JP4947640B2 - Waste acid solution treatment method - Google Patents

Description

  The present invention relates to a processing method and a processing apparatus for an iron-containing waste acid solution for treating waste hydrochloric acid discharged from various processing facilities of a steel manufacturing plant as a mixed waste acid solution, and in particular, a mixing amount / mixing amount ratio of a waste acid solution. Thus, it is possible to appropriately cope with changes in the liquid composition such as pH value and iron concentration and the change in the processing amount due to fluctuations in the amount, and to maintain an efficient and stable treatment.

  In a steel manufacturing plant, for example, in a pickling treatment line that dissolves and removes oxidized scale on the surface of a steel strip, high-pH waste hydrochloric acid containing iron at a high concentration is generated, and chromium-based waste acid solution is generated from the plating line. . In the premises of the steel manufacturing plant, waste acid treatment equipment for treating these waste acid solutions is attached to each line, and waste acid solution generated from each facility is collected and mixed waste acid solution. It is common to have a mixed waste acid treatment apparatus that treats as a liquid.

  An example is shown in FIG. A is a pickling processing equipment section, B is a plating processing equipment section, C is a pickling steel strip rinsing processing equipment section, and E is a mixed waste acid solution processing apparatus. In the pickling treatment equipment section (A), the waste hydrochloric acid discharged from the pickling line (a1) is introduced into the waste hydrochloric acid treatment equipment (a2), and subjected to, for example, spray roasting treatment to separate iron and remove hydrochloric acid. Regeneration and collection are performed. The regenerated and recovered hydrochloric acid is circulated and supplied to the pickling line, and the iron content (iron oxide powder) is reused as iron resources such as ferrite raw materials. In this pickling treatment facility (A), if a large amount of waste hydrochloric acid exceeding the treatment capacity of the waste hydrochloric acid treatment equipment (a2) is generated due to changes in the line operation status, a part of the generated waste hydrochloric acid is mixed waste acid solution. It is sent to the processing device (E). In addition, the treated water discharged from the plating line (b1) of the plating treatment equipment section (B) and passed through the chromium waste acid treatment equipment (b2), the rinse waste liquid of the pickling steel strip rinse treatment equipment section (C), and others Waste acid liquid generated in various treatment facilities (D) in which the acid liquid is used is introduced into the mixed waste acid treatment apparatus (E).

  Various waste acid solutions sent from various locations in the factory to the mixed waste acid solution processing apparatus (E) are uniformly mixed and subjected to a predetermined treatment. According to the neutralization-aggregation-precipitation method, which is one of the typical methods of waste acid solution treatment, the mixed waste acid solution produces a reaction product containing iron and the like by adding a neutralizer and adjusting the pH. Then, a treatment such as agglomeration / precipitation of the reaction product and separation of the precipitate (aggregated sludge sludge) is performed. The separated sludge is dehydrated and subjected to a predetermined iron recovery process, while the treatment liquid (supernatant) from which the precipitate has been separated is subjected to hydrochloric acid regeneration treatment, etc. It is discharged through a predetermined process such as monitoring.

Various proposals have been made for the treatment of the waste acid solution as follows.
(a) By adjusting the pH by adding sodium hydroxide to waste hydrochloric acid, ferrous chloride [FeCl ₂ ] in the liquid is converted to ferrous hydroxide [Fe (OH) ₂ ], and further hydroxylated. Ferrous oxide is converted into ferric oxide [Fe ₂ O ₃ ] by supplying oxygen, and then separated and recovered from the liquid by a magnetic separator (Patent Document 1).
(b) After mixing step of mixing sulfuric acid with waste acid solution containing metal ions (Fe ions, etc.), neutralize by adding calcium hydroxide to mixed waste acid, and slurry generated by neutralization reaction Take out as. A part of the taken-out slurry is returned to the mixing step, and the remainder is dehydrated with a filter press type dehydrator to collect the metal content together with gypsum particles (Patent Document 2).
(c) Mill scale and iron powder (or particles) are added to waste hydrochloric acid containing iron at a predetermined ratio, and further, iron powder (or particles) is added while blowing air to adjust the pH. Next, the impurities in the liquid are separated and removed as insolubilized substances by cooling the waste hydrochloric acid, adding a flocculant, etc. (Patent Document 3).

