JP5716892B2 - Cleaning method of sludge - Google Patents

Description

The present invention relates to a sludge cleaning method for efficiently cleaning chlorine adsorbed on sludge to reduce the chlorine concentration in the sludge. According to the cleaning method of the present invention, it is possible to reduce the chlorine concentration of neutralized sludge and the like generated from the treatment process of acidic wastewater generated from an industrial facility to the extent that it can be reused as a cement raw material.

Attempts have been made to reuse sludge generated in the wastewater treatment process of industrial facilities as cement raw material, but sludge having a high chlorine concentration cannot be used as cement raw material. Therefore, a method is known in which sludge is washed to remove chlorine.

For example, JP-A-11-156337 (Patent Document 1) describes that incineration fly ash is washed with water to remove chlorine and calcium. In JP-A-2003-19484 (Patent Document 2), an alkali agent is added to an iron chloride-containing solution to produce a hydroxide slurry, which is solid-liquid separated, washed with water, and desalted. A treatment method is described which enhances the desalting effect by precipitating hydroxide after oxidizing ferrous ions in a solution containing iron chloride to ferric ions.

Japanese Patent Laid-Open No. 2002-18394 (Patent Document 3) discloses a method of desalting by adjusting the aqueous slurry of waste to alkaline and then washing it with water to suppress elution of heavy metals (copper, lead, zinc). Have been described. In JP-A-2005-213527 (Patent Document 4), molten fly ash or zinc-containing gas is acid-treated to form a zinc-containing solution, and an alkali agent is added to the zinc-containing solution to precipitate zinc hydroxide. , A method of recovering zinc by washing the precipitate with water to remove chlorine in the precipitate is described.

JP-A-11-156337 Japanese Patent Laid-Open No. 2003-19484 JP 2002-18394 A JP 2005-213527 A

The conventional water washing method cannot sufficiently remove chlorine firmly adsorbed on sludge, and approximately 5,000 to 6,000 mg / kg of chlorine remains. Neutralized sludge generated from the treatment process of acidic wastewater generated from industrial facilities contains calcium, aluminum, magnesium, etc., so it is required to be reused for cement raw materials, etc., but those with high chlorine content are used as cement raw materials The amount available is limited. In addition, although it is described that the chlorine concentration can be reduced to 2,000 mg / kg or less in the method of Patent Document 2, there is a problem that a large amount of washing water is required.

The present invention solves the above-mentioned problems of conventional water washing methods, and provides a method for cleaning sludge that efficiently cleans chlorine adsorbed on sludge and reduces the chlorine concentration in the sludge.

According to this invention, the washing | cleaning method of the sludge which has the following structures is provided.
[1] About a sludge adsorbed with chlorine, a method of removing chlorine by adsorbing and cleaning sludge using a sulfuric acid compound solution or a carbonic acid compound solution to reduce the chlorine concentration in the sludge. A method for cleaning sludge, characterized in that after sludge is washed with water, the sludge is adsorbed and washed with a sulfuric acid compound solution or a carbonate compound solution, and the sludge is again washed with water.
[2] The sludge washing method according to the above [1], wherein the chlorine concentration of the washing filtrate is measured, the adsorption washing is terminated when the chlorine concentration starts to fall after temporarily rising, and the water washing is performed again.
[3] If the chlorine concentration in the sludge or washing filtrate exceeds 4000 mg / L, water washing and adsorption washing are performed while measuring the chlorine concentration or electrical conductivity. If the chlorine concentration is 4000 mg / L or less, the chlorine concentration is reduced. The sludge cleaning method according to the above [1] or [2], wherein the water cleaning and the adsorption cleaning are performed while measuring.
[4] A sulfuric acid compound solution or a carbonic acid compound solution is used as a cleaning liquid for cleaning dewatered sludge using a filter press, or the above-mentioned cleaning liquid for repulp cleaning in which dewatered sludge is dispersed in a cleaning liquid to form a slurry. The sludge washing method according to any one of [1] to [3] above, wherein the dewatered sludge is first washed with water and then adsorbed and washed using a sulfuric acid compound solution or a carbonate compound solution .
[5] The sludge cleaning method according to any one of [1] to [4] above, wherein the sludge adsorbing chlorine is neutralized sludge of wastewater generated in a treatment process of acidic wastewater generated from an industrial facility.
[6] The sludge cleaning method according to any one of [1] to [5] above, wherein the sludge having a reduced chlorine concentration is reused as a cement raw material.

