JPH01153517A - Method for treating aluminum-containing waste hydrochloric acid - Google Patents

Abstract

PURPOSE:To effectively utilize wastes and recover Al2(SO4)3 crystals useful as a reusable acid and flocculant, etc., by adding sulfuric acid to an Al- containing waste hydrochloric acid so as to provide a prescribed molar ratio of SO3/Al, regulating the resultant mixed acid solution so as to provide a supersaturated solution of Al2(SO4)3 therein, crystallizing and separating the formed crystals. CONSTITUTION:The surface of Al (alloy) is treated with hydrochloric acid or a mixed acid thereof and sulfuric acid, etc. In the process, sulfuric acid added to the generated Al-containing waste hydrochloric acid so as to provide 3/2-9/2 molar ratio of SO4/Al and the resultant mixed acid solution is then concentrated under reduced pressure, evaporated and concentrated or cooled and concentrated to regulate the solution so as to provide a supersaturated solution of Al2(SO4)3 therein. A seed crystal in an amount of 5-30% is added to the regulated solution or temperature of the supersaturated solution is increased or reduced to impart temperature history. Thereby crystals of the Al2(SO4)3 are formed and recovered by a centrifugal method, etc. The separated mother liquor is subsequently adjusted for reuse.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for treating waste hydrochloric acid containing aluminum generated when surface treating aluminum or aluminum alloy with hydrochloric acid or a mixed acid of hydrochloric acid and sulfuric acid. , relates to a method in which the aluminum content is recovered as crystals of aluminum sulfate, and the mother liquor can be reused after preparation.

Conventional technology Conventionally, aluminum-containing waste hydrochloric acid or aluminum-containing waste mixed acid discharged from factories related to the electrolytic foil industry that manufacture aluminum capacitors has been used for neutralization treatment or as a coagulant in paper mills, etc. Met.

Problems to be Solved by the Invention In neutralization treatment, a large amount of alkali is consumed, so the treatment cost is high, and in addition, sludge containing aluminum hydroxide as a main component is generated, and the treatment of this has been a problem. In the method of using waste acid as a coagulant in paper mills, etc., the aluminum content is extremely low at 1 to 2% as At, and the amount of free acid is large, resulting in a problem of pH drop during use.

Furthermore, since there is no balance between the amount consumed by users and the amount of waste acid discharged, a large storage tank is required, and the cost becomes enormous.

The present inventor previously obtained Japanese Patent No. 735107.

No. 782728, No. 830454, and No. 830482 proposed a method in which aluminum sulfate crystals are crystallized from an aluminum-containing sulfuric acid solution when aluminum or aluminum alloy is anodized, and the sulfuric acid is recovered and reused.

As a result of intensive study to apply these methods to aluminum-containing waste hydrochloric acid, we found that (1) aluminum sulfate is more likely to form crystals than aluminum chloride; (2)
(3) Adding sulfuric acid to waste hydrochloric acid containing aluminum can preferentially crystallize aluminum sulfate crystals; (3) adding aluminum sulfate seed crystals is more effective;
(4) It was discovered that hydrochloric acid can be recovered when concentrated to a concentration where aluminum sulfate crystals precipitate, (5) the recovered acid can be reused, and (6) the recovered aluminum sulfate crystals can be used as a flocculant. .

Means for Solving the Problems and Their Effects The present invention is based on these findings, and consists of adding sulfuric acid to waste hydrochloric acid containing aluminum so that the molar ratio of SO4/Al is 3/2 to 3/2.
The first step is to prepare the solution so that the ratio is 9/2, the second step is to prepare the mixed acid solution obtained in the first step so that the aluminum sulfate in the mixed acid solution becomes a supersaturated solution, and the supersaturated solution obtained in the second step. The third step of crystallizing aluminum sulfate crystals from
and a fourth step of separating the aluminum sulfate crystals obtained in the third step from the mother liquor.

The waste hydrochloric acid containing aluminum in the present invention may be a mixed acid with sulfuric acid. In this case, the first step of adjusting the δ molar ratio may be performed without adding sulfuric acid.