(d) Concentrate the waste hydrochloric acid, remove silica from the concentrate (coagulation precipitation separation with a flocculant), and then concentrate the ferric oxide [Fe ₂ O ₃ ] and hydrogen chloride gas [HCl] in a roasting furnace And pyrolyzed (4FeCl ₂ + 4H ₂ O + O ₂ → 2Fe ₂ O ₃ + 8HCl) and recovered respectively. The recovery rate of iron oxide and hydrochloric acid is increased by subjecting part or all of the silica agglomerated precipitate produced in the silica removal step to filtration treatment to separate the silica floc and then refluxing it to the concentrate line. (Patent Document 4).
(e) Iron (or iron compound) is brought into contact with waste hydrochloric acid to adjust the pH by neutralizing the free base, and further adjusted with alkali treatment while contacting with oxygen (or air, etc.). In this first stage treatment, ferric ions in the liquid are completely consumed (Fe ⁺³ + 1 / 2Fe → Fe ⁺² ). Also, part of the iron in the liquid is precipitated as hydrous ferric oxide [FeOOH] and ferric hydroxide [Fe (OH) ₃ ] by oxygen blowing, and impurities (Si, Al, P, etc.) are coprecipitated.・ Separated by adsorption. The ferrous chloride solution after the first stage treatment is subjected to a second stage treatment consisting of addition of an oxidizing agent (hydrogen peroxide, white powder, etc.) and alkali addition (pH adjustment). The ferrous chloride solution becomes a ferric chloride solution by adding an oxidizing agent, and ferric hydroxide [Fe (OH) ₃ ] produced by pH adjustment is separated and collected from the solution as a precipitate (Patent Document 5). .
JP 2004-123530 A JP 2002-292374 A JP-A-10-152788 JP 08-133743 A Japanese Patent Laid-Open No. 07-165427

The composition (pH value, iron concentration, etc.) of the waste acid solution generated from each facility in the steel manufacturing plant varies, and the amount of each generated varies depending on the operating status of each facility. Therefore, in the mixed waste acid solution processing apparatus (E) in which these waste acid solutions are accommodated, the composition of the mixed waste acid solution and the amount of waste acid solution discharged from each facility and the change in the mixing amount ratio The amount of processing varies. In the treatment by the “neutralization-aggregation-precipitation” method, appropriate treatment conditions corresponding to fluctuations in the composition of the mixed waste acid solution and the treatment amount are ensured so that the required neutralization reaction is sufficiently achieved. There must be. If it is sent to the next process with insufficient neutralization reaction, the recovery efficiency of hydrochloric acid and iron will be impaired, and environmental pollution will be caused by unreacted substances contained in the waste liquid discharged after the treatment. become. However, when the variation of the composition of the waste acid solution and the processing amount increases, it becomes difficult to appropriately cope with the variation, and the above-described problems are likely to occur.
The present invention has been made in view of the above, and requires a large-scale modification such as expansion of facilities and increase of a processing tank capacity in a situation where the composition and processing amount of the mixed waste acid solution greatly fluctuate. In addition, the present invention provides a waste acid solution processing method and apparatus that can ensure the treatment conditions necessary for the completion of the neutralization reaction with relatively simple measures and can efficiently treat the waste acid solution.

The waste acid solution processing method according to the present invention (Claim 1)
A waste acid solution mixing process that contains and mixes various types of waste hydrochloric acid generated from steel manufacturing plants, a pH adjustment process that adds a neutralizing agent to the mixed waste acid solution, and precipitates iron in the solution as ferric hydroxide, agglomeration In the treatment method of iron-containing waste hydrochloric acid having a coagulation step of coagulating ferric hydroxide by adding an agent, and a sludge separation step of separating the coagulated sludge from the waste acid solution, in the pH adjustment step of the mixed waste acid solution, Air is blown into the bath liquid to maintain the dissolved oxygen concentration at 2 ppm or higher, and by adding a neutralizing agent to adjust the pH of the bath liquid to 8 or higher, almost the total amount of ferrous ions in the liquid is water. It is characterized by conversion to ferric oxide.
As the neutralizing agent, calcium hydroxide [Ca (OH) ₂ ] is preferably used (Claim 2).

