JPH09155396A - Aluminum recovery method in sludge treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover aluminum efficiently from precipitated sludge produced in a water purifying plant and convert the dewatered sludge after the recovery of aluminum into cake of a low water content. SOLUTION: Precipitated sludge containing aluminum which is produced in the treatment process of a water purifying plant is concentrated and reduced of its volume by a filtrate concentrating apparatus 2. The sludge after being added with sulfuric acid as an aluminum dissolving chemical to be dispersed by a mixer 4, is introduced into an electroosmosis type dewaterer 5, direct current voltage is applied between an anode plate 5a and a cathode plate 5b, aluminum liquid is collected on the cathode side together with water contained in the sludge by the effect of electroosmosis and recovered efficiently by passing through a filter member 5c, and the sludge is converted into dewatered sludge cake of a low water content.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an aluminum recovery method for separating and recovering aluminum contained in a settled sludge generated in a water purification plant or the like from the sludge in the process of treating the settled sludge.

[0002]

2. Description of the Related Art In a water purification plant, water containing clay-based suspensions taken from rivers and lakes is purified by a process as shown in FIG. 9, and aluminum sulfate, or Sodium aluminate is added to the aluminum coagulant, and in the subsequent stirring and precipitation steps, the sludge containing aluminum components is transferred to an aluminum recovery facility for treatment.

Further, FIG. 10 shows aluminum sulfate as introduced in Volume 59, No. 9 (1990) “Aluminum recovery in purified water sludge treatment” (author: Miki Kobayashi), published by Japan Water Works Magazine. FIG. 10 is a process flow diagram of sludge treatment accompanied with recovery, in which after pre-concentrating the precipitated sludge generated in the process step of FIG. 9, sulfuric acid which is an aluminum-dissolving chemical is added so that the pH becomes 3.3 or less, and the sediment concentration is performed. It is introduced into the tank, where it is separated into supernatant water in which aluminum hydroxide is dissolved and sedimentation concentrated sludge, and the supernatant water is collected in a recovery aluminum liquid storage tank, and one sedimentation concentrated sludge is mixed by adding slaked lime. Introduce it into the tank to neutralize sludge,
After flocculation, dehydration is performed by vacuum or pressure dehydration with a dehydrator to convert to dehydrated sludge with low water content. The recovered supernatant is reused as an aluminum flocculant, and the remaining dehydrated sludge is disposed of in landfill, for example.

Here, when the sludge concentration after the preconcentration is set to 2%, the aluminum recovery rate recovered from the settled sludge sludge by the above-mentioned conventional process, the aluminum concentration, the sulfuric acid addition amount, etc. are calculated as follows. . That is, when treating 1000 kg of concentrated sludge, the sludge solid content contained in the sludge is 20 kg, and this sludge solid content is aluminum hydroxide produced by the injection of the aluminum coagulant in the water purification process of FIG. And the content rate is 20%, the amount of aluminum hydroxide is 4
Since it is Kg and the required amount of sulfuric acid that dissolves 1 kg of aluminum hydroxide (equivalent amount of sulfuric acid that reacts with aluminum hydroxide in sludge) is 1.9 kg, 1000 Kg
The required amount of sulfuric acid to be added to g of the settled sludge is 7.6 kg. The dissolution of aluminum hydroxide with sulfuric acid is represented by the following formula.

[0005]

Embedded image 2Al (OH) ₃ + 3H ₂ SO ₄ → Al (SO ₄ ) ₃ + 6H ₂ O In addition, it is assumed that this sulfuric acid-added sludge is concentrated to 8% in the next sedimentation concentration step, When the aluminum concentration and the aluminum recovery rate are calculated, the aluminum concentration is 0.264% and the aluminum recovery rate is 80.2%.

