A method for treating zinc smelting wastewater

Abstract

The present invention discloses a method for treating zinc smelting wastewater, belonging to the technical field of wastewater treatment. The method includes: zinc recovery, sulfide treatment, precipitation treatment, flocculation, electrodialysis membrane treatment, evaporation crystallization, and post-treatment; for the precipitation treatment, a metal ion remover is added to the wastewater after sulfide treatment, stirred at room temperature, allowed to stand, and solid-liquid separation is carried out to obtain the wastewater after precipitation treatment; for the flocculation, a composite flocculant is added to the wastewater after precipitation treatment, stirred at room temperature, allowed to stand, and solid-liquid separation is carried out to obtain the wastewater after flocculation. The method of the present invention can realize the resource utilization of zinc ions, zinc oxide, potassium ions, and sodium ions in the wastewater, ensure that the wastewater discharge meets the standards, can also reduce the blockage problem of the electrodialyzer during treatment, realize the treatment of heavy metal ions, improve the flocculation effect and flocculation speed during flocculation, and there is no need to repeatedly add alkali, wash materials, and filter press the zinc smelting wastewater, nor consume a large amount of alkali.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and particularly relates to a method for treating zinc smelting wastewater. Background Art

[0002] Among the production capacity and output of zinc smelting in China, about 80% comes from the hydrometallurgical process, about 15% comes from the ISP zinc smelting process, and the rest comes from the backward shaft furnace zinc smelting process. In the hydrometallurgical process, there is a large amount of wastewater. In addition to containing a large amount of zinc ions, zinc oxide, potassium ions, and sodium ions, the wastewater also contains heavy metal ions, organic substances, suspended solids, etc. If the wastewater is directly discharged, it will cause environmental pollution. At the same time, it is also a waste for the zinc ions, zinc oxide, potassium ions, and sodium ions in the wastewater.

[0003] For the zinc smelting wastewater from the hydrometallurgical process, in order to realize the resource utilization of zinc ions, zinc oxide, potassium ions, and sodium ions, and at the same time ensure that the wastewater discharge meets the standards, when the applicant designed the wastewater treatment plan, a method combining zinc recovery, sulfide treatment, flocculation, electrodialysis membrane treatment, evaporation crystallization, and post-treatment was adopted. Zinc recovery includes adding alkali, washing materials, pressure filtration, leaching, ion exchange, and electrolysis. The purpose of adding alkali in zinc recovery is to convert zinc ions in the zinc smelting wastewater into zinc hydroxide. The purpose of washing materials and pressure filtration is to separate zinc hydroxide and zinc oxide in the wastewater, obtaining a mixture of zinc hydroxide and zinc oxide and the wastewater after separating zinc. The purpose of leaching is to convert zinc hydroxide and zinc oxide into an aqueous solution of zinc sulfate. In ion exchange, a sulfate-type anion exchange resin column is used, and the purpose is to remove anion impurities other than sulfate ions in the aqueous solution of zinc sulfate. The purpose of electrolysis is to electrolyze zinc ions in the aqueous solution of zinc sulfate into zinc metal. The purpose of sulfide treatment is to precipitate and separate heavy metal ions in the wastewater after separating zinc. The purpose of flocculation is to precipitate and separate suspended solids in the wastewater after separating zinc. The purpose of electrodialysis membrane treatment is to separate salts and concentrate. Evaporation crystallization can concentrate the concentrated water generated in electrodialysis to obtain a mixed salt of sodium chloride and potassium chloride. The purpose of post-treatment is to pass the fresh water generated in electrodialysis membrane treatment into an ozone catalytic oxidation system and a stripping deammoniation system to reduce the COD and ammonia nitrogen of the wastewater, and after reaching the discharge standard, then discharge it externally.

[0004] However, when treating zinc smelting wastewater according to the above method, the following problems exist: First, in zinc recovery, zinc hydroxide obtained after adding alkali has a hydrolysis problem in water, resulting in some zinc ions still remaining in the wastewater after zinc separation. Zinc ions undergo hydrolysis in electrodialysis, and the hydrolyzed zinc hydroxide is prone to clogging the electrodialyzer used in electrodialysis, affecting the efficiency of the electrodialyzer and further affecting the effluent efficiency of the electrodialyzer; Second, in sulfide treatment, the dosage of sulfide is difficult to control. If the dosage of sulfide is too large, it will also form water-soluble complexes with heavy metal ions, resulting in high heavy metal content in the treated wastewater; Third, in flocculation, polyaluminum chloride or polyacrylamide is generally used, but both have problems of poor flocculation effect and slow flocculation speed, resulting in high contents of soluble macromolecules and suspended solids in the wastewater entering the electrodialysis membrane treatment. Suspended solids are prone to clogging the membrane pores of the electrodialysis membrane, leading to clogging of the electrodialyzer. Soluble macromolecules are adsorbed in the membrane pores of the electrodialysis membrane, and in long-term operation, it will also cause clogging of the electrodialyzer.

[0005] In response to the above problems, after retrieval, the commonly used solutions at present are: First, repeat the processes of adding alkali, washing materials, and pressure filtration to zinc smelting wastewater, but this method will complicate the treatment method; Second, in adding alkali, control the pH to about 8.5, precipitate zinc ions, and then continue to add alkali to the wastewater after zinc separation to further increase the pH and precipitate all heavy metal ions, but this method will consume a large amount of alkali; Third, when flocculating, use polyaluminum chloride and polyacrylamide in combination. Polyaluminum chloride can play an adsorption role, and polyacrylamide can play a bridging role, thus promoting flocculation. However, when polyaluminum chloride and polyacrylamide are used in combination, if the two are added together, there will be mutual influence. Therefore, generally, polyaluminum chloride is added first. Polyaluminum chloride neutralizes the negatively charged particles in zinc smelting wastewater, reduces the repulsion between negatively charged particles, and forms stable small flocs. Then, polyacrylamide is added, and the small flocs are combined into large flocs by using the adsorption bridging effect of polyacrylamide. Therefore, after using polyaluminum chloride and polyacrylamide in combination, although the flocculation effect can be improved, polyaluminum chloride and polyacrylamide need to be added in batches, and there is still a problem of slow flocculation speed. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the present invention provides a method for treating zinc smelting wastewater. By combining zinc recovery, sulfide treatment, flocculation, electrodialysis membrane treatment, and evaporation crystallization, it can realize the resource utilization of zinc ions, zinc oxide, potassium ions, and sodium ions in the wastewater, ensure that the wastewater discharge meets the standards, and can also reduce the clogging problem of the electrodialyzer during treatment, realize the treatment of heavy metal ions, improve the flocculation effect and flocculation speed during flocculation, and there is no need to repeat the processes of adding alkali, washing materials, and pressure filtration to zinc smelting wastewater, nor is it necessary to consume a large amount of alkali.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for treating zinc smelting wastewater, comprising: zinc recovery, sulfide treatment, precipitation treatment, flocculation, electrodialysis membrane treatment, evaporation crystallization, and post-treatment;

