WO2012165382A1

WO2012165382A1 - Method for extracting phosphorus from incinerated ash

Info

Publication number: WO2012165382A1
Application number: PCT/JP2012/063648
Authority: WO
Inventors: 雅郎田畑; 孝司木本; 博和坪井
Original assignee: メタウォーター株式会社
Priority date: 2011-05-27
Filing date: 2012-05-28
Publication date: 2012-12-06
Also published as: JPWO2012165382A1; JP5934706B2

Abstract

The objective of the present invention is to prevent clogging of a filter medium used in solid-liquid separation of a phosphorus extraction liquid and processed ash after extracting phosphorus in incinerated ash into an alkaline solution. This method for extracting phosphorus separates a solid component and a liquid component using a filter medium in a solid-liquid separation step performed after first performing a phosphorus extraction step for extracting phosphorus by mixing an alkaline reaction liquid (1) and incinerated ash (2) containing P. Of the incinerated ash (2), the P alkalinity dependence of the elution concentration of ionic silica on the alkaline reaction liquid (1) is measured, and the P alkalinity of the alkaline reaction liquid (1) is caused to be no greater than a predetermined P alkalinity of ionic silica at which the tendency for the P alkalinity dependence of the elution concentration of ionic silica changes. Of the incinerated ash, the P alkalinity dependence of the elution concentration of phosphorus on the alkaline reaction liquid (1) is also measured, and the P alkalinity of the alkaline reaction liquid (1) is caused to be at least the P alkalinity that is 1.0 (equivalents/kg) lower than a predetermined P alkalinity of P at which the tendency for the P alkalinity dependence of the elution concentration of phosphorus changes.

Description

Method for extracting phosphorus from incineration ash

The present invention relates to a method for extracting phosphorus from incinerated ash that performs filtration using a filter medium for solid-liquid separation.

Conventionally, most of the sludge incineration ash generated by incineration of sewage sludge and the like generated at a sewage treatment plant has been disposed of by landfill as wasteless. However, this sludge incineration ash contains a lot of phosphorus (P). Since this phosphorus is one of the resources that are currently in danger of being exhausted worldwide, various techniques for recovering and reusing phosphorus from sludge incineration ash have been proposed in recent years.

To recover phosphorus from sludge incineration ash, it is necessary to extract the phosphorus in sludge incineration ash with a chemical. As a method for extracting phosphorus, an extraction method using a strong alkaline solution such as an aqueous caustic soda solution is known (Patent Documents 1 and 2). Thus, phosphorus can be efficiently extracted from the sludge incineration ash containing phosphorus by using a strong alkaline solution in the extraction of phosphorus.

After extracting the phosphorus in the sludge incineration ash into the chemical, the liquid mixture containing the sludge incineration ash and the chemical is separated into solid and liquid to separate the insoluble components (treated ash) and the phosphorus extract from the sludge incineration ash Let Phosphorus can be recovered from sludge incinerated ash by adding slaked lime (calcium hydroxide (Ca (OH) ₂ )) to the separated phosphorus extract and precipitating it as a phosphate. On the other hand, the separated insoluble components are subjected to a washing process, a solid-liquid separation process, a weak acid washing process, and a dehydration process, and finally dried to form clean treated ash, which is used as asphalt filler and lower roadbed material (Patent Document 3).

JP 2007-246360 A JP 2007-246361 A JP 2008-229576 A

By the way, in the above-described treatment of sludge incineration ash, solid-liquid separation by filtration using a filter medium is performed in the solid-liquid separation of the treated ash and the phosphorus extract after extracting phosphorus in the sludge incineration ash into the chemical. It has been broken. However, when this inventor performed the process of the sludge incineration ash mentioned above, it discovered that the problem that this filter medium will be clogged arises.

If clogging occurs in the filter medium used for this solid-liquid separation, the solid-liquid separation is not sufficiently performed, the amount of extraction of the phosphorus extract is reduced, and the phosphorus recovery rate is also greatly reduced. In addition, replacement of the filter medium and regeneration processing are also required, resulting in a problem of high cost.

The present invention has been made in view of the above, and its object is to use it in a filtration process in the case of solid-liquid separation of the treated ash and the phosphorus extract after the phosphorus in the incinerated ash is extracted into the medicine. Another object of the present invention is to provide a method for extracting phosphorus from incinerated ash that can prevent clogging of the filter medium.

