A process method for pretreating electrolytic tank wastewater

Abstract

The present application relates to the technical field of water, wastewater or sewage multi-stage treatment, and particularly relates to a kind of electrolytic cell wastewater pretreatment process methods.Taking clinoptilolite as carrier, functional seed is prepared by ferrous sulfate and potassium permanganate oxidation co-precipitation loading and drying;electrolytic cell wastewater is neutralized to pH 7~7.5 by sodium hydroxide, then continuously passes through main crystallization section filled with functional seed, sodium carbonate is added and air is introduced, pH is controlled to 8.5~9.0, effluent enters the section of check and continues to add sodium carbonate, pH is controlled to 9.0~9.5, manganese and calcium are fixed on the surface of seed in the form of carbonate crystalline layer, fine particles reflux, and the weight of bed material is increased, calcium manganese carbonate particle residue is obtained by screening.The effluent of the method has stable manganese lower than 1mg / L and does not need deep adjustment, the yield and moisture content of dry residue are far lower than that of lime neutralization method, the hardness of effluent does not increase, and the effluent remains stable under the impact of influent manganese.

Description

Technical Field

[0001] This invention relates to the field of multi-stage treatment technology for water, wastewater or sewage, and specifically to a pretreatment process for wastewater from an electrolytic cell. Background Technology

[0002] The wastewater from electrolytic cells in the electrolytic manganese and other non-ferrous metal electrolysis industries contains Mn 2+ Ammonia nitrogen and high concentrations of sulfate require pretreatment to reduce heavy metals such as manganese to below the limits for subsequent biological treatment or reuse before entering the subsequent biological treatment or reuse units. With increasingly stringent water pollution control requirements, the pretreatment of such wastewater not only demands stable effluent compliance but also requires reducing the generation of heavy metal-containing sludge and improving its resource properties. The industry continuously needs highly efficient, low-slag water pollution control agents and materials, as well as specialized agents and materials for environmental pollution treatment.

[0003] The most common pretreatment route currently is lime neutralization-flocculation sedimentation: lime slurry is added to the wastewater to raise the pH to above 10, causing manganese to precipitate as hydroxides, followed by flocculation and sedimentation separation. While the reagents for this route are readily available, the lime simultaneously generates a large amount of gypsum slag in high sulfate water conditions. This slag has a high water content, is difficult to dewater, and significantly increases the calcium hardness of the effluent, requiring subsequent pH adjustments. To improve the resource properties of the slag, patent CN107522324B discloses adding carbonates to electrolytic manganese wastewater to precipitate Mn. 2+ The process of returning manganese carbonate slag to the production system; Patent CN111606487A discloses a continuous treatment method that combines ammonium bicarbonate precipitation of manganese with multi-stage precipitation and stripping to remove ammonia. This type of carbonate precipitation occurs homogeneously in a stirred tank, requiring the addition of organic flocculants such as polyacrylamide to separate fine precipitates. Patent CN120794119A discloses a method of sequentially adding calcite or garnet seed crystals and sodium carbonate to wastewater, followed by mixing, crystallization, and precipitation to remove calcium and manganese ions.

[0004] Homogeneous carbonate precipitation produces fine manganese carbonate crystals with small particle size and slow settling. The resulting slag has a high water content and contains organic flocculants, affecting its recycling. Although using inert mineral seeds such as calcite can induce crystallization, the seed surface is not conducive to the growth of Mn. 2+ Lacking selectivity, its deep manganese removal capacity is limited; when the influent manganese concentration fluctuates, fine crystals penetrate, and the effluent manganese easily exceeds the standard. How to achieve deep and stable manganese removal without increasing the calcium hardness and sludge volume of the effluent is an unsolved technical problem in the field of electrolytic cell wastewater pretreatment. Summary of the Invention

[0005] In existing electrolytic cell wastewater pretreatment, lime neutralization and precipitation require raising the pH to above 10 to reduce the manganese in the effluent to the limit, resulting in a large amount of slag and increased calcium hardness in the effluent. When using carbonate homogeneous precipitation, fine crystals are difficult to settle, requiring the addition of organic flocculants. When the manganese concentration in the influent fluctuates, fine crystals penetrate, causing unstable manganese in the effluent. It is difficult to simultaneously achieve deep and stable manganese removal and low slag and low hardness.