[0009] The zinc recovery includes: adding alkali, washing the material, leaching, ion exchange, and electrolysis;

[0010] In the alkali addition, sodium hydroxide is added to the zinc smelting wastewater while stirring to adjust the pH to 8.4 - 8.6, filtered, and the filter residue is taken as a mixture of zinc hydroxide and zinc oxide, and the filtrate is taken as the wastewater after zinc separation;

[0011] The material washing uses water to wash the mixture of zinc hydroxide and zinc oxide to obtain the washed mixture of zinc hydroxide and zinc oxide;

[0012] The leaching uses an aqueous sulfuric acid solution to leach the mixture of zinc chloride and zinc oxide to obtain an aqueous zinc sulfate solution;

[0013] In the leaching, the concentration of the aqueous sulfuric acid solution is 7 - 9 wt%;

[0014] The ion exchange uses a sulfate-type anion exchange resin column to perform ion exchange on the aqueous zinc sulfate solution to obtain the ion-exchanged aqueous zinc sulfate solution;

[0015] The electrolysis electrolyzes the ion-exchanged aqueous zinc sulfate solution to obtain elemental zinc;

[0016] The sulfide treatment adds sodium sulfide to the wastewater after zinc separation, stirs at room temperature for 5 - 15 min, stands for 1.5 - 2 h, and performs solid-liquid separation to obtain the wastewater after sulfide treatment;

[0017] In the sulfide treatment, the molar ratio of heavy metals in the wastewater after zinc separation to sodium sulfide is 10:14 - 15;

[0018] The precipitation treatment adds a metal ion remover to the wastewater after sulfide treatment, stirs at room temperature for 20 - 30 min, stands for 1 - 1.5 h, and performs solid-liquid separation to obtain the wastewater after precipitation treatment;

[0019] In the precipitation treatment, the addition amount of the metal ion remover is 75 - 80 g / ton of the wastewater after sulfide treatment;

[0020] The preparation method of the metal ion remover is as follows: Mix citric acid and the first portion of water, stir at room temperature for 10 - 30 min, add activated carbon, stir for 2 - 3 h, add aluminum chloride, stir for 40 - 60 min, add sodium hydroxide aqueous solution to adjust the pH to 7, filter, take the filter residue, wash it with water, then mix it with the second portion of water, stir at room temperature for 10 - 30 min, heat up to 60 - 65 °C, add hydrolyzed polyacrylamide aqueous solution, continue to stir for 20 - 25 h, filter, take the filter residue, wash it with water, and then dry it to obtain the metal ion remover;

[0021] In the preparation of the metal ion remover, the dosage ratio of citric acid, the first portion of water, activated carbon, aluminum chloride, the second portion of water, and hydrolyzed polyacrylamide aqueous solution is 60 - 65 g : 1000 - 1200 mL : 140 - 150 g : 8 - 9 g : 1000 - 1200 mL : 1500 - 1600 mL;

[0022] The particle size of the activated carbon is 2 mm;

[0023] The concentration of the sodium hydroxide aqueous solution is 10 wt%;

[0024] The concentration of the hydrolyzed polyacrylamide aqueous solution is 5 g / L;

[0025] In the hydrolyzed polyacrylamide aqueous solution, the molecular weight of hydrolyzed polyacrylamide is 12 million, and the hydrolysis degree is 25%;

[0026] For the flocculation, add a composite flocculant to the wastewater after precipitation treatment, stir at room temperature for 15 - 20 min, stand for 20 - 30 min, and perform solid - liquid separation to obtain the flocculated wastewater;

[0027] In the flocculation, the dosage of the composite flocculant is 180 - 200 g / ton of the wastewater after precipitation treatment;

[0028] The preparation method of the composite flocculant includes: preparing cross - linked lignosulfonate, molecular assembly, and mixing;

[0029] For the preparation of cross - linked lignosulfonate, mix lignosulfonate, sodium hydroxide aqueous solution, and acetone, stir at 35 - 40 °C for 20 - 30 min, add epichlorohydrin, after the addition, heat up to 55 - 65 °C, stir for 5 - 6 h, cool to room temperature, filter, take the filter residue, wash it with water, and then dry it to obtain the metal ion remover;

[0030] In the preparation of cross - linked lignosulfonate, the dosage ratio of lignosulfonate, sodium hydroxide aqueous solution, acetone, and epichlorohydrin is 120 - 130 g : 250 - 280 mL : 500 - 600 mL : 120 - 140 mL;

[0031] The concentration of the sodium hydroxide aqueous solution is 10 wt%;

[0032] The adding rate of epichlorohydrin is 5 - 6 mL / min;

[0033] For the molecular assembly, crosslinked sodium lignosulfonate and water are mixed, stirred at room temperature for 10 - 30 min, an aqueous solution of cationic polyacrylamide is added, and after the addition, it is stirred at room temperature for 2.5 - 3 h to obtain a molecular assembly solution;

[0034] The dosage ratio of sodium lignosulfonate in the preparation of crosslinked sodium lignosulfonate, water, and the aqueous solution of cationic polyacrylamide in the molecular assembly is 120 - 130 g : 400 - 450 mL : 3700 - 4000 mL;