In order to solve the above-described problems and achieve the above object, the method for extracting phosphorus from incineration ash according to the present invention includes mixing a chemical with incineration ash containing at least silicon, aluminum, and phosphorus, thereby adding phosphorus to the chemical. A method for extracting phosphorus from incinerated ash, comprising: a phosphorus extraction step for extracting a liquid; and a solid-liquid separation step for separating a liquid mixture of a solution containing phosphorus and an insoluble component into a liquid component and a solid component using a filter medium Based on the dependence of the amount of hydroxide ions per unit mass of incinerated ash on the elution concentration of ionic silica eluted from the incinerated ash into the chemical, Measure the amount of hydroxide ions per unit mass of incinerated ash, which has a tendency to depend on the amount of hydroxide ions, in advance as the predetermined amount of hydroxide ions of ionic silica. The hydroxide ions per unit mass of ash, characterized in that below a predetermined hydroxide ions of the ion-like silica.

The method for extracting phosphorus from incinerated ash according to the present invention includes a phosphorus extraction step of mixing a chemical and incinerated ash containing at least silicon, aluminum and phosphorus to extract phosphorus into the chemical, and a phosphorus-containing solution and insoluble A liquid-solid separation step of separating a liquid mixture with components into a liquid component and a solid component using a filter medium, and a method for extracting phosphorus from incinerated ash, the method comprising: Based on the dependence of the elution concentration on the P alkalinity, the P alkalinity at which the tendency of the elution concentration of the ionic silica on the P alkalinity changes is measured in advance as the predetermined P alkalinity of the ionic silica. The degree is set to be not more than a predetermined P alkalinity of ionic silica.

The method for extracting phosphorus from the incinerated ash according to the present invention is the above invention, wherein the elution concentration of phosphorus extracted from the incinerated ash to the chemical is dependent on the P alkalinity, and the elution concentration of phosphorus is dependent on the P alkalinity. The predetermined P alkalinity of phosphorus in which the tendency changes is measured in advance, and the P alkalinity of the drug is set to a P alkalinity of 1.0 (equivalent / kg) lower than the predetermined P alkalinity of phosphorus. .

The method for extracting phosphorus from the incinerated ash according to the present invention is the above invention, wherein the elution concentration of phosphorus extracted from the incinerated ash to the chemical is dependent on the P alkalinity, and the elution concentration of phosphorus is dependent on the P alkalinity. The predetermined P alkalinity of phosphorus in which the tendency changes is measured in advance, and the P alkalinity of the drug is made equal to or lower than the predetermined P alkalinity of phosphorus.

According to the method for extracting phosphorus from incinerated ash according to the present invention, clogging of the filter medium used for the filtration treatment in the solid-liquid separation of the treated ash and the phosphorus extract performed after extracting phosphorus in the incinerated ash into the alkaline solution is performed. It is possible to prevent this, and it is possible to reduce the labor of regeneration processing and replacement processing of the filter medium.

FIG. 1 is a flowchart showing a phosphorus recovery process according to the first embodiment of the present invention. FIG. 2 is a graph showing the P alkalinity dependency of the elution concentration of phosphorus in the alkaline reaction solution according to the first embodiment of the present invention. FIG. 3 is a graph showing the P alkalinity dependence of the elution concentration of aluminum in the alkaline reaction liquid according to the first embodiment of the present invention. FIG. 4 is a graph showing the P alkalinity dependency of the alkaline reaction liquid in the ionic silica according to the first embodiment of the present invention. FIG. 5 is a flowchart showing a phosphorus recovery process according to the second embodiment of the present invention. FIG. 6 is a graph showing the elemental analysis of the clogging for explaining the intensive study by the inventors of the present invention. FIG. 7 is a graph showing an X-ray diffraction analysis of a clogged material for explaining the earnest study by the inventors of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings of the following embodiments, the same or corresponding parts are denoted by the same reference numerals. Further, the present invention is not limited to the embodiments described below.

First, the P alkalinity will be described. The alkalinity used in the present invention is expressed by converting the amount of alkali components contained in water, that is, components that consume acid, into the amount of calcium carbonate (CaCO ₃ ), and represents a pH representing hydrogen ion concentration. Is different. Water with a high alkalinity is neutralized even when an acid is added, so that it is difficult for a change in pH to occur. In this sense, water is sometimes expressed as a buffering capacity for acid.

