JP4735359B2 - Treatment method of iron-containing waste liquid - Google Patents

Description

  The present invention relates to a method for treating an iron-containing waste liquid.

In general, in a steel sheet production line, hydrochloric acid pickling is performed before surface treatment to remove iron oxide scales and the like on the surface of the steel sheet. And after this process, in order to wash away hydrochloric acid, the steel sheet is washed with clean water.
Here, a waste liquid containing a large amount of hydrochloric acid and iron is generated from the hydrochloric acid pickling step for performing hydrochloric acid pickling and the rinsing step for washing with clean water. Usually, hydrochloric acid and iron are recovered from the waste liquid, and the remainder is discharged as purified water.

As a conventional method for recovering iron from the waste liquid, there are several methods.
For example, there may be mentioned a method in which an alkaline substance such as slaked lime or caustic soda is added to the waste liquid to precipitate iron present as ions in the waste liquid as water-insoluble hydroxide and then recovered. It is considered that iron is present as divalent or trivalent ions in the waste liquid, and when an alkaline substance is added, a hydroxide insoluble in water is precipitated by the reaction of the following formulas (1) and (2). Conceivable.

Fe ²⁺ + 2OH ⁻ → Fe (OH) ₂ ↓ Formula (1)
Fe ³⁺ + 3OH ⁻ → Fe (OH) ₃ ↓ Formula (2)

  Here, since the pH range in which divalent and trivalent iron ions are precipitated as hydroxides differs according to the above formulas (1) and (2), the pH is adjusted in two stages to cause hydroxide precipitation. In some cases.

Further, in such a method, the waste liquid may be oxidized before adding the alkaline substance.
This is because Fe (OH) ₂ produced by the above formula (1) has a higher solubility in water than Fe (OH) ₃ produced by the above formula (2) and is difficult to separate from the waste liquid. As shown in (3), a divalent iron ion is made trivalent, and then Fe (OH) ₃ hydroxide is precipitated (formula (4)).

Fe ²⁺ + O ₂ → Fe ^{3 +} ... Formula (3)
Fe ³⁺ + 3OH ⁻ → Fe (OH) ₃ ↓ Formula (4)

In such a method, Fe (OH) ₂ having high solubility is hardly generated, and Fe (OH) ₃ is increased, so that the iron recovery rate is increased.
However, Fe (OH) ₃ is very fine particles and has low agglomeration properties and poor sedimentation properties. Therefore, it may not be industrially endurable when recovered as a precipitate.
Therefore, the separation treatment is usually performed after the fine particles of Fe (OH) ₃ are aggregated using an inorganic flocculant or an organic polymer flocculant. For example, processing such as the flow shown in FIG. 2 has been performed.

This FIG. 2 will be described.
In FIG. 2, the waste liquid is oxidized in the first reaction tank 60. Air 62 is blown into the first reaction tank 60, and the oxygen in the air 62 oxidizes divalent iron ions to trivalent. Then, the waste liquid oxidized in the first reaction tank 60 is sent to the second reaction tank 64, where it reacts with an alkaline substance 66 such as slaked lime to produce Fe (OH) ₃ fine particles. And it is sent to the coagulation tank 70, and after adding the coagulant | flocculant 68 and coagulating, it is sent to the thickener 72 and iron content (Fe (OH) ₃ ) is collect | recovered as precipitation here. The supernatant of thickener 72 is discharged after further filtration 74.

By such a method, it is possible to recover iron with relatively high efficiency.
However, in this method, the addition of the flocculant 68 is essential. In addition, there are restrictions on the facilities, such as the need for a coagulation tank 70 and a large thickener 72.

Therefore, the DEFEX method was developed. This method is a method of generating iron oxyhydroxide (FeOOH) by performing neutralization with an alkaline substance while oxidizing divalent iron ions.
Since this iron oxyhydroxide is fine particles having good sedimentation properties, it is not necessary to add a flocculant. Further, this iron oxyhydroxide has a property of being precipitated (co-precipitated) while taking in fine particles of Fe (OH) ₃ (see, for example, Patent Document 1). Therefore, efficient iron content recovery is possible.
This DEFEX method is performed, for example, according to the flow shown in FIG.

