JPS61136914A - Purifying method of glauber's salt - Google Patents

Abstract

PURPOSE:To obtain Glauber's salt which is high in purity, odorless and colorless by separating and filtering the insoluble substance from the waste liquid of Glauber's salt, evaporating and condensating the mother liquor, dehydrating and drying the deposited crystal and subjecting it to the calcining treatment. CONSTITUTION:The following waste liquid of Glauber's salt (10-30wt% Na2SO4, <3pH) is made raw material that is formed in a sulfuric acid decomposition process in a recovery installation wherein tar acid is recovered from coal tar and aq. ammonia distilled in a period of the coal dry distillation and this mother liquor is temporarily allowed to stand to separate and filter the insoluble sub stance. Then after the mother liquor is regulated to <=7.0pH, it is evaporated and condensated. In the evaporation and condensation of the mother liquor, the crystal of Glauber's salt is deposited in the soln. by heating the mother liquor in 20-100Torr pressure at 30-70 deg.C temp. with an evaporator. The deposited crystal is separated in a slurry state, dehydrated by a dehydrator and thereafter kept at 100-200 deg.C for 0.5-2hr in a dryer to perform the dehydra tion, the drying and the calcining treatment and the dehydrated Glauber's salt is obtained.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is directed to the recovery of mirabilite waste liquid (
The present invention relates to a method for refining Glauber's salt with high purity as an industrial raw material from mother liquor (hereinafter referred to as mother liquor).

<Prior art and its problems> A general method for refining anhydrous mirabilite using mirabilite waste liquid generated in the process of recovering tar acid from coal tar and ammonia distilled during coal dry distillation as a raw material is to use mirabilite waste liquid (
After leaving the mother liquor to stand and separating insoluble substances, filter it, concentrate the mother liquor in an evaporator, precipitate crystals, separate, dehydrate in a dehydrator, and wash with water to remove impurities. The method used is to carry out a drying process and then purify the product through a drying process.

However, in this case, impurities in the sodium sulfate cannot be sufficiently removed by washing with water alone, resulting in odor and coloring, which has little utility as a raw material for T.

Therefore, it is desired to improve the method for removing impurities from Glauber's sulfate and obtain a highly pure sulfate.

<Object of the Invention> The object of the present invention is to solve the above-mentioned problems in the purification method of sulfate waste liquid, to reduce the degree of impurities in mirabilite, and to provide a purification method that can produce odorless and colorless mirabilite. The present invention aims to provide a method for purifying anhydrous sodium sulfate as an essential raw material that can be supplied as a raw material for synthetic detergents, dyes, pharmaceuticals, etc.

<Configuration of the Invention> The present invention is directed to a waste solution of mirabilite obtained in the process of recovering tar acid from coal tar and ammonia distilled during coal dry distillation.
(hereinafter referred to as mother liquor) to produce anhydrous sodium sulfate.

A process of separating and filtering insoluble substances from the mother liquor, a process of evaporating and condensing the mother liquor to bring the pH of the mother liquor from which the insoluble substances have been separated to 7.0 or less, and dehydrating and drying the crystals precipitated from the mother liquor. The present invention provides a method for refining Glauber's salt, which is characterized by performing a step and a calcination step.

The purification method of the present invention is carried out in the following steps.

Glauber's salt waste liquid (Na2SO,s 10-30% by weight, p
H<3) is used as a raw material, this mother liquor is temporarily left to stand, and insoluble substances are separated and filtered.

Next, in the step of evaporating and concentrating the mother liquor, the pH of the tzI solution before crystal precipitation is set to 7.0 or less. The reason is as follows. As mentioned later, the main component that colors the glass is iron cyanide, and iron cyanide is alkaline (
Sodium salt) is stable, and the impurities in Glauber's salt do not dissipate and the coloring does not disappear even after firing in the firing process described later.On the other hand, when the mother liquor is made acidic, it becomes a volatile acid during the entire concentration process and firing process. When this is done, the iron cyanide is removed and highly pure white Glauber's salt is obtained.

The mother liquor is concentrated using an evaporator at a pressure of 20 to 100 T.
orr, temperature 30-70℃ (preferably pressure 30-50℃)
By heating at a temperature of 40 to 60'C)-r, crystals of Glauber's salt are precipitated in the liquid.

The precipitated crystals are separated in the form of a slurry, and after dehydration in a dehydrator,
The mixture is kept in a dryer at 100 to 200°C for 0.5 to 2 hours to obtain anhydrous Glauber's Salt. In this case, as the degree of concentration in the evaporator increases, the degree of coloring of the mother liquor becomes stronger, and the mirabilite itself becomes similarly colored after dehydration and drying.