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

[0007] A pretreatment process for electrolytic cell wastewater includes the following steps: S1, dispersing clinoptilolite particles in water, adding ferrous sulfate, and dropwise adding potassium permanganate solution while stirring, maintaining the pH of the system at 8-9 with alkaline solution during the dropwise addition, aging after addition, filtering, washing, and drying to obtain zeolite particles with iron-manganese composite oxides loaded on the surface, which serve as functional seed crystals; S2, neutralizing the electrolytic cell wastewater with sodium hydroxide solution to a pH of 7-7.5; S3, continuously processing the neutralized wastewater... Through the main crystallization section filled with the aforementioned functional seed crystals, sodium carbonate is added to the main crystallization section and air is introduced to control the pH of the main crystallization section to 8.5~9.0; S4, the effluent from the main crystallization section enters the gate section, sodium carbonate is added to the gate section to control the pH of the gate section to 9.0~9.5; S5, the effluent from the gate section is discharged after sedimentation; during operation, the fine particles carried out with the effluent from the main crystallization section and captured by the settling zone are returned to the main crystallization section, the increased bed material is screened, and manganese calcium carbonate granular slag is collected.

[0008] This method is applicable to Mn-containing compounds. 2+ With Ca 2+ Wastewater from electrolytic cells.

[0009] Furthermore, in step S1, the amount of ferrous sulfate is 4% to 8% of the dry weight of clinoptilolite, calculated as iron, and the amount of potassium permanganate is 1.5% to 3% of the dry weight of clinoptilolite, calculated as manganese.

[0010] Furthermore, in step S1, the loading reaction is carried out at 20~35℃, the ripening time is 1~2h, the drying temperature is 60~105℃, and the drying time is 2~4h.

[0011] Furthermore, the particle size of the functional seed crystals is 0.1~0.3mm, and the loading amount of the functional seed crystals in the main crystallization section is 20~50g / L.

[0012] Furthermore, the total amount of sodium carbonate added is the amount of Mn in the wastewater. 2+ With Ca 2+ The sum of molar amounts corresponds to 1.1 to 1.4 times the stoichiometry, with 70% to 85% of it being added to the main crystallization section and the remainder to the control section.

[0013] Furthermore, the hydraulic residence time of the main crystallization section is 30-60 min, and the hydraulic residence time of the gate section is 15-30 min; in step S3, air is introduced to make the dissolved oxygen in the main crystallization section 2-4 mg / L; and fine particles carried out with the effluent from the main crystallization section and captured in the settling zone are continuously refluxed back to the main crystallization section at 10%-30% of the influent flow rate.

[0014] Furthermore, the wastewater from the electrolytic cell is wastewater from an electrolytic manganese electrolytic cell, and the collected manganese calcium carbonate granular slag is returned to the electrolytic manganese production system for use as a manganese-containing raw material.

[0015] The beneficial effects of this invention are as follows:

[0016] (1) A seed bed is constructed using zeolite particles with surface-loaded iron-manganese composite oxides as functional seeds. Combined with the segmented addition of sodium carbonate and two-stage pH window control, manganese and calcium are epitaxially fixed on the seed surface in the form of carbonate crystal layers. The functional seeds and sodium carbonate together constitute a combination of water pollution control agents and materials for treating wastewater from electrolytic cells. The steady-state effluent contains Mn 2+ The concentration is below 1 mg / L, the pH does not exceed 9.5 throughout the process, and no deep backflushing is required for the effluent.

[0017] (2) Sodium carbonate is used instead of lime, which does not introduce calcium or generate gypsum slag. Manganese leaves the system in a dense particulate state. The dry slag yield and slag moisture content are much lower than those of the lime neutralization method. The slag does not contain organic flocculants and has a high manganese grade, which meets the conditions for returning to the electrolytic manganese production system as a manganese-containing raw material. The calcium hardness of the effluent does not increase but decreases, which is conducive to subsequent reuse treatment.

[0018] (3) The iron-manganese oxide layer on the surface of the seed crystal rapidly adsorbs and reduces the peak when the manganese concentration of the influent is impacted. The adsorbed manganese is transferred into the lattice with epitaxial crystallization, which makes the surface continuously renewed. Under micro-aeration conditions, the oxidation active sites contact and oxidize the residual manganese. The peak value of manganese in the effluent and the penetration of suspended solids under impact conditions are significantly lower than those when inert seed crystals are used, which improves the operational stability of the water pollution prevention agent and material system under the fluctuation of influent load.

[0019] (4) 70% to 85% of the total sodium carbonate dosage is added to the main crystallization section and the remainder is added to the control section. It is combined with the two pH windows to maintain a heterogeneous crystallization path with low supersaturation. The formation of homogeneous fine mud is inhibited and the suspended solids in the effluent are low. The total dosage is 1.1 to 1.4 times the stoichiometry to stably meet the standard and the reagent is fully utilized.