In the official method, the alkalinity is measured by neutralization titration using hydrochloric acid in the liquid to be measured. The method for measuring P alkalinity is a method in which phenolphthalein is used as a reagent and the amount of alkali component is determined from the amount of hydrochloric acid until the pH reaches 8.3. This P alkalinity corresponds to the amount of hydroxide ions among the alkali components in water.

Moreover, in this invention, P alkalinity is prescribed | regulated by the equivalent per unit mass of incineration ash. Further, since the molecular weight of calcium carbonate (CaCO ₃ ) is 100.09 g / mol and the carbonate ion is divalent, the commonly used P alkalinity (mg-CaCO ₃ / l) and the equivalent (eq / l) The relationship with the P alkalinity defined by (1) is expressed by the following equation (1).

The unit “eq / l” is equivalent (equivalent / l) per unit volume (l) of the alkaline reaction liquid.

And when using the alkaline solution (chemical | medical solution) of predetermined P alkalinity (equivalent / l) with respect to incineration ash, according to the quantity (liquid-solid ratio) of the alkaline solution used with respect to the incineration ash per unit mass. P alkalinity changes. Therefore, the relationship with the P alkalinity (equivalent / kg) of the alkaline solution used for the unit mass of incinerated ash is expressed by the following equation (2).

That is, the P alkalinity (equivalent / kg) per unit mass of incinerated ash can be discussed in the same manner as the amount of hydroxide ions per unit mass of incinerated ash. Therefore, the tendency of the phenomenon that occurs when the P alkalinity (equivalent / kg) per unit mass of the incinerated ash in the alkaline solution is changed is essentially the hydroxylation per unit mass of the incinerated ash in the alkaline solution. This tends to occur when the amount of product ions is changed.

Next, in order to facilitate understanding of the present invention, various experiments and diligent studies conducted by the present inventor in order to solve the above problems and achieve the above objects will be described.

First, the present inventor conducted a process for recovering phosphorus from incinerated ash and extracted the filter medium used for the solid-liquid separation of the treated ash and the phosphorus extract after extracting phosphorus from the incinerated ash into the alkaline reaction liquid. The clogging condition was analyzed in detail. That is, according to the analysis by the present inventor, it was possible to remove the clogging of the filter medium and regenerate at the initial stage of the clogging using any of the acidic solution and the alkaline solution. However, at the stage where clogging actually occurs, the filter medium cannot be regenerated using an alkaline solution, and even when a highly concentrated acidic solution is used, a long regeneration process is required. From this, the present inventor considered that the cause of clogging was the growth of hardly soluble crystals, and this hardly soluble crystals were clogged.

Then, this inventor performed the elemental analysis of the clogging material of a filter medium. In this elemental analysis, a phosphorus extraction step using a NaOH solution having a P alkalinity of 11.0 to 12.0 (equivalent / kg) (55000 to 60000 (mg-CaCO ₃ / l)) as a reaction solution. The clogged filter material was clogged by repeating a series of operations of performing a solid-liquid separation step after 90 minutes in a temperature range of 50 to 60 ° C. The clogged material was observed using a scanning electron microscope, and elemental analysis was performed using a fluorescent X-ray analyzer (SEM-EDS) (manufactured by JEOL Ltd.). The results of this elemental analysis are shown in FIG. According to the elemental analysis results shown in FIG. 6, since the intensity of characteristic X-rays of sodium (Na), aluminum (Al), silicon (Si), phosphorus (P) and calcium (Ca) is large, the present inventor It was found that the filter material clogging material contained a large amount of Na, Al, Si, P and Ca. In addition, since it is thought that P of these elements was detected because it was contained in the phosphorus extract in large quantities, the present inventor used Na as the element constituting the filter material clogging. , Al, Si and Ca were considered to be contained.

The present inventor conducted X-ray diffraction analysis on the clogged crystals based on the knowledge that the clogged substances are hardly soluble crystals and the knowledge of the elements constituting the clogged substances. In this X-ray diffraction analysis, an X-ray diffraction apparatus (X 'Pert PRO, manufactured by PANalytical) was used. The results of X-ray diffraction analysis are shown in FIG.

From the X-ray diffraction analysis results shown in FIG. 7, it can be seen that many peaks derived from the A-type zeolite (Z peak in FIG. 7) are observed. From this, the present inventor came to obtain the knowledge that the main clogging material of the filter medium is A-type zeolite (aluminosilicate).

