High-concentration iron-based coagulant and method of manufacturing the same

Abstract

This method produces an ultra-high concentration polyferric sulfate solution in a short time, which was previously impossible to manufacture using conventional methods due to the long reaction times required. The solution is produced by adjusting the raw materials to satisfy the following relationship when the sulfate ion concentration is [SO42-] and the total iron concentration is [T-Fe] (molar concentration), and by a high-temperature, high-pressure reaction. The molar ratio of total iron to sulfate ions (SO42- / T-Fe) is 1.2 or higher, and when the weight concentration of sulfate ions is [SO42-], [SO42-] is 35 wt% or lower.

Description

Technology Field

[0001] The present invention relates to a high-concentration iron-based coagulant used in wastewater treatment and a method for manufacturing the same. Background Technology

[0002] The applicant of the present patent conducts sales of wastewater treatment agents centered on the independently developed iron-based inorganic polymer coagulant "Polytetsu" (registered trademark) and holds several patents related thereto.

[0003] Among these patents, Patent Document 1 describes adding sodium nitrite and an oxidizing agent as catalysts to a solution of ferrous sulfate (FeSO4), an iron-based raw material, and carrying out an oxidation reaction at room temperature and pressure for about 10 hours to produce ferric polysulfate ([Fe2(OH) n (SO4) 3-n / 2 〕 m Only 0 <n≤2, m은 자연수) 용액을 얻는 방법이 기재되어 있다.

[0004] However, since this method requires a long time for the reaction, it was required to shorten the reaction time by some method.

[0005] In addition, the method for manufacturing an iron-based inorganic coagulant 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 and iron ions, and then reacting them in a sealed container at a temperature of 120 to 180°C. This method aims to shorten the reaction time by carrying out the reaction under high temperature and high pressure, but it still required a reaction time of 0.8 to 1.5 hours.

[0006] Patent document 3 discloses a method for manufacturing an iron-based coagulant by dissolving iron-based raw material, ferric oxide (Fe2O3), in excess sulfuric acid to produce ferric sulfate (Fe2(SO4)3) and partially neutralizing it with hydrated iron-based oxide.

[0007] However, this method has a difficulty in that it cannot efficiently produce a polyferric sulfate solution because the manufacturing process becomes complex, as it includes two processes: dissolving ferric oxide in sulfuric acid and partially neutralizing the generated ferric sulfate. In the example, it is stated that the reaction must be carried out by maintaining the temperature at 100°C for about 3 hours. Prior art literature

[0008] Patent Document 1: Japanese Patent Publication No. Showa 51-17516 Patent Document 2: Japanese Patent Publication No. 3379204 Patent Document 3: Japanese Patent Publication No. 2741137 The problem to be solved

[0009] As mentioned above, in conventional technology, attempts have been made to produce a polyferric sulfate solution by selecting various types of iron compounds as iron-based raw materials and reacting them in various reaction forms; however, in addition to problems such as the generation of free sulfuric acid and reaction residues, there remained the problem of the manufacturing time being prolonged to produce a polyferric sulfate solution suitable for practical use.

[0010] In addition, although details will be provided later, it is stated that in the case of iron-based coagulants, the higher the total iron concentration, the higher the characteristics as a coagulant. Furthermore, the applicant of this patent manufactures and sells the iron-based inorganic polymer coagulant "Polytets" (trademark registered), and its total iron concentration is approximately 11.0 to 12.5% ​​(referred to as "commercial product"). Since iron-based inorganic polymer coagulants possess high coagulation ability and dewatering properties when their total iron concentration is high, recently, products with a total iron concentration of 12.5% ​​or higher have been manufactured and sold as "high-concentration products."

[0011] However, even if a coagulant with a high total iron concentration is manufactured, due to the problem of the aforementioned long manufacturing time, the limit is at most about 12.7% (less than 13%) of the total iron concentration, and it was not possible to manufacture a polyferric sulfate solution of 13.0% or more as a commercial product.

[0012] Furthermore, in the present invention, concentration refers to weight% unless molar concentration is specified, and [T-Fe] is the total weight concentration of iron, [SO4 2- ] is defined as representing the weight concentration of sulfate ions.

[0013] Here, the total iron concentration refers to the concentration that includes not only the iron dissolved in the raw material but also the iron present in the raw material solution as a solid (powder, etc.) that is not dissolved. Since even iron-based powders present in the raw material solution contribute to the reaction for manufacturing the ferric polysulfate solution, it is reasonable to include iron-based components that are not dissolved in the solution in the iron concentration.

