Modified acidic coagulant and application thereof in treatment of acid-base wastewater in aluminum plate processing

Abstract

The application discloses a modified acidic coagulant and application thereof in treatment of alkaline washing wastewater generated in aluminum plate processing, and the modified acidic coagulant is prepared by modifying natural high-molecular organic flocculant chitosan with an acidic solution in a certain proportion, and compounding the chitosan with inorganic flocculant ferrous sulfate and active cation etherifying agent 2,3-epoxypropyl trimethyl ammonium chloride; the hydroxyl groups existing in the chitosan molecules generate etherification, graft copolymerization and other chemical reactions with the etherifying agent and the inorganic flocculant, so that the modified acidic coagulant which can be used under acidic conditions is obtained; the alkaline washing wastewater in the aluminum plate processing industry which is high in salt, COD and pH change and difficult to treat is separately collected and stored, the pH is adjusted, and then the modified acidic coagulant is added, so that the generated flocculation body is more compact, the amount of generated sludge is small, and especially, the active molecules such as various surfactants in the alkaline washing wastewater have good flocculation and precipitation effects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of industrial wastewater treatment, and particularly relates to a modified acid coagulant and application thereof in treatment of alkaline cleaning wastewater generated in aluminum plate processing.

[0002] The application belongs to the 7.2.1 water pollution prevention and treatment equipment difficult-to-treat industrial wastewater treatment and recycling technology and equipment in the 7.2 advanced environmental protection industry key direction in the 7th section of the strategic new industry catalogue of energy conservation and environmental protection industry. BACKGROUND

[0003] Aluminum plates need to be chemically cleaned before being treated in the hot section during processing in the cold rolling workshop, specifically, alkaline cleaning is first performed and then acid cleaning is performed, and the main components of the alkaline cleaning agent are sodium tripolyphosphate, potassium octanoate, potassium sulfate, fatty alcohol polyoxyethylene ether, etc. Through alkaline cleaning and acid cleaning, oil stains, surfactants, emulsifiers and heavy metal ions such as copper, iron and magnesium added in the aluminum plates are cleaned and enter the cleaning liquid, and when the content of the pollutants reaches a certain concentration, the pollutants are discharged for treatment. The alkaline cleaning wastewater has many characteristics such as strong corrosiveness, high COD content, high conductivity and high suspended solids, and if the wastewater is directly discharged without treatment, it will have a great impact on external water bodies. The common treatment process for acid and alkali wastewater is neutralization process, that is, the acid and alkali wastewater is mixed and neutralized in a conditioning tank, and then coagulation and sedimentation are performed. Most of the inorganic high molecular flocculants existing on the market, such as polyaluminum chloride and polyferric sulfate, need to be adjusted to a specific use condition before use, such as pH 5-9 for polyaluminum and pH 6-9 for polyferric, which limits the use range of the flocculants in water bodies with acidic or alkaline conditions. In addition, the pH of the acid and alkali wastewater is disturbed by factors such as water quantity during neutralization treatment, and most of the pollutants will be redissolved after being precipitated at different pH values. Based on the above situation, it is necessary to separately treat the acid cleaning wastewater and the alkaline cleaning wastewater before deep treatment of the acid and alkali wastewater, and in order to avoid the flocculation of the alkaline cleaning wastewater under acidic conditions, the wastewater is directly flocculated and precipitated under acidic conditions, and at this time, a coagulant suitable for coagulation and precipitation under acidic conditions needs to be found. SUMMARY

[0004] To solve the above problems, the application provides a modified acid coagulant and application thereof in treatment of alkaline cleaning wastewater generated in aluminum plate processing.

[0005] The purpose of the application is achieved in the following manner:

[0006] A modified acid coagulant, and the preparation process is as follows:

[0007] Step one: mix chitosan and sodium tetraborate according to a mass ratio of 3-5:1 to obtain a mixed powder, mix an acetic acid solution with a mass concentration of 20% and a hydrochloric acid solution with a mass concentration of 10% according to a volume ratio of 1:1-2:1 to obtain a mixed acid solution, dissolve the mixed powder in the mixed acid solution, heat to 55-60 DEG C, and magnetically stir for 0.5-1 h to obtain a modified chitosan solution;

[0008] Step two: mix a ferrous sulfate solution with a mass concentration of 25-35% with the solution obtained in step one according to a volume ratio of 1-1.5:1 to obtain a coagulant base solution.

