[China Aluminum Industry Network] 1. Wastewater characteristics
The production process of aluminum profiles mainly includes the degreasing, alkaline etching, pickling, oxidation, sealing and coloring of formed aluminum materials. The profiles processed after the above-mentioned processes need to be cleaned with water. Some of these profiles are in the form of overflowing clean water. The discharge of the cleaning tank is the primary source of wastewater from the aluminum plant. Aluminum plant production wastewater is rich in many aluminum ions, but also rich in some metal ions such as zinc, nickel, copper, etc. The pH of wastewater varies depending on the production requirements, but it is mostly acidic. Table 1 Aluminium Profile Wastewater Quality Table Item pH Suspension (mg/L) Copper (mg/L) Zinc (mg/L) Nickel (mg/L) Concentration 2～4300～10000.5～31.5～41.5～4
2, wastewater treatment technology process
In view of the characteristics of aluminum waste water mainly containing various metal ions and suspended solids, neutralization conditioning and coagulation deposition technology are selected. Aluminium production wastewater is discharged from the workshop and flows into a neutral conditioning pond. The pool is equipped with air mixing to balance the water quality. After adjusting the water quality and quantity of water through the conditioning pond, the wastewater is treated with alkali-adjusting pH to 6-9, pumped into the sedimentation tank, and together with the flocculant (PAM) during the pumping process. After the metal ions in the waste water react with the alkali to form hydroxides, the flocculants will form larger particles and settle under the effect of gravity. The upper half of the sediment pool can be discharged directly. The water quality reached the secondary emission standard of the second-class regional emission standard DB4426-89 of Guangdong Province.
The sludge in the sedimentation tank is concentrated in the sludge tank and then pumped into the frame filter press for dehydration for clean landfill or comprehensive application.
3, the principle of technology
3.1 conditioning pool
In the treatment of aluminum waste water, the pool of conditioning ponds is divided into two types: intermittent and consecutive. When artificial conditioning is needed, the conditioning pool needs to be divided into two compartments. The residence time of each cell's wastewater is 1 to 2 hours. It is used intermittently to facilitate artificial conditioning. Only one conditioning pond is used for active conditioning, and the pH of the wastewater is controlled by a pH active conditioner. Value, because aluminum waste water is rich in aluminum, and aluminum is in amphoteric state in solution. When pH<3, aluminum predominates in the form of Al(H2O)3+6; when pH=7, aluminum hydroxide becomes the predominant shape of Al3+; when pH>8.5, some aluminum hydroxide hydrolyzes to Negatively charged complex anions. Therefore, during the commissioning of the project, it is necessary to control the pH value in an appropriate plan so that aluminum can be deposited in the form of aluminum hydroxide.
3.2 reaction pool
The effect of the reaction tank is mainly to make the Al3+ and OH- in the aluminum waste water reverberate to produce insoluble Al(OH)3 deposition. The vortex reverberators are usually used for vertical flow deposition tanks and the baffle counterflow is used for the advection deposition tanks.
3.3 coagulation sedimentation tank
The metal ions in the waste water react with the alkali in the conditioning pond to produce insoluble hydroxide. However, because the particles are small, they are not easy to settle under the effect of water flow. Therefore, it is necessary to participate in flocculants to bind these particles to each other. Aggregate into larger particles, which are removed by solid-liquid separation in the sedimentation tank. Sedimentation tanks use the advection or vertical flow type, especially the latter is more widely used. The vertical-flow sedimentation tank is particularly suitable for the settlement of flocs, and the operation is simple and easy to handle, and the supernatant can be directly discharged. The sedimentation tank residence time was 2 h, and the apparent load was 1 m3/(m2?h).
3.4 Sludge disposal
The moisture content of the aluminum sludge discharged through the sedimentation tank reaches more than 90%, and dehydration treatment is required. According to the production capacity of the plant and the sewage disposal plan, the two methods of natural drying and mechanical dewatering were used to dispose of the sludge.
Natural drying is the use of drying ponds to hold the sludge and use sunlight to dry it. The advantage of this method is that it is economical and economical, but it is only suitable for companies with a small amount of sludge, and it is very troublesome to encounter rainy weather. Mechanical dewatering includes the use of centrifuges, belt filter presses, and frame filter presses. However, because of the loose structure of aluminum sludge, and with certain corrosion, as long as the effect of the frame filter press is better. Therefore, in the engineering design, the sludge is discharged from the sedimentation tank using static pressure into the sludge concentration tank, and after being concentrated, it is pumped to the plate and frame filter press for pressure filtration. After disposal, the moisture content of the sludge can be reduced to 70%, and mud cakes can be transported externally or integratedly.
The key to 3.5 debugging
In the debugging of the aluminum waste water treatment project, the key is to control the pH of the waste water so that various metal ions will form insoluble hydroxides, and then reach a better removal effect. Table 2 Preferred pH values ​​for removing various metal ions Metal ion pH Residual concentration (mg/L) Remarks Aluminium 5.5 to 8 ≤ 3 pH 6.5 Above re-dissolved copper 7 to 14 ≤ 1 Zinc 9 to 10.5 ≤ 1 pH 10.5 and higher Re-dissolved nickel>9≤1
According to Table 2 and the debugging results of a number of aluminum waste water projects, the normal aluminum waste water, the pH value of 7.5 ~ 8.5 to get the deposition effect is better; about a certain metal ion wastewater, need to The pH is adjusted according to the characteristics of the metal ion. 4 monitoring results and analysis
The aluminum profile wastewater treatment technology has been put into use in more than 90% of aluminum plants in Nanhai City. The equipment works well and the effluent water quality is stable. Table 3 shows the sampling and monitoring results of some companies. Table 3 Monitoring Results of Wastewater from Aluminium Profile Plant Unit Water Sample pH Suspension (mg/L) Copper (mg/L) Zinc (mg/L) Nickel (mg/L) Xingfa Aluminum Plant Influent Water 1.8614540.550.242.12 Effluent 6.2920.80.020.020.08 Fengchi Wastewater Plant Water Intake 9.9738040.400.511.70 Water Effluent 7.9412.80.040.000.26 Liqueur Waste Water Plant Water Intake 4.3429521.613.224.92 Effluent 7.137.20.040.150.26 Emission Standards of Guangdong Province 6-9100121 Note Above Data For the supply of environmental monitoring stations in Nanhai City, the effluent performance standard is Guangdong Provincial “Standard for the Discharge of Industrial Wastes†DB4426-89.
4, summary
1 The engineering practice indicates that the technology is reasonable and feasible.
2 Because of the amphoteric nature of aluminum in solution, aluminum ions also play a role as water purifying agents in wastewater. Together with various flocculants and coagulants involved, they are also rich in aluminum, so the quality of water after disposal There is no demand for aluminum concentrations in the project.
3 The principle of aluminum waste water treatment technology is simple, operation, and convenience, but also suitable for the disposal of other metal waste water, acid and alkali wastewater. The current problem is the disposal of waste slag. Aluminum sludge still contains more hydroxides after dewatering by a filter press, and it can cause secondary pollution if it is disposed of at will. In fact, the sediment of aluminum waste water is rich in many aluminum hydroxides. If it is developed and used, it can be used to extract pure aluminum hydroxide as a chemical raw material, which has a wide range of uses.
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