Resourceful treatment process for dilute acid of waste lead-acid storage battery based on nanofiltration-electrodialysis synergetic waste heat evaporation

Abstract

The invention discloses a waste lead-acid storage battery dilute acid resourceful treatment process based on nanofiltration-electrodialysis synergetic waste heat evaporation, and belongs to the field of hazardous waste treatment. According to the process, impurities are removed through three-stage precision filtration (50 microns, 10 microns and 1 micron) and ultrafiltration (PVDF membrane) for the waste acid with the sulfuric acid concentration of 1.4%-2.3%, lead and cadmium ions are separated through an acid-resistant nanofiltration membrane (the molecular weight cutoff is 200-500 Da) (the rejection rate is larger than or equal to 95%), and low-heavy-metal acid liquor is obtained; and concentrating to 5-8% by electrodialysis, and purifying until the content of sulfuric acid is greater than or equal to 15% and the content of lead residue is less than or equal to 3.0 mg / L in combination with single-effect waste heat evaporation (60-80 DEG C), and directly recycling for electrolyte compounding. After the nanofiltration concentrated water and the electrodialysis waste liquid are neutralized and precipitated, the lead content of the sludge is greater than or equal to 5% (HW31 hazardous waste), and the lead curing rate is greater than or equal to 99.5%. Through a membrane separation and waste heat utilization synergistic technology, the recovery rate of sulfuric acid is greater than or equal to 85%, the sludge is reduced by 90%, the energy consumption is reduced by 50%, the problems of low recovery rate, high energy consumption and secondary pollution in low-concentration waste acid resourceful treatment are solved, and high efficiency and environmental friendliness are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource treatment of industrial hazardous waste, and particularly relates to a treatment process for low-concentration dilute acid (sulfuric acid concentration 1.4% - 2.3%) generated during the dismantling of waste lead-acid batteries. Through the integrated technology of three-stage precision filtration - ultrafiltration pretreatment, acid-resistant nanofiltration membrane heavy metal separation, electrodialysis preconcentration, and low-temperature waste heat evaporation, the present invention realizes the efficient recovery of sulfuric acid (concentration ≥ 15%) in waste acid and the deep removal of heavy metals (lead, cadmium) (residual ≤ 1.0 mg / L), and simultaneously completes the reduction of hazardous waste sludge (reduction by 90%) and the resource utilization of waste heat (evaporation energy consumption ≤ 0.5 tons of steam / ton of acid). The present invention is applicable to the clean and resource treatment of low-concentration waste acid in the lead-acid battery dismantling industry. Background Art

[0002] The dilute acid (sulfuric acid concentration 1.4% - 2.3%) generated from the dismantling of waste lead-acid batteries belongs to hazardous waste of HW31 class, and its treatment has long relied on the limestone neutralization method. This method neutralizes sulfuric acid by adding lime (Ca(OH)2) and precipitates heavy metals, but it has significant defects: (1) Resource waste: Sulfuric acid reacts with lime to form gypsum (CaSO4), which cannot be recycled; (2) Secondary pollution: Lead-containing sludge (lead content ≥ 5%) is generated, which needs to be disposed of as hazardous waste, and the sludge disposal cost of enterprises accounts for more than 40% of the total cost; (3) High energy consumption: If sulfuric acid needs to be recovered, the energy consumption of the traditional multi-effect evaporation process is as high as 1.2 tons of standard coal / ton of acid, and the economy is poor.

[0003] In recent years, membrane separation technologies (such as ultrafiltration, nanofiltration, electrodialysis) have been tried for waste acid treatment, but there are still bottlenecks: (1) Low recovery rate: According to the data in Table 2 of Paragraph

[0023] of the specification of CN112250218A, its sulfuric acid recovery rate is 68%, and the concentrated solution needs to be treated by additional evaporation, and the comprehensive energy consumption reaches 0.9 tons of steam / ton of acid; (2) Severe membrane fouling: Colloids and particulate matters in waste acid cause the ultrafiltration membrane flux to decay by > 30% per month, and the service life of ordinary membrane materials is less than 6 months under strong acid conditions (pH < 1); (3) Energy consumption contradiction: Although the "electrodialysis - reverse osmosis" process proposed in CN113880187A can purify to 15%, the reverse osmosis membrane is prone to hydrolysis at low pH, and the system energy consumption reaches 2.5 kWh / m 3 . Although the chemical polishing waste acid and the lead-acid battery waste acid belong to acidic hazardous waste, their heavy metal components (mainly aluminum and copper) and concentrations are significantly different, resulting in that the treatment process cannot be directly borrowed. The above problems seriously restrict the resource application of low-concentration waste acid. Summary of the Invention

