A composite decolorizing agent and its preparation method and application

Abstract

The present invention belongs to the technical field of wastewater treatment, and particularly relates to a composite decolorizing agent, a preparation method thereof and an application thereof. The composite decolorizing agent of the present invention comprises a composite dicyandiamide formaldehyde polycondensate, a flocculant and an adsorbent; the composite dicyandiamide formaldehyde polycondensate is obtained by modifying the dicyandiamide formaldehyde polycondensate with a modifier; the modifier comprises an iron salt and an aluminum salt; the flocculant comprises at least one of polydimethyldiallylammonium chloride and polyamine. The present invention combines a composite dicyandiamide formaldehyde polycondensate, a specific type of flocculant and an adsorbent, and multiple factors act together to improve the decolorizing performance and decolorizing rate of pollutants in the wastewater after adsorption, flocculation and precipitation. In addition, by modifying the dicyandiamide formaldehyde polycondensate with a specific type of modifier, the inorganic and organic composite decolorizing functions are fully utilized, the solid content and decolorizing flocculation performance of the product are improved, and then the decolorizing rate, COD removal rate and ammonia nitrogen removal rate are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and particularly relates to a composite decolorizing agent and a preparation method and application thereof. Background Art

[0002] Printing and dyeing wastewater contains a large amount of dyes, with complex composition, high chromaticity, and low biological oxygen demand / chemical oxygen demand (BOD / COD). It has become one of the most polluted and difficult to treat industrial wastewaters. High-chromatic textile printing and dyeing wastewater, leather dyeing wastewater, papermaking wastewater, etc. contain various dyes and chromophores in the water, resulting in high chromaticity of the wastewater and difficulty in degradation. It must be decolorized by coagulation pretreatment before entering the subsequent biochemical treatment system.

[0003] The removal of chromaticity is one of the main tasks of dyeing and printing wastewater treatment. Reactive dyes are commonly used in the dyeing and printing industry. Compared with other dyes, reactive dyes are easily soluble in water and difficult to remove from water. Therefore, the decolorization treatment of dyeing and printing wastewater containing reactive dyes has always been a difficult problem in the field of wastewater treatment. General aluminum salts, iron salts or aluminum-iron composite water purifiers cannot achieve good decolorization effects, especially when treating hydrophilic reactive dye wastewater, aluminum-iron water purifiers are almost powerless. Studies have found that dicyandiamide formaldehyde condensation polymer has the special function of removing high-chromaticity wastewater. It itself belongs to polyammonium salt cationic organic matter, which can neutralize and destabilize the negative charge of dyes and chromophores in wastewater, and form floccules to separate from water, completing partial decolorization function. However, in the actual wastewater treatment process, it is found that simple dicyandiamide formaldehyde condensation polymer also has many disadvantages. For example, due to its small molecular weight and limited cationicity, dicyandiamide formaldehyde condensation polymer has limited decolorization effect when used alone as a decolorization agent. At the same time, the process flow is long and the operation is complicated.

[0004] Therefore, it is of great significance to provide a composite decolorizer with good decolorization rate, COD removal effect and ammonia nitrogen removal effect. Summary of the invention

[0005] The present invention aims to solve one or more technical problems existing in the above-mentioned prior art, and at least provide a beneficial choice or create conditions. Specifically, the present invention provides a composite decolorizing agent, which has good decolorization rate, COD removal effect and ammonia nitrogen removal effect.

[0006] The inventive concept of the present invention: the composite decolorizing agent of the present invention comprises a composite dicyandiamide formaldehyde condensation product, a flocculant, and an adsorbent; the composite dicyandiamide formaldehyde condensation product is obtained by modifying the dicyandiamide formaldehyde condensation product with a modifier; the modifier comprises an iron salt and an aluminum salt; the flocculant comprises at least one of polydimethyldiallylammonium chloride and a polyamine. The present invention improves the decolorization performance and decolorization rate of pollutants in wastewater after adsorption, flocculation and precipitation through the compounding of composite dicyandiamide formaldehyde condensation product, a specific type of flocculant, and an adsorbent through the comprehensive action of multiple factors. In addition, by modifying the dicyandiamide formaldehyde condensation product with a specific type of modifier, the composite dicyandiamide formaldehyde condensation product has a larger charge density, which improves the flocculation and sedimentation effect of pollutants in the wastewater, increases the solid content of the product, and improves the decolorization and flocculation performance of the product, thereby improving the decolorization effect of the composite decolorizing agent. The composite dicyandiamide formaldehyde condensation product molecules contain active nitrile groups (-C≡N), which can be hydrolyzed into amide groups or react with modifiers. Adding modifiers for modification under certain conditions can make the dicyandiamide formaldehyde condensation product have a higher molecular weight, a larger charge density, etc., thereby improving the decolorization effect of the composite decolorizer.