In the neutralization step of the mixed waste acid solution, iron (Fe ²⁺ ) in the solution is converted to ferric hydroxide [Fe (OH) ₃ ] by a neutralization reaction of the following formula.
FeCl ₂ + Ca (OH) ₂ + 1 / 2O ₂ → Fe (OH) ₃ + CaCl ₂ ... [1]
This reaction [1] proceeds in the following two steps.
Fe ²⁺ + 2OH ⁻ → Fe (OH) ₂ ... [11]
2Fe (OH) ₂ + 1 / 2O ₂ + H ₂ O → 2Fe (OH) ₃ ... [12]

In order to convert the total amount of iron in the waste acid solution to ferric hydroxide [Fe (OH) ₃ ], in addition to the neutralizing agent commensurate with the iron concentration in the solution as described above, I need. Since the mixing and stirring are usually performed in the waste acid solution mixing tank, the mixed waste acid solution sent to the pH adjustment step contains about several ppm of dissolved oxygen (for example, 5 to 6 ppm) as an aeration effect by stirring. For this reason, when the iron content concentration of the mixed waste acid solution is relatively low, the oxygen necessary for the reaction [12] can be provided by the amount of dissolved oxygen. However, when the concentration of iron in the liquid rapidly increases due to a change in the state of inflow of the waste acid solution in the mixing tank, the neutralization reaction cannot be achieved. In the present invention, air is blown (supplement of dissolved oxygen) in the pH adjustment step for this point, thereby ensuring a necessary dissolved oxygen amount with respect to fluctuations in the composition of the mixed waste acid solution, and the neutralization reaction. This makes it possible to prevent reduction in the recovery efficiency of hydrochloric acid and iron, and to prevent environmental pollution (by discharging waste liquid containing unreacted substances).

FIG. 1 shows a flowchart of the waste acid solution treatment method of the present invention. The pickling treatment equipment section (A), the plating treatment equipment section (B), the pickling steel strip rinse treatment equipment section (C), etc. in the figure are the same as those in FIG. Waste hydrochloric acid from the pickling treatment equipment section (A) (pH value: about 1 or less, usually around 0.1), treated water discharged from the plating treatment equipment section (B) (pH value: about 7 to 8), acid The waste acid solution (pH value: usually about 2 to 4) in the rinsing section (C) of the steel washing zone and the waste acid solution discharged from the other various processing facilities (D) are mixed waste acid treatment equipment (E ) And collected in the mixing tank (1).
The waste acid solution collected in the mixing tank (1) is made uniform by a stirring and mixing action by a mixing means (for example, a stirring pump). In addition to homogenizing the liquid composition, the amount of dissolved oxygen in the liquid is increased as an aeration effect by the stirring treatment. Although depending on the stirring conditions, the amount of dissolved oxygen is several ppm (about 5 to 6 ppm).

  The waste acid solution uniformly mixed in the mixing tank (1) is sent to the pH adjusting tank (2). The pH adjusting tank (2) in the figure shows an example of a two-stage configuration having a preceding tank (No. 1 pH adjusting tank) (21) and a succeeding tank (No. 2 pH adjusting tank) (22). In addition to the neutralizer addition device (not shown), the pH adjusting tank (2) is provided with an air blowing device. As shown in FIG. 2, for example, the air blowing device is configured as an ejector (9) including an air blower (91) and a liquid circulation pump (92). The liquid circulation pump (92) pumps up the treatment liquid (waste acid liquid) in the tank and supplies it to the ejector as driving water for air drawing. The air fed by the air blower (91) is mixed with the treatment liquid by the ejector (9) and discharged. In the figure, ejectors (9) are horizontally arranged in two directions at the corners of the bottom of the tank, and the air supplied from each ejector (9) is uniformly distributed throughout the tank by the stirring action of the stirrer (8). I'm trying to make it spread.

