JPH06343978A - Removing process for iron content in aqueous solution containing alkaline earth metal chloride - Google Patents

Abstract

PURPOSE:To remove an iron content easily and quickly out of an aqua. solution of alkaline earth metal chloride by adding and mixing a mixture of sodium silicate aqua. soln. and acid into an aqua. soln. containing alkaline earth metal chloride, oxidizing, and then neutralizing by an alkali. CONSTITUTION:In a mixture prepared preliminarily by mixing a sodium silicate aqua. soln. of 4-10 Baume with acid (for example, hydrochloric acid, nitric acid or the like) is added into and mixed with an aqua. soln. containing alkaline earth metal chloride so that pH thereof becomes 5 or less, and then the mixture thus prepared is neutralized to pH 7-8 by an alkali (for example, calcium hydroxide, sodium hydroxide, potassium hydroxide or the like). The precipitate of fine alkali earth metal silicate is prepared easily by the treatment, and an iron content is adsorbed to the precipitate of fine alkali earth metal silicate thus prepared. The iron content can be removed easily and quickly out of the aqua. soln. of an alkali earth metal chloride by the treatment.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the removal of iron from an aqueous solution containing an alkaline earth metal chloride, and particularly to the removal of iron contained in liquid calcium chloride obtained by concentrating the distillation waste liquor of a sodium liquor separation mother liquor in the ammonia-soda method. Concerning the law.

[0002]

2. Description of the Related Art Conventionally, iron is removed from an aqueous solution containing an alkaline earth metal chloride by adding an aqueous solution of sodium silicate of 4 to 15 Baume while stirring the aqueous solution containing an alkaline earth metal chloride. A method of adsorbing iron while precipitating an earth metal silicate precipitate and separating the precipitate by sedimentation (Japanese Patent Publication No. Sho 46-23491) has been adopted.

[0003]

In the above method, when an aqueous solution containing an alkaline earth metal and an aqueous solution of sodium silicate having an appropriate concentration are brought into contact with each other, a precipitate of coarse-grained gel-like alkaline earth metal silicate is formed immediately. To do.

Since the removal of iron from the aqueous solution containing an alkaline earth metal chloride is adsorption on the surface of the precipitate of the produced alkaline earth metal silicate, sodium silicate must be removed in order to remove iron efficiently. It is necessary to form a fine precipitate from a sufficiently dispersed state, but it is difficult to finely pulverize the precipitate of the alkaline earth metal silicate formed by the conventional method, and the adsorption of iron content is a gel-like coarse particle. Since it is only adsorbed on the surface of the grains, an excess amount of sodium silicate aqueous solution has to be used in order to obtain a sufficient iron removal effect.

Further, when the amount of iron contained in the aqueous solution containing an alkaline earth metal chloride increases, when the treatment is carried out by the conventional technique, the treated liquid may be colored yellow. The solid product made from the above was colored, and the hue of the solid product deteriorated.

[0006]

[Means for Solving the Problems] As a result of intensive studies conducted by the present inventors to solve such problems, as a result of contact between an aqueous solution containing an alkaline earth metal chloride and an aqueous solution of sodium silicate, an alkali The inventors have found that the precipitate of the earth metal silicate dissolves acidicly and precipitates alkaline, and that the reaction rate of silica gel formation is slow even when mixed with an acid when the concentration of the sodium silicate aqueous solution is low, and reached the present invention.

That is, according to the present invention, a solution prepared by previously mixing an aqueous solution of sodium silicate of 4 to 10 Baume and an acid is added to and mixed with an aqueous solution containing an alkaline earth metal chloride so that the pH is 5 or less, and then the pH is adjusted to 7 with an alkali. A fine alkaline earth metal silicate precipitate can be easily obtained by neutralizing to ~ 8, and the alkaline earth metal is characterized in that the iron content is adsorbed to the formed fine alkaline earth metal silicate precipitate. It is intended to provide a method for removing iron in an aqueous solution containing a metal chloride.

In the present invention, the aqueous solution of sodium silicate added to the aqueous solution containing an alkaline earth metal chloride is preferably in the range of 4 to 10 Baume, and particularly preferably in the range of 5 to 6 Baume. If it exceeds 10 Baume, the reaction rate with an acid to form silica gel increases, which makes handling difficult, and if it is less than 4 Baume, the amount of water brought into the system increases, which is not preferable. The acid to be added is hydrochloric acid,
Common ones such as sulfuric acid and nitric acid are used.

