A method and system for resourceful treatment of silicon-carbon negative electrode framework carbon acid pickling wastewater

Abstract

This invention relates to the field of wastewater treatment technology, specifically to a resource-based treatment method and system for carbon acid washing wastewater from silicon-carbon anode skeletons. The resource-based treatment method includes: passing the carbon acid washing wastewater from silicon-carbon anode skeletons into a nanofiltration system to obtain permeate and retentate; subjecting the permeate to a first-stage vacuum evaporation to obtain a dilute hydrochloric acid solution, potassium salt, and a primary crystallization residue; mixing the primary crystallization residue and the retentate, and adding alkali to obtain iron sludge and filtrate; subjecting the filtrate to a second-stage vacuum evaporation to obtain water, salt, and a secondary crystallization residue, which is returned to the filtrate, thereby achieving the resource-based treatment of the carbon acid washing wastewater from silicon-carbon anode skeletons. This invention also provides a treatment system for carbon acid washing wastewater from silicon-carbon anode skeletons. This invention solves the problem that existing acid washing wastewater treatment methods are difficult to achieve efficient removal of iron ions, and also solves the problem that existing acid washing wastewater treatment methods are difficult to simultaneously recover high-purity potassium salt and hydrochloric acid.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a resource-based treatment method and system for washing wastewater from silicon-carbon anode skeleton carbon. Background Technology

[0002] Silicon-carbon anode materials, as a new generation of lithium-ion battery anode materials, have attracted widespread attention due to their high specific capacity and excellent fast-charging performance. In the acid washing process of the silicon-carbon anode skeleton carbon, a hydrochloric acid system is typically used to remove metal impurities, which in turn produces Fe-containing compounds. 2+ / Fe 3+ K + H + Cl - The wastewater is an acidic, high-salinity wastewater treated by plasma. This wastewater is characterized by strong acidity, high TDS (total dissolved solids approximately 89 g / L), and high ferric ion content (approximately 48.5 mg / L), which are significantly different from ordinary industrial wastewater, making it very difficult to treat.

[0003] Existing technologies for the treatment and resource recovery of this type of wastewater are still immature. The main shortcomings of existing technologies are as follows: First, the removal of iron ions and salt recovery are difficult to coordinate. For example, a publicly disclosed high-salt wastewater desalination device mainly focuses on the separation of conventional sodium chloride (NaCl) and sodium sulfate (Na2SO4), but does not address the deep removal of iron ions under high-acid conditions. Similarly, a publicly disclosed high-salt wastewater resource recovery method focuses on the separate crystallization of sulfates and chlorides, also lacking effective removal of interference from high-ferrous ions. Under high-acid and high-salt conditions, iron ions easily form stable complexes with chloride ions, significantly increasing the separation difficulty; the above technologies have failed to solve this key problem. Second, acid resource recovery efficiency is low. Existing salt separation technologies mostly employ a neutralization-evaporation crystallization process, converting acidic components in wastewater into salts for disposal, failing to achieve effective reuse of hydrochloric acid, resulting in waste of acid resources and increased costs of neutralizing agents. Third, the purity of potassium salt products is limited. Ferric ions tend to co-crystallize or encapsulate with potassium salts during the evaporation and crystallization process, resulting in potassium salt products with high color and insufficient purity, making it difficult to meet industrial reuse standards.

[0004] In summary, to address the technological gap in the treatment of carbon washing wastewater from silicon-carbon anode skeletons, this study develops a comprehensive resource-based treatment method that can efficiently remove iron ions and simultaneously recover high-purity potassium salts and hydrochloric acid. This method has significant industrial application value and practical implications for improving the green level of anode material production and reducing wastewater treatment costs. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a resource-based treatment method and system for acid washing wastewater of silicon-carbon anode skeleton carbon, so as to solve the problem that existing acid washing wastewater treatment methods are difficult to achieve efficient removal of iron ions, and can also solve the problem that existing acid washing wastewater treatment methods are difficult to simultaneously recover high-purity potassium salt and hydrochloric acid.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for resource-based treatment of carbonate washing wastewater from silicon-carbon anode skeletons includes the following steps: S1. Nanofiltration separation: The carbon washing wastewater from the silicon-carbon anode framework is passed into a nanofiltration system to obtain K-enriched K. + H + Cl - Permeate and enriched Fe 2+ Fe 3+ The retentate; thereby achieving Fe 2+ Fe 3+ With K + H + Cl - Precise separation; S2. Permeate treatment: The permeate is subjected to a first vacuum evaporation to obtain a dilute hydrochloric acid solution, potassium salt and a primary crystallization residue; S3. Adding alkali to remove iron: After mixing the residual liquid from the first crystallization and the retentate, alkali is added to obtain iron mud and filtrate; S4. Filtrate treatment: The filtrate is subjected to a second vacuum evaporation to obtain water, salt and secondary crystallization residue. The secondary crystallization residue is returned to the filtrate to achieve resource utilization treatment of carbon washing wastewater from silicon-carbon anode skeleton.

