029] The unwinding module is used to perform unwinding processing.

[0030] The nanofiltration module is used to perform nanofiltration processing;

[0031] The reduction module is used to provide the reducing agent for reduction processing;

[0032] The adsorption module is used to provide ion exchange resin for the adsorption of chromium and nickel.

[0033] The desorption module is used to desorb ion exchange resins containing chromium and nickel;

[0034] The first and second fluorine recovery modules are used to provide defluorinating agents for fluorine recovery.

[0035] The chromium recovery module is used to adjust the pH for chromium recovery;

[0036] The nickel recovery module is used to adjust the pH for nickel recovery;

[0037] The iron recovery module is used to adjust the pH for iron recovery.

[0038] The present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the above-described processing method.

[0039] The beneficial effects of this invention are as follows:

[0040] This invention uses a decomplexing agent to dissociate the complexes of fluorine with iron, chromium, and nickel into free fluorine (F). Nanofiltration is then used to separate the free fluorine from the iron, chromium, and nickel. A defluorinating agent is added to the separated fluorine-rich solution to recover the fluorine, thus solving the problem of difficult recovery of complexed F. Simultaneously, this method adds a reducing agent to the separated iron, chromium, and nickel-rich solution to promote the dissociation of Fe... 3+ Reduced to Fe 2+ Then, ion exchange resin is used to preferentially adsorb chromium and nickel. The ion exchange resin containing chromium and nickel is desorbed, and the pH is adjusted in stages to achieve the fractional recovery of Cr and Ni. Finally, the pH of the effluent after adsorption by the ion exchange resin can be adjusted to achieve iron recovery, thereby solving the problem of difficulty in separating iron and chromium precipitation due to their similar pH. Attached Figure Description

[0041] Figure 1 A schematic diagram of a pickling wastewater treatment system provided by the present invention;

[0042] Figure 2 This is a flowchart of a method for treating pickling wastewater according to an embodiment of the present invention. Detailed Implementation

[0043] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. 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.

[0044] Currently, the steel pickling industry generates a large amount of pickling wastewater containing fluorine (F), iron (Fe), chromium (Cr), and nickel (Ni). Existing pickling wastewater treatment methods generally use sodium hydroxide (NaOH) to adjust the pH value to recover Fe, Cr, and Ni, and then recover F resources through a defluorinating agent after recovering Fe, Cr, and Ni.

[0045] Through extensive research and experimentation, this invention has found that existing methods for treating pickling wastewater have the following shortcomings:

[0046] (1) The main forms of F in pickling wastewater are free F and complexed F. If Fe, Cr and Ni are recovered directly in the form of Fe(OH)3, Cr(OH)3 and Ni(OH)2 according to the existing treatment methods, it is easy to cause F and Fe, Cr and Ni complexes to precipitate together, which in turn leads to low recovery purity of Fe(OH)3, Cr(OH)3 and Ni(OH)2, and low recovery rate of F (only 40%-60%).

[0047] (2) The precipitation pH ranges of Fe(OH)3 and Cr(OH)3 are similar (Fe 3+ The initial precipitation occurs at a pH of approximately 2.5, Cr 3+ The initial precipitation occurs at a pH of approximately 3.5, making complete separation difficult by adjusting the pH, which further reduces the purity of Fe and Cr recovery.

[0048] To solve the above problems, this invention provides a method for treating pickling wastewater, which can not only recover F, Fe, Cr, and Ni, but also has a high recovery rate and the recovered F, Fe, Cr, and Ni have high purity.

[0049] The method for treating pickling wastewater provided by this invention includes the following steps:

[0050] Step 1: Use a de-complexing agent to treat the pickling wastewater to obtain a de-complexing solution;

[0051] Step 2: Perform nanofiltration on the complexation solution to obtain permeate and concentrate;

[0052] Step 3: Mix the produced water and the defluorinating agent to obtain a fluoride-containing product;

[0053] Step 4: Mix the concentrated water and the reducing agent to obtain the reducing solution;

[0054] Step 5: Use ion exchange resin to adsorb chromium and nickel in the reducing solution to obtain ion exchange resin and effluent containing chromium and nickel;

[0055] Step 6: Desorb the ion exchange resin containing chromium and nickel to obtain a resin regeneration solution containing chromium and nickel;

[0056] Step 7: Adjust the pH of the chromium- and nickel-containing resin regeneration solution to 4-6 to obtain the chromium-containing product and the first supernatant;

[0057] Step 8: Adjust the pH of the first supernatant to 9-10 to obtain the nickel-containing product and the second supernatant;

[0058] Step 9: Adjust the pH of the effluent to 9-10 to obtain the iron-containing product and the third supernatant.

[0059] Step 10: Mix the third supernatant with the defluorinating agent to obtain the fluorinated product and the fourth supernatant.

[0060] Specifically, in step 1, a complex-dissolving agent is used to treat the pickling wastewater to dissociate the complexes of F with Fe, Cr, and Ni into free F, thereby obtaining a complex-dissolving solution.

[0061] The above-mentioned decomposition treatment can be carried out under stirring conditions to improve the homogeneity of the reaction system. The stirring speed can be 300-500 rpm.

[0062] In step 2, the main components of the anti-complex solution are HF and F. - NO3 - The complexes of Fe, Cr, Ni, and the complexing agent were subjected to nanofiltration. The permeate obtained through the nanofiltration membrane was the product water, and the concentrate that did not permeate through the nanofiltration membrane and was retained was the concentrated water. Most of the HF and F were retained. - NO3 - In the product water, the complexes of Fe, Cr, Ni and the decomplexing agent remain in the concentrate water.

[0063] In step 3, mixing the product water and the defluorinating agent can yield a fluoride precipitate, which can be dehydrated and dried to obtain a fluoride-containing product.

[0064] In the above steps, lime or sodium hydroxide can be added when mixing the permeate water and the defluorinating agent to adjust the pH to 6-8. This provides a suitable chemical environment for the reaction between the defluorinating agent and fluoride ions, promoting the full combination of fluoride ions and the effective components (such as calcium salts) in the defluorinating agent to form stable fluoride precipitates. If the pH value is too low, it may inhibit the ionization or dissolution of the defluorinating agent, reducing its reactivity with fluoride ions; if the pH value is too high, it may cause the generated fluoride precipitate to dissolve or cause side reactions in the defluorinating agent, thus affecting the defluorination effect. In addition, the main components of lime are calcium oxide or calcium hydroxide. On the one hand, it can effectively adjust the pH value by generating hydroxide ions through its reaction with water; on the other hand, the calcium ions it contains can also react directly with fluoride ions to form insoluble calcium fluoride precipitates, further enhancing the defluorination effect and forming a synergistic effect with the defluorinating agent.

[0065] In the above steps, the process of mixing the permeate water and the defluorinating agent for defluorination can employ either single-stage or two-stage coagulation and sedimentation, and this invention is not limited thereto. For example, when the fluoride ion concentration in the permeate water is low, single-stage coagulation and sedimentation can be used. The permeate water is fed into the single-stage coagulation and sedimentation tank along with the defluorinating agent. The defluorinating agent reacts with the fluoride ions to form insoluble fluoride flocs or precipitates. Under stirring, these flocs and precipitates aggregate to form larger particles, achieving rapid solid-liquid separation through sedimentation, thereby recovering fluoride resources. When the fluoride ion concentration in the permeate water is high, two-stage coagulation and sedimentation can be used. If unreacted fluoride ions and small fluoride particles still exist in the system after the single-stage coagulation and sedimentation, a second-stage coagulation and sedimentation tank can be added, and the defluorinating agent is added again to allow the remaining fluoride ions to fully react and form precipitates, thereby significantly improving the fluoride recovery rate.