[0009] Step three: add a 2,3-epoxypropyltrimethylammonium chloride solution with a mass concentration of 60% dropwise to the coagulant base solution obtained in step two under heating in a water bath, the mass ratio of 2,3-epoxypropyltrimethylammonium chloride to chitosan is 0.5-1:1, uniformly stir for 1-1.5 h, then irradiate under ultraviolet light for 2 h, and then dry in a constant-temperature drying oven at 65 DEG C, and grind to obtain a powder-like modified acidic coagulant.

[0010] The solid-liquid ratio of the mixed powder to the mixed acid in step one is 1:3-5.

[0011] A modified acidic coagulant and its application in the treatment of alkaline washing wastewater generated in aluminum plate processing, the alkaline washing wastewater generated in aluminum plate processing is heated to 55-65 DEG C, then the pH is adjusted to 3.5-4.5 by adding acid, the modified acidic coagulant is added for flocculation and precipitation, and then enters the subsequent treatment process.

[0012] The modified acidic coagulant is added at 50-90 mg / L according to the amount of alkaline washing wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 It is an effect comparison chart of effluent water quality of alkaline washing wastewater treated by different coagulants. DETAILED DESCRIPTION

[0014] A modified acidic coagulant, the preparation process is as follows:

[0015] Step one: mix chitosan and sodium tetraborate according to a mass ratio of 3-5:1 to obtain a mixed powder, mix an acetic acid solution with a mass concentration of 20% and a hydrochloric acid solution with a mass concentration of 10% according to a volume ratio of 1:1-2:1 to obtain a mixed acid solution, dissolve the mixed powder in the mixed acid solution, heat to 55-60 DEG C, and magnetically stir for 0.5-1 h to obtain a modified chitosan solution; the sodium tetraborate acts as a structural support and cross-linking effect of the modified flocculant. Chitosan is preferably deacetylation degree 90%-95% chitosan.

[0016] Step two: mix the ferrous sulfate solution with a mass concentration of 25-35% with the solution obtained in step one at a volume ratio of 1-1.5:1 to obtain a coagulant base solution; the ferrous sulfate solution is prepared from ferrous sulfate heptahydrate solid powder.

[0017] Step three: add the coagulant base solution obtained in step two drop by drop to a 2,3-epoxypropyltrimethylammonium chloride solution with a mass concentration of 60% under the condition of heating in a water bath, the mass ratio of 2,3-epoxypropyltrimethylammonium chloride to chitosan is 0.5-1:1, uniformly stir and react for 1-1.5 h through a mechanical stirrer, then irradiate under ultraviolet light for 2 h, and then dry in a constant temperature drying oven at 65°C, and grind to obtain a modified acidic coagulant in powder form.

[0018] The cleaning process for aluminum plate processing is alkaline followed by acid, the alkaline cleaning wastewater mainly cleans the oil stains, surfactants and part of the emulsifiers on the surface of the aluminum plate, the pH of the alkaline cleaning wastewater is 9.61-12.53, the conductivity is 9500-22500 μs / cm, and the COD is 5590-18500 mg / L. According to the characteristics of the alkaline cleaning wastewater, the alkaline cleaning wastewater is heat exchanged to 55-65°C, the emulsified interface is destroyed by heat exchange, the oil molecules wrapped by water in the wastewater are released, some high molecular surfactants reach the cloud point, the hydrogen bonds between the high molecular surfactants and water molecules are destroyed, and dehydration occurs, thereby the surfactants are precipitated, which is conducive to coagulation and sedimentation. After the wastewater is heat exchanged, it enters the coagulation and sedimentation tank, the pH is adjusted to 3.5-4.5 by adding acid, the modified acidic coagulant is added to the coagulation and sedimentation tank for flocculation and precipitation, which can remove non-ionic surfactants, oils, fatty alcohols and ether cleaning agents in the alkaline cleaning wastewater, and then the wastewater enters the subsequent treatment process.