According to the cleaning method of the present invention, the chlorine concentration can be reduced to 1200 mg / kg or less by cleaning sludge having a chlorine concentration of 10 ⁴ to 10 ⁵ mg / kg. About the neutralized sludge etc. which arise from a processing process, chlorine concentration can be reduced significantly to such an extent that it can be reused as a cement raw material.

The cleaning method of the present invention can significantly reduce the amount of cleaning water as compared with a cleaning method that relies on water cleaning. Specifically, as shown in Example 1 of the present invention, with respect to the neutralized sludge generated from the treatment process of acidic wastewater generated from industrial facilities, the chlorine concentration in the sludge is about 1200 mg with a cleaning liquid amount of 126 ml per 1 g of dry sludge. / kg or less can be reduced. On the other hand, as shown in Comparative Example 1, the neutralized sludge similar to the example was washed with water only, and the chlorine concentration in the sludge was about 5000 mg / kg with a washing liquid amount of 126 ml per 1 g of dry sludge. Moreover, the chlorine concentration in the sludge hardly changed even if the amount of washing water was increased more than this.

The graph which shows the relationship between the chlorine concentration of the filtrate of Example 1, and the amount of cleaning liquids. The graph which shows the relationship between the chlorine concentration of the sludge of Example 1, and the amount of cleaning liquids. The graph which shows the relationship between the chlorine concentration of the filtrate of Example 2, and the amount of cleaning liquids. The graph which shows the relationship between the chlorine concentration of the sludge of Example 2, and the amount of cleaning liquids. The graph which shows the relationship between the chlorine concentration of the filtrate of Example 3, and the amount of cleaning liquids. The graph which shows the relationship between the chlorine concentration of the sludge of Example 3, and the amount of cleaning liquids. The graph which shows the relationship between the chlorine concentration of the filtrate of the comparative example 1, and the amount of cleaning liquids. The graph which shows the relationship between the chlorine concentration of the sludge of the comparative example 1, and the amount of cleaning liquids. The graph which shows the relationship between the chlorine concentration of a filtrate, and electrical conductivity. The graph which shows the relationship between the chlorine concentration of a filtrate, and the amount of cleaning liquids. The graph which shows the relationship between the electrical conductivity of a filtrate, and the amount of cleaning liquids. 2 is an X-ray diffraction chart of Example 1. FIG. The graph which compares and shows the cleaning effect of Example 1 and Comparative Example 1.

Hereinafter, the present invention will be specifically described based on embodiments.
The method of cleaning the invention, the sludge chlorine is adsorbed, a cleaning method is disengaged chlorine by adsorbing washing the sludge with sulfuric acid compound solution or a carbonic acid compound solution, to reduce the chlorine concentration of the sludge The sludge washing method is characterized in that after the sludge adsorbed with chlorine is washed with water, the sludge is adsorbed and washed using a sulfuric acid compound solution or a carbonate compound solution, and the sludge is washed with water again .

The sludge to which chlorine is adsorbed is, for example, neutralized sludge generated from a treatment process of acidic wastewater generated from an industrial facility. These waste liquids are neutralized by adding slaked lime or the like, and a large amount of chlorine is adsorbed (chlorine concentration: about 10 ⁴ to 10 ⁵ mg / kg, etc.). In addition, the cleaning method of the present invention is applied to sludge discharged from facilities using hydrochloric acid and chlorine, sludge and fly ash discharged from waste plastic processing facilities, and sludge and fly ash discharged from waste treatment facilities. can do.

