Treatment method for separating high-content zinc from iron-containing hot galvanizing pickling waste acid

Abstract

The invention provides a treatment method for separating high-content zinc from iron-containing hot galvanizing pickling waste acid, and belongs to the field of comprehensive utilization of hot galvanizing pickling waste water. The method comprises the following steps: dissolving hot galvanizing pickling sludge with acid, mixing the hot galvanizing pickling sludge with hot galvanizing pickling wastewater, filtering out impurity particles, pretreating with an oleophylic filter material to remove floating oil, adding phosphate within a certain range, oxidizing and adjusting pH to precipitate iron phosphate, separating zinc from iron, and thoroughly separating high-content zinc, adding sulfuric acid into a zinc salt solution for treatment, industrial-grade zinc sulfate is obtained through filtration, evaporation and crystallization, ferric phosphate meets the grade for batteries, and the method is low in cost and environmentally friendly.

Description

Technical Field

[0001] The invention relates to the field of comprehensive utilization of hot-dip galvanizing pickling wastewater, and more specifically, to a treatment method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid. Background Art

[0002] With the rapid development of national industrialization, my country has moved from a major steel industry country to a technological power in the steel industry. However, corroded steel not only causes economic losses, but also causes various structural defects and a decrease in effective cross-sectional area. Hot-dip galvanizing, as a type of hot-dip method, has become an important protection technology for steel surface corrosion. In the pickling process of hot-dip galvanizing of steel, strong acid (generally 31%~36% hydrochloric acid or 5%~20% sulfuric acid) is currently used to remove rust and impurities from the pickling surface, which will produce a large amount of zinc-containing and iron-containing waste acid. The conventional lime acid-base neutralization process is used to convert metal ions into precipitation, and the waste liquid is discharged after meeting the standards. However, the waste acid contains a large amount of zinc, iron and a certain concentration of acid, and the process cannot be recycled, resulting in a waste of resources. Therefore, the waste acid after separating the heavy metal ion zinc can be converted into valuable resources through comprehensive treatment, thereby realizing the resource utilization of waste acid and the reuse of metal resources.

[0003] In the process of galvanizing, a large amount of zinc-containing and iron-containing sludge or iron-containing waste liquid is generated, that is, hot-dip galvanizing pickling wastewater containing iron. The conventional treatment method is to make it into iron-based flocculants through acid dissolution oxidation and other processes. However, since such zinc-containing and iron-containing waste contains a large amount of zinc, the iron-based flocculants finally produced will cause secondary pollution during use. Therefore, it is necessary to separate high-content zinc from zinc-containing and iron-containing wastes, so that iron ions can be fully utilized as resources, and zinc can be recycled and reused.

[0004] The prior art discloses a hot-dip galvanizing pickling wastewater comprehensive utilization process and a method for preparing battery-grade iron phosphate, wherein the iron in the wastewater is first reacted with phosphate and then oxidized to obtain dihydrate iron phosphate to obtain an iron phosphate product, and then the zinc in the filtrate is reacted with carbonate ions to obtain a basic zinc carbonate product, thereby realizing the recovery and reuse of iron and zinc in the wastewater. However, the purity of the obtained zinc solution is not enough, and it is difficult to ensure the separation effect for waste liquid with higher content of zinc and iron. In addition, the repeated addition of oxidants, precipitants and other agents is costly and pollutes the environment to a certain extent.

[0005] Therefore, it is of great research significance and application value to develop a treatment method for separating high-content zinc from iron-containing hot-dip galvanizing pickling wastewater with good zinc separation effect, thorough pretreatment and low cost. Summary of the invention

[0006] The present invention aims to overcome the shortcomings of the prior art. The primary purpose of the present invention is to provide a treatment method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid, wherein oleophilic filter material is used for pretreatment to remove floating oil, and zinc and iron phosphate are precipitated and separated by adding phosphate, oxidation and adjusting pH to obtain industrial-grade zinc sulfate, and the iron phosphate meets the battery grade, thereby achieving a thorough separation effect of high-content zinc, and the method has low cost and is environmentally friendly.

[0007] Another object of the present invention is to provide an application of the above-mentioned treatment method for separating high-content zinc from iron-containing hot-dip galvanizing pickling wastewater.