[0019] The modified acidic coagulant is added at 50-90 mg / L according to the amount of the alkaline cleaning wastewater.

[0020] Example 1

[0021] A modified acidic coagulant is prepared by the following process:

[0022] Step one: mix chitosan and sodium tetraborate at a mass ratio of 4:1, dissolve the mixed solid in a mixed solution of acetic acid with a mass concentration of 20% and hydrochloric acid with a mass concentration of 10%, the volume ratio of acetic acid to hydrochloric acid is 2:1, heat to 55°C, and magnetically stir for 1 h, then adjust the total solid-liquid ratio to 1:3 to obtain a modified chitosan solution;

[0023] Step two: take ferrous sulfate heptahydrate, prepare a ferrous sulfate solution with a mass concentration of 35%, and mix it with the modified chitosan solution obtained in step one at a volume ratio of 1:1 to obtain a coagulant base solution;

[0024] Step three: the coagulant base fluid obtained in step two is added dropwise into a 60% mass concentration 2,3-epoxypropyltrimethylammonium chloride solution under heating in a water bath, the mass ratio of 2,3-epoxypropyltrimethylammonium chloride to chitosan being 1:1, then the mixture is uniformly stirred on a mechanical stirrer for 1 h, then irradiated under ultraviolet light for 2 h, and then dried in a constant temperature drying oven at 65°C, and ground to obtain a powder-like modified acidic coagulant.

[0025] The alkaline washing wastewater discharged by a production workshop has a quantity of 33 m³ / h, and the wastewater quality indexes are shown in Table 1.

[0026] Table 1

[0027]

[0028] The wastewater in the alkaline washing wastewater collection tank is lifted to the alkaline washing wastewater pretreatment system by a lifting pump, the alkaline washing wastewater is heat-exchanged to 60°C in a heat-exchange reactor, and then enters a coagulation sedimentation tank, sulfuric acid is added to adjust the pH to 3.5, and 70 mg / L of the above-mentioned modified acidic coagulant is added under acidic conditions according to the quantity of the alkaline washing wastewater for coagulation sedimentation, the effluent turbidity of the alkaline washing wastewater after flocculation and sedimentation is 22 NTU, the total oil is 1.87 mg / L, and the COD is 5569 mg / L.

[0029] Example 2

[0030] A modified acidic coagulant is prepared by the following process:

[0031] Step one: chitosan and sodium tetraborate are mixed according to a mass ratio of 3:1, the mixed solid is dissolved in a mixed solution of a 20% mass concentration acetic acid solution and a 10% mass concentration hydrochloric acid solution, the volume ratio of acetic acid to hydrochloric acid is 2:1, the temperature is raised to 60°C, and magnetic stirring is performed for 0.5 h, and the total solid-liquid ratio is adjusted to 1:4 to obtain modified chitosan;

[0032] Step two: ferrous sulfate heptahydrate is taken to prepare a 30% mass concentration ferrous sulfate solution, and the solution obtained in step one is mixed according to a volume ratio of 1.5:1 to obtain a coagulant base fluid;

[0033] Step three: the coagulant base fluid obtained in step two is added dropwise into a 60% mass concentration 2,3-epoxypropyltrimethylammonium chloride solution under heating in a water bath, the mass ratio of 2,3-epoxypropyltrimethylammonium chloride to chitosan being 0.5:1, then the mixture is uniformly stirred on a mechanical stirrer for 1.5 h, then irradiated under ultraviolet light for 2 h, and then dried in a constant temperature drying oven at 65°C, and ground to obtain a powder-like modified acidic coagulant.

[0034] The alkaline washing wastewater discharged by a production workshop has a quantity of 33 m³ / h, and the wastewater quality indexes are shown in Table 2.