The cleaning method of the present invention uses a sulfuric acid compound solution or a carbonate compound solution as a cleaning liquid, and utilizes sulfate ions (SO ₄ ^2- ) and carbonate ions (CO ₃ ^2- ) present in these solutions to produce chloride ions (Cl ^-) is allowed to withdrawal from the sludge. Since sulfate ions (SO ₄ ^2- ) and carbonate ions (CO ₃ ^2- ) have a higher affinity for sludge than chlorine ions (strong adsorption power), using a sulfate compound solution or a carbonate compound solution as a cleaning solution Since chlorine ions in the sludge are replaced by sulfate ions and carbonate ions, and sulfate ions and carbonate ions are adsorbed by the sludge and the chlorine ions are released into the cleaning liquid, the chlorine concentration in the sludge can be greatly reduced. As described above, cleaning using a sulfate compound solution or a carbonate compound solution utilizes the strength of adsorption of sulfate ions (SO ₄ ^2- ) and carbonate ions (CO ₃ ^2- ). This is called adsorption cleaning. Sulfuric acid ions (SO ₄ ²⁻ ) and carbonate ions (CO ₃ ²⁻ ) are preferable because they have strong adsorptive power and are inexpensive.

The sulfuric acid compound solution to be used is not particularly limited, and for example, sodium sulfate, calcium sulfate, potassium sulfate, aluminum sulfate, alum or magnesium sulfate can be used. Gypsum and regenerated gypsum may be used as calcium sulfate.

The carbonate compound solution to be used is not particularly limited, and sodium carbonate, sodium hydrogen carbonate, calcium carbonate, potassium carbonate, aluminum carbonate, magnesium carbonate, or carbonated water in which carbon dioxide is dissolved in water and is present as carbonate ions may be used. it can.

Preferably, sodium sulfate, calcium sulfate, sodium carbonate, or sodium bicarbonate is used. The sulfate ions adsorbed on the sludge react with calcium in the sludge to produce calcium sulfate (gypsum), but since calcium sulfate is an ordinary cement raw material component, it does not interfere with the reuse of the washed sludge as a cement raw material. . Further, sodium is removed by being contained in the washing filtrate together with chlorine released from the sludge. When sodium carbonate or calcium carbonate is used, most of the carbonic acid component is vaporized and removed during cement clinker firing.

In addition, since sulfuric acid aqueous solution dissolves sludge, it is not suitable for the cleaning liquid of the present invention. However, a sulfuric acid compound aqueous solution obtained by mixing a sulfuric acid aqueous solution with an alkali metal hydroxide such as sodium hydroxide or an aqueous solution thereof can be used as the cleaning liquid of the present invention.

Adsorption washing improves the washing effect at pH 3-12, and the pH range 5-9 is optimal. Therefore, it is preferable to adjust the solution during washing to this pH range.

In the cleaning method of the present invention, it is preferable to first remove chlorine that is easily removed by performing water washing first, and then perform adsorption washing to promote the removal of chlorine, and then perform water washing again to remove the remaining chlorine. The number of times of water cleaning and adsorption cleaning and the amount of water may be determined according to the state of sludge.

The cleaning method of the present invention can be applied to cake sludge cleaning, slurry sludge repulp cleaning, and the like. As the cake washing liquid or the repulp washing liquid, a sulfuric acid compound solution or a carbonate compound solution may be used.

In the cleaning method of the present invention, it is preferable to perform water cleaning and adsorption cleaning while measuring the chlorine concentration or electrical conductivity (conductivity) of sludge and cleaning filtrate. In the high chlorine concentration range (approximately 4,000 to 40,000 mg / L), the chlorine concentration correlates with the electrical conductivity, but in the low chlorine concentration range (approximately 4,000 mg / L or less), the electrical conductivity depends on the chlorine concentration. Since it does not depend, the electrical conductivity is preferably used in a cleaning region where the chlorine concentration is relatively high.

An example of washing while measuring the chlorine concentration or electrical conductivity of sludge and washing filtrate is shown below.
(I) Wash the sludge cake with water, measure the electrical conductivity of the filtrate, and when the electrical conductivity becomes constant, finish washing with water and perform adsorption cleaning.
(B) The chlorine concentration of the washing filtrate obtained along with the adsorption cleaning is measured, and the adsorption cleaning is terminated when the chlorine concentration begins to decrease after temporarily increasing, and then water cleaning is performed again.
(C) Since the chlorine concentration of the filtrate continuously decreases as the amount of the cleaning solution increases in water cleaning, the chlorine concentration of the filtrate is used as an index, and the water cleaning is terminated when the chlorine concentration of the filtrate decreases to the target value.