[0008] To achieve the above object, the present invention adopts the following technical solutions: The present invention provides a method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid, comprising the following steps: S1. Pretreatment: dissolving the hot-dip galvanizing pickling sludge in acid, mixing it with the hot-dip galvanizing pickling wastewater, removing the impurity particles, obtaining a filtrate, and then filtering the filtrate with an oleophilic filter material to obtain a zinc-iron waste liquid; S2. adding phosphate to the zinc-iron waste liquid for reaction; S3. Pass oxygen or air to remove Fe 2+ Oxidized to Fe 3+ , heating and heat preservation; S4. adjusting the pH of the solution to 1.0-2.0 for reaction, and performing solid-liquid separation to obtain a zinc salt solution and an iron phosphate precipitate; S5. The filtered zinc salt solution was added with sulfuric acid to control the pH to 5 to 6, and then filtered, evaporated and crystallized to obtain industrial grade zinc sulfate; Wherein, the molar ratio of the phosphate to the iron element in the phosphate in step S2 is 1-1.5:1.

[0009] The present invention provides a treatment method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid. In step S1, the waste liquid containing high concentrations of zinc and iron is filtered in two steps, and the impurity particles and suspended matter contained therein are removed by conventional filtration, and the floating oil in the waste liquid is filtered through an oleophilic filter material, because when the waste acid passes through the filter material, a small amount of floating oil and part of the emulsified oil are adsorbed or retained, thereby achieving separation of oil and waste acid. In step S2, phosphate is added to introduce phosphate ions to prepare for the subsequent generation of iron phosphate precipitation. In step S3, oxygen or air is used for oxidation to convert all iron elements in the solution into iron ions. In step S4, the acidity is adjusted to generate iron phosphate precipitation, and iron and zinc are successfully and completely separated.

[0010] The amount of phosphate added directly affects the reaction balance between iron ions and phosphate. When the amount of phosphate added exceeds the stoichiometric ratio, excess phosphate will be present in the solution, reacting with other metal ions in the solution to form unwanted byproducts. Excess phosphate may cause zinc ions to be precipitated, affecting the zinc removal effect. The pH value of step S4 is fixed because when phosphate is introduced, the precipitation pH values ​​of iron and zinc are different. When the pH value is about 2 or below, the reaction forms an insoluble FePO4 precipitate (Fe 3+ +PO4 3− →FePO4↓). Zinc phosphate precipitation occurs at a higher pH range, generally starting at around pH 5 to 6.

[0011] Preferably, the hot-dip galvanizing pickling sludge is acid-dissolved and mixed with the hot-dip galvanizing pickling wastewater to obtain a solution having a zinc content of 10% to 15%.

[0012] Preferably, the oleophilic filter material in step S1 is selected from one or more of activated carbon, fiber balls, ceramsite or quartz sand.

[0013] More preferably, the oleophilic filter material is a mixture of activated carbon and quartz sand.

[0014] Specifically, the mass ratio of the quartz sand to the activated carbon is 2:1.

[0015] Preferably, the filtration separation in step S1 comprises the following steps: loading the filter material into the filter column in sequence. Pumping the waste acid solution into the filter column with a pump, and then adjusting the filtration rate with a flow meter. During the filtration separation process, the waste liquid solution is continuously stirred to keep the solution uniform.

[0016] The filtering device is selected according to the prior art.

[0017] Specifically, the filter of the oleophilic filter material is one of: an organic glass filter column, a multi-media filter or a V-type filter tank.

[0018] Specifically, the pretreatment of step S1 is multi-media filtration. The upper layer of activated carbon filter material has the largest particles and the smallest density; the lower layer of quartz sand filter material has a small particle size and a large density; the upper layer of filter material plays a coarse filtration role, with low resistance and small head loss, and the lower layer of filter material plays a fine filtration role with strong pollution interception ability.

[0019] Preferably, the phosphate in step S2 is one or both of diammonium phosphate or triammonium phosphate.

[0020] Preferably, the molar ratio of the phosphate to the iron element in the phosphate in step S2 is 1.2-1.3:1.

[0021] Preferably, the temperature of the heating and heat preservation in step S3 is 90-98°C.

[0022] Preferably, the heating and heat preservation time in step S3 is 1 to 2 hours.

[0023] Preferably, the flow rate of the oxygen or air in step S3 is 5-25 mL / min.

[0024] Preferably, the oxygen content of the air in step S3 is 20%.

[0025] Preferably, the pH is adjusted in step S4 by adding one or more of ammonia water, sodium carbonate or sodium hydroxide.

[0026] More preferably, the pH is adjusted by adding sodium hydroxide in step S4.