[0066] In step 4, mixing the concentrated water and the reducing agent can promote Fe 3+ Reduced to Fe 2+ The resulting reducing solution is used for subsequent use of ion exchange resin to preferentially adsorb Cr. 3+ Ni 2+ Provide prerequisites.

[0067] The reduction reaction described above can be carried out under stirring conditions to improve the homogeneity of the reaction system. The stirring speed can be 300-500 rpm.

[0068] The reduction reaction time can be controlled within 0.5-1.5 hours to ensure a complete decomposition reaction without wasting resources and costs due to excessive time.

[0069] After the reduction reaction is completed, alkaline substances such as sodium hydroxide or lime can be added to the reducing solution to adjust the pH to 3-5, so as to enhance the adsorption effect of the subsequent ion exchange resin on Cr and Ni and avoid the resin adsorption capacity from decreasing due to too low pH.

[0070] In step 5, because the ion exchange resins have different selective adsorption orders for different ions (Fe... 3+ >Hg 2+ >Cu 2+ >Pb 2+ >Ni 2+ >Cr 3+ >Zn 2+ >Cd 2+ >Co 2+ >Fe 2+ >Mn 2+ >Al 3+ >>>Ca 2+ >Mg 2+ >Sr 2+ >Ba 2+ >>Li + Na+ Therefore, compared to Fe 2+ Ion exchange resins will preferentially adsorb Cr 3+ and Ni 2+ By using ion exchange resins to adsorb chromium and nickel from a reducing solution, ion exchange resins containing chromium and nickel and effluent containing iron can be obtained.

[0071] In step 6, after the ion exchange resin containing chromium and nickel is saturated, the ion exchange resin containing chromium and nickel can be desorbed to obtain a resin regeneration solution containing chromium and nickel.

[0072] This invention does not limit the specific method of desorption treatment; conventional techniques in the art can be used. For example, acid regeneration can be used for desorption treatment, utilizing H+ in hydrochloric acid or sulfuric acid with a concentration of 3-10% (w / v). + With Cr already adsorbed on the ion exchange resin 3+ Ni 2+ A competitive exchange occurs, causing the ion exchange resin to revert to an adsorption-active H-type resin. This H-type resin can be used directly, or, depending on the specific circumstances, those skilled in the art can use sodium hydroxide to convert the H-type resin into a Na-type resin for use.

[0073] In one embodiment of the present invention, 10% (w / v) sulfuric acid is used for desorption treatment, and the desorption flow rate is controlled at 2-4 m / h. Each liter of adsorption saturated ion exchange resin is equivalent to consuming 60-120 g of 100% (w / v) sulfuric acid. The total content of Cr2(SO4)3 and NiSO4 in the obtained chromium and nickel-containing resin regeneration solution is about 3.5-8%.

[0074] In step 7, adjusting the pH of the chromium- and nickel-containing resin regeneration solution to 4-6 yields a chromium-containing product and a first supernatant.

[0075] This invention does not limit the type of reagent used to adjust pH. For example, sodium hydroxide can be used to adjust pH. In this case, the chromium-containing product obtained is Cr(OH)3 precipitate. After solid-liquid separation, the chromium-containing product and the first supernatant can be obtained.

[0076] In step 8, the pH of the first supernatant is adjusted to 9-10 to obtain the nickel-containing product and the second supernatant.

[0077] This invention does not limit the type of reagent used to adjust pH. For example, sodium hydroxide can be used to adjust pH. In this case, the nickel-containing product obtained is Ni(OH)2 precipitate. After solid-liquid separation, the nickel-containing product and the second supernatant can be obtained.

[0078] If hydrochloric acid or sulfuric acid is used for acid regeneration in step 6, and sodium hydroxide is used to adjust the pH in steps 7 and 8, then the main component of the second supernatant is NaCl or Na2SO4, which can be sold as a by-product after evaporation and crystallization.

[0079] In actual production, steps 7 and 8 can be achieved through a two-stage chemical reaction sedimentation tank. That is, after the resin regeneration liquid containing chromium and nickel is put into the first-stage chemical reaction sedimentation tank, the pH is adjusted to 4-6 with alkaline substances such as sodium hydroxide, so that Cr precipitates out in the form of Cr(OH)3. The first supernatant is then put into the second-stage chemical reaction sedimentation tank, where the pH is adjusted to 9-10 with alkaline substances such as sodium hydroxide, so that Ni precipitates out in the form of Ni(OH)2.

[0080] In step 9, Fe, Cr, and Ni have been removed from the effluent containing iron in step 5, and the main component is Fe. 2+ By resolving the complex of the complexing agent and adjusting its pH to 9-10, an iron-containing product and a third supernatant can be obtained.

[0081] This invention does not limit the type of reagent used to adjust pH. For example, sodium hydroxide can be used to adjust pH. In this case, the iron-containing product obtained is Fe(OH)2 precipitate and a small amount of Fe(OH)3 precipitate. After solid-liquid separation, the iron-containing product and the third supernatant can be obtained.

[0082] In step 10, the third supernatant from step 9 is mixed with the defluorinating agent to obtain a fluorine-containing product and a fourth supernatant.

[0083] In the above steps, a small amount of free F ions still exist in the third supernatant. Therefore, adding a defluorinating agent and mixing can maximize the recovery of fluorine.

[0084] When mixing the third supernatant with the defluorinating agent, hydrochloric acid or sulfuric acid can be added to adjust the pH to 6-8, thereby providing a suitable chemical environment for the reaction between the defluorinating agent and fluoride ions, promoting the full combination of fluoride ions and the effective components (such as calcium salts) in the defluorinating agent to form stable fluoride precipitates.

[0085] Furthermore, the defluorinating agent can be calcium chloride.

[0086] Furthermore, the concentration of calcium chloride can be 20-40% (w / v).