Based on the above knowledge, the present inventor further examined a method for suppressing the generation of A-type zeolite from the viewpoint that the clogging of the filter medium can be prevented by suppressing the generation of A-type zeolite. Repeated. The present inventor has found that the A-type zeolite is produced by the reaction of soluble Al and soluble Si, and when performing phosphorus extraction from the incinerated ash using a strong alkaline solution, the ease of extraction is determined by the combination of P and Al. It was found that the elution easiness of Si is lower than that of P or Al. That is, when the inventor treated the incinerated ash by experiment, when the amount of hydroxide ions in the alkaline reaction liquid, that is, the P alkalinity was increased, first, the elution amount of P and Al increased first. As a result, it was found that as the amount of hydroxide ions and P alkalinity were further increased, the amount of elution of Si began to increase. Thereby, this inventor came to the idea that in order to suppress the production | generation of A-type zeolite, it is necessary to suppress the production | generation of soluble Si.

Therefore, the present inventor paid attention to the amount of hydroxide ions per unit mass of the incinerated ash in the alkaline reaction liquid for extracting phosphorus, particularly the P alkalinity per unit mass of the incinerated ash. Hereinafter, the P alkalinity per unit mass of the incinerated ash is referred to as P alkalinity. Then, the inventors in an alkaline reaction solution, hydroxide ions per unit mass of ash, the concentration of ions like silica eluting the alkaline reaction mixture (SiO _2), per unit mass of ash By setting the value to be less than the value at which the tendency of dependence on the amount of hydroxide ions changes, specifically, to the value at which the tendency to dependence on P alkalinity changes (predetermined P alkalinity) or less, the generation of soluble Si is reduced. It came to recall that the extraction of P can be secured while suppressing the generation of A-type zeolite. The present invention has been devised based on the above studies.

Next, a method for extracting phosphorus from incinerated ash according to the first embodiment of the present invention devised based on the above examination will be described. FIG. 1 shows a flowchart of the phosphorus recovery method according to the first embodiment.

As shown in FIG. 1, first, an alkaline reaction liquid 1 such as a sodium hydroxide (NaOH) aqueous solution is adjusted as a drug (reaction liquid adjustment step, step ST1). In this reaction liquid adjustment step, the P alkalinity is adjusted while mixing an aqueous NaOH solution and a regeneration liquid described later. In addition, as the alkaline reaction liquid 1, a potassium hydroxide (KOH) aqueous solution can be used in addition to the NaOH aqueous solution, and so-called various chemicals capable of controlling the amount of hydroxide ions (OH ⁻ ) can be used. .

Here, Table 1 shows the properties of the three types of incineration ash A to C to be processed by the phosphorus extraction method in the first embodiment. These incineration ash A to C are incineration ash obtained from sludge collected at completely different points.

As shown in Table 1, the incineration ash A is an incineration ash in which both the concentration of P and the concentration of Ca are normal concentrations, and P is relatively easily extracted. In contrast, the incineration ash B has a lower Ca concentration than the normal Ca concentration, and is therefore an incineration ash that is relatively difficult to extract P. Further, the incineration ash C is an incineration ash that is relatively difficult to extract P as compared with the incineration ash A because the concentration of P is normal but the concentration of Ca is high. And in this 1st Embodiment, the method of extracting P by employ | adopting three types of incineration ash A, B, and C from which such a property differs as the incineration ash 2 is demonstrated.

Here, the P alkalinity of the alkaline reaction liquid 1 according to the first embodiment of the present invention is determined as follows.

First, the P alkalinity dependency per unit mass of the incinerated ash (hereinafter referred to as P alkalinity dependency) in the concentrations of P, Al, and ionic silica (SiO ₂ ) eluted from the incinerated ash into the alkaline reaction liquid 1 is measured. To do. And the P alkalinity of the alkaline reaction liquid 1 is determined based on these measurement results. 2, 3 and 4 show the P alkalinity dependency of the concentration of the substance eluted in the alkaline reaction liquid 1 according to the first embodiment. FIG. 2 shows the P alkalinity dependency of the elution concentration of P in the incineration ash A to C, FIG. 3 shows the P alkalinity dependency of the elution concentration of Al in the incineration ash A to C, and FIG. a C ions like silica (SiO ₂₎ P alkalinity dependence of the measurement results of the dissolution concentration of.