[0007] Therefore, a first aspect of the present invention provides a composite decolorizing agent.

[0008] Specifically, the composite decolorizing agent includes a composite dicyandiamide formaldehyde condensation product, a flocculant, and an adsorbent;

[0009] The composite dicyandiamide formaldehyde polycondensate is obtained by modifying dicyandiamide formaldehyde polycondensate with a modifier;

[0010] The modifier includes iron salt and aluminum salt;

[0011] The flocculant includes at least one of polydimethyldiallylammonium chloride and polyamine.

[0012] Preferably, the composite decolorizing agent comprises, by weight, 18-55 parts of composite dicyandiamide formaldehyde polycondensate, 1-5.5 parts of flocculant, and 2.7-12 parts of adsorbent.

[0013] Further preferably, the composite decolorizing agent comprises, by weight, 20-50 parts of composite dicyandiamide formaldehyde condensation product, 1-5 parts of flocculant, and 3-11 parts of adsorbent.

[0014] Specifically, the performance of the product is closely related to the dosage ratio of each raw material component. By limiting the ratio of the composite dicyandiamide formaldehyde condensation product, flocculant, and adsorbent, a better dosage relationship is achieved among the three, which can further improve the decolorization and flocculation performance of the product, thereby improving the decolorization effect of the composite decolorizer, and improving the COD removal rate and ammonia nitrogen removal rate.

[0015] Specifically, the present invention selects a specific type of flocculant, and through the combined action of the composite dicyandiamide formaldehyde condensation product, the adsorbent and the specific type of flocculant, the treatment effect of the composite decolorizer on wastewater can be improved, such as improving the decolorization effect, COD removal rate and ammonia nitrogen removal rate.

[0016] Preferably, the adsorbent comprises diatomaceous earth and activated carbon.

[0017] Preferably, the adsorbent comprises 0.9-3.5 parts of diatomaceous earth and 1.8-8.5 parts of activated carbon by weight.

[0018] Further preferably, the adsorbent comprises 1-3 parts of diatomaceous earth and 2-8 parts of activated carbon by weight.

[0019] Specifically, the present invention adopts specific types of adsorbents diatomaceous earth and activated carbon. The combination of the two can improve the decolorization rate, COD removal rate and ammonia nitrogen removal rate of the composite decolorizer. In addition, the decolorization rate, COD removal rate and ammonia nitrogen removal rate of the composite decolorizer can be further improved by a reasonable dosage ratio between diatomaceous earth and activated carbon.

[0020] Preferably, in the modifier, the molar ratio of the iron salt to the aluminum salt is 0.01-0.11:0.01-0.11.

[0021] More preferably, in the modifier, the molar ratio of the iron salt to the aluminum salt is 0.01-0.1:0.01-0.1.

[0022] Preferably, the iron salt comprises iron sulfate.

[0023] Preferably, the aluminum salt includes at least one of calcium aluminate, aluminum sulfate and aluminum chloride.

[0024] Specifically, the iron salt and the aluminum salt in the present invention are both indispensable as modifiers. By compounding the two as modifiers to modify the dicyandiamide formaldehyde condensation product, the composite dicyandiamide formaldehyde condensation product has a larger charge density, which improves the flocculation and sedimentation effect of pollutants in the wastewater, thereby improving the solid content, decolorization rate, COD removal rate and ammonia nitrogen removal rate of the composite decolorizer.

[0025] The second aspect of the present invention provides a method for preparing the composite decolorizing agent described in the first aspect of the present invention.

[0026] Specifically, the preparation method of the composite decolorizing agent comprises the following steps:

[0027] The raw material components are mixed to prepare the composite decolorizing agent.

[0028] Preferably, the method for preparing the composite dicyandiamide formaldehyde polycondensate comprises the following steps:

[0029] The dicyandiamide formaldehyde polycondensate and a modifier are mixed to obtain the composite dicyandiamide formaldehyde polycondensate.

