PCB Technical - The treatment process of circuit board wastewater

The concentration of low-concentration cleaning wastewater and high-concentration waste liquid discharged from PCB manufacturing plants are very different, and the corresponding treatment methods are also very different. Therefore, the terminal treatment of the waste water pipe of the printed circuit board, the collection of the first waste water and the separate treatment of different properties avoid mutual interference and increase the difficulty of the waste water treatment of the printed circuit board.

The wastewater produced by the printed board factory is very large, and the main pollution components are COD and heavy metals. In the past, my country usually used heavy metal chemical coagulation precipitation method to form hydroxide plumes with lye, and then separated and removed by precipitation. However, it is difficult to handle because it contains chelating components such as EDTA and ammonia.

1. Collection and classification of circuit board wastewater

a. Collect wastewater and waste liquid separately

Most of the process wastewater comes from the continuous discharge of clean water from various units. The concentration of pollutants in the wastewater is low, and the waste liquid is discharged in batches on a regular basis, and the concentration of pollutants is high. In order to avoid the sudden increase in the load caused by the discharge of wastewater into the sewage treatment system, it is necessary to treat each waste liquid according to its properties, separate collection and pretreatment, and then discharge it into the wastewater treatment system in a continuous and quantitative manner.

b. Interpret the wastewater and waste liquid according to the nature of it

(1) Brushing and sandblasting wastewater
Waste water contains a large amount of copper powder, so the copper powder should be separated and recycled during the treatment process, and the separated liquid should be added to general clean wastewater for treatment.

(2) Acidic waste liquid
Collect the waste liquid of concentrated acid and heavy metal pollutants to keep the water quality of the treatment system stable and avoid frequent changes in the dosage of the treatment agent.

(3) Deinking, developing, green paint concentrated alkali waste liquid
The COD concentration of the ink removal, development, and green paint waste liquid is very high, and agglomeration occurs in strong acid conditions, so it should be collected separately, treated first, and then incorporated into the wastewater biological treatment system. The concentrated alkali waste liquid generally comes from degreasing, the amount of water is small, and the COD is very high, so it is also incorporated.

Etching, tin stripping, gold plating and MEK waste liquids can generally be recycled outside the factory, so they should be collected separately.

2. Circuit board wastewater treatment

a. Organic dry film method: Add FeCl 3 to the wastewater, adjust the pH to 2 with dilute hydrochloric acid (slowly add HCL), and then slowly adjust the pH to 7 with CaCO 3). Then the treated solution is mixed with ordinary organic wastewater for treatment. The mechanism is: neutralize some negatively charged organic charges in the precipitation wastewater with high-charge Fe3+, adjust PE to 2 with dilute hydrochloric acid, so that the organic matter in the wastewater is not neutralized by the charge, and acidify the precipitated organic matter to form a dry film. The precipitation effect of CaCO 3 on suspended particles in wastewater is similar to that of coagulant.

b. Fenton process: After acidification treatment of high-concentration organic wastewater, remove the dry film, adjust the pH to 4≤5, add Fenton reagent to oxidize certain organics in the wastewater, add Na2S03 after the reaction or adjust the pH to 7 ≤10, get excess H20. After the pretreatment liquid is mixed with general organic wastewater, it is treated together with general organic wastewater. The reaction mechanism is as follows:

Fe2+H 202-Fe3+OH-+OH

Fe3+H 202 Fe2+>+OOH+.h

c. UV-Fenton method: This method is similar to the separate Fenton method, but the addition of ultraviolet light in the process promotes the generation of more and faster OH hydrogen and oxygen radicals, thereby accelerating the oxidation reaction. The advantage of the method is that the OH hydrogen and oxygen radicals produced by ultraviolet light far exceed the simple Fenton method, which shortens the reaction time, so the oxidation reaction is more thorough.

d. UV-H 202 process: adjust the pH of wastewater to acidity, irradiate the added H2O2 in the reaction system with ultraviolet light, generate OH and oxygen free radicals, oxidize the organic matter in the wastewater, thereby reducing COD, the reaction mechanism is H 202 + HV -20H, after that, the oxidation effect of 0H hydrogen and oxygen free radicals on the organic matter in the wastewater is the same as above.
In the treatment of high-concentration organic wastewater, it is recommended that the acidification treatment of wastewater can reduce the post-treatment load. Due to acidification, a large amount of waste dry film with high viscosity will be produced. If it is not treated in time, it will adhere to the wall of the treatment tank, no matter what kind of chemical method, it cannot be treated after a long time.