The washing | cleaning method of this invention can be used suitably for the washing | cleaning of the neutralized sludge etc. which arise from the process of the acidic waste water which generate | occur | produces from an industrial facility, for example. A large amount of chlorine is contained in sludge neutralized by adding slaked lime to acidic wastewater generated from industrial facilities. According to the cleaning method of the present invention, the chlorine concentration of sludge can be reduced to a chlorine concentration acceptable as a cement raw material with a small amount of cleaning water (about 126 ml per 1 g of dried sludge). Accordingly, the washed neutralized sludge can be reused as a cement raw material.

Examples of the present invention are shown below together with comparative examples. Measurement of chlorine concentration and electrical conductivity of the washing filtrate, measurement of chlorine concentration of sludge, and X-ray analysis of sludge were performed as follows.
(I) The chlorine concentration in the filtrate was measured by the ion electrode method. The filtrate was diluted to give a measurement solution, and after adding potassium nitrate to the measurement solution for conditioning, the chlorine ion electrode was immersed in the measurement solution, and the chlorine ion concentration was measured with an ion meter calibrated in advance.
(B) Chlorine concentration in sludge was measured by combustion volatilization. Put sludge in the combustion tube and heat it to volatilize the chlorine. Volatilized chlorine content was recovered in the liquid at the collection section, and the chlorine concentration of the recovered liquid was measured by ion chromatography.
(C) In the powder X-ray analysis of sludge, the sludge was dried and then finely pulverized, and an X-ray diffraction chart was obtained using a powder X-ray diffractometer (manufactured by RIGAKU).
(D) The electrical conductivity of the filtrate was measured using an electrical conductivity meter.

[Example 1]
Hydrochloric acid waste liquid (chlorine concentration: 4,800 mg / L) was added with slaked lime to neutralize to pH 7 to make a slurry containing this neutralized sludge. The slurry was suction filtered with a Buchner funnel. The sludge remaining on the filter paper was filtered with 100 ml of water. This filtration operation for the sludge remaining on the filter paper is called filtration cleaning. The filtrate was collected and the chlorine concentration was measured. This water washing and measurement of chlorine concentration were performed three times. Next, the sludge was filtered and washed with 100 ml each of an aqueous sodium sulfate solution (concentration 4,400 mg / L), and the chlorine concentration of the filtrate was measured. This adsorption cleaning and the measurement of chlorine concentration were performed twice. Thereafter, the sludge was again washed with 100 ml of water and the chlorine concentration of the filtrate was measured. This water washing and measurement of chlorine concentration were performed three times. In this example, the total amount of cleaning liquid was 800 ml, and the amount of cleaning liquid per 1 g of dried sludge was about 126 ml. The relationship between the chlorine concentration of the filtrate and the amount of cleaning liquid is shown in FIG. The relationship between the sludge chlorine concentration and the amount of cleaning liquid is shown in FIG. The chlorine concentration in the final washing filtrate was 60 mg / L, and the chlorine concentration in the sludge after washing was 1,110 mg / kg. The sludge after washing was dried and pulverized, and the form of the contained components was examined by powder X-ray analysis. The powder X-ray diffraction pattern is shown in FIG. This diffraction chart shows a peak of gypsum (CaSO ₄ ), and it can be seen that sulfate ions in the cleaning liquid are combined with calcium in the sludge and are contained in the sludge as gypsum.

[Example 2]
A slurry containing the same neutralized sludge as in Example 1 was suction filtered with a Buchner funnel. The sludge remaining on the filter paper was filtered and washed with 100 ml of water. The filtrate was collected and the chlorine concentration was measured. This water washing and measurement of chlorine concentration were performed 5 times. Next, the sludge was filtered and washed with 100 ml each of an aqueous calcium sulfate solution (concentration 2,000 mg / L), and the chlorine concentration of the filtrate was measured. This adsorption washing and measurement of the chlorine concentration were performed 10 times. In this example, the total amount of the cleaning solution was 1500 ml, and the amount of the cleaning solution per 1 g of dried sludge was about 237 ml. The relationship between the chlorine concentration of the filtrate and the amount of cleaning liquid is shown in FIG. The relationship between the chlorine concentration in the sludge and the amount of cleaning liquid is shown in FIG. The chlorine concentration of the final washing filtrate was 60 mg / L, and the chlorine concentration in the sludge after washing was 230 mg / kg.