[0087] In short, this invention first uses a decomplexing agent to dissociate the complexes of F with Fe, Cr, and Ni into free F. Then, nanofiltration is used to separate the free F from the metal ions (Fe, Cr, Ni). A defluorinating agent is added to the separated F-rich solution (i.e., the product water) to recover F, thus solving the problem of difficult recovery of complexed F in existing technologies. Simultaneously, this invention adds a reducing agent to the separated Fe, Cr, and Ni-rich solution (i.e., the concentrated water) to promote the dissociation of Fe... 3+ Reduced to Fe 2+ Then, ion exchange resin is used for adsorption, and ion exchange resin is effective against Fe. 2+ Its adsorption capacity is weaker than that of Cr. 3+ Ni 2+ Therefore, it will preferentially adsorb Cr. 3+ and Ni 2+ For Cr 3+ and Ni 2+ The ion exchange resin is used for desorption treatment, and then the pH is adjusted in stages to achieve fractional recovery of Cr and Ni. At this point, the recovery rate and purity of Cr and Ni are significantly improved. Furthermore, by adjusting the pH of the effluent after adsorption by the ion exchange resin, Fe can also be recovered, thus solving the Fe problem. 3+ and Cr 3+ The problem of separation due to near-close pH levels during precipitation is addressed. Finally, adding a defluorinating agent to the supernatant after Fe recovery allows for secondary recovery of remaining fluorine, maximizing fluorine recovery. Through the above treatment method, this invention effectively improves the recovery rate of fluorine, iron, chromium, and nickel from pickling wastewater, and significantly enhances the purity of the recovered fluorine, iron, chromium, and nickel products. Furthermore, this invention is simple and convenient to operate, using inexpensive and readily available raw materials. It not only directly generates product revenue, especially from high-purity recovered products, but also significantly reduces the cost of pickling wastewater treatment. In addition, this invention provides new practical ideas for blocking the diffusion of fluorine, chromium, and nickel, protecting water and soil ecology and human health, reducing hazardous waste generation, and facilitating wastewater reuse or near-zero discharge. It also lays the foundation for promoting resource recycling, recovering industrial resources, and achieving a green transformation.

[0088] It is understood that the processing method of the present invention does not limit the order of steps 3 and 4. Step 3 can be performed first and then step 4, or step 4 can be performed first and then step 3, or steps 3 and 4 can be performed simultaneously.

[0089] In the processing method of the present invention, the order of steps 6 and 9 is not limited. Step 6 can be performed first and then step 9, or step 9 can be performed first and then step 6, or steps 6 and 9 can be performed simultaneously.

[0090] For example, after step 1 is completed, step 2 is performed. After step 2 is completed, steps 3 and 4 can be performed simultaneously or separately. After step 4 is completed, step 5 is performed. After step 5 is completed, steps 6 and 9 can be performed simultaneously or separately. After step 6 is completed, step 7 is performed, followed by step 8. After step 9 is completed, step 10 is performed.

[0091] Based on the above research, this invention also found that there are two main types of commonly used decomposition treatments. One type involves adding a strong acid (such as hydrochloric acid or sulfuric acid) as a decomposition agent to promote the formation of more stable HF from the F in Fe-F, Cr-F, and Ni-F complexes, thereby releasing Fe ions, Cr ions, and Ni ions. The other type involves selecting a weak acid (such as citric acid or oxalic acid) with a stronger complexing ability for Fe, Cr, and Ni than F, as a decomposition agent to form complexes of Fe, Cr, Ni, and the weak acid, thereby releasing F ions.

[0092] Based on long-term research and experiments, this invention has found that when strong acids are used as decomplexing agents, subsequent nanofiltration treatment is ineffective in separating HF from hydrochloric acid and sulfuric acid, requiring additional processes for separation and resulting in a long process flow. Therefore, in step 1, the decomplexing agent may include at least one of citric acid and oxalic acid. Using the aforementioned weak acid as a decomplexing agent can promote the formation of complexes between metal ions and the weak acid, releasing F ions from the complexes, thus achieving a high recovery rate of F with simple and convenient operation.

[0093] In a preferred embodiment, when the complexing agent is citric acid, the amount of the complexing agent added is 1-1.5 times the molar amount of the metal element in the pickling wastewater; the molar amount of the metal element is the sum of the molar amounts of iron, chromium, and 2 / 3 of the molar amounts of nickel.

[0094] In pickling wastewater, iron is mainly in the form of Fe. 3+ Chromium exists primarily as Cr. 3+ Nickel exists primarily in the form of Ni. 2+ It exists in a certain form, and citric acid is a tribasic acid, so 1 mol of Fe... 3+ Reacts with 1 mol of citric acid, 1 mol of Cr 3+ Reacts with 1 mol of citric acid, 1 mol of Ni 2+ It reacts with 2 / 3 mol of citric acid. Therefore, when citric acid is the uncoating agent, the amount of uncoating agent added is 1-1.5 times the sum of the molar amounts of iron, chromium, and 2 / 3 of nickel.

[0095] Similarly, oxalic acid is a dicarboxylic acid, so 1 mol of Fe... 3+ Reacts with 3 / 2 mol of oxalic acid, 1 mol of Cr 3+ Reacts with 3 / 2 mol of oxalic acid, 1 mol of Ni2+ It reacts with 1 mol of oxalic acid. Therefore, when the complexing agent is oxalic acid, the amount of complexing agent added is 1 to 1.5 times the sum of 3 / 2 the molar amount of iron, 3 / 2 the molar amount of chromium, and the molar amount of nickel.

[0096] In the above technical solution, the conditions for the decomposition treatment include: a time of 0.5-1 h and a pH value of 2.5-3.5. Adjusting the time and pH value of the decomposition treatment is beneficial for precisely controlling the decomposition reaction process and guiding it towards the target direction.

[0097] Specifically, the decomplexing treatment can be achieved by adding alkaline substances such as sodium hydroxide or lime to adjust the pH of the decomplexing treatment system to 2.5-3.5, so as to enhance the decomplexing effect of the decomplexing agent on the complexes of F and Fe, Cr, and Ni.

[0098] In the above technical solution, the nanofiltration treatment conditions include: a temperature of 20-40℃, a pressure of 2-6 MPa, a molecular weight cutoff of 150-600 Da, and a recovery rate of 40-75%, thereby accurately separating fluoride ions and metal-uncomplexing agent complexes. Testing showed that within the above range, Fe in the concentrated water... 3+ Cr 3+ Ni 2+ The retention rate is ≥90%.

[0099] Furthermore, the nanofiltration membrane element used in the above nanofiltration process can be an acid-resistant special membrane element, which is more suitable for the above nanofiltration conditions.

[0100] In the above technical solution, the defluorinating agent includes at least one of calcium chloride and lime.

[0101] Lime, as a defluorinating agent, can both regulate pH and provide calcium. 2+ Used for defluorination; calcium chloride, as a defluorinating agent, is mainly used to provide Ca. 2+ .

[0102] In a preferred embodiment, lime can be added first to adjust the pH value. When the lime provides Ca... 2+ Insufficient and pickling wastewater F - Complete reaction (i.e., Ca) 2+ / F - When the molar ratio is <0.5, add calcium chloride to supplement the Ca. 2+ , so that the total Ca added 2+ Excess (approximately 200-600 mg / L). In the above technical solution, the reducing agent includes at least one of iron powder, sodium thiosulfate, hydrogen sulfide, sulfides, sulfites, and bisulfites, which can effectively promote Fe... 3+ Reduced to Fe 2+ .

[0103] Furthermore, the concentration of calcium chloride can be 20-40% (w / v).

[0104] In the above technical solution, the functional groups of the ion exchange resin include at least one of polyamino and iminodiacetic acid groups. For example, it can be Purolite MTS9300 or 9850.

[0105] Anti-complexing agents such as citric acid can convert iron-fluorine complexes and chromium-fluorine complexes into iron-citric acid complexes and chromium-citric acid complexes, releasing free fluorine. Therefore, when the functional groups of ion exchange resin are polyamino or iminodiacetic acid groups, the complexing ability of polyamino or iminodiacetic acid groups is stronger than that of citric acid, and they can replace and adsorb Cr and Ni complexed by citric acid.

