KR20220069092A - High-concentration iron-based coagulant and manufacturing method thereof - Google Patents

Abstract

In the conventional production method, an ultra-high concentration ferric polysulfate solution, which could not be produced because the reaction time is long, is produced in a short time. When the sulfate ion concentration is [SO ₄ ^2- ] and the total iron concentration is [T-Fe] (molar concentration), the raw material is adjusted so as to satisfy the following relationship, and it is prepared by high-temperature and high-pressure reaction. When the molar ratio of total iron and sulfate ions (SO ₄ ^2- /T-Fe) is 1.2 or more, when the weight concentration of sulfate ions is [SO ₄ ^2- ], [SO ₄ ^2- ] is 35 wt% or less

Description

High-concentration iron-based coagulant and manufacturing method thereof

The present invention relates to a high-concentration iron-based coagulant used in wastewater treatment and a method for producing the same.

The applicant of this patent is selling a wastewater treatment agent centering on "Polytetsu" (registered trademark), an iron-based inorganic polymer coagulant developed independently, and has several patents related thereto.

Among these patents, in Patent Document 1, sodium nitrite and an oxidizing agent are added as a catalyst to a solution of ferrous sulfate (FeSO ₄ ), which is an iron-based raw material, and the oxidation reaction is carried out at room temperature and pressure for about 10 hours, and polysulfuric acid A method for obtaining a solution of ferric ([Fe ₂ (OH) _n (SO ₄ ) _3-n/2 ] _m provided that 0<n≤2, m is a natural number) is described.

However, since this method requires a long time for reaction, shortening of reaction time was calculated|required by some method.

Moreover, the manufacturing method of the iron-type inorganic flocculant described in patent document ₂ uses magnetite (Fe3O4) as an iron _- type raw material, and after adjusting the molar ratio of sulfate ion and iron ion, the temperature of 120-180 degreeC in an airtight container. method of reacting in Although this method is a production method aiming at shortening the reaction time by advancing the reaction under high temperature and high pressure, a reaction time of 0.8 to 1.5 hours was still required.

In Patent Document 3, iron trioxide (Fe ₂ O ₃ ), an iron-based raw material, is dissolved in excess sulfuric acid to produce ferric sulfate (Fe ₂ (SO ₄ ) ₃ ), and an iron-based coagulant is partially neutralized with hydrous ferric trioxide. A method is disclosed.

However, since this method includes two steps: a step of dissolving ferric trioxide in sulfuric acid and a step of partially neutralizing the produced ferric sulfate, the manufacturing process becomes complicated and a ferric polysulfate solution cannot be efficiently produced. have. In the examples, it is said that it is necessary to advance the reaction by holding it for about 3 hours in a state heated to 100°C.

Patent Document 1: Japanese Patent Publication Digestion No. 51-17516 Patent Document 2: Japanese Patent No. 3379204 Patent Document 3: Japanese Patent No. 2741137

As described above, in the prior art, attempts have been made to prepare ferric polysulfate solutions by selecting various types of iron compounds as iron-based raw materials and reacting them in various reaction forms, but generation of free sulfuric acid or reaction residues. In addition to these many problems, the problem that the manufacturing time for manufacturing a ferric polysulfate solution which can withstand practical use becomes long remained.

In addition, although the detail is described later, in an iron-type coagulant|flocculant, it is said that the characteristic as a coagulant|flocculant is high, so that total iron concentration is high. And, the applicant of this patent manufactures and sells "Polytetsu" (trademark registered), an iron-based inorganic polymer flocculant, and the total iron concentration is approximately 11.0 to 12.5% (referred to as "commodity"). Iron-based inorganic polymer flocculants have high coagulation ability and dehydration properties when the total iron concentration is high. In recent years, those having a total iron concentration of 12.5 or more have been manufactured and sold as “high concentration products”.

However, even if a coagulant with a high total iron concentration is produced, it is also related to the problem that the above-mentioned production time becomes long. At most, the total iron concentration is about 12.7% (less than 13%), and the limit is 13.0% or more of polysulfuric acid. A ferric solution could not be prepared as a commercial product.

In the present invention, the concentration in the present invention means all weight% except when specified as a molar concentration, [T-Fe] is the weight concentration of total iron, and [SO ₄ ^2- ] is the weight concentration of sulfate ions. is assumed to represent

Here, the total iron concentration means a concentration including not only the iron dissolved in the raw material, but also the iron present in the raw material solution as a solid (powder, etc.) without being dissolved. Even iron-based powder present in the raw material solution contributes to the production reaction of the ferric polysulfate solution, so it is reasonable to include iron-based components not dissolved in the raw material solution in the iron concentration.