[0030] Preferably, the method for preparing the composite dicyandiamide formaldehyde polycondensate comprises the following steps:

[0031] Dicyandiamide, urea, formaldehyde and a catalyst are mixed and reacted to obtain the dicyandiamide formaldehyde polycondensate; then the modifier is added and reacted to obtain the composite dicyandiamide formaldehyde polycondensate.

[0032] Specifically, dicyandiamide and formaldehyde undergo nucleophilic addition under the action of a catalyst, the amino groups are hydroxymethylated, and then water molecules are removed and polymerized to form linear macromolecules. The dicyandiamide formaldehyde polycondensate molecules contain active nitrile groups (-C≡N) which can be hydrolyzed into amide groups and can also react with a modifier. Therefore, the present invention first uses a modifier to modify the dicyandiamide formaldehyde polycondensate, and then mixes it with other components to prepare a composite decolorizing agent, which can make the composite dicyandiamide formaldehyde polycondensate have a higher molecular weight, a larger charge density, etc., thereby improving the decolorizing effect.

[0033] Preferably, the molar ratio of the dicyandiamide, urea, formaldehyde, catalyst and the modifier is 1: (0.27-1.4): (1.4-2.7): (0.7-1.8): (0.02-0.22).

[0034] Further preferably, the molar ratio of dicyandiamide, urea, formaldehyde, catalyst and modifier is 1: (0.3-1.3): (1.5-2.5): (0.8-1.6): (0.02-0.2).

[0035] Specifically, the present invention reasonably limits the dosage relationship of dicyandiamide, urea, formaldehyde, catalyst and modifier, so that the reaction is more complete, which is conducive to obtaining a composite dicyandiamide formaldehyde polycondensate with better wastewater treatment effect.

[0036] Preferably, the catalyst comprises at least one of ammonium chloride, acetic acid and aluminum chloride.

[0037] Preferably, the dicyandiamide, urea and formaldehyde are first mixed, and then the catalyst is added to react to obtain the dicyandiamide formaldehyde polycondensate; and then the modifier is added to react to obtain the composite dicyandiamide formaldehyde polycondensate.

[0038] Preferably, after the mixing, the temperature is first raised, and then part of the catalyst is added to carry out a first reaction, the temperature is lowered, and then the remaining catalyst is added to carry out a second reaction, and then iron salt is added to carry out a third reaction, and aluminum salt is added to carry out a fourth reaction to obtain the composite dicyandiamide formaldehyde condensation product.

[0039] Preferably, the temperature after heating is 35-65°C; further preferably, the temperature after heating is 40-60°C.

[0040] Preferably, the reaction time of the first reaction is 25-65 minutes; further preferably, the reaction time of the first reaction is 30-60 minutes.

[0041] Preferably, the temperature of the first reaction is less than or equal to 100°C; more preferably, the temperature of the first reaction is 80-90°C.

[0042] Preferably, the temperature after cooling is 60-80°C; further preferably, the temperature after cooling is 65-75°C; further preferably, the temperature after cooling is 70°C.

[0043] Preferably, the reaction time of the second reaction is 9-65 minutes; further preferably, the reaction time of the second reaction is 10-60 minutes.

[0044] Preferably, the temperatures of the third reaction and the fourth reaction are both 30-50°C; further preferably, the temperatures of the third reaction and the fourth reaction are both 35-45°C.

[0045] Preferably, the reaction time of the third reaction and the fourth reaction is 25-65 minutes; further preferably, the reaction time of the third reaction and the fourth reaction is 30-60 minutes.

[0046] Specifically, the present invention adopts the above-mentioned reasonable preparation process and optimizes the process and process parameters to further improve the decolorization effect of the prepared composite decolorizer.

[0047] The third aspect of the present invention provides an application of the composite decolorizing agent described in the first aspect of the present invention in the field of wastewater treatment.

[0048] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0049] (1) The present invention uses a composite of a composite dicyandiamide formaldehyde polycondensate, a flocculant, and an adsorbent, and the combined effects of multiple factors can improve the decolorization performance and decolorization rate of pollutants in wastewater after adsorption, flocculation, and precipitation. At the same time, iron salt and aluminum salt are used as modifiers to modify the dicyandiamide formaldehyde polycondensate. Iron salt and aluminum salt are indispensable. The dicyandiamide formaldehyde polycondensate is first modified by using the composite of the two as modifiers, and the inorganic and organic composite decolorization functions are fully utilized, so that the composite dicyandiamide formaldehyde polycondensate has a larger charge density, and the flocculation and sedimentation effect of pollutants in wastewater is improved. Then, the composite dicyandiamide formaldehyde polycondensate is used together with a specific flocculant and adsorbent to increase the solid content of the composite decolorizer, improve the decolorization and flocculation performance of the composite decolorizer, and make the composite decolorizer have a good decolorization rate, COD removal rate, and ammonia nitrogen removal rate.