[0027] Preferably, the reaction time in step S4 is 1 to 3 h.

[0028] Preferably, the acidity test in step S4 is measured by a pH sensor.

[0029] Preferably, step S4 further comprises the following step: washing the iron phosphate precipitate with deionized water to remove residual zinc salt.

[0030] Preferably, step S5 further comprises the following steps: stirring the filtered zinc salt solution, adding 15-25% sulfuric acid solution, controlling the reaction temperature to 75-85° C., and the pH to 5-6, filtering to remove insoluble impurities after the reaction is completed, evaporating the filtrate, cooling and crystallizing, and centrifuging and dehydrating to obtain an industrial-grade zinc sulfate product.

[0031] Industrial zinc sulfate is mainly used in artificial fibers, electrolytic industry, electroplating, inorganic pigments, etc. It is used as a chemical raw material for metal surface treatment and galvanizing industry. It can be used to remove oxide layers and impurities on the metal surface and form an anti-corrosion layer on the metal surface.

[0032] Compared with the prior art, the present invention has the following beneficial effects: The invention provides a treatment method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid, wherein oleophilic filter material is used for pretreatment to remove floating oil, and zinc and iron phosphate are precipitated and separated by adding phosphate, oxidation and adjusting pH, so as to achieve a thorough separation effect of high-content zinc, and the method has low cost and is environmentally friendly. The yield of zinc in the obtained liquid is above 89%, the separation rate is above 95%, and industrial-grade zinc sulfate is obtained, and the iron phosphate can meet the battery grade. DETAILED DESCRIPTION

[0033] In order to more clearly and completely describe the technical solution of the present invention, the present invention is further described in detail through specific embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention. Various changes can be made within the scope of the rights of the present invention.

[0034] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0035] Test indicators: The high-zinc iron-containing sludge and waste acid used in the examples and comparative examples were tested for ferrous iron content, ferric iron content, total phosphorus, zinc content and acidity. The test methods are as follows: Content of ferrous and ferric iron: o-phenanthroline spectrophotometric method; (2) Total phosphorus: quinoline molybdate gravimetric method; (3) Zinc content: Test the zinc salt solution obtained in step S4; run X-ray fluorescence analysis (XRF) to detect the corresponding zinc content (ppm); (4) Zinc separation rate: Separation rate calculation formula = Zn after separation / Zn before separation × 100%; (5) Acidity: Use a pH sensor.

[0036] Embodiments 1 to 7 Table 1 Related indicators of high-zinc and iron-containing wastewater before and after pretreatment in Example

[0037] Example 1 A method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid S1. dissolving the high-zinc and iron-containing sludge with acid, mixing it with the high-zinc and iron-containing waste acid, filtering and separating it, and obtaining the zinc-containing iron waste liquid through a filter whose internal lipophilic filter material is quartz sand and activated carbon in a mass ratio of 2:1; S2. According to the molar ratio of phosphate to iron element of 1.2:1, the corresponding mass of ammonium dihydrogen phosphate was added to the zinc-containing and iron-containing waste liquid, and stirred to form a mixed solution; S3. Pass oxygen at a flow rate of 22 mL / min into the mixed solution to remove Fe 2+ Oxidized to Fe 3+ , detect the ferrous ion content, and after complete conversion, heat to 95°C and keep warm for 2h; S4. Sodium hydroxide was introduced at a flow rate of 3 mL / min to adjust the acidity to pH=1.2, and solid-liquid separation was performed after the reaction for 2 hours, and finally a zinc salt solution and a purified iron-containing precipitate after zinc separation were obtained, thereby achieving zinc and iron separation; S5. Stir the filtered zinc salt solution, add 20% sulfuric acid solution, control the reaction temperature to 80°C, and the pH to 5. After the reaction is completed, filter to remove insoluble impurities, evaporate the filtrate, cool and crystallize, and centrifuge to dehydrate to obtain industrial-grade zinc sulfate products.

[0038] Example 2 A method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid The experimental method is the same as that of Example 1, except that the molar ratio of phosphate to iron is 1:1.

[0039] Example 3 A method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid The experimental method is the same as that of Example 1, except that the molar ratio of phosphate to iron is 1.5:1.

[0040] Example 4 A method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid The experimental method is the same as that of Example 1, except that the pH in step S4 is adjusted to 1.

[0041] Example 5 A method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid The experimental method is the same as that of Example 1, except that the pH in step S4 is adjusted to 2.

