Dilute sulfuric acid wastewater treatment method

Abstract

The invention discloses a dilute sulphuric acid wastewater treatment method which comprises the following steps: sequentially carrying out lime neutralization and replacement electrodialysis salt removal on dilute sulphuric acid wastewater, and sequentially carrying out reverse osmosis concentration, resin weight removal and evaporation crystallizer salt production on calcium chloride feed liquid after replacement electrodialysis salt removal to obtain a calcium chloride product; sequentially carrying out reverse osmosis concentration and evaporation crystallizer salt production on the sodium sulfate feed liquid subjected to replacement electrodialysis salt removal to obtain a sodium sulfate product; and carrying out first reverse osmosis concentration on the dilute calcium sulfate feed liquid subjected to replacement electrodialysis salt removal to obtain concentrated calcium sulfate feed liquid, and refluxing the concentrated calcium sulfate feed liquid to the replacement electrodialysis salt removal. The treatment process is simple, the treatment efficiency is high, the recovery rate of calcium ions and sulfate radicals is high, the product purity is high, the calcium sulfate mother liquor can be treated in a low-energy-consumption and pollution-free mode, and secondary economic benefits can be generated.

Description

Technical Field

[0001] The present invention belongs to the technical field of industrial wastewater treatment and resource utilization, and particularly relates to a method for treating dilute sulfuric acid wastewater. Background Art

[0002] Lead-acid batteries mainly consist of lead plates, electrolyte, and a casing. The electrolyte is a sulfuric acid solution. When recycling and disassembling lead-acid batteries, this sulfuric acid is released, forming dilute sulfuric acid wastewater. In addition to sulfuric acid, it also contains heavy metals such as lead, cadmium, and arsenic generated from the corrosion of the plates during battery use. For this type of dilute sulfuric acid wastewater, the existing treatment processes generally adopt a process route of "lime neutralization + resin heavy metal removal + sodium carbonate softening + multi-media + ultrafiltration + resin softening + membrane concentration + evaporation crystallization". The consumption of sodium carbonate and resin acid-base regeneration agents is large, the efficiency of resin heavy metal removal is low, and the treatment cost of the mixed salt solid waste generated by evaporation crystallization is relatively high. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the existing technology and provide a method for treating dilute sulfuric acid wastewater.

[0004] The technical solution of the present invention is outlined as follows:

[0005] A method for treating dilute sulfuric acid wastewater, comprising the following steps:

[0006] (1) Adding lime milk to the dilute sulfuric acid wastewater for lime neutralization to obtain a calcium sulfate mother liquor and sludge;

[0007] (2) Treating the sludge to obtain gypsum mud cake and filtrate under pressure, and the filtrate under pressure is combined with the dilute sulfuric acid wastewater for lime neutralization;

[0008] (3) Passing an aqueous sodium chloride solution, water, and the calcium sulfate mother liquor through a permselective electrodialysis for salt splitting to obtain a calcium chloride feed liquid, a dilute calcium sulfate feed liquid, and a sodium sulfate feed liquid respectively;

[0009] (4) Passing the calcium chloride feed liquid successively through a second reverse osmosis concentration, a third reverse osmosis concentration, resin heavy metal removal, and a first evaporator for salt production to obtain a calcium chloride product;

[0010] (5) Passing the sodium sulfate feed liquid successively through a fourth reverse osmosis concentration, a fifth reverse osmosis concentration, and a second evaporator for salt production to obtain a sodium sulfate product;

[0011] (6) Passing the dilute calcium sulfate feed liquid through a first reverse osmosis concentration, and the concentrated calcium sulfate feed liquid is combined with the calcium sulfate mother liquor after lime neutralization for permselective electrodialysis salt splitting;

[0012] (7) Combine the produced water from the first reverse osmosis concentration, the second reverse osmosis concentration, the third reverse osmosis concentration, the fourth reverse osmosis concentration, the fifth reverse osmosis concentration, the salt production in the first evaporation crystallizer, and the salt production in the second evaporation crystallizer as product water.

[0013] Preferably, the salt content of the dilute calcium sulfate feed liquid is 100 - 200 mg / L.

