System and method for neutralizing and recovering aluminum hydroxide and sodium sulfate in oxidizing liquid and potting liquid

Abstract

The invention discloses a system and method for neutralizing and recovering aluminum hydroxide and sodium sulfate from an oxidation solution and a mold alkaline-water soaking solution. The system sequentially comprises a mold alkaline-water soaking solution generation system, an oxidation solution collection system, a mold alkaline-water soaking solution addition system, a reaction solution separation system, a primary filtrate collection system, a primary filtrate recovery system, a sodium sulfate recovery system and a secondary filtrate collection system. The online recovery treatment of thealkaline-water soaking solution accounting for 28% of the total slag amount of waste slags generated by aluminum extrusion enterprises and the oxidation solution accounting for 27% of the total slagamount is involved, the oxidation waste solution is utilized as a reaction solution, and the mold alkaline-water soaking solution or other alkaline solutions containing sodium metaaluminate and sodiumhydroxide are added, wherein other alkaline solutions include the oxidation line alkaline-etching solution without an alkaline-etching agent, the alkaline dissolution solution of aluminum ash and thelike, R is greater than or equal to 3.5, and the pH is between 7.00 and 7.50; by-products of aluminum hydroxide and sodium sulfate are recovered to achieve zero discharge of mold alkaline-water soaking wastewater and waste slags, and the contamination of sodium ions to the center of the wastewater is completely blocked.

Description

technical field [0001] The invention relates to the technical field of aluminum processing, in particular to a system and a method for neutralizing and recovering aluminum hydroxide and sodium sulfate in oxidizing liquid and potting liquid. Background technique [0002] After the aluminum profile extrusion die is used, it should be put into a high-concentration lye for boiling to corrode the aluminum in the cavity. The concentration of sodium hydroxide in the potting liquid reaches 200-300g / L. As the reaction progresses, the content of aluminum ions increases continuously. Drain, the drained waste liquid contains a large amount of aluminum ions and sodium hydroxide, the potential economic value is very large. [0003] Chinese patent 201320875536.9 proposes the method of recovering aluminum hydroxide by neutralizing the anodizing solution with potting liquid, which can indeed recover aluminum hydroxide meeting the requirements of the national standard GB4294-2010, but does n...

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Problems solved by technology

[0003] Chinese patent 201320875536.9 proposes the method of recovering aluminum hydroxide by neutralizing the anodizing solution with potting liquid, which can indeed recover aluminum hydroxide meeting the requirements of the national standard GB4294-2010, but does not recover sulfate ions and sodium ions, and sodium ions are reclaimed water Biggest Barrier to Reuse

[0004] Chinese patents CN201710461889.7 and CN201010273267.X provide a method for recycling mold liquid, that is, recovering aluminum hydroxide and sodium hydroxide by crystallization. There are two technical obstacles that may hinder the implementation of these patents

The first obstacle is that the potting liquid is different from the alkali etching liquid. When the potting liquid is discharged, the free alkali is about 250g / L, the aluminum ion is about 50g / L, and the R value (the ratio of free alkali to aluminum ion concentration) is above 5.0. The free base of the alkali etching solution is about 60g / L, the aluminum ion is about 20g / L, and the R value is about 3.0. The R value interval of the alkaline bath solution, the decomposition of sodium metaaluminate and the precipitation of aluminum hydroxide is: R3.5, aluminum hydroxide is not decomposed; the R value of the alkaline etching solution is about 3.0, and Bayer can be used method, using crystallization means to recover aluminum hydroxide and reuse sodium hydroxide; but the R value of the pot mold liquid is above 5.0, which is too far from the decomposition range of sodium metaaluminate, and a large amount of free alkali hinders the decomposition of sodium metaaluminate , to dissolve the aluminum hydroxide that may be generated; in order to decompose the sodium metaaluminate in the pot mold liquid and recover aluminum hydroxide, it is necessary to add a large amount of acid, consume free alkali, reduce the R value, and make the R value return to the decomposition range before it can be recycled Aluminum hydroxide; however, the addition of a large amount of acid has lost a large amount of alkali, and this recovery method has lost the original design intention of alkali recovery; the second obstacle is that aluminum hydroxide is easy to decompose and scale, and equipment maintenance is very troublesome, and the recycled aluminum hydroxide Too thin, not worth much

[0005] Chinese patent CN201610128702.7 proposes a method of treating the potting liquid with lime to generate calcium aluminate and recover sodium hydroxide; under strong alkali conditions, calcium aluminate is dissolved, and this invention cannot generate calcium aluminate and cannot recycle the potting liquid

[0006] The current treatment methods are too simple: one is to discharge directly into the wastewater treatment center, which not only increases the treatment cost, but also wastes aluminum and sodium resources, and also introduces a large amount of sodium ions into the reclaimed water, hindering the reuse of reclaimed water; The processing factory pulls away. If these processing plants process a large amount of waste caustic soda, they will consume a large amount of acid and will pay high processing costs.

The national annual output of extruded aluminum is 20 million tons, resulting in 750,000 tons of mold-cooking waste liquid, containing 150,000 tons of sodium hydroxide and 30,000 tons of aluminum. Ten thousand tons of hazardous waste alkali slag! Not only paid a huge amount of wastewater treatment costs, but also lost about 30,000 tons of aluminum and 150,000 tons of sodium hydroxide, and produced 450,000 tons of hazardous waste alkali residue. This waste is shocking!

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