[China Aluminum Industry Network] 1. Crystallization recovery alkali etching:
The recovery of such alkaline solution by adding water to the water does not need to add any additives, and only one corresponding crystallization tank (that is, one more sub tank) is needed. When the Al3+ in the lye reaches 28g/L (that is, the concentration of NaALO2 is high), the lye is pumped into the crystallization tank (pre-added seed crystals), diluted, cooled and stirred to promote NaALO2 in the lye. Decompose and regenerate the NaOH solution overflowing into the recovery tank, and then pump it into the alkali bath to continue the production and form a closed cycle production; Al(OH)3 slurry is periodically discharged from the bottom of the crystallization tank, and the dewatering is performed with a centrifuge. The dried Al(OH)3 crystals were obtained and the washing solution was withdrawn back into the crystallization cell. Dry Al(OH)3 crystals can be sold for other uses.
2. The crystallization tank is grooved (after the seed crystals are put into use), special precautions:
2.1 alkali tank and crystallization tank temperature control at 42 ± 3 °C.
2.2 Uninterrupted power system, crystallization tank mixer can only stop more than 4 hours, otherwise the seeds will precipitate.
2.3 The crystallization tank is periodically inverted and cleaned once a year.
2.4 The lye recovery process, the total alkali content unchanged, the free base increased, aluminum ions decreased.
3. Control of alkali etching baths NaOH and Al3+ 3.1 Because of the closed circuit production, the total alkali content in the alkali etching bath is stable, and the aluminum ion is also controlled at about 28g/L. The amount of alkali taken away by the aluminum material only needs to be supplemented during production. The composition of the bath is stable, and the alkali etching temperature and time are well controlled. No additives are added. The ideal surface quality can also be achieved, and the surface quality is always kept relatively consistent.
3.2 The lye treated by the crystallization tank is left in the alkali etching tank. After being decomposed, the lye concentration returned to the alkali etching tank is higher than the lye concentration of the effluent, which can supplement the consumption of NaOH in the production process and effectively reduce the NaOH loss.
3.3 Seed crystals in the crystallization tank are added at one time in the mixing tank. The lye extracted from the crystallization tank during production contains a large amount of NaAlO2. Under the influence of seed crystals in the crystallization tank, some Al(OH) will also be precipitated. ) 3 crystal nucleus, this cycle production, no need to add seed.
Alkaline corrosion recovery equipment, Al3 + {Al (OH) 3} can be effectively recovered in the alkaline solution, the Al3 + removal rate in the bath can reach 55%; but the bath can not add additives, otherwise it will reduce the removal of dissolved aluminum Rate; The NaOH in the crystallization tank can be recycled in a large amount and reused. In production, only the amount of alkali taken away by the aluminum material is replenished, and the composition of the bath liquid is stable. Each ton of silver can produce about 25-30kg of water containing 10-15% Al(OH)3.
Dry Al(OH)3 has great economic benefits, such as alum and cryolite. And effectively reduce the wastewater treatment sludge, to achieve the purpose of pollution prevention.
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