Circuit board wastewater
Circuit board production enterprises in the circuit board grinding, etching, electroplating, hole metallization, development, stripping process will produce circuit board wastewater. Circuit board wastewater mainly includes the following:
Complexing and chelating copper-containing wastewater produced by chemical copper deposition and etching processes, with a pH value of 9~10 and a concentration of Cu2+ of 100~200mg/l.
A large amount of acidic heavy metal wastewater (non-complexed copper wastewater) generated in the pre-cleaning process of electroplating, grinding and brushing plates contains Sn/Pb wastewater with a pH value of 3-4, Cu2+ less than 100mg/l, Sn2+ less than 10mg/l and trace amounts of heavy metals such as Pb2+.
Dry film, decoating, development, deinking, screen cleaning and other processes produce relatively high concentration of organic ink waste liquid,COD concentration is generally 3000~4000mg/l.
According to the different characteristics of circuit board wastewater, different wastewater must be separated and treated by different methods.
1. Copper complex wastewater (copper ammonia complex wastewater)
In this kind of wastewater, the heavy metal Cu2+ and ammonia form a relatively stable complex, and the general hydroxide coagulation reaction method cannot form copper hydroxide precipitation, so the structure of the complex must be destroyed first, and then coagulated and precipitated. Vulcanization method is generally adopted for treatment. Vulcanization method means that S2- in sulfide and Cu2+ in cu-ammonia complex ions are used to form CuS precipitation to separate copper from wastewater, while excess S2- is used to make it produce FeS precipitation to remove.
Cupric ammonia complex wastewater → regulating tank → breaking reaction tank → coagulation reaction tank → inclined tube sedimentation tank → intermediate tank → filter →pH callback tank → discharge
The control of reaction conditions should be determined during debugging according to the difference of water quality in each plant. Generally before adding the breaking agent such as sulfide to adjust the pH value to neutral or slightly alkaline, to prevent the formation of hydrogen sulfide, some will also adjust the pH value to slightly acidic. The dosage of sulfide is determined by the amount of copper ammonia in the waste water. An ORP meter was installed in the breaker tank and measured. When the potential reached -300mv(empirical value), the reaction was considered excessive and complete. The excessive sulfide was removed by the method of adding ferrous iron salt, and the amount of ferrous iron was determined according to the debugging, and was added quantitatively through the flowmeter. The reaction time was 15~20 minutes and 15~20 minutes respectively.
2. Ink wastewater
Remove waste film and printing ink wastewater due to less water, generally USES the batch processing, using organic ink under acid condition, separated from the waste water nature of the production suspension and removal, after pretreatment, the printing ink wastewater, can be mixed in the synthetic wastewater with subsequent processing, such as water can separate the biochemical method is adopted for processing.
Organic ink wastewater → acidification slag pool → discharge into the comprehensive wastewater pool or biochemical treatment
When the amount of wastewater is small, the ink particles in the reaction tank float to the surface of the water under the action of buoyancy bubble scum, can be manually skimmed; When the amount of water is large, the plate and frame filter can be dehydrated, or after skimming for biochemical treatment, further removal of COD.
3. Integrated waste water of circuit board
This kind of wastewater mainly includes the comprehensive wastewater containing acid and base, Cu2+, Sn2+, Pb2+ and other heavy metals.
4. Integrated treatment of various circuit board wastewater
When a circuit board factory contains the above kinds of circuit board wastewater, the copper-ammonia complex wastewater, ink waste water and integrated heavy metal waste water should be collected separately. After pretreatment, the ink waste water is mixed into the comprehensive waste water for subsequent treatment. The copper-ammonia complex waste water is separately treated and then entered into the comprehensive waste water treatment system.