[0004] [Technical Problem]

[0005] The traditional process for disassembling and treating dilute acid from waste lead-acid batteries has several problems, such as serious resource waste (sulfuric acid reacts with lime to form unrecoverable gypsum), high risk of secondary pollution (the disposal cost of lead-containing hazardous waste sludge accounts for more than 40% of the total cost), low recovery rate of membrane separation technology (the sulfuric acid recovery rate is only 60% - 70%), serious membrane pollution (the lifespan of ordinary membranes under strong acid conditions is less than 6 months), and excessive energy consumption (the energy consumption of the traditional evaporation process reaches 1.2 tons of standard coal per ton of acid). These problems have restricted the resource utilization of low-concentration waste acid.

[0006] [Technical Solution]

[0007] In the present invention, impurities are removed through three-stage precision filtration - ultrafiltration pretreatment. By combining an acid-resistant nanofiltration membrane (with a retention molecular weight of 200 - 500 Da), lead and cadmium ions are efficiently separated (the retention rate is ≥95%). Electrodialysis pre-concentration (acid recovery rate ≥80%) and low-temperature waste heat evaporation (energy consumption ≤0.5 tons of steam per ton of acid) are used to fractionally purify sulfuric acid to ≥15%, and at the same time, the co-disposal of neutralization precipitation hazardous waste is realized (lead solidification rate ≥99.5%). This process integrates membrane separation and waste heat utilization technologies, solves the problems of low recovery rate, high energy consumption, and secondary pollution in the treatment of low-concentration waste acid, and finally achieves a sulfuric acid recovery rate ≥85%, a 90% reduction in sludge volume, and a 50% reduction in comprehensive energy consumption, combining high efficiency and environmental protection.

[0008] To solve the technical problems and implement the technical solution, a process for resource utilization of dilute acid from waste lead-acid batteries based on the synergistic waste heat evaporation of nanofiltration - electrodialysis includes the following steps:

[0009] S1: Waste acid collection. The original acid solution generated from disassembling waste lead-acid batteries is collected into a waste acid collection tank, and the sulfuric acid concentration in the original acid solution is 1.4 - 2.3%.

[0010] S2: Pretreatment. The original acid solution in S1 is successively passed through three-stage precision filters (50μm, 10μm, and 1μm) and an ultrafiltration membrane device (PVDF) hollow fiber membrane with a pore size of 0.01 - 0.1μm and an operating pressure of (0.2 - 0.5 MPa) to obtain a filtered acid solution with COD < 150 mg / L, SS < 50 mg / L, and turbidity ≤ 1 NTU.

[0011] S3: Heavy metal separation. The filtered acid solution in S2 is treated by an acid-resistant nanofiltration membrane device. The acid-resistant nanofiltration membrane device includes two series-connected nanofiltration units. The first stage has a retention molecular weight of 300 - 500 Da, and the second stage has a retention molecular weight of 200 - 300 Da. The operating pressure is 12 - 25 bar, the lead ion retention rate is ≥97%, and the cadmium ion retention rate is ≥96%. A low-heavy metal acid solution (Pb 2+ ≤1.0 mg / L) and nanofiltration concentrate are obtained.

[0012] S4: Electro-dialysis concentration. The low heavy metal acid solution from S3 is concentrated through an electro-dialysis device (current density 20 - 50 mA / cm 2 ) to a sulfuric acid concentration of 5 - 8%, and the acid recovery rate in the electro-dialysis section is ≥80%;

[0013] S5: Waste heat evaporation. The concentrated acid solution from S4 is concentrated to a sulfuric acid concentration of ≥15% through a single-effect evaporator (evaporation temperature 60 - 80 °C) using the waste heat of lead smelting flue gas, and the evaporation energy consumption is ≤0.5 tons of steam / ton of acid;

[0014] S6: The finished acid is reused for the compounding of battery electrolyte;

[0015] S7: Hazardous waste disposal. The nanofiltration concentrated water from S3 and the electro-dialysis waste liquid from S4 are neutralized and precipitated (pH 8.5 - 9.5). The lead content in the resulting sludge is ≥5% (hazardous waste HW31), and the lead solidification rate is ≥99.5%;

[0016] The total sulfuric acid recovery rate of the process is ≥85%, and the sludge production is reduced by 90% compared with the traditional neutralization method.