[0014] Advantages of the present invention:

[0015] The treatment process of the present invention is simple and efficient, and product recovery can be achieved synchronously. By using displacement electrodialysis to remove salt, the neutralized slightly soluble calcium sulfate mother liquor is converted into calcium chloride feed liquid and sodium sulfate feed liquid with high solubility, and further concentrated and crystallized into high-value industrial products, realizing secondary economic benefits. The present invention uses displacement electrodialysis to remove salt to enrich heavy metal trace impurity ions in the calcium chloride feed liquid with high solubility, increases the concentration of impurity ions by concentration, and then removes them by resin adsorption, solving the problem of difficult removal of low-concentration impurity ions in dilute sulfuric acid wastewater. Description of the Drawings

[0016] Figure 1 It is a schematic diagram of a method for treating dilute sulfuric acid wastewater of the present invention. Detailed Embodiments

[0017] The present invention will be further described below through specific embodiments and the accompanying drawings of the specification.

[0018] Example 1

[0019] A method for treating dilute sulfuric acid wastewater, as shown in Figure 1 , includes the following steps:

[0020] (1) Add lime milk to the dilute sulfuric acid wastewater for lime neutralization to obtain calcium sulfate mother liquor and sludge;

[0021] The treatment volume of the dilute sulfuric acid wastewater is 500 m 3 / d, and the mass fraction of sulfuric acid is 0.5%;

[0022] The purity of lime is 98%, the consumption is 2.7 t / d, the mass concentration of lime milk is 10%, and the lime neutralization reaction time is 2 hours;

[0023] The moisture content of the sludge produced by the neutralization reaction is 95%, and the sludge volume is 105 m 3 / d;

[0024] The main ion contents in the dilute sulfuric acid wastewater and the calcium sulfate mother liquor are shown in Table 1:

[0025]

[0026] (2) The sludge is subjected to sludge treatment to obtain gypsum cake and filtrate under pressure. The filtrate under pressure is combined with dilute sulfuric acid wastewater and neutralized with lime.

[0027] The sludge treatment uses plate and frame pressure filtration. The operating pressure is 0.8 MPa, the water content of the gypsum cake is 70%, and the mass of the gypsum cake is 17.5 t / d.

[0028] The main ion contents in the filtrate under pressure are shown in Table 2:

[0029]

[0030] (3) The sodium chloride aqueous solution, water and the calcium sulfate mother liquor are subjected to salt removal by displacement electrodialysis to obtain calcium chloride feed liquid, dilute calcium sulfate feed liquid (the salt content of the dilute calcium sulfate feed liquid is adjusted to 124 mg / L, and any number between 100 - 200 mg / L can also be selected, such as: 100 mg / L, 120 mg / L, 150 mg / L, 170 mg / L, 190 mg / L, 200 mg / L) and sodium sulfate feed liquid respectively.

[0031] The displacement electrodialysis adopts a four - compartment structure, and the electrode water is a 2% sodium sulfate aqueous solution by mass fraction.

[0032] The purity of sodium chloride is 99.9%, the consumption is 0.904 t / d, and the mass concentration of the prepared sodium chloride solution is 36.38%.

[0033] The amounts of the sodium chloride aqueous solution, water, calcium chloride feed liquid, sodium sulfate feed liquid, and dilute calcium sulfate feed liquid are 25 m 3 / d, 175 m 3 / d, 100 m 3 / d, 100 m 3 / d, 625 m 3 / d.

[0034] The main ion contents are shown in Table 3:

[0035]

[0036] (4) The calcium chloride feed liquid is successively concentrated by the second reverse osmosis, the third reverse osmosis, de - weighted by resin and salt - made in the first evaporation crystallizer to obtain calcium chloride products.