[0007] Based on the aforementioned technical methods, firstly, precise separation of multi-ion systems is effectively achieved through the selective sieving of nanofiltration membranes. This is achieved by utilizing nanofiltration membranes to separate divalent metal ions (Fe... 2+ Fe 3+ The high rejection rate of ) and the high rejection rate of monovalent ions (K) + H + Cl - The high permeability difference allows for the pre-separation of iron ions from potassium salts / acids at the molecular level, avoiding the problems associated with traditional chemical precipitation methods. 3+ With K +The problem of potassium salt purity reduction caused by co-precipitation is solved by addressing the difficulty of efficiently removing iron ions in existing pickling wastewater treatment methods. Secondly, after the permeate is evaporated under reduced pressure, hydrochloric acid is preferentially separated and recovered in the gas phase due to the different volatility of components in the HCl-KCl-H2O ternary system, while potassium salt precipitates through crystallization, effectively achieving efficient acid-salt fractional recovery. Thirdly, after mixing the retentate with the primary crystallization residue, alkali is added to convert the enriched iron ions into ferric hydroxide precipitate, eliminating the interference of iron ions on subsequent potassium salt crystallization and recovering iron resources. Finally, the secondary crystallization residue reflux design improves potassium salt recovery rate through mother liquor circulation, ultimately achieving the synergistic goal of high-value recovery of the "iron-potassium-acid" three-phase system and zero wastewater discharge. This ingeniously solves the problem that existing pickling wastewater treatment methods cannot simultaneously achieve efficient removal of iron ions and recovery of high-purity potassium salt and hydrochloric acid.

[0008] Preferably, in S1, the nanofiltration system is a high-pressure nanofiltration system, which includes an industrial-grade 8040 acid-resistant aromatic polyamide spiral wound nanofiltration membrane module.

[0009] Preferably, the high-pressure nanofiltration system operates at a pressure of 1.0~1.5MPa during the nanofiltration separation process, and the pressure is precisely controlled by using three acid-resistant centrifugal pumps connected in series to increase the pressure in stages.

[0010] By precisely controlling the operating pressure of the high-pressure nanofiltration system between 1.0 and 1.5 MPa, the volume ratio of permeate to raw wastewater is controlled between 68% ± 2%, and the volume ratio of retentate to raw wastewater is controlled between 32% ± 2%. Furthermore, the industrial-grade 8040 acid-resistant aromatic polyamide spiral wound nanofiltration membrane module effectively controls Fe... 2+ Fe 3+ The retention rate was consistently ≥92% for K + H + Cl - The transmittance is consistently ≥90%, thus effectively achieving Fe... 2+ Fe 3+ With K + H + Cl - Precise physical separation.

[0011] Preferably, the operating pressure is 1.2 MPa. Under this operating pressure, the volume ratio of permeate to retentate remains stable at a baseline of 68% and 32%, respectively, achieving an optimal balance between separation efficiency, volume distribution, and equipment energy consumption.

[0012] Preferably, in step S2, the operating pressure for the first depressurization evaporation is -0.095 to -0.1 MPa, and the evaporation temperature is 88 to 93°C.

[0013] By utilizing negative pressure to lower the boiling point of a strongly acidic system, while ensuring H... + and Cl - While efficiently condensing and recovering hydrochloric acid components, it avoids the ineffective volatilization of hydrochloric acid at high temperatures.

[0014] Preferably, in step S2, the pressure of the first depressurization evaporation is -0.1 MPa, and the evaporation temperature is 91°C.

[0015] Preferably, in S3, the alkali is selected from potassium hydroxide.

[0016] By using potassium hydroxide (KOH) as a precipitant, iron ions are effectively precipitated, while the introduction of impurities such as sodium ions is avoided, thus improving the purity of the recovered potassium chloride salt.

[0017] Preferably, in step S3, after mixing the crystallization residue and the retentate, an alkali is added to adjust the pH of the mixed solution to 8.0-8.6 to precipitate iron ions and obtain iron sludge and filtrate.

[0018] Preferably, in step S3, after mixing the crystallization residue and the retentate, an alkali is added to adjust the pH of the mixed solution to 8.34.

[0019] Preferably, in step S4, the operating pressure for the second vacuum evaporation is -0.095 to -0.1 MPa, and the evaporation temperature is 85 to 90°C. After iron removal, the system has been transformed into a near-neutral potassium salt system, and the volatile acid components have been largely removed. Therefore, by cleverly lowering the temperature, i.e., slightly below the evaporation temperature of the first vacuum evaporation, efficient condensation and recovery of water resources and further concentration and precipitation of potassium chloride are effectively achieved.

[0020] Preferably, in step S4, the pressure of the second vacuum distillation is -0.1 MPa and the temperature is 89°C.

[0021] Preferably, step S2 specifically includes: subjecting the permeate to a first-stage vacuum evaporation to obtain a first-stage distillate and a first-stage bottom liquid, wherein the first-stage distillate is a dilute hydrochloric acid solution; and subjecting the first-stage bottom liquid to a first-stage low-temperature crystallization at 0°C to obtain potassium chloride, wherein the remaining saturated solution after the first-stage low-temperature crystallization is the first-stage crystallization residue.

[0022] Preferably, step S4 specifically includes: subjecting the filtrate to a second vacuum evaporation to obtain a second distillate and a second bottom liquid, wherein the second distillate is water; subjecting the second bottom liquid to a second low-temperature crystallization at 0°C to obtain potassium chloride; the remaining saturated solution after the second low-temperature crystallization is the second crystallization residue, which is returned to the filtrate to achieve resource utilization treatment of the carbon washing wastewater from the silicon-carbon anode skeleton.

[0023] Preferably, the iron (Fe) content in the carbonate washing wastewater of the silicon-carbon anode framework is 48.5 mg / L, and the Cl content is... - The content was 34.5 g / L, K + The content is 28g / L, H + The content of [unspecified substance] is 0.427 g / L, and the TDS (total dissolved solids / total dissolved solids) content is 89 g / L; the EC (conductivity) of the silicon-carbon anode skeleton carbon acid washing wastewater is 214 mS / cm.