[0017] The nanofiltration operating pressure of S3 is 18 - 22 bar, and the lead ion retention rate is ≥98%.

[0018] The electro-dialysis current density of S4 is 30 - 40 mA / cm 2 , and the concentration multiple is 2.8 - 3.2 times.

[0019] The evaporation temperature of S5 is 70 ± 2 °C, and the waste heat temperature of the lead smelting flue gas used is ≥150 °C.

[0020] For the neutralization precipitation in S7, lime milk is used, and the dosage is 3 - 5% of the waste liquid volume.

[0021] Material source

[0022] Ultrafiltration system. A polyvinylidene fluoride (PVDF) hollow fiber ultrafiltration membrane module is used. The membrane pore size is 0.01 - 0.1 μm, and the single membrane area is ≥40 m 2 , the operating pressure is 0.2 - 0.5 MPa, and the acid resistance is (pH 0 - 3);

[0023] Nanofiltration system. A two-stage acid-resistant nanofiltration membrane series process is configured: The first stage: the molecular weight cut-off is 300 - 500 Da, and the operating pressure is 18 - 22 bar; The second stage: the molecular weight cut-off is 200 - 300 Da, and the operating pressure is 12 - 15 bar; The membrane material is a sulfonated polyethersulfone (SPES) composite layer, and it can withstand pH 0 - 5;

[0024] Electro-dialysis device. It contains 200 pairs of anion and cation exchange membrane groups, and the effective area of a single membrane is 0.8 m 2 , and the current density is 20 - 50 mA / cm2 The ruthenium-coated titanium electrode can resist sulfuric acid with a concentration ≤ 15%.

[0025] Raw material source: The waste acid is taken from the dismantling workshop of a lead-acid battery recycling enterprise. The sulfuric acid concentration is 1.4 - 2.3%, the lead content is 8 - 15 mg / L, and other main water quality parameters are shown in Table 1.

[0026] Table 1 Main water quality parameters of the waste acid from the dismantling of waste lead-acid batteries

[0027]

[0028] [Beneficial effects]

[0029] Through the collaborative innovation of multi-stage membrane separation and waste heat evaporation technologies, this process has achieved a double breakthrough in the treatment efficiency and resource utilization level of low-concentration waste acid. By adopting a three-stage pretreatment coupled with an acid-resistant nanofiltration process, the interception rates of lead, cadmium and other ions are stabilized above 97%. The residual lead concentration in the produced water is ≤ 3.0 mg / L, and the heavy metal removal efficiency is increased by more than 40% compared with the traditional neutralization method, thus eliminating the risk of heavy metal leaching from hazardous waste sludge at the source. The combined design of electrodialysis preconcentration and low-temperature waste heat evaporation has increased the sulfuric acid recovery rate to above 85%, and at the same time, the evaporation energy consumption is controlled at 0.5 tons of steam / ton of acid, saving more than 50% energy compared with the traditional multi-effect evaporation process.

[0030] The system operation cost has been significantly optimized, mainly reflected in three aspects: First, through the separate treatment of heavy metal separation - acid concentration, the generation amount of hazardous waste sludge is reduced by 90%, and the annual hazardous waste disposal cost is reduced by more than 800,000 yuan; Second, using the waste heat of lead smelting flue gas (≥150 °C) to drive the evaporation process without external heat source, the steam consumption of single-effect evaporation is reduced by 60% compared with the conventional process; Third, the modular membrane system design extends the equipment maintenance cycle to 12 months and reduces the membrane module replacement frequency by 50%, and the comprehensive operation cost is reduced by 35% compared with the traditional membrane process.

[0031] The environmental protection benefits are prominently reflected in the whole-process closed treatment system without external discharge of waste gas and waste water. After the collaborative neutralization of nanofiltration concentrate and electrodialysis waste liquid, the lead solidification rate is ≥ 99.5%, and the final sludge lead content is stabilized at 5% - 7%, meeting the HW31 hazardous waste standard and the total amount is reduced by 90%. The recovered sulfuric acid purity is ≥ 15%, which can be directly used for electrolyte compounding, replacing more than 10,000 tons of new acid procurement annually, and realizing the closed-loop management of hazardous waste resource utilization. Description of the drawings

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will further explain the present invention in conjunction with the drawings and embodiments. The drawings in the following description are only partial embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts:

[0033] Figure 1 System flow block diagram of the present invention based on the synergistic waste heat evaporation process of nanofiltration and electrodialysis

[0034] Figure 2 Schematic diagram of process parameter control of the present invention Specific implementation manners

[0035] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will further describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present application. The described embodiments are only a part of the embodiments of the present application and are not limited to these embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present application.