As shown in FIG. 2, the concentration tendency of P extracted into the alkaline reaction liquid 1 has the following tendency even when any of the incineration ash A to C is treated. That is, when the P alkalinity of the alkaline reaction liquid 1 is relatively low, the concentration of extracted P increases rapidly as the P alkalinity increases. And when the P alkalinity of the alkaline reaction liquid 1 becomes a certain value or more, the increase in the concentration of P extracted becomes moderate. Therefore, the P alkalinity at which the increasing tendency of the P concentration changes is defined as a predetermined P alkalinity of P (P _{P in} FIG. 2). The predetermined P alkalinity of P can be the P alkalinity at the intersection of a straight line having a large slope where the P alkalinity is relatively low and a straight line having a small slope where the P alkalinity is relatively high. In other words, in the graph shown in FIG. 2, the P alkalinity dependency of any incineration ash A to C has a large slope up to a predetermined P alkalinity, and the slope exceeds a predetermined P alkalinity. The tendency of the elution concentration of P to be dependent on the P alkalinity changes before and after the predetermined P alkalinity so as to decrease.

Further, as shown in FIG. 3, the concentration tendency of Al eluted in the alkaline reaction liquid 1 is the same as in the case of P, regardless of which of the incineration ash A to C is treated. It has the following tendency. That is, when the P alkalinity of the alkaline reaction solution 1 is relatively low, as the P alkalinity increases, the Al concentration rapidly increases, and when the P alkalinity exceeds a certain value, the Al concentration increases. The trend is moderate. Therefore, the P alkalinity at which the increasing tendency of the Al concentration changes is defined as the predetermined P alkalinity of Al (P _{Al in} FIG. 3). As in the case of deriving the predetermined P alkalinity of P, the predetermined P alkalinity of Al is a straight line having a large slope where the P alkalinity is relatively low and a straight line having a small slope where the P alkalinity is relatively high. The P alkalinity at the intersection of That is, the tendency of the elution concentration of Al to depend on the P alkalinity changes before and after the predetermined P alkalinity of Al.

Further, as shown in FIG. 4, the concentration tendency of the ionic silica eluted in the alkaline reaction liquid 1 has the following tendency regardless of which of the incineration ash A to C is treated. . That is, when the P alkalinity of the alkaline reaction liquid 1 is relatively low, the concentration of ionic silica gradually increases as the P alkalinity increases, and when the P alkalinity exceeds a certain value, Concentration increases rapidly. The P alkalinity at which the increasing tendency of the concentration of ionic silica changes is defined as the predetermined P alkalinity of ionic silica (P _{Si in} FIG. 4). The predetermined P alkalinity of this ionic silica is the intersection of a straight line with a small slope where the P alkalinity is relatively low and a straight line with a large slope where the P alkalinity is relatively high, as in the case of P and Al. P alkalinity can be obtained. That is, the tendency of the elution concentration of the ionic silica on the P alkalinity changes before and after the predetermined P alkalinity of the ionic silica.

From FIG. 2, in the first embodiment, in the incinerated ash A in which both the P concentration and the Ca concentration are normal concentrations and P is relatively easily extracted, the predetermined P alkalinity of P Is about 6.0 (equivalent / kg) (30000 mg / l), and FIG. 3 shows that the predetermined P alkalinity of Al is about 8.0 (equivalent / kg) (40000 mg / l). . FIG. 4 also shows that the predetermined P alkalinity of the ionic silica in the first embodiment is about 9.4 (equivalent / kg) (47000 mg / l).

In addition, according to the knowledge obtained by the inventor's experiments and diligent studies described above, when extracting phosphorus from various incineration ash using a strong alkaline solution, the ease of extraction is P and Al. The elution easiness of Si is lower than that of P or Al. Thereby, the predetermined P alkalinity of Si becomes larger than the predetermined P alkalinity of P or Al.

From the above, it can be seen that the elution concentration of the ionic silica is not significantly increased by setting the P alkalinity of the alkaline reaction liquid 1 to be greater than 0 (equivalent / kg) and below the predetermined P alkalinity of the ionic silica. Furthermore, in the range where the P alkalinity of the alkaline reaction liquid 1 is greater than 0 and less than or equal to the predetermined P alkalinity of P or Al, the elution concentration of P or Al increases rapidly as the P alkalinity increases. The increase in the elution concentration of ionic silica is gradual. Therefore, according to the knowledge of the present inventor, in order to suppress the elution of ionic silica while securing the extraction amount of P, the P alkalinity of the alkaline reaction liquid 1 is set to 1. from the predetermined P alkalinity of P. If the P alkalinity is set to 0 (equivalent / kg) (5000 mg / l) or lower, the recovery rate of P in the phosphorus extraction method can be ensured within a desired range.

