JP2002079003A - Inorganic flocculant using highly purified ferric salt and manufacturing method thereof and processing apparatus in water-purification processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferric inorganic flocculant and a manufacturing method thereof capable of only remaining several ppb (μg/liter) order of a divalent manganese ion in a flocculant separation processing liquid in a water-purification processing. SOLUTION: In the inorganic flocculant using the highly purified ferric salt, a (Mn/Fe) ratio in the inorganic flocculant is 0.0009 or less of four decimal place at a mass ratio. In a manufacturing method of an inorganic flocculant liquid, a (Mn/Fe) concentration ratio of in the inorganic flocculant liquid is reduced by adding an alkalizing agent and an oxidizing agent selected from the group consisting of a permanganate ion, a persulfate ion and a perchlorate ion to an aqueous ferric slat solution containing a manganese ion and removing the manganese ion. In the method and the apparatus for aggregation-processing of raw water, the flocculant liquid is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel iron-based coagulant and a method for producing the same, and a coagulation / separation method and apparatus in water purification treatment. In particular, a divalent manganese ion contains several ppb (μg
The present invention relates to a novel ferric inorganic coagulant capable of remaining only to the extent of about 1 / liter), a method for producing the same, and a method and apparatus for treating with the ferric inorganic coagulant.

[0002]

2. Description of the Related Art Conventionally, in the coagulation and sedimentation process in a water purification (tap water) treatment facility in Japan, only an aluminum-based inorganic coagulant (for example, PAC, sulfate) is used, and No inorganic coagulant (hereinafter sometimes simply referred to as "coagulant" for simplicity) has not been applied at all. However, in recent water purification treatments, when an aluminum-based flocculant is used, it has been pointed out that aluminum ions are likely to remain in the coagulation-sedimentation treatment water, and that this aluminum ion is a cause of Alzheimer's disease. In addition, when an aluminum-based flocculant is used, there is also a problem that floc with good sedimentation properties is not generated when raw water having a large amount of algae with advanced organic pollution is flocculated.

[0003]

In order to cope with such a situation, in the field of water purification treatment, there is a tendency to change from an aluminum-based coagulant to an iron-based coagulant. This is because in the case of an iron-based flocculant, aluminum hardly remains in drinking water, and flocs having relatively good sedimentation are generated even in raw water that has been highly contaminated.
However, in iron-based flocculants (eg, ferric chloride, ferric polysulfate, ferric sulfate, etc.), manganese ions exist as impurities at a high concentration in the form of divalent manganese ions. . For example, a JIS standard 38% ferric chloride solution and a ferric polysulfate product (Fe content of about 10%)
%) Contains about 400 to 1000 manganese ions.
It exists in a high concentration of mg / liter and has a (Mn / Fe) mass ratio of 0.003 to 0.01 (two to three decimal places).
Shows a high value.

[0004] The cause of such a phenomenon is that manganese and iron are contained in the same family in the periodic table in metallic iron (which mainly uses scrap iron), which is a raw material for producing ferric chloride and ferric polysulfate. This is because a large amount of manganese coexists because it is an element. For this reason, when a conventional ferric coagulant having a very large (Mn / Fe) weight ratio of 0.003 to 0.01 is added as a coagulant for water purification treatment, drinking water is added to the coagulation treatment water. Comfortable water quality standards (10 μg /
There is a major problem that divalent Mn ions of a concentration exceeding 1 liter remain, and it is still difficult to simply change an aluminum-based flocculant such as PAC to an iron-based flocculant. .

Similarly, in the field of industrial water treatment, manganese remaining in the treated water may cause manganese contamination. Therefore, the use of a ferric coagulant has a disadvantage in that the coagulation effect of aluminum-based coagulation is low. Despite being larger than the drug, it was inevitable. In addition, divalent Mn ions remaining in the coagulation treatment water can be removed by a catalytic oxidation method after chlorine is added to the coagulation precipitation treatment water and then passed through a manganese sand packed bed. It is much more rational to use a technique in which Mn ions do not remain in the treated water without adding a manganese removal step.