[0024] The resource-based treatment method for the washing wastewater of silicon-carbon anode skeleton carbon of the present invention has the following advantages: The four-step treatment process of this invention addresses the core water quality characteristics of silicon-carbon anode skeleton carbon acid washing wastewater, which is highly acidic, has high TDS, and high ferric ion content. It is specifically designed from the principles of ion separation, acid salt recovery, iron sludge removal, and resource recycling. Each step solves the core technical defects of existing acid washing wastewater treatment methods, achieving full ion recovery and zero wastewater discharge. The principle advantages of each step compared with existing methods are analyzed as follows: S1. Nanofiltration separation: Utilizing a high-pressure nanofiltration system of 1.0~1.5 MPa, and relying on the dual effects of molecular sieving and the Donnan effect of acid-resistant aromatic polyamide spiral wound nanofiltration membranes, Fe... 2+ Fe 3+ With K + H + Cl - This process achieves precise physical separation, while simultaneously controlling the operating pressure to precisely regulate the permeate / retentate volume ratio to 68%±2% / 32%±2%. In contrast to traditional chemical precipitation methods, which easily lead to iron-potassium co-precipitation and potassium salt loss, and the limitations of ordinary low-pressure membranes such as high TDS osmotic pressure, poor acid resistance, and low iron rejection, reverse osmosis also exhibits high rejection and lack of selectivity for monovalent ions. This process, however, involves no added chemicals and introduces no impurities. The acid-resistant membrane is adapted to the strongly acidic characteristics of the wastewater, and the high-pressure design ensures high throughput. The dual separation effect blocks iron ion contamination at the source, laying the foundation for subsequent high-purity resource recovery.

[0025] S2, Permeate treatment, for K enrichment + H + Cl -The permeate is cleverly treated using a reduced-pressure evaporation process at -0.095 to -0.1 MPa and 88 to 93°C, leveraging the volatility differences in the HCl-KCl-H₂O ternary system to achieve thermodynamic fractional recovery. Compared to existing methods, traditional neutralization-evaporation crystallization methods directly neutralize hydrochloric acid, resulting in wasted acid resources and increased reagent and energy costs. Atmospheric pressure evaporation leads to ineffective hydrochloric acid volatilization due to its high boiling point, and premature crystallization of potassium salts results in low purity due to impurities. Reverse osmosis is prone to corrosion and scaling in high-acid, high-salt environments and has poor concentration effects. This new step directly condenses and recovers hydrochloric acid with a reuse rate ≥90%. Negative-pressure evaporation lowers the system's boiling point, reducing energy consumption. Only potassium salts are concentrated without crystallization, avoiding impurity encapsulation. No neutralization pretreatment is required to directly treat strongly acidic solutions, significantly simplifying the process.

[0026] S3. Iron removal by adding alkali: After enriching iron ions by mixing the residual liquid from the primary crystallization with the retentate, potassium hydroxide is added to adjust the pH to 8.0-8.6 (preferably 8.34). Deep iron removal is achieved by utilizing the solubility product of iron ions and hydroxides. Compared to existing methods, traditional methods using NaOH / lime to remove iron introduce foreign impurities, leading to a decrease in potassium salt purity. Treating the retentate alone results in high reagent consumption and easy loss of potassium salts. This step cleverly uses KOH as a precipitant, avoiding the introduction of impurities and precisely controlling the pH range to ensure an iron ion precipitation rate ≥99%. It also avoids reagent redundancy and iron sludge gelation, significantly reducing unit reagent consumption for iron enrichment and removal. Simultaneously, the dried iron sludge can be recycled at high value, reducing hazardous waste disposal costs.

[0027] S4. Filtrate Treatment: For near-neutral iron-removed filtrate, a second vacuum evaporation at -0.095~-0.1MPa and 88~93℃ is cleverly employed, further combined with 0℃ low-temperature crystallization and complete reflux recycling of the secondary crystallization residue. This utilizes the near-neutral system's absence of volatile components and the temperature dependence of KCl solubility to achieve resource recovery. Compared to existing methods, traditional atmospheric pressure evaporation has high energy consumption and low water recovery efficiency. Direct discharge of the mother liquor results in significant potassium salt loss and water pollution. The lack of a low-temperature crystallization process easily leads to potassium salt encapsulating impurities and producing small, difficult-to-separate crystals. This step, low-temperature vacuum evaporation, further reduces energy consumption, achieves a water reuse rate ≥93.3%, low-temperature crystallization forms large-particle potassium salt crystals with a purity ≥99%, and mother liquor recycling ensures a total potassium salt recovery rate ≥95%, ultimately forming a closed-loop material system and achieving zero wastewater discharge.

[0028] This invention also provides a treatment system for carbon washing wastewater from silicon-carbon anode frameworks, comprising: High-pressure nanofiltration system: Used to pass the carbonate washing wastewater from the silicon-carbon anode framework into the high-pressure nanofiltration system to obtain enriched K. + H + Cl - Permeate and enriched Fe 2+ Fe 3+ retentate; First-stage vacuum evaporation system: connected to the high-pressure nanofiltration system, used to perform a first-stage vacuum evaporation of the permeate to obtain a dilute hydrochloric acid solution, potassium salt, and a primary crystallization residue; Alkali precipitation and filtration system: connected to the high-pressure nanofiltration system, used to mix the primary crystallization residue and the retentate, and then add alkali to obtain iron mud and filtrate; Secondary vacuum evaporation system: connected to the alkali precipitation and filtration system, used to perform secondary vacuum evaporation on the filtrate to obtain water, salt and secondary crystallization residue. The secondary crystallization residue is returned to the filtrate to realize the resource utilization treatment of carbon washing wastewater from silicon-carbon anode skeleton.