Further, as can be seen from FIGS. 2 and 3, according to the knowledge of the present inventor, in the range where the P alkalinity of the alkaline reaction liquid 1 is larger than the predetermined P alkalinity of P or Al, the increase in the P alkalinity is accompanied. The rate of increase in the elution amount of P and Al is small compared to a range of a predetermined P alkalinity or less. Therefore, considering that the elution amount of P per a predetermined amount of hydroxide ions, that is, the required P alkalinity is as low as possible to improve the P recovery efficiency, the P alkali of the alkaline reaction liquid 1 is considered. By setting the degree to be equal to or less than the predetermined P alkalinity of P, the recovery rate of P by the phosphorus extraction process can be ensured within a desired range while suppressing the amount of hydroxide ions required for the alkaline reaction liquid 1. .

From these findings, in this first embodiment, when extracting P from the incineration ash A, the P alkalinity of the alkaline reaction liquid 1 is 9.4 (equivalent / kg) (47000 mg / l) or less. Further, (6.0−1.0 =) 5.0 (equivalent / kg) or more and 9.4 (equivalent / kg) or less (25000 mg / l or more and 47000 mg / l or less) is preferable. More preferably, it is 0 (equivalent / kg) or more and 6.0 (equivalent / kg) or less (25000 mg / l or more and 30000 mg / l or less).

Also, when extracting P from the incineration ash B, the degree of P alkalinity of the alkaline reaction liquid 1 is determined in the same manner as when extracting P from the incineration ash A described above. That is, in the incinerated ash B in which the Ca concentration is normal but the P content is low and P is relatively difficult to be extracted, the predetermined P alkalinity of P is about 6.6 from FIG. (Equivalent / kg) (33000 mg / l), and FIG. 3 shows that the predetermined P alkalinity of Al is about 7.0 (equivalent / kg) (35000 mg / l). 4 that the predetermined P alkalinity of the ionic silica in the incinerated ash B is about 8.0 (equivalent / kg) (40000 mg / l).

Therefore, when extracting P from the incinerated ash B, the alkalinity of the alkaline reaction solution 1 is set to 8.0 (equivalent / kg) (40000 mg / l) or less, and (6.6-1.0 =) 5.6 (equivalent / kg) or more and 8.0 (equivalent / kg) or less (28000 mg / l or more and 40000 mg / l or less), preferably 5.6 (equivalent / kg) or more and 6.6 (equivalent) / Kg) or less (28000 mg / l or more and 33000 mg / l or less).

In the case where P is extracted from the incinerated ash C, the P alkalinity of the alkaline reaction liquid 1 is determined in the same manner. That is, in the incinerated ash C in which the P concentration is normal but the Ca concentration is high and P is relatively difficult to be extracted, the predetermined P alkalinity of P is about 6.4 (equivalent weight) from FIG. / Kg) (32000 mg / l), and FIG. 3 shows that the predetermined P alkalinity of Al is about 5.6 (equivalent / kg) (28000 mg / l). 4 that the predetermined P alkalinity of the ionic silica in the incinerated ash C is about 8.4 (equivalent / kg) (42000 mg / l).

Therefore, when extracting P from the incineration ash C, the alkalinity of the alkaline reaction liquid 1 is set to 8.4 (equivalent / kg) (42000 mg / l) or less, and (6.4-1.0). =) 5.4 (equivalent / kg) or more and 8.4 (equivalent / kg) or less (27000 mg / l or more and 42000 mg / l or less), preferably 5.4 (equivalent / kg) or more and 6.4 (equivalent) / Kg) or less (27000 mg / l or more and 32000 mg / l or less).

(Phosphorus extraction method)
After adjusting the P alkalinity of the alkaline reaction liquid 1 according to the properties of the respective incineration ash A to C as described above, as shown in FIG. 1, sludge incineration ash containing at least P, Al, and Si. Incineration ash 2 such as the above is mixed with the alkaline reaction liquid 1 to obtain a phosphorus extract, so-called phosphorus extraction is performed (phosphorus extraction step, step ST2). Thereby, P extract which is a solution containing P is obtained. At this time, the incinerated ash 2 contains a large amount of phosphorus and harmful components such as arsenic (As), but these components are extracted to the liquid side by contact with the alkaline reaction liquid 1. Next, by performing solid-liquid separation by filtration using a filter cloth as a filter medium, the treated ash as a solid component and the phosphorus extract as a liquid component are separated (solid-liquid separation step, step ST3). .

