High-concentration iron-based flocculant and its production method

Abstract

It is possible to continuously produce an ultra-high concentration ferric polysulfate solution that cannot be produced by conventional production methods due to a long reaction time. Ferrous sulfate, sulfuric acid, and oxygen are used as raw materials; a raw material liquid containing ferrous sulfate and sulfuric acid that satisfies the following relationship, and oxygen are supplied to a reaction vessel under high temperature and high pressure; and the ferric polysulfate solution is continuously withdrawn. The molar ratio of sulfate ions to total iron (SO4 2‑ / T-Fe) is 1.2 or more; and when the weight concentration of sulfate ions is specified as [SO4 2‑ , [SO4 2‑ is 35% by weight or less.

Description

Technical Field

[0001] The present invention relates to a high-concentration iron-based flocculant for wastewater treatment and a production method thereof. Background Art

[0002] The applicant of this patent application sells wastewater treatment chemicals centered around the initially developed iron-based inorganic polymer flocculant "Polytetsu" (registered trademark) and holds a number of related patents.

[0003] Among these patents, Patent Document 1 describes a method of adding sodium nitrite as a catalyst and an oxidizing agent to ferrous sulfate (FeSO4) as an iron-based raw material and causing an oxidation reaction to proceed at normal temperature and pressure for about 10 hours to thereby obtain a solution of polyferric sulfate ([Fe2(OH) n (SO4) 3-n / 2 m , where 0 < n ≤ 2 and m is a natural number).

[0004] However, since this method requires a long reaction time, there is a need to shorten the reaction time by some method.

[0005] Then, the production method of the iron-based inorganic flocculant described in Patent Document 2 is a method of using magnetite (Fe3O4) as an iron-based raw material, adjusting the molar ratio of sulfate ions to iron ions, and then reacting in a reaction vessel at a temperature of 120 to 180°C. This method is a production method aimed at shortening the reaction time by reacting under high temperature and high pressure, but this method still requires a reaction time of 0.8 to 1.5 hours.

[0006] Patent Document 3 discloses a production method of an iron-based flocculant in which iron(III) oxide (Fe2O3) as an iron-based raw material is dissolved in excess sulfuric acid to form iron(III) sulfate (Fe2(SO4)3), and then it is partially neutralized with iron(III) hydroxide.

[0007] However, this method has the following disadvantages: Since this method consists of two steps, namely, the step of dissolving iron(III) oxide in sulfuric acid and the step of partially neutralizing the formed iron(III) sulfate, the production method becomes complicated and it is impossible to efficiently form a polyferric sulfate solution. In the examples, it is described that the reaction needs to be carried out while maintaining a state of heating at 100°C for about 3 hours.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: Japanese Patent Laid-Open No. S51-17516

[0011] ​Patent Document 2: Japanese Patent No. 3379204

[0012] Patent Document 3: Japanese Patent No. 2741137 Summary of the Invention

[0013] Problems to be Solved by the Invention

[0014] As described above, in the conventional technology, although attempts have been made to produce a polyferric sulfate solution by selecting various iron compounds as iron-based raw materials and reacting them in various reaction forms, there are still problems including the generation of a large amount of free sulfuric acid and reaction residues, and there is also a problem of an extended production time for producing a polyferric sulfate solution that can withstand actual use.

[0015] Although it will be described in detail later, it is considered that among iron-based flocculants, the higher the total iron concentration of the flocculant, the higher the characteristics as a flocculant. The applicant of this patent application produces and sells an iron-based inorganic polymer flocculant, "Polytetsu"(R), with a total iron concentration of about 11.0 to 12.5% (referred to as "ordinary product"). Since iron-based inorganic polymer flocculants have high flocculation ability and dewatering performance if the total iron concentration is high, recently, iron-based inorganic polymer flocculants with a total iron concentration of more than 12.5% have been produced and sold as "high-concentration products".

[0016] However, even when producing a flocculant with a high total iron concentration, the maximum total iron concentration is limited to 12.7% (less than 13%), and it is also affected by the above-mentioned problem of extended production time.