In the present invention, sulfate (SO4) and aluminum (A
The mole value of t) is set to 3/2 or more because the mole value of the sulfate group of aluminum sulfate and aluminum is 3/2, and if it is less than this, aluminum sulfate crystals cannot be obtained. Furthermore, Table 1 shows the relationship between the molar ratio of sulfate radicals and aluminum from which aluminum sulfate crystals are obtained. As can be seen from this table, when the molar ratio of sulfate radicals to aluminum is 9/2 or less, aluminum sulfate crystals are obtained, but when it is 10/2 or more, acid salt crystals are obtained. Crystals of this acid salt have poor crystallinity and are difficult to separate from the mother liquor.

Next, the method for preparing the mixed acid bath liquid in the second step into a supersaturated solution of aluminum sulfate may be any of a vacuum concentration method, an evaporation concentration method, a cooling concentration method, and the like.

Here, a supersaturated solution of aluminum sulfate means supersaturated with respect to the crystallization temperature, and the temperature is 60°C or lower, preferably 55°C or lower. This is because the concentration of aluminum sulfate that crystallizes at 60° C. or higher is high, and the crystallization rate is fast, so that it tends to become sticky.

In the third step, crystallization of aluminum sulfate, 5 to 30
It is best to add water or increase or decrease the temperature of the supersaturated solution to provide a temperature history.

For the separation of the crystals and the mother liquor in the fourth step, a conventional centrifugation method or the like is used. The separated mother liquor can then be reused after adjustment. Further, the waste hydrochloric acid and waste mixed acid of sulfuric acid and hydrochloric acid of the present invention may contain nitric acid and phosphoric acid.

Example (1) Waste hydrochloric acid (At
15t7t, ct95y7t) 1.7K9 of 95thiosulfuric acid was added to Ioz and concentrated under reduced pressure to reduce At to 51
? /l, H, So4 is 550171%C160? /
1 of mixed acid solution was obtained.

This solution was cooled from 65°C at a rate of 3°C/Hr.
After cooling to 25°C, aluminum sulfate crystals were added to the aluminum sulfate crystals using a centrifuge. 33KL1
Obtained. The mother liquor at this time was 2.451, and At was 27.8.
? /l, H, So, is 310? /l, HCl was 72 fl/l.

(2) At is 17. (1/1%H, So4 is 120 f
/1%HC6 is 136? /l waste mixed acid 10t was concentrated under reduced pressure to obtain A4 of 51? /1%H,SO4360? /l
, HCl70? A mixed acid solution of 3.3/l was obtained. This was cooled at a rate of 3°C/Hr from 60°C, 1,502 seeds of aluminum sulfate crystals were added at 58°C, and after cooling to 25°C, the aluminum sulfate crystals were separated from the mother liquor using a centrifuge.

The aluminum sulfate crystal is 1.3~, the mother liquor is 2.8t, and the analysis results show that the aluminum sulfate crystal has an At content of 7.5t, S0
4 was 42.6 inches. Also, the At of the mother liquor is 27.8?
/l, H, SO4300? /l, HCl 72 t
/l.

Effects of the Invention According to the present invention, recovered waste acid can be reused after adjustment, and useful aluminum sulfate crystals can be obtained, so it has great practical value.

(1 other person)

Claims (2)

[Claims] (1) Sulfuric acid is added to waste hydrochloric acid containing aluminum and S
The first step is to prepare the O_4/Al molar ratio from 3/2 to 9/2, and the second step is to prepare the mixed acid solution obtained in the first step so that the aluminum sulfate becomes a supersaturated solution. step, a third step of crystallizing aluminum sulfate crystals from the supersaturated solution obtained in the second step, and a fourth step of separating the aluminum sulfate crystals obtained in the third step from the mother liquor. A method for treating aluminum-containing waste hydrochloric acid. (2) Waste hydrochloric acid containing aluminum is a mixed acid with sulfuric acid, and SO_4/Al
2. The method for treating aluminum-containing waste hydrochloric acid according to claim 1, which comprises the first step of preparing the aluminum so that the molar ratio thereof is from 3/2 to 9/2.