[0020] (5) The entire process is carried out at normal temperature and pressure. The raw materials are common industrial products such as clinoptilolite, ferrous sulfate, potassium permanganate, and sodium carbonate. The functional seed crystals are prepared by a two-step conventional loading process and can be implemented with conventional wastewater treatment equipment. Detailed Implementation

[0021] The present invention will be further described below with reference to preparation examples, embodiments, and comparative examples. The clinoptilolite powder used in the preparation examples, embodiments, and comparative examples was sourced from Jinyun Zeolite Powder Factory in Zhejiang Province. It is a clinoptilolite-type natural zeolite with a clinoptilolite content of not less than 65% and a particle size of 0.1-0.3 mm. The calcite particles used in the comparative example were heavy calcium carbonate sand produced in Hezhou, Guangxi, with a particle size of 0.1-0.3 mm. Among the remaining raw materials, ferrous sulfate was of water treatment grade, potassium permanganate, sodium hydroxide, and sodium carbonate were of industrial grade, and the reagents used to prepare the simulated wastewater were of analytical grade.

[0022] Preparation Example 1: Iron-manganese composite oxide supported zeolite functional seed crystals

[0023] 1000g of clinoptilolite powder was added to 5L of deionized water and stirred to disperse. 298.7g of ferrous sulfate heptahydrate was added and stirred at 25℃ until dissolved and evenly dispersed. Potassium permanganate aqueous solution (containing 63.3g of potassium permanganate) was added dropwise while stirring. During the addition, the pH of the system was maintained at 8.5 with 100g / L sodium hydroxide solution. After the addition was completed, stirring was continued for 1.5h to mature the mixture. The iron-manganese composite oxide layer was anchored on the surface of the zeolite particles through redox coprecipitation. The mixture was filtered and washed three times with deionized water until the washing liquid was colorless. The filter cake was dried at 80℃ for 3h, cooled, and sieved to collect particles with a particle size of 0.1~0.3mm, yielding 1029g of zeolite functional seed crystals supported on iron-manganese composite oxide.

[0024] Preparation Example 2:

[0025] Except for changing the amount of ferrous sulfate heptahydrate to 199.1g and the amount of potassium permanganate to 43.1g, the other raw materials, amounts and preparation conditions were the same as in Preparation Example 1, and 1000g of zeolite functional seed crystals supported on iron-manganese composite oxide were obtained.

[0026] Preparation Example 3:

[0027] Except for changing the amount of ferrous sulfate heptahydrate to 398.2g and the amount of potassium permanganate to 86.3g, the other raw materials, amounts and preparation conditions were the same as in Preparation Example 1, and 1057g of zeolite functional seed crystals supported on iron-manganese composite oxide were obtained.

[0028] Preparation Example 4: Simulated wastewater from an electrolytic manganese cell

[0029] The wastewater from a simulated manganese electrolytic cell was prepared by adding 0.615 g manganese sulfate monohydrate, 1.100 g calcium chloride dihydrate, 1.415 g ammonium sulfate, and 20.14 g anhydrous sodium sulfate per liter of water, and adjusting the pH to 5.5 with dilute sulfuric acid. The wastewater contained in the simulated manganese electrolytic cell contained Mn. 2+ The mass concentration is 200 mg / L, Ca 2+The mass concentrations are 300 mg / L, ammonia nitrogen, and sulfate, respectively. The water used for the impact test has its manganese sulfate monohydrate dosage changed to 1.230 g (Mn). 2+ Except for the concentration of 400 mg / L, the other components are the same as the water preparation method described above.

[0030] Example 1:

[0031] Step (1): Add 175g of the functional seed crystals obtained in Preparation Example 1 (bed loading amount 35g / L) to the stirred crystallization reactor of the main crystallization section (hereinafter referred to as the main section) with an effective volume of 5L. Turn on the stirring to suspend the particles and introduce air through the microporous aerator to maintain the dissolved oxygen in the main section at 3mg / L. The effluent from the main section overflows into the stirred reactor of the gate section with an effective volume of 2.5L through the conical settling zone. The fine crystals in the settling zone are continuously refluxed back to the main section by the circulating pump at 20% of the influent flow rate.

[0032] Step (2): The simulated wastewater obtained in Example 4 was continuously fed into the neutralization tank at a rate of 6.7 L / h. The pH was adjusted to 7.2 with 100 g / L sodium hydroxide solution before entering the main section.

[0033] Step (3): Continuously add 100 g / L sodium carbonate aqueous solution to the main section at a rate of 77.1 mL / h, controlling the pH of the main section to 8.8 and the hydraulic retention time to 45 min. Mn 2+ With Ca 2+ Heterogeneous nucleation and epitaxial growth of carbonate crystal layers occur on the surface of functional seed crystals.

