JPS62152592A - Treatment of desulfurized slag washing waste liquid - Google Patents

Abstract

PURPOSE:To remove efficiently phosphorus component and iron component and purify waste water by utilizing efficiently washing waste liquid and pickling waste solution. CONSTITUTION:In a unit equipped with a desulfurized slag washing waste liquid tank, a pickling waste liquid tank 2, a primary reaction tank 3, a secondary reaction tank 4, a thickener 5, a solid-liquid separation unit 6 and an air diffusing tube 7, the waste liquid A is sent into a primary reaction tank 3 by a pump P1 and controlled to be weak acid less than pH6. The formation of insoluble iron phosphate is carried out by sucking air from the air diffusing tube 7 and agitating. A formed up iron phosphate is extracted by a pump P3. The mixed liquid after phosphorus component being removed is sent gradually into a secondary reaction tank 4 by a pump P4 to be up more than pH6. Bivalent iron ion is exchanged to trivalent iron ion by leading air in from the air diffusing pipe 7 and agitating, and settled Fe(OH)3 is extracted and removed by a pump P5.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for treating waste liquid obtained by washing with water dephosphorization slag, which is a large amount of by-product from steel processing, etc. The present invention relates to a method of detoxifying a washing waste liquid of dephosphorization slag formed by using a refining dephosphorizing agent using a pickling waste liquid generated from a rust removal process of steel materials.

[Prior Art] A method using a dephosphorizing agent containing soda ash as a main component has been put into practical use as a dephosphorization treatment method carried out in the hot metal pretreatment or refining process in steel manufacturing.

The dephosphorization slag discharged by this method contains a large amount of unreacted soda ash in the form of Na2CO3 and Na2O, and also contains a considerable amount of phosphorus, so it can be directly transferred to the blast furnace. When slag or converter slag is used as roadbed material or aggregate for concrete, the alkaline components and phosphorus contained in the dephosphorization slag may be leached out by rainwater, etc. For this reason, the dephosphorization slag described above is used as roadbed material, etc. after the alkaline and phosphorus components are eluted and removed by washing with water, but at this time, the washing waste liquid that is produced as a by-product contains a large amount of alkaline components. Since it contains phosphorus and phosphorus, post-treatment of the washing waste liquid becomes difficult.

-1 In the processing of steel materials, large amounts of acids (hydrochloric acid and sulfuric acid) are used mainly for the purpose of removing rust, and as a result, large amounts of pickling waste liquid are discharged. Therefore, the pickling waste liquid is used repeatedly as much as possible to prevent the total amount of waste liquid from increasing. For example, in hydrochloric acid pickling, a 5-15% hydrochloric acid aqueous solution is repeatedly used, but the reaction product iron Salt (FeC12) gradually accumulates. and F e C12 in the pickling solution
? When the lA degree reaches 15 to 20%, the pickling function cannot be achieved and the acidic waste solution is disposed of as waste pickling solution.In addition to containing a large amount of iron, the acidic waste solution contains unreacted acid. Because there are so many of them, it is impossible to just throw them away. Therefore, in the past, the waste liquid was neutralized with an alkali such as lime, and the iron ions were converted into insoluble ferric hydroxide and separated to purify the waste liquid and recover the iron content.

[Problems to be Solved by the Invention] Based on the above-mentioned known technology, the present invention aims to detoxify the alkaline dephosphorization slag washing waste liquid and the acidic pickling waste liquid by mutually utilizing them as neutralizing agents. However, simply mixing the two in a car and neutralizing it cannot achieve the purpose of making it harmless. In other words, if the waste liquid is simply neutralized, it is sufficient to mix the two in neutralizing equivalent amounts, but with this method, it is not possible to remove the phosphorus component that is mixed in, especially from the dephosphorization residue washing waste liquid. As a result, a large amount of phosphorus remains as a nutrient source in the neutralization solution, causing pollution.

The present invention has been made with attention to these problems, and its purpose is not only to effectively utilize pickling waste liquid as a neutralizing agent for dephosphorization slag washing waste liquid, but also to study the detailed procedure,
The present invention aims to provide a treatment method that can effectively separate and remove not only iron but also phosphorus components in mixed waste liquid.

