JPS5988325A - Treatment of spent sulfuric acid solution - Google Patents

Abstract

PURPOSE:To obtain economically ferrous sulfate of high quality from a spent sulfuric acid soln. by changing the soln. into an iron scrap vessel to bring the soln. into contact with iron scraps and by concentrating the soln. to separate and recover ferrous sulfate. CONSTITUTION:A spent sulfuric acid soln. discharged from a pickling apparatus 1 after pickling the surface of steel contains dissolved ferrous sulfate. The soln. is charged into an iron scrap vessel 12 contg. a large amount of iron scraps, and it is brought into contact with the scraps. The soln. is then fed from the vessel 12 to heat-eveporators 3 through an acid feeding tank 2 with a pump 13. The soln. concentrated in the evaporators 3 is fed to a precooling tower 5, cooled, fed to crystallizers 7, and further cooled to deposit ferrous sulfate crystals. A prepared slurry with a high sulfuric acid content and low specific gravity is returned to the crystallizers 7 and repeatedly subjected to said operation. A prepared slurry with a high ferrous sulfate content and high specific gravity is fed to a centrifugal separator 9, where sulfuric acid is separated from ferrous sulfate 10 and recovered. The recovered sulfuric acid is returned to the apparatus 1 through a tank 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating sulfuric acid waste liquid produced after pickling steel with sulfuric acid.

Traditionally, when hot rolling of steel paulownia, wire paulownia, shaped steel, steel, etc. is carried out, scale is formed on the surface, and this scale interferes with subsequent processes such as cold forming and painting. In such cases, it is common practice to pickle iron and copper to remove scale. However, the sulfuric acid waste solution after pickling contains unreacted sulfuric acid and iron sulfate.
Since it is a pollution problem to discharge this into rivers and oceans at this time, the sulfuric acid waste liquid is heated and concentrated by J1C air evaporation, and then a cooling separation operation is performed to remove the ferrous sulfate (Fe3O3, 7H20), iron oxide (Fe20g ・Fe, Q4 or FiFe0
The sulfuric acid waste solution is treated by a method in which the sulfuric acid radicals are removed as gypsum. By the way, the former iron sulfate crystal method is processed as shown in the flow sheet of FIG. That is, the sulfuric acid waste liquid discharged from the fij and fll after pickling is collected in the acid tank (2), and then the waste liquid is sent from the acid tank (2) to the heating evaporator (3) where it is heated and evaporated. The water in the waste liquid is heated in the can (3) to evaporate it, and the evaporation is accelerated by reducing the pressure using the water sieve vacuum device C'4), thereby concentrating the sulfuric acid waste liquid. Next, the concentrated sulfuric acid waste liquid is sent to the pre-cooling tower (5) to be cooled, and then injected into the crystallizer (7) whose outer periphery has been cooled by the cooling tower (6). The concentrated sulfuric acid waste solution is further cooled while stirring, and crystals of sulfuric acid 11 are poured out into the concentrated sulfuric acid waste solution. The slurry-like concentrated sulfuric acid waste solution containing ferrous sulfate crystallizer IL is then injected from the crystallizer (7) into the liquid crystallizer (8), which contains sulfuric acid with a high specific gravity of T4. The slurry with a low specific gravity is separated into a small slurry and a slurry with a high specific gravity with a high content of ferrous sulfate, and the slurry with a low specific gravity is crystallized by R: ÷
(7), and the slurry with high specific gravity is sent to the KL centrifuge (91) and sulfuric acid and ferrous sulfate (7 water) tray (10
). In this way, sulfuric acid deliquification is processed, but in the 1111 method,
Since the residual liquid after discharging the ferrous lt acid still contains 4if acid, it is used as the recovered acid (It) by 1]bionic acid washing f.
I returned it to +11 and am using this.

However, the demand for iron sulfate obtained in this way is low in the United States, and since iron sulfate is produced as a by-product from Chitashi Industries in addition to the treatment of steel pickling waste, an attempt was made to obtain a large amount of iron sulphate. It can be said that there was no such thing. However, in recent years, scissors bodies with low carbon quality and close to pure iron have been produced, and it has become easier to obtain cheap and high-quality iron sulfate from the pickling solution used to pickle such steel.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a method for treating sulfuric acid waste liquid that can produce L by economically increasing the production of high-quality ferrous sulfate.