[0017] Here, unless otherwise specified as molar concentration, the concentration in the present invention refers to weight %, and [T-Fe] represents the weight concentration of total iron; and [SO4 2- represents the weight concentration of sulfate ions.

[0018] Here, the total iron concentration refers to not only the iron dissolved in the raw material liquid but also the iron that is not dissolved in the raw material liquid and exists as a solid (powder, etc.) in the raw material liquid. Since even the iron-based powder present in the raw material liquid contributes to the production reaction of the polyferric sulfate solution, it is reasonable to include the iron-based components that are not dissolved in the raw material liquid in the iron concentration.

[0019] However, in the polyferric sulfate solution produced by the present invention, the concentration is also expressed as the total iron concentration, but it is natural that all the iron is dissolved.

[0020] The present invention is achieved to solve these problems, and an object thereof is to provide a production method capable of continuously producing a polyferric sulfate solution having a high total iron concentration as compared with conventional products. An object of the present invention is to provide a high-concentration polyferric sulfate solution at low cost by continuously producing a solution using a reaction vessel under pressure.

[0021] Means for Solving the Problems

[0022] To solve these problems, the present invention is constituted by the following technical means.

[0023] (1) A continuous production method of an iron-based flocculant containing a polyferric sulfate solution, comprising: using ferrous sulfate, sulfuric acid, and oxygen as raw materials; continuously supplying the raw material liquid and oxygen into a reaction vessel, wherein the raw material liquid contains ferrous sulfate and sulfuric acid satisfying the following conditions; reacting under high temperature and high pressure; and continuously taking out the polyferric sulfate solution produced by the reaction:

[0024] The molar ratio of sulfate ion to total iron (SO4 2- / T-Fe) is 1.2 or more; and

[0025] When the weight concentration of sulfate ion is represented by [SO4 2- , the [SO4 2- is 35% by weight or less.

[0026] 2. The continuous production method of the iron-based flocculant according to (1), further comprising adding nitric acid or nitrite as a catalyst to the reaction vessel.

[0027] 3. The continuous production method of the iron-based flocculant according to (1) or (2), wherein the reaction conditions of high temperature and high pressure are a temperature of 100 °C or more and a pressure of 0.3 MPa or more.

[0028] 4. The continuous production method of the iron-based flocculant according to any one of (1) to (3), comprising filling 9 L of the polyferric sulfate solution in the reaction vessel and heating the raw material liquid containing ferrous sulfate and sulfuric acid to be supplied to the reaction vessel to 55 to 70 °C.

[0029] 5. The continuous production method of the iron-based flocculant according to any one of (1) to (4), wherein the residence time is 10 minutes or less.

[0030] 6. The continuous production method of the iron-based flocculant according to any one of (1) to (5), wherein the temperature in the reaction vessel is maintained at 100 °C to 150 °C throughout the reaction process.

[0031] Effects of the Invention

[0032] The ultra-high concentration iron-based flocculant of the present invention is characterized in that its concentration is higher than that of the high-concentration iron-based flocculant commercially available from the applicant of the present invention, and it has high flocculation ability and dewatering performance. In addition, since the ultra-high concentration iron-based flocculant has a lower water content than ordinary products, the product transportation cost can be reduced.

[0033] In addition, according to the production method of the iron-based flocculant of the present invention, the iron-based flocculant can be continuously produced by significantly shortening the production time of more than 10 hours required by the conventional method, and the iron-based flocculant can be efficiently produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Figure 1 is the area where polyferric sulfate solution can be produced by high temperature and high pressure reaction.

[0035] Figure 2 Figure 2 is the flow chart of the continuous production method. DETAILED DESCRIPTION OF THE INVENTION

[0036] Here, before describing the technical features of the production method of the iron-based flocculant according to the present invention, inorganic flocculants will first be described.

[0037] Generally, in sewage sludge treatment, suspended particles and colloidal particles in the sludge are flocculated with a flocculant, and dewatering treatment and solid-liquid separation are carried out. The suspended particles and colloidal particles in sewage sludge usually carry negative charges on their surfaces and are in a stable state due to the repulsive force of the surface charges and hydration. The flocculant is a chemical that adsorbs on the surfaces of these particles to neutralize the surface charges and weaken the repulsive force between the particles, thereby causing the particles to flocculate.

