JPS5913447B2 - Method for treating sulfuric acid containing Glauber's salt - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing aluminum sulfate by treating waste sulfuric acid containing Glauber's salt.

A typical process for producing sulfuric acid containing Glauber's salt is considered to be a process in which chlorine dioxide is produced by using a suitable reducing agent from chlorate of sulfuric acid.

The main methods used in Japan to generate chlorine dioxide, which is consumed in large quantities for bleaching kraft pulp, are: ■) Method of reducing chlorate with sulfur dioxide 2NaCtO
3+SO2→2Ct02+Na2S042) Method of reducing chlorate with chloride NaC10+NaCt+H2SO4 →CtO2+%Ct2+Na2SO4+H20.

It is essential that these reactions be carried out under strong sulfuric acid acidity of 9-10.5 N, and the reaction waste liquid overflowing from the reactor is also strongly acidic with sulfuric acid of this concentration.

These waste liquids are conventionally sent to the kraft pulp cooking liquor system and are typically used as replenishment chemicals necessary for pulp production.

However, in recent years, the release of sulfur compounds into the atmosphere has become strictly regulated, and as each pulp mill has strengthened its dust collectors, scrubbers, and other abatement equipment, the recovery rate of chemicals has also improved, and the use of refills has improved. The amount of chemicals required has also decreased significantly.

For this reason, it has become impossible to inject the entire amount of chlorine dioxide-generating waste liquid into the kraft pulp cooking liquor, and the method for disposing of the excess waste liquid has become a problem.

A common method for treating acidic sulfuric acid waste liquid is to neutralize it with alkali, but if it is sodium-based, sodium sulfate is produced, and if it is calcium-based, calcium sulfate is produced, and both of these have no utility value. It is a low-priced item that is scarce.

In the case of aluminum bases, aluminum sulfate is produced, which is a useful material that is consumed in large quantities in pulp and paper mills for sizing and wastewater treatment.

On the other hand, the chlorine dioxide generating waste liquid contains not only sulfuric acid but also sodium sulfate as shown in the reaction formula.

An example of the composition is Na25O4360g/t in the case of 1) sulfite reduction method.

H2SO4460 g/l, Na2SO,340 g/l for the salt reduction method in 2), H2SO4480
When aluminum sulfate is produced by reacting this sodium sulfate (9/l) with aluminum hydroxide without separating it, the resulting solution contains a mixture of aluminum sulfate and sodium sulfate, and sodium alum It is in the form of an aqueous solution.

The solubility of this product is lower than that of pure aluminum sulfate in water as shown in Table 1, and the crystal precipitation temperature is also higher, so it is classified as JIS K-1423 or 145.
It must be handled at a dilute concentration of 4% or less compared to the 8% concentration of At203 (as At203).

This required large reactors and storage tanks, which was uneconomical.

The present invention eliminates this drawback, and by adding hydrochloric acid or hydrogen chloride gas to the sulfur-IJium content in the chlorine dioxide generation waste liquid, it is precipitated as common salt, and if necessary, the amount of precipitated salt is increased. After performing a water evaporation operation for
This involves recovering salt through solid-liquid separation and using chlorine dioxide generated waste liquid from which sodium content has been removed, and neutralizing it with aluminum compounds such as aluminum hydroxide to produce aluminum sulfate at the same time as waste liquid treatment. be.

Next, an outline of the present invention will be explained with reference to the drawings.

In FIG. 1, sodium chlorate 21 and sulfuric acid 22 are continuously charged into a chlorine dioxide generation tank 1, and sulfur dioxide 23 is blown in the sulfite method, air 23 is blown in the chloride method, and chlorine dioxide 24 is blown into the chlorine dioxide generating tank 1. is generated continuously.

The waste liquid that has completed the reaction overflows from the generating tank 1 and enters the receiving tank 2.

The waste liquid is further fed into a salt precipitation tank 4 by a pump 3.

When hydrochloric acid or hydrogen chloride gas 25 is added to the precipitation tank 4, and the mixture is stirred for an appropriate period of time for aging, salt crystals are precipitated and the content becomes a slurry.

Point 31 is the location where a water evaporator is installed to increase the yield of salt.

This is separated in a solid-liquid separator 5, and the mother liquor enters a receiving tank 6.

The separated salt falls into the dissolution tank 8 and is dissolved in water 26 to become a salt solution.

The mother liquor in the receiving tank 6 is then transferred to the band reaction tank 10 by the pump 7.
be prepared for.

Further, aluminum hydroxide 27 is charged into the reaction tank 10, and aluminum sulfate is produced by heating and reacting.

The product is received in a sedimentation tank 11, and after separating unreacted aluminum hydroxide, it is transported to a place of use by a pump 12.

The advantage of the present invention is that it not only lowers the crystallization temperature of the produced aluminum sulfate aqueous solution and makes it possible to produce a product with a higher concentration, but also produces a by-product of common salt that is useful for recycling into chlorate. be.

Example A reaction waste liquid discharged from a chlorine dioxide generator of a sulfite reduction method was used as sulfuric acid containing mirabilite.

Its composition is shown in Table 2.

To 10,100 O of this waste liquid, add 35 weight percent hydrochloric acid 4
After adding 60 ml of the solution and stirring, the produced common salt was passed from house to house at 20°C using a suction filter.

183 g of common salt crystals were recovered as a filter residue, the composition of which was as shown in Table 3.

On the other hand, mother liquor 27909 was obtained, and its composition was sulfuric acid 5
61 g/l and sodium chloride 121 i/l.

This mother liquor contains aluminum hydroxide 627 with a purity of 87.5%.
g and 1498 g of water were added, and a neutralization reaction was carried out at 80 to 110°C to obtain an 8% aluminum sulfate aqueous solution as At203.

The crystal precipitation temperature of this aqueous solution was 30°C.

Furthermore, 4915 g of water was added to this aqueous solution, and At203
A 4% aluminum sulfate aqueous solution was prepared, and the crystal precipitation temperature was measured to be -5°C.

Comparative Example 10100 with the same composition as the reaction waste liquid used in Example
388 g of aluminum hydroxide with a purity of 87.5% and 418!11 of water were added to O, and a neutralization reaction was carried out at 80 to 110°C to obtain a 4% aluminum sulfate aqueous solution as At203.

The high temperature of this crystallization was measured and was 10°C.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is an example of a flow sheet for industrially implementing the present invention, in which 4 is a salt precipitation tank, 5 is a solid-liquid separator,
10 indicates a neutralization reaction tank.

Claims (1)

[Claims] 1. In a processing method for producing aluminum sulfate using sulfuric acid containing Glauber's salt, existing alkali metal ions are removed by adding hydrochloric acid or hydrogen chloride gas,
A method for treating sulfuric acid containing Glauber's salt, which comprises removing the alkali metal chloride in advance and then neutralizing the liquid with an aluminum compound to produce aluminum sulfate.