[0029] First, the high-pressure nanofiltration system utilizes the synergistic effect of membrane pore size sieving and the Donnan effect to achieve Fe under high pressure. 2+ / Fe 3+ With K + / H + / Cl - The system employs several techniques: First, charge-selective separation blocks the contamination pathway of iron ions for subsequent potassium salt recovery at the source. Second, a first-stage vacuum evaporation system lowers the azeotropic point of HCl by reducing operating pressure, enabling preferential low-temperature volatilization and recovery of hydrochloric acid. Simultaneously, the temperature-dependent solubility of KCl facilitates potassium salt crystallization, achieving thermodynamic separation of acid and salt. Third, an alkali precipitation filtration system mixes the high-concentration iron ions retained by nanofiltration with the potassium-containing mother liquor, adjusting the pH to reduce iron ions... 2+ / Fe 3+ The iron is converted into Fe(OH)3 / Fe(OH)2 precipitate, which not only eliminates iron impurities but also recovers iron resources. Finally, the second vacuum evaporation system adopts a mother liquor reflux circulation design, which maximizes the potassium salt yield through repeated concentration-crystallization processes. The evaporation condensate is reused to achieve a closed-loop water system, and finally a zero-emission resource utilization system with multi-unit synergy of "membrane separation-thermal separation-chemical precipitation" is constructed.

[0030] Preferably, the high-pressure nanofiltration system includes a connected 8040 type acid-resistant aromatic polyamide spiral wound nanofiltration membrane module and three acid-resistant centrifugal pumps connected in series for pressurizing the carbonate washing wastewater of the silicon-carbon anode skeleton. The inlet of the first vacuum evaporation system is connected to the permeate outlet of the high-pressure nanofiltration system. The bottom liquid outlet of the first vacuum evaporation system is also connected to a first low-temperature crystallization system. The first low-temperature crystallization system is used to crystallize the bottom liquid at low temperature to obtain potassium salt and saturated primary crystallization residue. The inlet of the alkali precipitation filtration system is connected to the outlet of the retentate of the high-pressure nanofiltration system and the outlet of the primary crystallization residue of the low-temperature crystallization system, respectively. The inlet of the second vacuum evaporation system is connected to the filtrate outlet of the alkali precipitation filtration system. The bottom liquid outlet of the second vacuum evaporation system is also connected to a second low-temperature crystallization system. The second low-temperature crystallization system is used to crystallize the bottom liquid at low temperature to obtain potassium salt and saturated secondary crystallization residue. The saturated secondary crystallization residue is recycled back to the second vacuum evaporation system for further processing, thereby achieving material balance throughout the entire process.

[0031] The beneficial effects of this invention are: The resource-based treatment method for carbon washing wastewater from silicon-carbon anode frameworks of the present invention firstly achieves precise separation of a multi-ion system through selective sieving using a nanofiltration membrane. This is achieved by utilizing the nanofiltration membrane to separate divalent metal ions (Fe... 2+ Fe 3+ The high rejection rate of ) and the high rejection rate of monovalent ions (K) + H + Cl - The high permeability difference allows for the pre-separation of iron ions from potassium salts / acids at the molecular level, avoiding the problems associated with traditional chemical precipitation methods. 3+ With K + The problem of potassium salt purity reduction caused by co-precipitation is addressed. Secondly, after the permeate is evaporated under reduced pressure, based on the difference in volatility of each component in the HCl-KCl-H2O ternary system, hydrochloric acid is preferentially separated and recovered in gaseous form, while potassium salt is precipitated through crystallization, effectively achieving efficient fractional recovery of acid and salt. Thirdly, after mixing the retentate with the primary crystallization residue, alkali is added to convert the enriched iron ions into ferric hydroxide precipitate, which not only eliminates the interference of iron ions on subsequent potassium salt crystallization but also recovers iron resources. Finally, the design of secondary crystallization residue reflux improves the potassium salt recovery rate through mother liquor circulation, ultimately achieving the synergistic goal of high-value recovery of the "iron-potassium-acid" three-phase system and zero wastewater discharge.

[0032] The silicon-carbon anode framework carbon washing wastewater treatment system of the present invention firstly utilizes the synergistic effect of membrane pore size sieving and the Donnan effect to achieve Fe under high pressure drive. 2+ / Fe 3+ With K + / H + / Cl - The system employs several techniques: First, charge-selective separation blocks the contamination pathway of iron ions for subsequent potassium salt recovery at the source. Second, a first-stage vacuum evaporation system lowers the azeotropic point of HCl by reducing operating pressure, enabling preferential low-temperature volatilization and recovery of hydrochloric acid. Simultaneously, the temperature-dependent solubility of KCl facilitates potassium salt crystallization, achieving thermodynamic separation of acid and salt. Third, an alkali precipitation filtration system mixes the high-concentration iron ions retained by nanofiltration with the potassium-containing mother liquor, adjusting the pH to reduce iron ions... 2+ / Fe 3+The iron is converted into Fe(OH)3 / Fe(OH)2 precipitate, which eliminates iron impurities and recovers iron resources. Finally, the second vacuum evaporation system employs a mother liquor reflux circulation design, maximizing potassium salt yield through repeated concentration-crystallization processes. The evaporation condensate is reused to achieve a closed-loop water system, ultimately constructing a zero-discharge resource recovery system with multi-unit synergy of "membrane separation-thermal separation-chemical precipitation." This truly achieves zero liquid discharge, demonstrating significant environmental and economic benefits. It has application value in the field of wastewater treatment technology. Attached Figure Description

[0033] Figure 1 A flowchart of a resource-based treatment method for carbon washing wastewater from silicon-carbon anode skeletons; Figure 2 This is a photograph of the product from a low-temperature crystallization process at the bottom of the reactor. Figure 3 A photograph of the iron sludge obtained from the alkali removal process; Figure 4 A photograph of dried iron sludge; Figure 5 This is a photograph of the product from the low-temperature crystallization of the secondary bottom liquid. Detailed Implementation

[0034] The following description, with reference to preferred embodiments, illustrates the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are merely illustrative of the present invention and not intended to limit the scope of protection of the present invention.