The main component of this coloring is iron cyanide, which is heated at a temperature of 300 to 900"C (preferably 50"C) in the next firing process.
0 to 800°C) for 0.5 to 2 hours to decompose and obtain white neutral anhydrous Glauber's salt. Firing temperature is 300℃
If it is less than 900°C, impurities cannot be decomposed, and if it exceeds 900°C, Glauber's salt itself will be affected by heat. Therefore, it is preferable to bake at 500 to 800°C.

In addition, if the iron concentration in the waste solution of Glauber's salt becomes high, and as a result, the iron concentration in the sodium sulfate after firing exceeds 100 pp-, the color of iron oxide itself will appear, and the crystals of Glauber's salt after firing will turn a pale pink color. Color. In this case, add excess sodium hydroxide to the mirabilite waste solution in advance to adjust the pH to an alkaline side, remove most of the iron impurities as ferric hydroxide precipitation, reduce the iron concentration, and then add sulfuric acid. After making the mother liquor acidic again and replacing the stable sodium salt with a volatile acid, it is fed to an evaporator, and the same process as above is carried out to obtain white neutral anhydrous sodium sulfate.

<Examples> Hereinafter, the present invention will be explained in detail with reference to Examples and Comparative Examples.

(Example 1) Glauber's salt waste liquid (Na2S046 degrees 14, 7 @ clear%, F
e=2 lppm, pH=1.5) 1000
After leaving the msL for 1 hour, filter it with No. 5A filter paper.
At a pressure of 40 Torr and a temperature of 50°C, 150
The mixture was heated and reduced to mM. The precipitated crystals were dehydrated by suction using a 17G-1 glass filter, and dried in a drying oven at 100'o.
Dry for an hour. After that, ao o'c in a square electric furnace.
, Calcined for 0.5 hours to obtain 132 g of neutral anhydride and nitric acid.

The quality of the obtained mirabilite is shown in Table 1.

Table 1 (Example 2) Glauber's salt waste liquid (Na2 SO4 concentration 15.8% by weight, Fe=
116ppm, pH=1.9) 1000 an
After standing for 1 hour, it was filtered through No. 5A filter paper, made alkaline by adding excess NaOH, and precipitated Fe(OH)3, which was filtered. Add excess H2SO4 to the mother liquor again to adjust the pH to 1.8, pressure 40 Torr, temperature 50°
The mixture was heated and condensed to 150 mJl in a C evaporator. The precipitated crystals were suction dehydrated using a 17G-1 glass filter and dried at 100° C. for 1 hour in a drying oven. After that, it was fired in a rectangular electric furnace for 0.5 hours, and the neutral anhydrous sodium sulfate 12
8g was obtained. The quality of the obtained mirabilite is shown in Table 2.

(Comparative Example) As a separate comparative example, the same waste liquid as in Example 1 was treated in the same manner, but no electric furnace firing was performed. )l
7.13) and heat it in an evaporator to reduce it.

Table 2 shows the quality of the Glauber's salt of Comparative Example 2, which was dried in a drying oven and then fired in an electric oven under the same conditions.

Table 2 <Effects of the Invention> By using the method for refining anhydrous mirabilite of the present invention, 1) using the mirabilite waste liquid generated in the sulfuric acid decomposition process in which tar acid is recovered from coal tar and ammonium water collected during coal dry distillation as a raw material, 8
White, odorless, neutral anhydrous sodium sulfate with a high purity of 9.0% by weight or more is obtained.

The obtained neutral anhydrous sodium sulfate can be supplied as an industrial raw material for synthetic detergents, dyes, medicines, etc.

Claims (2)

[Claims] (1) When producing anhydrous mirabilite from the waste solution of mirabilite (hereinafter referred to as mother liquor) obtained in the process of recovering tar acid from coal tar and ammonia distilled during coal dry distillation, insoluble substances are separated and filtered from the mother liquor. A step of evaporating and concentrating the mother liquor by adjusting the pH of the mother liquor after separating and filtering insoluble substances to 7.0 or less, a step of dehydrating and drying crystals precipitated from the mother liquor, and a calcination treatment step. A method for refining mirabilite. (2) When producing anhydrous mirabilite from the waste solution of mirabilite (hereinafter referred to as mother liquor) obtained in the process of recovering tar acid from coal tar and ammonia distilled during coal dry distillation, insoluble substances are separated and filtered from the mother liquor. The iron concentration of the mother liquor after separating and filtering insoluble substances is reduced to 100p.
pm or less, a step of evaporating and concentrating the mother liquor by adjusting the pH of the mother liquor to 7.0 or less, a step of dehydrating and drying crystals precipitated from the mother liquor, and a firing treatment step. .