Example 3
A slurry containing the same neutralized sludge as in Example 1 was suction filtered with a Buchner funnel. The sludge remaining on the filter paper was filtered and washed with 100 ml of water. The filtrate was collected and the chlorine concentration of the filtrate was measured. This water washing and measurement of chlorine concentration were performed three times. Next, the sludge was filtered and washed with 100 ml each of an aqueous sodium carbonate solution (concentration 5,300 mg / L), and the chlorine concentration of the filtrate was measured. This adsorption cleaning and the measurement of chlorine concentration were performed twice. Next, the sludge was again filtered and washed with 100 ml of water, and the chlorine concentration of the filtrate was measured. This water washing and measurement of chlorine concentration were performed three times. In this example, the total amount of cleaning liquid was 800 ml, and the amount of cleaning liquid per 1 g of dried sludge was about 126 ml. The relationship between the chlorine concentration of the filtrate and the amount of cleaning liquid is shown in FIG. The relationship between the chlorine concentration in the sludge and the amount of cleaning liquid is shown in FIG. The chlorine concentration in the final washing filtrate was 40 mg / L, and the chlorine concentration in the sludge after washing was 1,000 mg / kg.

[Comparative Example 1]
The slurry containing the same neutralized sludge as in Example 1 was suction filtered with a Buchner funnel. The sludge remaining on the filter paper was filtered and washed with 100 ml of water. The filtrate was collected and the chlorine concentration was measured. This water washing and measurement of chlorine concentration were performed 8 times. In this comparative example, the total amount of cleaning liquid was 800 ml, and the amount of cleaning liquid per 1 g of dried sludge was about 126 ml. FIG. 7 shows the relationship between the chlorine concentration of the filtrate and the amount of cleaning liquid. FIG. 8 shows the relationship between the chlorine concentration in the sludge and the amount of cleaning liquid. The chlorine concentration in the final washing filtrate was 190 mg / L, and the chlorine concentration in the sludge after washing was 4960 mg / kg.
The sludge after washing was dried and pulverized, and the form of the contained components was examined by powder X-ray analysis. The powder X-ray diffraction pattern is shown in FIG. In this diffraction chart, NaCl and gypsum peaks were not recorded.

[Comparative Example 2]
The slurry containing the same neutralized sludge as in Example 1 was suction filtered with a Buchner funnel. The sludge on the filter paper was collected, dried, and the form of the contained components was examined by powder X-ray analysis. The powder X-ray diffraction pattern is shown in FIG. This diffraction chart had a NaCl peak, and it was confirmed that the sludge after washing contained a large amount of chlorine.

The result of comparing Example 1 and Comparative Example 1 is shown in FIG. The chlorine concentration of the washing filtrate of Example 1 subjected to the adsorption cleaning is significantly lower than the chlorine concentration of Comparative Example 1, and it is understood that the chlorine removal is promoted by sulfate ions. Moreover, as shown in FIG. 12 which compared the powder X-ray diffraction pattern of the sludge of Example 1, Comparative Example 1, and Comparative Example 2, when chlorine in the sludge is not washed (Comparative Example 2), it is NaCl as sludge. When NaCl is removed by water washing (Comparative Example 1), NaCl is removed, but a large amount of chlorine that does not appear in the X-ray diffraction pattern is adsorbed (see FIG. 8). On the other hand, when the cleaning of the present invention (water cleaning + adsorption cleaning) is performed (Example 1), most of the chlorine in the sulfate ion sludge is removed (FIG. 2), and instead, the gypsum is replaced by sulfate ions in the cleaning liquid and calcium in the sludge. Is formed.

In Example 2, a calcium sulfate aqueous solution was used as the adsorbing cleaning liquid. As shown in FIGS. 3 and 4, the chlorine concentration in the filtrate and sludge was much lower than the chlorine concentration in Comparative Example 1, and sulfate ions It can be seen that the chlorine removal by is promoted. Further, Example 3 uses an aqueous sodium carbonate solution as the adsorbing cleaning liquid, but as shown in FIGS. 5 and 6, the chlorine concentrations of the filtrate and the sludge are both significantly lower than the chlorine concentration of Comparative Example 1, It can be seen that the removal of chlorine by carbonate ions is promoted. As is clear from this result, the neutralized sludge recovered from the treatment process of acidic wastewater generated from industrial facilities contains a large amount of chlorine. However, it can be put into a cement kiln by performing the adsorption cleaning of the present invention. It can be used as a raw material without.