[0006]

In the above-mentioned conventional aluminum recovery method, in order to increase the aluminum concentration of the recovered aluminum liquid, it is necessary to reduce the water content of the pre-concentrated sludge as much as possible, and to increase the aluminum recovery rate. It is necessary to increase the concentration of concentrated sludge. Then
Since the conventional method uses the sedimentation concentration method to concentrate the sludge, the sludge concentration is about 8% at most and no further increase in concentration can be expected, so the aluminum recovery rate is low.
Further, the concentrated sludge obtained by solid-liquid separation of the aluminum liquid as the supernatant liquid also contains a large amount of unrecovered aluminum liquid as pore water in the sludge. It is necessary to add a large amount of slaked lime (about 20% by weight), and there is also an environmental problem that alkaline components are eluted from the sludge at the landfill disposal destination of the dehydrated sludge.

The present invention has been made in view of the above points, and an object thereof is to solve the above problems and to achieve high aluminum recovery efficiency, and to reduce sludge after aluminum recovery without adding slaked lime. Provided is a method for recovering aluminum in sludge treatment, which makes it possible to obtain a dehydrated sludge caked to a water content and also allows an aluminum-soluble chemical used for recovering aluminum to be generated in the system without externally supplying it. Especially.

[0008]

In order to achieve the above object, the aluminum recovery method of the present invention is carried out as follows. 1) After adding aluminum-soluble chemicals to the sludge whose volume has been reduced through the concentration step, the sludge is introduced into an electro-osmotic dehydrator and a DC voltage is applied between its electrodes, and the water contained in the sludge is subjected to electro-osmosis. The aluminum liquid should be collected on one electrode side together with the above and collected through a filtering member.The aluminum soluble chemical used here should be an acidic chemical such as sulfuric acid or an alkaline chemical such as sodium hydroxide. You can

2) Sludge is introduced into an electroosmotic dehydrator, a DC voltage is applied between its electrodes, and aluminum-soluble chemicals are supplied to the sludge from one electrode side, and the sludge is permeated into the sludge by the electroosmotic action. While dissolving the aluminum component with the aluminum-soluble chemical, the aluminum liquid is collected on the other electrode side together with the water contained in the sludge and then collected through the filtering member.

3) Initially, an electrolyte such as sodium sulfate was added to the sludge, and then the sludge was introduced into an electroosmotic dehydrator and a DC voltage was applied between the electrodes to remove the components of the electrolyte ionized by the electroosmotic action. Along with the water contained in the sludge, it is collected as a filtrate, and this filtrate is added to the sludge introduced into the electroosmotic dehydrator as an aluminum-soluble chemical to recover aluminum.

As described above, by adopting the electroosmotic dehydration method for recovering the aluminum contained in the sludge, the aluminum liquid produced by the reaction with the aluminum-soluble chemical is sludge under the electroosmotic action. It is collected together with the contained water in the one electrode side of the electroosmotic dehydrator, and is efficiently separated and recovered from the sludge. Further, in this case, if an alkaline chemical such as sodium hydroxide is adopted as the aluminum-soluble chemical, the dehydrated sludge is neutralized by the action of the alkali ions ionized by the electroosmotic dehydration action, and a substantially neutral dehydrated sludge is obtained. .

In the method of supplying the aluminum-soluble chemicals to the sludge through the electrodes of the electroosmotic dehydrator as in the item 2), the chemicals are directly added to the sludge by utilizing the electroosmotic action without using a mixer. It can penetrate and effectively dissolve aluminum. Further, according to the method of the item 3), without preparing an expensive aluminum-soluble chemical such as sulfuric acid,
It is possible to generate an aluminum-dissolving chemical in the system by utilizing the electroosmotic effect only by supplying an inexpensive electrolyte such as sodium sulfate at the beginning of operation.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. [Embodiment 1] FIG. 1 is a flow chart of an embodiment corresponding to claims 1 and 2 of the present invention. In this example, the settled sludge generated in the water purification plant (the settled sludge containing the aluminum flocculant obtained in the water purification process of FIG. 9) was pre-concentrated, and sulfuric acid was added to this as an aluminum-soluble chemical, followed by electroosmotic dehydration. Introduced into the machine to separate and collect the dissolved aluminum together with the filtrate, to obtain a dehydrated sludge with a low water content,
As shown in the figure, the aluminum recovery treatment facility is provided with a sedimentation concentration tank 1, a filtration concentration device 2, an acidic sulfuric acid storage tank 3, a kneader 4, an electroosmotic dehydrator 5, a recovered aluminum liquid storage tank 6, a dehydrated sludge storage 7, and the like. It is configured. The filtration concentrator 2 in the figure is, for example, the concentrator described in JP-B-60-59002 and JP-B-61-57043, and as the electroosmotic dehydrator 5, JP-B-60-25.
The device described in Japanese Patent No. 597 can be adopted.