[0034] Step (4): The effluent from the main section enters the control section. A 100 g / L sodium carbonate aqueous solution is added to the control section at a rate of 21.7 mL / h, controlling the pH at 9.2 and the residence time at 22 min. No additional aeration is provided in the control section; it relies on the dissolved oxygen carried by the effluent from the main section. Fine crystals enter the control section with the effluent from the main section, and residual Mn... 2+ Under low supersaturation, it continues to deposit and grow on its surface, and is trapped by inclined plate precipitation; under impact conditions, excess Mn 2+ The iron-manganese oxides are mainly adsorbed and contacted for oxidation and retention at the active sites on the surface of the functional seed crystals within the main bed.

[0035] Step (5): The effluent from the control section is continuously discharged after passing through the inclined plate sedimentation zone; it runs continuously for 72 hours, treating a total of 482L of simulated wastewater, with a cumulative addition of 711g of sodium carbonate; after the operation is completed, the bed material is removed, screened with 0.3mm, and combined with the fine mud from the sedimentation zone for collection, to obtain pretreated effluent and calcium manganese carbonate granular slag.

[0036] Example 2:

[0037] Step (1): Add 100g of the functional seed crystals obtained in Preparation Example 2 (bed filling amount 20g / L) to the main section stirred crystallization reactor with an effective volume of 5L. Turn on the stirring to suspend the particles. Introduce air through the microporous aerator to maintain the dissolved oxygen in the main section at 2mg / L. The effluent from the main section overflows into the gate section stirred reactor with an effective volume of 2.5L through the conical settling zone. The fine crystals in the settling zone are continuously refluxed back to the main section by the circulating pump at 10% of the influent flow rate.

[0038] Step (2): The simulated wastewater obtained in Example 4 was continuously fed into the neutralization tank at a rate of 10 L / h. The pH was adjusted to 7.2 with 100 g / L sodium hydroxide solution before entering the main section.

[0039] Step (3): Continuously add 100 g / L sodium carbonate aqueous solution to the main section at a rate of 90.8 mL / h, controlling the pH of the main section to 8.5 and the hydraulic retention time to 30 min. Mn 2+ With Ca 2+ Heterogeneous nucleation and epitaxial growth of carbonate crystal layers occur on the surface of functional seed crystals.

[0040] Step (4): The effluent from the main section enters the control section. A 100 g / L sodium carbonate aqueous solution is added to the control section at a rate of 38.9 mL / h, controlling the pH at 9.0 and the residence time at 15 min. No additional aeration is provided in the control section; it relies on the dissolved oxygen carried by the effluent from the main section. Fine crystals enter the control section with the effluent from the main section, and residual Mn... 2+ Under low supersaturation, it continues to deposit and grow on its surface, and is trapped by inclined plate precipitation; under impact conditions, excess Mn 2+ The iron-manganese oxides are mainly adsorbed and contacted for oxidation and retention at the active sites on the surface of the functional seed crystals within the main bed.

[0041] Step (5): The effluent from the control section is continuously discharged after passing through the inclined plate sedimentation zone; it runs continuously for 72 hours, treating a total of 720L of simulated wastewater, with a cumulative addition of 934g of sodium carbonate; after the operation is completed, the bed material is removed, screened through a 0.3mm sieve, and combined with the fine mud from the sedimentation zone for collection, to obtain pretreated effluent and calcium manganese carbonate granular residue.

[0042] Example 3:

[0043] Step (1): Add 250g of the functional seed crystals obtained in Preparation Example 3 (bed filling amount 50g / L) to the main section stirred crystallization reactor with an effective volume of 5L. Turn on the stirring to suspend the particles. Introduce air through the microporous aerator to maintain the dissolved oxygen in the main section at 4mg / L. The effluent from the main section overflows into the gate section stirred reactor with an effective volume of 2.5L through the conical settling zone. The fine crystals in the settling zone are continuously refluxed back to the main section by the circulating pump at 30% of the influent flow rate.

[0044] Step (2): The simulated wastewater obtained in Example 4 was continuously fed into the neutralization tank at a rate of 5 L / h. The pH was adjusted to 7.2 with 100 g / L sodium hydroxide solution before entering the main section.

[0045] Step (3): Continuously add 100 g / L sodium carbonate aqueous solution to the main section at a rate of 70.2 mL / h, controlling the pH of the main section to 9.0 and the hydraulic retention time to 60 min. Mn 2+ With Ca 2+ Heterogeneous nucleation and epitaxial growth of carbonate crystal layers occur on the surface of functional seed crystals.

