ã€China Aluminum Industry Net】 Water is one of the indispensable sources of energy for industrial production. Surface treatment plants are often users with large amounts of water. How to save water usage in surface treatment production has always been the subject of current research. For example, a foreign aluminum production conglomerate uses 6,300 tons of water per day, of which surface treatment accounts for 30%. In order to save water consumption, each factory is working to study the issue of repetitive and recycling water, and most of the surface treatment workshops Water reuse and recycling have been done to varying degrees. Some plants can reuse 60% of the water. Some of the rivers in the vicinity of the river are drained. The treated water can be used to raise fish. After adopting new water treatment technologies, The amount of new water used is greatly reduced. For example, the surface treatment of a factory was previously 1 000 t/d. Now it is recycled, and the amount of new water is reduced to l00 t/d. I. Neutralization and precipitation treatment The waste water containing alkali, trace acid and trace aluminum ions discharged from the washing tank is first mixed in the workshop and discharged to the integrated treatment station in the middle and in the pool. The pH is firstly determined, and if it meets the requirements, it will flow into the multi-stage sedimentation tank if it does not meet the requirements. That is, adjust with acid and alkali. If the acid is acidified and neutralized with sodium hydroxide, aluminum ions form a precipitate of aluminum hydroxide in a pH-neutral environment. After the neutralization, the suspension polymer solution is further subjected to coagulation sedimentation and separation, and the upper clear water can be directly discharged or utilized if it meets the requirements for environmental protection discharge. The remaining sludge is then dewatered and shipped out. The process is as follows: Figure 5-6-4 wastewater treatment system 1) Fill the solution (1) waste water tank full of waste (2) Inject waste solution into neutralization tank (3) Inject water into the overflow of the flocculation tank, concentrator, and discharge tank. (4) Dissolve and stir the flocculant with water and stir it for no more than 5 h. (5) Inject the water into the middle of the lye tank and fill it with the same amount of 25% lye. (6) Inject acid waste into the acid tank. 2) Neutralization processing The effluent contains more sulfuric acid and needs to be neutralized with NaOH. The reaction is as follows: During the neutralization process, the pH should be controlled within the range of 7±0.5. 3) flocculation sedimentation The neutralized waste liquid is poured into the coagulation tank, and the flocculant is added while stirring. The flocculants use high molecular weight organic compounds, generally polyacrylamide, with a molecular weight of about 10 million. The addition of flocculant makes the suspended Al(4OH) flocculent, and then it is injected into the sedimentation tank and precipitated while stirring, so that the sediment is separated from the water, and the clear water overflows from the sedimentation tank to the discharge tank, and then discharged to outdoor. The flocculant injection amount is calculated as follows: Q2=0.7Q1T Wherein Q1 - flocculant injection / L · h-1; Q2 - amount of mud extracted / L · min-1; T - Agglutination time/min. 4) Separation The slurry in the sedimentation tank is pumped out and sent to the filter press or dewatering machine for dehydration treatment. The water content of the dewatered sludge is as high as 85% to 90%, and its main component is Al(40H)3·l8H2O. The composition (%) contained in the sludge is roughly as follows: Second, the treatment of fluoride-containing wastewater When using ammonium bifluoride for aluminum surface treatment process, the generated sewage contains fluoride ions, so the user needs to comprehensively deal with fluoride ions in the sewage treatment, as shown in Figure 5-6-5. 1) Wastewater treatment process method (1) The acid effluent is discharged into the neutralization tank, and the pH is adjusted to 3 to 4 with NaOH, and then adjusted to pH 7 to 8 with Ca0. (2) Pump to a high sedimentation tank and add polyacrylamide diluent (containing 20-30 g/m3 polyacrylamide). (3) Absorb the sediments from the bottom of the sedimentation tank and separate the slag water through the filter press. The residue is bagged and the water flows into the neutralization tank. (4) Users can also conduct comprehensive treatment according to corporate pollution control standards, and meet the national emission standards. 2) Examples of process procedures (1) Concentrate the concentration of fluorine-containing wastewater into the special neutralization tank and test the fluorine content of the fluorine-containing wastewater discharged from the workshop. Use the data to calculate the operation of the next process. (2)Preliminarily make lime with tap water, and add 5~2 kg/m3 lime according to the specification of fluoride-containing waste water. After the lime is made well, start the lime mixer. The fluoride-containing waste water is stirred in the lime mixing tank and flows into the neutralization tank, and the air pump or the adjustment Valve, open air stirring. (3) The storage tank should be prepared with a certain amount of hydrochloric acid solution and a certain amount of waste alkali liquor. (4) The polyacrylamide is added to the stirring tank beforehand and diluted until it is used. (5) When the neutralization tank is substantially full of water, the basic aluminum chloride that is stirred must be added to the sump, and hydrochloric acid is added to adjust the pH to 7 to 8.5. The gas is left to stand and stirred. (6) After adjusting the pH value for 10 minutes, the high sedimentation tank on the pump is started to condense and separate, and the polyacrylamide dilution liquid is pumped (or the sewage is directly pumped into the press filter press residue treatment). (7) The sedimentation pool has increased aggregates, and it is necessary to timely discharge slag to the reserve slag pool, prevent the discharge of sediments from countercurrent flow, and strictly control the discharge of water quality standards. (8) Start filter press dregs, pressurize the dregs water to find that there is turbid water outflow needs to deal with or replace the filter cloth in time, the clear dregs water can discharge directly, the turbidity water of the dregs must be returned to the secondary pool , Unqualified water is not allowed to drain.