[0014] However, even in the polyferric sulfate solution prepared in the present invention, although the concentration is indicated as the total iron concentration, it is natural that all the iron is dissolved.

[0015] The present invention was made to solve these problems and provides a manufacturing method capable of producing a polyferric sulfate solution with a high total iron concentration in a short time compared to conventional products. means of solving the problem

[0016] In order to solve these problems, the present invention is composed of the following technical means.

[0017] (1) A method for producing an iron-based coagulant containing a polyferric sulfate solution, comprising reacting a raw material solution containing ferrous sulfate and sulfuric acid that satisfies the following conditions in a sealed container under high temperature and high pressure conditions.

[0018] Molar ratio of total iron to sulfate ions (SO4 2- / T-Fe) is 1.2 or higher

[0019] The weight concentration of sulfate ions [SO4 2- When set to ], [SO4 2- ] is 35 weight% or less

[0020] (2) A method for manufacturing an iron-based coagulant of (1) characterized by adding nitric acid or nitrite as a catalyst into a sealed container.

[0021] (3) A method for manufacturing an iron-based coagulant of (1) or (2) characterized by high temperature and high pressure reaction conditions, such that the temperature is 100°C or higher and the pressure is 0.3 MPa or higher.

[0022] (4) An iron-based coagulant that is a high-concentration polyferric sulfate solution with a total iron concentration of 13 to 16 weight percent. Effects of the invention

[0023] The ultra-high concentration iron-based coagulant of the present invention is characterized by having a high concentration even when compared to the high concentration iron-based coagulant commercially available to the applicant of the present invention, and possesses high coagulation ability and dewatering properties. In addition, since it contains less moisture compared to conventional products, product transportation costs can be reduced.

[0024] In addition, according to the method for manufacturing an iron-based coagulant of the present invention, the manufacturing time, which required more than 10 hours in conventional methods, can be significantly reduced, and the iron-based coagulant can be manufactured efficiently. Brief explanation of the drawing

[0025] Figure 1 shows the region where ferric polysulfate can be produced by high temperature and high pressure reaction. Figure 2 shows the concentration shift after filtration of a sample in which precipitate was generated. Figure 3 shows the concentration shift after concentration of a sample in which no precipitate was generated. Specific details for implementing the invention

[0026] Here, before describing the technical features of the method for manufacturing an iron-based coagulant according to the present invention, first, an inorganic coagulant is described.

[0027] Generally, in sewage sludge treatment, solid-liquid separation is performed by coagulating suspended particles or colloidal particles in the sludge with a coagulant and dewatering them. The surfaces of suspended particles or colloidal particles in sewage sludge are usually negatively charged and remain in a stable state due to repulsive forces caused by surface charges and hydration. A coagulant is an agent that adsorbs to the surface of these particles, neutralizes the surface charges, and weakens the repulsive forces between the particles, thereby causing them to coagulate.

[0028] Iron-based coagulants are representative inorganic coagulants that perform coagulation by neutralizing the negative surface charge of suspended substances, such as suspended particles or colloidal particles, with positively charged iron ions. For this reason, iron-based coagulants always exhibit coagulation whenever iron ions are present; as the coagulation ability of suspended substances increases with higher iron ion concentrations, the amount of coagulant added can be reduced.

[0029] Furthermore, for iron ions in the coagulant to exist stably, a certain amount of negative ions must be present. In the case of iron-based coagulants, sulfate ions typically fulfill this role. Iron-based coagulants are stable when the amount of negative ions is in an appropriate molar ratio with the amount of iron ions; however, if the amount of negative ions is excessive or insufficient, the coagulant becomes unstable and precipitates out as crystals.

[0030] In addition, when sewage sludge is treated using such iron-based coagulants, iron ions are adsorbed onto the surface of suspended particles or colloidal particles and are separated and recovered as solids, but sulfate ions remain in the treated water.

[0031] For this reason, since the treated water becomes highly acidic, it needs to be neutralized with a large amount of neutralizing agent before being discharged into rivers, and it is said that this is one of the factors increasing the cost of sewage sludge treatment. In other words, as a characteristic required of iron-based coagulants, the total iron concentration ([T-Fe]) contained in the coagulant is high, and the sulfate ion concentration ([SO4) 2- It was required that ]) be low.

[0032] In the preparation of a polyferric sulfate solution using ferrous sulfate as a raw material, the following chemical reaction is believed to proceed.