[0036] Calculation method of performance indicators in the present invention

[0037] Calculation of sulfuric acid recovery rate:

[0038]

[0039] In the formula: η is the recovery rate of sulfuric acid (%), Q 原酸 is the volume of the original acid (m3), Q 浓水 is the volume of the nanofiltration concentrate (m 3 ), C 原酸 is the mass-volume concentration of sulfuric acid in the original acid (g / L), C 浓水 is the mass-volume concentration of sulfuric acid in the nanofiltration concentrate (g / L).

[0040] Calculation of heavy metal rejection rate:

[0041]

[0042] In the formula: R is the heavy metal rejection rate (%), C 产水 is the mass-volume concentration of heavy metals in the nanofiltration influent (mg / L).

[0043] Calculation of concentration multiple:

[0044]

[0045] In the formula: N is the concentration multiple, C 浓缩液 is the mass-volume concentration of sulfuric acid in the electrodialysis concentrate (mg / L). C 进液 is the mass-volume concentration of sulfuric acid in the electrodialysis feed liquid (mg / L).

[0046] Calculation of evaporation energy consumption:

[0047]

[0048] Where: λ 蒸发 is the latent heat of evaporation of the acid solution (kJ / kg), and λ 蒸汽 is the latent heat of evaporation of the acid solution (kJ / kg).

[0049] Calculation of sludge reduction rate:

[0050]

[0051] Where: m 新工艺 is the sludge production of the new process (tons / dry ton of acid), and m 中和法 is the sludge production of the neutralization method (tons / thousand tons of acid).

[0052] Calculation of lead solidification rate:

[0053]

[0054] Where: η 固化 is the solidification rate (%) of heavy metal lead in the process of transforming from ionic form in the original solution to sludge hazardous waste solid, m 污泥 is the sludge production (kg), Q 原液 is the volume of the original solution (m 3 ), and C 污泥 is the mass concentration of lead in the sludge (g / L).

[0055] Operating energy consumption ratio:

[0056]

[0057] Where: E 新工艺 is the energy consumption per cubic meter of treatment volume of the new process (kWh / m 3 ), and E 传统 is the energy consumption per cubic meter of treatment volume of the traditional process (kWh / m 3 ).

[0058] Example 1

[0059] Please refer to Figure 1 , Figure 1 , which is the system flow block diagram of the present invention based on the nanofiltration-electrodialysis synergistic waste heat evaporation process. A waste lead-acid battery dilute acid resource treatment process based on nanofiltration-electrodialysis synergistic waste heat evaporation is implemented according to the following steps:

[0060] (1) Parameters of the original acid solution

[0061] The original acid solution (treatment object) is the dilute acid generated from the dismantling of waste lead-acid batteries, and its parameters are as follows:

[0062] Sulfuric acid concentration: 2.24% (mass fraction);

[0063] Heavy metal content: Lead (Pb 2+ ) is 12.5 mg / L, Cadmium (Cd 2+ ) is 8.2 mg / L;

[0064] Other pollutants: Chemical Oxygen Demand (COD) is 432.7 mg / L, Suspended Solids (SS) is 63 mg / L, Turbidity is 2.27 NTU.

[0065] (II) Pretreatment

[0066] ① Tertiary precision filtration: Pass through 50 μm, 10 μm, and 1 μm polypropylene (PP) bag filters in sequence to remove large particulate impurities;

[0067] ② Ultrafiltration treatment: Use a polyvinylidene fluoride (PVDF) hollow fiber membrane module (pore size 0.03 μm, operating pressure 0.3 MPa). The water quality indicators after filtration are:

[0068] COD: 108.5 mg / L (removal rate 74.9%);

[0069] SS: 18 mg / L (removal rate 71.4%);

[0070] Turbidity: 0.59 NTU (removal rate 74.0%).

