TWI858149B - High-concentration iron-based flocculant and manufacturing method thereof - Google Patents

Abstract

An ultra-high concentration ferric polysulfate solution, which could not be produced because the reaction time is long by the conventional production method, is continuously produced.

Ferrous sulfate, sulfuric acid and oxygen gas are used as raw materials in the present invention, a raw material solution containing ferrous sulfate and sulfuric acid, which satisfies the following relationship, and oxygen gas are supplied into a high- temperature and high-pressure reaction vessel, and the ferric polysulfate solution is continuously taken out.

The molar ratio of total iron to sulfate ion (SO₄ ^2-/T-Fe) is 1.2 or more,

when the weight concentration of sulfate ion is [SO₄ ^2-], [SO₄ ^2-] is 35 mass% or less.

Description

High concentration iron-based coagulant and its manufacturing method

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

The patent applicant in this case sells wastewater treatment chemicals centered on the iron-based inorganic polymer flocculant "Polyferric" (registered trademark) that it developed independently, and has some patents related to this.

Among these patents, Patent Document 1 describes a method in which sodium nitrite and an oxidant are added as catalysts to an iron sulfate (II) (FeSO ₄ ) solution as an iron-based raw material, and an oxidation reaction is carried out at room temperature and pressure for about 10 hours to obtain a polyiron sulfate (III) (〔Fe ₂ (OH) _n (SO ₄ ) _3-n/2 〕 _m , where 0<n≦2 and m is a natural number) solution.

However, this method requires a long time for reaction, so some methods are sought to shorten the reaction time.

In addition, the method for producing an iron-based inorganic coagulant described in Patent Document 2 uses magnetite (Fe ₃ O ₄ ) as an iron-based raw material, adjusts the molar ratio of sulfate ions to iron ions, and then reacts them in a reaction vessel at a temperature of 120 to 180° C. This method aims to shorten the reaction time by reacting at high temperature and high pressure, but even so, it still requires a reaction time of 0.8 to 1.5 hours.

Patent document 3 discloses a method for producing an iron-based coagulant, wherein ferrous oxide (Fe ₂ O ₃ ) as an iron-based raw material is dissolved in excess sulfuric acid to generate iron sulfate (III) (Fe ₂ (SO ₄ ) ₃ ), which is then partially neutralized with water-containing ferrous oxide.

However, since the method consists of two steps, namely, dissolving ferric oxide in sulfuric acid and partially neutralizing the generated iron sulfate (III), the manufacturing steps become complicated and the polyiron sulfate (III) solution cannot be efficiently generated. In the embodiment, the reaction must be carried out by heating to 100°C for about 3 hours.

[Prior technical literature]

[Patent Literature]

Patent document 1: Japanese Patent Publication No. 51-17516

Patent document 2: Japanese Patent No. 3379204

Patent document 3: Japanese Patent No. 2741137

As mentioned above, in the prior art, attempts have been made to select various types of iron compounds as iron-based raw materials and to react in various reaction forms to produce polyiron sulfate (III) solutions. However, there are problems such as the generation of more free sulfuric acid or reaction residues, and the problem of a longer production time for producing a durable polyiron sulfate (III) solution remains.

The details will be described later, but in iron-based flocculants, the higher the total iron concentration, the higher the characteristics of the flocculant. Next, the patent applicant in this case manufactures and sells the iron-based inorganic polymer flocculant "Polyferrite" (trademark registration), and its total iron concentration is about 11.0 to 12.5% (called "general product"). If the total iron concentration of the iron-based inorganic polymer flocculant is high, it has high flocculant ability and dehydration properties, so in recent years, it has manufactured and sold products with a total iron concentration of 12.5 or more as "high-concentration products."

However, even if a coagulant with a high total iron concentration is produced, it is also related to the problem of prolonged production time mentioned above, and the maximum total iron concentration is around 12.7% (less than 13%).