This FIG. 3 will be described.
The waste liquid generated from the hydrochloric acid pickling process 80 and the rinsing process 82 is mixed in the mixing tank 84 to become a mixed liquid. Then, an alkaline substance 88 such as slaked lime is added in the second reaction tank 86, and air 90 is further blown. Since the iron oxyhydroxide generated by this treatment is easily precipitated by the thickener 92, it can be easily separated. Further, the thickener 92 may be relatively small.
The supernatant of the thickener 92 is discharged after being further filtered 94.
JP-A-5-310430

As described above, according to the DEFEX method, iron is easily settled without adding a flocculant, so that iron can be efficiently recovered. In addition, there is an advantage in terms of equipment, such as the need for a large thickener.
However, in order to recover the iron content stably by this method, it is necessary that the properties of the waste liquid are always stable, and if this changes, there is a problem that precipitation is difficult to occur and recovery of the iron content becomes difficult. And if you pay attention to any of the various indicators that indicate the properties of the waste liquid, and manage and adjust the indicator so that it falls within the range, it is possible to stably cause precipitation of iron. It was unclear if it could be done.
Accordingly, an object of the present invention is to provide a method for stabilizing the properties of the waste liquid, particularly the components that are important in recovering the iron content contained in the waste liquid, and stably precipitating and recovering the iron content. .

  In the DEFEX method as described above, the present inventor is required to manage the divalent and trivalent iron ion concentrations in order to recover the iron content contained in the waste liquid, so that these concentrations fall within a specific range. As a result of the adjustment, the inventors have found that stable precipitation can be generated and iron can be recovered, leading to the present invention.

That is, the present invention includes the following (a) and (b).
(A) An iron-containing waste liquid treatment method for treating a waste liquid generated from a hydrochloric acid pickling process and a subsequent rinse process in a steel sheet production line, wherein the hydrochloric acid waste liquid generated from the hydrochloric acid pickling process is oxidized and oxidized An iron oxide recovery step for recovering iron and generating hydrogen chloride gas; a hydrochloric acid recovery step for recovering hydrochloric acid by absorbing the hydrogen chloride gas into water and generating exhaust gas; An exhaust gas purification process for generating purified gas; a mixing process for mixing the weak acid waste liquid and the rinse waste liquid generated from the rinse process to obtain a mixed liquid; and measuring the mass concentrations of Fe ²⁺ and Fe ³⁺ in the mixed liquid. , (Fe ²⁺ ) / (Fe ²⁺ + Fe ³⁺ ) ≧ 0.6, Fe ²⁺ is added to the mixed solution to obtain an adjusted waste solution, and the adjusted waste solution is alkali-added. A method for treating an iron-containing waste liquid comprising: an insolubilization process for supplying a substance and oxygen to insolubilize iron in the adjusted waste liquid; and a separation process for separating the iron insolubilized in the insolubilization process from the adjusted waste liquid.
(B) The iron ion concentration adjusting step measures the mass concentration of Fe ²⁺ and Fe ^{3+ in} the mixed solution, and the mixed solution is made to satisfy (Fe ²⁺ ) / (Fe ²⁺ + Fe ³⁺ ) ≧ 0.6. The method for treating an iron-containing waste liquid according to (a) above, wherein the hydrochloric acid waste liquid generated from the hydrochloric acid pickling process is added to obtain a regulated waste liquid.

  According to the present invention, it is possible to provide a method for stabilizing and precipitating and recovering iron components by stabilizing the properties of the waste liquid, particularly components that are important in recovering the iron component contained in the waste liquid.

The processing method of the iron-containing waste liquid of this invention is demonstrated in detail using FIG.
The present invention is a method for treating an iron-containing waste liquid that treats waste liquids (hydrochloric acid waste liquid 20 and rinse waste liquid 32) generated from a hydrochloric acid pickling process 10 and a rinsing process 30 subsequent thereto in a steel sheet production line.
Here, the hydrochloric acid pickling step 10 is a general steel plate surface cleaning treatment performed before performing a surface treatment such as plating in a general steel plate production line, and the iron oxide scale on the surface of the steel plate 1 using hydrochloric acid. It is a process of removing the etc. For example, the process which immerses the steel plate 1 in hydrochloric acid aqueous solution for the specific time is mentioned.
The rinsing step 30 is also a general step performed after the hydrochloric acid pickling step 10, and the steel plate 1 treated with hydrochloric acid in the hydrochloric acid pickling step 10 is washed with clean water and adhered to the surface of the steel plate 1. Wash away any hydrochloric acid that is present.