[Means for Solving the Problems] The structure of the treatment method according to the present invention is such that the waste water from washing the dephosphorization slag obtained using a dephosphorizing agent for metal refining containing soda ash is It is mixed with steel pickling waste liquid and oxidized in a weakly acidic region of pH 6.0 or less to remove some of the divalent iron ions.
In addition to converting into valent iron ions, phosphorus ions brought in by the washing waste liquid are reacted with trivalent iron ions to be precipitated and removed as trivalent iron salts, and then an alkaline component is added to the treatment liquid to adjust the pH to 6 or more. The gist is that the remaining iron ions are converted into trivalent iron salts and removed by precipitation.

[Function] As mentioned above, the main harmful components contained in the dephosphorization slag washing waste solution are alkalis such as Na, Co3 and Na2O, and phosphorus, while the main harmful components in the pickling waste solution are divalent iron salts ( FeC12)
and unreacted acid. Therefore, the purpose of neutralizing the waste liquid can be achieved by mixing the washing waste liquid and the acidic waste liquid in neutralizing equivalent amounts. Moreover, in this neutralization step, ferrous hydroxide is generated by the following reaction, Na20 +H20-=2NaOHHa2Co3+
H20-+2NaOH+CO,t FeC12+2NaOH-Fe (OH)2+2NaC
1 This neutralized solution is oxidized (by blowing oxygen or air, etc.)
Then, ferrous hydroxide is converted to water-insoluble ferric hydroxide and precipitated, making it possible to remove iron from the treatment liquid. It has been confirmed that such an oxidation reaction of iron compounds proceeds efficiently in a neutral or alkaline atmosphere. In addition, the relationship between the solubility of ferrous hydroxide and ferric hydroxide and the pH of the aqueous solution is shown in Figures 2 and 3.
Iron exhibits high solubility even in a pH range of slightly alkaline or lower, whereas the solubility of ferric hydroxide is almost constant in a neutral to alkaline pH range. Therefore, considering these characteristics of iron hydroxide, it is possible to remove iron from wastewater by converting divalent iron salt into trivalent iron salt (ferric hydroxide in this case) through oxidation after neutralization. It can be done efficiently. However, if this method is applied as is,
It is not possible to efficiently remove phosphorus components that come into the dephosphorization slag washing waste liquid. Therefore, various studies were conducted to efficiently convert the phosphorus component into insoluble substances in the above neutralization and oxidation treatment process. First, the two waste liquids were mixed and adjusted to a weakly acidic pH of 6.0 or less, and air was added to the mixture. It was found that the phosphorus component could also be successfully insolubilized by raising the pH to slightly acidic and performing the oxidation treatment again by blowing in air or the like. The reason why such a result was obtained can be considered as follows. In other words, it is thought that phosphorus in an aqueous solution reacts with trivalent iron ions to produce insoluble iron compounds (FePO4, etc.), and unless a considerable amount of trivalent iron ions coexists, it is impossible to separate the phosphorus component by sedimentation. Can not.

However, when a mixture of both waste liquids is oxidized in a neutral to weakly acidic atmosphere, the solubility of the trivalent iron salt hydroxide produced by the oxidation reaction is essentially zero, so it precipitates immediately after it is produced. It can no longer exist in the system in the form of trivalent iron ions. As a result, the phosphorus component in the system cannot react with trivalent iron ions and cannot be insolubilized as trivalent iron phosphate. On the other hand, when the above-mentioned mixture of both waste liquids is first oxidized in a weakly acidic region below p)I6, θ to convert some of the divalent iron ions into trivalent iron ions, the Fe (OH) produced As shown in Figure 3, 3 has a slight solubility and can coexist in the system as trivalent iron ions, so the phosphorus component in the system reacts with the trivalent iron ions. It precipitates as insoluble iron phosphate and can be separated and removed from the mixed waste solution. However, if the oxidation treatment is simply carried out in a weakly acidic region, the oxidation reaction rate is slow, so not only does it take a long time to convert the iron ions into just 3 iron ions, but even if all the iron ions could be converted into trivalent iron ions, However, some of the ions remain dissolved in the system, making it impossible to completely remove the iron ions by filtration or the like. Therefore, in the present invention, oxidation treatment is performed in a weakly acidic region for an appropriate period of time to react with trivalent iron ions to precipitate and remove all of the phosphorus compounds present in the system, and then an alkaline component is added to the treatment solution to pH 6. After the above steps, oxidation treatment i is performed again by blowing air or oxygen, etc., so that the conversion to trivalent iron ions proceeds efficiently and the generated Fe(OH)3 is immediately precipitated.