  In FIG. 1, air is blown into the waste acid solution in the pH adjusting tank (2) in both the first and second tanks (21) and (22), but this is not necessarily the case. However, depending on the iron concentration of the waste hydrochloric acid, the capacity of the air blowing device (ejector 9), etc., air blowing is carried out only to one (for example, the pH adjusting tank 22 in the latter stage), and the other It is also possible to adopt a configuration in which air blowing in the (preceding pH adjusting tank 21) is omitted.

In the pH adjusting tank (2), by adding an appropriate amount of a neutralizing agent according to the composition of the mixed waste acid solution, the reaction [Fe ²⁺ + 2OH ⁻ → Fe (OH) ₂ ] represented by the above formula [11] The total amount of iron ions in the liquid is converted to ferrous hydroxide [Fe (OH) ₂ ], and in the presence of a sufficient amount of dissolved oxygen by air blowing, the reaction [12] 2Fe (OH) ₂ + 1 / 2O ₂ + H ₂ O → 2Fe (OH) ₃ ] proceeds, and the total amount of ferrous hydroxide in the liquid is converted to ferric hydroxide.

The type of neutralizing agent used for the neutralization reaction is not particularly limited, but calcium hydroxide [Ca (OH) ₂ ] is preferably used in terms of reactivity, ease of handling, transportability, and price. Is done. Sodium hydroxide (NaOH) can also be used, but in this case, Na ions remain in the recovered iron, which is not preferable when iron is reused as a ferrite raw material, and therefore sodium hydroxide is used. Should be kept in a small amount of auxiliary use.

The addition amount of the neutralizing agent is preferably adjusted so that the pH value of the treatment liquid is about 8-9. This is to reduce the solubility of ferric hydroxide [Fe (OH) ₃ ] produced in the reaction [12] in the liquid to promote crystallization from the liquid and increase the separation efficiency by coagulation precipitation.
In addition, air blowing for replenishing the amount of dissolved oxygen in the liquid is desirably adjusted so that the amount of dissolved oxygen is maintained at about 2 ppm or more in order to efficiently advance the reaction [12].
Under a condition in which a sufficient amount of dissolved oxygen is ensured, the above reaction [12] (Fe ²⁺ → Fe ³⁺ ) proceeds instantaneously, and the solution after the reaction is reddish brown. When the amount of dissolved oxygen in the solution is insufficient and the reaction [12] is insufficient, the treatment solution exhibits a green color due to Fe ^2+, so the appropriateness of the dissolved oxygen amount is visually observed by the color of the treatment solution. be able to.

After completing the neutralization treatment in the pH adjustment tank (2), the treatment liquid (waste hydrochloric acid) is introduced into the coagulation tank (3), and an aggregating agent (for example, acrylamide polymer) is added to ferric hydroxide. Aggregate [Fe (OH) ₃ ]. Then, the treatment liquid is sent to the settling tank (4) to separate and discharge the aggregated sludge precipitate (sludge). A part of the sludge separated and discharged from the settling tank (4) is returned to the pH adjusting tank (2) through the circuit (5) if desired. Thereby, ferric hydroxide [Fe (OH) ₃ ] is changed to iron oxyhydroxide [FeOOH]. Circulating sludge in this way to form iron oxyhydroxide is effective for improving the efficiency of dehydration efficiency and separating and recovering iron from the liquid.

The precipitate of the coagulated sludge (including iron oxyhydroxide) separated from the treatment liquid is further concentrated with a sludge thickener (6), and then subjected to pressure dehydration with a dehydrator (7). The cake containing iron that has been pressure-dehydrated is useful as a raw material for, for example, an aggregate blended with cement or an aggregate of non-shrinkable mortar.
On the other hand, the supernatant liquid from which the coagulated sludge has been separated is sent out from the sedimentation tank, and is then subjected to final neutralization treatment with other treated water, liquid temperature adjustment in the cooling tower, monitoring of oil content, turbidity, pH, COD, etc. It is released after that.