Example 4
The slurry containing neutralized sludge similar to that in Example 1 was subjected to pressure filtration (filter press), and the sludge remaining on the filter cloth was washed with water and adsorbed. During the washing, the filtrate was collected, and its chlorine concentration and electric conductivity were measured using an ion electrode or an electric conductivity meter. FIG. 9 shows the relationship between the chlorine concentration of the filtrate and the electrical conductivity when this sludge is washed. Moreover, the change of the chlorine concentration and electrical conductivity accompanying sludge washing | cleaning is shown in FIG. 10 and FIG. 11, respectively.

As shown in FIG. 9, in the region where the chlorine concentration is high (4,000 to about 40,500 mg / L), there is a correlation between the chlorine concentration and the electric conductivity, but in the region where the chlorine concentration is low (4,000 mg / L or less), It can be seen that the electrical conductivity is constant regardless of the chlorine concentration. Therefore, it is preferable to use the electrical conductivity in the cleaning region where the chlorine concentration is relatively high.

The washing method was performed while measuring the chlorine concentration and electrical conductivity of the filtrate as follows.
(1) The sludge remaining on the filter cloth was washed with water, and the electrical conductivity of the filtrate was measured. When the electrical conductivity became constant, the water washing was terminated.
(2) Next, adsorption cleaning was performed. As the washing solution, an aqueous sodium sulfate solution (4,400 mg / L) was used. This adsorption cleaning increased the electrical conductivity as shown in FIG. This is because chlorine in the sludge is released, and sulfate ions in the cleaning liquid flow out. The sludge is washed with about 200 ml of an aqueous sodium sulfate solution to complete the adsorption washing. At this time, the chlorine concentration of the filtrate is lowered as shown in FIG.
(3) Next, the sludge is washed again with water. As shown in FIG. 11, the electrical conductivity decreases and becomes constant over time, but as shown in FIG. 10, the chlorine concentration of the filtrate increases continuously as the amount of the cleaning liquid increases.
(4) Water washing was terminated when the chlorine concentration of the filtrate was reduced to 60 mg / L.

In this example, the total amount of cleaning solution was about 1000 ml. The chlorine concentration in the final filtrate was 60 mg / L, and the chlorine concentration in the sludge cake after washing was 1,000 mg / kg.

As shown in the results of Examples 1 to 4, if the chlorine concentration of the washing filtrate is 400 to 500 mg / L or less, the chlorine concentration in the sludge is about 1,000 to 2,000 mg / kg. Reduced to

Claims (6)

This is a cleaning method that removes chlorine by adsorbing and cleaning sludge using a sulfuric acid compound solution or carbonate compound solution to reduce the chlorine concentration in the sludge . A method for cleaning sludge, characterized in that after sludge is washed with water, the sludge is adsorbed and washed with a sulfuric acid compound solution or a carbonate compound solution, and the sludge is washed with water again. The method for cleaning sludge according to claim 1, wherein the chlorine concentration of the washing filtrate is measured, and when the chlorine concentration begins to decrease after temporarily increasing, the adsorption cleaning is terminated and the water cleaning is performed again. When the chlorine concentration of sludge or washing filtrate exceeds 4000 mg / L, water washing and adsorption washing are performed while measuring the chlorine concentration or electrical conductivity, and when the chlorine concentration is 4000 mg / L or less, the chlorine concentration is measured. The method for cleaning sludge according to claim 1 or 2, wherein water cleaning and adsorption cleaning are performed. As a cleaning solution for cleaning dewatered sludge using a filter press, or as a cleaning solution for repulp cleaning in which dewatered sludge is dispersed in a cleaning solution to form a slurry, a sulfuric acid compound solution or a carbonate compound solution is used for the above dehydration. The sludge washing method according to any one of claims 1 to 3, wherein the sludge is first washed with water and then adsorbed and washed using a sulfuric acid compound solution or a carbonate compound solution .
The sludge washing method according to any one of claims 1 to 4, wherein the sludge to which chlorine is adsorbed is neutralized sludge of wastewater generated in a treatment process of acidic wastewater generated from an industrial facility. The method for cleaning sludge according to any one of claims 1 to 5, wherein sludge having a reduced chlorine concentration is reused as a cement raw material.

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