[0033] m[2FeSO4+(1-n / 2)H2SO4+1 / 2O2+(n-1)H2O]

[0034] → 〔Fe2(OH) n (SO4) 3-n / 2 〕 m

[0035] Only 0 <n≤2, m은 자연수

[0036] The present invention provides a method for forming a solution with high [T-Fe] in a short time for an iron-based coagulant comprising the above-described polyferric sulfate solution, and an iron-based coagulant produced by this method.

[0037] In the present invention, when an oxidation reaction is carried out under high temperature and high pressure conditions using ferrous sulfate (FeSO4) as a solid raw material, the relationship between the total iron concentration and the sulfate ion concentration of the input raw material liquid is set to a specific range. The present invention relates to the molar ratio of total iron to sulfate ions (SO4 2- / T-Fe) is above a specific value, and sulfate ion concentration [SO4 2- By making ] below a specific value, the reaction can be terminated in a short time that is unpredictable from conventional technology, and furthermore, the produced ferric polysulfate solution can be produced with an ultra-high total iron concentration ([T-Fe]) that cannot be produced from conventional technology, thereby achieving a particularly remarkable effect.

[0038] That is, the present invention is characterized by reacting a raw material solution containing ferrous sulfate and sulfuric acid that satisfies the following conditions under high temperature and high pressure conditions.

[0039] Molar ratio of total iron to sulfate ions (SO4 2- / T-Fe) is 1.2 or higher

[0040] The weight concentration of sulfate ions [SO4 2- When set to ], [SO4 2- ] is 35 weight% or less

[0041] It is a new finding discovered by the inventors that when the total iron concentration of ferrous sulfate and the sulfate ion concentration are in this relationship, an ultra-high concentration polyferric sulfate solution can be obtained in a short time without generating a precipitate.

[0042] (High temperature and high pressure reaction)

[0043] The method described in Patent Document 1 is a conventional manufacturing method practiced by the inventors. In this method, the reaction is thought to proceed under room temperature and pressure with three phases—solid, liquid, and gas—interacting with one another. This is because, while the reaction is proceeding, NO x Generation of yellowish-brown gas or NO x It is because the smell was perceived.

[0044] However, in the method of the present invention, even if the autoclave is opened after the reaction is finished, NO x No odor was detected. For this reason, it is presumed that in the high-temperature and high-pressure reaction of the present invention, a reaction involving solid and liquid phases is carried out, in which the solid raw material FeSO4·7H2O is dissolved in the sulfuric acid solution and an oxidation reaction proceeds.

[0045] Then, as the reaction occurs under high temperature conditions, the dissolution of the solid raw material FeSO4·7H2O proceeds more easily, and as the reaction occurs under high pressure conditions, the partial pressure of oxygen rises, increasing the amount of dissolved oxygen in the liquid phase; consequently, the dissolved oxygen [contains] sulfite ions NO2 - I Fe 2+ It is thought that the oxidation reaction of iron ions is dramatically accelerated by directly contributing to the oxidation of iron.

[0046] (Reaction temperature and pressure)

[0047] It is necessary to adjust the temperature inside the container to a range of 100 to 150°C.

[0048] If the reaction temperature is less than 100°C, the oxidation reaction of ferrous sulfate does not proceed sufficiently. In addition, it has been confirmed that if the temperature exceeds 150°C, a yellow precipitate remains, and this precipitate has been identified as Fe(OH)SO4 by X-ray analysis.

[0049] Although specific experimental data is omitted, the inventors have confirmed that the reaction proceeds more effectively as the reaction pressure increases. This is considered natural given the reaction mechanism of the aforementioned high-temperature and high-pressure reaction.

[0050] Therefore, the reaction pressure of the present invention can be set under realistic conditions considering manufacturing costs, etc., and the reaction pressure should be 0.3 MPa or higher.

[0051] (catalyst)

[0052] To promote the reaction for the formation of the above-mentioned ferric polysulfate solution, it is desirable to use a catalyst. Preferred catalysts for promoting the reaction include nitric acid and nitrites, and examples of nitrites include sodium and potassium salts of nitrite. Nitric acid is preferred in terms of reaction-promoting function and cost.

[0053] [Experiment 1]

[0054] 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 high-temperature and high-pressure reaction conditions, and adjusted the raw material solution containing ferrous sulfate and sulfuric acid to various concentrations. They then added nitric acid as a catalyst to carry out a high-temperature and high-pressure reaction. After the reaction time had elapsed, they examined whether a precipitate was formed.

