JP2000178027A - Production of iron (i) polysulfate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production process which enables inhibition of any precipitate from being formed, by utilizing iron carbonate separated from a waste iron salt solution containing iron (II) chloride, such as used iron (III) etching solution. SOLUTION: This production process comprises: supplying a carbonate to a solution consisting essentially of iron (II) chloride to form iron carbonate; separating the formed iron carbonate from the solution by filtration, or the like; adding sulfuric acid to the separated iron carbonate in an amount at least 1.5 times or preferably 1.5-1.8 times as much as the amount of iron carbonate on the molar basis, to oxidize the iron carbonate to form iron (III) sulfate solution from which any precipitate is hardly separated; supplying a small amount of iron carbonate to the iron (III) sulfate solution; and then oxidizing the resulting solution to produce the objective iron (III) polysulfate solution capable of being utilized as a flocculant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing ferric polysulfate which can be used as a coagulant from an iron salt solution such as a ferrous chloride solution or an etching waste solution.

[0002]

2. Description of the Related Art Ferric polysulfate (Fe2 (OH) n (SO4) 3-n / 2), which is known as a flocculant having a water purification effect, contains 0.1 mol of sulfuric acid per mol of ferrous sulfate (FeSO4). Less than 5 moles,
(Preferably 0.35 to 0.45 mol) is known to be obtained by a method of oxidizing the solution.

[0003] By the way, for example, an iron salt waste liquid such as an etching waste liquid after etching a metal plate using a ferric chloride etching solution (FeCl3) contains a large amount of metal salt and a strong acid in the solution. For reasons, it cannot be released as it is. Therefore, waste liquid containing this type of iron salt is discharged after neutralization, etc., but in this case, waste treatment such as neutralization is expensive, so it is one of the effective uses. Reuse as a ferric polysulfate solution, which has been recognized as being useful as a flocculant, is also being studied. For example, JP-A-8-48527 discloses a method for producing a ferric polysulfate solution using a ferric chloride etching waste liquid. In this method, first, ferric (Fe3 +) in the waste liquid is almost completely replaced with ferrous (F3).
e2 +), and in order to remove iron from the processing solution, water-insoluble iron carbonate (FeCO3) is formed, which is filtered off with suction to separate from the waste solution. This iron carbonate is mixed with sulfuric acid and oxidized to obtain ferric polysulfate. These reactions proceed in the following order (1) and (2).

FeCO3 + H2SO4 → FeSO4 + H2O + CO2 ↑ (1) 2FeSO4 + (1-n / 2) H2SO4 + 1 / 2O2 + (n-1) H2O → (Fe2 (OH) n (SO4) 3-n / 2) (2) Mixing of iron carbonate and sulfuric acid is carried out at 1 mol or more and less than 1.5 mol of sulfuric acid per 1 mol of iron carbonate. The reason is that less than 1 mole of sulfuric acid is hardly soluble (Fe2 (OH) n (SO4) 3-n /
2) (n ≧ 1) is produced, and at 1.5 mol or more, ferric sulfate (Fe2 (SO4) 3) is formed and ferric polysulfate (Fe2 (OH) n (SO4) 3) -n / 2) is not generated. Accordingly, in this production method, 1 mol of iron carbonate reacts with 1 mol of sulfuric acid in the step of formula (1), and in the step of formula (2), 0 to 0.5 mol of sulfuric acid reacts with 1 mol of ferrous sulfate. This is the same as the above-described method for producing ferric polysulfate in which ferrous sulfate and sulfuric acid are mixed to perform oxidation.

[0005]

However, FeSO4:
In the oxidation of a solution in which H2SO4 = 1: (0-0.5), a slight change in conditions may cause a slightly soluble substance such as (Fe2
A precipitate of (OH) n (SO4) 3-n / 2) (n ≧ 1) is formed, and the solution becomes a slurry. In the slurry solution, it is difficult to uniformly supply an oxidizing gas into the solution, so that it is difficult to control the oxidation, and the yield of ferric polysulfate is reduced by the amount of the precipitate. Furthermore,
Such a solution also has a problem in that a post-process of filtering a hardly soluble substance is required.

Accordingly, the present invention has been made under such circumstances, and an object of the present invention is to provide a high-yield ferric polysulfate which suppresses generation of a hardly soluble substance capable of forming a precipitate or the like by a simple method. It is intended to provide a method for producing a solution.

Another object of the present invention is to provide a method for producing a ferric polysulfate solution by effectively utilizing iron carbonate, and to effectively regenerate an iron salt waste liquid such as a ferric chloride etching waste liquid. The purpose is to provide a way to use it.