[0038] Iron-based flocculants are typical inorganic flocculants, and the positively charged iron ions neutralize the negative charges on the surfaces of suspended substances such as suspended particles and colloidal particles to carry out the flocculation effect. Therefore, the iron-based flocculant always shows the flocculation effect as long as iron ions exist, and a higher iron ion concentration, due to the improved flocculation ability for suspended substances, results in a reduced addition amount of the flocculant.

[0039] In order for the iron ions in the flocculant to exist stably, a certain amount of negative ions must exist. In the case of iron-based flocculants, sulfate ions usually play such a role. When the amount of negative ions has a suitable molar ratio relationship with the amount of iron ions, the iron-based flocculant becomes stable, but in the case of excessive negative ions, or when its amount is insufficient, the iron-based flocculant becomes unstable and causes deposition as crystals, etc.

[0040] ​​​​Then, in the case of treating sewage sludge by using such an iron-based flocculant, iron ions are adsorbed on the surfaces of suspended particles and colloidal particles and separated and recovered as solid components, but sulfate ions ultimately remain in the treated water.

[0041] Therefore, since the treated water becomes strongly acidic, in order to discharge the treated water into a river, the treated water needs to be neutralized with a large amount of neutralizing agent; this is considered to be one of the factors increasing the cost of sewage sludge treatment. That is, as a characteristic required for an iron-based flocculant, it is required that the total iron concentration ([T-Fe]) contained in the flocculant is high and the sulfate ion concentration ([SO4 2- ) is low.

[0042] (Raw materials used)

[0043] In the production of a polyferric sulfate solution using ferrous sulfate as a raw material, the following chemical reactions are considered to occur.

[0044] m[2FeSO4+(1-n / 2)H2SO4+1 / 2O2+(n-1)H2O]→[Fe2(OH) n (SO4) 3-n / 2 m

[0045] where 0 < n ≤ 2 and m is a natural number.

[0046] The present invention provides a method for continuously forming a solution with a high [T-Fe] for an iron-based flocculant composed of the above polyferric sulfate solution, and an iron-based flocculant produced therefrom.

[0047] In the present invention, first, when a raw material liquid containing ferrous sulfate (FeSO4) and sulfuric acid and oxygen are used as raw materials and an oxidation reaction is carried out under high temperature and high pressure conditions, the relationship between the total iron concentration and the sulfate ion concentration of the added raw material liquid is set within a specific range. The present invention makes the molar ratio of sulfate ion to total iron (SO4 2- / T-Fe) be above a specific value and [SO4 2- be below a specific value, and obtains the following extremely remarkable effects: continuous production that cannot be predicted by conventional techniques can be carried out, and in addition, a polyferric sulfate solution with an extremely high total iron concentration ([T-Fe]) that cannot be produced by conventional techniques can be produced.

[0048] That is, in the present invention, the first feature is that a raw material liquid containing ferrous sulfate and sulfuric acid and satisfying the following conditions reacts with oxygen under high temperature and high pressure conditions:

[0049] The molar ratio of sulfate ion to total iron (SO4 2- / T-Fe) is 1.2 or more; and ​

[0050] When the weight concentration of sulfate ions is represented by [SO4 2- , [SO4 2- is 35% by weight or less.

[0051] The new discovery made by the present inventors is that when the total iron concentration of ferrous sulfate and the concentration of sulfate ions have such a relationship, an ultra-high concentration polyferric sulfate solution can be obtained in a short time without forming a precipitate.

[0052] The following experimental setting ranges are determined.

[0053] As the high-temperature and high-pressure reaction conditions, the inventors of the present invention set (1) a reaction temperature of 110°C, a reaction pressure of 0.30 MPa, and a reaction time of 10 minutes, and (2) a reaction temperature of 120°C, a reaction pressure of 10 MPa, and a reaction time of 10 minutes, and prepared a raw material solution containing various concentrations of ferrous sulfate and sulfuric acid. Nitric acid as a catalyst was added thereto and the high-temperature and high-pressure reaction was carried out in a batch manner. Then, after the reaction time, it was checked whether a precipitate was formed.