[0106] In the above technical solution, the adsorption conditions (i.e. the operating conditions of ion exchange resin adsorption) include: flow rate of 5-15 m / h and pH of 3.5-5.

[0107] During the adsorption process of ion exchange resins, controlling the flow rate and pH within the aforementioned ranges ensures adsorption efficiency, selectivity, and stability. If the flow rate is too low, although it prolongs the contact time between the reducing solution and the ion exchange resin, allowing the target ions to fully bind with the resin's functional groups, it reduces the throughput per unit time, leading to low process efficiency and potentially causing unnecessary side reactions due to excessive contact. If the flow rate is too high, the residence time of the reducing solution in the ion exchange resin is too short, and the target ions are discharged before they have sufficient time to exchange with the resin, significantly reducing the adsorption rate and wasting resources. Within the pH range of 3.5-5, Cr... 3+ Ni 2+ It mainly exists in the form of free ions or stable simple ions, with a relatively thin hydrated ion layer, making it easier to undergo exchange reactions with resin functional groups. At the same time, the weakly acidic environment can inhibit Fe 2+ Adsorption of interfering ions reduces their influence on Cr. 3+ Ni 2+ Competition for adsorption sites enhances the resin's selectivity for target ions. Furthermore, this pH range prevents the ion exchange resin from experiencing a decrease in adsorption capacity due to excessive acidity or from hydrolyzing target ions to form hydroxide precipitates due to neutrality, ensuring that the ion exchange resin remains in an active state of highly efficient adsorption.

[0108] In addition, in order to further improve the resource utilization and reduce the cost of the processing method of the present invention, the above processing method further includes: filtering the fourth supernatant and adjusting the pH to 1-3 to obtain a complex-dissolving agent.

[0109] The fourth supernatant mainly consists of a salt solution of the complex-resolving agent. For example, if the complex-resolving agent is oxalic acid, the main component of the third supernatant is oxalate. Filtering the third supernatant sequentially concentrates the salt solution of the complex-resolving agent. Then, adjusting the pH to 1-3 under acidic conditions converts it into the complex-resolving agent. This complex-resolving agent can then be returned to step 1 for further use.

[0110] Further, in an optional embodiment, the filtration process consists of sequential ultrafiltration and nanofiltration; the ultrafiltration conditions include a pH of 6-9, a pressure of 0.1-0.4 MPa, a temperature of 20-40°C, and a recovery rate of 85-95%; the nanofiltration conditions include a pH of 6-9, a pressure of 2-8 MPa, a temperature of 20-40°C, and a recovery rate of 60-80%.

[0111] The ultrafiltration membrane used in ultrafiltration treatment and the nanofiltration membrane used in nanofiltration treatment can be conventional commercially available membrane elements. The ultrafiltration permeate can be reused as production water, while the nanofiltration permeate is mixed with other permeate and discharged.

[0112] In one optional embodiment, the filtration process consists of sequential sand filtration and nanofiltration; the nanofiltration conditions include a pH of 6-9, a pressure of 2-8 MPa, a temperature of 20-40°C, and a recovery rate of 60-80%.

[0113] The nanofiltration membrane used in nanofiltration treatment can be a conventional commercially available membrane element. The sand filtration permeate can be reused as production water, while the nanofiltration permeate is mixed with other permeate and discharged.

[0114] In one optional embodiment, the filtration process is a sequential process of precision filtration and nanofiltration; the nanofiltration conditions include a pH of 6-9, a pressure of 2-8 MPa, a temperature of 20-40°C, and a recovery rate of 60-80%.

[0115] Precision filtration can use precision filters (or security filters), while nanofiltration can use conventional commercially available membrane elements. Precision filtration permeate can be reused as production water, while nanofiltration permeate is mixed with other permeate and discharged.

[0116] The present invention also provides a treatment system for pickling wastewater, comprising a decomposition module, a nanofiltration module, a reduction module, an adsorption module, and a desorption module connected in sequence; the nanofiltration module is also connected to a first fluorine recovery module; the desorption module is also connected to a chromium recovery module and a nickel recovery module in sequence; the adsorption module is also connected to an iron recovery module and a second fluorine recovery module in sequence.

[0117] For example, the processing system is visible Figure 1The system comprises the following modules: a decomplexing module for performing decomplexing treatment (i.e., step 1 of the method); a nanofiltration module for performing nanofiltration treatment (i.e., step 2 of the method); a reduction module for providing a reducing agent for reduction treatment (i.e., step 4 of the method); an adsorption module for providing ion exchange resin for adsorption treatment of chromium and nickel (i.e., step 5 of the method); a desorption module for desorbing chromium and nickel-containing ion exchange resin (i.e., step 6 of the method); a first fluorine recovery module and a second fluorine recovery module for providing a defluorinating agent for fluorine recovery (i.e., step 3 or step 10 of the method); a chromium recovery module for adjusting pH for chromium recovery (i.e., step 7 of the method); a nickel recovery module for adjusting pH for nickel recovery (i.e., step 8 of the method); and an iron recovery module for adjusting pH for iron recovery (i.e., step 9 of the method).

[0118] Finally, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the above-described processing method.

[0119] The technical solution of this application will be further explained below with reference to specific embodiments. Experimental methods without specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise specified, all reagents used are commercially available or obtained through public channels.

[0120] Example 1:

[0121] This embodiment provides a method for treating pickling wastewater, the process of which is as follows: Figure 2 As shown, it includes the following steps:

[0122] (1) Decomposition: Add 93.0 g of decomposition agent citric acid to 10 L of stainless steel pickling wastewater to be treated for decomposition treatment. Add NaOH to adjust the pH to 2.5 and stir the reaction at 400 rpm for 30 min with a mechanical stirrer to promote the decomposition of F in the stainless steel pickling wastewater into free F, and obtain the decomposition treatment solution.

[0123] (2) Nanofiltration: The solution obtained in step (1) is subjected to nanofiltration (NF) treatment. The permeate obtained through the NF membrane is NF permeate, and the concentrate that does not permeate through the membrane and is retained is NF concentrate. The NF treatment temperature is 35°C, the pressure is 4MPa, the recovery rate is 75%, the NF membrane element is an acid-resistant membrane element, and the molecular weight cutoff is 400 Da.

[0124] (3) F recovery: Lime is added to the NF permeate obtained in step (2) to adjust the pH to 6.5, and CaF2 sludge is obtained. The CaF2 sludge is dewatered and dried to obtain CaF2 product.

[0125] (4) Fe 3+ Reduction: Add 4.63 g of iron powder to the NF concentrate obtained in step (2), stir the mixture at 400 rpm for 1 h with a mechanical stirrer, and adjust the pH to 4 with NaOH after the reaction is complete to obtain the reduction treatment solution.

[0126] (5) Adsorption: The reduced solution obtained in step (4) is passed through an ion exchange resin (with iminodiacetic acid groups) with a packing volume of 10 L at a filtration rate of 10 m / h. Cr and Ni in the resin will be adsorbed by the ion exchange resin. When the ion exchange resin is saturated, it is regenerated using 8 L of 10% (w / v) H2SO4 at a regeneration flow rate of 2 m / h to obtain a regenerated solution. The regenerated solution contains Cr. 2( The total content of SO4)3 and NiSO4 is approximately 7.5%.