[0035] The present invention aims to disclose a resource-based treatment method and system for acid washing wastewater from silicon-carbon anode skeleton carbon, in order to solve the problem that existing acid washing wastewater treatment methods are difficult to achieve efficient removal of iron ions, and can also solve the problem that existing acid washing wastewater treatment methods are difficult to simultaneously recover high-purity potassium salts and hydrochloric acid.

[0036] A method for resource-based treatment of carbonate washing wastewater from silicon-carbon anode skeletons includes the following steps: S1. Nanofiltration separation: The carbon washing wastewater from the silicon-carbon anode framework is passed into a nanofiltration system to obtain K-enriched K. + H + Cl - Permeate and enriched Fe 2+ Fe 3+ The retentate; thereby achieving Fe 2+ Fe 3+ With K + H+ Cl - Precise separation; S2. Permeate treatment: The permeate is subjected to a first vacuum evaporation to obtain a dilute hydrochloric acid solution, potassium salt, and primary crystallization residue. S3. Adding alkali to remove iron: Mix the residual liquid from the first crystallization and the retentate, then add alkali to obtain iron mud and filtrate; S4. Filtrate treatment: The filtrate is subjected to a second vacuum evaporation to obtain water, salt and secondary crystallization residue. The secondary crystallization residue is returned to the filtrate to achieve resource utilization of the carbon washing wastewater of silicon-carbon anode skeleton.

[0037] In some embodiments, in S1, the nanofiltration system is a high-pressure nanofiltration system, which includes an industrial-grade 8040 acid-resistant aromatic polyamide spiral wound nanofiltration membrane module; the operating pressure of the high-pressure nanofiltration system during the nanofiltration separation process is 1.0~1.5MPa, and the pressure is precisely controlled by three acid-resistant centrifugal pumps connected in series to pressurize in stages.

[0038] In some embodiments, in order to control the volume ratio of permeate to retentate to remain stable at a baseline of 68% and 32% respectively, so as to achieve an optimal balance between separation efficiency, volume distribution and equipment energy consumption, the operating pressure of the high-pressure nanofiltration system is controlled at 1.2 MPa.

[0039] In some embodiments, in S2, the operating pressure for the first vacuum evaporation is -0.095 to -0.1 MPa, and the evaporation temperature is 88 to 93°C. This utilizes negative pressure to lower the boiling point of the strongly acidic system, while ensuring the H... + and Cl - While efficiently condensing and recovering hydrochloric acid components, it avoids the ineffective volatilization of hydrochloric acid at high temperatures.

[0040] For example, in S2, the pressure of the first vacuum evaporation is -0.1 MPa and the temperature is 91°C.

[0041] In some embodiments, in S3, potassium hydroxide is selected as the alkali in order to effectively precipitate iron ions while avoiding the introduction of impurities such as sodium ions to improve the purity of the recovered potassium chloride salt.

[0042] In some embodiments, in S3, after mixing the crystallization residue and the retentate, an alkali is added to adjust the pH of the mixed solution to 8.0-8.6 to precipitate iron ions and obtain iron sludge and filtrate.

[0043] In some embodiments, during S4, since the system has been transformed into a near-neutral potassium salt system after iron removal and the volatile acid components have been largely removed, the operating pressure of the second vacuum distillation is controlled at -0.095 to -0.1 MPa, and the evaporation temperature is controlled at 85 to 90°C. That is, by using an evaporation temperature slightly lower than that of the first vacuum evaporation, efficient condensation and recovery of water resources and further concentration and precipitation of potassium chloride can be achieved.

[0044] For example, in S4, the pressure of the second vacuum distillation is -0.1 MPa and the temperature is 89°C.

[0045] In some embodiments, S2 specifically includes: subjecting the permeate to a first vacuum evaporation to obtain a first distillate and a first bottom liquid, wherein the first distillate is a dilute hydrochloric acid solution; subjecting the first bottom liquid to a first low-temperature crystallization at 0°C to obtain potassium chloride, wherein the remaining saturated solution after the first low-temperature crystallization is the first crystallization residue.

[0046] In some embodiments, S4 specifically includes: subjecting the filtrate to a second vacuum evaporation to obtain a second distillate and a second bottom liquid, wherein the second distillate is water; subjecting the second bottom liquid to a second low-temperature crystallization at 0°C to obtain potassium chloride; the remaining saturated solution after the second low-temperature crystallization is the second crystallization residue, which is returned to the filtrate to achieve resource utilization treatment of the carbon washing wastewater from the silicon-carbon anode skeleton.

[0047] In some embodiments, the iron (Fe) content in the carbonate washing wastewater of the silicon-carbon anode framework is 48.5 mg / L, and the Cl content is... - The content was 34.5 g / L, K + The content is 28 g / L, H + The content of [unspecified substance] is 0.427 g / L, and the TDS (total dissolved solids / total dissolved solids) content is 89 g / L; the EC (conductivity) of the silicon-carbon anode skeleton carbon acid washing wastewater is 214 mS / cm.

[0048] In some embodiments, a treatment system for carbon washing wastewater from silicon-carbon anode frameworks is also provided, comprising: High-pressure nanofiltration system: Used to pass the carbonate washing wastewater from the silicon-carbon anode framework into the high-pressure nanofiltration system to obtain enriched K. + H + Cl - Permeate and enriched Fe 2+ Fe 3+ retentate; First-stage vacuum evaporation system: connected to the high-pressure nanofiltration system, used to perform the first vacuum evaporation of the permeate to obtain dilute hydrochloric acid solution, potassium salt and primary crystallization residue; Alkali precipitation filtration system: connected to a high-pressure nanofiltration system, used to mix the residual liquid from primary crystallization and the retentate, and then add alkali to obtain iron sludge and filtrate; Secondary vacuum evaporation system: Connected to the alkali precipitation and filtration system, it is used to perform secondary vacuum evaporation of the filtrate to obtain water, salt and secondary crystallization residue. The secondary crystallization residue is returned to the filtrate to achieve resource utilization of the carbon washing wastewater of silicon-carbon anode skeleton.

