JPH06171953A - Production of ferric chloride solution - Google Patents

Abstract

PURPOSE:To obtain a ferric chloride soln. suitable for use as an auxiliary water treating and flocculating agent by purifying an iron chloride soln. contg. impurity metals such as Ni. CONSTITUTION:Iron powder is added to an iron chloride soln. prepd. by dissolving iron as starting material in hydrochloric acid and/or a ferric chloride soln. and they are brought into a reaction to remove impurity metals in the iron chloride soln. The iron powder is then regenerated by removing the deposited impurity metals by washing with hydrochloric acid and the resulting purified soln. is oxidized to produce the objective ferric chloride soln.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a ferric chloride solution used as a coagulation aid for water treatment.

[0002]

2. Description of the Related Art As a conventional method for producing a ferric chloride solution, an iron raw material such as iron powder or iron scraps is dissolved in hydrochloric acid or a ferric chloride solution to first produce a ferrous chloride solution, Then, a method is known in which an oxidizing agent such as chlorine gas is added to the ferrous chloride solution to produce a ferric chloride solution.

When a ferric chloride solution is used as a coagulation aid for water treatment, heavy metals such as chromium and nickel and other substances having a low impurity concentration are required due to environmental problems. It is said that the concentration of impurities in the ferric chloride solution is below the value shown in Table 1.

[0004]

[Table 1]

When the impurity concentration in the iron raw material is high, the impurity concentration in the iron chloride solution produced by dissolving the iron raw material becomes high. However, it is not practical to use a high-purity iron raw material because the raw material cost becomes high. Therefore, it is necessary to purify the iron chloride solution generated to reduce the impurity concentration.

[0006] For example, as a method for removing nickel in an etching waste liquid of an iron-nickel alloy using ferric chloride, ferric chloride is reduced to ferrous chloride, and then iron powder is added to the solution. A method (Japanese Patent Laid-Open No. 62-191428) for removing nickel deposited by a reaction is known. However, as the reaction progresses, a strong nickel coating is formed on the surface of the iron powder deposited, and the reaction is hindered.
In such a case, a method has been proposed in which iron powder coated with nickel is pulverized to renew the surface of the iron to further promote the reaction of iron (JP-A-1-167235). This method has a problem that the crushing process and its equipment are required in addition to the nickel removal process and the operation becomes complicated.

[0007]

The object of the present invention is to reduce the concentration of impurities by renewing and activating the surface of iron powder coated with a metal such as nickel without requiring a complicated process. It is to provide a method for producing a ferric chloride solution.

In the present invention, iron powder is added to an iron chloride solution produced by dissolving an iron raw material in hydrochloric acid and / or a ferric chloride solution to cause a reaction, thereby precipitating an impure metal in the iron chloride solution. After the removal, the purified solution is oxidized to produce a ferric chloride solution, and the surface of the iron powder is intermittently washed with hydrochloric acid, which is a method for producing a ferric chloride solution. Hereinafter, this process will be described in order with reference to the flow sheet of FIG.

(A) An iron raw material such as iron powder or iron scrap is dissolved in hydrochloric acid or ferric chloride solution to form an iron chloride solution. When only hydrochloric acid is used, if the pure iron content in the iron raw material is high, hydrogen gas is generated by the reaction of formula (1) and there is a risk of explosion or the like. Further, when the iron raw material is dissolved in a mixed solution of ferric chloride and hydrochloric acid, pure iron in the iron raw material is reacted by the equation (2), and iron oxide in the iron raw material is reacted by the equation (3). Dissolves to produce ferrous chloride. Fe + 2HCl → FeCl ₂ + H ₂ (1) Fe + 2FeCl ₃ → 3FeCl ₂ (2) FeO + 2HCl → FeCl ₂ + H ₂ O (3) In this case, it is better to add hydrochloric acid in a slightly excess amount than that necessary to dissolve iron oxide. Dissolution rate becomes faster. However, when hydrochloric acid is added in a large excess, the amount of hydrogen gas generated increases. Therefore, 1.05 to 1.10 times the required amount of hydrochloric acid is suitable. Further, when ferric chloride is added in excess of the amount required to dissolve pure iron, the generation of hydrogen gas is less and the dissolution rate is faster. The melting temperature in this case is 40 to 100 ° C, preferably 60 to 90 ° C.

(B) The iron chloride solution produced in the step of dissolving the iron raw material is a ferrous chloride solution containing ferric chloride.
The amount of ferric chloride in this solution was determined by the amount of Fe (I
It depends on the amount of II) and the amount of ferric chloride added in excess when dissolving the iron raw material.

This iron chloride solution is heated to react with iron powder. The heating temperature is 60 ° C or higher, preferably 80 ° C or higher. The particle size of the iron powder is preferably about 0.3 to 2 mm. In this case, Fe (III) is obtained by the reaction of the above equations (1) and (2).
And the iron powder is consumed by reacting with the free acid, and ferric chloride in the iron chloride solution is also reduced to ferrous chloride. In this case, if the concentration of ferric chloride before reacting with the iron powder is high, the consumption of the iron powder will increase, and more reaction heat with the iron powder will be generated, making it difficult to control the temperature. It is preferable that the iron concentration is low. On the other hand, nickel or the like contained in the iron chloride solution has a high oxidation-reduction potential, so under normal conditions, it is reduced when iron is dissolved and deposited on the surface of iron powder as shown in the following formula. NiCl ₂ + Fe → FeCl ₂ + Ni (4)

The amount of iron powder added in this step varies depending on the concentration of ferric iron in the iron chloride solution produced in step (a), the concentration of free acid, the concentration of impure metals such as nickel, the liquid temperature, and the reaction time. 40 to 1000 kg is suitable for 1 m ^{3 of} the solution. Nickel deposited on the surface of the iron powder forms a strong nickel film and inhibits the reaction.