[0055] [Experiment 2]

[0056] In addition, as high-temperature and high-pressure reaction conditions, the reaction temperature was set to 120°C, the reaction pressure to 10.00 MPa, and the reaction time to 10 minutes, and the raw material solution containing ferrous sulfate and sulfuric acid was adjusted to various concentrations. Nitric acid was added as a catalyst to this, and a high-temperature and high-pressure reaction was carried out. Then, whether a precipitate was formed after the reaction time had elapsed was examined.

[0057] The experimental results regarding whether precipitates occur are summarized in Tables 1 and 2.

[0058] It was found that the occurrence of precipitates was completely identical in Experiment 1, conducted at a reaction temperature of 110°C and a reaction pressure of 0.30 MPa, and in Experiment 2, conducted at 120°C and 10.00 MPa. In other words, the results in Table 1 and Table 2 are common to both Experiment 1 and Experiment 2.

[0059] Total iron concentration [T-Fe] and total sulfuric acid concentration [SO4] shown in Table 1 2- In the case of ], a ferric polysulfate solution was formed without the formation of a precipitate, and this is an example of the present invention. In addition, in the case shown in Table 2, the occurrence of a precipitate was confirmed, and this is a comparative example of the present invention.

[0060]

[0061]

[0062] (Specific area)

[0063] The results of these are summarized in FIG. 1. The area marked with a circle in the figure is the area where a ferric polysulfate solution was formed without the formation of a precipitate. This is the area defined in the present invention and is referred to as the "specific area" hereinafter. The [T-Fe] and [SO4] indicated by the white circle included in this specific area 2- ] is the raw material composition of the embodiment of the present invention. By reacting this composition under high temperature and high pressure conditions, a reddish-brown solution of ferric polysulfate could be obtained.

[0064] Meanwhile, a comparative example of the present invention is one in which a reaction is carried out under high temperature and high pressure using the raw material composition indicated by the ▲ symbol located outside a specific region. In the case of using these compositions, the occurrence of precipitates is confirmed in all cases, and the molar ratio of total iron to sulfate ions (SO4 2- In samples in the region where / T-Fe) is lower than 1.2, the precipitate is confirmed to be hydronium jarcite.

[0065] The inventors defined this specific region from the following two formulas.

[0066] First, the upper limit of this region is the weight concentration of sulfate ions [SO4 2- ] can be set to 35 weight% or less.

[0067] Next, the lower limit of this region can be defined by an oblique straight line that rises toward the right. This oblique straight line represents the molar ratio of total iron to sulfate ions (SO4 2- The straight line representing the relationship where / T-Fe) is 1.2 or higher was converted into a diagram where the vertical axis and horizontal axis represent the weight concentration of sulfate ions and the weight concentration of total iron, and recorded.

[0068] The [T-Fe] and [SO4] specified in the present invention as described above 2- The specific region regarding the raw material composition of ] indicates a region in which the production of a ferric polysulfate solution can be stably carried out under high temperature and high pressure conditions.

[0069] The technical significance of this specific area can also be confirmed from the following additional experiments 1 and 2.

[0070] (Additional Experiment 1)

[0071] [T-Fe] and [SO4] in Fig. 1 2- Samples with concentrations of ] 14% and 28%, respectively (hereinafter referred to as (14.0:28.0)) and (15.0:30.0) have precipitates. After filtration of these samples to remove the precipitates, the concentration of the solution was measured, and the composition of the solution was found to be (12.8:27.2) and (14.5:29.8), respectively.

[0072] This is a numerical value within the range defined in the present invention. That is, even in a sample in which a precipitate has formed, it was found that a portion of the solution has a composition included within a specific range of total iron concentration and total sulfate ion concentration defined in the present invention. The details are illustrated in FIG. 2.

[0073] (Additional Experiment 2)

[0074] According to Figure 1, samples (15.0:32.0) and (15.0:34.0) are samples in which no precipitate is formed. These samples were maintained under three environments: (i) 50°C in a dryer, (ii) about 20°C in a laboratory, and (iii) 10°C in an incubator, and changes were observed after one month. As a result, precipitate was observed only in sample (15.0:34.0) maintained at 50°C in a dryer.

[0075] This cause is thought to lie in the following points.