[0127] (6) Cr and Ni graded recovery: NaOH is added to the regenerated liquid obtained in step (5) to adjust the pH to 6, so that Cr is recovered in the form of Cr(OH)3 precipitate to obtain Cr(OH)3 product; after solid-liquid separation, NaOH is added to the supernatant to adjust the pH to 10, so that Ni is recovered in the form of Ni(OH)2 precipitate to obtain Ni(OH)2 product; the main component of the tail liquid after Cr and Ni recovery is Na2SO4, which is sold as a by-product sodium sulfate after evaporation and crystallization.

[0128] (7) Fe recovery: The main component of the residual liquid after treatment with ion exchange resin in step (5) is Fe. 2+ Small amount of free F - The complex with citric acid was used to adjust the pH to 10 with NaOH to generate a Fe(OH)2 precipitate and a supernatant. The Fe(OH)2 precipitate was dehydrated to obtain the Fe(OH)2 product.

[0129] (8) F recovery: The main components of the supernatant obtained in step (7) are citric acid complexes and a small amount of free F. - 76.46 g of 30% (w / v) CaCl2 solution was added and the pH was adjusted to 8 with HCl to obtain CaF2 sludge and supernatant. After dehydration and drying, CaF2 product was obtained.

[0130] (9) Recovery of the anti-complexing agent: The supernatant obtained in step (8) is successively subjected to ultrafiltration (UF) to remove suspended solids and NF treatment for concentration. The obtained NF concentrate is converted back into anti-complexing agent citric acid under the condition of pH 1.5-3.5 and then returned to step (1) for reuse. The NF permeate is discharged. Among them, the pH of UF treatment is 6-9, the temperature is 40℃, the pressure is 0.2MPa, the recovery rate is 90%, the membrane pore size of UF membrane element is 0.1-0.5 μm, and the membrane material is alumina ceramic membrane. The pH of NF treatment is 6-9, the temperature is 40℃, the pressure is 3.5 MPa, the recovery rate is 75%, the membrane material of NF membrane element is polyamide, and the molecular weight cutoff is 400 Da.

[0131] Example 2:

[0132] This embodiment provides a method for treating pickling wastewater. The process can be referred to in Embodiment 1. The main difference is that the anti-complexing agent used in step (1) of this embodiment is a strong acid. Step (1) of this embodiment is as follows:

[0133] (1) Decomposition: 70 g of 98% (w / v) H2SO4 was added to 10 L of stainless steel pickling wastewater to be treated and heated to 80℃ for decomposition treatment. NaOH was added to adjust the pH to 2.5, and the mixture was stirred at 400 rpm for 30 min with a mechanical stirrer to promote the decomposition of complexed F in the stainless steel pickling wastewater into free F, thus obtaining the decomposition treatment solution. After the decomposition treatment solution obtained in step (1) was cooled to 35℃, step (2) nanofiltration was carried out.

[0134] Furthermore, the type of anti-complexing agent changes, and correspondingly, step (3) of this embodiment, Fe... 3+ During the reduction process, the amount of iron powder added changed to 1.94 g.

[0135] Example 3:

[0136] This embodiment provides a method for treating pickling wastewater. The process can be referred to in Embodiment 1. The main difference is that the nanofiltration treatment conditions in step (2) of this embodiment are different. Step (2) of this embodiment is as follows:

[0137] (2) Nanofiltration: The solution obtained in step (1) is subjected to nanofiltration (NF) treatment. The permeate obtained through the NF membrane is NF permeate, and the concentrate that does not permeate through the membrane and is retained is NF concentrate. The NF treatment temperature is 35°C, the pressure is 2.5 MPa, the recovery rate is 48%, the NF membrane element is an acid-resistant membrane element, and the molecular weight cutoff is 400 Da.

[0138] Furthermore, the conditions for nanofiltration change, and correspondingly, step (3) of this embodiment, Fe... 3+During the reduction process, the amount of iron powder added changed to 4.71 g.

[0139] Example 4:

[0140] This embodiment provides a method for treating pickling wastewater. The process can be referred to in Embodiment 1. The main difference is that the defluorinating agent in step (3) of this embodiment is different. Step (3) of this embodiment is as follows:

[0141] (3) F recovery: 401.64 g of 30% (w / v) CaCl2 solution was added to the NF permeate obtained in step (2), and the pH was adjusted to 6.5 using NaOH to obtain CaF2 sludge. The CaF2 sludge was dewatered and dried to obtain CaF2 product.

[0142] Furthermore, the type of defluorinating agent has changed, and correspondingly, step (3) of Fe in this embodiment... 3+ During the reduction process, the amount of iron powder added changed to 4.70 g.

[0143] Comparative Example 1:

[0144] This comparative example provides a method for treating existing pickling wastewater, the specific process of which is as follows:

[0145] Lime was added to 10 L of stainless steel pickling wastewater to adjust the pH to 8, resulting in a mixed sludge containing CaF2, Fe(OH)3, Cr(OH)3 and Ni(OH)2. The remaining water was discharged.

[0146] Comparative Example 2:

[0147] This comparative example provides a method for treating existing pickling wastewater, the specific process of which is as follows:

[0148] NaOH was first added to 10 L of stainless steel pickling wastewater to adjust the pH to 3.5. After reaction and solid-liquid separation, a mixed sludge containing CaF2, Fe(OH)3, Cr(OH)3 and Ni(OH)2 and supernatant 1 were obtained.

[0149] Add NaOH to the supernatant 1 to adjust the pH to 9. After reaction and solid-liquid separation, sludge containing Cr(OH)3 and Ni(OH)2 and supernatant 2 are obtained.

[0150] 332.08 g of 30% (w / v) CaCl2 solution was added to the supernatant 2, and the pH was adjusted to 7.8 with HCl. After reaction and solid-liquid separation, CaF2 sludge was obtained. After dewatering and drying, CaF2 product was obtained; the remaining water was discharged.

[0151] Test example:

[0152] 1. The test results of Example 1 are as follows:

[0153] In step (1), the concentration of free F in the stainless steel pickling wastewater to be treated is 2.24 g / L, the concentration of FeF3 is 2.02 g / L, the concentration of CrF3 is 2.10 g / L, the concentration of NiF2 is 1.65 g / L, and the concentration of NO3 is... - The mass concentration is 10 g / L, and the total volume is 10 L (i.e., the total mass concentration of F is approximately 5.00 g / L, the total mass concentration of Cr is approximately 1.00 g / L, the total mass concentration of Fe is approximately 1.00 g / L, and the total mass concentration of Ni is approximately 1.00 g / L).

[0154] In step (1) the decomplexing treatment solution (i.e., NF influent), the mass concentration of free F is 5 g / L, the mass concentration of ferric citrate (FeCit) is 4.38 g / L, the mass concentration of chromium citrate (CrCit) is 4.64 g / L, the mass concentration of nickel citrate (Ni3(Cit)2) is 2.63 g / L, and the mass concentration of NO3 is... - The mass concentration is 10 g / L, and the total volume is 10 L.

[0155] In step (2), the NF permeate contained 5.5 g / L of free F, 0.44 g / L of ferric citrate (FeCit), 0.46 g / L of chromium citrate (CrCit), 0.32 g / L of nickel citrate (Ni3(Cit)2), and NO3-. - The mass concentration is 11 g / L, and the total volume is 7.5 L.