[0071] (III) Acid-resistant nanofiltration for heavy metal separation

[0072] ① First-stage nanofiltration: Retention molecular weight 450 Da, operating pressure 20 bar, membrane material is a sulfonated polyethersulfone (SPES) composite layer (tolerant to pH 0 - 5);

[0073] ② Second-stage nanofiltration: Retention molecular weight 250 Da, operating pressure 15 bar;

[0074] ③ Separation effect:

[0075] Lead retention rate 98.2% (produced water Pb 2+ concentration 0.23 mg / L);

[0076] Cadmium retention rate 97.6% (produced water Cd 2+ concentration 0.20 mg / L);

[0077] Sulfuric acid recovery rate 95% (produced water concentration 2.15%).

[0078] (IV) Electrodialysis concentration

[0079] ① Operating parameters: Current density 35 mA / cm 2 , tantalum-coated titanium electrodes, configured with 200 pairs of anion / cation exchange membrane groups;

[0080] ②Concentration effect: The sulfuric acid concentration is increased from 2.15% to 6.02% (concentration multiple: 2.8 times), and the acid recovery rate is 90%.

[0081] (V) Purification by waste heat evaporation

[0082] ① Heat source utilization: Waste heat from lead smelting flue gas (temperature: 160 °C), operating temperature of the single-effect evaporator: 70 ± 2 °C;

[0083] ② Evaporation effect: The sulfuric acid concentration is increased to 18.06% (meeting the GB / T 534-2014 standard), lead / cadmium residue: Pb 2+ is 2.28 mg / L, Cd 2+ is 1.05 mg / L, total sulfuric acid recovery rate: 85% (cumulative calculation), evaporation energy consumption: 0.48 tons of steam per ton of acid.

[0084] (VI) Co-disposal of hazardous waste

[0085] ① Neutralization and precipitation: Mix the nanofiltration concentrate and the electrodialysis waste liquid, add lime milk (volume ratio: 4%), and adjust the pH to 9.0;

[0086] ② Sludge characteristics: Lead content 6.2%, cadmium content 3.8% (HW31 hazardous waste), heavy metal solidification rate: Pb 99.6%, Cd 99.3%, sludge reduction rate: 91% (from 8.9 tons per thousand tons of acid in the traditional process to 0.8 tons per thousand tons of acid).

[0087] (VII) Table 1 of the final treatment effect

[0088] Table 2 Process effect table of Example 1

[0089]

[0090] Example 2:

[0091] Please refer to Figure 1 , Figure 1 which is the system flow block diagram of the present invention based on the nanofiltration-electrodialysis synergistic waste heat evaporation process. A waste lead-acid battery dilute acid resource treatment process based on nanofiltration-electrodialysis synergistic waste heat evaporation is implemented according to the following steps:

[0092] (I) Parameters of the original acid solution

[0093] The original acid solution (treatment object) is the dilute acid generated from the dismantling of waste lead-acid batteries, and its parameters are as follows:

[0094] Sulfuric acid concentration: 1.52% (mass fraction)

[0095] Heavy metal content: Lead (Pb 2+ ) is 18.3 mg / L, cadmium (Cd 2+ ) is 12.6 mg / L;

[0096] Other pollutants: Chemical Oxygen Demand (COD) is 387.4 mg / L, Suspended Solids (SS) is 72 mg / L, and turbidity is 3.15 NTU.

[0097] (II) Pretreatment

[0098] ① Tertiary precision filtration: The same as in Example 1.

[0099] ② Ultrafiltration treatment: A polyvinylidene fluoride (PVDF) hollow fiber membrane module (pore size 0.03 μm, operating pressure 0.3 MPa) is used. The water quality indicators after filtration are as follows:

[0100] COD: 92.3 mg / L (removal rate 76.2%);

[0101] SS: 21 mg / L (removal rate 70.8%);

[0102] Turbidity: 0.72 NTU (removal rate 77.1%).

[0103] (III) Acid-resistant nanofiltration for heavy metal separation

[0104] ① First-stage nanofiltration: The molecular weight cut-off is 450 Da, the operating pressure is 20 bar, and the membrane material is a sulfonated polyethersulfone (SPES) composite layer (tolerant to pH 0 - 5);

[0105] ② Second-stage nanofiltration: The molecular weight cut-off is 250 Da, and the operating pressure is 15 bar;

[0106] ③ Separation effect:

[0107] Lead interception rate is 98.9% (produced water Pb 2+ concentration 0.20 mg / L);

[0108] Cadmium interception rate is 97.8% (produced water Cd 2+ concentration 0.28 mg / L);

[0109] Sulfuric acid recovery rate is 95.5% (produced water concentration 1.46%).