[0008]

The method for producing ferric polysulfate of the present invention comprises a step of mixing an acid solution containing ferric sulfate as a main component with a small amount of iron carbonate, And oxidizing a solution in which a small amount of iron carbonate is mixed with an acid solution as a main component.

The ferric sulfate is preferably produced by itself from the viewpoint of cost. For example, in the case of an iron salt solution obtained by etching iron with ferric chloride, ferric iron in a waste liquid is almost completely converted to ferrous iron in advance. Reducing, and then reacting ferrous chloride in the solution with a carbonate to form iron carbonate, separating the generated iron carbonate from the reaction solution, and adding a mole to the separated iron carbonate. And adding a 1.5-fold to 1.8-fold sulfuric acid in quantity.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention in which a ferric chloride etching waste liquid is used as an example to remove iron in the liquid as ferric polysulfate.
In FIG. 1, the steps up to the production of ferric polysulfate are conveniently divided into four steps, which are steps for reducing ferric chloride etching waste liquid to ferrous iron.
(B) a step of reacting this solution with a carbonate to separate the resulting iron carbonate from the filtrate (b), and mixing the iron carbonate separated in this step (b) with sulfuric acid to obtain ferric sulfate ( Fe2
(C) for producing (SO4) 3) and (d) a step of adding a small amount of iron carbonate to ferric sulfate and oxidizing the solution to obtain ferric polysulfate. FIG. 2 is a detailed explanatory view of the step (c) and the step (d) in FIG. 1. The step (c) is performed separately in the water tank 20 and the step (d) is performed in the water tank 30. However, this is merely a convenient expression, and it goes without saying that, for example, the steps (c) and (d) may be performed in a batch process in the same water tank.

Each of the water tanks 1, 10, 20, and 30 is provided with a stirring means 32, and the water tank 30 is provided with a bubbling device 31 for supplying an oxidizing gas. The oxidizing gas supply means is not limited to the bubbling device 31, and an aspirator or the like for drawing gas into a high-pressure fluid or a high-speed reaction in a high-pressure reaction vessel is also possible. The oxidizing gas is not limited to oxygen, but ozone (O3),
NO2 or the like may be used. Oxidation is also possible with an oxidizing agent aqueous solution, but it is often impossible to use it due to contamination of accompanying impurities. In this case, it is preferable to oxidize using an H2O2 aqueous solution.

Next, each step in FIG. 1 will be described. First, the ferric chloride etching waste liquid is put into the water tank 1 in the step (a). In this waste liquid, ferrous chloride generated by etching and unreacted ferric chloride are mixed. Therefore, in order to make most of the ferric iron in the waste liquid ferrous, an iron material is introduced and the reaction according to the equation (3) is performed.

[0013] Next, this reaction solution is sent to the water tank 10 where carbonate is supplied into the water tank 10 to form iron carbonate insoluble in water.
Precipitates in 0. As the carbonate, various alkali metal and alkaline earth metal carbonates can be used. For example, when 15% by weight of sodium carbonate (Na2CO3) is added so that the pH becomes about 7 to 8 or more, (4) It reacts like a formula.

FeCl 2 + Na 2 CO 3 → FeCO 3 ↓ + 2 NaCl (4) Although not shown in the present invention, for example, sodium hydroxide (NaOH) is supplied into the water tank 10 without supplying the carbonate itself into the water tank 10. Carbon dioxide gas (CO2) may be blown to generate sodium carbonate in the water tank 10, and this also means that carbonate is supplied.

The produced iron carbonate is separated by, for example, suction filtration, and the separated filtrate can be directly passed to a wastewater treatment system. However, salts can be removed by passing through an ion exchange resin or the like.

As shown in FIG. 2C, sulfuric acid (H2SO4) and O2 supplied to the water tank 20 are filtered.
Alternatively, it reacts with H2O2 as in the following formula (5). If the molar ratio of the sulfuric acid supplied at this time is not less than 1 and less than 1.5 times the iron content as in the conventional example, the poorly soluble in the next oxidation step.
Precipitation of (Fe2 (OH) n (SO4) 3-n / 2) (n≥1) occurs. On the other hand, if the amount of sulfuric acid is too large, the iron and unreacted sulfuric acid react with a small amount of iron carbonate supplied in the next oxidation step and change into ferrous sulfate. Preferably, the sulfuric acid has a molar ratio of 1.5 times or more and less than 1.8 times the iron content, and is preferably as close to 1.5 as possible.