From the hydrochloric acid pickling process 10 and the rinsing process 30, waste liquids (hydrochloric acid waste liquid 20 and rinsing waste liquid 32) containing hydrochloric acid and iron are generated.
Specifically, the hydrochloric acid pickling step 10 generates a hydrochloric acid waste liquid 20 having a pH similar to that of hydrochloric acid used for cleaning the surface of the steel sheet 1. The hydrochloric acid waste liquid 20 contains iron. The iron may be contained in the form of a scale or the like in the form of particles or lumps, or may be dissolved in the hydrochloric acid waste liquid 20 and contained as divalent or trivalent ions.
Moreover, compared with this, the hydrochloric acid concentration of the rinse waste liquid 32 which is the waste liquid generated from the rinse process 30 is low, and the iron content is relatively low. The presence form of iron is the same as that of the hydrochloric acid waste liquid 20 described above.

  Thus, since the waste liquid generated from the hydrochloric acid pickling process 10 and the rinsing process 30 contains hydrochloric acid and iron, these are usually recovered. Then, hydrochloric acid is usually reused in the hydrochloric acid pickling step 10, and the iron content is reused for other purposes, or is reused as a steelmaking raw material in a steel production line.

  In the present invention, this recovery of hydrochloric acid and iron is performed in an iron oxide recovery step 12, a hydrochloric acid recovery step 14, an exhaust gas purification step 16, a mixing step 40, an iron ion concentration adjustment step 42, which will be described in detail below, This is carried out by an iron-containing waste liquid treatment method comprising an insolubilization step 44 and a separation step 46.

Each step will be described in detail.
<Iron oxide recovery process>
The iron oxide recovery step 12 included in the present invention is a step of generating the hydrogen chloride gas 22 by oxidizing the hydrochloric acid waste liquid 20 generated from the hydrochloric acid pickling step 10 to recover the iron oxide 21.
Here, the method of oxidizing the hydrochloric acid waste liquid 20 is a method in which iron ions contained in the hydrochloric acid waste liquid 20 can be precipitated as iron oxide 21 by bringing the hydrochloric acid waste liquid 20 into contact with a gas containing oxygen. If it is, it will not specifically limit.
For example, the hydrochloric acid waste liquid 20 is blown in the form of a mist in a shaft-type roasting furnace whose inside is about 800 ° C., and air is further blown from the bottom of the roasting furnace. Then, the mist-like hydrochloric acid waste liquid 20 moves from the upper part to the lower part in the roasting furnace, and conversely, the air blown from the bottom part flows from the lower part to the upper part, so the hydrochloric acid waste liquid 20 and the air are moved in the roasting furnace. Oppositely, the hydrochloric acid waste liquid 20 can be oxidized. By such a method, iron ions contained in the hydrochloric acid waste liquid 20 can be precipitated as iron oxide 21. In the case of this roasting furnace, the iron oxide 21 that has become solid can usually be recovered from the bottom of the furnace.

Moreover, hydrogen chloride gas 22 which is a gas containing hydrochloric acid is generated by performing such oxidation treatment. For example, when the above-described roasting furnace is used, hydrogen chloride gas 22 is generated from the upper part of the roasting furnace.
The hydrogen chloride gas 22 is treated in the next hydrochloric acid recovery step 14 to recover hydrochloric acid.