That is, in the present invention, the sulfuric acid waste solution after pickling steel with sulfuric acid is injected into the iron scrap tank containing iron scraps to bring the iron scraps into contact with the sulfuric acid waste solution, and then after concentrating this waste solution, the sulfuric acid waste solution is The above objective 1 has been achieved by a method for treating sulfuric acid waste liquid, which is characterized by separating and recovering iron.

The present invention will be explained in detail below. As shown in fA2 diagram,
The sulfuric acid waste liquid discharged from the pickling device f+) has dissolved ferrous sulfate because the surface of the steel has been pickled. This sulfuric acid waste liquid is first injected into the iron scrap tank 02) in which iron scraps are accommodated in large quantities, and the iron scraps are brought into contact with the amount of the sulfuric acid waste liquid. As the iron scrap, high-quality iron scrap with few impurities such as low carbon hot-rolled steel plate scraps is used, and the contact conditions on the sulfuric acid waste liquid, i.e., liquid temperature, liquid IT, quantity, quality and shape of iron scrap, are used. The amount of dissolved iron a is adjusted to 1JIAl by adjusting the contact time, contact area, iron content in the waste acid, sulfuric acid concentration, etc. Next, sulfuric acid Ps'7& is sent from the iron scraps to the acid supply tank (2), and then from the acid supply tank (2) to the heating evaporator (3)
Send the sulfuric acid waste liquid. Acid supply tank (2) and heating evaporator (3)
) is connected with a spare iron scrap tank (14) as shown in Figure 3. If the iron concentration is lower than the set concentration, the sulfuric acid waste liquid is further sent into this preliminary iron scrap tank (1→) to dissolve the iron scraps in the preliminary iron scrap tank (14), and the sulfuric acid waste in the sulfuric acid waste liquid is dissolved. This is to increase the concentration of ferrous sulfate.Also, if the concentration of ferrous sulfate in the sulfuric acid waste liquid sent to the acid supply tank (2) is higher than the set concentration, the preliminary iron scrap tank (14) is used. Heated evaporator (3)
In this case, while heating, the pressure is reduced by a water jet vacuum device (4), and all of the moisture in the sulfuric acid waste liquid sent into the heating evaporator (3) is efficiently evaporated and concentrated.

, - Next, concentrated sulfuric acid j) concentrated in the heating evaporator (3)
6 liquid is sent to the pre-cooling tower (5) to be cooled, and then to the crystallizer (7).
) The concentrated sulfuric acid waste solution is further cooled while being stirred in the -C crystallizer (7), and ferrous sulfate crystals are precipitated.

Since the concentrated sulfuric acid waste liquid is highly concentrated, the solubility decreases as the temperature decreases, and ferrous sulfate precipitates. The precipitated ferrous sulfate is dispersed in the concentrated sulfuric acid waste liquid, and the concentrated IRa sulfuric acid waste liquid becomes a slurry. Next, this slurry-formed concentrated sulfuric acid waste liquid is sucked by the pump (I5) and transferred to the cyclone (8). The slurry is fed and separated into a slurry with a high specific gravity with a high content of ferrous sulfate and a slurry with a low specific gravity with a high content of sulfuric acid in a cyclone (8).The slurry with a low specific gravity with a high content of sulfuric acid is sent to a crystallizer ( 7) and repeat the same operation again. On the other hand, the slurry with a high specific gravity and high content of ferrous sulfate is sent to a centrifuge (9).
Here, sulfuric acid and ferrous sulfate (heptahydrate) for recovery +IO+
The sulfuric acid is returned to the pickling device (1) through the recovery acid tank (I6). 07) in the figure is a refrigerator.

Therefore, by injecting the sulfuric acid waste solution after pickling the steel into the iron scrap tank O''4 and dissolving the iron scraps in the sulfuric acid waste solution, the contact conditions between the sulfuric acid waste solution and the iron scraps are adjusted, and the sulfuric acid waste solution is The concentration of ferrous sulfate in the ferrous sulfate can be raised to any desired concentration, and therefore a large amount of ferrous sulfate (heptahydrate) (10) can be produced, which is separated and recovered in subsequent operations. Moreover, in recent years, the quality of steel has become low-carbon and close to that of iron, and by selecting and using low-carbon, high-quality iron scrap, it has become possible to achieve a quality that does not contain impurities. It is possible to obtain excellent ferrous sulfate (heptahydrate) +101.It is an essential equipment for treating sulfuric acid waste liquid.
For C, in addition to conventional equipment, it is only necessary to install an iron scrap tank (one quart), so there is no particular increase in electricity/steam, labor costs, etc., and ferrous sulfate can be produced at low cost. On the other hand, when making ferrous sulfate using only sulfuric acid and iron scrap, it is necessary to newly install all of the above equipment, and also record electricity, steam, labor costs, etc. as new expenses. Furthermore, the sulfuric acid waste liquid normally dissolves iron scrap at a temperature of 70 to 98°C, and its sensible heat is used to evaporate water in heating X generation (3). In addition, in heating and emitting (3), since it contains a large amount of iron compared to the conventional method, the degree of concentration can be reduced compared to the conventional method, and it is possible to save energy. In addition, although the recovered acid returned to the pickling device f1+ has approximately the same temperature as before, the amount of sulfuric acid has decreased, so new sulfuric acid must be used in the pickling device fil. Since the addition of fresh sulfuric acid is an exothermic reaction, heating in the pickling device (1) can be omitted, which is advantageous from a thermoeconomic perspective, and this waste liquid treatment device achieves total energy savings. This is something that can be achieved.

