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Condensation-type flocculants are not widely used, and are only suitable for wastewater treatment in some special fields.
Condensation-type flocculants mainly include urea-formaldehyde condensates, phenol-formaldehyde condensates, and aniline-formaldehyde condensates
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3.
2.
2.
1 Urea-formaldehyde condensate
[Preparation method] Urea-formaldehyde condensate is mainly used as an adhesive and embedding agent.
Because of its short storage time (1 to 3 months), its application in flocculants is limited
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The preparation process of urea-formaldehyde condensate includes two-step method and one-step method
(1) One-step preparation process
Add liquid formaldehyde or paraformaldehyde into the reaction flask, adjust the pH value to 9 with sodium hydroxide aqueous solution, and raise the temperature to 60°C
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After the solution is transparent, add urea and keep it at 70～80℃ for 30min
(2) Two-step preparation process
Put a certain amount of formaldehyde aqueous solution into a three-necked flask with a reflux condenser, thermometer and stirrer, and place it in a constant temperature water bath, raise the temperature, and add sodium hydroxide solution under stirring to make the system pH=8.
0～8.
5 When the reaction system is heated to 65～75℃, put in the first batch of urea, keep the temperature rising trend, and keep the temperature in the range of 80～85℃ for 30～40min to make the viscosity reach a certain value; when the viscosity reaches the requirement, adjust the temperature And adjust the pH value to 5-6 with formic acid solution, keep the temperature until the turbidity point appears, adjust the pH=7, add the second urea, keep the temperature to measure the viscosity, until the polymerization reaction is stable, cool down, and discharge
.
The molar ratio of urea and formaldehyde is (1.
[Application] The author has used urea-formaldehyde condensate, polyaluminum chloride and polyacrylamide to treat stone wastewater, and found that if urea-formaldehyde condensate is not added, the stone wastewater treated with polyaluminum chloride and polyacrylamide will be turbid.
the removal of only about 65.
0%, which may contain an organic wastewater and stone coolant, and if added 10.
0mg / L urea-formaldehyde condensate, was added 50 ~ 120mg / L aluminum chloride and 10 ~ 30mg / L poly With acrylamide , the removal rate of turbidity is as high as 98.
6%, the removal rate of suspended solids (SS) is up to 99.
7%, and the settling speed of flocs is significantly accelerated
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3.
2.
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2 Phenolic condensate
[Preparation method] Like urea-formaldehyde condensate, phenol-formaldehyde condensate is mainly used as an adhesive, but phenol-formaldehyde condensate is used to treat wastewater containing resin and surfactants, which has a better flocculation and sedimentation effect when the pH of the wastewater is neutral or acidic.
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The specific process for the preparation of phenolic condensate: Weigh an appropriate amount of phenol, heat it to 40-50°C, melt it and put it in the reactor, then add the catalyst sodium hydroxide solution, react for 10-20min, add the first formaldehyde (addition The dosage is 80% of the total dosage), then keep the temperature of the reaction system at 80～85℃, slowly add the remaining 20% formaldehyde after reacting for 1h, after the addition , increase the reaction temperature to 85～95℃, continue to stir the reaction 2 After ~5h, a bright brown-red phenolic condensate product is obtained, which is completely soluble in water
[Application] Phenolic condensate can be used to treat resin-containing and surfactant-containing wastewater, and it also has a good flocculation and sedimentation effect when the pH is neutral or acidic
Related link: Preparation method of polyvinyl alcohol (PVA)
