PCB circuit board nickel-containing wastewater treatment process
Chemical precipitation method
The wastewater generated in the preparation and treatment of PCB circuit boards contains a large amount of nickel. The chemical precipitation method is used. First of all, the nickel-containing wastewater is treated to balance the water quality and quantity, and then added to the oxidation tank through a pH adjustment tank with a pH value of about 3 to 4. Fenton’s reagent, converts hypophosphite in nickel-containing wastewater, generates orthophosphate, completes the decontamination of wastewater, introduces it into the alkalization tank, and adds an aqueous solution of calcium hydroxide to generate nickel hydroxide and calcium phosphate precipitates, increasing the Macromolecule flocculant, which aggregates the generated particulate matter in order to achieve solid-liquid separation.
Neutralize the supernatant, filter with a sand filter tank and discharge. The lower sediment after solid-liquid separation is concentrated in the sludge tank, dewatered by dewatering equipment, and processed into dewatered cake.
Chemical precipitation is a traditional treatment method for nickel-containing wastewater. In the process, a large amount of chemical agents are required, and more treatment equipment is used. The process application cost is high, the process flow is long, and the treated wastewater is difficult to reach the environmental pollution index. control requirements.
Ion exchange method
In the adjustment tank, the water quality and quantity of the nickel-containing wastewater are treated in a balanced manner, and the sodium-type cation exchange resin is exchanged with Ni2+ through a multi-stage ion exchanger, and the Ni2+ will be adsorbed on the exchange resin to remove the nickel ions in the wastewater. The waste water is then discharged.
This processing method is relatively simple and does not need to use a large number of equipment, but it also has certain technical defects.
First, when the nickel ions adsorbed by the sodium-type cation exchange resin used are close to saturation, the exchange capacity of the cation resin is effectively reduced, the treatment effect of nickel-containing wastewater is reduced, and it is impossible to effectively judge whether the exchange resin is saturated; The sodium-type cation exchange resin used needs to be replaced frequently, and the process cost is high; again, the sodium-type cation exchange resin is easy to lose its effectiveness under the influence of high toxicity.
Membrane system treatment process and use
3.1 Process method
The membrane system treatment method is relatively advanced, and its application in sewage treatment in recent years has gradually shown its technical advantages. and reused in water treatment. The processing flow of this process is:
In the adjustment tank, the water quality and quantity of the nickel-containing wastewater are balanced, and the wastewater is lifted to the first-level reverse osmosis water treatment system by the lifting pump. The precision filter in the system is used for pre-filtration to remove suspended solids and particulate matter. Lift out the water.
The primary reverse osmosis treatment system is used to circulate and concentrate to separate and dissolve the inorganic salt pollutants in the water.
When the concentrated water in the primary reverse osmosis water treatment system meets certain standards, it is pumped into the tertiary reverse osmosis water treatment system for concentration and filtration treatment. Until the nickel ion concentration in the produced water reaches the standard of nickel content in the reuse water or discharge water.
The concentrated water in the secondary reverse osmosis water treatment system is returned to the primary concentrated water treatment system for treatment, and the recycled water tank is used to transfer the produced water to the nickel plating production line for reuse.
The concentrated water produced by the primary concentrated water treatment system is recycled and concentrated by the tertiary concentrated water treatment system, and the produced water is processed by the secondary concentrated water treatment system. The treated concentrated water meets the reuse standard and enters the concentrated water tank for recycling.
3.2 Process advantages
The membrane system treatment method does not require additional chemical reagents, and uses physical principles for separation treatment to reduce costs.
The element structure of the reverse osmosis membrane is relatively unique, which can realize the separation of solute and water, and has a stable treatment effect. The treated wastewater can meet the requirements of environmental pollution control and management.
The reused water produced by the effluent can be directly applied to the nickel plating process of the PCB production line to reduce the waste of resources.
The produced concentrate has recycling value and can recover heavy metals in the concentrate; the produced concentrate is low in volume and high in concentration; the process application is simple, a high degree of automation can be achieved, and labor costs can be reduced; the equipment is highly integrated and easy to concentrate Management, the production line can be set up together with the wastewater treatment process to build a continuous production and wastewater treatment system.
3.3 Process application
Taking circuit board factory A as an example, the total amount of wastewater produced in this factory per day is 3300m3, including 100m3 of nickel-containing wastewater. In 2012, a membrane system treatment facility was introduced for wastewater treatment.
After the introduction of membrane system treatment facilities, the plant has achieved great results in the treatment of nickel-containing wastewater. The average wastewater treatment data in October 2014 is used as an example to demonstrate.
After the introduction of membrane system treatment facilities, the plant has achieved good results in the treatment of nickel-containing wastewater, met the requirements for wastewater discharge, and produced a relatively high proportion of recycled water, reducing the waste of heavy metal materials and ensuring the plant’s environment. At the same time, good economic benefits have been achieved.
With the continuous development of membrane technology, it has gradually become the dominant process in industrial wastewater treatment, and has been widely promoted and used. It can achieve better treatment effects, control sewage discharge and environmental pollution, and reduce the cost of process application. In practical applications, it is also necessary to continuously explore the refined management mode of PCB circuit board production and wastewater treatment, and use the management mechanism as an aid to better exert the treatment effect of the membrane system and reduce the nickel ions in the discharged wastewater.