In addition, except for the case where the molar concentration is explicitly described, all concentrations in the present invention mean weight %, [T-Fe] represents the weight concentration of total iron, and [SO ₄ ^2- ] represents the weight concentration of sulfate ions.

The total iron concentration mentioned here includes not only the iron dissolved in the raw material, but also the iron that is not dissolved and exists in the raw material liquid in the form of solid (powder, etc.). Even if it is iron-based powder existing in the raw material liquid, it also helps the manufacturing reaction of polyiron sulfate (III) solution, so it is reasonable that the iron concentration also includes the iron-based components that are not dissolved in the raw material liquid.

However, in the polyiron sulfate (III) solution produced in the present invention, the concentration is also expressed in terms of total iron concentration, but of course all the iron is dissolved.

The present invention is developed to solve these problems, and provides a method for continuously producing a polyferric sulfate (III) solution with a high total iron concentration compared to conventional products. The purpose of the present invention is to provide a high-concentration polyferric sulfate (III) solution at a low cost by continuously producing while pressurizing a reaction vessel.

In order to solve these problems, the present invention is composed of the following technical means.

(1) A continuous method for producing an iron-based coagulant, the iron-based coagulant containing a polyiron sulfate (III) solution, and the method using iron sulfate (II), sulfuric acid and oxygen as raw materials, continuously supplying a raw material liquid containing iron sulfate (II) and sulfuric acid and oxygen satisfying the following conditions to a reaction vessel, and continuously taking out the polyiron sulfate (III) solution generated by the reaction at high temperature and high pressure from the reaction vessel.

The molar ratio of total iron to sulfate ions (SO ₄ ^2- /T-Fe) is above 1.2.

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

(2) The continuous production method of the iron-based coagulant as described in (1) is to further add nitric acid or nitrite as a catalyst into the reaction vessel.

(3) A continuous method for producing an iron-based coagulant as described in (1) or (2), wherein the high temperature and high pressure reaction conditions are above 100°C and above 0.3MPa.

(4) A continuous method for producing an iron-based coagulant as described in any one of (1) to (3), wherein 9 liters of polyiron sulfate (III) solution is filled in a reaction vessel, and the raw material solution containing iron sulfate (II) and sulfuric acid supplied to the reaction vessel is heated to 55 to 70°C.

(5) A continuous method for producing an iron-based coagulant as described in any one of (1) to (4), wherein the retention time is within 10 minutes.

(6) A continuous method for producing an iron-based coagulant as described in any one of (1) to (5), wherein the temperature in the reaction container is maintained at 100°C to 150°C during the reaction.

The characteristics of the ultra-high concentration iron-based coagulant of the present invention are that it has high concentration characteristics compared to the high concentration iron-based coagulants currently on the market by the applicant of the present invention, and has high coagulability and dehydration properties. In addition, compared with general products, it contains less water, so the transportation cost of the product can be reduced.

Furthermore, if the manufacturing method of the iron-based coagulant according to the present invention is used, the manufacturing time required for more than 10 hours in the conventional method can be greatly shortened to carry out continuous production, and the iron-based coagulant can be manufactured efficiently.

Figure 1 shows the area where polyiron sulfate (III) can be produced by high temperature and high pressure reaction.

Figure 2 is a flow chart of the continuous manufacturing method

Here, before explaining the technical features of the method for producing the iron-based coagulant of the present invention, first, the inorganic coagulant is explained.

Generally, in sewage sludge treatment, coagulants are used to agglomerate the suspended particles or colloidal particles in the sludge and then dehydrate them to separate solids from liquids. The suspended particles or colloidal particles in sewage sludge usually have negative charges on their surfaces, and are in a stable state due to the repulsive force generated by the surface charge and hydration. Coagulants are agents that have the following effects: they are adsorbed on the surface of these particles to neutralize the surface charge, weaken the repulsive force between the particles, and cause them to agglomerate.