That is, in the present invention, (1) a phosphorus compound efficiently reacts with trivalent iron ions to convert it into insoluble iron phosphate; (2) Fe
(OH)3 has some solubility in a weakly acidic region of pH 6.0 or lower, and can promote insolubilization of phosphorus compounds. (3) When oxidized in a pH region of 6 or higher, , divalent iron ions in the system can be efficiently converted to trivalent iron ions, and the trivalent iron ions immediately precipitate as insoluble Fe(OH)3. By skillfully combining them, it is possible to skillfully insolubilize and separate the phosphorus components and iron compounds in the mixed solution of dephosphorization slag washing waste and pickling waste. In highly alkaline conditions, even if air blowing is omitted, Fe(OH)2 precipitates are easily formed and solid-liquid separation can be performed. However, the pH of the wastewater becomes high, making it necessary to add acid to neutralize it, and the remaining divalent iron ions in the wastewater may be oxidized and turn red, so there is no way to avoid these problems. It is better to blow air in the neutral range, and F e (OH
) 3 has better precipitation separation properties and better dehydration properties.

[Example] FIG. 1 is a schematic process diagram showing an example of the present invention,
In the figure, 1 is the dephosphorization slag washing waste tank, 2 is the pickling waste tank, and 3 is the first
A reaction tank, 4 is a second reaction tank, 5 is a thickener, 6 is a solid-liquid separator, 7 is an aeration pipe, 8 is a stirrer, and 9 is a pH meter, so that waste liquid treatment can be carried out continuously. An example of the configuration is shown below. That is, in carrying out the present invention, the dephosphorization slag washing waste liquid (
The pickling waste liquid B (hereinafter simply referred to as water washing waste liquid) is sent to the first reaction tank 3 by a pump P, and the pickling waste liquid B stored in the pickling waste liquid tank 2 is also sent to the first reaction tank 3 by a pump P2. Said washing waste liquid A and pickling waste? ri and B are weakly acidic (with a pH of 6.0 or less) of the mixed waste liquid in the first reaction tank 3.
The feed rate is controlled so that the pH is preferably 5 to 6). In this case, it is of course possible to electrically link the measurement result by the pH meter 8 with the opening/closing of the pumps PI and P2 to automatically control each feeding amount. Then, in the first reaction tank 3, by stirring while blowing air (or other oxidizing gas) through the aeration pipe 7, as mentioned above,
The following reactions occur: mutual neutralization of water washing waste liquid and pickling waste liquid; ■ partial oxidation of divalent iron ions in the mixed liquid; and ■ production of insoluble iron phosphate by reaction between generated trivalent iron ions and phosphorus compounds. The produced iron phosphate is continuously or intermittently extracted by pump P3.