<Hydrochloric acid recovery process>
The hydrochloric acid recovery step 14 provided by the present invention is a step of absorbing the hydrogen chloride gas 22 generated from the iron oxide recovery step 12 as described above into the water 27 and recovering the hydrochloric acid 23 as an aqueous hydrochloric acid solution to generate the exhaust gas 24. is there.
Here, the method of absorbing the hydrogen chloride gas 22 into the water 27 is not particularly limited as long as it can be recovered as an aqueous hydrochloric acid solution in which hydrochloric acid is dissolved by bringing the hydrogen chloride gas 22 into contact with the water 27.
For example, in a tower type absorption tower, for example, water 27 such as industrial water is blown in the form of a mist, for example, from the top, and hydrogen chloride gas 22 is blown from the bottom of the absorption tower. Then, the mist-like water 27 moves from the upper part to the lower part in the absorption tower, and conversely, the hydrogen chloride gas 22 blown from the bottom part flows from the lower part to the upper part. Therefore, the water 27 and the hydrogen chloride gas inside the absorption tower. The hydrogen chloride gas 22 is dissolved in the water 27 so that the hydrochloric acid aqueous solution can be obtained. When such treatment is performed, an aqueous hydrochloric acid solution accumulates at the bottom of the absorption tower, so that the hydrochloric acid 23 can be recovered. The hydrochloric acid 23 can be reused, for example, in the hydrochloric acid pickling step 10.

Further, exhaust gas 24 is generated by performing such treatment. For example, if the above absorption tower is used, exhaust gas 24 is generated from the upper part of the absorption tower.
The exhaust gas 24 is processed in the next exhaust gas purification step 16.

<Exhaust gas purification process>
The exhaust gas purification step 16 included in the present invention is a step of cleaning the exhaust gas 24 generated from the hydrochloric acid recovery step 14 as described above to generate a weak acid waste liquid 26 and a purified gas 25.
Here, the exhaust gas 24 is washed by bringing the exhaust gas 24 into contact with a liquid 28 such as water to dissolve hydrochloric acid contained in the exhaust gas 24 into the liquid 28, separating hydrochloric acid from the exhaust gas 24, and If it is the method which can be set as the gas (purified gas 25) which can be diffused in this, it will not specifically limit.
For example, in a tower-type washing tower, for example, a liquid 28 such as industrial water is blown in, for example, in the form of a mist from the top, and further, exhaust gas 24 is blown from the bottom of the washing tower. Then, the mist-like liquid 28 moves from the upper part to the lower part in the cleaning tower, and conversely, the exhaust gas 24 blown from the bottom part flows from the lower part to the upper part, so that the liquid 28 and the exhaust gas 24 face each other inside the cleaning tower. Thus, the weak acid waste liquid 26 can be obtained by dissolving hydrochloric acid in the exhaust gas 24 in the liquid 28. When such treatment is performed, a weak acid waste liquid 26 having a pH of about 2.0 to 3.5 is accumulated at the bottom of the cleaning tower. The weak acid waste liquid 26 is sent to the next mixing step 40 for processing. Further, purified gas 25 is generated from the upper part of the cleaning tower. Since this purified gas 25 usually has a hydrochloric acid content of about 5 ppm or less, it can be diffused into the atmosphere.

<Mixing process>
The mixing step 40 included in the present invention is a step of obtaining the mixed solution 50 by mixing the weak acid waste solution 26 and the rinse waste solution 32 generated from the rinse step 30.
Here, the method of mixing the weak acid waste liquid 26 and the rinse waste liquid 32 is not particularly limited. For example, a method of charging them together in one mixing tank and mixing them by stirring as necessary.

<Iron ion concentration adjustment process>
In the iron ion concentration adjusting step 42 included in the present invention, the mass concentration of Fe ²⁺ and Fe ³⁺ in the mixed solution 50 is measured, and the mixed solution is satisfied so as to satisfy (Fe ²⁺ ) / (Fe ²⁺ + Fe ³⁺ ) ≧ 0.6. In this step, Fe ²⁺ is added to 50 to obtain the adjusted waste liquid 52.
Here, the mass concentration of Fe ²⁺ and Fe ³⁺ contained in the mixed solution 50 is measured by an atomic absorption method, an ICP emission analysis method, a potentiometric titration method, a photometric titration method, or a combination method thereof.
Here, in the mixing step 40, a detector capable of continuously measuring the concentrations of Fe ²⁺ and Fe ^{3+ by} the above method is installed, and these concentrations in the mixed solution 50 are continuously monitored. Is preferred. This is because the concentration can be adjusted quickly in response to these changes in concentration, and the iron recovery rate can be maintained at a high level.