First, the settled sludge is supplied to the settling / concentrating tank 1 for the recovery treatment facility. As shown in FIG. 2, the composition of the settled sludge consists of insoluble sludge particles, aluminum hydroxide, and water. The settled sludge introduced into the settling / concentrating tank 1 is separated into supernatant water and settled concentrated sludge by gravity settling action. The settled concentrated sludge is introduced into the next filtration / concentration device 2. In the filtration / concentration device 2, the settled concentrated sludge is separated into separated water and high-concentration filtered concentrated sludge by the filtering material that has received negative pressure. Next, sulfuric acid is added to the filtered concentrated sludge from the sulfuric acid storage tank 3 and introduced into the mixer 4, and the sulfuric acid is uniformly dispersed in the filtered concentrated sludge to adjust the pH to about 2 to 3 and contained in the sludge. A sludge added with sulfuric acid in which aluminum hydroxide is dissolved by sulfuric acid is obtained. This sulfuric acid-added sludge is then supplied to the passage between the anode plate 5a of the electroosmotic dehydrator 5 and the filter member (filter cloth) 5c that is superposed on the cathode plate (perforated plate) 5b, and is pressurized. Electro-osmotic dehydration is performed by applying a DC voltage from the DC power supply 5e between the anode plate 5a and the cathode plate 5b while applying mechanical squeezing force with the device 5d. As a result, the aluminum liquid, together with the water contained in the sludge, passes through the filtering member 5c by the electroosmotic action and is collected in the cathode plate 5b, and is collected in the recovered aluminum liquid storage tank 6 as a filtrate. The filtrate is reused as the aluminum coagulant shown in FIG. The dehydrated sludge that has been dehydrated and made into a cake is discharged to the outside from between the electrodes and stored in the dehydrated sludge storage 7.

Next, in the electroosmotic dehydrator 5 described above
The state of electroosmosis is shown in FIG. That is, DC voltage
The insoluble sludge particles (clay, sand,
(Vegetables, etc.) are negatively charged, and the water (H
_TwoO) is positively charged, and water is attracted to the cathode plate 5b.
Permeate through the filtration member 5c and is discharged as a filtrate out of the system.
It is. In addition, S generated in the water by addition of sulfuric acid
O_Four ^2-, Al formed by melting aluminum hydroxide³⁺， This
Na contained in sedimented sludge from the beginning⁺, Cl^-, Fe ³⁺Such as
Contains ions, of which SO_Four ^2-, Cl^-The shadow of
ON moves to the anode plate 5a, and Al³⁺, Na⁺Fe³⁺Such as
The ON moves to the cathode plate 5b and the water content H_TwoWith O and filtrate
And then discharged.

As a result, the aluminum hydroxide contained in the precipitated sludge can be efficiently separated and recovered as a high-concentration aluminum liquid (filtrate) by the electroosmotic action, while the precipitated sludge is dehydrated to a low water content. It can be turned into a dehydrated cake that is easy to dispose of. In addition, the evaluation test carried out by the inventors to confirm the effect of the above-mentioned recovery method is as follows: 2000 kg of precipitated sludge having a sludge solid content of 1.0% and an aluminum hydroxide content of 20%.
1 was treated according to the flow chart of FIG. 1, the sludge solid content was concentrated to 2% by sedimentation and concentration, and
The volume was reduced to 00 kg, and the sludge fixed content was reduced by subsequent filtration and concentration.
It was concentrated to 8.5% to obtain 235 Kg of filtered concentrated sludge. Next, 7.6 Kg of sulfuric acid was added to the filtered concentrated sludge, and the sludge added with sulfuric acid adjusted to pH 3.3 was electroosmotically dehydrated to obtain 55.5 Kg of dehydrated sludge and 20
7.1 kg of filtrate was separated and collected separately. As a result of investigating the properties of the filtrate and the dehydrated sludge, the aluminum concentration in the filtrate was 1.2% (as Al ₂ O ₃ ), and the caked dehydrated sludge had a pH of 3.0, The water content was 55%.