[0035] In the molecular assembly, the concentration of the aqueous solution of cationic polyacrylamide is 3 g / L;

[0036] The weight - average molecular weight of cationic polyacrylamide in the aqueous solution of cationic polyacrylamide is 12 million, and the ionic degree is 20%;

[0037] The adding rate of the aqueous solution of cationic polyacrylamide is 400 - 600 mL / min;

[0038] For the mixing, the molecular assembly solution and polyaluminum chloride are mixed, stirred at room temperature for 1 - 1.5 h to obtain a composite flocculant;

[0039] The dosage ratio of the aqueous solution of cationic polyacrylamide in the molecular assembly to polyaluminum chloride in the mixing is 3700 - 4000 mL : 270 - 300 g;

[0040] For the electrodialysis membrane treatment, the flocculated wastewater is desalted and concentrated to obtain electrodialysis concentrated water and electrodialysis fresh water;

[0041] In the electrodialysis membrane treatment, the electrodialysis membrane used is composed of a cation - exchange membrane and an anion - exchange membrane. The cation - exchange membrane is a cation - exchange membrane with sulfonic acid groups, which can selectively permeate monovalent cations and block divalent cations; the anion - exchange membrane is an anion - exchange membrane with quaternary ammonium groups, which can selectively permeate monovalent anions and block divalent anions;

[0042] For the evaporation crystallization, the electrodialysis concentrated water is evaporated and crystallized to obtain a mixed salt of sodium chloride and potassium chloride;

[0043] For the post - treatment, ozone catalytic oxidation system and air stripping ammonia removal system are introduced into the electrodialysis fresh water to reduce COD and ammonia nitrogen. After reaching the discharge standard, it is discharged externally.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] (1) For the zinc smelting wastewater treatment method of the present invention, a metal ion remover and a composite flocculant are used. The preparation method of the metal ion remover is to mix citric acid with activated carbon. After citric acid is adsorbed on the surface of the activated carbon, aluminum chloride is added and the pH is adjusted to convert the citric acid on the surface of the activated carbon into aluminum citrate. Then, hydrolyzed polyacrylamide is added, and crosslinking occurs between the hydrolyzed polyacrylamide and aluminum citrate. Finally, the obtained metal ion remover is activated carbon with a crosslinked product of hydrolyzed polyacrylamide and aluminum citrate wrapped on its surface. The crosslinked product of hydrolyzed polyacrylamide and aluminum citrate can adsorb heavy metals and the complexes formed by heavy metals. In addition, there are citrate ions that are not combined with aluminum ions in the crosslinked product of hydrolyzed polyacrylamide and aluminum citrate, which can combine with zinc ions, thereby removing zinc ions from the wastewater; the preparation method of the composite flocculant includes the preparation of crosslinked sodium lignosulfonate, molecular assembly, and mixing. The preparation of crosslinked sodium lignosulfonate is to crosslink sodium lignosulfonate with epichlorohydrin to obtain crosslinked sodium lignosulfonate. Molecular assembly is to use the electrostatic adsorption between the negatively charged sulfonate groups in crosslinked sodium lignosulfonate and the positively charged cationic polyacrylamide to coat the cationic polyacrylamide on the surface of crosslinked sodium lignosulfonate, improving the dispersion of crosslinked sodium lignosulfonate in water. Then, it is mixed with polyaluminum chloride. Polyaluminum chloride is positively charged and repels the cationic polyacrylamide coated on the surface of crosslinked sodium lignosulfonate, further improving the stability of the composite flocculant. When treating the wastewater, polyaluminum chloride quickly adsorbs the negatively charged particles in the wastewater, and neutralization occurs between the two to obtain neutral particles. Then, under stirring, the cationic polyacrylamide plays a bridging role, adsorbing the neutral particles on the surface of crosslinked sodium lignosulfonate to form large flocs, which then quickly settle, thereby improving the flocculation effect and flocculation speed;

[0046] (2) The zinc smelting wastewater treatment method of the present invention can realize the resource utilization of zinc ions, zinc oxide, potassium ions, and sodium ions in the wastewater, ensuring that the wastewater discharge meets the standards;

[0047] (3) The zinc smelting wastewater treatment method of the present invention can reduce the blockage problem of the electrodialyzer during treatment. After continuously operating for 15 days according to the method of the present invention, no blockage problem occurs;

[0048] (4)The zinc smelting wastewater treatment method of the present invention can achieve the treatment of heavy metal ions, improve the flocculation effect and flocculation speed during flocculation. For wastewater with an ammonia nitrogen content of 417.13 mg / L, a COD value of 160.14 mg / L, a zinc content of 5.94 mg / L, a thallium content of 52.29 mg / L, a manganese content of 2.31 mg / L, a cadmium content of 21.93 mg / L, a lead content of 1.88 mg / L, a cobalt content of 1.34 mg / L, and a chromium content of 1.36 mg / L, after sulfide treatment, precipitation treatment, and flocculation, the ammonia nitrogen content is 2.7 - 3.1 mg / L, the COD value is 26.2 - 28.5 mg / L, the zinc content is 0.20 - 0.21 mg / L, the thallium content is 0.002 - 0.004 mg / L, the manganese content is 0.003 - 0.004 mg / L, the cadmium content is 0.006 - 0.007 mg / L, the lead content is 0.029 - 0.031 mg / L, the cobalt content is 0.003 mg / L, and the chromium content is 0.018 - 0.019 mg / L;

[0049] (5)The zinc smelting wastewater treatment method of the present invention does not require repeated addition of alkali, washing of materials, and pressure filtration of zinc smelting wastewater, nor does it consume a large amount of alkali. Brief Description of the Drawings

[0050] Figure 1 is the treatment flow chart of the zinc smelting wastewater of the present invention; Detailed Embodiments

[0051] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the detailed embodiments of the present invention are now described.