(C) In the method of the present invention, every time the activity of the iron powder decreases, the surface of the iron powder is washed with hydrochloric acid to dissolve the precipitates on the surface of the iron powder and renew the surface to activate the iron powder. It is a big feature to raise. That is, the present invention repeats the steps of purification with iron powder → washing of iron powder surface → purification with activated iron powder. Further, after the iron powder surface is dissolved, the impurities deposited on the iron powder surface can be recovered from the hydrochloric acid cleaning solution.

Impurities such as chromium in the iron chloride solution are not reduced when the iron is dissolved because they have a lower oxidation-reduction potential than iron, but the free acid is consumed during the purification with iron powder, and the pH rises. When it is 1 or more, it becomes hydroxide and precipitates.
This hydroxide is removed by filtering the purified iron chloride solution from the iron powder. Among the metallic impurities, zinc and manganese have lower redox potential than iron and further have a relatively high solubility of hydroxide, so that they are difficult to remove even at pH 1 or higher. Therefore, it is desirable to use iron powder for refining that has a low content of zinc and manganese.

(D) The iron chloride solution containing mainly ferrous chloride purified in the above steps is contacted with an oxidizing agent such as chlorine gas to oxidize ferrous chloride to ferric chloride, Add a small amount of hydrochloric acid and water to adjust the pH and the concentration to obtain a ferric chloride solution product. It is also possible to circulate a part thereof and use it for melting the iron raw material in the step (a).

According to the method of the present invention, the concentration of impure metals such as nickel and chromium contained in the iron chloride solution is from several tens of ppm to several ppm.
Is particularly effective in reducing the water content to a low level, and the resulting ferric chloride solution is suitable as a coagulation aid for water treatment.

[0017]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples. In the examples,% is based on weight.

(Experimental example: Ni and Cr removal test) An iron chloride solution (ferric chloride 26.1%, ferric chloride) produced by dissolving an iron raw material in a mixed solution of hydrochloric acid and ferric chloride. 13.
2 and 3 show the Cr and Ni concentrations after reacting with 70 g of 1%, free hydrochloric acid concentration of 0.3%) and 15 g of iron powder (average particle size 1 mm, pure iron content of 88%). The reaction temperature is 40,
The reaction time was 60 to 80 ° C. and 0.5 to 6 hours. It can be seen that as the reaction temperature rises, the removal rate of Ni and Cr increases, and the rate rapidly increases at 80 ° C.

EXAMPLE An iron chloride solution (ferrous chloride 26%, produced by dissolving an iron raw material such as iron powder and iron scraps in a mixed solution of hydrochloric acid and ferric chloride)
Add 30 g of iron powder (average particle size 1 mm, iron content 88%) to 70 g of ferric chloride (13%, free hydrochloric acid concentration 0.3%), and add 8
The reaction was carried out at 0 ° C for 1 hour. After the ferrous chloride solution having a pH of 2 was filtered to make the first purified solution, the remaining iron powder was
The mixture was reacted with 25 ml of 0% hydrochloric acid at 30 ° C for 15 minutes. After the hydrochloric acid was filtered, the remaining iron powder was reacted with 70 g of an iron chloride solution (having the same composition as above) at 80 ° C. for 1 hour. The ferrous chloride solution having a pH of 2 again was filtered to obtain a second purified solution. Table 2 shows C of the first and second purified liquids.
The r and Ni concentrations are shown. By the washing with hydrochloric acid, the Cr and Ni concentrations were lowered in the second time as well as in the first time.

[0020]

[Table 2]

The first and second purified liquids are combined 153
After reacting 8.1 g of chlorine with gr, a small amount of hydrochloric acid and water were added to 94.5 g of a ferric chloride solution (FeCl ₃ 39
%, HCl 0.2%).

Comparative example

[Table 3] The results of purifying the iron chloride solution under exactly the same conditions as in the example except that the same iron chloride solution and iron powder as those in the example were used and the iron powder was not washed with hydrochloric acid after the first purification were obtained. It shows in Table 3. In the second time, the amount of Ni and Cr removed was reduced by about 60% compared to the first time.

[0023]

According to the method of the present invention, when the impure metal such as nickel contained in the iron chloride solution is deposited and removed by the iron powder, the nickel deposited on the surface of the iron powder is washed away with hydrochloric acid to remove the iron powder. By keeping the activity of the surface and repeating this, the iron chloride solution can be efficiently purified. Further, through the oxidation step, a ferric chloride solution suitable as a coagulation aid for water treatment can be obtained.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an example of the method of the present invention.

FIG. 2 is a graph showing an effect of removing chromium contained in an iron chloride solution of an experimental example by iron powder.

FIG. 3 is a graph showing an effect of removing iron contained in a ferric chloride solution of nickel by an iron powder.

Claims (2)

[Claims] 1. After the impure metal in the iron chloride solution is precipitated and removed by adding iron powder to an iron chloride solution produced by dissolving an iron raw material in a ferric chloride solution and / or hydrochloric acid to cause a reaction. A method for producing a ferric chloride solution, characterized in that the surface of the iron powder is intermittently washed with hydrochloric acid when the purified solution is oxidized to produce a ferric chloride solution. 2. The production method according to claim 1, wherein the impure metal deposited on the surface of the iron powder is nickel.