However, even in the ferric polysulfate solution prepared in the present invention, although the concentration is indicated by the total iron concentration, it is natural that all of the iron is dissolved.

The present invention has been made in order to solve these problems, and an object of the present invention is to provide a production method capable of producing a ferric polysulfate solution having a higher total iron concentration in a short time as compared with conventional products.

In order to solve these problems, this invention is comprised by the following technical means.

(1) A method for producing an iron-based coagulant containing a ferric polysulfate solution, comprising reacting a raw material solution containing ferrous sulfate and sulfuric acid that satisfies the following conditions in an airtight container under high-temperature and high-pressure conditions.

Molar ratio of total iron and sulfate ions (SO ₄ ^2- /T-Fe) is 1.2 or more

When the weight concentration of sulfate ion is [SO ₄ ^2- ], [SO ₄ ^2- ] is 35 wt% or less

(2) The method for producing an iron-based flocculant according to (1), wherein nitric acid or nitrite is further added as a catalyst in an airtight container.

(3) The method for producing an iron-based flocculant according to (1) or (2), wherein the high-temperature and high-pressure reaction conditions are a temperature of 100°C or higher and a pressure of 0.3 MPa or higher.

(4) An iron-based coagulant having a high concentration of ferric polysulfate solution having a total iron concentration of 13 to 16% by weight.

The ultra-high-concentration iron-based flocculant of the present invention is characterized in that it has a high concentration even compared to a commercially available high-concentration iron-based flocculant by the applicant of the present invention, and has high coagulation ability and dewatering properties. Moreover, since there is little moisture content compared with a normal product, product transportation cost can be reduced.

Moreover, according to the manufacturing method of the iron-type coagulant|flocculant of this invention, the manufacturing time which required 10 hours or more in the conventional method can be shortened significantly, and the iron-type flocculent can be efficiently manufactured.

1 is an area in which ferric polysulfate can be prepared by high-temperature and high-pressure reaction.
2 is a concentration shift after filtration of a sample in which a precipitate has been generated.
3 is a concentration shift after concentration of a sample in which no precipitate has occurred.

Here, before describing the technical characteristics of the method for manufacturing the iron-based coagulant according to the present invention, first, the inorganic-based coagulant will be described.

Generally, in sewage sludge treatment, the suspended particles and colloidal particles in sludge are aggregated with a coagulant, dehydration treatment is performed, and solid-liquid separation is performed. The surface of the suspended particles and colloidal particles in sewage sludge is usually negatively charged, and is in a stable state by the repulsive force and hydration by the surface charge. Flocculant is a drug having the action of aggregating by adsorbing on the surface of these particles to neutralize the surface charge, thereby weakening the repulsive force between the particles.

An iron-based coagulant is a typical inorganic coagulant, in which positively charged iron ions neutralize negative charges on the surface of suspended substances such as suspended particles and colloidal particles to perform agglomeration action. For this reason, the iron-based coagulant always has a coagulant action when iron ions are present. However, when the iron ion concentration is high, the agglomeration ability of the suspended material increases, so that the amount of the coagulant added is reduced.

In addition, in order for the iron ion in a coagulant|flocculant to exist stably, a certain amount of negative ion must exist. In the case of an iron-based coagulant, sulfate ions usually play this role. When the negative ion amount and the appropriate molar ratio are in the relationship, the iron-based coagulant is stable, but when the negative ion amount is excessive or insufficient, it becomes unstable and precipitates as crystals or the like.

In addition, when sewage sludge is treated using such an iron-based coagulant, iron ions are adsorbed to the surface of suspended particles or colloidal particles, and are separated and recovered as solid content, but sulfate ions remain in the water to be treated.

For this reason, since the to-be-treated water becomes acidic in intensity, in order to discharge this to a river, it is necessary to neutralize with a large amount of neutralizing agents, It is said that this is one of the factors which raise the cost of sewage sludge treatment. That is, as characteristics required for the iron-based coagulant, it was required that the total iron concentration ([T-Fe]) contained in the coagulant was high and the sulfate ion concentration ([SO ₄ ^2- ]) was low.