[0017]

2FeCO 3 + 3H 2 SO 4 + 1 / 2O 2 → Fe 2 (SO 4) 3 + 3H 2 O + 2CO 2 (5) Thereafter, oxidation is performed as shown in step (d) of FIG. The reaction proceeds as shown in the following formula (6) by reacting a small amount of iron carbonate and an oxidizing gas with the ferric sulfate solution obtained in the step (c). A ferric solution will be obtained.

4 (3-n / 2) Fe2 (SO4) 3 + 4nFeCO3 + nO2 + 6nH2O → 12Fe2 (OH) n (SO4) 3-n / 2 + 4nCO2... (6) According to the above-described embodiment, the process (c) The solution of (2) contains Fe2 (SO4) 3 and excess sulfuric acid, and it can be said that there is a shortage of iron for producing ferric polysulfate.
Therefore, if the reaction of the formula (6) is carried out using the ferric sulfate solution prepared as described above, it is sufficient to add a small amount of iron carbonate to compensate for the insufficient iron content.

For example, in the case of producing ferric polysulfate (Fe2 (OH) (SO4) 2.5) having a basicity of about 17%, it is contained in ferric sulfate as a raw material as in the following formula (7). The iron content equivalent to 1/5 of the iron content (Fe) is changed to iron carbonate (Fe).
It is only necessary to supplement with CO3) and oxidize. In fact, considering that the basicity is around 10%, this ratio further decreases, and about 1/10 of iron carbonate supplementation is sufficient.

5Fe2 (SO4) 3 + 2FeCO3 + 3H2O + 1 / 2O2 → 6Fe2 (OH) (SO4) 2.5 + 2CO2 (7) Thus, in the above-described embodiment, 1.5 times or more by mole of sulfuric acid is first added to iron carbonate. Since ferric sulfate having high solubility is produced, and then a small amount of iron carbonate is mixed with the ferric sulfate and oxidized by, for example, O2, (Fe2 (OH) n (SO4) 3- n / 2) (n ≧ 1) precipitate is hardly formed. That is, theoretically, it is sufficient to react iron carbonate with sulfuric acid in a molar amount of 1.5 times. However, in order to surely obtain ferric sulfate, 1.5 times of sulfuric acid slightly more than 1.5 times is required. It is preferable to supply sulfuric acid up to about 1.8 times, preferably about 1.5 to 1.6 times. For this reason, a small amount of unreacted sulfuric acid remains and reacts with iron carbonate in the next step to produce FeSO4, which is also oxidized to ferric polysulfate. Therefore, a little more iron carbonate is required than the above formula (7). However, the amount is small when viewed from the whole solution,
Ferric polysulfate can be obtained at a high yield, and there is no hindrance to the control of oxidation because the slurry is hardly formed in the step (d).

That is, in the conventional method, the iron carbonate is added in a molar amount of 1 to 1.
Oxidize ferrous sulfate produced by adding 1.5 times sulfuric acid,
In this method, sulfuric acid was used to make up for the insufficient SO4 to make ferric sulfate with respect to ferrous sulfate. However, in the above-described embodiment, the molar amount of sulfuric acid added to iron carbonate was 1.5 times.
To obtain ferric sulfate which does not easily precipitate as more than twice,
Since a small amount of Fe, which is insufficient for ferric sulfate to be ferric sulfate, is supplemented with iron carbonate, an increase in chemical cost can be ignored not only in O2 oxidation but also in H2O2 oxidation. Further, in this method, the iron carbonate obtained in the step (b) can be used also in the step (d), so that this method is also effective.

As described above, the steps (c) and (d) can be efficiently performed by performing the reaction in the same water tank in the batch reaction. The timing of supplying the oxidizing gas is determined based on data measured in advance according to the liquid amount, the concentration and the temperature, or determined by a control device (not shown) or the like. The temperature of the series of steps (c) and (d) is 60 ° C to 10 ° C.
The reaction is carried out at 0 ° C., and the pressure may be normal pressure or pressurization. At the time of pressurization, the reaction is accelerated.

As the ferric sulfate used as a raw material in the step (d), an ore or a commercially available ore can be used in addition to the method of self-production as in the above-described embodiments. The self-made method is advantageous in cost.

By the way, in the steps (c) and (d), the reactions of the equations (5) and (6) proceed, and the concentration of ferrous iron decreases.
In consideration of the case where the oxidation reaction stagnates,
(D) A method using a hydrogen peroxide solution may be employed.
However, since the hydrogen peroxide solution is expensive, it is possible to achieve cost reduction and downsizing of the apparatus by supplying it when the concentration of ferrous iron decreases and the reaction rate starts to slow down.