[0050] (2) The present invention uses specific types of adsorbents, diatomaceous earth and activated carbon, which work together and are indispensable. The combined use of the two can improve the decolorization rate, COD removal rate and ammonia nitrogen removal rate of the composite decolorizer, especially significantly improve the decolorization rate.

[0051] (3) The preparation process of the present invention is simple and convenient for industrial production and application. DETAILED DESCRIPTION

[0052] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0053] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0054] Example 1

[0055] A composite decolorizing agent comprises, by weight, 40 parts of composite dicyandiamide formaldehyde condensation product, 3 parts of polydimethyldiallylammonium chloride, 2 parts of diatomaceous earth and 5 parts of activated carbon.

[0056] The preparation method of the composite decolorizing agent comprises the following steps:

[0057] The raw material components are mixed evenly to prepare a composite decolorizing agent.

[0058] Wherein, the preparation method of the composite dicyandiamide formaldehyde polycondensate comprises the following steps:

[0059] In a four-necked flask equipped with a stirrer, a condenser reflux tube and a thermometer, 21.02 g of dicyandiamide, 7.51 g of urea and 35.6 mL of formaldehyde solution were added, and then the above ingredients were fully mixed until uniform, and slowly heated to 50°C, 12.04 g of ammonium chloride was added, and stirred to react at 90°C for 45 minutes. When the temperature dropped to 70°C, 4.01 g of ammonium chloride was added, and the reaction was carried out for 30 minutes. Then, 8.00 g of ferric sulfate was added, and the temperature was maintained at 40°C for 45 minutes. 7.56 g of calcium aluminate was added, and the reaction was continued at 40°C for 45 minutes to obtain a transparent viscous solid, which is a composite dicyandiamide formaldehyde condensation product.

[0060] Example 2

[0061] The only difference between Example 2 and Example 1 is that the weight portion of the composite dicyandiamide formaldehyde condensation product in Example 2 is 50 parts, and an equal amount of aluminum sulfate is used to replace the calcium aluminate in Example 1, and the rest is the same as Example 1.

[0062] Example 3

[0063] The only difference between Example 3 and Example 1 is that the weight portion of the composite dicyandiamide formaldehyde condensation product in Example 3 is 30 parts, and an equal amount of aluminum chloride is used to replace the calcium aluminate in Example 1, and the rest is the same as Example 1.

[0064] Example 4

[0065] The only difference between Example 4 and Example 1 is that in the preparation process of the composite dicyandiamide formaldehyde polycondensate in Example 4, the amount of each raw material used is different.

[0066] Specifically, in Example 4, the preparation method of the composite dicyandiamide formaldehyde polycondensate is:

[0067] In a four-necked flask equipped with a stirrer, a condenser reflux tube and a thermometer, 21.02 g of dicyandiamide, 6.01 g of urea and 39.5 mL of formaldehyde solution were added, and then the above ingredients were fully mixed until uniform, and slowly heated to 50°C, 8.02 g of ammonium chloride was added, and stirred to react at 90°C for 45 minutes. When the temperature dropped to 70°C, 2.67 g of ammonium chloride was added, and the reaction was carried out for 30 minutes. Then, 4.00 g of ferric sulfate was added, and the temperature was maintained at 40°C for 45 minutes. 7.56 g of calcium aluminate was added, and the reaction was continued at 40°C for 45 minutes to obtain a transparent viscous solid, which is a composite dicyandiamide formaldehyde condensation product.

[0068] Example 5

[0069] The only difference between Example 5 and Example 1 is that in the preparation process of the composite dicyandiamide formaldehyde polycondensate in Example 5, the amount of each raw material used is different.

