ã€China Aluminum Industry Network】 1 Characteristics of Waste Water The production process of aluminum profiles mainly includes degreasing, alkaline etching, pickling, oxidation, plugging and coloring of formed aluminum materials, and the profiles processed after the above processes need to be cleaned with water. Part of the profile cleaning water is discharged out of the cleaning tank in an overflow form and is the main source of waste water from the aluminum plant. In addition to containing a large amount of aluminum ions, aluminum factory wastewater contains some metal ions such as zinc, nickel, and copper. The acidity and alkalinity of the wastewater varies depending on the production requirements, but it is 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 process The aluminum waste water mainly contains the characteristics of various metal ions and suspended solids. Neutralization and coagulation and sedimentation processes are used. The waste water from the production of aluminum profiles is discharged from the workshop and flows into the neutralization conditioning tank. The tank is equipped with air agitation to balance the water quality. After adjusting the water quality and quantity of water in the adjusted pool, alkali is added to adjust the pH to 6-9, pumped into the sedimentation tank, and a flocculant (PAM) is added during the pumping process. After the metal ions in the waste water react with the alkali to form hydroxides, under the action of the flocculant, larger particles are formed and are quickly settled under the action of gravity. The upper half of the sedimentation tank can be discharged directly. To achieve the secondary emission standard of the local emission standard DB4426-89 in Guangdong Province.
The sludge in the sedimentation tank is concentrated in the sludge tank and pumped into the frame filter press for dehydration and then used for sanitary landfill or comprehensive utilization.
3 Process principle 3.1 Adjusting the pool In the aluminum waste water treatment, the pool of the conditioning pool is divided into intermittent and continuous two. When adjusting manually, it is necessary to divide the adjustment tank into two compartments. The residence time of each cell's wastewater is 1 to 2 hours, which is used intermittently in order to facilitate manual adjustment; the automatic adjustment requires only one cell to adjust the cell, and the pH is automatically controlled by the pH regulator to control the pH of the wastewater. The value is due to aluminum waste water containing a large amount of aluminum, while aluminum is in amphoteric state in the solution. When pH<3, the main form of aluminum is Al(H2O)3+6; when pH=7, aluminum hydroxide becomes the main form of Al3+; when pH>8.5, most of aluminum hydroxide is hydrolyzed to form Negatively charged complex anions. Therefore, the pH must be controlled in an appropriate range during the commissioning of the project so that aluminum can be sufficiently precipitated in the form of aluminum hydroxide.
3.2 Reaction tank The main role of reaction tank is to fully react Al3+ and OH- in aluminum profile wastewater to produce insoluble Al(OH)3 precipitate. The vertical-flow sedimentation tank is usually a vortex reactor, and the advection-type sedimentation tank is a baffled reactor.
3.3 The metal ions in the coagulation sedimentation tank's wastewater react with the alkali to form insoluble hydroxide, but due to the small particles formed, it is not easy to settle under the action of water flow, so it is necessary to add flocculants. These particles are bound to each other, aggregated into larger particles, and removed by solid-liquid separation in the sedimentation tank. Sedimentation tanks use advection or vertical flow, especially the latter is more widely used. The vertical-flow sedimentation tank is particularly suitable for sedimentation of flocs and is simple to operate, easy to manage, and the supernatant can be directly discharged. The sedimentation tank residence time is 2h and the surface load is 1m3/(m2?h).
3.4 Treatment of Sludge The moisture content of the aluminum sludge discharged from the sedimentation tank reaches more than 90% and it needs to be dehydrated. According to the factory's production capacity and the size of the sewage, the natural drying and the mechanical dehydration were used to treat the sludge.
Natural drying is the use of drying ponds to hold the sludge and use sunlight to dry it. This method has the advantages of economy and economy, but it is only suitable for enterprises with small sludge volume, and it is very troublesome to encounter rainy weather. Mechanical dehydration includes the use of centrifuges, belt filter presses, and frame filter presses. However, due to the loose structure of aluminum sludge and a certain degree of corrosion, only the frame filter press has a good effect. 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, pumped to the plate and frame filter press for pressure filtration. After treatment, the moisture content of the sludge can be reduced to about 70%, and mud cakes can be shipped out or used comprehensively.
3.5 The key to debugging In the debugging of the aluminum profile wastewater treatment project, the key is to control the pH value of the wastewater, so that various metal ions generate insoluble hydroxide, so as to achieve a better removal effect. Table 2 Preferred pH values ​​for removal of various metal ions Metal ions pH range Residual concentration (mg/L) Remarks Aluminium 5.5~8 ≤ 3 pH6.5 Above re-dissolved copper 7~14 ≤ 1 Zinc 9~10.5 ≤ 1Re-dissolved nickel above pH 10.5 >9≤1
According to Table 2 and the debugging results of a number of aluminum profile waste water projects, for the general aluminum profile waste water, the precipitation effect obtained when the pH value is controlled at 7.5 to 8.5 is better; for a certain metal ion is more The wastewater needs to adjust the pH according to the characteristics of the metal ions. 4 Monitoring results and analysis The aluminum waste water treatment process has been put into operation in more than 90% of the aluminum plant in Nanhai City. The equipment is in good operation and the water quality is stable. Table 3 shows the sampling and monitoring results of some enterprises. Table 3 Monitoring results of wastewater from aluminum factory Units Water samples pH suspended solids (mg/L) Copper (mg/L) Zinc (mg/L) Nickel (mg/L) Xingfa Aluminum Plant Influent Water 1.8614540.550 .242.12 Effluent 6.2920.80.020.020.00.08 Water from the Fengchi Wastewater Plant 9.9738040.400.511.70 Effluent 7.9412.80.040.000.26 Liquefied Waste Water Plant Water Inlet 4 .3429521.613.224.92 Effluent 7.137.20.040.150.26 The Emission Standard of Guangdong Province 6-9100121 Note The above data is provided for the Nanhai City Environmental Monitoring Station. The implementation standard for the effluent is Guangdong Province's "Emission Standard for Industrial Wastes". DB4426-89.
5 Summary 1 The engineering practice shows that the process is reasonable and feasible.
2 Because of the amphoteric state of aluminum in solution, aluminum ions also play a role of water purifying agent in the waste water. At the same time, a large amount of aluminum is contained in various flocculants and coagulants added, so the treated water quality items There is no requirement for aluminum concentration.
3 Aluminum waste water treatment process is simple in principle, convenient in operation and management, and also suitable for the treatment of other metal waste water and acid-alkali waste water. The current problem is the disposal of waste slag. Aluminum sludge still contains more hydroxides after dewatering by a filter press. Any secondary disposal will cause secondary pollution. In fact, the precipitation of aluminum waste water contains a large amount of aluminum hydroxide. If it is developed and utilized, it can be used to extract a very pure aluminum hydroxide as a chemical raw material, which has a wide range of uses.
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