[0026]

EXAMPLES (Example) Iron powder 55 was added to 1000 g of an etching waste liquid containing 7% by weight of ferrous chloride and 32% by weight of ferric chloride.
g was added and the mixture was reacted by heating. As a result, 1055 g of 42.2% by weight of ferrous chloride was obtained.

After mixing 2480 g of a 15% by weight sodium carbonate solution prepared in advance with this solution, 20 g was further added to adjust the pH to 7.8, and iron carbonate was precipitated. This was separated, washed and dehydrated to obtain 556 g of an iron carbonate cake having a water content of 27%.

548 g of the iron carbonate was added to 60% by weight sulfuric acid 8
Dissolved in 73 g and diluted with water to 2000 g. This solution was vigorously stirred for 24 hours in a jacketed high-speed stirring vessel equipped with a reflux device while flowing O2 gas to obtain 2000 g of a 34.5% by weight solution of ferric sulfate without precipitation. However, the water reduced by evaporation was supplied.

Next, 94 g of the above-mentioned iron carbonate having a water content of 27% was added to this solution, and dissolved by stirring. Then, 50 g of a 35% by weight aqueous hydrogen peroxide solution was gradually added, and almost all of ferrous iron was added. Is oxidized to precipitate without ferric concentration 10.5%, basicity 12
%, PH 1.25, and 2144 g of ferric polysulfate were obtained.

(Comparative Example 1) 350 g of iron carbonate (dry) and 421 g of 95% by weight sulfuric acid were mixed, and water was further added thereto to prepare 1600 g.
g. This solution was oxidized in a jacketed high-speed stirring vessel equipped with a reflux device at 80 ° C. by supplying O 2 gas. The calculated basicity was 10%, and the Fe concentration (Fe 2+ and trace amount of Fe 3+) was increased. Despite being about 10%, precipitation started immediately after the start of the reaction, and this tendency remained the same even after a lapse of time, and precipitation continued. As a result, after 7 hours, the Fe ion concentration (Fe2 + and Fe3 +) in the solution was 6.18%.
Thus, ferric polysulfate having a target Fe3 + concentration of 10% or more could not be obtained. By the way, when the precipitate was examined by X-ray, it was found to be mainly Fe6S4O21.x.
An H2O peak was obtained.

Comparative Example 2 Water was added to 459 g of ferrous sulfate (anhydrous FeSO4 salt) and 110 g of 95% sulfuric acid to obtain 1
The weight was 600 g. When this solution was oxidized under the same apparatus and reaction conditions as in Comparative Example 1, precipitation also occurred as in Comparative Example 1, and the Fe ion concentration in the solution (Fe concentration in the filtrate) was 5. It was reduced to 95%, and the desired concentration of iron polysulfate could not be obtained. The result of X-ray diffraction of the precipitate was the same as that of Comparative Example 1.

[0032]

According to the present invention, the precipitation in the solution can be suppressed as much as possible, so that the load of the post-step of separating the precipitate from the produced ferric polysulfate solution can be reduced, and the polysulfate can be reduced. The acquisition rate of ferrous iron can be increased. Also,
According to another aspect of the present invention, ferric polysulfate is produced using iron carbonate separated from an iron salt waste liquid such as a ferric chloride etching waste liquid, so that an effective waste liquid treatment method can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a step (c) and a step (d) in FIG. 1 in detail.

[Explanation of symbols]

 10, 20, 30 water tank 31 bubbling means 32 stirring means

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shiji Matsuki 1-7 Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture F-term in Tsurumi Soda Co., Ltd. 4D015 BA04 BA10 DA16 4G048 AA07 AB02 AC08 AE01

Claims (3)

[Claims] 1. A method for producing ferric polysulfate, comprising mixing a ferric sulfate solution with a small amount of iron carbonate and oxidizing the mixture. 2. The ferric polysulfate according to claim 1, wherein the ferric sulfate is formed by adding 1.5 to 1.8 times sulfuric acid in a molar amount to iron carbonate. Iron manufacturing method. 3. An iron salt treatment liquid which has been subjected to a treatment for reducing ferric chloride in iron salt waste liquid to ferrous chloride is used, and ferrous chloride contained in the iron salt treatment liquid is converted to carbonic acid. The method according to claim 1, further comprising a step of producing iron carbonate by reacting with a salt, and a step of separating iron carbonate generated by the reaction from the reaction solution, wherein iron carbonate is used as a raw material. 3. The method for producing ferric polysulfate according to item 2.