[0156] In step (2), the NF concentrate contains 3.5 g / L of free F, 16.19 g / L of ferric citrate (FeCit), 17.15 g / L of chromium citrate (CrCit), 11.64 g / L of nickel citrate (Ni3(Cit)2), and NO3. - The mass concentration is 7 g / L, and the total volume is 2.5 L.

[0157] In step (3), the mass of the CaF2 product is 90.9 g, of which the mass fraction of CaF2 is 93.14%, the mass fraction of iron hydroxide (Fe(OH)3) is 3.15%, the mass fraction of chromium hydroxide (Cr(OH)3) is 3.27%, and the mass fraction of nickel hydroxide (Ni(OH)2) is 0.43%.

[0158] In step (6), the mass of the Cr(OH)3 product is 18.68 g, of which the mass fraction of Cr(OH)3 is 88.27% and the mass fraction of Ni(OH)2 is 11.73%; the mass of the Ni(OH)2 product is 14.25 g, of which the mass fraction of Cr(OH)3 is 12.86% and the mass fraction of Ni(OH)2 is 87.14%.

[0159] In step (7), the mass of the Fe(OH)2 product is 22.37 g, of which the mass fraction of Fe(OH)3 is 1.98% and the mass fraction of Fe(OH)2 is 98.02%.

[0160] In step (8), the mass of the CaF2 product is 16.12g, of which the mass fraction of CaF2 is 95%.

[0161] (1) The formula for calculating the recovery rate of F is as follows:

[0162]

[0163] Where A represents the mass (g) of CaF2 product, B represents the mass fraction (%) of F element in CaF2 product, X represents the volume (L) of stainless steel pickling wastewater to be treated, and C represents the total mass concentration of F in the stainless steel pickling wastewater to be treated, in g / L. The calculated recovery rate of F is 97.40%.

[0164] (2) The formula for calculating the recovery rate of Cr is as follows:

[0165]

[0166] Where D represents the mass (g) of Cr(OH)3 product, E represents the mass fraction (%) of Cr element in Cr(OH)3 product, X represents the volume (L) of stainless steel pickling wastewater to be treated, and F represents the total mass concentration of Cr in stainless steel pickling wastewater to be treated, in g / L. The calculated Cr recovery rate is 83.25%.

[0167] (3) The formula for calculating the recovery rate of Ni is as follows:

[0168]

[0169] Where G represents the mass (g) of Ni(OH)2 product, H represents the mass fraction (%) of Ni element in Ni(OH)2 product, X represents the volume (L) of stainless steel pickling wastewater to be treated, and I represents the total mass concentration of Ni in stainless steel pickling wastewater to be treated, in g / L. The calculated Ni recovery rate is 78.63%.

[0170] (4) The formula for calculating the Fe recovery rate is as follows:

[0171]

[0172] Where J represents the mass (g) of Fe(OH)2 product, K represents the mass fraction (%) of Fe element in Fe(OH)2 product, X represents the volume (L) of stainless steel pickling wastewater to be treated, L represents the total mass concentration of Fe in stainless steel pickling wastewater to be treated (g / L), and M represents the mass (g) of reducing agent iron powder added in step (4). The calculated Fe recovery rate is 92.50%.

[0173] 2. The test results of Example 2 are as follows:

[0174] In step (1), the concentration of free F in the stainless steel pickling wastewater to be treated is 2.24 g / L, the concentration of FeF3 is 2.02 g / L, the concentration of CrF3 is 2.10 g / L, the concentration of NiF2 is 1.65 g / L, and the concentration of NO3 is... - The mass concentration is 10 g / L, and the total volume is 10 L.

[0175] In step (1), the decomplexing treatment solution (i.e., NF influent) has the following concentrations: free F (5 g / L), sulfuric acid (H2SO4) (6.85 g / L), ferric sulfate (Fe2(SO4)3) (3.57 g / L), chromium sulfate (Cr2(SO4)3) (3.77 g / L), nickel sulfate (NiSO4) (2.64 g / L), and NO3-. - The mass concentration is 10 g / L, and the total volume is 10 L.

[0176] In step (2), the NF permeate contained the following concentrations: free F at 5 g / L, ferric sulfate (Fe2(SO4)3) at 2.5 g / L, chromium sulfate (Cr2(SO4)3) at 2.64 g / L, nickel sulfate (NiSO4) at 1.85 g / L, and NO3-. - The mass concentration is 11 g / L, and the total volume is 7.5 L.

[0177] In step (2), the NF concentrate contains 5 g / L of free F, 6.79 g / L of ferric sulfate (Fe2(SO4)3), 7.16 g / L of chromium sulfate (Cr2(SO4)3), 5.0 g / L of nickel sulfate (NiSO4), and NO3-. - The mass concentration is 7 g / L, and the total volume is 2.5 L.

[0178] In step (3), the mass of the CaF2 product is 105.7 g, of which the mass fraction of CaF2 is 72.83%, the mass fraction of iron hydroxide (Fe(OH)3) is 9.49%, the mass fraction of chromium hydroxide (Cr(OH)3) is 9.84%, and the mass fraction of nickel hydroxide (Ni(OH)2) is 7.84%.

[0179] In step (6), the mass of the Cr(OH)3 product is 9.12 g, of which the mass fraction of Cr(OH)3 is 87.67% and the mass fraction of Ni(OH)2 is 12.33%; the mass of the Ni(OH)2 product is 7.79 g, of which the mass fraction of Cr(OH)3 is 18.12% and the mass fraction of Ni(OH)2 is 81.88%.

[0180] In step (7), the mass of the Fe(OH)2 product is 10.80 g, of which the mass fraction of Fe(OH)3 is 2.74% and the mass fraction of Fe(OH)2 is 97.26%.

[0181] In step (8), the mass of the CaF2 product is 23.05 g, of which the mass fraction of CaF2 is 94.52%.

[0182] (1) The recovery rate of F is 96.33%, calculated according to the aforementioned formula.

[0183] (2) The recovery rate of Cr was calculated using the aforementioned formula and the result was 40.38%.

[0184] (3) The recovery rate of Ni is 40.38%, calculated according to the aforementioned formula.

[0185] (4) The recovery rate of Fe was calculated using the aforementioned formula and the result was 48.91%.

[0186] 3. The detection results of Example 3 are as follows:

[0187] In step (1), the concentration of free F in the stainless steel pickling wastewater to be treated is 2.24 g / L, the concentration of FeF3 is 2.02 g / L, the concentration of CrF3 is 2.10 g / L, the concentration of NiF2 is 1.65 g / L, and the concentration of NO3 is... - The mass concentration is 10 g / L, and the total volume is 10 L.

[0188] In step (1) the decomplexing treatment solution (i.e., NF influent), the mass concentration of free F is 5 g / L, the mass concentration of ferric citrate (FeCit) is 4.38 g / L, the mass concentration of chromium citrate (CrCit) is 4.64 g / L, the mass concentration of nickel citrate (Ni3(Cit)2) is 2.63 g / L, and the mass concentration of NO3 is...- The mass concentration is 10 g / L, and the total volume is 10 L.