Iron-based coagulants are representative inorganic coagulants, which use positively charged iron ions to neutralize the negative charge on the surface of suspended particles or colloidal particles to perform coagulant action. Therefore, if iron ions exist in iron-based coagulants, they will definitely have coagulant effects. However, if the iron ion concentration increases, the coagulant ability of suspended matter will increase, so the amount of coagulant added can be reduced.

In addition, in order for the iron ions in the coagulant to exist stably, a certain amount of negative ions must exist. In the case of iron-based coagulants, sulfate ions usually bear this role. If the negative ions are in an appropriate molar ratio with the iron ions, the iron-based coagulant is stable, but when the negative ions are excessive or insufficient, it becomes unstable and crystals precipitate.

Furthermore, when such iron-based coagulants are used to treat sewage sludge, iron ions are adsorbed on the surface of suspended particles or colloidal particles and separated and recovered as solids, but sulfate ions remain in the treated water.

Therefore, the treated water becomes highly acidic, so in order to discharge it into the river, it must be neutralized with a large amount of neutralizer, which is said to be one of the reasons for increasing the cost of sewage sludge treatment. In other words, the characteristics required of iron-based coagulants are that the total iron concentration ([T-Fe]) contained in the coagulant is high and the sulfate ion concentration ([SO ₄ ^2- ]) is low.

(Raw materials used)

It is generally believed that the following chemical reactions occur in the production of polyiron sulfate (III) solution using iron sulfate (II) as raw material.

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

→ ₂ (OH) _n (SO ₄ ) _3-n/2 〕 _m

Among them, 0<n≦2, m is a natural number

The present invention provides a method for continuously forming a solution with high [T-Fe] for the iron-based coagulant composed of the above-mentioned polyiron sulfate (III) solution and the iron-based coagulant produced thereby.

In the present invention, first, when a raw material liquid containing iron (II) sulfate (FeSO ₄ ) and sulfuric acid and oxygen gas are used as raw materials for oxidation reaction under high temperature and high pressure conditions, the relationship between the total iron concentration and the sulfate ion concentration of the raw material liquid fed is set within a specific range. The present invention achieves the following particularly remarkable effects by making the molar ratio of total iron to sulfate ions (SO ₄ ^2- /T-Fe) above a specific value and making the sulfate ion concentration [SO ₄ ^2- ] below a specific value: continuous production that cannot be predicted by conventional techniques can be carried out, and the produced polyiron sulfate (III) solution can produce a total iron concentration ([T-Fe]) of an ultra-high concentration that cannot be produced by conventional techniques.

That is, in the present invention, the first feature is to react a raw material liquid containing iron sulfate (II) and sulfuric acid satisfying the following conditions with oxygen gas at high temperature and high pressure.

The molar ratio of total iron to 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

When the total iron concentration of iron sulfate (II) and the sulfate ion concentration are in such a relationship, no precipitate will be produced, and an ultra-high concentration polyiron sulfate (III) solution can be obtained in a short time. This is a new insight discovered by the inventors.

This area is set through the following experiments.

The inventors of the present invention set the reaction conditions of high temperature and high pressure as follows: (1) setting the reaction temperature to 110°C, the reaction pressure to 0.3 MPa, and the reaction time to 10 minutes; (2) setting the reaction temperature to 120°C, the reaction pressure to 10 MPa, and the reaction time to 10 minutes, and adjusting the raw material liquid containing iron sulfate (II) and sulfuric acid to various concentrations. Nitric acid was added as a catalyst, and a high temperature and high pressure reaction was carried out in a batch manner. Then, it was investigated whether a precipitate was generated after the reaction time had passed.

The results are summarized in the following table. It can be seen that the same results were obtained when either of the above conditions (1) and (2) was used. That is, in the case of the total iron concentration [T-Fe] and the total sulfuric acid concentration [SO ₄ ^2- ] shown in Table 1, no precipitate was formed but a polyiron sulfate (III) solution was formed, while in the case shown in Table 2, the formation of a precipitate was confirmed.