[0070] Specifically, in Example 5, the preparation method of the composite dicyandiamide formaldehyde polycondensate is:

[0071] In a four-necked flask with a stirring flow tube and a thermometer, 21.02 g of dicyandiamide, 6.01 g of urea and 43.5 mL of formaldehyde solution were added, and then the above ingredients were fully mixed until uniform, and slowly heated to 50°C, 14.04 g of ammonium chloride was added, and the reaction was stirred at 90°C for 45 minutes. When the temperature dropped to 70°C, 4.68 g of ammonium chloride was added, and the reaction was carried out for 30 minutes. Then, 6.00 g of ferric sulfate was added, and the reaction was maintained at 40°C for 45 minutes. 5.67 g of calcium aluminate was added, and the reaction was continued at 40°C for 45 minutes to obtain a transparent viscous solid, which was a composite dicyandiamide formaldehyde condensation product.

[0072] Example 6

[0073] The only difference between Example 6 and Example 1 is that Example 6 uses an equal amount of polyamine to replace polydimethyldiallylammonium chloride, and the rest is the same as Example 1.

[0074] Comparative Example 1

[0075] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses an equal amount of aluminum sulfate to replace ferric sulfate, and the rest is the same as Example 1.

[0076] Comparative Example 2

[0077] The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses an equal amount of calcium sulfate to replace calcium aluminate, and the rest is the same as Example 1.

[0078] Comparative Example 3

[0079] The only difference between Comparative Example 3 and Example 1 is that no calcium aluminate is added in Comparative Example 3, that is, no aluminum salt is added in Comparative Example 3, and the rest is the same as Example 1.

[0080] Comparative Example 4

[0081] The only difference between Comparative Example 4 and Example 1 is that Comparative Example 4 uses an equal amount of charcoal to replace activated carbon, and the rest is the same as Example 1.

[0082] Comparative Example 5

[0083] The difference between Comparative Example 5 and Example 1 is that Comparative Example 5 uses an equal amount of bentonite to replace diatomaceous earth, and the rest is the same as Example 1.

[0084] Comparative Example 6

[0085] The difference between Comparative Example 6 and Example 1 is that Comparative Example 6 uses an equal amount of cationic polyacrylamide to replace polydimethyldiallylammonium chloride, and the rest is the same as Example 1.

[0086] Performance Testing

[0087] The composite decolorizers prepared in Examples 1-6 and Comparative Examples 1-6 were tested for solid content, decolorization rate, COD removal rate and ammonia nitrogen removal rate. The test methods are as follows:

[0088] Solid content: The solid content is measured by the drying method. The washed and dried weighing bottle is weighed with an analytical balance, and the weight is recorded as A. 10 g of the composite decolorizing agent of Examples 1-6 and Comparative Examples 1-6 are weighed respectively and recorded as W0. The composite decolorizing agents of Examples 1-6 and Comparative Examples 1-6 are respectively put into weighing bottles, and then placed in an oven and dried at 103°C for 4 hours. After drying, the weight is weighed (the total weight of the sample and the weighing bottle), recorded as W. The solid content is calculated as follows: w / %=(WA) / W0×100%.

[0089] Decolorization rate: In wastewater with a K-type active dye concentration of 1000 mg / L, the composite decolorizers prepared in Examples 1-6 and Comparative Examples 1-6 were added in an amount of 200 mg / L, and then the chromaticity was determined by the dilution multiple method. The decolorization rate was calculated as follows: F / %=[(U0-U1) / U0]×100%;

[0090] Among them, F is the decolorization rate; U0 is the chromaticity of the wastewater before treatment; U1 is the chromaticity of the wastewater after treatment.

[0091] COD removal rate: In wastewater with a COD concentration of 900 mg / L, the composite decolorizing agents prepared in Examples 1-6 and Comparative Examples 1-6 were added in an amount of 200 mg / L, and the COD content before and after wastewater treatment was tested by potassium dichromate method. The COD removal rate was calculated as follows: c / %=[(C0-C1) / C0]×100%;

[0092] Among them, c is the COD removal rate; C0 is the chromaticity of the wastewater before treatment; C1 is the chromaticity of the wastewater after treatment.

[0093] Ammonia nitrogen removal rate: In wastewater with an ammonia nitrogen content of 550 mg / L, the composite decolorizing agents prepared in Examples 1-6 and Comparative Examples 1-6 were added in an amount of 200 mg / L. The ammonia nitrogen content before and after the wastewater treatment was tested by spectrophotometry. The ammonia nitrogen removal rate was calculated as follows: n / %=[(N0-N1) / N0]×100%;

[0094] Wherein, n is the ammonia nitrogen removal rate; N0 is the chromaticity of the wastewater before treatment; N1 is the chromaticity of the wastewater after treatment.

