What makes a purifier difficult to treat?
Many aqueous metal purifiers used in the industry have a simple composition of caustic, surfactant and sodium carbonate. These cleaners are not very aggressive and are easy to handle with standard wastewater treatment methods. However, when more aggressive cleaning agents are used, this creates problems for water purification. The strength of the purifier increases when complexing agents are used, such as ammonia, citrates, carboxylic acids, EDTA, NTA TEA, phosphonates, etc. When they are discharged into wastewater containing metals, they form a complex or bind to metals in solution. This connection makes it difficult to remove metals from the waste stream using standard processing methods.
How do we process wastewater with complex cleaners and metals?
The treatment can be carried out in several different ways. One of the traditional methods is to mix in complex wastewater with all other wastewater and perform the following procedure (in a compensation tank):
- Lower the pH to 2.0-2.5 (this helps break down the complexes)
- Add coagulant
- Raise the pH to 9.0 – 10.0
- Add 50 to 200 ppm metal precipitator (these complex metals in the form to be assembled)
- Add anionic polymer for production.
However, if there is an empty reaction tank, the best way to clean concentrated complex cleaners is to separate them in a separate tank. At the moment there are several treatment options.
It is acidified with dilute sulfuric acid, which leads to a pH of 1.5-2.5, and then it is stirred for 24-48 hours. After this time, the solution can be gradually poured into the industrial wastewater treatment stream and treated without the need for a metal precipitator. Note that tests must be done on the bottle to determine:
- How long does the acid need to destroy the complexes?
- How much (% b / v) of the acidified purifier can be drained into the wastewater stream and treated successfully
Lower the pH to 3.0-4.0, add a reducing agent, such as sodium met bisulfite, and allow the solution to settle and react for 24 hours. The equation for this reaction is Na2S2O5 → Na2SO3 + SO2
The disadvantage of using the sodium met bisulfite treatment is that gaseous sulfur dioxide is formed during the reaction. This gas is toxic and has a pungent odor.
The jar test should be performed to determine how long the acidified cleaner should react and what concentration of acidified cleaner can be diverted to the wastewater stream to process the metals below the permitted discharge limits.