[0046] Step (4): The effluent from the main section enters the control section. A 100 g / L sodium carbonate aqueous solution is added to the control section at a rate of 12.4 mL / h, controlling the pH at 9.5 and the residence time at 30 min. No additional aeration is provided in the control section; it relies on the dissolved oxygen carried by the effluent from the main section. Fine crystals enter the control section with the effluent from the main section, and residual Mn... 2+ Under low supersaturation, it continues to deposit and grow on its surface, and is trapped by inclined plate precipitation; under impact conditions, excess Mn 2+ The iron-manganese oxides are mainly adsorbed and contacted for oxidation and retention at the active sites on the surface of the functional seed crystals within the main bed.

[0047] Step (5): The effluent from the control section is continuously discharged after passing through the inclined plate sedimentation zone; it runs continuously for 72 hours, treating a total of 360L of simulated wastewater, with a cumulative addition of 595g of sodium carbonate; after the operation is completed, the bed material is removed, screened through a 0.2mm sieve, and combined with the fine mud from the sedimentation zone for collection, to obtain pretreated effluent and calcium manganese carbonate granular residue.

[0048] Example 4:

[0049] Step (1): Add 175g of the functional seed crystals obtained in Preparation Example 2 (bed loading amount 35g / L) to the main section stirred crystallization reactor with an effective volume of 5L. Turn on the stirring to suspend the particles. Introduce air through the microporous aerator to maintain the dissolved oxygen in the main section at 3mg / L. The effluent from the main section overflows into the gate section stirred reactor with an effective volume of 2.5L through the conical settling zone. The fine crystals in the settling zone are continuously refluxed back to the main section by the circulating pump at 20% of the influent flow rate.

[0050] Step (2): The simulated wastewater obtained in Example 4 was continuously fed into the neutralization tank at a rate of 6.7 L / h. The pH was adjusted to 7.2 with 100 g / L sodium hydroxide solution before entering the main section.

[0051] Step (3): Continuously add 100 g / L sodium carbonate aqueous solution to the main section at a rate of 77.1 mL / h, controlling the pH of the main section to 8.8 and the hydraulic retention time to 45 min. Mn 2+ With Ca 2+ Heterogeneous nucleation and epitaxial growth of carbonate crystal layers occur on the surface of functional seed crystals.

[0052] Step (4): The effluent from the main section enters the control section. A 100 g / L sodium carbonate aqueous solution is added to the control section at a rate of 21.7 mL / h, controlling the pH at 9.2 and the residence time at 22 min. No additional aeration is provided in the control section; it relies on the dissolved oxygen carried by the effluent from the main section. Fine crystals enter the control section with the effluent from the main section, and residual Mn... 2+ Under low supersaturation, it continues to deposit and grow on its surface, and is trapped by inclined plate precipitation; under impact conditions, excess Mn 2+ The iron-manganese oxides are mainly adsorbed and contacted for oxidation and retention at the active sites on the surface of the functional seed crystals within the main bed.

[0053] Step (5): The effluent from the control section is continuously discharged after passing through the inclined plate sedimentation zone; it runs continuously for 72 hours, treating a total of 482L of simulated wastewater, with a cumulative addition of 711g of sodium carbonate; after the operation is completed, the bed material is removed, screened with 0.3mm, and combined with the fine mud from the sedimentation zone for collection, to obtain pretreated effluent and calcium manganese carbonate granular slag.

[0054] Comparative Example 1:

[0055] The simulated wastewater obtained in Preparation Example 4 was continuously fed into the treatment system at a rate of 6.7 L / h: in the first stage, the pH was adjusted to 7.5 with 100 g / L lime slurry, and in the second stage, the pH was adjusted to 10.5 with lime slurry and stirred for 30 min. 3 mg / L polyacrylamide was added for flocculation. After sedimentation on an inclined plate, the pH of the effluent was adjusted back to 7.5 with sulfuric acid. The system was run continuously for 72 h to obtain effluent and lime neutralization residue.

[0056] Comparative Example 2:

[0057] Except for the fact that no functional seed crystals are loaded in the main section and all sodium carbonate is continuously added in the main section (no sodium carbonate is added in the control section), the other raw materials, dosages and operating conditions are the same as in Example 1, and effluent and sediment are obtained.

[0058] Comparative Example 3:

[0059] Except for replacing the functional seed crystals obtained in Preparation Example 1 with calcite particles of equal mass, the other raw materials, dosages, and operating conditions were the same as in Example 1, resulting in effluent and slag.