[0095] The test results of solid content, decolorization rate, COD removal rate and ammonia nitrogen removal rate of the composite decolorizer prepared in Examples 1-6 and Comparative Examples 1-6 are shown in Table 1.

[0096] Table 1: Test results of solid content, decolorization rate, COD removal rate and ammonia nitrogen removal rate of the composite decolorizer of Examples 1-6 and Comparative Examples 1-6

[0097]

[0098] It can be seen from Table 1 that the composite decolorizing agent prepared by the present invention has a good solid content. When it is applied to wastewater treatment, it has a good decolorization effect on the wastewater, a high decolorization rate of up to 97.7%, and a good COD removal rate and ammonia nitrogen removal rate, and can achieve a good comprehensive treatment effect on the wastewater.

[0099] Comparative Example 1 uses an equal amount of aluminum sulfate to replace the iron sulfate in Example 1, and the rest is the same as Example 1. As a result, the solid content of the composite decolorizer in Comparative Example 1 is lower than that in Example 1, and the decolorization rate, COD removal rate and ammonia nitrogen removal rate during wastewater treatment are also lower than those in Example 1, indicating that the addition of iron sulfate in the preparation process of the composite dicyandiamide formaldehyde condensation product has better effects on decolorization, COD removal and ammonia nitrogen removal.

[0100] Comparative Example 2 uses an equal amount of calcium sulfate to replace the calcium aluminate in Example 1, and the rest is the same as Example 1. As a result, the solid content of the composite decolorizer in Comparative Example 2 is lower than that in Example 1, and the decolorization rate, COD removal rate and ammonia nitrogen removal rate after wastewater treatment are also lower than those in Example 1, indicating that in the preparation process of the composite dicyandiamide formaldehyde condensation product, the addition of the modifier calcium aluminate can improve the decolorization treatment effect during wastewater treatment, that is, it has good decolorization rate, COD removal effect and ammonia nitrogen removal effect.

[0101] Comparative Example 3 does not add calcium aluminate, and the rest is the same as Example 1. As a result, the solid content of the composite decolorizer of Comparative Example 3 is lower than that of Example 1, and the decolorization rate, COD removal rate and ammonia nitrogen removal rate during wastewater treatment are also lower than those of Example 1, indicating that in the preparation process of the composite dicyandiamide formaldehyde condensation product, only adding ferric sulfate will make the solid content, decolorization treatment effect, COD removal and ammonia nitrogen removal effects worse than those of the composite decolorizer to which ferric sulfate and calcium aluminate are added at the same time, which illustrates the importance of compounding the modifiers ferric sulfate and calcium aluminate.

[0102] It can be seen from Comparative Examples 1, 2 and 3 that when Comparative Example 1 lacks iron salt, the decolorization rate, COD removal rate and ammonia nitrogen removal rate of the composite decolorizer will be reduced; when Comparative Example 2 lacks aluminum salt, the decolorization rate, COD removal rate and ammonia nitrogen removal rate of the composite decolorizer will also be reduced. It shows that the iron salt and aluminum salt in the modifier of the present invention are indispensable, and the lack of any one of them will reduce the treatment effect of the wastewater. Only when the two exist at the same time and work together can the solid content of the prepared composite decolorizer and the decolorization rate, COD removal rate and ammonia nitrogen removal rate in the wastewater treatment process be better improved.

[0103] Comparative Example 4 uses an equal amount of charcoal to replace activated carbon, and the rest is the same as Example 1. As a result, the decolorization rate, COD removal rate and ammonia nitrogen removal rate of the composite decolorizer in Comparative Example 4 for wastewater treatment are lower than those in Example 1, indicating that the addition of a specific type of activated carbon in the adsorbent is more conducive to improving the effects of decolorization treatment, COD removal and ammonia nitrogen removal, especially can significantly improve the decolorization rate during wastewater treatment.

[0104] Comparative Example 5 uses an equal amount of bentonite to replace diatomaceous earth, and the rest is the same as Example 1. As a result, the decolorization rate, COD removal rate and ammonia nitrogen removal rate of the composite decolorizer in Comparative Example 5 during wastewater treatment are lower than those in Example 1, indicating that the addition of a specific type of diatomaceous earth in the adsorbent is more conducive to improving the decolorization treatment effect, COD removal and ammonia nitrogen removal effects, especially can significantly improve the decolorization rate during wastewater treatment.