As described above, conventionally, when a ferric chloride solution containing manganese as an impurity or a ferric polysulfate solution is used as a coagulant in a water treatment step, divalent manganese ions are converted into water. Since an oxide is not formed, if an iron-based coagulant containing manganese as an impurity is added to the coagulation / separation step, manganese cannot be separated as SS and remains as divalent manganese ions without changing the form. Inevitably, divalent manganese will inevitably remain in the coagulation separation treatment water. Selective and high-level separation of manganese alone from coexisting liquids of manganese and iron (atomic numbers: Mn25, Fe26), which are homologous in the periodic table and have similar chemical properties, is based on the second chloride. In fact, even researchers at companies involved in the production of iron and ferric polysulfate have made it technically impossible.

[0007]

SUMMARY OF THE INVENTION However, the present inventor has proposed a novel idea for using an iron-based flocculant containing manganese as an impurity, such as ferric chloride or polyferric sulfate, in water purification treatment. Even when a ferric coagulant is added at an appropriate injection rate at which the raw water to be treated can be coagulated well (usually good coagulation occurs at an injection rate of 10 to 50 mg / l ferric chloride). This problem has been solved by developing a high-purity ferric coagulant having a mass ratio (Mn / Fe) in which only a few μg / liter or less of manganese remains in the coagulation-separated water and having a 4-digit decimal place of 0.0009 or less. The point could be solved.

That is, the present invention has solved the above-mentioned problems by the following means. (1) A high-purity ferric inorganic coagulant, wherein the (Mn / Fe) ratio in the ferric inorganic coagulant is 0.0009 or less, which is four digits after the decimal point in terms of mass ratio. (2) A high-purity ferric inorganic flocculant characterized in that the (Mn / Fe) concentration ratio in the ferric inorganic flocculant liquid is 0.0009 or less, which is 4 digits after the decimal point in terms of mass ratio. liquid. (3) To an aqueous ferric salt solution containing manganese ions, an alkali agent and an oxidizing agent selected from the group of permanganate ions, persulfate ions and perchlorate ions are added,
A method for producing a ferric salt-based inorganic flocculant solution, characterized by reducing the (Mn / Fe) concentration ratio of a ferric salt-based inorganic flocculant solution by removing manganese ions. (4) In the water purification facility, the ferric salt-based inorganic coagulant described in (1) or (2) is added to the raw water to be treated for water purification to coagulate the raw water, and then the generated floc is separated. Coagulation separation method. (5) In a water purifying apparatus for coagulating water using a ferric inorganic coagulant, the ferric salt inorganic coagulant according to (1) or (2), wherein manganese ions are reduced, is used. Characteristic coagulation separation treatment equipment for purified water.

The gist of the present invention is that manganese conventionally contained in a ferric coagulant in the form of divalent manganese ions is separated from permanganate ions, persulfate ions and perchlorate ions. Manganese dioxide (tetravalent) is converted to manganese dioxide (tetravalent) form by chemical oxidation means using a combination of an oxidizing agent and an alkaline agent of a specific type selected from the group consisting of: The ferric-based flocculant was removed from the ferric-based flocculant by means such as centrifugal separation and filtration to produce a ferric-based flocculant having a (Mn / Fe) mass ratio of 0.0009 or less, which is much smaller than the conventional one. . Incidentally, without separating the precipitated manganese dioxide, it may be used as a coagulant in that state,
In this case, since the amount of manganese dioxide in the coagulated sediment sludge increases, it is necessary to pay attention to the fact that manganese dioxide may be reduced to generate divalent manganese during the sludge treatment.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a method for producing a high-purity ferric coagulant solution of the present invention will be described below.
Alternatively, a case where a ferric polysulfate solution is used will be described in detail. Either permanganate ion, persulfate ion or perchlorate ion is added to a ferric chloride or ferric polysulfate solution 3 containing manganese as an impurity, which is placed in a reaction tank 1 equipped with a stirrer 2. The resulting oxidizing agent 4 and an appropriate amount of an alkaline agent 5 selected from sodium hydroxide, potassium hydroxide, slaked lime, sodium carbonate, etc. are added and reacted for a required period of time. Even if a ferric coagulant is added to the process, manganese does not remain in the treated water (Mn / Fe).
A ferric chloride solution and a ferric polysulfate solution of not more than 09 can be produced.