[0060] Comparative Example 4:

[0061] Except for replacing the functional seed crystals obtained in Preparation Example 1 with an equal mass of unloaded clinoptilolite particles (particle size 0.1~0.3 mm), the other raw materials, dosages and operating conditions were the same as in Example 1, and effluent and slag were obtained.

[0062] Comparative Example 5:

[0063] Except for not installing a seed bed, grinding the functional seed crystals obtained in Preparation Example 1 to a particle size of less than 0.045 mm and continuously adding them to the main section at 0.363 g / L with the influent, the other raw materials, dosages and operating conditions are the same as in Example 1, and effluent and slag are obtained.

[0064] Comparative Example 6:

[0065] Except for the main section and the control section where no air is introduced and nitrogen is used for micro-purging to keep the dissolved oxygen below 0.5 mg / L, the other raw materials, dosages and operating conditions are the same as in Example 1, and the resulting effluent and slag are obtained.

[0066] Comparative Example 7:

[0067] Except for changing the total sodium carbonate dosage to 0.95 times the stoichiometric amount (541g added cumulatively over 72 hours of operation, still allocated as 78% in the main section and 22% in the control section), and no longer using pH as the control target and adding it at a fixed rate (the pH of the main section drops below 8.5 during operation), the other raw materials, dosages and operating conditions are the same as in Example 1, and the effluent and slag are obtained.

[0068] Comparative Example 8:

[0069] Except for changing the sodium carbonate addition ratio of the main section and the control section to 60% and 40% respectively, the other raw materials, dosages and operating conditions are the same as in Example 1, and the effluent and slag are obtained.

[0070] Comparative Example 9:

[0071] Except for changing the sodium carbonate addition ratio of the main section and the control section to 90% and 10% respectively, the other raw materials, dosages and operating conditions are the same as in Example 1, and the effluent and slag are obtained.

[0072] Comparative Example 10:

[0073] Except for sodium carbonate, which is continuously added in the main section and not added in the control section, the other raw materials, dosages and operating conditions are the same as in Example 1, and the resulting effluent and slag are obtained.

[0074] Performance testing:

[0075] Each indicator was measured in triplicate, and the arithmetic mean was taken. Effluent water quality: Effluent from each embodiment and comparative example was collected during the steady-state operation period (24h, 48h, and 72h). Mn 2+The following standards were applied: Iron and Manganese were determined according to GB 11911-89 "Determination of Iron and Manganese in Water - Flame Atomic Absorption Spectrophotometry"; Total Hardness was determined according to GB / T 7477-87 "Determination of Total Calcium and Magnesium in Water - EDTA Titration Method" (calculated as CaCO3); pH was determined according to HJ 1147-2020 "Determination of pH Value in Water - Electrode Method"; Suspended Solids were determined according to GB / T 11901-89 "Determination of Suspended Solids in Water - Gravimetric Method"; Sulfate was determined according to GB / T 11899-89 "Determination of Sulfate in Water - Gravimetric Method". Results are shown in Table 1.

[0076] Slag properties: Solids discharged during operation (granular slag and fine mud from the sedimentation zone, including seed crystals) were collected, drained for 30 minutes, weighed wet, and then kept at constant weight at 55-60℃. The dry slag yield was expressed as the ratio of constant weight to treated water volume, and the slag moisture content was expressed as the percentage of the difference between wet and dry weight to the wet weight. After mixing the slag samples, they were dissolved in hydrochloric acid, and the Mn content in the solution was determined according to GB 11911-89 to obtain the mass fraction of Mn in the dry slag. The results are shown in Table 2.

[0077] Impact Conditions: The device and operating conditions are the same as in the corresponding embodiment or comparative example. After 24 hours of steady-state operation, the influent is switched to the impact water distribution (Mn) described in Preparation Example 4. 2+ Run at 400 mg / L for 2 hours, taking water samples every 20 minutes. Mn 2+ The peak values ​​during operation were recorded according to GB 11911-89 for measured solids and GB / T 11901-89 for suspended solids. The average value of three independent impact tests was taken. The results are shown in Table 3.

[0078] Table 1. Steady-state effluent water quality of each embodiment and comparative example

[0079]

[0080] Table 2 Slag properties of each embodiment and comparative example

[0081]

[0082] Table 3 Peak effluent flow rates of each embodiment and comparative example under impact conditions

[0083]