[Embodiment 2] FIG. 4 shows claims 1 and 3 of the present invention.
It is a flowchart of the Example corresponding to. In this example,
Basically the same as in Example 1, but with alkaline sodium hydroxide (NaOH) as the aluminum-dissolving chemical.
The sludge to which is added is introduced into an electroosmotic dehydrator to separate and recover the aluminum component to obtain a dehydrated sludge having a low water content. In this Example, the sludge was adjusted to pH 9 to 14 by adding sodium hydroxide supplied from a sodium hydroxide storage tank 8 as an aluminum-dissolving chemical after the settled sludge was settled and concentrated, and filtered and concentrated. Four
Sodium hydroxide-added sludge obtained by mixing so as to uniformly disperse sodium hydroxide in the sludge was introduced into the next stage electroosmosis dehydrator, and the sludge was dehydrated in the same manner as in Example 1 to obtain aluminum. Separate and collect the liquid.

In this electroosmotic dehydration step, as shown in FIG. 5, the surface of the insoluble sludge particles is negatively charged, and the water in contact therewith is positively charged and moves to the cathode plate 5b side,
It passes through the filtration member 5c and is discharged to the outside of the system. Here, the aluminum contained in the sludge is dissolved by the reaction with sodium hydroxide, and most of it is recovered as aluminate from the cathode side as a filtrate together with the water contained in the sludge. In this case, the reaction between sodium hydroxide and aluminum
AlO ₂ ^- as in (aluminate ion) a force attracted to the anode, but the force is weak in comparison with the movement of the liquid by electroosmosis, sludge-containing water, is recovered from the cathode side along with Na ⁺ ions Become. The residual water of the dewatered sludge will have a slight increase in the concentration of SO ₄ ²⁻ , Cl ^−, etc. contained in the settled sludge from the beginning. Moreover, by using sodium hydroxide, which is an alkaline chemical as the aluminum-soluble chemical, it is possible to prevent the pH of the dehydrated sludge from decreasing due to anions moving to the anode side due to electroosmosis, so the dehydrated sludge becomes neutral. It has a low water content and is advantageous for subsequent landfill disposal.

The present inventors have found that 2000 kg of sedimented sludge having a solid content of 1.0% and an aluminum hydroxide content of 20%.
The following results were obtained when the test was performed using the above as a sample. That is, the sedimentation sludge in the sedimentation concentration tank 1 has a concentration of 2%.
The concentrated sludge of 1000 kg was concentrated to a concentration of 8.5% by the filter concentrator 2 to reduce its volume, then 2.2 kg of sodium hydroxide was added to the filtered concentrated sludge, and the mixture was further mixed by the mixer 4. The pH of the sludge was adjusted to 12.7 and the sludge was introduced into the electroosmotic dehydrator 5 for dehydration, and 200 kg of filtrate was recovered and 37.5
Kg of dehydrated sludge was obtained. Moreover, as a result of examining the properties of this filtrate and dehydrated sludge, the concentration of the filtrate was 1.35%.
Of aluminum (as Al ₂ O ₃ ) was included, and it was found from this value that the aluminum recovery rate was 90.4%. On the other hand, the moisture content of caked dehydrated sludge is 57%
And contained 21.4 Kg of residual water, its pH
It was confirmed in 7.3 that it was almost neutral.

[Embodiment 3] FIG. 6 shows an embodiment corresponding to claim 4 of the present invention. In this embodiment, an aluminum-soluble chemical is introduced into the machine by an electroosmotic dehydrator 5. The aluminum contained in the sludge is dissolved by electroosmosis and recovered as a filtrate.