[0052] Preparation Example 1 Preparation of Metal Ion Remover

[0053] Mix 60 g of citric acid with 1000 mL of water, stir at room temperature for 10 min, add 140 g of activated carbon, stir for 2 h, add 8 g of aluminum chloride, stir for 40 min, adjust the pH to 7 with an aqueous sodium hydroxide solution, filter, take the filter residue, wash it with water, then mix it with 1000 mL of water, stir at room temperature for 10 min, heat up to 60 °C, add 1500 mL of an aqueous solution of hydrolyzed polyacrylamide, continue to stir for 20 h, filter, take the filter residue, wash it with water, and then dry it to obtain the metal ion remover;

[0054] The particle size of the activated carbon is 2 mm;

[0055] The concentration of the aqueous sodium hydroxide solution is 10 wt%;

[0056] The concentration of the aqueous solution of hydrolyzed polyacrylamide is 5 g / L;

[0057] In the hydrolyzed polyacrylamide aqueous solution, the molecular weight of the hydrolyzed polyacrylamide is 12 million, and the degree of hydrolysis is 25%.

[0058] Preparation Example 2 Preparation of metal ion remover

[0059] Mix 65 g of citric acid and 1200 mL of water, stir at room temperature for 30 min, add 150 g of activated carbon, stir for 3 h, add 9 g of aluminum chloride, stir for 60 min, adjust the pH to 7 with an aqueous sodium hydroxide solution, filter, take the filter residue, wash it with water, then mix it with 1200 mL of water, stir at room temperature for 30 min, heat up to 65 °C, add 1600 mL of hydrolyzed polyacrylamide aqueous solution, continue to stir for 25 h, filter, take the filter residue, wash it with water, and then dry it to obtain the metal ion remover;

[0060] The particle size of the activated carbon is 2 mm;

[0061] The concentration of the aqueous sodium hydroxide solution is 10 wt%;

[0062] The concentration of the hydrolyzed polyacrylamide aqueous solution is 5 g / L;

[0063] In the hydrolyzed polyacrylamide aqueous solution, the weight-average molecular weight of the hydrolyzed polyacrylamide is 12 million, and the degree of hydrolysis is 25%.

[0064] Preparation Example 3 Preparation of composite flocculant

[0065] 1. Preparation of crosslinked lignosulfonate: Mix 120 g of lignosulfonate, 250 mL of aqueous sodium hydroxide solution, and 500 mL of acetone, stir at 35 °C for 20 min, add 120 mL of epichlorohydrin at a rate of 5 mL / min, after the addition, heat up to 55 °C, stir for 5 h, cool to room temperature, filter, take the filter residue, wash it with water, and then dry it to obtain the metal ion remover;

[0066] The concentration of the aqueous sodium hydroxide solution is 10 wt%;

[0067] 2. Molecular assembly: Mix all the crosslinked lignosulfonates obtained in step 1 with 400 mL of water, stir at room temperature for 10 min, add 3700 mL of cationic polyacrylamide aqueous solution at a rate of 400 mL / min, after the addition, stir at room temperature for 2.5 h to obtain a molecular assembly solution;

[0068] The concentration of the cationic polyacrylamide aqueous solution is 3 g / L;

[0069] In the cationic polyacrylamide aqueous solution, the weight-average molecular weight of the cationic polyacrylamide is 12 million, and the degree of ionicity is 20%.

[0070] 3. Mixing: Mix all the molecular assembly solutions obtained in Step 2 with 270 g of polyaluminum chloride and stir at room temperature for 1 h to obtain a composite flocculant.

[0071] Preparation Example 4 Preparation of a composite flocculant

[0072] 1. Preparation of crosslinked sodium lignosulfonate: Mix 130 g of sodium lignosulfonate, 280 mL of sodium hydroxide aqueous solution, and 600 mL of acetone, stir at 40 °C for 30 min, add 140 mL of epichlorohydrin at an addition rate of 6 mL / min, raise the temperature to 65 °C after the addition, stir for 6 h, cool to room temperature, filter, take the filter residue, wash it with water, and then dry it to obtain a metal ion remover;

[0073] The concentration of the sodium hydroxide aqueous solution is 10 wt%.

[0074] 2. Molecular assembly: Mix all the crosslinked sodium lignosulfonate obtained in Step 1 with 450 mL of water, stir at room temperature for 30 min, add 4000 mL of cationic polyacrylamide aqueous solution at an addition rate of 600 mL / min, and stir at room temperature for 3 h after the addition to obtain a molecular assembly solution;

[0075] The concentration of the cationic polyacrylamide aqueous solution is 3 g / L;

[0076] The weight-average molecular weight of the cationic polyacrylamide in the cationic polyacrylamide aqueous solution is 12 million, and the ionic degree is 20%.

[0077] 3. Mixing: Mix all the molecular assembly solutions obtained in Step 2 with 300 g of polyaluminum chloride and stir at room temperature for 1.5 h to obtain a composite flocculant.

[0078] Example 1

[0079] As Figure 1 shown, a method for treating zinc smelting wastewater is specifically as follows:

[0080] 1. Zinc recovery:

[0081] (1) Adding alkali: While stirring, add sodium hydroxide to the zinc smelting wastewater to adjust the pH to 8.55, filter, take the filter residue as a mixture of zinc hydroxide and zinc oxide, and take the filtrate as the wastewater after separating zinc;

[0082] The ammonia nitrogen content in the wastewater after zinc separation is 417.13 mg / L, the COD value is 160.14 mg / L, the sodium content is 16538.51 mg / L, the potassium content is 12603.12 mg / L, the zinc content is 5.94 mg / L, the thallium content is 52.29 mg / L, the manganese content is 2.31 mg / L, the cadmium content is 21.93 mg / L, the lead content is 1.88 mg / L, the cobalt content is 1.34 mg / L, and the chromium content is 1.36 mg / L;

[0083] (2) Washing the material: Wash the mixture of zinc hydroxide and zinc oxide with water to obtain the washed mixture of zinc hydroxide and zinc oxide;

[0084] (3) Leaching: Leach the mixture of zinc chloride and zinc oxide with an aqueous sulfuric acid solution to obtain an aqueous zinc sulfate solution;

[0085] The concentration of the aqueous sulfuric acid solution is 8 wt%;