Then, (Fe ²⁺ ) / (Fe ²⁺ + Fe ³⁺ ) is calculated from the measurement result, and Fe ²⁺ is added so that this value becomes 0.6 or more, thereby obtaining the adjusted waste liquid 52. Therefore, when this value is less than 0.6, Fe ²⁺ may not be added. As a result of measuring the concentrations of Fe ²⁺ and Fe ³⁺ as described above, the mixed liquid 50 in which Fe ²⁺ was not added because this value was 0.6 or more is regarded as the adjusted waste liquid 52.
Further, here, the value of (Fe ²⁺ ) / (Fe ²⁺ + Fe ³⁺ ) is preferably 0.6 to 1.0, and more preferably 0.7 to 1.0. Thus, even if this value is 0.6 or more, Fe ²⁺ may be added. Such a range is preferable because the separation efficiency of iron 54 in the separation step 46 described later is higher.

Moreover, the method of adding Fe ^<2+> here is not specifically limited, For example, the method of adding the aqueous solution containing Fe ^<2+> suitably is mentioned.
Moreover, it is preferable to use the hydrochloric acid waste liquid 20 generated from the hydrochloric acid pickling step 10 as the aqueous solution containing Fe ²⁺ .
In other words, the iron ion concentration adjusting step 42 measures the mass concentration of Fe ²⁺ and Fe ³⁺ in the mixed solution 50 and adds hydrochloric acid to the mixed solution 50 so as to satisfy (Fe ²⁺ ) / (Fe ²⁺ + Fe ³⁺ ) ≧ 0.6. It is preferable that the hydrochloric acid waste liquid 20 generated from the pickling process 10 is added to obtain the adjusted waste liquid 52.
Usually, the hydrochloric acid waste liquid 20 has a higher Fe ²⁺ content than the mixed liquid 50. Therefore, when the hydrochloric acid waste liquid 20 is added to the mixed solution 50, the concentration of Fe ²⁺ can be adjusted to be increased.

<Insolubilization process>
The insolubilization step 44 provided by the present invention is a step of supplying the alkaline substance 53 and oxygen 55 to the adjusted waste liquid 52 to insolubilize iron in the adjusted waste liquid 52.
Here, the type and addition method of the alkaline substance 53 are not particularly limited. Examples of the alkaline substance include sodium hydroxide, potassium hydroxide, and ammonia. And what is necessary is just to add these to the adjustment waste liquid 52 by the well-known method, for example in the solid form or the aqueous solution which melt | dissolved these.
Further, the method for supplying the oxygen 55 to the adjusted waste liquid 52 is not limited. For example, it may be blown into the prepared waste liquid 52 by a known method. The oxygen 55 is oxygen or an oxygen-containing gas (for example, air).

By adding the alkaline substance 53 while supplying the oxygen 55 to the prepared waste liquid 52 by such a method, it is possible to suppress a decrease in pH of the adjusted waste liquid 52 due to oxygen oxidation, which is a process in the insolubilization process. Moreover, pH can be adjusted arbitrarily. By such a method, Fe ²⁺ in the adjusted waste liquid 52 is oxidized and precipitated into iron oxyhydroxide (FeOOH), and at the same time, Fe ³⁺ can be generated as a hydroxide and efficiently coagulated and precipitated.

<Separation process>
The separation step 46 included in the present invention is a step of separating the iron component 54 insolubilized in the insolubilization step 44 from the adjusted waste liquid 52.
The method for separating the iron content 54 from the adjusted waste liquid 52 is not particularly limited. Since the iron component 54 insolubilized in the insolubilization step 44 is relatively agglomerated as described above, it can be separated by a relatively simple method such as gravity sedimentation.
For example, a method of separating the iron component 54 by separating a large portion of the iron component 54 by a gravity settling method using a thickener and then filtering the supernatant with a filter is preferable.
The remaining portion 56 after the iron component 54 is separated from the adjusted waste liquid 52 by such a separation step 46 is normally discharged.

Examples of the present invention are shown below, but the present invention is not limited thereto.
A 10% by mass hydrochloric acid aqueous solution was filled with 5 times the theoretical consumption scrap (cold rolled steel plate scraps generated in the steelworks), heated to 70 ° C., and stirred for 1 hour. Then, the scrap was taken out from the beaker. While diluting the solution so that the pH is 1.0, 2.0, 2.5, 3.0, or 3.5, and warming to either 70 ° C. or 90 ° C., 1. Stirring while blowing air for either 0, 2.5 or 4.0 hours.
The aqueous hydrochloric acid solution subjected to such treatment is hereinafter referred to as a treatment solution.
Next, the concentration of Fe ²⁺ and Fe ^{3+ in} each treatment solution was measured. As a result, the value of (Fe ²⁺ ) / (Fe ²⁺ + Fe ³⁺ ) of each treatment liquid was any value of 0.4 to 0.75.