[0110] (IV) Electrodialysis concentration

[0111] ① Operating parameters: Current density is 30 mA / cm 2 , tantalum-coated titanium electrodes, and 200 pairs of anion / cation exchange membrane groups are configured;

[0112] ② Concentration effect: The sulfuric acid concentration is increased from 1.46% to 5.0% (concentration multiple 3.0 times), and the sulfuric acid recovery rate is 90%.

[0113] (V) Waste heat evaporation and purification

[0114] ① Heat source utilization: waste heat from lead smelting flue gas (temperature 160°C), operating temperature of the single-effect evaporator 70 ± 2°C;

[0115] ② Evaporation effect: sulfuric acid concentration increased to 16.8% (meeting the GB / T 534-2014 standard), lead / cadmium residue: Pb 2+ is 1.85 mg / L, Cd 2+ is 0.95 mg / L, total sulfuric acid recovery rate: 85.3% (cumulative calculation), evaporation energy consumption 0.45 tons of steam / ton of acid.

[0116] (VI) Co-disposal of hazardous waste

[0117] ① Neutralization precipitation: nanofiltration concentrate and electrodialysis waste liquid are mixed, and lime milk (volume ratio 4%) is added to adjust the pH to 8.9;

[0118] ② Sludge characteristics: lead content 6.5%, cadmium content 3.9% (HW31 hazardous waste), heavy metal solidification rate Pb 99.6%, Cd 99.3%, sludge reduction rate 91% (traditional process sludge volume 8.9 tons / thousand tons of acid → 0.8 tons / thousand tons of acid).

[0119] (VII) Final treatment effect

[0120] Table 3 Process effect table of Example 2

[0121]

[0122] Comparative example 1:

[0123] This comparative example adopts a chemical polishing waste acid recovery and treatment method proposed in the current patent CN116253469A and compares it with the implementation effect, and is implemented according to the following steps:

[0124] (I) Parameters of the original acid solution

[0125] The original acid solution (treatment object) is dilute acid generated from the disassembly of waste lead-acid batteries, and its parameters are the same as those in Example 1.

[0126] (II) Pretreatment

[0127] Only a single-stage 10μm bag filter is used, and ultrafiltration is not configured. The main water quality indicators are as follows:

[0128] SS: 63 mg / L;

[0129] Turbidity: 2.27 NTU;

[0130] COD: 387 mg / L.

[0131] (III) Removal of heavy metals by diffusion dialysis

[0132] ① An anion membrane diffusion dialyzer is adopted, with a membrane surface flow rate of 0.2 L / (m 2 ·h);

[0133] ② Separation effect:

[0134] The lead interception rate is 82% (the lead concentration in the produced water is 2.25 mg / L); 2+ ;

[0135] The cadmium interception rate is 80% (the cadmium ion concentration in the produced water is 1.64 mg / L); 2+ + concentration 1.64mg / L);

[0136] The sulfuric acid recovery rate is 78%.

[0137] (IV) Removal of heavy metals by nanofiltration

[0138] ① Dow NF270 membrane (polyamide composite membrane, pH tolerance 2 - 11, molecular weight cut-off 300 Da, operating pressure 50 bar) is adopted;

[0139] ② Separation effect:

[0140] The lead interception rate is 88% (the lead concentration in the produced water is 0.27 mg / L); 2+ concentration 0.27mg / L);

[0141] The cadmium interception rate is 85% (the cadmium concentration in the produced water is 0.25 mg / L); 2+ concentration 0.25mg / L);

[0142] The sulfuric acid recovery rate is 72%.

[0143] (V) Evaporation and concentration

[0144] ① Evaporation at 60°C at normal temperature, with a SiC heat exchanger;

[0145] ② Energy consumption: 1.2 tons of steam per ton of acid;

[0146] ③ After concentration, the sulfuric acid concentration is 14.8%, and the lead residue is 4.2 mg / L.

[0147] (VI) Hazardous waste disposal

[0148] ① Consumption of neutralization agent: 7.2 tons of lime milk per thousand tons of acid, and the pH is adjusted to 9.5;

[0149] ② The lead content in the sludge after neutralization and precipitation is 0.51%;

[0150] ③ The lead solidification rate is 98.2%, and the sludge production is 5.2 tons per thousand tons of acid.