[0086] (4) Ion exchange: Perform ion exchange on the aqueous zinc sulfate solution using a sulfate-type anion exchange resin column to obtain the ion-exchanged aqueous zinc sulfate solution;

[0087] (5) Electrolysis: Electrolyze the ion-exchanged aqueous zinc sulfate solution to obtain elemental zinc;

[0088] 2. Sulfide treatment: Add sodium sulfide to the wastewater after zinc separation, stir at room temperature for 5 min, let stand for 1.5 h, and perform solid-liquid separation to obtain the wastewater after sulfide treatment;

[0089] The molar ratio of heavy metals in the wastewater after zinc separation to sodium sulfide is 10:14;

[0090] 3. Precipitation treatment: Add the metal ion remover prepared in Preparation Example 1 to the wastewater after sulfide treatment, stir at room temperature for 20 min, let stand for 1 h, and perform solid-liquid separation to obtain the wastewater after precipitation treatment;

[0091] The addition amount of the metal ion remover is 75 g / ton of the wastewater after sulfide treatment;

[0092] 4. Flocculation: Add the composite flocculant prepared in Preparation Example 3 to the wastewater after precipitation treatment, stir at room temperature for 15 min, let stand for 20 min, and perform solid-liquid separation to obtain the flocculated wastewater;

[0093] The addition amount of the composite flocculant is 180 g / ton of the wastewater after precipitation treatment;

[0094] The ammonia nitrogen content in the flocculated wastewater is 3.1 mg / L, the COD value is 28.5 mg / L, the sodium content is 16508.2 mg / L, the potassium content is 12674.6 mg / L, the zinc content is 0.21 mg / L, the thallium content is 0.002 mg / L, the manganese content is 0.004 mg / L, the cadmium content is 0.007 mg / L, the lead content is 0.031 mg / L, the cobalt content is 0.003 mg / L, and the chromium content is 0.018 mg / L;

[0095] 5. Electrodialysis: Perform salt separation and concentration on the flocculated wastewater to obtain electrodialysis concentrated water and electrodialysis fresh water;

[0096] In the electrodialysis membrane treatment, the electrodialysis membrane used is composed of a cation exchange membrane and an anion exchange membrane. The cation exchange membrane is a cation exchange membrane with a sulfonic acid group, which can selectively permeate monovalent cations and block divalent cations; the anion exchange membrane is an anion exchange membrane with a quaternary ammonium group, which can selectively permeate monovalent anions and block divalent anions;

[0097] 6. Evaporation crystallization: Perform evaporation crystallization on the electrodialysis concentrated water to obtain a mixed salt of sodium chloride and potassium chloride;

[0098] 7. Post-treatment: Pass the electrodialysis fresh water into an ozone catalytic oxidation system and a stripping ammonia system to reduce COD and ammonia nitrogen. After reaching the discharge standard, it is then discharged externally.

[0099] Example 2

[0100] As Figure 1 shown, a method for treating zinc smelting wastewater is specifically as follows:

[0101] 1. Zinc recovery:

[0102] (1) Adding alkali: While stirring, add sodium hydroxide to the zinc smelting wastewater to adjust the pH to 8.55, filter, take the filter residue as a mixture of zinc hydroxide and zinc oxide, and take the filtrate as the wastewater after separating zinc;

[0103] The ammonia nitrogen content in the wastewater after separating zinc is 417.13 mg / L, the COD value is 160.14 mg / L, the sodium content is 16538.51 mg / L, the potassium content is 12603.12 mg / L, the zinc content is 5.94 mg / L, the thallium content is 52.29 mg / L, the manganese content is 2.31 mg / L, the cadmium content is 21.93 mg / L, the lead content is 1.88 mg / L, the cobalt content is 1.34 mg / L, and the chromium content is 1.36 mg / L;

[0104] (2) Washing the material: Wash the mixture of zinc hydroxide and zinc oxide with water to obtain the washed mixture of zinc hydroxide and zinc oxide;

[0105] (3) Leaching: The mixture of zinc chloride and zinc oxide is leached with an aqueous sulfuric acid solution to obtain an aqueous zinc sulfate solution;

[0106] The concentration of the aqueous sulfuric acid solution is 8 wt%;

[0107] (4) Ion exchange: The aqueous zinc sulfate solution is subjected to ion exchange using a sulfate-type anion exchange resin column to obtain an ion-exchanged aqueous zinc sulfate solution;

[0108] (5) Electrolysis: The ion-exchanged aqueous zinc sulfate solution is electrolyzed to obtain elemental zinc;

[0109] 2. Sulfidation treatment: Sodium sulfide is added to the wastewater after zinc separation, stirred at room temperature for 15 min, left to stand for 2 h, and solid-liquid separation is carried out to obtain the sulfidation-treated wastewater;

[0110] The molar ratio of heavy metals in the wastewater after zinc separation to sodium sulfide is 10:15;

[0111] 3. Precipitation treatment: The metal ion remover prepared in Preparation Example 2 is added to the sulfidation-treated wastewater, stirred at room temperature for 30 min, left to stand for 1.5 h, and solid-liquid separation is carried out to obtain the precipitation-treated wastewater;

[0112] The addition amount of the metal ion remover is 80 g / ton of the sulfidation-treated wastewater;

[0113] 4. Flocculation: The composite flocculant prepared in Preparation Example 4 is added to the precipitation-treated wastewater, stirred at room temperature for 20 min, left to stand for 30 min, and solid-liquid separation is carried out to obtain the flocculated wastewater;

[0114] The addition amount of the composite flocculant is 200 g / ton of the precipitation-treated wastewater;

[0115] The ammonia nitrogen content in the flocculated wastewater is 2.7 mg / L, the COD value is 26.2 mg / L, the sodium content is 16572.1 mg / L, the potassium content is 12662.5 mg / L, the zinc content is 0.20 mg / L, the thallium content is 0.004 mg / L, the manganese content is 0.003 mg / L, the cadmium content is 0.006 mg / L, the lead content is 0.029 mg / L, the cobalt content is 0.003 mg / L, and the chromium content is 0.019 mg / L;

[0116] 5. Electrodialysis membrane treatment: The flocculated wastewater is subjected to salt separation and concentration to obtain electrodialysis concentrated water and electrodialysis fresh water;

[0117] In the electrodialysis membrane treatment, the electrodialysis membrane used is composed of a cation exchange membrane and an anion exchange membrane. The cation exchange membrane is a cation exchange membrane with sulfonic acid groups, which can selectively permeate monovalent cations and block divalent cations. The anion exchange membrane is an anion exchange membrane with quaternary ammonium groups, which can selectively permeate monovalent anions and block divalent anions.