The results of the inventor's previous research (Japanese Patent Application No. 11-3)
As shown in 74009), when potassium permanganate is added alone, if the ferric chloride concentration is 20% or less, divalent manganese ions can be sufficiently oxidized only with potassium permanganate. Yes, but the ferric chloride concentration is 3
If it is 0% or more, potassium permanganate alone becomes 2%
A phenomenon was observed in which it was not possible to sufficiently oxidize the multivalent manganese ion. However, after further research, after pursuing a technique capable of highly removing manganese even from a ferric chloride solution having a concentration of 30% or more, it was selected from permanganate ion, persulfate ion, and perchlorate ion. By using an oxidizing agent and a trace amount of an alkaline agent together, even when the concentration of ferric chloride is 30% or more, 2
It has been found that highly manganese ions can be highly oxidized to manganese dioxide (tetravalent) and removed. In particular, permanganate ion as an oxidizing agent and Na as an alkaline agent
It has been found that the best manganese removal effect is obtained when OH is used. In addition, as a strong oxidizing agent,
Ozone and hydrogen peroxide are well known, but as described below,
When applied to the present invention, no effect was observed.

The potassium permanganate and the alkali agent to the 38% ferric chloride stock solution have proper addition amounts, and the proper addition amount of potassium permanganate is 2000 to 4000 m.
g / liter, and the appropriate amount of sodium hydroxide to be added is such that the pH of the solution after the addition of the alkali agent is preferably in the range of 0.01 to 1. pH 1
When the value exceeds 3, iron ions tend to polymerize and change into iron hydroxide colloid, so it is better to avoid them. In addition, when the amount of potassium permanganate and the alkali agent is too large, a large amount of manganese ions will remain in the iron-based flocculant. It was recognized that divalent manganese ions could not be sufficiently oxidized. Furthermore, even if the amount of potassium permanganate is in an appropriate amount, the alkali agent is excessive, and if the pH after the addition of the alkali agent exceeds 2, trivalent iron ions precipitate as ferric hydroxide, and the coagulant is effectively used. It must be avoided because the components are reduced.

The mechanism by which manganese does not remain in the coagulation-separated water by the coagulant of the present invention is, for example, in the case of permanganate ions, due to the combined action of permanganate ions and a trace amount of an alkali agent, the ferric acid solution has The divalent manganese ion, which is an impurity of the above, is effectively oxidized by the reaction shown in the following formula 1 to be converted into SS (solid) manganese dioxide, and the divalent manganese ion disappears. There was found.

[0014]

(Equation 1)

A few hundred meters of a solution containing a very large amount of ferric ion and having a very high acidity (pH 0 or less), such as a 38% ferric chloride solution and a ferric polysulfate solution.
The finding that g / liter of trace manganese ion is oxidized to manganese dioxide by the combined use of permanganate ion, persulfate ion, perchlorate ion and a trace amount of alkali is quite unexpected because there is no description in the literature. It was not a phenomenon. The reason why such a small amount of alkaline agent exhibits such a large effect has not yet been elucidated at this time, but it is supposed that manganese dioxide produced by the presence of a small amount of alkali may cause 2
It is presumed that this is because the reaction of reducing to a multivalent manganese ion is suppressed. When the high-purity ferric coagulant of the present invention completed based on the above findings is added to the coagulation / separation step of the water treatment step and coagulation / separation is performed, divalent manganese ions hardly remain in the treated water. There is a big effect that it disappears. Therefore, the manganese ion concentration in the coagulated water is significantly reduced as compared with the case where conventional ferric chloride is used for water treatment, and the comfortable water quality standard (1
0 μg / liter).