[0054] The results are summarized in the following table. It is confirmed that either of the above conditions (1) and (2) gives the same result. That is, it is confirmed that in the case of the total iron concentration [T-Fe] and the total sulfuric acid concentration [SO4 2- shown in Table 1, a polyferric sulfate solution is formed without forming a precipitate; and in the case shown in Table 2, a precipitate is formed.

[0055] [Table 1]

[0056] Addition concentrations without forming a precipitate

[0057]

[0058] [Table 2]

[0059] Addition concentrations forming a precipitate

[0060]

[0061] (Specific range)

[0062] These results are summarized in Figure 1 . The area occupied by the ○ mark is the area where a polyferric sulfate solution is formed without forming a precipitate. This area is the area defined by the present invention and is hereinafter referred to as the "specific range". The [T-Fe] and [SO4 2-The raw material composition can stably produce a polyferric sulfate solution in the continuous production of the present invention. By reacting each composition under high temperature and high pressure conditions, a reddish-brown polyferric sulfate solution can be obtained.

[0063] On the other hand, in any case where the raw material composition represented by markings outside the specific region is used, a reaction is carried out under high temperature and high pressure, and it is confirmed that a precipitate is formed; and in the samples in the region where the molar ratio of sulfate ion to total iron (SO4 2- / T-Fe) is less than 1.2, the precipitate is confirmed to be copiapite.

[0064] The present inventors specified the specific region from the following two viewpoints.

[0065] First, the upper limit of the region can be set such that the weight concentration of sulfate ion [SO4 2- is 35 wt% or less.

[0066] Then, the lower limit of the region can be specified by an upward-sloping straight line. Each of the straight lines is a straight line representing the relationship that the molar ratio of sulfate ion to total iron (SO4 2- / T-Fe) is 1.2 or more, and is plotted in a graph where the vertical axis and the horizontal axis are the weight concentration of sulfate ion and the weight concentration of total iron, respectively.

[0067] It can be said that the specific region of the raw material composition of [T-Fe] and [SO4 2- specified by the present invention represents the region where the formation of a polyferric sulfate solution can proceed stably in a short time under high temperature and high pressure conditions.

[0068] (Continuous production)

[0069] The second feature of the present invention is that the production of the polyferric sulfate solution is carried out continuously.

[0070] Although the specific region shown above Figure 1 is the result obtained by carrying out a high temperature and high pressure reaction in a batch manner using an autoclave, since the reaction is carried out under high temperature and high pressure conditions similarly, in the continuous production of the present invention, the specific region is also a region applicable to the adjustment of the raw material composition. Since it has been clarified that by using the raw materials in the above specific region and carrying out an oxidation reaction under high temperature and high pressure conditions, a polyferric sulfate solution can be produced in a short time, the present inventors studied the production conditions for continuous production in order to change the production method from a batch method to a continuous method.

[0071] Since the production reaction of polyferric sulfate involves an oxidation reaction using iron sulfate (FeSO4) under high temperature and high pressure conditions, when continuously producing polyferric sulfate, some conditions need to be adjusted.

[0072] (Setting of production conditions)

[0073] First, since this reaction is a reaction accompanied by heat generated from the dissolution reaction of ferrous sulfate as a raw material and the oxidation reaction of ferrous ions, in the case of continuous reaction, it is necessary to control the temperature in the reaction vessel. Further, it is necessary to ensure a reaction time sufficient to form polyferric sulfate in the reaction vessel by adjusting the feeding rate of the raw materials added to the reaction vessel and the withdrawal rate of the polyferric sulfate solution as a reaction product.

[0074] By adjusting these reaction conditions, the present inventors have been able to successfully produce polyferric sulfate solution continuously, which was unexpected conventionally.

[0075] (Flow of production method)

[0076] Figure 2 The flow of the continuous production method of the high-concentration polyferric sulfate solution adopted by the present invention is shown. The reaction vessel is equipped with a heating device for startup.

[0077] The equipment for supplying raw materials is connected to the reaction vessel, water, ferric sulfate, sulfuric acid, and oxygen are supplied, and a catalyst is supplied as needed. The produced polyferric sulfate solution is stored in the product tank.

