PCB Technical - Wastewater treatment in PCB board industry

The composition of PCB wastewater is complex and difficult to treat. How to effectively remove harmful substances and reduce environmental pollution is a major task facing China's PCB industry.

PCB wastewater is PCB wastewater, which is a kind of wastewater in the wastewater from the printing industry and circuit board factories. Currently, the world produces 300 to 400 million tons of toxic and hazardous chemical waste each year. Among them, persistent organic pollutants (POPs) are the most harmful to the ecology and the most widespread on the earth. In addition, PCB wastewater is divided into : Cleaning wastewater, ink wastewater, complexation wastewater, concentrated acid waste liquid, concentrated alkali waste liquid, etc. The production of printed circuit boards (PCB) consumes a lot of water, and there are many types of wastewater pollutants and complex components. According to the characteristics of wastewater from different PCB manufacturers, a reasonable classification collection and quality treatment are the key to ensuring that wastewater treatment meets the standards.

For wastewater treatment in the PCB board industry, there are chemical methods (chemical precipitation, ion exchange, electrolysis, etc.), physical methods (various decantation methods, filtration methods, electrodialysis, reverse osmosis, etc.). Chemical methods are The pollutants are converted into easily separable state (solid or gas). The physical method is to enrich the pollutants in the wastewater or separate the easily separable state from the wastewater, so that the wastewater can meet the discharge standard. There are several methods adopted at home and abroad.

1. Decantation method

The decantation method is actually a filtration method, which is one of the physical methods in the wastewater treatment methods of PCB manufacturers. The flushing water containing copper scraps discharged from the deburring machine can be filtered to remove copper scraps after being treated by a decanter. The effluent filtered by the decanter can be reused as the cleaning water of the burr machine.

2. Chemical Law

Chemical methods include oxidation-reduction methods and chemical precipitation methods. The oxidation-reduction method uses an oxidizing agent or a reducing agent to convert harmful substances into harmless substances or substances that are easy to precipitate and precipitate. The cyanide-containing wastewater and chromium-containing wastewater in the circuit board often adopt the oxidation-reduction method, please refer to the following description for details.

The chemical precipitation method uses one or several chemical agents to convert harmful substances into easily separated sediments or precipitates. There are many kinds of chemicals used in circuit board wastewater treatment, such as NaOH, CaO, Ca(OH)2, Na2S, CaS, Na2CO3, PFS, PAC, PAM, FeSO4, FeCl3, ISX, etc. Precipitating agents can convert heavy metal ions into The sediment is then passed through the inclined plate sedimentation tank, sand filter, PE filter, filter press, etc. to separate the solid from the liquid.

3. Chemical precipitation-ion exchange method

Chemical precipitation treatment of high-concentration circuit board wastewater is difficult to meet the discharge standard in one step, and it is often used in combination with ion exchange. First, use chemical precipitation to treat high-concentration circuit board wastewater to reduce the content of heavy metal ions to about 5 mg/L, and then use ion exchange to reduce heavy metal ions to discharge standards.

Four, electrolysis-ion exchange method

Among the wastewater treatment methods in the PCB board industry, the electrolysis method can reduce the content of heavy metal ions in the treatment of high-concentration circuit board wastewater, and its purpose is the same as the chemical precipitation method. However, the disadvantages of the electrolysis method are: it is only effective for the treatment of high-concentration heavy metal ions, the concentration is reduced, the current is significantly reduced, and the efficiency is significantly weakened; the power consumption is large, and it is difficult to promote; the electrolysis method can only process a single metal. Electrolysis-ion exchange method is copper plating, etching waste liquid, for other waste water, but also use other methods to deal with.

Five, chemical method-membrane filtration method

The waste water of PCB board industry enterprises is chemically pretreated to precipitate filterable particles (diameter> 0.1μ) from harmful substances, and then filtered through a membrane filter device to meet the emission standards.

Sixth, gaseous condensation-electric filtration method

Among the wastewater treatment methods in the PCB industry, gaseous condensation-electric filtration is a novel wastewater treatment method without chemicals developed in the United States in the 1980s. It is a physical method to treat printed circuit board wastewater. It consists of three parts. The first part is an ionized gas generator. Air is sucked into the generator, and its chemical structure can be changed by an ionizing magnetic field to become highly activated magnetic oxygen ions and nitrogen ions. This gas is treated with a jet device. Introduced into the waste water, the metal ions, organic matter and other harmful substances in the waste water are oxidized and aggregated, which is easy to filter and remove; the second part is an electrolyte filter, which filters and removes the agglomerates produced in the first part; the third part is high-speed ultraviolet Irradiation device, ultraviolet rays into the water can oxidize organics and chemical complexing agents, reducing CODcr and BOD5. At present, a complete set of integrated equipment has been developed for direct application.