[0049] In some embodiments, the high-pressure nanofiltration system includes an 8040 type acid-resistant aromatic polyamide spiral wound nanofiltration membrane module and three acid-resistant centrifugal pumps connected in series for pressurizing the carbonate washing wastewater of the silicon-carbon anode skeleton. The inlet of the first vacuum evaporation system is connected to the permeate outlet of the high-pressure nanofiltration system. The bottom liquid outlet of the first vacuum evaporation system is also connected to the first low-temperature crystallization system. The first low-temperature crystallization system is used to crystallize the bottom liquid at low temperature to obtain potassium salt and primary crystallization residue. The inlet of the alkali precipitation filtration system is connected to the outlet of the retentate of the high-pressure nanofiltration system and the outlet of the primary crystallization residue of the low-temperature crystallization system, respectively. The inlet of the second vacuum evaporation system is connected to the filtrate outlet of the alkali precipitation and filtration system. The bottom liquid outlet of the second vacuum evaporation system is also connected to the second low-temperature crystallization system, which is used to crystallize the bottom liquid at low temperature to obtain potassium salt and secondary crystallization residue.

[0050] In practical applications, the raw wastewater from the washing of silicon-carbon anode skeleton carbon is processed through a nanofiltration membrane system for salt separation, yielding nanofiltration permeate and nanofiltration concentrate (retentate). The nanofiltration permeate is enriched with potassium. + / H + / Cl - Monovalent salt ions, nanofiltration concentrate enriches Fe 2+ Fe 3+ After passing through vacuum evaporation system 1 (first vacuum evaporation system) with high-valence salt ions, the nanofiltration permeate yields dilute hydrochloric acid evaporate that can be directly reused. The liquid at the bottom of the evaporation vessel is used to prepare pure potassium chloride salt through a low-temperature crystallization system. The remaining saturated liquid is mixed with the nanofiltration concentrate and then enters an alkali precipitation filtration system. After reaction and solid-liquid separation, filtrate and iron sludge are obtained. The iron sludge is transported off-site for disposal. The filtrate enters vacuum evaporation system 2 (second vacuum evaporation system). The pure water evaporate produced by evaporation is reused. The liquid at the bottom of the evaporation vessel is again used to prepare pure potassium chloride salt through a low-temperature crystallization system. The remaining saturated liquid is combined with the filtrate and then recycled.

[0051] Because nanofiltration concentrate enriched with high-valent salt ions still retains a small amount of monovalent ions, and nanofiltration leachate enriched with monovalent salt ions also contains trace amounts of high-valent ions, this process employs a dual-path coupled circulation system to ensure full resource utilization of all types of salt ions in the wastewater and further improve product purity and yield. After iron removal via an alkali precipitation filtration system, the high-valent nanofiltration concentrate (retentate) is followed by a filtrate that enters a vacuum evaporation system 2 and a low-temperature crystallization system to produce potassium chloride. Similarly, after potassium chloride production via a vacuum evaporation system 1 and a low-temperature crystallization system, the monovalent nanofiltration leachate (leachate) is mixed with the high-valent nanofiltration concentrate and then separated from the iron sludge via an alkali precipitation filtration system.

[0052] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the method for treating stainless steel pickling wastewater of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. Obviously, the specific embodiments described are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its application. Based on the specific embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0053] Where specific techniques or conditions are not specified in the detailed embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products. Example 1

[0054] The acid washing wastewater used below for silicon-carbon anode skeleton carbon comes from the raw acid washing wastewater of the acid washing process in the silicon-carbon anode skeleton carbon production line. Testing revealed that the iron (Fe) content in the silicon-carbon anode skeleton carbon acid washing wastewater was 48.5 mg / L, and the Cl content was... - The content was 34.5 g / L, K + The content is 28 g / L, H + The content of [unspecified substance] was 0.427 g / L, and the TDS (total dissolved solids / total dissolved solids) content was 89 g / L; the EC (conductivity) of the silicon-carbon anode skeleton carbon washing wastewater was 214 mS / cm. The specific water quality indicators of the silicon-carbon anode skeleton carbon washing wastewater are shown in Table 1. Table 1 shows the specific water quality indicators of the carbonate washing wastewater from the silicon-carbon anode framework. Among them, the determination of iron (Fe) content in the carbonate washing wastewater of silicon-carbon anode framework refers to GB 11911-89 "Determination of Iron and Manganese in Water - Flame Atomic Absorption Spectrophotometry"; the determination of pH value refers to HJ 1147-2020 "Determination of pH Value in Water - Glass Electrode Method"; Cl - The determination of the content was performed in accordance with GB / T 11896-1989 "Determination of Chloride in Water - Silver Nitrate Titration Method"; K + The determination of content refers to GB / T 11904-1989 "Determination of Potassium and Sodium in Water - Flame Atomic Absorption Spectrophotometry"; the determination of TDS content refers to HJ 51—2024 "Determination of Total Salt Content in Water - Gravimetric Method" (General Gravimetric Method for Determination of Total Dissolved Solids in Water); the determination of EC (conductivity) refers to GB / T 6908-2018 "Analytical Methods for Boiler Water and Cooling Water - Determination of Conductivity", and the subsequent determination of pickling wastewater refers to the same method.