[0016]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited by these examples.

Example 1 An example of producing a high-purity ferric chloride flocculant having a (Mn / Fe) mass ratio of 0.0009 or less. Industrial ferric chloride stock solution (38% FeCl ₃ ) containing 405 mg / liter of manganese ions as impurities
After adding 800 mg / l of sodium hydroxide, 3000 mg / l of an aqueous potassium permanganate solution was added as potassium permanganate, and the mixture was further stirred at room temperature for 3 days. As a result, a precipitate of manganese dioxide was deposited. The pH of this solution was 0.6. This solution was centrifuged to remove SS, and manganese in the separated solution was analyzed by an IPC emission spectrometer.
The amount was as small as 10.2 mg / liter, and an extremely high manganese removal rate of 97.48% was obtained.
The (Mn / Fe) mass ratio of this liquid was reduced to an extremely small value of 7.8 × 10 ⁻⁵ .

Next, a test was conducted to determine the optimum amount of NaOH to be added. That is, manganese ions 40 as impurities
Industrial ferric chloride stock solution containing 5 mg / l (3
8% FeCl ₃ ), NaOH was added at various addition rates, and potassium permanganate was added to each sample at 300%.
0 mg / liter was added, and the mixture was stirred at room temperature (20 to 25 ° C) for 3 days. The precipitated manganese dioxide precipitate was removed by a centrifugal separator, and manganese in the separated solution was analyzed by an ICP emission spectrometer. Table 1 shows the results.

[0019]

[Table 1]

Next, the case where ozone, hydrogen peroxide, sodium persulfate and sodium perchlorate were used instead of potassium permanganate as the oxidizing agent was examined. That is, 405 mg of manganese ions as impurities
/ L industrial ferric chloride stock solution (38% F
eCl ₃ ), after adding 800 mg / liter of sodium hydroxide (addition amount when the removal rate of manganese ions is the maximum in Table 1), ozone, hydrogen peroxide, sodium persulfate and sodium perchlorate. Was added in a molar ratio of 4 times the amount of Mn, and the mixture was added at room temperature (20
After stirring for 3 days at ２５25 ° C.), the mixture was centrifuged and the separated solution was analyzed for manganese. Table 2 shows the results.

[0021]

[Table 2]

From the results shown in Table 2, ozone and hydrogen peroxide, which are known as strong oxidizing agents, did not function at all for the oxidative decomposition of divalent Mn ions, and were ineffective for the purpose of the present invention.

Example 2 Production example of ferric polysulfate liquid having a (Mn / Fe) mass ratio of 0.0009 or less Ferric polysulfate liquid containing 890 mg / l of manganese ion as an impurity (Nippon Steel Mining Company products, F
e content of 10%) and 200 mg of NaOH /
After adding 1 liter, add potassium permanganate solution to 5000
mg / L, and the mixture was stirred at room temperature (20 to 25 ° C) for 3 days. As a result, a precipitate of manganese dioxide was deposited. The precipitated SS was separated by centrifugation, and manganese in the separated solution was analyzed by an IPC emission spectrometer. As a result, manganese ions were extremely small at 8.3 mg / liter.
A highly pure ferric polysulfate solution having an extremely small (Mn / Fe) ratio of 8.3 × 10 ⁻⁵ was obtained.

Example 3 Measurement of Manganese Concentration in Coagulated and Precipitated Water When Using the Coagulant of the Present Invention The ferric chloride coagulant of the present invention prepared in Example 1 was added to raw water in the A waterworks. The coagulation test was conducted by injecting 15 mg / liter of iron, and the manganese ion concentration in the supernatant water was measured. Was few.