(Specific area)

The results are summarized in Figure 1. The area marked with a circle in the figure is where no precipitate is formed but a polyiron sulfate (III) solution is formed. This is the area specified in the present invention, hereinafter referred to as the "specific area". The [T-Fe] and [SO ₄ ^2- ] contained in the specific area represented by the white circle are the raw material composition that can stably produce the polyiron sulfate (III) solution in the continuous production of the present invention. By reacting the composition under high temperature and high pressure conditions, a reddish brown solution of polyiron sulfate (III) can be obtained.

On the other hand, when the raw material compositions indicated by the ▲ symbol outside the specific region were used and the reaction was carried out under high temperature and high pressure, precipitates were confirmed to be produced in all of them. In the samples in the region where the molar ratio of iron to sulfate ions (SO ₄ ^2- /T-Fe) was lower than 1.2, the precipitate was confirmed to be hydrogenium jarosite.

The inventors of the present invention assume that the specific area is defined by the following two viewpoints.

First, the upper limit of the region can be set to a weight concentration of sulfate ions [SO ₄ ^2- ] of 35 wt % or less.

Next, the lower limit of the region can be defined by the diagonal straight line that increases toward the upper right. The diagonal straight line is written by converting the straight line representing the relationship between the molar ratio of total iron and sulfate ions (SO ₄ ^2- /T-Fe) of 1.2 or more into a graph with the vertical axis and the horizontal axis representing the weight concentration of sulfate ions and the weight concentration of total iron.

The specific region of the raw material composition of [T-Fe] and [SO ₄ ^2- ] specified in the present invention refers to a region where a polyiron sulfate (III) solution can be stably generated in a short time under high temperature and high pressure conditions.

(Continuous Manufacturing)

The second feature of the present invention is to continuously produce the polyiron sulfate (III) solution.

The specific area shown in FIG1 is the result of a high temperature and high pressure reaction using an autoclave in a batch process. However, since the reaction is carried out under the same high temperature and high pressure conditions, it is also an area that can be applied to the adjustment of the raw material composition in the continuous production of the present invention. It is obvious that by using the raw materials in the specific area and carrying out an oxidation reaction under high temperature and high pressure conditions, a polyiron sulfate (III) solution can be produced in a short time. Therefore, in order to shift from batch production to continuous production, the inventors of the present invention have studied the production conditions for continuous production.

The production reaction of polyiron sulfate (III) uses iron sulfate (II) (FeSO ₄ ) as a raw material and undergoes an oxidation reaction under high temperature and high pressure conditions. Therefore, certain conditions must be adjusted during continuous production.

(Setting of manufacturing conditions)

First, the reaction is a heat-generating reaction of the dissolution reaction of the raw material iron sulfate (II) and the accompanying oxidation reaction of divalent iron ions, so the temperature in the reaction vessel must be managed when the reaction is carried out continuously. In addition, by adjusting the input speed of the raw materials into the reaction vessel and the withdrawal speed of the reaction product polyiron sulfate (III) solution, it is necessary to ensure sufficient reaction time in the reaction vessel to generate polyiron sulfate (III).

The inventors of the present invention have successfully achieved the continuous production of polyiron sulfate (III) solution, which is unimaginable in the past, by adjusting these reaction conditions.

(Process of manufacturing method)

FIG2 shows the process of the continuous production method of high-concentration polyiron sulfate (III) used in the present invention. The reaction vessel is equipped with a heating device for start-up.

The reaction vessel is connected to a device for supplying raw materials, and is also supplied with water, iron sulfate, sulfuric acid and oxygen, and a catalyst as needed. The produced polyiron sulfate (III) solution is stored in a product tank.

(Input raw materials)

The raw materials are a raw material liquid containing iron sulfate (II) and sulfuric acid, and oxygen gas. In the batch method, oxygen does not need to be supplied, but in the continuous method, oxygen will be consumed by the reaction, so it must be continuously supplied to the reaction container. In addition, nitric acid can be added as a catalyst as needed.

The reaction vessel is pre-filled with the final product of heated polyiron sulfate (III). When continuous production begins, a high temperature and high pressure state is formed, and these raw materials are heated and added to the reaction vessel at a certain flow rate. At the same time, the polyiron sulfate (III) solution of the reaction product is removed at a certain flow rate.

In order to promote the formation reaction of the aforementioned polyiron sulfate (III) solution, it is preferred to use a catalyst. In order to promote the reaction, the preferred catalysts include nitric acid and nitrite, and nitrite is sodium salt or potassium salt of nitrite. In terms of the function of promoting the reaction or the cost, nitric acid is preferred.

(Reaction temperature)

The temperature in the reaction vessel must be adjusted to a range of 100 to 150°C.

If the reaction temperature is less than 100°C, the oxidation reaction of iron sulfate (II) will not proceed sufficiently. If the reaction temperature exceeds 150°C, a yellow precipitate will remain, which is Fe(OH)SO ₄ as determined by X-ray analysis. Therefore, the temperature in the reaction vessel is preferably adjusted to a range of 110°C to 130°C, more preferably 115°C to 125°C.

In addition, the heat generated by the reaction can be used to preheat the raw materials, thereby recovering the reaction heat and producing polyiron sulfate (III) at a low cost.

(pressure)

The pressure in the reaction vessel must be above 0.3MPa.

The method for producing the iron-based coagulant of the present invention is to dissolve iron sulfate (II) (FeSO ₄ ‧7H ₂ O) as a solid raw material in sulfuric acid and oxidize it to react. Therefore, the iron sulfate (II) is dissolved under high temperature conditions, and the oxygen partial pressure is increased under high pressure conditions to promote the oxidation reaction. Therefore, from the perspective of promoting the reaction, higher pressure is theoretically better.

However, from the perspective of industrial production, low pressure is of course better. In the present invention, the lower limit of the pressure is set to 0.3MPa. If the reaction is carried out at a lower pressure than this, the oxidation reaction of the solution will be suppressed, the normal reaction conditions will collapse, and it will not be possible to carry out continuous operation stably. In addition, by setting the pressure in the reaction container to about 5.0MPa, the production efficiency of polyiron sulfate (III) can be significantly improved.

(Retention time)

In the continuous production of polyiron sulfate (III) solution, the raw material liquid and oxygen gas supplied separately in the reaction vessel undergo chemical reaction in the reaction vessel, and the time until the polyiron sulfate (III) solution is taken out from the reaction vessel (this time is expressed as the retention time here) is very important.

In the present invention, the retention time is defined as follows. That is, when the amount of liquid pre-filled in the reaction container before starting the manufacturing reaction is set to M [L], the amount of raw material liquid input and the amount of reaction liquid removed are set to Q [L/min], the retention time t [min] is expressed by the following formula.

t=M/Q

In the case of batch production, the raw materials can be kept in the reaction vessel until the oxidation reaction is completed. However, in the case of continuous production, if the reaction takes a long time to complete, since the input of raw material liquid and the removal of reaction products are carried out continuously, it is necessary to take measures to enlarge the reaction vessel or slow down the input of raw materials and the removal of products.

Therefore, in order to make continuous industrial manufacturing possible, ensuring an appropriate residence time is a major issue. On the other hand, in order to manufacture efficiently, a shorter residence time in the reaction vessel is of course preferred.

In particular, in the production of polyiron sulfate (III) solution, it takes at least several hours before the reaction is completed in the conventional technology, so the continuous production of polyiron sulfate (III) solution is unimaginable in the conventional technology.

As mentioned above, the inventors of the present invention used iron sulfate (II) and sulfuric acid as raw materials and reacted them under high temperature and high pressure conditions, thereby successfully shortening the batch reaction time significantly. However, when the total iron concentration of the raw material solution is less than 13%, the reaction time must be within 10 minutes, and when the total iron concentration of the raw material solution is a high concentration of 13% to 16%, the reaction time must be within 30 minutes.

However, surprisingly, by switching the production of polyiron sulfate (III) solution from batch production to continuous production, the time required for the reaction, i.e. the residence time, was experimentally confirmed to be completed in about 8 minutes when the reaction pressure was 0.3MPa and 5.0MPa using a 20-liter reaction vessel.

There is no theoretical explanation for the continuous production of polyiron sulfate (III) solution to shorten the reaction time (residence time), but the inventors of the present invention believe that it may be based on the following mechanism. However, the technical content of the present invention should not be interpreted based on the following inference.

That is, in the continuous production, the raw material liquid containing iron sulfate (II) and sulfuric acid is put into the polyiron sulfate (III) solution maintained at the high temperature and high pressure required for the reaction together with the catalyst, and the reaction starts in the polyiron sulfate (III) solution, so it is believed that the reaction may be accelerated compared to the batch method that starts the reaction from an environment with only the raw material liquid.

Furthermore, by considering various means to promote the oxidation reaction of iron sulfate (II), it is technically possible to further shorten the residence time. For example, it is generally believed that the residence time can be shortened by using more stringent high temperature and high pressure conditions, highly active catalysts, efficient stirring methods, etc. If the economical operation in industry is considered, the residence time is preferably within 10 minutes.

Furthermore, by using a larger reaction vessel or inputting raw materials and removing products at a low flow rate, etc., regardless of economics, even if the residence time is set to a long time, polyiron sulfate (III) can of course be produced continuously.

The efficiency that can be achieved by continuously producing polyiron sulfate (III) solution is compared with the conventional batch production method, and is summarized in Table 3.

The known method performed in batch mode is a known method for producing polyferric sulfate (III) solution proposed by the applicant in patent document 1. In batch mode, the steps of raw material input, oxidation reaction, and product removal must be carried out in sequence, so it takes a long time for production. Specifically, in order to produce 1,000 tons of polyferric sulfate (III) solution per month, a large reaction vessel with a capacity of ^45m3 must be used, and the operation must be carried out for 12 hours a day for 20 consecutive days.

However, if the continuous manufacturing method of the present invention is used, the above manufacturing steps can be carried out simultaneously, thereby shortening the manufacturing time, increasing the manufacturing volume, and miniaturizing the reaction container.

Specifically, using a 0.6 ^m3 container, which is about 1/10 of the capacity of the reaction container used in the conventional method, three times the amount of polyferric sulfate (III) solution of the conventional method can be produced within 20 days if the operation is carried out continuously for 24 hours. Furthermore, even if the reaction container is miniaturized to a capacity of 0.2 ^m3 , the same amount of polyferric sulfate (III) solution as the conventional method can be produced.

Such an effect can generate immeasurable economic benefits in factory production.

[Example]

The following is a summary of the embodiments of the present invention. However, the present invention is not limited to these embodiments.

Embodiment 1

A 20-liter autoclave was filled with 9 liters of polyferric sulfate (III) solution, and the temperature in the container was adjusted to 120°C and the pressure was adjusted to 0.3 MPa. The filled polyferric sulfate (III) solution had a total iron concentration [T-Fe] and a sulfate ion concentration [SO ₄ ^2- ] at 0 minutes as shown in Table 4 below.

Iron sulfate (II), sulfuric acid, sodium nitrite and oxygen gas heated to 60°C were added. The total iron concentration [T-Fe] and sulfate ion concentration [SO ₄ ^2- ] of the raw material solution containing iron sulfate (II) and sulfuric acid were 12.7 wt% and 32.5 wt%, respectively. The molar ratio of total iron to sulfate ion (SO ₄ ^2- /T-Fe) was 1.49.