[0042] Example 6 A method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid The experimental method is the same as that of Example 1, except that the temperature in step S3 is raised to 90° C. for 1 h.

[0043] Example 7 A method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid The experimental method is the same as that of Example 1, except that the temperature in step S3 is raised to 98° C. for 3 h.

[0044] Comparative Example 1 A method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid The experimental method is the same as that of Example 1, except that: in step S1, no lipophilic filter material filtration is performed.

[0045] Comparative Example 2 A method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid The experimental method is the same as that of Example 1, except that the molar ratio of phosphate to iron is 0.5:1.

[0046] Comparative Example 3 A method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid The experimental method is the same as that of Example 1, except that the molar ratio of phosphate to iron is 1:2.

[0047] Comparative Example 4 A method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid The experimental method is the same as that of Example 1, except that the pH in step S5 is adjusted to 4.

[0048] Comparative Example 5 A method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid The experimental method is the same as that of Example 1, except that the pH in step S5 is adjusted to 7.

[0049] Table 2 Test results of embodiments and comparative examples

[0050] The yield of zinc in the zinc salt solution separated by the methods of Examples 1 to 7 is above 89%, and the separation rate is above 95%, indicating that the methods given in the embodiments of the present invention can achieve a thorough separation of zinc and iron, and the methods are simple, among which the separation effect of Example 1 is the best. According to the methods of Examples 1 to 7, after flash drying treatment, the purity of the iron phosphate product can reach 99%, wherein the zinc (Zn) content is less than 0.005%, which meets the quality requirements of HG / T 4701-2021 standard for iron phosphate for batteries. The purity of zinc sulfate produced by this process is as high as 99.0%, wherein the iron (Fe) content is less than 0.002%, which meets the relevant quality indicators of the "Industrial Zinc Sulfate" (HG / T 2326-2015) standard, therefore, the present invention has significant value in terms of application.

[0051] Comparative Example 1 does not perform step S1, and the separation rate of zinc and iron is significantly reduced; Comparative Examples 2 and 3 show that the amount of phosphoric acid added has a great influence on the yield and separation rate of zinc; Comparative Examples 4 and Comparative Examples 5 show that adjusting step S5 within a certain pH range will significantly affect the yield and separation effect of zinc.

[0052] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for separating high-content zinc from iron-containing hot-dip galvanizing pickling waste acid, characterized in that: The following steps are involved: S1. Pretreatment: dissolving the hot-dip galvanizing pickling sludge with acid, mixing it with the hot-dip galvanizing pickling wastewater, removing the impurity particles, obtaining a filtrate, and then filtering the filtrate with an oleophilic filter material to obtain a zinc-iron waste liquid; S2. adding phosphate to the zinc-iron waste liquid for reaction; S3. Pass oxygen or air to remove Fe 2+ Oxidized to Fe 3+ , heating and heat preservation; S4. adjusting the pH of the solution to 1.0-2.0, reacting, and separating the solid and liquid to obtain a zinc salt solution and an iron phosphate precipitate; S5. The filtered zinc salt solution was added with sulfuric acid to control the pH to 5 to 6, and then filtered, evaporated and crystallized to obtain industrial grade zinc sulfate; Wherein, the molar ratio of the phosphate to the iron element in the phosphate in step S2 is 1-1.5:

1.

2. The method according to claim 1, characterized in that The lipophilic filter material in step S1 is selected from one or more of activated carbon, fiber balls, ceramsite or quartz sand.

3. The method according to claim 1, characterized in that The phosphate in step S2 is one or both of diammonium phosphate or triammonium phosphate.

4. The method according to claim 1, characterized in that: The temperature of the heating and heat preservation in step S3 is 90-98°C.

5. The method according to claim 1, characterized in that The heating and heat preservation time in step S3 is 1 to 2 hours.

6. The method according to claim 1, characterized in that The flow rate of oxygen or air in step S3 is 5-25 mL / min.

7. The method according to claim 1, characterized in that The reaction time in step S4 is 1 to 3 h.

8. The method according to claim 1, characterized in that The pH value in step S4 is adjusted by adding one or more of ammonia water, sodium carbonate or sodium hydroxide.

9. The method according to claim 1, characterized in that: The method for further treating the zinc salt solution in step S4 comprises the following steps: using an evaporation system to evaporate water in the zinc salt solution, and separating zinc from other salts by crystallization to achieve separation of zinc.

10. Use of the method according to any one of claims 1 to 9 in treating hot-dip galvanizing pickling wastewater.

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