[0189] In step (2), the NF permeate contained 5.75 g / L of free F, 0.53 g / L of ferric citrate (FeCit), 0.56 g / L of chromium citrate (CrCit), 0.38 g / L of nickel citrate (Ni3(Cit)2), and NO3-. - The mass concentration is 11 g / L, and the total volume is 4.8 L.

[0190] In step (2), the NF concentrate contained 4.31 g / L of free F, 7.93 g / L of ferric citrate (FeCit), 8.40 g / L of chromium citrate (CrCit), and 5.70 g / L of nickel citrate (Ni3(Cit)2). - The mass concentration was 9.10 g / L, and the total volume was 5.2L.

[0191] In step (3), the mass of the CaF2 product is 61.44 g, of which the mass fraction of CaF2 is 92.21%, the mass fraction of iron hydroxide (Fe(OH)3) is 3.58%, the mass fraction of chromium hydroxide (Cr(OH)3) is 3.71%, and the mass fraction of nickel hydroxide (Ni(OH)2) is 0.49%.

[0192] In step (6), the mass of the Cr(OH)3 product is 17.24 g, of which the mass fraction of Cr(OH)3 is 88.78% and the mass fraction of Ni(OH)2 is 11.22%; the mass of the Ni(OH)2 product is 16.31 g, of which the mass fraction of Cr(OH)3 is 20.60% and the mass fraction of Ni(OH)2 is 79.40%.

[0193] In step (7), the mass of the Fe(OH)2 product is 22.8 g, of which the mass fraction of Fe(OH)3 is 2.76% and the mass fraction of Fe(OH)2 is 97.24%.

[0194] In step (8), the mass of the CaF2 product is 41.3 g, of which the mass fraction of CaF2 is 96.2%.

[0195] (1) The recovery rate of F is 93.42% according to the aforementioned calculation formula.

[0196] (2) The recovery rate of Cr was calculated using the aforementioned formula and the result was 77.28%.

[0197] (3) The recovery rate of Ni is 81.99%, which is calculated using the formula mentioned above.

[0198] (4) The recovery rate of Fe was calculated using the aforementioned formula and the result was 94.24%.

[0199] 4. The detection results of Example 4 are as follows:

[0200] In step (1), the concentration of free F in the stainless steel pickling wastewater to be treated is 2.24 g / L, the concentration of FeF3 is 2.02 g / L, the concentration of CrF3 is 2.10 g / L, the concentration of NiF2 is 1.65 g / L, and the concentration of NO3 is... - The mass concentration is 10 g / L, and the total volume is 10 L.

[0201] In step (1) the decomplexing treatment solution (i.e., NF influent), the mass concentration of free F is 5 g / L, the mass concentration of ferric citrate (FeCit) is 4.38 g / L, the mass concentration of chromium citrate (CrCit) is 4.64 g / L, the mass concentration of nickel citrate (Ni3(Cit)2) is 2.63 g / L, and the mass concentration of NO3 is... - The mass concentration is 10 g / L, and the total volume is 10 L.

[0202] In step (2), the NF permeate contained 5.5 g / L of free F, 0.35 g / L of ferric citrate (FeCit), 0.37 g / L of chromium citrate (CrCit), and 0.25 g / L of nickel citrate (Ni3(Cit)2). NO3- - The mass concentration is 11 g / L, and the total volume is 7.5 L.

[0203] In step (2), the NF concentrate contains 3.5 g / L of free F, 16.45 g / L of ferric citrate (FeCit), 17.43 g / L of chromium citrate (CrCit), 11.83 g / L of nickel citrate (Ni3(Cit)2), and NO3-. - The mass concentration is 7 g / L, and the total volume is 2.5 L.

[0204] In step (3), the mass of the CaF2 product is 89.66 g, of which the mass fraction of CaF2 is 94.44%, the mass fraction of iron hydroxide (Fe(OH)3) is 2.56%, the mass fraction of chromium hydroxide (Cr(OH)3) is 2.65%, and the mass fraction of nickel hydroxide (Ni(OH)2) is 0.35%.

[0205] In step (6), the mass of the Cr(OH)3 product is 18.98 g, of which the mass fraction of Cr(OH)3 is 88.27% and the mass fraction of Ni(OH)2 is 11.73%; the mass of the Ni(OH)2 product is 14.48 g, of which the mass fraction of Cr(OH)3 is 12.86% and the mass fraction of Ni(OH)2 is 87.14%.

[0206] In step (7), the mass of the Fe(OH)2 product is 22.8 g, of which the mass fraction of Fe(OH)3 is 3.94% and the mass fraction of Fe(OH)2 is 96.06%.

[0207] In step (8), the mass of the CaF2 product is 16.1 g, of which the mass fraction of CaF2 is 96.21%.

[0208] (1) The recovery rate of F was calculated using the aforementioned formula and the result was 97.42%.

[0209] (2) The recovery rate of Cr was calculated using the aforementioned formula and the result was 84.60%.

[0210] (3) The recovery rate of Ni is 79.90% according to the aforementioned calculation formula.

[0211] (4) The recovery rate of Fe was calculated using the aforementioned formula and the result was 94.00%.

[0212] 5. The test results of Comparative Example 1 are as follows:

[0213] The mixed sludge contained 62.56% CaF₂, 11.67% ferric hydroxide (Fe(OH)₃), 12.03% chromium hydroxide (Cr(OH)₃), and 9.62% nickel hydroxide (Ni(OH)₂). Since this mixed sludge could only be treated as hazardous waste, the recovery rates of F, Cr, Ni, and Fe were 0%; the removal rates of F, Cr, Ni, and Fe, calculated using the same method as above, were all 99.90%.

[0214] 6. The test results of Comparative Example 2 are as follows:

[0215] The mass of the mixed sludge containing CaF2, Fe(OH)3, Cr(OH)3 and Ni(OH)2 was 30.40 g, of which the mass fraction of CaF2 was 50.12%, the mass fraction of Fe(OH)3 was 33.09%, the mass fraction of Cr(OH)3 was 11.51%, and the mass fraction of Ni(OH)2 was 5.28%.

[0216] The sludge containing Cr(OH)3 and Ni(OH)2 had a mass of 29.59 g, of which the mass fraction of CaF2 was 12.45%, the mass fraction of Cr(OH)3 was 44.48%, and the mass fraction of Ni(OH)2 was 43.06%.

[0217] The CaF2 product weighs 70 g, of which the mass fraction of CaF2 is 97.52%.

[0218] (1) The recovery rate of F is 68.21%, calculated using the formula mentioned above.

[0219] (2) The recovery rate of Cr was calculated using the aforementioned formula and the result was 66.44%.

[0220] (3) The recovery rate of Ni is 80.68%, calculated according to the aforementioned formula.

[0221] (4) The recovery rate of Fe was calculated using the aforementioned formula and was 99.81%. The recovery rates of each element in the above test examples are shown in Table 1, and the purity (%) of the products are shown in Table 2.

[0222] Table 1

[0223]

[0224] As shown in Table 1, Example 1 showed the highest recovery rates of F, Cr, Ni, and Fe, indicating that the pickling wastewater treatment method provided by this invention can effectively recover F, Cr, Ni, and Fe from pickling wastewater. This not only provides a practical means to solve environmental pollution problems, but also provides an important way to achieve resource recycling, reduce economic costs, and promote sustainable development.