Next, test results obtained by performing the waste hydrochloric acid treatment of the present invention in the waste hydrochloric acid treatment apparatus having the configuration shown in FIGS. 1 and 2 will be described.
[1] Equipment
(1) Mixing tank 1: Tank capacity 200m ³ Stirring pump (11)
(2) pH adjustment tank 2
・ Capacity of pH adjustment tank: No.1 pH adjustment tank (21) ... 50m ³ No.2 pH adjustment tank (22) ... 50m ³
・ Air supply device 9: Two ejectors installed in No. 2 pH adjustment tank (22) Air blower 91… 5.0 m ³ / min / unit Liquid circulation pump 92… 0.7 m ³ / min / unit

[2] Properties of waste hydrochloric acid to be treated Rinse waste liquid (pH: 2 to 4) discharged from the pickling steel strip rinsing equipment section (C) (rinsing liquid is industrial water) is used as the main treatment liquid. Waste hydrochloric acid (pH: about 0.1) from the treatment equipment section (A) is mixed to obtain a waste acid solution to be treated. The amount of waste hydrochloric acid is 4.0m ³ / day on the first day of the test, and 4.5m ³ / day, 5.2m ³ / day, 6.0m ³ / day, and 7.0m ³ / day from the second day. Increased the amount.
In addition, the supply capacity of the neutralizing agent in the pH adjusting tank (2) has a sufficient supply capacity that can cover the supply amount that can cope with the increase of the waste hydrochloric acid.

[3] Waste hydrochloric acid treatment results Fig. 3 shows the results of measurement of dissolved oxygen content (ppm) in the treatment liquid in the mixing tank (1) and pH adjustment tank (2) in the above treatment test. The concentration of iron (Fe ²⁺ ) The measurement results are shown in FIG.

In FIG. 3, the leftmost plot in the figure shows the case of treatment of the rinse waste liquid (pH: 2 to 4) (no air blowing in No. 2 pH adjustment tank 22), and the graph on the right side is mixed with waste hydrochloric acid. The cases where the high pH treatment liquid (mixed amount of waste hydrochloric acid increases toward the right side of the figure) treated under air blowing conditions are respectively shown.
In the figure, as shown in the leftmost plot, when there is no air blowing, the amount of dissolved oxygen in the No. 2 pH adjustment tank (22) is almost zero. This means that even if the treatment solution is a dilute rinse waste solution containing hydrochloric acid or iron, almost all of the dissolved oxygen in the solution is consumed in the neutralization reaction [12]. This suggests that when high-concentration waste hydrochloric acid is mixed with the waste liquid, the amount of dissolved oxygen required for the neutralization reaction [12] will be deficient. On the other hand, by performing air blowing in the No. 2 pH adjustment tank (22), as shown in the graph on the right side, even when processing mixed waste acid (including high concentration waste hydrochloric acid) In addition, a sufficient amount of dissolved oxygen (about 2 ppm or more) for achieving the neutralization reaction [12] can be maintained.

As shown in FIG. 4, when high concentration waste hydrochloric acid is mixed, ferrous ions (Fe ²⁺ ) increase in the mixing tank (1) as the mixing amount increases. By performing appropriate air blowing (oxygen replenishment), the detected amount of ferrous ions (Fe ²⁺ ) in the pH adjusting tank (2) becomes almost zero. This reaction [12] is fully achieved by the air supply, indicates that the total amount of the ferrous hydroxide [Fe (OH) _2] was converted to ferric hydroxide [Fe (OH) _3] ing.
In the figure, the detected amount of ferrous ions (Fe ²⁺ ) in the pH adjustment tank in the leftmost plot (without air supply) is zero. This is because the treatment liquid is rinse waste liquid (both pH and iron concentration). If high concentration waste hydrochloric acid is mixed with this, the reaction [12] cannot proceed sufficiently due to the lack of oxygen, and the ferrous ion (Fe ²⁺ ) It is clear that a large amount of residue is detected.

