Electroplating wastewater chemical treatment method
Electroplating is the use of chemical and electrochemical methods to plate various metals on the surface of metal or other materials. Electroplating technology is widely used in machine manufacturing, light industry, electronics and other industries.
The composition of electroplating wastewater is very complex. In addition to cyanide (CN-) wastewater and acid-base wastewater, heavy metal wastewater is a potentially harmful wastewater category in the electroplating industry. According to the classification of heavy metal elements contained in heavy metal wastewater, it can generally be divided into chromium (Cr) wastewater, nickel (Ni) wastewater, cadmium (Cd) wastewater, copper (Cu) wastewater, zinc (Zn) wastewater, Gold (Au) wastewater, silver (Ag) wastewater, etc. The treatment of electroplating wastewater has generally received attention at home and abroad, and a variety of treatment technologies have been developed to eliminate and reduce the emission of heavy metals through measures such as treating toxic to non-toxic, converting harmful to harmless, recycling precious metals, and recycling water. With the rapid development of the electroplating industry and the increasing environmental protection requirements, electroplating wastewater treatment has begun to enter the stage of clean production technology, total volume control and circular economy integration. Resource recycling and closed-circuit circulation are the mainstream directions of development.
1 Current status of electroplating heavy metal wastewater treatment technology
Based on statistics and surveys of the current status of wastewater treatment in the electroplating industry in China, there are 7 different classification methods that are widely used: (1 ) chemical precipitation method, which is further divided into neutralization precipitation method and sulfide precipitation method. (2) Redox treatment, divided into chemical reduction method, ferrite method and electrolysis method. (3) Solvent extraction separation method. (4) Adsorption method. (5) Membrane separation technology. (6) Ion exchange method. (7) Biological treatment technology, including bioflocculation, biosorption, biochemical, and phytoremediation. However, there are currently certain drawbacks or serious irrationality.
2 Disadvantages of traditional electroplating wastewater treatment methods
Currently, electroplating wastewater treatment methods generally use physical and chemical diversion-comprehensive two-stage treatment. The front-end treatment is divided into three types of water: chromium water, cyanide water and comprehensive water (copper-nickel-zinc water). The chromium water is reduced with a reducing agent at a reduced price, the cyanide water is broken down by two-stage oxidation, and the copper-nickel-zinc water directly merges with the first two streams of water to become comprehensive water. The post-processing of comprehensive water basically uses alkali (caustic soda or lime), polyaluminum chloride (PAC) and organic flocculant (PAM). The specific operation is: raise the pH value of the comprehensive water to 10~13, and adjust the alkali concentration. This forces the reaction between alkali and heavy metals to proceed in the direction of generating hydroxides. Since the pH is >9, the discharge port must be neutralized with acid to reduce the pH value to below 9.
The above is a traditional treatment process, and there are many serious theoretical and practical errors: 1. The division of the three streams of sewage in the pre-treatment is not in line with the actual production, because no matter which stream of water is in your water, I, you are in me, but the chromium water is mainly chromium, the cyanide water is mainly cyanide, and the copper-nickel-zinc triple water is mostly composed of 3 elements. We discovered these actual situations in the practice of wastewater treatment, and this is true for electroplating wastewater from almost all companies. We have asked relevant personnel at the electroplating factory, and they can actually explain the cause of this phenomenon very clearly. What is strange is that the sewage management department actually regards the diversion-integrated two-stage treatment as a normative model that cannot be violated. Since various pollutants are present in the sewage treated in the second stage, how can it be possible to use simple treatment chemicals and methods to make the terminal water discharge meet the standards?
2. Many specialized discussions will mention that cyanide water must be treated separately because cyanide in acid solution will generate extremely toxic HCN (cyanic acid), and its volatilization will inevitably cause human poisoning. This is theoretically true, and we really need to pay great attention to it. However, we found that most cyanide water itself is a liquid with pH <6. If it wants to volatilize, it may be in the workshop instead of flowing to the sewage tank to volatilize again. Besides, cyanic acid itself is a liquid, but its volatilization temperature is low (26°C), so there is no volatilization problem when the external temperature is <26°C.
3. It is unscientific to artificially use super-alkali to form hydroxides of heavy metals and precipitate them in the sludge:
(1) From the perspective of chemical reaction principles, No matter what the pH conditions are, there is a reaction equilibrium, which means that there can never be a certain amount of heavy metals in the water.
(2) The optimal pH value (pH value) for different heavy metals to form hydroxides is different. The most suitable pH value range for some heavy metals may have been re-dissolved for other metals. pH conditions.