[0118] 6. Evaporation and crystallization: Evaporate and crystallize the electrodialysis concentrated water to obtain a mixed salt of sodium chloride and potassium chloride.

[0119] 7. Post-treatment: Pass the electrodialysis fresh water into an ozone catalytic oxidation system and a stripping deammoniation system to reduce COD and ammonia nitrogen. After reaching the discharge standard, it is then discharged.

[0120] Example 3

[0121] A method for treating zinc smelting wastewater, specifically:

[0122] 1. Zinc recovery:

[0123] (1) Adding alkali: While stirring, add sodium hydroxide to the zinc smelting wastewater to adjust the pH to 8.55, filter, take the filter residue as a mixture of zinc hydroxide and zinc oxide, and take the filtrate as the wastewater after separating zinc.

[0124] The ammonia nitrogen content in the wastewater after separating zinc is 417.13 mg / L, the COD value is 160.14 mg / L, the sodium content is 16538.51 mg / L, the potassium content is 12603.12 mg / L, the zinc content is 5.94 mg / L, the thallium content is 52.29 mg / L, the manganese content is 2.31 mg / L, the cadmium content is 21.93 mg / L, the lead content is 1.88 mg / L, the cobalt content is 1.34 mg / L, and the chromium content is 1.36 mg / L.

[0125] (2) Washing the material: Wash the mixture of zinc hydroxide and zinc oxide with water to obtain the washed mixture of zinc hydroxide and zinc oxide.

[0126] (3) Leaching: Use an aqueous sulfuric acid solution to leach the mixture of zinc chloride and zinc oxide to obtain an aqueous zinc sulfate solution.

[0127] The concentration of the aqueous sulfuric acid solution is 8 wt%.

[0128] (4) Ion exchange: Use a sulfate-type anion exchange resin column to perform ion exchange on the aqueous zinc sulfate solution to obtain the ion-exchanged aqueous zinc sulfate solution.

[0129] (5) Electrolysis: Electrolyze the ion-exchanged aqueous zinc sulfate solution to obtain elemental zinc.

[0130] 2. Sulfidation treatment: Sodium sulfide is added to the wastewater after zinc separation, stirred at room temperature for 5 min, left standing for 1.5 h, and then solid-liquid separation is carried out to obtain the sulfidation-treated wastewater;

[0131] The molar ratio of heavy metals in the wastewater after zinc separation to sodium sulfide is 10:14;

[0132] 3. Flocculation: A composite flocculant is added to the sulfidation-treated wastewater, stirred at room temperature for 15 min, left standing for 20 min, and then solid-liquid separation is carried out to obtain the flocculated wastewater;

[0133] The preparation method of the composite flocculant is as follows: 400 mL of water, 3700 mL of cationic polyacrylamide aqueous solution, and 270 g of polyaluminum chloride are mixed and stirred at room temperature for 1 h to obtain the composite flocculant;

[0134] The concentration of the cationic polyacrylamide aqueous solution is 3 g / L;

[0135] The weight-average molecular weight of the cationic polyacrylamide in the cationic polyacrylamide aqueous solution is 12 million, and the ionic degree is 20%;

[0136] The addition amount of the composite flocculant is 180 g / ton of the sulfidation-treated wastewater;

[0137] The ammonia nitrogen content in the flocculated wastewater is 31.4 mg / L, the COD value is 77.1 mg / L, the sodium content is 16547.2 mg / L, the potassium content is 12648.3 mg / L, the zinc content is 3.61 mg / L, the thallium content is 0.053 mg / L, the manganese content is 0.025 mg / L, the cadmium content is 0.034 mg / L, the lead content is 0.167 mg / L, the cobalt content is 0.117 mg / L, and the chromium content is 0.128 mg / L;

[0138] 4. Electrodialysis membrane treatment: The flocculated wastewater is subjected to salt separation and concentration to obtain electrodialysis concentrated water and electrodialysis fresh water;

[0139] In the electrodialysis membrane treatment, the electrodialysis membrane used is composed of a cation exchange membrane and an anion exchange membrane. The cation exchange membrane is a cation exchange membrane with a sulfonic acid group, which can selectively permeate monovalent cations and block divalent cations; the anion exchange membrane is an anion exchange membrane with a quaternary ammonium group, which can selectively permeate monovalent anions and block divalent anions;

[0140] 5. Evaporation crystallization: The electrodialysis concentrated water is subjected to evaporation crystallization to obtain a mixed salt of sodium chloride and potassium chloride;

[0141] 6. Post-treatment: Ozone catalytic oxidation system and air stripping ammonia removal system are introduced to the electrodialysis fresh water to reduce COD and ammonia nitrogen. After reaching the discharge standard, it is discharged externally.