[0035] Table 2

[0036]

[0037] The alkaline washing wastewater collected in the wastewater collecting tank is lifted to the alkaline washing wastewater pretreatment system by a lifting pump, the heat exchange reaction kettle exchanges the alkaline washing wastewater to 65℃, and then enters the coagulation sedimentation tank, sulfuric acid is added to adjust the pH to 4.0, 90 mg / L of the above-mentioned modified acid coagulant is added under the acidic condition according to the amount of the alkaline washing wastewater to carry out flocculation and precipitation, the effluent turbidity of the flocculation and precipitation alkaline washing wastewater is 18 NTU, the total oil is 1.46 mg / L, and the COD is 6795 mg / L.

[0038] Example 3

[0039] The preparation process of the modified acid coagulant is the same as that in Example 1, except that the mass ratio of chitosan and sodium tetraborate in step one is 5:1, and the mass concentration of the ferrous sulfate solution in step two is 25%.

[0040] The alkaline washing wastewater discharged by a production workshop has a washing water amount of 40 m³ / h, and the wastewater quality indexes are shown in Table 3.

[0041] Table 3

[0042]

[0043] The alkaline washing wastewater collected in the wastewater collecting tank is lifted to the alkaline washing wastewater pretreatment system by a lifting pump, the heat exchange reaction kettle exchanges the alkaline washing wastewater to 55℃, and then enters the coagulation sedimentation tank, sulfuric acid is added to adjust the pH to 4.5, 50 mg / L of the above-mentioned modified acid coagulant is added under the acidic condition according to the amount of the alkaline washing wastewater, the effluent turbidity of the flocculation and precipitation alkaline washing wastewater is 23 NTU, the total oil is 2.01 mg / L, and the COD is 7258 mg / L.

[0044] Comparative Example 1: Comparison of coagulation and sedimentation effects of alkaline washing wastewater under different pH conditions

[0045] Five 100 ml alkaline washing wastewater samples are taken, hydrochloric acid is added to adjust to different pH, and the same amount of modified coagulant and PAM is added to the five water samples, the modified coagulant is added at a dosage of 60 mg / L, after flocculation and precipitation, the supernatant is taken to observe and measure the following indexes, and the results are shown in Table 4.

[0046] Table 4

[0047]

[0048] As can be seen from Table 4, the flocculation and precipitation effect of alkaline wastewater in an acidic environment is stronger than that in an alkaline environment, therefore, preferably, the best reaction pH is set to 3.5-4.5.

[0049] Through analysis, the non-ionic surfactant, i.e. fatty alcohol polyoxyethylene ether, in the caustic washing wastewater is a stable surfactant, such ether group substances can be destroyed in the hydrogen bond combined with water molecules under heating conditions when the temperature reaches the cloud point, and dehydration phenomenon occurs, thereby causing the surfactant to precipitate, and the surfactant can only produce precipitation with a coagulant under acidic conditions, and when the pH is greater than 6.5, the flocculation precipitate is redissolved, therefore, the caustic wastewater needs to be adjusted to a pH of 3.5-4.5.

[0050] Comparative Example 2: Comparison of solubility of modified chitosan

[0051] According to the preparation process of the modified acidic coagulant, the modified chitosan prepared is dissolved in dilute hydrochloric acid, and a sodium hydroxide solution is added dropwise to adjust the pH to 2, 4, 6, 8, 10 and 12, and the solubility of the modified chitosan is observed.

[0052] Table 5

[0053]

[0054] As can be seen from Table 5, the modified chitosan has good acid-base solubility, especially in an acidic environment, and can exert excellent coagulation and precipitation effect.

[0055] The global annual output of chitosan is as high as 100 billion tons, which widely exists in nature and is widely used. Chitosan molecules can be adsorbed and combined with various metal ions and charged groups through van der Waals force, hydrogen bond and other self properties, have the advantages of large specific surface area, suitable porous structure, etc., and can be used as adsorbent. However, due to the hydrogen bond between the molecules, it is difficult to dissolve in water and can be dissolved in acid, and if it is used for the preparation of flocculants, inorganic acid can be used to destroy the hydrogen bond to modify it to be easily soluble in water, especially in an acidic environment to exert the coagulation effect. In addition, due to the small porosity and low mechanical strength of chitosan powder, its use as an adsorbent is limited, and the cross-linking property can be increased by adding borax and other substrates.