(3) Since the second-stage treatment is to remove heavy metals from super-alkali, the final discharge water must also be super-alkaline, so it is necessary to add acid to the water at the discharge outlet to ensure that the pH value reaches the discharge standard. As a result of adding acid, those fine hydroxides that have not yet precipitated rapidly decompose, and the heavy metals return to the water.
(4) Due to the diversion and merging of two sewage treatment lines, the engineering installation is naturally more complicated, resulting in large investment and long construction time.
3 Treatment of electroplating wastewater by mineral method
3.1 Concept of mineral method
Mineral method uses pure natural minerals as raw materials and is processed through certain special processes. It is a method of mixing and treating electroplating wastewater by using patented natural mineral wastewater treatment and mineral powder, and adding certain additives.
3.2 The main mechanism of the mineral method
Since this method mainly uses pure natural minerals as the main raw material, its characteristics include ion exchange, adsorption, chemical Transformation, catalysis, etc.
3.3 The main advantages of the mineral method
The main advantages of this method are as follows:
1. Completely change the long-standing traditional process of split treatment, and combine chromium water, Cyanide water, comprehensive water, etc. are mixed for treatment, which corrects some serious errors in the diversion treatment and makes up for the shortcomings of the traditional process.
2. The problem can be completely solved in one stage of processing, changing the traditional two-stage processing model.
3. Due to the above two points, the engineering equipment for sewage treatment has been greatly simplified, and infrastructure investment and engineering construction time have been greatly reduced.
4. Traditional treatment methods cannot meet the emission standards from a theoretical analysis. A large amount of practice has also proved that this process cannot meet the emission standards. If the electroplating wastewater is treated by the mineral method, both principle and practicality show that it can stably meet the discharge standards.
5. The cost of chemicals for treating electroplating wastewater using traditional processes is mainly used for caustic soda to neutralize acidic water. Generally, the cost of caustic soda for treating one ton of sewage is 10 to 15 yuan. Including other pharmaceuticals, the total pharmaceutical cost is more than 15 yuan. It is true that if you only want to clarify wastewater, it will be difficult to set a standard for the cost. To apply the mineral law, the prerequisite is that emissions meet emission standards. The cost of chemicals to treat one ton of wastewater is about 4 to 8 yuan.
3.4 Schematic diagram of electroplating wastewater treatment process
3.4.1 Schematic diagram of electroplating wastewater treatment process 1 (intermittent electroplating wastewater treatment process)
Schematic diagram of electroplating wastewater treatment process 2 (Continuous electroplating wastewater treatment process)
3.4.2 Process Description
Various types of wastewater from the workshop are mixed and adjusted in the same regulating tank, and then pumped into the first reaction The reducing agent can be ferrous sulfate or other reducing agents. The dosage is 1/3~1/2 less than that in the diversion treatment. The specific dosage depends on the water quality. After the reaction is completed, it enters the second reaction tank and adds mineral sewage treatment. The comprehensive reaction of agent and mineral powder (part of which acts as a neutralizer, can save most of the alkali, and also has the effect of removing heavy metals) can adjust the pH of the wastewater to 5~6. This stage generally requires no less than 20 minutes before entering In the third reaction tank, the pH of the wastewater is adjusted to 8~8.5 with alkali, and oxidants such as bleach are added to break the cyanide. Finally, it is discharged after sedimentation in the sedimentation tank.
4 Conclusion
After a long period of research and practice, as well as theoretical discussions, combined with the current reality, we are making a complete comparison of various processes (including pharmaceuticals After considering the cost-effectiveness, project construction investment, operation and management, etc.), it is believed that the use of mineral methods to treat electroplating can ensure that the quality of the effluent reaches the national first-level discharge standard.
Pictures of electroplating wastewater treatment chemicals
Dongguan Yuze Water Treatment Technology Co., Ltd.
Yuze Water Treatment Co., Ltd. is a company with many key universities in South China The Department of Environmental Engineering integrates research and development into a high-tech enterprise.
A high-tech entity that integrates sewage treatment technology development, manufacturing, marketing and service. It specializes in engineering design, equipment installation, and project operations in the field of water environmental protection. It independently researches and develops different treatment agents according to different customer wastewater quality conditions to make their wastewater more efficient. Standard discharge, business areas and environmental planning of living quarters, industrial wastewater, especially the treatment of industrial wastewater that is difficult to degrade and refractory, industrial production water treatment, domestic sewage treatment and wastewater treatment and water reuse in other industries. Specializing in electroplating wastewater treatment, oil and wax removal wastewater treatment and reuse, electroplating wastewater treatment substandard renovation projects, wastewater treatment and reuse, heavy metal recovery and water reuse; ultrapure water for production in the photovoltaic industry, softened water for boilers, Circulating cooling water; circuit board industry wastewater treatment and water reuse project
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