In the production of a polyferric sulfate solution using ferrous sulfate as a raw material, the following chemical reaction is considered to be in progress.

m[2FeSO ₄ +(1-n/2)H ₂ SO ₄ +1/2O ₂ +(n-1)H ₂ O]

→ [Fe ₂ (OH) _n (SO ₄ ) _3-n/2 ] _m

However, 0<n≤2, m is a natural number

The present invention is to provide a method for forming a high [T-Fe] solution in a short time with respect to the iron-based flocculant containing the ferric polysulfate solution, and the iron-based flocculant prepared by the method.

In the present invention, when the oxidation reaction is performed under high temperature and high pressure conditions using ferrous sulfate (FeSO ₄ ) as a solid raw material, the relationship between the total iron concentration of the raw material solution and the sulfate ion concentration is set to a specific range. . In the present invention, the molar ratio of total iron and sulfate ions (SO ₄ ^2- /T-Fe) is greater than or equal to a specific value and the sulfate ion concentration [SO ₄ ^2- ] is less than or equal to a specific value, so that prediction can be made from the prior art. The reaction can be terminated in a short time without is to achieve

That is, the present invention is characterized in that a raw material solution containing ferrous sulfate and sulfuric acid, which satisfies the following conditions, is reacted under high temperature and high pressure conditions.

Molar ratio of total iron and sulfate ions (SO ₄ ^2- /T-Fe) is 1.2 or more

When the weight concentration of sulfate ion is [SO ₄ ^2- ], [SO ₄ ^2- ] is 35 wt% or less

It is a new knowledge discovered by the present inventors that, when the total iron concentration of ferrous sulfate and the sulfate ion concentration are in such a relationship, an ultra-high concentration of ferric polysulfate solution can be obtained in a short time without generating a precipitate.

(high temperature and high pressure reaction)

The method described in Patent Document 1 is a conventional manufacturing method performed by the present inventors. In this method, it is thought that the reaction progresses with the three phases of a solid phase, a liquid phase, and a gaseous phase mutually interrelate under normal temperature and normal pressure. This is because generation of yellowish-brown gas derived from NO _x and the smell of NO _x were sensed while the reaction was in progress.

However, in the method of the present invention, even when the autoclave was opened after completion of the reaction, NO _x smell was not perceived. For this reason, in the high-temperature and high-pressure reaction of the present invention, it is presumed that a reaction involving a solid phase and a liquid phase in which FeSO ₄ ·7H ₂ O, which is a solid raw material, is dissolved in a sulfuric acid solution and an oxidation reaction proceeds, is progressing.

Then, the reaction under high temperature conditions facilitates dissolution of FeSO ₄ 7H ₂ O as a solid raw material, and the reaction under high pressure conditions increases the oxygen partial pressure and increases the amount of dissolved oxygen in the liquid phase, whereby the dissolved oxygen becomes sulfurous acid It is thought that it directly contributes to the oxidation of ions NO ₂ ⁻ and Fe ²⁺ , and the oxidation reaction of iron ions is greatly accelerated.

(reaction temperature and pressure)

It is necessary to adjust the temperature in a container in the range of 100-150 degreeC.

If the reaction temperature is less than 100°C, the oxidation reaction of ferrous sulfate does not proceed sufficiently. Moreover, when it exceeds 150 degreeC, it is confirmed that a yellow precipitate remains, and it becomes clear that this precipitate is Fe(OH)SO4 by X _- ray analysis.

Although specific experimental data are omitted, the present inventors have confirmed that the reaction proceeds effectively as the reaction pressure increases. This can be said to be natural when considering the reaction mechanism of the above-described high-temperature and high-pressure reaction.

Therefore, the reaction pressure of the present invention may set realistic conditions in consideration of manufacturing cost and the like, and the reaction pressure may be 0.3 MPa or more.

(catalyst)

In order to promote the production reaction of the above-described ferric polysulfate solution, it is preferable to use a catalyst. In order to accelerate the reaction, preferred catalysts include nitric acid and nitrite, and examples of the nitrite include sodium salt and potassium salt of nitrite. Nitric acid is preferable in terms of the function of promoting the reaction and cost.

[Experiment 1]

The inventors of the present invention set the reaction temperature to 110° C., the reaction pressure to 0.30 MPa, and the reaction time to 10 minutes as reaction conditions of high temperature and high pressure, and adjusted the raw material solution containing ferrous sulfate and sulfuric acid to various concentrations. did. Nitric acid was added thereto as a catalyst to perform a high-temperature and high-pressure reaction. Then, it was examined whether or not a precipitate was generated after the lapse of the reaction time.