The feed rate of the raw material solution containing iron sulfate (II) and sulfuric acid is set at 1.2 liters per minute. By adding the raw material solution, the formation reaction of polyiron sulfate (III) is initiated, and the temperature in the reaction container will rise, but by cooling, the temperature in the container is maintained in the range of 110 to 130°C. The removal of the reaction product is carried out at 1.2 liters per minute. In the 9 liters of polyiron sulfate (III) solution in the reaction container, 1.2 liters of raw material solution is added per minute, so the retention time is 8 minutes.

The product solution removed from the reaction vessel was periodically chemically analyzed to determine the value of divalent iron, which confirmed the formation of polyiron sulfate (III).

Embodiment 2

Except for adjusting the pressure in the reaction vessel to 5.0MPa, the rest of the reaction was carried out under the same conditions as Example 1 in terms of the composition of the raw materials, the rate of raw material input, the rate of removing the reaction products, the retention time, etc.

As in Example 1, the reaction product was sampled and extracted periodically for chemical analysis. As in Example 1, the generation of polyiron sulfate (III) was confirmed.

The reaction products were sampled at predetermined intervals, and the results of studying the changes in their component concentrations are summarized in Table 4.

As is apparent from Table 4, a high-concentration polyferric sulfate (III) solution with a total iron concentration of 12.5% or more can be stably produced within about 100 minutes from the start of the reaction. In addition, since the Fe ²⁺ concentration is below the detection limit, it can be confirmed that there are no unreacted residues.

In Example 2, the conditions such as the input speed of raw materials, the removal speed of reaction products, and the retention time are set to the same conditions as those in Example 1 in consideration of the safety of the experimental results. However, the pressure in the reaction vessel is much higher than that in Example 1, so the input speed of raw materials and the removal speed of reaction products can be increased to shorten the retention time in the reaction vessel. In this way, it is believed that the production efficiency of polyiron sulfate (III) can be significantly improved.

[Industrial application areas]

Regarding the coagulants used in sewage treatment, etc., coagulants with high coagulability can be produced in a short time, so they can be widely used in the field of wastewater treatment.

Claims (6)

A continuous production method for an iron-based coagulant, the iron-based coagulant containing a polyiron sulfate (III) solution, and the production method uses iron sulfate (II), sulfuric acid and oxygen gas as raw materials, and continuously supplies a raw material solution containing iron sulfate (II) and sulfuric acid and oxygen gas that meet the following conditions to a reaction container, and continuously takes out the polyiron sulfate (III) generated by reacting at 100°C or above and 0.3MPa or above from the reaction container _{; the molar ratio of total iron to sulfate ions (SO42-/T-Fe) is 1.2 or above, when the weight concentration of sulfate ions is set to [SO42- ]} ^{, [} _SO42- ] is 35% by weight or less, and the total iron concentration in the raw material solution is 13% by ^weight or more. The continuous manufacturing method of the iron-based coagulant as described in claim 1 is to further add nitric acid or nitrite as a catalyst into the reaction container. A continuous method for producing an iron-based coagulant as described in claim 1 or 2, wherein the total iron concentration in the raw material liquid is greater than 13% by weight and less than 16% by weight. A continuous method for producing an iron-based coagulant as described in claim 1 or 2, wherein 9 liters of polyiron sulfate (III) solution is filled in a reaction vessel, and the raw material solution containing iron sulfate (II) and sulfuric acid supplied to the reaction vessel is heated to 55 to 70°C. A continuous method for producing an iron-based coagulant as described in claim 1 or 2, wherein the retention time is within 10 minutes. The continuous manufacturing method of the iron-based coagulant as described in claim 1 or 2 is to keep the temperature in the reaction container at 100°C to 150°C during the reaction.

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