[0056] Comparative Example 3: Comparison of use effect of modified coagulant and ordinary coagulant

[0057] An equal amount of caustic washing wastewater 3 parts was taken, the pH was adjusted to 3.5, and the same amount of modified coagulant, polyferric sulfate (PFS) and polyaluminum chloride (PAC) was added, respectively, and the supernatant index was observed and determined, as shown in Table 6.

[0058] Table 6

[0059]

[0060] As can be seen from Table 6, under the condition of the same dosing amount, the effluent water quality after adding the modified coagulant is obviously better than that of the common high molecular coagulant. The effluent water quality effect comparison after adding polyaluminum chloride (PAC), polyferric sulfate (PFS) and the modified coagulant respectively is shown in Table 7. Figure 1 .

[0061] The application discloses a modified acid coagulant and application of the modified acid coagulant in treatment of caustic washing wastewater generated in aluminum plate processing, and the natural high-molecular organic flocculant chitosan is modified by an acid solution in a certain proportion, is compounded with inorganic flocculants ferrous sulfate and active cation etherifying agent 2,3-epoxypropyl trimethyl ammonium chloride, etherification, graft copolymerization and other chemical reactions are generated between hydroxyl groups existing in chitosan molecules and the etherifying agent and the inorganic flocculants, and the modified acid coagulant which can be used under acid conditions is obtained; the caustic washing wastewater in the aluminum plate processing industry which is high in salt, COD, pH change and difficult to treat is separately collected and stored, the modified acid coagulant is added after pH adjustment, the generated flocs are more compact, the sludge yield is small, and especially, the active molecules such as various surfactants in the caustic washing wastewater have good flocculation and precipitation effects.

[0062] The above only describes the preferred embodiments of the present application, and it should be noted that, for those skilled in the art, without departing from the overall concept of the present application, a number of changes and improvements can be made, and these should also be considered as the protection scope of the present application.

Claims

1. A modified acidic coagulant, characterized by, The modified acidic coagulant is used in the treatment of alkaline cleaning wastewater in aluminum plate processing, and the preparation process is as follows: Step one: mix chitosan and sodium tetraborate according to the mass ratio of 3-5:1 to obtain a mixed powder, mix an acetic acid solution with a mass concentration of 20% and a hydrochloric acid solution with a mass concentration of 10% according to the volume ratio of 1:1-2:1 to obtain a mixed acid solution, dissolve the mixed powder in the mixed acid solution, heat to 55-60 DEG C, and magnetically stir for 0.5-1 h to obtain a modified chitosan solution; Step two: mix the ferrous sulfate solution with a mass concentration of 25-35% with the solution obtained in step one according to the volume ratio of 1-1.5:1 to obtain a coagulant base solution; Step three: add the 2,3-epoxypropyltrimethylammonium chloride solution with a mass concentration of 60% dropwise to the coagulant base solution obtained in step two under the condition of heating in a water bath, the mass ratio of 2,3-epoxypropyltrimethylammonium chloride to chitosan is 0.5-1:1, uniformly stir for 1-1.5 h, then irradiate under ultraviolet light for 2 h, then dry in a constant temperature drying oven at 65 DEG C, and grind to obtain a powder-shaped modified acidic coagulant.

2. The modified acidic coagulant according to claim 1, characterized in that, The solid-liquid ratio of the mixed powder to the mixed acid in step one is 1:3-5.

3. The use of a modified acidic coagulant in the treatment of alkaline cleaning wastewater in aluminum plate processing, characterized in that: The alkaline cleaning wastewater generated in aluminum plate processing is heated to 55-65 DEG C, then the pH is adjusted to 3.5-4.5 by adding acid, the modified acidic coagulant of claim 1 or 2 is added for flocculation and precipitation, and then enters the subsequent treatment process.

4. The modified acidic coagulant according to claim 3, wherein the modified acidic coagulant is used in the treatment of alkaline cleaning wastewater in aluminum plate processing. Add 50-90 mg / L of the modified acidic coagulant according to the amount of alkaline cleaning wastewater.

Images