[0037] The second reverse osmosis concentration has an operating pressure of 20 bar, a recovery rate of 75%, a water production of 75 m 3 / d, and a concentrated water volume of 25 m 3 / d;

[0038] The third reverse osmosis concentration has an operating pressure of 50 bar, a recovery rate of 68%, a water production of 17 m 3 / d, and a concentrated water volume of 8 m 3 / d;

[0039] The heavy metal removal treatment capacity of the resin (except for the heavy metal chelating resin CH-90Na) is 8 m 3 / d;

[0040] The salt production in the first evaporation crystallizer adopts the MVR process, with a water production of 8.0 m 3 / d, 841 kg / d of calcium chloride solid salt, with a purity of 99.8%;

[0042] The main ion contents are shown in Table 4:

[0043] Table 4:

[0044]

[0045] (5) Pass the sodium sulfate feed liquid through the fourth reverse osmosis concentration, the fifth reverse osmosis concentration, and the second evaporation crystallizer for salt production in sequence to obtain sodium sulfate products;

[0046] The operating pressure of the fourth reverse osmosis concentration is 20 bar, the recovery rate is 75%, and the water production is 75 m 3 / d, and the concentrated water volume is 25.0 m 3 / d;

[0047] The operating pressure of the fifth reverse osmosis concentration is 50 bar, the recovery rate is 68%, and the water production is 17.0 m 3 / d, and the concentrated water volume is 8.0 m 3 / d; The second evaporation crystallizer for salt production adopts the MVR process, with a water production of 8.0 m 3 / d, 1078 kg / d of sodium sulfate solid salt, with a purity of 99.2%;

[0049] The main ion contents are shown in Table 5:

[0050]

[0051] (6) Pass the dilute calcium sulfate feed liquid through the first reverse osmosis concentration, and the concentrated calcium sulfate feed liquid is combined with the calcium sulfate mother liquor after neutralization with lime for displacement electrodialysis to remove salt;

[0052] The operating pressure of the first reverse osmosis is 15 bar, the recovery rate is 80%, and the water production is 500.0 m 3 / d, and the concentrated water volume is 125.0 m 3 / d;

[0053] The main ion contents are shown in Table 6:

[0054]

[0055] (7) Combine the produced water from the first reverse osmosis concentration, the second reverse osmosis concentration, the third reverse osmosis concentration, the fourth reverse osmosis concentration, the fifth reverse osmosis concentration, the salt production in the first evaporation crystallizer, and the salt production in the second evaporation crystallizer as the final product water;

[0056] Part of the product water is used to prepare sodium chloride solution and replace the make-up water for electrodialysis;

[0057] The main ion content of the product water is shown in Table 7:

[0058]

[0059] Replace the sodium chloride in this embodiment with potassium chloride, and the others are the same as this embodiment, and the dilute sulfuric acid wastewater can be treated, and the effect is similar to that of this embodiment.

Claims

1. A method for treating dilute sulfuric acid wastewater, characterized in that It includes the following steps: (1) Adding lime milk to dilute sulfuric acid wastewater for lime neutralization to obtain calcium sulfate mother liquor and sludge; (2) Treating the sludge to obtain gypsum cake and filtrate under pressure, and combining the filtrate under pressure with the dilute sulfuric acid wastewater for lime neutralization; (3) Separately obtaining calcium chloride feed liquid, dilute calcium sulfate feed liquid and sodium sulfate feed liquid by desalting through permselective electrodialysis of the sodium chloride aqueous solution, water and the calcium sulfate mother liquor; (4) Sequentially passing the calcium chloride feed liquid through second reverse osmosis concentration, third reverse osmosis concentration, resin heavy metal removal and first evaporative crystallizer for salt production to obtain calcium chloride product; (5) Sequentially passing the sodium sulfate feed liquid through fourth reverse osmosis concentration, fifth reverse osmosis concentration and second evaporative crystallizer for salt production to obtain sodium sulfate product; (6) Concentrating the dilute calcium sulfate feed liquid through first reverse osmosis concentration, combining the concentrated concentrated calcium sulfate feed liquid with the calcium sulfate mother liquor after lime neutralization, and performing desalting through permselective electrodialysis; (7) Combining the produced water from first reverse osmosis concentration, second reverse osmosis concentration, third reverse osmosis concentration, fourth reverse osmosis concentration, fifth reverse osmosis concentration, first evaporative crystallizer for salt production and second evaporative crystallizer for salt production as product water.

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