Comparative Example 1 An industrial ferric chloride stock solution (38% FeCl ₃ ) containing 405 mg / liter of manganese ions as impurities.
After adding 3000 mg / L of potassium permanganate aqueous solution without adding alkali, the mixture was stirred at room temperature (20-25 ° C) for 3 days, and then divalent manganese ions in the solution were measured. As a result, a large amount of manganese ions remained at 304 mg / liter. From these results, it was confirmed that the combined use of an alkali plays an important role in enhancing the manganese removal effect.

Comparative Example 2 An industrial ferric chloride stock solution (38% FeCl ₃ ) containing 405 mg / liter of manganese ions as impurities.
After adding 400 mg / l of sodium hydroxide to the mixture, the mixture was stirred at room temperature (20 to 25 ° C) for 3 days, and the manganese ion in the ferric chloride was analyzed. As a result, the manganese ion was 405 mg / l. The treatment did not remove any manganese ions.

Comparative Example 3 As a comparative example, a conventional ferric chloride (having a manganese content of 85) was used.
(0 mg / liter), the manganese concentration in the coagulated sedimentation treated water was 23.6 μg / liter, which was a value far exceeding the manganese concentration regulation value of 10 μg / liter of the comfortable water quality item.

[0028]

Since the present invention is configured as described above, the following effects can be obtained.
It is extremely large that contributes to water treatment. (1) Since the manganese impurities in the ferric coagulant can be removed to a high degree, even when the high-purity iron coagulant of the present invention is used for water purification treatment, the content of manganese ions is extremely small. Coagulation separation treatment water can be obtained. (2) From the processability of the above (1), there is no need to provide a manganese removal facility in the water treatment process, and the water purification process can be simplified, which is extremely beneficial. (3) Since manganese ions can be removed from the ferric coagulant solution by simple means, the practicability is high. (4) Since the manganese ion in the ferric coagulant solution used for actual use can be precipitated and separated as an insoluble substance, the purification process is simple.

[Brief description of the drawings]

FIG. 1 is a diagram showing a production example of a high-purity ferric coagulant liquid of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction tank 2 Stirrer 3 Ferric salt aqueous solution 4 Oxidizing agent 5 Alkaline agent

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D015 BA03 BA10 BB05 CA14 DA17 DC02 DC04 DC10 EA02 EA32 4D062 BA03 BA10 BB05 CA14 DA17 DC02 DC04 DC10 EA02 EA32

Claims (5)

[Claims] 1. (Mn / Fe) in a ferric inorganic coagulant
A high-purity ferric inorganic coagulant, characterized in that the mass ratio is 0.0009 or less, which is four digits after the decimal point in terms of mass ratio. 2. The method according to claim 1, wherein (Mn / F) in the ferric inorganic coagulant solution is
e) The concentration ratio is 0.0009 with four digits after the decimal point in terms of mass ratio.
A high-purity ferric-based inorganic flocculant solution characterized by the following: 3. An aqueous solution of a ferric salt containing a manganese ion, comprising adding an alkali agent and an oxidizing agent selected from the group consisting of permanganate ion, persulfate ion and perchlorate ion to obtain a manganese ion. A method for producing a ferric salt-based inorganic coagulant liquid, characterized by reducing the (Mn / Fe) concentration ratio of the ferric salt-based inorganic coagulant liquid by removing the above. 4. In a water purification facility, after adding the ferric salt-based inorganic coagulant according to claim 1 or 2 to the raw water to be treated for water purification to coagulate the raw water, separating the generated floc. Characterized by the method of coagulation and separation of purified water. 5. The use of the ferric salt-based inorganic coagulant according to claim 1 or 2, wherein manganese ions are reduced in a water purifying apparatus for coagulating water using a ferric-based inorganic coagulant. A coagulation separation treatment apparatus characterized in that: