China's electrolytic coloring technology began in the 1980s, and is currently dominated by electroless coloring of single nickel salts, single tin salts or tin-nickel mixed salts. AC coloring is mainly based on tin-nickel mixed salt and tin salt electrolysis coloring process. The color shade is controlled by AC coloring, which is mainly controlled by voltage and time. This process has problems such as single color, poor stability of coloring liquid, and poor dispersion, which have not been well solved. It is also necessary to add some additives to improve the anti-interference ability of the electrolytic coloring solution. DC coloring is dominated by single nickel salt. Single nickel salt injection coloring is controlled by DC coloring with reversal control, which is controlled by adjusting the waveform and time period. The process has stable bath, uniform coloration and repetition. Good sex and stable color.
The wastewater treatment caused by the anodizing surface treatment of aluminum profiles has always been the focus of environmental protection. The wastewater mainly comes from the discharge of water washing tanks. In order to reduce the consumption of chemicals and reduce the discharge of wastewater, the recycling of chemicals should be recycled as much as possible to achieve energy saving and emission reduction. the goal of.
First, production control
1. Production process parameters and environmental protection comparison table 1
2. Chemical loss and coloring schedule
It can be seen from Tables 1 and 2 that the single tin salt or the tin-nickel mixed salt is generally added with harmful organic reducing agents and complexing agents containing different components and concentrations to improve the stability of the bath. These have a large impact on the environment and a large amount of chemical consumption. The time for the black material is more than twice that of the single nickel salt, and the power loss is high. The single nickel salt production line is equipped with a recovery device, which can reduce the production cost and reduce the pollution and emission of nickel ions.
Second, the advantages and disadvantages
1, tin salt coloring
Tin salt coloring is divided into single tin salt coloring and tin-nickel mixed salt coloring. In the nickel-tin mixed salt coloring process, nickel ions are not deposited in the oxide film pores, only play an auxiliary role, so tin-nickel salt coloring It can also be called tin salt coloring.
Tin salt coloring is relatively simple in control compared to single nickel salt, and equipment cost is low, and it is widely used in oxidized horizontal production line; however, SnSO4 in tin salt coloring bath is easily oxidized to produce tetravalent tin precipitate; The bath is mixed with double salt, and nickel ions can not be recovered. After washing, the wastewater is discharged to the wastewater treatment station for treatment, which increases the difficulty of wastewater treatment. Both kinds of coloring methods need to add additives to keep the bath clear and stable; when a certain amount is produced, the bath liquid is easy to be turbid, and it is necessary to stop production for regeneration and precipitation treatment to obtain a clear bath liquid, otherwise the bath liquid is cloudy. The quality of the product cannot be guaranteed. In the vertical production line, tin salt is used for coloring. Because the tank body is relatively deep, it is generally more than 7 meters. The deposition of tetravalent tin will cause the bath liquid concentration to be uneven, showing a gradient state, and it is easy to produce obvious upper and lower chromatic aberration when coloring. Tin salt coloring has defects in weather resistance, and signs of fading gradually increase with the increase of sunshine time.
2, injection method single nickel salt coloring
The DC coloring with commutation is used, and the pH value of the bath is stabilized by H3BO3 as a buffer. The nickel ions are uniformly and electrically resolved at the bottom of the anodized film hole by a special positive voltage and a negative voltage waveform. The aluminum alloy profile has a stable, uniform color.
The color depth is controlled by calculating the number of boosters. The dark material needs to superimpose 1 to N wave waves of the same or similar to the basic waveform on the basic waveform to achieve the purpose of making dark materials.
The nickel ion content of the single nickel salt coloring process of the injection method is very high, and the surface of the profiled material after stripping is very large. The direct discharge of the water washing bath is wasteful and pollutes the environment, and is recycled by the principle of RO reverse osmosis. The recycled wastewater can be directly discharged without harm to the environment.
2.1RO recovery principle
RO is a method in which the water of the coloring liquid is transmitted from the semipermeable membrane when the pressure above the osmotic pressure of the solution is applied (normally 10 kg/cm 2 ), and the nickel ions are prevented from permeating and remaining on the membrane surface, so that the solution is in the solution. Salts, ions, etc. are retained on the membrane surface for separation purposes.
2.2 recycling process
The nickel recovery treatment system is used to reuse the nickel ions in the coloring tank, and the bath liquid from the coloring tank is pressurized into the filter to remove the particulate matter and colloid in the water, and enters the nickel recovery processing system. The nickel ions in the bath are exchanged, adsorbed, and enriched to obtain a higher concentration of the nickel-containing recovery liquid, which is reused in the coloring tank. On the other hand, after the bath is treated by the system, most of the impurities and nickel ions are removed, so that the water quality is improved and can be reused in the production process. The whole system can realize double recovery of wastewater and nickel, and has good economic and environmental benefits. The treated water is directly reused for recycling in the washing tank. The recycling device effectively reduces the loss of nickel ions, reduces the sewage charges, creates economic benefits, improves product quality, and meets environmental protection and cleaning requirements.
After the recovery, the nickel ions in the water are low, and the amount of the nickel ions produced by the RO2 production is small, and flows together with other production wastewater to the wastewater station for uniform treatment.
In actual production, all nickel sulfate is not used for the micro-porous nickel ion electrodeposition coloring of the anodized film, but more than 2/3 of the nickel sulfate is dissolved in the clean water and discharged with the clear water brought out by the profile; the single nickel salt is injected. The coloring process does not use additives, and has a RO recovery device. The nickel salt can be recycled and utilized, with low loss and environmental protection. A nickel recovery unit is installed, which can reduce the emission of nickel sulphate by about 15 tons per year based on the capacity of 6,000 tons of coloring material for oxidation vertical line.
Advantages: Energy saving: 10~15μm oxide film can make uniform black material. Time-saving and efficient: pure black coloring time is 6 to 7 minutes, saving 2/3 than traditional coloring time. Low loss: a coloring tank for continuous, batch production including champagne, bronze and black. The coloring tone is stable, the reproduction repeatability is good, the color is uniform, and the weather resistance of the profile is good.
Tin salt (or tin-nickel salt) has electrolytic coloring additives containing harmful organic reducing agents and complexing agents of different compositions and concentrations, which seriously affect the pollution indicators such as COD and BOD in wastewater treatment. The tin-nickel salt bath has both organic reducing agent complexing agent and nickel ion double pollution, and the complexing agent also affects the removal of nickel ions in the double salt. The composition of the single nickel salt bath is simple, and there is no organic reducing agent complexing agent. The nickel ion removal is relatively simple and easy, and the degree of automation is improved. Therefore, the discharge treatment of single nickel salt is more convenient than the tin-nickel mixed salt, that is, the environmental protection treatment measures are relatively simple.