That is, as shown in the figure, the anode plate 5a of the electroosmotic dehydrator 5 is used as a perforated plate and a chemical supply tank 5f is provided on the upper surface side thereof, and an aluminum-soluble chemical (sulfuric acid, sulfuric acid,
Or sodium hydroxide). With such a configuration, when the filtered concentrated sludge concentrated through the sedimentation concentration and filtration concentration steps as in the above-described example is introduced into the electroosmotic dehydrator 5 and a DC voltage is applied between the electrodes, the insoluble sludge particles become negative. After being charged, the surrounding water is positively charged and attracted to the cathode side by the electroosmotic action, permeates the filtering member 5c and is collected as a filtrate. At the same time, the aluminum-soluble chemical penetrates into the sludge from the chemical supply tank 5f through the hole 5g formed in the anode plate 5a in such a manner that it is replaced by the interstitial water between the insoluble sludge particles of the sludge, and is contained in the sludge. While dissolving aluminum hydroxide, it moves to the cathode side together with the contained water and is discharged and collected. By repeating this operation, almost all the aluminum contained in the filtered concentrated sludge can be recovered as a filtrate. In addition, after the aluminum recovery operation is completed, the chemical supply tank 5
If f is filled with normal water and a direct current voltage is applied between the electrodes again, the aluminum-soluble chemical remaining in the sludge due to the electroosmotic action will be discharged together with the water supplied from the outside, and the chemical of the dehydrated sludge will be discharged. Residue can be reduced. Moreover, according to this embodiment, the kneading machine 4 shown in FIG. 1 of the first embodiment can be omitted.

The inventors of the present invention conducted a test on this embodiment using a fixed concentration 9% filtered concentrated sludge as a sample, and when an aluminum-soluble chemical was used as a 10% sulfuric acid solution, the recovery was 99%. The aluminum liquid could be recovered at a rate. The dehydrated sludge had a water content of 59% and a pH of 3. [Embodiment 4] FIGS. 7 and 8 show an embodiment corresponding to claim 5 of the present invention, in which an electrolyte is added to the filtered concentrated sludge at the beginning of operation for treating the sludge, and the sludge is electroosmotic. It is introduced into a rotary dehydrator 5 and an electrolyte is ionized by an electroosmotic action to generate an aluminum-soluble chemical in the system.

That is, as shown in FIG. 7, with respect to the filtered concentrated sludge obtained by settling, concentrating and concentrating the precipitated sludge, sodium sulfate as an electrolyte is supplied from the sodium sulfate storage tank 9 to the mixer 4 at the beginning of the treatment operation, and then the sludge is Is introduced into the electroosmotic dehydrator 5 and a DC voltage is applied between the electrodes. As a result, sodium sulfate is ionized by electrolysis and electroosmosis is performed.
Na ⁺ ions are collected in the storage tank 6 as a filtrate, and Na ⁺ ions and water form caustic soda. Then, when the caustic soda is sufficiently stored in the storage tank 6, the supply of sodium sulfate is stopped, and then the caustic soda stored in the storage tank 6 is returned to the filtered concentrated sludge through the mixer 4 by the return pump 10. Supplied and used as a strong alkaline aluminum dissolving chemical. As a result, the aluminum component contained in the settled sludge can be recovered at a high recovery rate by the same operation as described in Example 2.

FIG. 8 is an explanatory diagram showing the behavior of the sodium sulphate-added sludge introduced into the electroosmotic dehydrator 5 due to the electroosmotic action. Sodium sulphate is ionized into Na ⁺ ions and SO ₄ ^2- Existing in the interstitial water, Na ⁺ ions move to the cathode plate 5b and SO ₄ ²⁻ to the anode plate 5a due to the direct-current electric field between the electrodes. Since the filtrate is discharged by the osmotic action, strong alkaline caustic soda having a high Na ⁺ ion concentration is recovered as the filtrate.

Therefore, in treating the sludge of the sludge, without using an expensive powerful drug such as sulfuric acid or sodium hydroxide as an aluminum-soluble chemical, the sodium-soluble chemical that can be obtained at a low cost is used as a raw material in the system. Can be generated.

[0026]

As described above, according to the aluminum recovery method of the present invention, an electroosmotic dehydrator is used, and its electroosmotic effect is skillfully utilized to dehydrate the precipitated sludge and to contain it in the sludge. Since the aluminum that is being collected is collected in parallel, it is possible to efficiently separate and collect the high-concentration aluminum liquid as a filtrate from the dehydrator. Moreover,
The dehydrated sludge after the aluminum recovery is dehydrated to a low water content, which is convenient for landfill disposal.