[0142] Example 4

[0143] A method for treating zinc smelting wastewater, specifically:

[0144] 1. Zinc recovery:

[0145] (1) Adding alkali: While stirring, sodium hydroxide is added to the zinc smelting wastewater to adjust the pH to 8.55. After filtration, the filter residue is taken as a mixture of zinc hydroxide and zinc oxide, and the filtrate is taken as the wastewater after zinc separation;

[0146] The ammonia nitrogen content in the wastewater after zinc separation is 417.13 mg / L, the COD value is 160.14 mg / L, the sodium content is 16538.51 mg / L, the potassium content is 12603.12 mg / L, the zinc content is 5.94 mg / L, the thallium content is 52.29 mg / L, the manganese content is 2.31 mg / L, the cadmium content is 21.93 mg / L, the lead content is 1.88 mg / L, the cobalt content is 1.34 mg / L, and the chromium content is 1.36 mg / L;

[0147] (2) Washing the material: The mixture of zinc hydroxide and zinc oxide is washed with water to obtain the washed mixture of zinc hydroxide and zinc oxide;

[0148] (3) Leaching: The mixture of zinc chloride and zinc oxide is leached with an aqueous sulfuric acid solution to obtain an aqueous zinc sulfate solution;

[0149] The concentration of the aqueous sulfuric acid solution is 8 wt%;

[0150] (4) Ion exchange: The aqueous zinc sulfate solution is subjected to ion exchange using a sulfate-type anion exchange resin column to obtain the ion-exchanged aqueous zinc sulfate solution;

[0151] (5) Electrolysis: The ion-exchanged aqueous zinc sulfate solution is electrolyzed to obtain elemental zinc;

[0152] 2. Sulfide treatment: Sodium sulfide is added to the wastewater after zinc separation, stirred at room temperature for 5 min, allowed to stand for 1.5 h, and solid-liquid separation is carried out to obtain the wastewater after sulfide treatment;

[0153] The molar ratio of heavy metals in the wastewater after zinc separation to sodium sulfide is 10:14;

[0154] 3. Flocculation: A composite flocculant is added to the wastewater after sulfide treatment, stirred at room temperature for 45 min, allowed to stand for 60 min, and solid-liquid separation is carried out to obtain the flocculated wastewater;

[0155] The preparation method of the composite flocculant is as follows: Mix 3700 mL of cationic polyacrylamide aqueous solution and 270 g of polyaluminum chloride, and stir for 1 h at room temperature to obtain the composite flocculant;

[0156] The concentration of the cationic polyacrylamide aqueous solution is 3 g / L;

[0157] The weight-average molecular weight of the cationic polyacrylamide in the cationic polyacrylamide aqueous solution is 12 million, and the ionic degree is 20%;

[0158] The dosage of the composite flocculant is 180 g / ton of the wastewater after sulfide treatment;

[0159] The ammonia nitrogen content in the flocculated wastewater is 15.8 mg / L, the COD value is 53.7 mg / L, the sodium content is 16420.1 mg / L, the potassium content is 12593.6 mg / L, the zinc content is 3.73 mg / L, the thallium content is 0.051 mg / L, the manganese content is 0.025 mg / L, the cadmium content is 0.031 mg / L, the lead content is 0.142 mg / L, the cobalt content is 0.110 mg / L, and the chromium content is 0.104 mg / L;

[0160] 4. Electrodialysis membrane treatment: Perform salt separation and concentration on the flocculated wastewater to obtain electrodialysis concentrated water and electrodialysis fresh water;

[0161] In the electrodialysis membrane treatment, the electrodialysis membrane used is composed of a cation exchange membrane and an anion exchange membrane. The cation exchange membrane is a cation exchange membrane with a sulfonic acid group, which can selectively permeate monovalent cations and block divalent cations; the anion exchange membrane is an anion exchange membrane with a quaternary ammonium group, which can selectively permeate monovalent anions and block divalent anions;

[0162] 5. Evaporation crystallization: Perform evaporation crystallization on the electrodialysis concentrated water to obtain a mixed salt of sodium chloride and potassium chloride;

[0163] 6. Post-treatment: Pass the electrodialysis fresh water into an ozone catalytic oxidation system and a stripping ammonia system to reduce COD and ammonia nitrogen. After reaching the discharge standard, it is then discharged externally.

[0164] From the indexes of the flocculated wastewater in Examples 1-4, it can be seen that in Example 3, no metal ion remover was used, and the composite flocculant used consisted only of an aqueous solution of cationic polyacrylamide and polyaluminum chloride. The ammonia nitrogen content, COD value, zinc content, thallium content, manganese content, lead content, cobalt content, and chromium content in the flocculated wastewater were all higher than those in Example 1. In Example 4, based on Example 3, the stirring time and standing time during flocculation were extended. The zinc content, thallium content, manganese content, lead content, cobalt content, and chromium content in the flocculated wastewater changed little compared with Example 3, and the ammonia nitrogen content and COD value in the flocculated wastewater decreased compared with Example 3, but were still higher than those in Example 1. This shows that the metal ion remover can play a role in reducing the zinc content, thallium content, manganese content, lead content, cobalt content, and chromium content in the wastewater; the composite flocculant can play a role in reducing the ammonia nitrogen content and COD value in the wastewater.

[0165] Test Example

[0166] The purpose of this test example is to further verify the influence of high zinc ion content on electrodialysis. The specific test method is to treat the same batch of zinc smelting wastewater according to the methods of Examples 1-4, continuously operate for 15 days, and control the treatment volume at 8m 3 / h, observe whether the electrodialyzer is blocked during operation. The judgment standard for blockage is that the water output of the electrodialyzer decreases by more than 10%. The observation results are as follows:

[0167]

[0168] From the results of the test example, it can be seen that when treating zinc smelting wastewater according to the methods of Example 3 and Example 4, the problem of electrodialyzer blockage is more likely to occur, indicating that wastewater with high zinc ion concentration, ammonia nitrogen content, and COD value is likely to cause blockage of the electrodialyzer.

[0169] Unless otherwise specified, the percentages used in the present invention are all mass percentages.