[0076] For samples (15.0:32.0)(15.0:34.0) maintained at 50°C in a dryer for 1 month, [T-Fe] and [SO4 2- As a result of measuring ] again, the respective measurements were (16.0:34.0)(16.0:36.0). The details are illustrated in FIG. 3.

[0077] The sample maintained in the dryer was concentrated as moisture evaporated, but even with concentration, [T-Fe] and [SO4] remain within the range defined in this invention. 2- In samples having a concentration relationship of ], no precipitate is detected. However, in samples where the concentration relationship between the two has deviated from the above range due to concentration, a precipitate is generated as a result of concentration.

[0078] For this reason, precipitates occur only in the (15.0:34.0) sample under condition (i).

[0079] (Reaction time)

[0080] The manufacturing 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 oxidizing agent is devised, at most a solution with a total iron concentration ([T-Fe]) of about 12.5% ​​is obtained, and the reaction time is more than 16 hours.

[0081] In this invention, by employing a high-temperature and high-pressure method, the reaction time was successfully shortened significantly.

[0082] In the embodiment illustrated in FIG. 1, the reaction is terminated within 30 minutes for all samples, ranging from a high-concentration solution with a total iron concentration of 12.5% ​​to an ultra-high-concentration solution with a total iron concentration of 16%. Naturally, the reaction time depends on the total iron concentration; for a total iron concentration of 12.5%, the reaction is terminated in 7.5 minutes, and for a total iron concentration of 16%, the reaction is terminated within 30 minutes. Additionally, the termination of the reaction was determined by measuring the divalent iron concentration in the sample solution.

[0083] The ability to perform a reaction in such a short period of time is a remarkably significant effect that could not be anticipated with conventional technology.

[0084] (Ultra-high concentration solution)

[0085] In order to confirm the effect of the polyferric sulfate solution being of ultra-high concentration, an aggregation test was performed on the following samples A and B. Sample A is a sample having the same total iron concentration as that prepared in the prior art by taking more than 16 hours. Meanwhile, Sample B is a sample with an ultra-high total iron concentration prepared in the present invention.

[0086]

[0087] As a mock solution, the color water of acrylic paint was used as the liquid to be treated, and the amount of Sample B added was reduced so that the total iron content of Sample A and Sample B became equal; that is, the aggregation ability by iron ions was made equal, and the aggregation abilities of the two were compared.

[0088] The conditions for the coagulation test are shown in Table 4.

[0089]

[0090] Since Sample B is of ultra-high concentration, if it is made to have a flocculation ability equivalent to Sample A, its addition amount can be reduced by as much as 32% compared to Sample A. In addition, in the case of Sample B, as shown in Table 1, [SO4 2- Because ] is low, the decrease in pH of the treated liquid after coagulation treatment can be suppressed, and for this reason, the amount of caustic soda added for neutralization can be reduced by 47% compared to the case where sample A is used.

[0091] Furthermore, observing the appearance after floc formation, Sample B, with its ultra-high concentration, exhibited a higher floc formation ability and a faster settling velocity. Thus, despite having the same iron content as Sample A, Sample B demonstrated a higher aggregation ability.

[0092] The reason for this is thought to be that Sample B is more polymerized, which is advantageous for the 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. Industrial applicability

[0093] This invention relates to a coagulant used in the treatment of wastewater such as sewage. Since a coagulant with high coagulation performance can be manufactured in a short time, it can be widely used in the field of wastewater treatment.

Claims

Claim 1 A method for manufacturing an iron-based coagulant containing a polyferric sulfate solution, wherein the method comprises adding nitric acid or nitrite as a catalyst into a sealed container and then reacting a raw material solution containing ferrous sulfate and sulfuric acid in a sealed container under high temperature and high pressure conditions, 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, and wherein the raw material solution is under the following conditions: molar ratio of total iron to sulfate ions (SO4 2- / T-Fe) is 1.2 or higher; the weight concentration of sulfate ions is [SO4 2- When set to ], [SO4 2- A method for manufacturing an iron-based coagulant satisfying that ] is 35 weight% or less; and the total iron concentration in the raw material liquid is 13 to 16 weight%. Claim 2 As an iron-based coagulant in the form of a high-concentration polyferric sulfate solution having a total iron concentration of 13.5 to 16 wt%, the molar ratio of total iron to sulfate ions (SO4 2- / T-Fe) is 1.2 or higher; and the weight concentration of sulfate ions is [SO4 2- When set to ], [SO4 2- Iron-based coagulant having ] 35 weight% or less. Claim 3 delete Claim 4 delete

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