[0084] Results Analysis

[0085] As shown in Tables 1 and 2, the steady-state effluent Mn in Examples 1 to 4 2+ The concentrations were 0.20~0.77 mg / L, all below 1 mg / L, while the effluent Mn from the comparative example 1, which used lime neutralization-flocculation sedimentation, was much higher. 2+ The concentration was 1.44 mg / L, the total hardness of the effluent reached 1200 mg / L, and the dry residue yield was 14.2 kg / m³.3 The slag moisture content was 91.1%; the dry slag yield of Example 1 was 1.29 kg / m³. 3 The slag moisture content was 49.9%, and the Mn grade in the slag increased from 1.4% in Comparative Example 1 to 16.0%. The total hardness of the effluent was 215 mg / L, and the pH of the effluent was 8.9, requiring no deep backflushing. This indicates that using sodium carbonate segmental crystallization granulation instead of lime neutralization and precipitation effectively reduced the Mn content in the effluent. 2+ While reducing the value below the limit, the amount of slag and the moisture content of the slag were reduced, avoiding the increase of calcium hardness. The resulting granular slag had a Mn grade of 13.1%~18.9%, which is comparable to the low-grade manganese carbonate ore powder used as raw material in the electrolytic manganese industry. It does not contain organic flocculants and can be dissolved in sulfuric acid and incorporated into the electrolytic manganese liquid preparation process, thus having the grade basis for return to the electrolytic manganese production system.

[0086] Comparative Example 2 used seedless homogeneous sodium carbonate precipitation, with an effluent suspended solids content of 46 mg / L and a slag moisture content of 86.9%. Under impact conditions, the effluent Mn... 2+ The peak concentrations reached 3.41 mg / L and suspended solids reached 105 mg / L, both significantly worse than in Example 1. This indicates that the seed bed promotes heterogeneous growth of carbonates on the particle surface, inhibiting the formation of homogeneous fine sludge, which is the basis for the dense granular state of the sludge and the stability of the effluent. Comparative Example 10 retained the seed bed and only added all sodium carbonate to the main section, resulting in a significantly lower Mn concentration in the impact effluent. 2+ The peak value was 1.31 mg / L and the slag moisture content was 58.2%, which was between that of Example 1 and Comparative Example 2. It can be seen that the deterioration of Comparative Example 2 mainly came from the elimination of the seed bed, and the rest came from the elimination of the segmented addition.

[0087] Comparative Example 3 used calcite particles as seed crystals, and Comparative Example 4 used unsupported zeolite as seed crystals. Steady-state effluent Mn 2+ The concentrations were 0.57 mg / L and 0.62 mg / L, respectively, higher than the 0.32 mg / L in Example 1; the effluent Mn under shock conditions was also higher in both cases. 2+ The peak values ​​were 1.62 mg / L and 1.46 mg / L, respectively, more than three times that of Example 1 (0.41 mg / L). The iron-manganese composite oxide supported layer reduced the effluent Mn content under steady-state conditions. 2+ It suppressed the penetration of fine mud and the increase of peak value under impact conditions.

[0088] Comparative Example 5: The same functional seed crystals were ground into powder and added directly to the influent water, resulting in a steady-state effluent Mn. 2+ The concentration was 0.48 mg / L, slightly higher than the 0.32 mg / L in Example 1, but the effluent Mn under shock conditions was higher. 2+The peak concentration reached 2.69 mg / L, the peak concentration of suspended solids reached 117 mg / L, and the slag moisture content was 84.1%. It can be seen that when the powder is added directly, the adsorption sites are quickly saturated and lost with the slag. Only when it operates in the form of a seed bed and the adsorbed manganese is transferred into the crystal lattice through epitaxial crystallization to continuously renew the surface can the peak-shaving ability be maintained under impact conditions. This effect comes from the combination of functional seed crystals and crystallization bed, which cannot be achieved by ordinary addition methods.

[0089] Comparative Example 6 operated with dissolved oxygen below 0.5 mg / L, steady-state effluent Mn 2+ The concentration was 0.51 mg / L, and the peak impact concentration was 0.96 mg / L, both lower than in Example 1. This indicates that under micro-aeration conditions, the active sites of iron-manganese oxides contact and oxidize the residual manganese at the end of the crystallization reaction, ultimately ensuring that the manganese concentration in the effluent meets the standard.

[0090] Comparative Example 7 reduced the sodium carbonate dosage to 0.95 times the stoichiometric amount, and the effluent Mn 2+ The concentration was 2.63 mg / L, exceeding 1 mg / L, and the total hardness of the effluent rose to 390 mg / L. This indicates that when the dosage was lower than the stoichiometric level, the precipitation of crystal-forming ions was incomplete, and the pH values ​​at both stages were below the window specified by this method, thus failing to achieve the pretreatment target. Example 2 showed that the effluent Mn at 1.1 times the stoichiometric level... 2+ The concentration was 0.77 mg / L, which still meets the standard.