[0055] like Figure 1 As shown, the treatment method for the washing wastewater of silicon-carbon anode skeleton carbon includes the following steps: S1. Nanofiltration Separation: The raw wastewater from the washing of the silicon-carbon anode framework carbon acid is pressurized to 1.2 MPa by three acid-resistant centrifugal pumps connected in series and then enters an industrial-grade 8040 acid-resistant aromatic polyamide spiral wound nanofiltration membrane module. The membrane units in the spiral wound nanofiltration module sieve multivalent ions, removing a large amount of Fe... 2+ Fe 3+ Ions are retained by the nanofiltration membrane module, yielding a retentate (Q2=0.32), while K... + H + Cl - Monovalent ions pass through the nanofiltration membrane module to obtain permeate (Q=0.68). Three parallel samples each of the raw water and permeate from the carbon washing wastewater of the silicon-carbon anode skeleton were taken. Using GB 11911-89 "Determination of Iron and Manganese in Water - Flame Atomic Absorption Spectrophotometry", the average total iron ion concentration (C0) in the raw water of the silicon-carbon anode skeleton carbon washing wastewater of the three parallel samples was measured to be 48.5 mg / L. The total iron ion concentration (including Fe) in the permeate of the three parallel samples was also measured. 2+ and Fe 3+ The average concentration C1 was 3.88 mg / L, and then the iron ion removal rate η was calculated according to formula (Ⅰ).

[0056] In formula (Ⅰ), This indicates the iron ion removal rate. C1 represents the average iron ion concentration in the raw water of the silicon-carbon anode skeleton carbon washing wastewater of the three parallel samples, in mg / L. C2 represents the average iron ion concentration in the permeate of the three parallel samples, in mg / L.

[0057] The iron ion removal rate was significantly improved to 92.0% as calculated by formula (Ⅰ). The relative standard deviation (RSD) of the three parallel experiments was ≤0.5%, indicating the reliability of the data. This removal rate is significantly improved compared to the commonly used low-pressure nanofiltration membrane separation method (operating pressure 0.3~0.5MPa, iron ion removal rate 65%~70%) and traditional chemical precipitation pre-iron removal method (iron ion removal rate 75%~80%) in the field of silicon-carbon anode skeleton carbon washing wastewater treatment.

[0058] S2. Permeate Treatment: The 300 mL permeate obtained in S1 is subjected to a first vacuum evaporation at 91℃ and -0.1 MPa, resulting in 270 mL of dilute hydrochloric acid distillate (evaporator 1). This dilute hydrochloric acid distillate is directly reused in production. The remaining 30 mL of the bottom liquid is crystallized at 0℃. Figure 2 As shown, 4.22g of white granular solid was produced (tested according to GB / T 646-2011 "Chemical Reagents Potassium Chloride", purity ≥99.2%), which is potassium chloride salt 1, and the residual liquid from the first crystallization. S3. Iron Removal by Alkali Addition: Mix the residual liquid from the primary crystallization in S2 with the retentate from S1, resulting in a total mixed solution of 150 mL. Add 2 mL of a 40% potassium hydroxide aqueous solution to the mixed solution to adjust the pH to 8.34, so that the Fe in the mixed solution... 3+ Directly with OH - Combined to form Fe(OH)3 precipitate, Fe 2+ In the mixed solution, under the action of dissolved oxygen, it is first oxidized to Fe. 3+ Then with OH - Combined to form a stable Fe(OH)3 precipitate, such as Figure 3 As shown, filtration yielded iron sludge and filtrate. The iron sludge was dried to obtain 1.126g of solid iron sludge. Figure 4 As shown, the iron sludge concentration in the mixed solution is 7.5 g / L. S4. Filtrate Treatment: The filtrate (152 mL) obtained in S3 is subjected to a second vacuum evaporation at a temperature of 89℃ and a pressure of -0.1 MPa, producing 140 mL of recycled water (evaporated liquid 2) and 12 mL of secondary bottom liquid. The secondary bottom liquid is then crystallized at a temperature of 0℃. Figure 5As shown, 13.106g of white powdery solid was produced, which is potassium chloride salt 2 (tested according to GB / T 646-2011 "Chemical Reagents Potassium Chloride", purity ≥99.0%), as well as secondary crystallization residue. The secondary crystallization residue was returned to the filtrate to achieve resource utilization treatment of carbon washing wastewater from silicon-carbon anode skeleton.

[0059] In summary, the resource-based treatment method for the washing wastewater of silicon-carbon anode framework carbon of the present invention firstly achieves Fe... 2+ Fe 3+ With K + H + Cl - The precise physical separation is achieved; subsequently, the pH value is adjusted to alkaline by adding alkali in a targeted manner, thus completely solving the problem of iron ions being difficult to remove in a strong acid environment without introducing new impurities such as sodium ions; at the same time, the vacuum evaporation process is used to replace the traditional reverse osmosis concentration process, and the boiling point is lowered by negative pressure to achieve efficient component retention and direct reuse of dilute hydrochloric acid. In the end, multiple resource recovery of water, hydrochloric acid and potassium chloride salt is achieved. While ensuring the high purity of potassium chloride crystal salt, the generation of a large amount of difficult-to-treat solid impurities is avoided, which significantly reduces the hazardous waste disposal cost of enterprises. It has promotion and application value in the field of wastewater treatment technology.

[0060] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A method for the resource-based treatment of carbon washing wastewater from silicon-carbon anode frameworks, characterized in that, Includes the following steps: S1, nanofiltration separation: the silicon carbon negative electrode framework carbon acid pickling wastewater is passed into a nanofiltration system, and a permeate liquid rich in K + , H + , Cl - and a retentate liquid rich in Fe 2+ , Fe 3+ are obtained; S2. Permeate treatment: The permeate is subjected to a first vacuum evaporation to obtain a dilute hydrochloric acid solution, potassium salt and a primary crystallization residue; S3. Adding alkali to remove iron: After mixing the residual liquid from the first crystallization and the retentate, alkali is added to obtain iron mud and filtrate; S4. Filtrate treatment: The filtrate is subjected to a second vacuum evaporation to obtain water, salt and secondary crystallization residue. The secondary crystallization residue is returned to the filtrate to achieve resource utilization treatment of carbon washing wastewater from silicon-carbon anode skeleton.