Further, particularly when the method of claim 4 is adopted,
Aluminum soluble chemicals can be added and permeated directly into the sludge introduced by an electroosmotic dehydrator, and there is no need to install an admixer before the dehydrator. Furthermore, by adopting the method of claim 5, when treating the settled sludge,
Economical operation is possible because aluminum sulfate-soluble chemicals can be produced in the system using sodium sulfate, which is available at low cost, as a raw material without purchasing expensive powerful chemicals such as sulfuric acid and sodium hydroxide as aluminum-soluble chemicals. .

[Brief description of the drawings]

FIG. 1 is a process step diagram of an aluminum recovery method corresponding to Example 1 of the present invention.

FIG. 2 is a diagram showing the composition of settled sludge.

FIG. 3 is an explanatory diagram of an electroosmotic action in the electroosmotic dehydrator of FIG.

FIG. 4 is a process step diagram of an aluminum recovery method corresponding to Example 2 of the present invention.

FIG. 5 is an explanatory diagram of an electroosmotic action in the electroosmotic dehydrator of FIG.

FIG. 6 is an explanatory view showing an aluminum recovery method corresponding to Example 3 of the present invention together with the configuration of an electroosmotic dehydrator and the electroosmotic action.

FIG. 7 is a process step diagram of an aluminum recovery method corresponding to Example 4 of the present invention.

FIG. 8 is an explanatory diagram of electroosmotic action in the electroosmotic dehydrator of FIG. 7.

FIG. 9 is a river in a water purification plant to which the present invention is applied,
Figure showing lake water intake purification process

FIG. 10 is a treatment process diagram of a method for recovering aluminum from settled sludge according to the prior art

[Explanation of symbols]

 1 Settling Concentrator 2 Filtration Concentrator 3 Sulfuric Acid Storage Tank 4 Mixer 5 Electroosmotic Dehydrator 5a Anode Plate 5b Cathode Plate 5c Filtering Member 5d Pressurizing Device 5e DC Power Supply 5f Chemical Supply Tank 6 Recovery Aluminum Liquid Storage Tank 7 Dehydration Sludge Place 8 Sodium hydroxide storage tank 9 Sodium sulfate (electrolyte) storage tank

Claims (5)

[Claims] 1. In an aluminum recovery method for separating and recovering aluminum contained in sludge by using an aluminum-soluble chemical, after adding the aluminum-soluble chemical to the sludge reduced in volume through a concentration step, the sludge is removed. It was introduced into an electroosmotic dehydrator, and a DC voltage was applied between its electrodes, and the aluminum liquid was collected together with the water containing sludge on one electrode side by electroosmosis and then collected through a filtering member. A method for recovering aluminum in sludge treatment, comprising: 2. The aluminum recovery method according to claim 1, wherein the aluminum-soluble chemical is an acidic chemical such as sulfuric acid. 3. The aluminum recovery method according to claim 1, wherein the aluminum soluble chemical is an alkaline chemical such as sodium hydroxide. 4. An aluminum recovery method for separating and recovering aluminum contained in sludge using an aluminum-soluble chemical, and introducing sludge into an electroosmotic dehydrator to apply a DC voltage between its electrodes. , Supplying aluminum-soluble chemicals to sludge from one electrode side, while dissolving aluminum components with aluminum-soluble chemicals that permeate into the sludge by electroosmotic action, aluminum liquid together with water contained in the sludge is applied to the other electrode A method for recovering aluminum in sludge treatment, characterized in that it is collected on the side and then collected through a filtering member. 5. In an aluminum recovery method for separating and recovering aluminum contained in sludge by using an aluminum-soluble chemical, sludge is electro-osmotic dehydrator after an electrolyte such as sodium sulfate is added to the sludge. DC component is applied between the electrodes and the components of the electrolyte ionized by the electroosmotic action are collected as a filtrate together with the water contained in the sludge, and this filtrate is electroosmotic as an aluminum-soluble chemical. A method for recovering aluminum in sludge treatment, which is characterized in that it is added to sludge to be introduced into a dehydrator.