[0078] (Raw materials added)

[0079] As raw materials, a raw material liquid containing ferrous sulfate and sulfuric acid, and oxygen are supplied. Compared with the batch method that does not require the supply of oxygen, the continuous method in which the reaction consumes oxygen requires intermittent supply of oxygen to the reaction vessel. Nitric acid can be added as a catalyst as needed.

[0080] The reaction vessel is pre-filled with heated polyferric sulfate as the final product, and when continuous production starts, the inside of the reaction vessel is in a high-temperature and high-pressure state, and these raw materials are heated and added to the reaction vessel at a constant flow rate. At the same time, the polyferric sulfate solution as a reaction product is extracted at a constant flow rate.

[0081] In order to promote the above production reaction of the polyferric sulfate solution, it is preferable to use a catalyst. Preferred catalysts for promoting the reaction include nitric acid and nitrites, and the nitrites include sodium salts and potassium salts of nitrous acid, etc. From the viewpoints of the function of promoting the reaction and cost, nitric acid is preferred.

[0082] (Reaction temperature)

[0083] It is necessary to adjust the temperature in the reaction vessel within the range of 100 to 150 °C.

[0084] If the reaction temperature is lower than 100 °C, the oxidation reaction of ferrous sulfate will not proceed sufficiently. If it is higher than 150 °C, yellow precipitates are confirmed, and X-ray analysis of the precipitates indicates that the precipitates are Fe(OH)SO4. Thus, it is preferable to adjust the temperature in the reaction vessel so that it falls within the range of 110 °C to 130 °C, and it is more preferable to further adjust the temperature so that it falls within the range of 115 °C to 125 °C.

[0085] Then, by preheating the raw materials using the heat generated by the reaction and recovering the reaction heat, polyferric sulfate solution can be produced at low cost.

[0086] (Pressure)

[0087] The pressure in the reaction vessel needs to be 0.3 MPa or more.

[0088] In the production method of the iron-based flocculant of the present invention, since the reaction of dissolving ferrous sulfate (FeSO4·7H2O) as a solid raw material in sulfuric acid and oxidizing it is carried out, the dissolution of ferrous sulfate proceeds due to high-temperature conditions; and due to high-pressure conditions, the oxygen partial pressure increases and the oxidation reaction is promoted. Therefore, theoretically, from the viewpoint of promoting the reaction, a higher pressure is preferable.

[0089] However, from the viewpoint of industrial production, it is natural to prefer a lower pressure. In the present invention, the lower limit of the pressure is set to 0.3 MPa. When the reaction is carried out at a pressure lower than this, the oxidation reaction of the solution is inhibited and the normal reaction conditions are damaged, making it impossible to carry out stable continuous operation. Then, by making the pressure in the reaction vessel about 5.0 MPa, the production efficiency of the polyferric sulfate solution can be significantly improved.

[0090] (Residence time)

[0091] In the continuous production of polyferric sulfate solution, the time from the chemical reaction of the raw material liquid added to the reaction vessel and the oxygen separately supplied to the reaction vessel until the product taken out from the reaction vessel as the polyferric sulfate solution (hereinafter referred to as the residence time) becomes important.

[0092] In the present invention, the residence time is defined as follows. That is, when the amount of the liquid pre-filled in the reaction vessel before the start of the production reaction is represented by M [L], and the addition amount of the raw material liquid and the extraction amount of the reaction liquid are represented by Q [L / minute], the residence time t [minute] is represented by the following formula.

[0093] t = M / Q

[0094] In the case of batch production, the added raw materials can be present in the reaction vessel until the oxidation reaction of the raw materials terminates. However, in the case of continuous production, when a long time is required until the reaction terminates, since the addition of the raw material liquid and the extraction of the reaction product are continuously carried out, measures such as expanding the reaction vessel and reducing the rates of raw material addition and product extraction are required.

[0095] Therefore, in order to enable industrial continuous production, ensuring an appropriate residence time is a major problem. On the other hand, in order to carry out production effectively, it is natural that the residence time in the reaction vessel is as short as possible.