Next, it is preferable that the aqueous solution of sodium silicate added for adjusting the pH of the aqueous solution containing the alkaline earth metal chloride and the acid are sufficiently mixed in advance. However, it is desirable to use silica gel as soon as possible after mixing, since silica gel is formed after a long time and the adsorption ability is lowered. The mixing ratio of the sodium silicate aqueous solution and the acid is
It may be appropriately determined depending on the amount of acid necessary for adjusting the pH of the aqueous solution containing an alkaline earth metal chloride to 5 or less and the amount of iron content to be removed. The mixture is added in an appropriate amount so that the pH is 5 or less, preferably pH 1 or less.

[0010] Next, after adding to an aqueous solution containing an alkaline earth metal chloride and stirring sufficiently to confirm that the pH of the aqueous solution has become 5 or less, the pH of the aqueous solution is adjusted to 7 to 7 with alkali.
Neutralize to 8. As the alkali used here, common ones such as calcium hydroxide, sodium hydroxide and potassium hydroxide are used, but calcium hydroxide is particularly preferable since it has a mild reactivity. Neutralization to pH 7-8 produces fine precipitates of finely divided alkaline earth metal silicates well dispersed in an aqueous solution containing alkaline earth metal chlorides. Iron, which is an impurity, is adsorbed and removed by this fine precipitate. If the pH exceeds 8, it does not affect the effect of removing iron, but the amount of alkali for neutralization becomes excessive, which is not economical.

The supernatant liquid obtained by settling and separating the fine silicate precipitates thus produced is a liquid from which most of the iron content has been removed.

[0012]

EXAMPLES The present invention will be described below with reference to examples.
This does not limit the present invention.

Example 1 As a stock solution, an aqueous calcium chloride solution (CaCl 2) was prepared by concentrating a distillation waste solution of a mother liquor separated from sodium bicarbonate in the ammonia-soda method.
₂ : 37-40%) was used. As the acid, commercially available 35% hydrochloric acid is used as it is, and as the sodium silicate aqueous solution, commercially available No. 3 silicic acid (Na ₂ O: 9.31%, SiO ₂ : 28.39%) is used.
Was diluted to 5 baume and used.

To 1 L of the calcium chloride aqueous solution, hydrochloric acid in an amount to bring the pH of the solution to 5 and 3 mL of the sodium silicate aqueous solution were sufficiently mixed and then added to the calcium chloride aqueous solution. After sufficiently stirring and mixing, it was confirmed that the pH of the calcium chloride aqueous solution was 5 or less, and then slaked lime was added as a slurry to adjust the pH of the calcium chloride aqueous solution to 7.5. After the solid matter such as the generated precipitate was separated by sedimentation, the supernatant was collected and the iron content was measured. The results show that the iron content was significantly reduced as compared with the conventional method.

In the conventional method, a diluted sodium silicate aqueous solution is added to a calcium chloride aqueous solution to form a precipitate to adsorb iron, and then hydrochloric acid is added to adjust the pH of the calcium chloride aqueous solution to 7-8. It is something to do.

[0016]

[Table 1]

Example 2 The results of carrying out the calcium chloride concentration / purification step in a continuous state are shown below. As the acid, commercially available 35% hydrochloric acid is used as it is, and the aqueous solution of sodium silicate is commercially available No. 3 silica (Na ₂
O: 9.31%, SiO ₂ : 28.39%) diluted to 5 Baume was used.

To 1 m ^{3 of the} calcium chloride aqueous solution, 2.9 to 3.3 L of hydrochloric acid and 3 L of the sodium silicate aqueous solution were sufficiently mixed and then added to the calcium chloride aqueous solution. After sufficiently stirring and mixing, it was confirmed that the pH of the calcium chloride aqueous solution was 5 or less, and then slaked lime was added as a slurry to adjust the pH of the calcium chloride aqueous solution to 7.5. After the solid matter such as the generated precipitate was separated by sedimentation, the supernatant was collected and the iron content was measured. The results are shown below, and the iron content was significantly reduced even with continuous industrial equipment.

[0019]

[Table 2]

[0020]

EFFECTS OF THE INVENTION According to the present invention, the iron content can be easily and quickly removed from the aqueous solution of the alkaline earth metal chloride, and the hue of the solid product using the liquid from which the iron content has been removed as a raw material is significantly improved. Made it possible. In addition, the amount of sodium silicate used as a refining material can be reduced compared to the conventional method, and the amount of water flowing into the process from outside the system can be reduced, thus suppressing the concentration decrease of the aqueous solution containing alkaline earth metal chloride. it can.

Claims (1)

[Claims] 1. An aqueous solution containing an alkaline earth metal chloride is added and mixed with a solution prepared by previously mixing an aqueous solution of sodium silicate of 4 to 10 Baume and an acid so that the pH is 5 or less, and then adjusting the pH to 7 to 8 with an alkali. A method for removing iron in an aqueous solution containing an alkaline earth metal chloride, characterized in that the iron is adsorbed to the precipitate of the alkaline earth metal silicate by neutralizing.