[0105] It can be seen from Comparative Examples 4-5 that the present invention requires the use of specific types of adsorbents diatomaceous earth and activated carbon, which work together and are indispensable. By using the two in combination and combining with other components, the decolorization rate, COD removal rate and ammonia nitrogen removal rate of the composite decolorizer can be improved, especially the decolorization rate during wastewater treatment can be significantly improved.

[0106] Comparative Example 6 uses an equal amount of cationic polyacrylamide to replace polydimethyldiallylammonium chloride, and the rest is the same as Example 1. As a result, the decolorization rate, COD removal rate and ammonia nitrogen removal rate of the composite decolorizer of Comparative Example 6 for wastewater treatment are lower than those of Example 1, especially the decolorization rate of Comparative Example 6 is significantly lower than that of Example 1, indicating that the specific type of flocculant and other components in the adsorbent work together to better improve the decolorization treatment effect, COD removal and ammonia nitrogen removal effect.

[0107] In summary, the present invention is compounded by composite dicyandiamide formaldehyde polycondensation product, flocculant, adsorbent, and multiple factors act together, so that the pollutants in the waste water can improve decolorization performance and decolorization rate after adsorption, flocculation precipitation. Meanwhile, by adopting iron salt and aluminum salt as modifier to modify dicyandiamide formaldehyde polycondensation product, inorganic and organic composite decolorization function can be fully utilized, so that composite dicyandiamide formaldehyde polycondensation product has larger charge density, and the flocculation sedimentation effect of pollutants in waste water is improved. In addition, the present invention adopts specific types of adsorbent diatomite and activated carbon, and both act together, and neither of them is indispensable, and the decolorization rate of composite decolorant can be improved by the composite use of both, COD removal rate and ammonia nitrogen removal rate, especially can significantly improve decolorization rate. In summary, the present invention adopts a specific flocculant, a composite dicyandiamide formaldehyde modified by a specific modifier and a specific type of adsorbent to increase the solid content of the composite decolorizer, improve the decolorization and flocculation performance of the composite decolorizer, and enable the composite decolorizer to have a good decolorization rate, COD removal rate and ammonia nitrogen removal rate when treating wastewater.

[0108] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A composite decolorizing agent, It is characterized in that It is composed of a composite dicyandiamide formaldehyde condensation product, a flocculant, and an adsorbent; and the adsorbent is composed of 0.9-3.5 parts of diatomaceous earth and 1.8-8.5 parts of activated carbon by weight; The composite dicyandiamide formaldehyde polycondensate is obtained by modifying dicyandiamide formaldehyde polycondensate with a modifier; The modifier is an iron salt and an aluminum salt; in the modifier, the molar ratio of the iron salt to the aluminum salt is 0.01-0.11:0.01-0.11; The flocculant is selected from at least one of polydimethyldiallylammonium chloride and polyamine; The preparation method of the composite dicyandiamide formaldehyde polycondensate comprises the following steps: First, the dicyandiamide, urea and formaldehyde are mixed, and after the mixing, the temperature is first raised, and then part of the catalyst is added to carry out a first reaction, the temperature is lowered, and then the remaining catalyst is added to carry out a second reaction, and then iron salt is added to carry out a third reaction, and aluminum salt is added to carry out a fourth reaction to obtain the composite dicyandiamide formaldehyde polycondensate; The temperature of the third reaction and the fourth reaction is 40-50°C; The molar ratio of dicyandiamide, urea, formaldehyde, catalyst and modifier is 1: (0.27-1.4): (1.4-2.7): (0.7-1.8): (0.02-0.22).

2. The composite decolorizing agent according to claim 1, It is characterized in that In parts by weight, the composite decolorizing agent comprises 18-55 parts of composite dicyandiamide formaldehyde polycondensate, 1-5.5 parts of flocculant, and 2.7-12 parts of adsorbent.

3. The composite decolorizing agent according to claim 1, It is characterized in that The iron salt includes iron sulfate; and / or the aluminum salt includes at least one of calcium aluminate, aluminum sulfate, and aluminum chloride.

4. A method for preparing the composite decolorizing agent according to any one of claims 1 to 3, It is characterized in that The following steps are involved: The raw material components are mixed to prepare the composite decolorizing agent.

5. Use of the composite decolorizing agent according to any one of claims 1 to 3 in the field of wastewater treatment.

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