The amount of phosphorus compounds contained in the water washing waste liquid is very small compared to the iron ions contained in the pickling waste liquid B, and the trivalent iron required to precipitate phosphorus as an iron compound is within the stoichiometry of phosphorus. Since about 2 to 3 times the target equivalent is sufficient, the purpose of removing the phosphorus component can be sufficiently achieved by simply converting some of the divalent iron ions into trivalent iron ions in the above oxidation reaction. The mixed liquid from which the phosphorus component has been removed is sequentially sent to the second reaction tank 4 by a pump P4. Here, by adding an appropriate amount of alkaline component C, the pH is adjusted to 6 or more (preferably 6 to 8).
), and by stirring while blowing air (or other oxidizing gas) through the aeration pipe 7, divalent iron ions that were not oxidized in the first reaction 4i3 are converted to trivalent iron ions. . The trivalent iron ions that are generated quickly become Fe(O
H)3, but Fe(OH)3 in the pH range
Since its solubility is substantially zero, it immediately precipitates and sinks to the bottom of the second reaction tank 4. In addition, a small amount of Fe(OH)3 generated in the first reaction 4!3 and dissolved in the mixed liquid is
(Because they precipitate and settle at the same time as the adjustment, all of the iron ions in the mixture will eventually be separated as insoluble Fe(OH)3. As an alkaline component for pH adjustment, industrial chemicals such as caustic soda or It is also possible to use milk of lime, etc., but the most rational method is to use a small amount of washing waste liquid together with them.

The precipitated Fe (OH) is continuously or intermittently extracted by a pump P, and the liquid tank is continuously fed to the thickener 5 by a pump P6, so that the insoluble matter drawn in with the liquid is separated by sedimentation.

The sediment is continuously or intermittently extracted from the pump P7, while the purified supernatant liquid is extracted from the pump P8 and reused as discharged water or industrial water.

In the above-described example, the final removal of insoluble matter is performed by the thickener 5, but instead of this, a filtration device such as a cartridge filter may be provided in the extraction line from the pump P6 to remove the insoluble matter.

The slurry extracted from the pump P3+PS+P7 is sent to the solid-liquid separator 6, and the solid matter is taken out as a cake-like substance, while the liquid tank is sent to the thickener 5 for treatment. In particular, the slurry extracted from the pump P3 contains a large amount of phosphorus, which is effective as a fertilizer or soil conditioner, so it can be effectively used by forming it into pellets after solid-liquid separation. . In this case, it is also effective to increase the fertilizing effect by mixing lime, magnesia lime, etc. to make a two-pour product. Since the generated phosphate co-precipitates with the Fe(OH)3 precipitate, it does not increase the phosphorus concentration in the final drainage system. It is also possible to dilute the treated water by injecting the supernatant liquid of the thickener 5 or industrial water into the second reaction tank, and by diluting it, solid-liquid separation in the second reaction tank and sedimentation separation in the shaffner can be improved. can further improve performance.

In the above description, the first and second reaction tanks are connected in series so that waste liquid treatment can be performed continuously, but it is of course possible to perform batch processing using one reaction tank. Further, the shape of the reaction 4!3.4, the diffuser tube 7, etc. can be arbitrarily changed within the range that can comply with the above-mentioned purpose, and all of these are included in the technical scope of the present invention.

[Effects of the Invention] The present invention is configured as described above, and while effectively utilizing the washing waste liquid and the pickling waste liquid, it is possible to efficiently remove the phosphorus component and the iron content, thereby making effective use of the waste liquid. Many benefits can be enjoyed, such as the purification of wastewater and the reuse of phosphorus and iron as secondary sources.

[Brief explanation of drawings]

FIG. 1 is a schematic process explanatory diagram showing an embodiment of the present invention, and FIG.
Figure 3 is a graph showing the relationship between the solubility of Fe(OH)2 and Fe(OH)3 and pl. A... Water washing waste liquid B... Pickling waste liquid C... Alkaline component

Claims (1)

[Claims] Water washing waste of dephosphorization slag obtained using a dephosphorizing agent for metal refining containing soda ash is mixed with steel pickling waste containing divalent iron ions, and oxidation treatment is performed in a weakly acidic region with a pH of 6.0 or less. to convert some of the divalent iron ions into trivalent iron ions,
Phosphorous ions brought in by the washing waste liquid are reacted with trivalent iron ions, precipitated and removed as trivalent iron salts, and then an alkaline component is added to the treatment liquid to adjust the pH to 6 or more, and then oxidized, and the remaining iron ions are removed. 1. A method for treating dephosphorization slag washing waste, characterized by converting it into a trivalent iron salt and removing it by precipitation.