2. The method for resource-based treatment of carbon washing wastewater from silicon-carbon anode frameworks according to claim 1, characterized in that, In S1, the nanofiltration system is a high-pressure nanofiltration system, which includes an industrial-grade 8040 type acid-resistant aromatic polyamide spiral wound nanofiltration membrane module. The high-pressure nanofiltration system operates at a pressure of 1.0~1.5MPa during the nanofiltration separation process.

3. The method for resource-based treatment of washing wastewater from silicon-carbon anode skeleton carbon according to claim 2, characterized in that, The industrial-grade 8040 type acid-resistant aromatic polyamide spiral wound nanofiltration membrane module.

4. The method for resource-based treatment of washing wastewater from silicon-carbon anode framework carbon as described in claim 1, characterized in that, In S2, the operating pressure for the first depressurization evaporation is -0.095 to -0.1 MPa, and the evaporation temperature is 88 to 93°C.

5. The method for resource-based treatment of washing wastewater from silicon-carbon anode framework carbon as described in claim 1, characterized in that, In S3, the base is selected from potassium hydroxide; And / or, in step S3, after mixing the crystallization residue and the retentate, an alkali is added to adjust the pH of the mixed solution to 8.0~8.6 to precipitate iron ions and obtain iron sludge and filtrate.

6. The method for resource-based treatment of washing wastewater from silicon-carbon anode framework carbon as described in claim 1, characterized in that, In S4, the operating pressure of the second vacuum distillation is -0.095 to -0.1 MPa, and the evaporation temperature is 85 to 90 °C.

7. The method for resource-based treatment of washing wastewater from silicon-carbon anode framework carbon as described in claim 1, characterized in that, S2 specifically includes: subjecting the permeate to a first vacuum evaporation to obtain a first distillate and a first bottom liquid, wherein the first distillate is a dilute hydrochloric acid solution; the first bottom liquid is subjected to a first low-temperature crystallization at 0°C to obtain potassium chloride, and the remaining saturated solution after the first low-temperature crystallization is the first crystallization residue. And / or, S4 specifically includes: subjecting the filtrate to a second vacuum evaporation to obtain a second distillate and a second bottom liquid, wherein the second distillate is water; subjecting the second bottom liquid to a second low-temperature crystallization at 0°C to obtain potassium chloride; the remaining saturated solution after the second low-temperature crystallization is the second crystallization residue, which is returned to the filtrate to achieve resource utilization of the carbon washing wastewater from the silicon-carbon anode skeleton.

8. The method for resource-based treatment of washing wastewater from silicon-carbon anode framework carbon as described in claim 1, characterized in that, The silicon carbon negative electrode framework carbon pickling wastewater contains 48.5 mg / L of iron (Fe) elements, 34.5 g / L of Cl - , 28 g / L of K + , 0.427 g / L of H + , and 89 g / L of TDS (total dissolved solids / dissolved total solids); the EC (electrical conductivity) of the silicon carbon negative electrode framework carbon pickling wastewater is 214 mS / cm.

9. A treatment system for carbonized washing wastewater from silicon-carbon anode skeletons, characterized in that, include: High-pressure nanofiltration system: Used to pass the carbonate washing wastewater from the silicon-carbon anode framework into the high-pressure nanofiltration system to obtain enriched K. + H + Cl - Permeate and enriched Fe 2+ Fe 3+ retentate; First-stage vacuum evaporation system: connected to the high-pressure nanofiltration system, used to perform a first-stage vacuum evaporation of the permeate to obtain a dilute hydrochloric acid solution, potassium salt, and a primary crystallization residue; Alkali precipitation and filtration system: connected to the high-pressure nanofiltration system, used to mix the primary crystallization residue and the retentate, and then add alkali to obtain iron mud and filtrate; Secondary vacuum evaporation system: connected to the alkali precipitation and filtration system, used to perform secondary vacuum evaporation on the filtrate to obtain water, salt and secondary crystallization residue. The secondary crystallization residue is returned to the filtrate to realize the resource utilization treatment of carbon washing wastewater from silicon-carbon anode skeleton.

10. The treatment system for carbon washing wastewater from silicon-carbon anode framework according to claim 9, characterized in that, The high-pressure nanofiltration system includes a connected 8040 type acid-resistant aromatic polyamide spiral wound nanofiltration membrane module and three acid-resistant centrifugal pumps connected in series to pressurize the carbonate washing wastewater of the silicon-carbon anode skeleton. The inlet of the first vacuum evaporation system is connected to the permeate outlet of the high-pressure nanofiltration system. The bottom liquid outlet of the first vacuum evaporation system is also connected to a first low-temperature crystallization system. The first low-temperature crystallization system is used to crystallize the bottom liquid at low temperature to obtain potassium salt and primary crystallization residue. The inlet of the alkali precipitation filtration system is connected to the outlet of the retentate of the high-pressure nanofiltration system and the outlet of the primary crystallization residue of the low-temperature crystallization system, respectively. The inlet of the second vacuum evaporation system is connected to the filtrate outlet of the alkali precipitation filtration system. The bottom liquid outlet of the second vacuum evaporation system is also connected to a second low-temperature crystallization system, which is used to crystallize the bottom liquid at low temperature to obtain potassium salt and secondary crystallization residue.

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