[0225] Compared to Example 1, Example 2 replaced the citric acid (weak acid) complexing agent with sulfuric acid (strong acid) complexing agent. Since the NF membrane has different rejection rates for sulfuric acid and hydrofluoric acid, the mass concentration of free F in the NF permeate and NF concentrate differs from that in Example 1, resulting in a decrease in the purity of CaF2 and consequently a decrease in F recovery rate. This indicates that using a weak acid (e.g., citric acid) as a complexing agent helps improve F recovery rate. Furthermore, the operation of Example 2 requires coordinated heating and cooling, which can easily lead to increased overall energy consumption.

[0226] Compared with Example 1, Example 3 changed the pressure and recovery rate of nanofiltration, resulting in incomplete separation of free F, which had a more significant impact on the F recovery rate. This shows that the regulation of nanofiltration conditions helps to improve the F recovery rate.

[0227] Compared to Example 1, Example 4 used calcium chloride and sodium hydroxide instead of lime. Although the impact on the recovery rates of F, Cr, Ni and Fe was not significant, the reagent cost increased by about 4 times.

[0228] Compared to Example 1, the traditional pickling wastewater treatment method represented by Comparative Example 1 cannot recover F, Cr, Ni, and Fe, resulting in a significant waste of resources. Compared to Example 1, the pickling wastewater treatment method represented by Comparative Example 2 is also unable to effectively recover F, Cr, and Ni, still resulting in substantial resource waste.

[0229] Table 2

[0230]

[0231] As shown in Table 2, the CaF2, Cr(OH)3, Ni(OH)2, and Fe(OH)2 products obtained in Examples 1, 3, and 4 have similar qualities, but the CaF2 product obtained in Example 2 has lower quality, indicating that the type of uncomplexing agent has a significant impact on the purity of the recovered fluorine product. The mixed sludge obtained in Comparative Example 1 has low quality and can only be treated as hazardous waste, making it difficult to utilize. The mixed sludge containing CaF2, Fe(OH)3, Cr(OH)3, and Ni(OH)2 obtained in Comparative Example 2 has low quality and is difficult to utilize; the sludge containing Cr(OH)3 and Ni(OH)2 cannot be used directly and still requires subsequent steps to distinguish chromium and nickel; the obtained CaF2 product has high purity, but the yield is low, which also results in a large waste of resources.

[0232] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating pickling wastewater, characterized in that, Includes the following steps: Step 1: Treat the pickling wastewater with a complex-resolving agent to obtain a complex-resolving solution; the complex-resolving agent includes at least one of citric acid and oxalic acid; Step 2: Perform nanofiltration on the complex-resolving solution to obtain permeate and concentrate; Step 3: Mix the produced water and the defluorinating agent to obtain a fluoride-containing product; Step 4: Mix the concentrated water and the reducing agent to obtain a reducing solution; Step 5: Use ion exchange resin to adsorb chromium and nickel in the reducing solution to obtain ion exchange resin containing chromium and nickel and effluent; Step 6: Desorb the chromium- and nickel-containing ion exchange resin to obtain a chromium- and nickel-containing resin regeneration solution; Step 7: Adjust the pH of the chromium- and nickel-containing resin regeneration solution to 4-6 to obtain the chromium-containing product and the first supernatant; Step 8: Adjust the pH of the first supernatant to 9-10 to obtain the nickel-containing product and the second supernatant; Step 9: Adjust the pH of the effluent to 9-10 to obtain an iron-containing product and a third supernatant; Step 10: Mix the third supernatant with the defluorinating agent to obtain a fluorine-containing product and a fourth supernatant.

2. The processing method according to claim 1, characterized in that, The conditions for the decomposition treatment include: a time of 0.5-1 h and a pH value of 2.5-3.5; When the anti-complexing agent is citric acid, the amount of the anti-complexing agent added is 1-1.5 times the molar amount of the metal element in the pickling wastewater; the molar amount of the metal element is the sum of the molar amounts of iron, chromium, and 2 / 3 of the molar amounts of nickel. When the anti-complexing agent is oxalic acid, the amount of the anti-complexing agent added is 1-1.5 times the molar amount of the metal element in the pickling wastewater; the molar amount of the metal element is the sum of 3 / 2 the molar amount of iron, 3 / 2 the molar amount of chromium, and the molar amount of nickel.

3. The processing method according to claim 1 or 2, characterized in that, The conditions for nanofiltration treatment include: temperature of 20-40℃, pressure of 2-6 MPa, molecular weight cutoff of 150-600 Da, and recovery rate of 40-75%.

4. The processing method according to claim 1 or 2, characterized in that, The defluorinating agent includes at least one of calcium chloride and lime.

5. The processing method according to claim 1 or 2, characterized in that, The reducing agent includes at least one of iron powder, sodium thiosulfate, hydrogen sulfide, sulfides, sulfites, and bisulfites.

6. The processing method according to claim 1 or 2, characterized in that, The functional groups of the ion exchange resin include at least one of polyamino and iminodiacetic groups; The adsorption conditions include a flow rate of 5-15 m / h and a pH of 3.5-5.

7. The processing method according to claim 1 or 2, characterized in that, The processing method further includes: filtering the fourth supernatant and adjusting the pH to 1-3 to obtain the anti-complexing agent.

8. The processing method according to claim 7, characterized in that, The filtration process consists of sequential ultrafiltration and nanofiltration; the ultrafiltration conditions include a pH of 6-9, a pressure of 0.1-0.4 MPa, a temperature of 20-40°C, and a recovery rate of 85-95%; the nanofiltration conditions include a pH of 6-9, a pressure of 2-8 MPa, a temperature of 20-40°C, and a recovery rate of 60-80%; or, The filtration process consists of sequential sand filtration and nanofiltration; the nanofiltration conditions include a pH of 6-9, a pressure of 2-8 MPa, a temperature of 20-40℃, and a recovery rate of 60-80%; or, The filtration process consists of a precision filtration process and a nanofiltration process performed sequentially; the conditions for the nanofiltration process include a pH of 6-9, a pressure of 2-8 MPa, a temperature of 20-40℃, and a recovery rate of 60-80%.

9. A pickling wastewater treatment system for performing the treatment method according to any one of claims 1-8, characterized in that, It includes a decomposition module, a nanofiltration module, a reduction module, an adsorption module, and a desorption module connected in sequence; the nanofiltration module is also connected to a first fluorine recovery module; the desorption module is also connected to a chromium recovery module and a nickel recovery module in sequence; the adsorption module is also connected to an iron recovery module and a second fluorine recovery module in sequence. The unwinding module is used to perform unwinding processing; The nanofiltration module is used to perform nanofiltration processing; The reduction module is used to provide a reducing agent for reduction processing; The adsorption module is used to provide ion exchange resin for the adsorption of chromium and nickel. The desorption module is used to desorb ion exchange resins containing chromium and nickel. The first fluorine recovery module and the second fluorine recovery module are used to provide a defluorinating agent for fluorine recovery; The chromium recovery module is used to adjust the pH for chromium recovery. The nickel recovery module is used to adjust the pH for nickel recovery. The iron recovery module is used to adjust the pH for iron recovery.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the processing method according to any one of claims 1-8.

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