As described above, in the present invention, the sulfuric acid waste solution after pickling steel with sulfuric acid is injected into the iron scrap tank containing iron scraps, the iron scraps are brought into contact with the sulfuric acid solution 1) (6), and then: After reducing this layer solution, ferrous sulfate was separated and recovered, and the sulfuric acid waste solution containing ferrous sulfate was used to further dissolve iron scraps, resulting in a high concentration of ferrous sulfate. It is possible to produce a large amount of ferrous sulfate by preparing waste liquid, and it may be possible to simply install a new iron scrap tank in the existing waste liquid treatment equipment, and it is also possible to process highly concentrated sulfuric acid waste liquid. As a result, ferrous sulfate can be obtained at low cost by processing with less heat energy f- in the concentration step and the like.

Furthermore, high-quality ferrous sulfate can be produced by pickling recent low-carbon steel that is close to pure iron and using high-quality iron scrap with few impurities.

The xylophone IJ14 will be explained in detail below based on conventional examples and examples.

<Conventional example> The sulfuric acid waste liquid discharged from the pickling equipment is stored in the acid supply tank,
Next is 46 containing 10.7% sulfuric acid and 13.7% iron.
sulfuric acid at
After concentrating at a flow rate of 1.1 tons/hour), it is cooled in a pre-cooling tower and a crystallizer to crystallize C ferrous sulfate, and then separated in a separator at an average rate of 1.1 tons/hour. The recovered acid solution at 7°C containing 8.0% was collected at a flow rate of 2.8%.
-7 hours (3.5h'J7 hours) was returned to the pickling equipment.

<Example> 10 tons of low carbon hot-rolled steel sheet selvedge iron scraps (thickness 2 mm, 11 mm 5-20 mm, length 15-50 fl) were put into the iron scrap tank and discharged from the pickling equipment. Sulfuric acid waste liquid is poured into the iron scrap tank to dissolve the iron scraps, and the iron scraps are poured so that the sulfuric acid content in the waste liquid supplied to the heating evaporator is 8.2 g, sulfuric acid content is 1 g, and 5 g. The solid-liquid contact conditions in the tank were adjusted (a spare iron scrap tank was also used if necessary). The subsequent treatment was carried out in the same manner as in the conventional example, separating the ferrous sulfate for r 1.4) tons/hour, and heating it at 8°C containing 14 sulfuric acid and 7.8 sulfuric acid.
The recovered acid solution was returned to the pickling device at a flow rate of 2.75 m'/hour.

From the above results, it can be seen that in the example, a larger amount of ferrous sulfate was obtained compared to the conventional example using existing equipment.

[Brief explanation of drawings]

FIG. 1 is a schematic process diagram showing a conventional apparatus, FIG. 2 is a schematic process diagram showing an apparatus according to an embodiment of the present invention, and FIG. 3 is an explanatory diagram of the main parts of the same. (1) is a pickling device, (2) is an acid supply tank, (3) is a heating evaporator, (4) is a water die/seat vacuum device, (6) is a pre-cooling tower, (6) is a water line, ( 7) is a crystallizer, (8) is a cycler, (9) is a centrifuge, (lo) is a ferrous sulfate (
7-hydrate salt LU2) is an iron scrap tank. Agent Patent Attorney Ishi 1) Choshichi

Claims (1)

[Claims] (1) After pickling steel with sulfuric acid, the sulfuric acid waste liquid is injected into the iron Mn+1 containing iron scraps to bring the iron scraps into contact with the sulfuric acid waste liquid, and then after concentrating this waste liquid, ferrous acid A method for treating acid waste liquid, which is characterized by separating and recovering the acid waste.