[Experiment 2]

In addition, as the reaction conditions of high temperature and high pressure, the reaction temperature was set to 120° C., the reaction pressure was set to 10.00 MPa, and the reaction time was set to 10 minutes, and the raw material solution containing ferrous sulfate and sulfuric acid was adjusted to have various concentrations. Nitric acid was added thereto as a catalyst to carry out a high-temperature and high-pressure reaction. Then, it was examined whether or not a precipitate was generated after the lapse of the reaction time.

The experimental results of whether or not a precipitate was generated are summarized in Tables 1 and 2.

In the case of carrying out under the conditions of the reaction temperature of 110 degreeC of Experiment 1, and reaction pressure 0.30 MPa, and the case of carrying out at 120 degreeC, 10.00 MPa of the experiment 2, it turned out that it is completely the same with respect to the generation|occurrence|production of a precipitate. That is, the results of Table 1 and Table 2 are common to Experiment 1 and Experiment 2.

In the case of the total iron concentration [T-Fe] and the total sulfuric acid concentration [SO ₄ ^2- ] shown in Table 1, a ferric polysulfate solution was formed without a precipitate, which is an example of the present invention. In addition, when shown in Table 2, generation|occurrence|production of a precipitate was confirmed, and it is a comparative example of this invention.

(specific area)

A summary of these results is shown in FIG. 1 . The area occupied by a circle in the drawing is an area in which no precipitate is formed but a solution of ferric polysulfate is formed. This is a region defined in the present invention, and is hereinafter referred to as a "specific region". [T-Fe] and [SO ₄ ^2- ] indicated by white circles included in this specific region are the raw material compositions of Examples of the present invention. By reacting this composition under high-temperature and high-pressure conditions, a reddish-brown solution of ferric polysulfate was obtained.

On the other hand, the comparative example of the present invention corresponds to a comparative example of the present invention in which the reaction was carried out under high temperature and high pressure using the raw material composition indicated by the table ▲ outside the specific region. In the case of using these compositions, the occurrence of precipitates was confirmed in all of them, and in the samples in the region where the molar ratio of total iron and sulfate ions (SO ₄ ^2- /T-Fe) was lower than 1.2, it was confirmed that the precipitate was hydroniumjarosite. is being confirmed

The present inventors specified this specific area|region from the following two formula|equation.

First, the upper limit of this region may be set such that the weight concentration of sulfate ions [SO ₄ ^2- ] is 35 wt% or less.

Next, the lower limit of this region can be defined by an oblique straight line that rises toward the right. This oblique straight line is a straight line representing a relationship in which the molar ratio of total iron to sulfate ions (SO ₄ ^2- /T-Fe) is 1.2 or more, and the vertical and horizontal axes are the weight concentration of sulfate ions and the weight concentration of total iron. converted and recorded.

The specific region regarding the raw material composition of [T-Fe] and [SO ₄ ^2- ] specified in the present invention indicates a region in which the ferric polysulfate solution can be stably produced under high-temperature and high-pressure conditions.

The technical meaning of this specific area can also be confirmed from the following additional experiments 1 and 2.

(Additional Experiment 1)

In FIG. 1, the samples having [T-Fe] and [SO ₄ ^2- ] concentrations of 14% and 28%, respectively (hereinafter referred to as (14.0:28.0)) and (15.0:30.0) samples are Precipitation is occurring. As a result of measuring the concentration of the solution after removing the precipitate by filtration of this sample, the composition of the solution is (12.8:27.2) and (14.5:29.8), respectively.

This is a numerical value within the area|region prescribed|regulated by this invention. That is, even in a sample in which a precipitate was generated, it was found that a portion of the solution was a composition contained within a specific region of the total iron concentration and the total sulfate ion concentration prescribed in the present invention. Fig. 2 shows the contents.

(Additional Experiment 2)

According to FIG. 1, the samples of (15.0:32.0) (15.0:34.0) are all samples in which the sediment did not generate|occur|produce. These samples were maintained in three environments: (i) 50° C. in a dryer, (ii) about 20° C. in a laboratory, and (iii) 10° C. in an incubator to observe the change after 1 month. As a result, precipitates were observed only in the sample of (i) (15.0:34.0) maintained at 50° C. in the dryer.