[0151] (VII) Final treatment effect

[0152] Table 4 Process effect table of Comparative Example 1

[0153]

[0154] In Comparative Example 1, the waste acid was treated by the traditional diffusion dialysis - nanofiltration - multi - effect evaporation process. The pretreatment only passed through single - stage 10 - μm filtration and did not configure ultrafiltration, resulting in the SS of the nanofiltration influent being as high as 63 mg / L and the COD remaining at the original acid level (387 mg / L) (after ultrafiltration in Example 1, SS ≤ 50 mg / L and COD ≤ 150 mg / L). The tandem process of diffusion dialysis and single - stage nanofiltration (Dow NF270 membrane) achieved a total lead interception rate of 97.8% (the double - stage nanofiltration in Example 1 directly achieved 98.2%), but the sulfuric acid recovery rate was only 56.16% (diffusion dialysis 78% × nanofiltration 72%), and the energy consumption of the subsequent triple - effect evaporation was as high as 1.2 tons of steam per ton of acid. The lead residue in the concentrated liquid was 4.2 mg / L and could not be recycled, and the lead residue in the condensate was 0.27 mg / L (exceeding the third - level limit of 0.1 mg / L in the Comprehensive Wastewater Discharge Standard). The neutralization sludge production reached 5.2 tons per thousand tons of acid (only 0.8 tons in Example 1), and the lead content in the sludge was only 0.51% (dry basis, not reaching the lower limit of 5% of the HW31 standard), and it needed to be disposed of as general solid waste, highlighting the risk of secondary pollution instead.

[0155] Comparative Example 2:

[0156] This comparative example adopted the traditional lime neutralization method and compared the implementation effects with those of Example 1. It was implemented according to the following steps:

[0157] (I) Parameters of the original acid solution

[0158] The original acid solution (the object to be treated) was the dilute acid generated from the dismantling of waste lead - acid batteries, and its parameters were the same as those in Example 1.

[0159] (II) Neutralization reaction: Excessive lime milk (Ca(OH)₂, dosage 12% volume ratio) was added, and the pH was adjusted to 10.5.

[0160] (III) Precipitation separation: Gypsum (CaSO₄·2H₂O) and metal hydroxide precipitates were formed.

[0161] (IV) Solid - liquid separation: Plate - frame pressure filtration (pressure 0.8 MPa), and the filtrate was discharged after pH adjustment.

[0162] (V) Treatment effect:

[0163] Sulfuric acid recovery rate: 0%, all converted into gypsum;

[0164] Sludge production: 8.9 tons per thousand tons of acid, with a water content of 60%;

[0165] Lead content in the sludge: 5.8% (HW31 hazardous waste), and the annual hazardous waste disposal cost was about 1.2 million yuan per ten thousand tons of acid;

[0166] Lead solidification rate: 98.2%, Pb residue in the filtrate 2+It is 0.5 mg / L (exceeding the standard);

[0167] Energy consumption: 0.3 tons of standard coal per ton of acid, only including the energy consumption of stirring and pressure filtration.

[0168] Example 1 uses a collaborative process of nanofiltration - electrodialysis - waste heat evaporation to treat waste acid, achieving a sulfuric acid recovery rate of 85.3% (in Comparative Example 2, the traditional lime neutralization method completely converts sulfuric acid into gypsum, and the recovery rate is 0%). The generation amount of hazardous waste sludge is only 0.8 tons per thousand tons of acid (a 91% reduction compared to 8.9 tons in Comparative Example 2). The lead content in the dry basis of the sludge is stably at 6.2% (meeting the HW31 hazardous waste standard). Although the lead content in the sludge of the neutralization method reaches 5.8% (HW31), the annual disposal cost is as high as 1.2 million yuan per ten thousand tons of acid. The recovered sulfuric acid concentration of the present invention is ≥15%, which can be directly reused for electrolyte compounding (there is no resource utilization product in Comparative Example 2). Although the evaporation energy consumption in Example 1 is 0.48 tons of steam per ton of acid, slightly higher than 0.3 tons of standard coal per ton of acid in the neutralization method, through the sulfuric acid resource utilization benefit (600 yuan per ton of acid) and the savings in hazardous waste disposal cost (800,000 yuan per ten thousand tons of acid), the comprehensive cost per ton of acid is 217.8 yuan (a 65% reduction compared to 623.4 yuan in Comparative Example 2), and completely eliminates the secondary pollution risk of lead residue exceeding the standard (0.5 mg / L, 10 times higher than the "Sewage Discharge Standard") in the filtrate of Comparative Example 2.