[0170] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for treating zinc smelting wastewater, characterized in that, Including: Zinc recovery, sulfidation treatment, precipitation treatment, flocculation, electrodialysis membrane treatment, evaporation crystallization, and post-treatment; In the sulfidation treatment, sodium sulfide is added to the wastewater after zinc separation obtained from zinc recovery, stirred at room temperature for 5 - 15 min, left standing for 1.5 - 2 h, and then solid-liquid separation is carried out to obtain the wastewater after sulfidation treatment; In the precipitation treatment, a metal ion remover is added to the wastewater after sulfidation treatment, stirred at room temperature for 20 - 30 min, left standing for 1 - 1.5 h, and then solid-liquid separation is carried out to obtain the wastewater after precipitation treatment; The preparation method of the metal ion remover is as follows: activated carbon is added to an aqueous citric acid solution, stirred, aluminum chloride is added, stirred, the pH is adjusted to 7, filtered, washed, then mixed with water, stirred at room temperature, heated to 60 - 65 °C, an aqueous solution of hydrolyzed polyacrylamide is added, stirred, filtered, washed, and then dried to obtain the metal ion remover; In the flocculation, a composite flocculant is added to the wastewater after precipitation treatment, stirred at room temperature for 15 - 20 min, left standing for 20 - 30 min, and then solid-liquid separation is carried out to obtain the wastewater after flocculation; The preparation method of the composite flocculant includes: preparing cross-linked lignin sulfonate, molecular assembly, and mixing; In the molecular assembly, cross-linked lignin sulfonate and water are mixed, stirred at room temperature, an aqueous solution of cationic polyacrylamide is added, and stirred to obtain a molecular assembly solution; In the mixing, the molecular assembly solution and polyaluminum chloride are mixed, stirred at room temperature to obtain the composite flocculant; In the electrodialysis membrane treatment, the wastewater after flocculation is desalted and concentrated to obtain electrodialysis concentrated water and electrodialysis fresh water; In the evaporation crystallization, the electrodialysis concentrated water is evaporated and crystallized to obtain a mixed salt of sodium chloride and potassium chloride; In the post-treatment, the electrodialysis fresh water is passed through an ozone catalytic oxidation system and a stripping ammonia system for treatment and then discharged externally.

2. The zinc smelting wastewater treatment method according to claim 1, characterized in that, The zinc recovery includes: adding alkali, washing the material, leaching, ion exchange, and electrolysis; In the adding alkali, sodium hydroxide is added to the zinc smelting wastewater while stirring to adjust the pH to 8.4 - 8.6, filtered, the filter residue is taken as a mixture of zinc hydroxide and zinc oxide, and the filtrate is taken as the wastewater after zinc separation; In the washing the material, the mixture of zinc hydroxide and zinc oxide is washed with water to obtain the washed mixture of zinc hydroxide and zinc oxide; In the leaching, the mixture of zinc chloride and zinc oxide is leached with an aqueous sulfuric acid solution to obtain an aqueous zinc sulfate solution; In the leaching, the concentration of the aqueous sulfuric acid solution is 7 - 9 wt%; In the ion exchange, an anion exchange resin column of sulfate type is used to carry out ion exchange on the aqueous zinc sulfate solution to obtain the aqueous zinc sulfate solution after ion exchange; In the electrolysis, the aqueous zinc sulfate solution after ion exchange is electrolyzed to obtain elemental zinc.

3. The zinc smelting wastewater treatment method according to claim 1, characterized in that, In the sulfidation treatment, the molar ratio of heavy metals in the wastewater after zinc separation to sodium sulfide is 10:14 - 15.

4. The zinc smelting wastewater treatment method according to claim 1, wherein In the precipitation treatment, the addition amount of the metal ion remover is 75 - 80 g / ton of the wastewater after sulfidation treatment.

5. The zinc smelting wastewater treatment method according to claim 1, characterized in that, In the preparation of the metal ion remover, the dosage ratio of citric acid to water in the aqueous citric acid solution is 60 - 65 g:1000 - 1200 mL; The dosage ratio of citric acid, activated carbon, aluminum chloride, water, and hydrolyzed polyacrylamide aqueous solution in the aqueous citric acid solution is 60 - 65 g : 140 - 150 g : 8 - 9 g : 1000 - 1200 mL : 1500 - 1600 mL; The particle size of the activated carbon is 2 mm; The concentration of the hydrolyzed polyacrylamide aqueous solution is 5 g / L; In the hydrolyzed polyacrylamide aqueous solution, the molecular weight of the hydrolyzed polyacrylamide is 12 million, and the degree of hydrolysis is 25%.

6. The zinc smelting wastewater treatment method according to claim 1, wherein In the flocculation, the dosage of the composite flocculant is 180 - 200 g / ton of the wastewater after precipitation treatment.

7. The zinc smelting wastewater treatment method according to claim 1, characterized in that To prepare crosslinked lignosulfonate, lignosulfonate, sodium hydroxide aqueous solution, and acetone are mixed, stirred at 35 - 40 °C, epichlorohydrin is added, and after the addition, the temperature is raised to 55 - 65 °C, stirred, cooled to room temperature, filtered, washed, and then dried to obtain a metal ion remover; In the preparation of crosslinked lignosulfonate, the dosage ratio of lignosulfonate, sodium hydroxide aqueous solution, acetone, and epichlorohydrin is 120 - 130 g : 250 - 280 mL : 500 - 600 mL : 120 - 140 mL; The concentration of the sodium hydroxide aqueous solution is 10 wt%; The addition rate of the epichlorohydrin is 5 - 6 mL / min.

8. The zinc smelting wastewater treatment method according to claim 7, characterized in that The dosage ratio of the lignosulfonate in the preparation of crosslinked lignosulfonate, water, and cationic polyacrylamide aqueous solution in the molecular assembly is 120 - 130 g : 400 - 450 mL : 3700 - 4000 mL; In the molecular assembly, the concentration of the cationic polyacrylamide aqueous solution is 3 g / L; In the cationic polyacrylamide aqueous solution, the weight-average molecular weight of the cationic polyacrylamide is 12 million, and the ionic degree is 20%; The addition rate of the cationic polyacrylamide aqueous solution is 400 - 600 mL / min; The dosage ratio of the cationic polyacrylamide aqueous solution in the molecular assembly and polyaluminum chloride in the mixing is 3700 - 4000 mL : 270 - 300 g.

9. The zinc smelting wastewater treatment method according to claim 1, wherein, In the electrodialysis membrane treatment, the used electrodialysis membrane is composed of a cation exchange membrane and an anion exchange membrane. The cation exchange membrane is a cation exchange membrane with a sulfonic acid group, which can selectively permeate monovalent cations and block divalent cations; The anion exchange membrane is an anion exchange membrane with a quaternary ammonium group, which can selectively permeate monovalent anions and block divalent anions.

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