[0096] In particular, in the production of polyferric sulfate solution, the prior art requires at least several hours until the reaction terminates, and thus its continuous production is unthinkable in the prior art.

[0097] As described above, the present inventors have successfully greatly shortened the reaction time in the batch mode by using ferrous sulfate and sulfuric acid as raw material liquids and reacting under high temperature and high pressure conditions. However, even in this case, when the total iron concentration of the raw material liquid is less than 13%, a reaction time of less than 10 minutes is required; and when the total iron concentration of the raw material liquid is as high as 13% to 16%, a reaction time of less than 30 minutes is required.

[0098] However, surprisingly, it was experimentally found that by changing the production of polyferric sulfate solution from batch production to continuous production, even when using a reaction vessel with a capacity of 20 L and reacting under pressure conditions of a reaction pressure of 0.3 MPa and 5.0 MPa, the time required for the reaction, that is, the residence time, is as short as about 8 minutes.

[0099] Although the fact that the reaction time (residence time) is shortened by carrying out continuous production of polyferric sulfate solution has not been theoretically elucidated, the present inventors believe that the mechanism is as follows. However, the technical content of the present invention should not be interpreted based on the following assumptions.

[0100] That is, in continuous production, it is considered that since the raw material liquid containing ferrous sulfate and sulfuric acid is added together with the catalyst to the polyferric sulfate solution maintained at the high temperature and high pressure required for the reaction, and the reaction starts in the polyferric sulfate solution, the reaction is promoted compared with batch production that starts the reaction only from the environment of the raw material liquid.

[0101] Note that it is natural technically that the residence time can be further shortened by promoting the oxidation reaction of ferrous sulfate in various ways. It can be conceived that, for example, the residence time can be shortened by adopting more severe high temperature and high pressure conditions, a catalyst with higher activity, a more efficient stirring method, etc. Considering the industrial and operational economic benefits, the residence time is preferably less than 10 minutes.

[0102] Naturally, even in a case where, for example, a large reaction vessel is used or the charging of raw materials and the discharging of products are carried out at a low flow rate, and the residence time is set to a long time regardless of economic efficiency, continuous production of a polyferric sulfate solution is possible.

[0103] Table 3 shows how much efficiency improvement can be obtained by continuous production of a polyferric sulfate solution as compared with production by a conventional batch production method.

[0104] [Table 3]

[0105]

[0106] The conventional batch production method is a conventional method for producing a polyferric sulfate solution proposed by the present applicant in Patent Document 1. In the batch method, since the steps of charging raw materials, oxidation reaction, and discharging products need to be carried out in sequence, production takes a long time. Specifically, in order to produce 1,000 tons of a polyferric sulfate solution per month, a large reaction vessel with a capacity of 45 m 3 is used, and operation for 12 hours a day must be continuous for 20 days.

[0107] However, according to the continuous production method of the present invention, since the above production steps can be carried out simultaneously, shortening of production time, increase in production amount, and miniaturization of the reaction vessel can be achieved.

[0108] Specifically, when continuous operation for 24 hours is carried out using a 0.6 m 3 vessel which is almost 1 / 10 the capacity of the reaction vessel used in the conventional method, a polyferric sulfate solution can be produced in an amount three times that of the conventional method in 20 days. Even when the reaction vessel is further miniaturized to a capacity of 0.2 m 3 , a polyferric sulfate solution can be produced in the same amount as the conventional method.

[0109] Such effects bring great economic benefits to factory production.

[0110] Examples

[0111] Hereinafter, examples of the present invention will be shown in a summary. However, the present invention is not limited to these examples.

[0112] Example 1

[0113] A 20 L autoclave was filled with 9 L of a polyferric sulfate solution, and the temperature inside the vessel was adjusted to 120°C and its pressure was adjusted to 0.3 MPa. The filled polyferric sulfate solution had a total iron concentration [T-Fe] and a sulfate ion concentration [SO4 2- at a time elapsed of 0 minutes as shown in Table 4 below.