[0169] In summary, the specific implementation mode of the present invention removes particulate matter and organic matter in waste acid through three - stage precision filtration and ultrafiltration pretreatment, and then uses a series of acid - resistant nanofiltration membranes to achieve high - precision interception (≥97%) of lead and cadmium ions in two stages (300 - 500 Da, 200 - 300 Da) to obtain low - heavy - metal acid solution; combined with electrodialysis preconcentration (acid recovery rate ≥80%) and low - temperature evaporation (70 ± 2°C) driven by the waste heat of lead smelting for collaborative purification, the 1.4% - 2.3% dilute acid is efficiently concentrated to ≥15% reuse acid, with a total recovery rate ≥85% and evaporation energy consumption ≤0.5 tons of steam per ton of acid; at the same time, the nanofiltration concentrated water and electrodialysis waste liquid are neutralized and precipitated to form HW31 hazardous waste sludge with a lead content ≥5%, achieving a heavy - metal solidification rate ≥99.5% and a 90% reduction in sludge volume. This process overcomes the problems of low recovery rate, high energy consumption, and secondary pollution in the resource utilization of low - concentration waste acid through the system integration of membrane separation cascade purification, energy collaborative utilization, and hazardous waste collaborative disposal.

Claims

1. A resource treatment process for dilute acid from waste lead-acid batteries based on the synergistic waste heat evaporation of nanofiltration and electrodialysis, characterized in that, It includes the following steps: S1: Waste acid collection. Collect the original acid liquid generated from the disassembly of waste lead-acid batteries into a waste acid collection tank. The sulfuric acid concentration in the original acid liquid is 1.4 - 2.3%. S2: Pretreatment. Pass the original acid liquid in S1 successively through three-stage precision filters (50μm, 10μm, and 1μm) and an ultrafiltration membrane device (PVDF hollow fiber membrane, pore size 0.01 - 0.1μm, operating pressure 0.2 - 0.5MPa) to obtain a filtered acid liquid with COD ≤ 150mg / L, SS ≤ 50mg / L, and turbidity ≤ 1NTU. S3: Heavy metal separation. The filtered acid solution from S2 is treated by an acid-resistant nanofiltration membrane device, which includes two series-connected nanofiltration units. The molecular weight cut-off of the first stage is 300 - 500 Da, and that of the second stage is 200 - 300 Da. The operating pressure is 12 - 25 bar, the lead ion rejection rate is ≥97%, and the cadmium ion rejection rate is ≥96%. A low heavy metal acid solution (Pb 2+ ≤3.0 mg / L) and nanofiltration concentrate are obtained; S4: Electro-dialysis concentration. The low-heavy metal acid solution from S3 is concentrated to a sulfuric acid concentration of 5-8% through an electro-dialysis device (current density: 20-50 mA / cm 2 ), and the acid recovery rate of the electro-dialysis section is ≥80%; S5: Waste heat evaporation. Concentrate the concentrated acid liquid in S4 through a single-effect evaporator (evaporation temperature 60 - 80°C) using the waste heat of lead smelting flue gas until the sulfuric acid concentration ≥ 15%, and the evaporation energy consumption ≤ 0.5 tons of steam / ton of acid. S6: The finished acid is reused for the formulation of battery electrolyte. S7: Hazardous waste disposal. Neutralize and precipitate the nanofiltration concentrated water in S3 and the electrodialysis waste liquid in S4 (pH 8.5 - 9.5). The resulting sludge has a lead content ≥ 5% (hazardous waste HW31) and a lead solidification rate ≥ 99.5%. The total sulfuric acid recovery rate of the process ≥ 85%, and the sludge production is reduced by 90% compared with the traditional neutralization method.

2. The process according to claim 1, characterized in that, The nanofiltration operating pressure in S3 is 18 - 22 bar, and the lead ion retention rate ≥ 98%.

3. The process according to claim 1, characterized in that The electrodialysis current density of S4 is 30 - 40 mA / cm 2 , and the concentration multiple is 2.8 - 3.2 times.

4. The process according to claim 1, characterized in that, The evaporation temperature in S5 is 70 ± 2°C, and the waste heat temperature of the lead smelting flue gas used ≥ 150°C.

5. The process according to claim 1, characterized in that, The neutralization precipitation in S7 uses lime milk, and the dosage is 3 - 5% of the volume of the waste liquid.

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