  Next, an equivalent amount of sodium hydroxide was added to each treatment solution (1 liter), and air was blown simultaneously. And it stirred for further 30 minutes after that.

After performing such a treatment, it was allowed to stand indoors for 20 minutes, and each beaker was visually observed.
As a result, in the case of a treatment liquid having a value of (Fe ²⁺ ) / (Fe ²⁺ + Fe ³⁺ ) of 0.6 or more, precipitation occurred and it was clearly separated from the supernatant liquid.
On the other hand, in the case of the treatment liquid of less than 0.6, the whole liquid was cloudy, and the precipitate and the supernatant liquid were not clearly separated as in the case of 0.6 or more.

FIG. 1 is a flowchart showing a method for recovering iron from the waste liquid of the present invention. FIG. 2 is a flowchart showing a conventional iron recovery method from waste liquid. FIG. 3 is a flow chart showing another iron recovery method from the conventional waste liquid.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel plate 10 Hydrochloric acid pickling process 12 Iron oxide recovery process 14 Hydrochloric acid recovery process 16 Exhaust gas cleaning process 20 Hydrochloric acid waste liquid 21 Iron oxide 22 Hydrogen chloride gas 23 Hydrochloric acid 24 Exhaust gas 25 Purified gas 26 Weak acid waste liquid 27 Water 28 Liquid 30 Rinse process liquid 32 Rinse waste liquid 40 Mixing Process 42 Iron Ion Concentration Adjusting Process 44 Insolubilization Process 46 Separation Process 50 Mixture 52 Adjusted Waste Liquid 53 Alkaline Substance 54 Iron Content 55 Oxygen 56 Remaining 60 First Reaction Tank 62 Air 64 Second Reaction Tank 66 Alkaline Substance 68 Flocculant 70 Aggregation Tank 72 Thickener 74 Filtration treatment 80 Pickling process 82 Rinse process 84 Mixing tank 85 First reaction tank 86 Second reaction tank 88 Alkaline substance 90 Air 92 Thickener 94 Filtration

Claims (2)

A method for treating a waste liquid containing iron for treating a waste liquid generated from a hydrochloric acid pickling process and a rinsing process subsequent to the pickling process in a steel sheet production line,
An oxidation treatment of the hydrochloric acid waste solution generated from the hydrochloric acid pickling step to recover iron oxide, and an iron oxide recovery step to generate hydrogen chloride gas;
A hydrochloric acid recovery step of absorbing the hydrogen chloride gas into water to recover hydrochloric acid and generating exhaust gas;
An exhaust gas purification step for washing the exhaust gas to generate weak acid waste liquid and purified gas;
A mixing step of mixing the weak acid waste solution and the rinse waste solution generated from the rinse step to obtain a mixed solution;
Iron to obtain adjusted waste liquid by measuring mass concentrations of Fe ²⁺ and Fe ^{3+ in} the mixed solution and adding Fe ²⁺ to the mixed solution so as to satisfy (Fe ²⁺ ) / (Fe ²⁺ + Fe ³⁺ ) ≧ 0.6 An ion concentration adjustment step;
An insolubilization step of supplying an alkaline substance and oxygen to the adjusted waste liquid to insolubilize iron in the adjusted waste liquid;
A method for treating an iron-containing waste liquid comprising: a separation step of separating the iron component insolubilized in the insolubilization step from the adjusted waste liquid. In the iron ion concentration adjusting step, the mass concentration of Fe ²⁺ and Fe ³⁺ in the mixed solution is measured, and the hydrochloric acid is added to the mixed solution so as to satisfy (Fe ²⁺ ) / (Fe ²⁺ + Fe ³⁺ ) ≧ 0.6. The processing method of the iron containing waste liquid of Claim 1 which is the process of adding the hydrochloric acid waste liquid generated from a washing process, and obtaining adjustment waste liquid.

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