[0114] Ferrous sulfate, sulfuric acid, sodium nitrite, and oxygen heated at 60 °C are added thereto. The total iron concentration [T-Fe] and the sulfate ion concentration [SO4 2- of the raw material liquid containing ferrous sulfate and sulfuric acid are 12.7 wt% and 32.5 wt%, respectively. The molar ratio of sulfate ion to total iron (SO4 2- / T-Fe) is 1.49.

[0115] The addition rate of the raw material liquid containing ferrous sulfate and sulfuric acid is set to 1.2 L / min. By adding the raw material liquid, the production reaction of the polyferric sulfate solution is started, and the temperature in the reaction vessel increases, but by performing a cooling operation, the temperature in the vessel is maintained in the range of 110 to 130 °C. The extraction of the reaction product is carried out at a rate of 1.2 L / min. Since the raw material liquid is added to the 9 L polyferric sulfate solution in the reaction vessel at a rate of 1.2 L / min, the residence time is 8 minutes.

[0116] The product solution extracted from the reaction vessel is periodically subjected to chemical analysis, and the value of divalent iron is checked, and the formation of the polyferric sulfate solution can be confirmed.

[0117] Example 2

[0118] The reaction is carried out under the same conditions as in Example 1, except that the pressure in the reaction vessel is adjusted to 5.0 MPa. The conditions include the composition of the raw materials added, their addition rate, the extraction rate of the reaction product, and the residence time, etc.

[0119] As in Example 1, the reaction product is periodically sampled and chemically analyzed. As in Example 1, the formation of the polyferric sulfate solution is confirmed.

[0120] The reaction product is sampled at predetermined intervals, and the concentration changes of the components are checked; the results are summarized in Table 4.

[0121] [Table 4]

[0122]

[0123] It is clear from Table 4 that a polyferric sulfate solution having a high total iron concentration of 12.5% or more can be stably produced within about 100 hours from the start of the reaction. Then, since the Fe 2+ concentration is below the detection limit, it can be confirmed that there is no unreacted residue.

[0124] In Example 2, considering the safety of the experimental results, conditions such as the addition rate of raw materials, the extraction rate of reaction products, and the residence time were the same as those in Example 1. However, since the pressure in the reaction vessel was overwhelmingly higher than that in Example 1, the residence time could be shortened by increasing the addition rate of raw materials and the extraction rate of reaction products. By doing so, the production efficiency of the polyferric sulfate solution could be significantly improved.

[0125] Industrial applicability

[0126] The present invention relates to a flocculant used in the treatment of wastewater such as sewage, and since a flocculant showing high flocculation performance can be produced in a short time, the flocculant can be widely used in the field of wastewater treatment.

Claims

1. A continuous production method of an iron-based flocculant containing polyferric sulfate solution, comprising: Using ferrous sulfate, sulfuric acid and oxygen as raw materials; Continuously supplying the raw material liquid and oxygen to a reaction vessel, wherein the raw material liquid contains ferrous sulfate and sulfuric acid satisfying the following conditions; Carrying out the reaction under high temperature and high pressure; and Continuously taking out the polyferric sulfate solution produced by the reaction: The molar ratio of sulfate ion to total iron (SO4 2- / T-Fe) is 1.2 or more; When the weight concentration of sulfate ions is represented by [SO4 2- , the [SO4 2- is 28% by weight or more and 35% by weight or less, and the total iron concentration of the raw material liquid is 13% to 16%, The reaction conditions of the high temperature and high pressure are a temperature of 100 to 150 °C and a pressure of 0.3 MPa or more, The residence time t is 10 minutes or less, and the residence time t is represented by the following formula: t = M / Q, wherein, M represents the amount of the liquid pre-filled in the reaction vessel before the start of the production reaction, Q represents the addition amount of the raw material liquid and the extraction amount of the reaction liquid, the unit of t is minutes, the unit of M is L, and the unit of Q is L / minute.

2. The continuous production method of the iron-based flocculant according to claim 1, further comprising adding nitric acid or nitrite as a catalyst to the reaction vessel.

3. The continuous production method of the iron-based flocculant according to claim 1 or 2, comprising filling 9 L of polyferric sulfate solution in the reaction vessel and heating the raw material liquid containing ferrous sulfate and sulfuric acid to be supplied into the reaction vessel to 55 to 70 °C.

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