By carrying out air supply in the pH adjustment tank as described above, the neutralization reaction [1] can be sufficiently achieved, and the total amount of iron in the liquid can be almost completely converted to ferric hydroxide, It becomes possible to efficiently collect iron. In addition, when a part of ferrous ion (Fe ²⁺ ) remains due to a shortage of dissolved oxygen in the liquid, the first hydroxylation in the wastewater discharged through the subsequent treatment process. Iron reacts with oxygen in the seawater and oxidizes to ferric hydroxide, causing environmental pollution of red water generation. According to the present invention, such inconvenience is avoided by achieving the neutralization reaction [1].

In the above-mentioned waste acid treatment test, the maximum increase in waste hydrochloric acid to be mixed is 7 m ³ / day, but even in the treatment conditions in which this was further increased, the amount of air blown by the ejector (9) (oxygen) The neutralization reaction [1] of iron in the liquid can be achieved by adjusting the replenishment amount). The air blowing in the above embodiment is carried out in the No. 2 pH adjustment tank (22). However, if there is concern about liquid level swell and overflow with the increase in blowing, the ejector (9) should be set to No. .2 The above concerns can be alleviated by placing in the pH adjustment tank (22) and the No.1 pH adjustment tank (21) and changing the number of ejector units appropriately according to the composition of the mixed waste acid and its treatment status. .

According to the present invention, it becomes possible to quickly and appropriately cope with large fluctuations in the composition and processing amount of the mixed waste acid solution, to efficiently achieve the required neutralization reaction, and to separate and recover the iron content in the solution. The advanced purification treatment effect of the waste acid solution can be stably maintained. Therefore, the problem of environmental pollution (red water generation) due to insufficient neutralization reaction is also solved.
The present invention attaches an air blowing device to the mixed waste acid neutralization treatment step, and performs air blowing to replenish the amount of dissolved oxygen in the liquid in accordance with variations in the composition of the treatment liquid and the treatment amount. Therefore, it does not require major modifications such as expansion of the treatment tank and large capacity, and it can be easily applied to existing equipment and has practical value.

It is a figure which shows the flowchart of the processing method of this invention. It is a figure ([1] is a front view, [2] is a bird's-eye view) which shows the example of arrangement | positioning of the air supply apparatus in a pH adjustment tank. Graph showing dissolved oxygen amount in mixing tank and pH adjustment tank Graph showing ferrous ion concentration in mixing tank and pH adjustment tank It is explanatory drawing which shows the example of the waste acid liquid processing system | strain in a steel manufacturing factory.

Explanation of symbols

1: Waste acid mixing tank 2: pH adjustment tank
21; No.1 pH adjustment tank
22: No. 2 pH adjustment tank 3: Coagulation tank 4: Precipitation tank 5: Sludge return circuit 6: Sludge thickener 7: Dehydrator 8: Stirrer 9: Ejector
91: Air blower
92: Liquid circulation pump

A: Pickling equipment section
a1: Pickling line
a2: Waste hydrochloric acid treatment equipment (spray roasting treatment)
B: Plating treatment equipment
b1: Plating line
b2: Chromium waste liquid treatment equipment C: Pickling steel strip rinse treatment equipment D: Other treatment equipment section E: Mixed waste acid treatment equipment

Claims (2)

A waste acid solution mixing process that contains and mixes various types of waste hydrochloric acid generated from steel manufacturing plants, a pH adjustment process that adds a neutralizing agent to the mixed waste acid solution, and precipitates iron in the solution as ferric hydroxide, agglomeration In the treatment method of iron-containing waste hydrochloric acid having a coagulation step of coagulating ferric hydroxide by adding an agent, a sludge separation step of separating the coagulated sludge from the waste acid solution,
In the pH adjustment step of the mixed waste acid solution, air is blown into the bath solution to maintain the dissolved oxygen concentration at 2 ppm or more, and the pH of the bath solution is adjusted to 8 or more by adding a neutralizer. A method for treating a waste acid solution, comprising converting substantially the entire amount of ferrous ions therein to ferric hydroxide.   The waste acid solution treatment method according to claim 1, wherein the neutralizing agent is calcium hydroxide.

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