It is thought that this cause exists in the following point.

[T-Fe] and [SO ₄ ^2- ] were measured again for the sample (15.0:32.0) (15.0:34.0) maintained at 50° C. for 1 month in a dryer, and as a result, each measured value was (16.0 :34.0) (16.0:36.0). Fig. 3 shows the contents.

The sample maintained in the dryer was concentrated by evaporation of moisture, but even if there was concentration, no precipitate was detected in the sample having a concentration relationship between [T-Fe] and [SO ₄ ^2- ] within the region stipulated in the present invention. However, in the sample in which the concentration relationship between the two deviates from the above region due to the concentration, a precipitate is generated as a result of the concentration.

For this reason, a precipitate is generated only in the sample of (15.0:34.0) under the conditions of (i).

(reaction time)

The production method according to the prior art described in Patent Document 1 is a method of oxidizing ferrous sulfate at room temperature and pressure, and even if a catalyst or an oxidizing agent is devised, at most a solution having a total iron concentration ([T-Fe]) of about 12.5% This was only obtained, and the reaction time was a method of reaching 16 hours or more.

In the present invention, by employing a high-temperature and high-pressure method, the reaction time was significantly shortened.

In the example shown in FIG. 1 , the reaction is completed within 30 minutes in all samples from a high concentration solution having a total iron concentration of 12.5% to an ultra-high concentration solution having a total iron concentration of 16%. It goes without saying that the reaction time depends on the total iron concentration, and the reaction is completed in 7.5 minutes when the total iron concentration is 12.5%, and the reaction is completed within 30 minutes even when the total iron concentration is 16%. In addition, the completion of the reaction was judged by measuring the concentration of divalent iron in the sample solution.

Being able to react in such a short time is a remarkably remarkable effect that cannot be expected in the prior art.

(Ultra high concentration solution)

In order to confirm the effect of the ultra-high concentration of the ferric polysulfate solution, the following samples A and B were subjected to an aggregation test. Sample A is a sample having the same total iron concentration as that prepared in the prior art over 16 hours. On the other hand, sample B is a sample having an ultra-high concentration of total iron prepared in the present invention.

Using the color number of acrylic paint as the liquid to be treated as a simulation liquid, the amount of sample B added is reduced so that the total amount of iron added to samples A and B is the same, that is, the aggregation ability by iron ions is the same. Thus, the aggregation ability of both was compared.

Table 4 shows the conditions of the aggregation test.

Since sample B has an ultra-high concentration, when it is set to have the same aggregation ability as sample A, the amount added can be reduced by 32% compared to sample A. In addition, in the case of Sample B, as shown in Table 1, [SO ₄ ^2- ] is low, so it is possible to suppress a decrease in the PH of the liquid to be treated after the flocculation treatment, and for this reason, the amount of caustic soda added for neutralization , could be reduced by 47% compared to the case of using Sample A.

Moreover, when observing the state after floc formation, the ultra-high concentration sample B had a higher floc formation ability, and the floc sedimentation rate was also faster. In this way, although sample B has the same iron content as sample A, sample B has a higher aggregation ability.

The reason is considered to be that the sample B is more polymerized and is advantageous for cross-linking adsorption of flocs. This is also supported by the fact that the ultra-high concentration sample of Sample B has a higher liquid viscosity than Sample A.

It relates to the coagulant used in the treatment of wastewater such as sewage, and since a coagulant with high coagulation performance can be produced in a short time, it can be widely used in the field of wastewater treatment.

Claims (4)

A method for producing an iron-based coagulant containing a ferric polysulfate solution, comprising reacting a raw material solution containing ferrous sulfate and sulfuric acid, which satisfies the following conditions, in an airtight container under high-temperature and high-pressure conditions.
Molar ratio of total iron and sulfate ions (SO ₄ ^2- /T-Fe) is 1.2 or more
When the weight concentration of sulfate ion is [SO ₄ ^2- ], [SO ₄ ^2- ] is 35% by weight or less. The method for producing an iron-based flocculant according to claim 1, wherein nitric acid or nitrite is further added as a catalyst in an airtight container. The method for producing an iron-based coagulant according to claim 1 or 2, wherein the reaction conditions of high temperature and high pressure are a temperature of 100°C or higher and a pressure of 0.3 MPa or higher. An iron-based flocculant having a high concentration of ferric polysulfate solution having a total iron concentration of 13 to 16% by weight.

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