[0091] Comparative Examples 8 and 9 had their main section dosage adjusted to 60% and 90%, respectively, resulting in effluent suspended solids of 28 mg / L and 25 mg / L, and Mn in the shock effluent. 2+ The peak values ​​were 0.94 mg / L and 1.18 mg / L, respectively. In Comparative Example 10, when all the additives were added in the main stage, the effluent suspended solids were 32 mg / L, and the peak shock concentration was 1.31 mg / L, both of which were worse than those in Examples 1 to 3, where the main stage additive ratio was 70% to 85%. When the main stage ratio was too low, the local supersaturation in the control stage increased; when the ratio was too high or the additives were not added in stages, the supersaturation in the main stage became uncontrolled, both of which led to an increase in homogeneous fine sludge and a decrease in shock stability.

[0092] Example 4 differs from Example 1 only in the seed loading; its impact-induced water discharge Mn 2+ The peak concentration was 0.58 mg / L, higher than 0.41 mg / L in Example 1, while the steady-state effluent concentration was similar. This shows that the load primarily affects the buffering capacity under shock conditions. Example 3 showed that the effluent Mn concentration was [not specified] at a dosage factor of 1.4. 2+ The lowest, but the dry slag yield is 1.65 kg / m³. 3 The pH of the effluent was 9.4, which was higher than that of Example 1. The sulfate content of the effluent in each example of this process was 14.9~15.1 g / L, which was higher than that of Comparative Example 1 (8.1 g / L). The removal of sulfate was undertaken by the subsequent treatment unit.

Claims

1. A pretreatment process for wastewater from an electrolytic cell, characterized in that, Includes the following steps: S1. Disperse clinoptilolite particles in water, add ferrous sulfate, and add potassium permanganate solution dropwise while stirring. During the dropwise addition, maintain the pH of the system at 8-9 with alkaline solution. After the dropwise addition is complete, allow it to mature, filter, wash, and dry to obtain zeolite particles with iron-manganese composite oxides loaded on the surface, which are used as functional seed crystals. S2. Neutralize the electrolytic cell wastewater with sodium hydroxide solution to a pH of 7-7.5; S3. The neutralized wastewater is continuously passed through the main crystallization section filled with the functional seed crystals. Sodium carbonate is added to the main crystallization section and air is introduced to control the pH of the main crystallization section to 8.5~9.

0. S4. The effluent from the main crystallization section enters the control section. Sodium carbonate is continuously added to the control section to control the pH of the control section to 9.0~9.

5. S5. The effluent from the control section is discharged after sedimentation; during operation, the fine particles carried out with the effluent from the main crystallization section and captured in the settling zone are returned to the main crystallization section, and the increased bed material is screened to collect manganese calcium carbonate granular slag.

2. The pretreatment process for electrolytic cell wastewater according to claim 1, characterized in that, In step S1, the amount of ferrous sulfate is 4% to 8% of the dry weight of clinoptilolite, calculated as iron, and the amount of potassium permanganate is 1.5% to 3% of the dry weight of clinoptilolite, calculated as manganese.

3. The pretreatment process for electrolytic cell wastewater according to claim 1, characterized in that, The particle size of the functional seed crystals is 0.1~0.3 mm.

4. The pretreatment process for electrolytic cell wastewater according to claim 1, characterized in that, The amount of functional seed crystals in the main crystallization section is 20~50 g / L.

5. The pretreatment process for electrolytic cell wastewater according to claim 1, characterized in that, The total amount of sodium carbonate added is Mn in the wastewater 2+ With Ca 2+ The sum of molar amounts corresponds to 1.1 to 1.4 times the stoichiometry.

6. The pretreatment process for electrolytic cell wastewater according to claim 5, characterized in that, 70% to 85% of the total sodium carbonate dosage is added to the main crystallization section, and the remainder is added to the control section.

7. The pretreatment process for electrolytic cell wastewater according to claim 1, characterized in that, The hydraulic residence time in the main crystallization section is 30-60 minutes, and the hydraulic residence time in the control section is 15-30 minutes.

8. The pretreatment process for electrolytic cell wastewater according to claim 1, characterized in that, In step S3, air is introduced to make the dissolved oxygen in the main crystallization section 2~4 mg / L.

9. The pretreatment process for electrolytic cell wastewater according to claim 1, characterized in that, In step S5, the fine particles are continuously refluxed to the main crystallization section at a rate of 10% to 30% of the influent flow rate.

10. The pretreatment process for electrolytic cell wastewater according to claim 1, characterized in that, The wastewater from the electrolytic cell is wastewater from the electrolytic manganese electrolytic cell, and the collected manganese calcium carbonate granular slag is returned to the electrolytic manganese production system for use as a manganese-containing raw material.

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