Thereafter, the treated ash, which is a solid component separated by solid-liquid separation, and the alkaline reaction liquid 1 are mixed again, and the second phosphorus extraction step is performed (step ST4). Subsequently, the second solid-liquid separation step is performed in the same manner as in step ST3 (step ST5). By these steps, a treated ash and a phosphorus extract subjected to two phosphorus extraction steps are obtained. As described above, the phosphorus recovery rate can be improved by performing the phosphorus extraction step and the solid-liquid separation step twice.

Next, the treated ash is washed to remove harmful components such as alkaline reaction liquid and As, Se adhering to the treated ash (ash washing step, step ST6). In the first embodiment, water cleaning using cleaning water (tap water, well water, processing water, etc.) is performed as cleaning of the processing ash. Subsequently, by performing solid-liquid separation by filtration using a filter cloth, the solid ash is separated from the waste liquid that is a liquid component and discarded (solid-liquid separation step, step ST7). Thereafter, the treated ash, which is a solid component separated by solid-liquid separation, is mixed with treated water again, and the second ash washing step is performed (step ST8). Subsequently, a solid-liquid separation process is performed in the same manner as in step ST7 (step ST9).

As a result, the treated ash that has been subjected to the ash washing process twice and the waste liquid are separated into solid and liquid. Of these, the waste liquid is disposed of by a conventionally known method such as neutralization. As described above, by performing the ash washing step and the solid-liquid separation step twice, As and Al can be efficiently removed, and the pH can be lowered to be closer to neutrality.

Next, weak acid cleaning is performed on the treated ash by adding an acid such as sulfuric acid (H ₂ SO ₄ ) while adding treated water (weak acid cleaning step, step ST10). In the first embodiment, H ₂ SO ₄ that is easy to handle is used as the acid to be used, but hydrochloric acid (HCl), nitric acid (HNO ₃ ), or the like can also be used. By this weak acid washing process, the alkaline reaction liquid, As, Se, etc. adhering to the treated ash are removed. Subsequently, concentration using a belt concentrator is performed on the mixture of the treated ash and the acidic solution (belt concentration step, step ST11). As a result, the mixture of the treated ash and the acidic solution is separated into the concentrated and cleaned treated ash and the waste liquid discharged by the concentration. Of these, the waste liquid is disposed of by a conventionally known method such as neutralization.

Next, the concentrated treated ash is dried to remove water adhering to the treated ash (drying step, step ST12). As a result, a clean treated ash 3 having a minimum moisture content is finally obtained. Since this clean treated ash 3 satisfies the soil environmental standards, it can be used as, for example, asphalt filler or lower roadbed material.

Now, Ca phosphate 4 is precipitated by adding the Ca component 4 to the phosphorus extract separated in the solid-liquid separation step of Step ST3 and Step ST5 (phosphate precipitation step, Step ST13). In the first embodiment, slaked lime (calcium hydroxide (Ca (OH) ₂ )) can be used as the Ca component, and the amount of phosphoric acid in the phosphorus extract is determined according to the formula (1). Assuming that the reaction takes place, the amount of calcium hydroxide reacting without excess or deficiency (hereinafter referred to as reaction equivalent) is 1.3 to 1.5 times.
2PO ₄ ³⁻ + 3Ca (OH) ₂ ⇒Ca ₃ (PO ₄ ) ₂ + 6OH ⁻ (1)

Then, by performing solid-liquid separation on the mixture in which the phosphate is precipitated, phosphate crystals such as Ca phosphate are taken out (solid-liquid separation step, step ST14). In this solid-liquid separation process, a filtration process using a filter cloth is performed in the same manner as the solid-liquid separation for the treated ash in step ST3 and step ST5, but gravity sedimentation can also be adopted in addition to the filtration process. is there. And the liquid component isolate | separated by the solid-liquid separation process is mixed with the alkaline reaction liquid 1 as a reproduction | regeneration liquid, and is circulated and used. On the other hand, the phosphate crystals as solids separated by solid-liquid separation are washed by adding treated water (washing step, step ST15). Thereby, various harmful components adhering to the phosphate crystals are removed, and clean phosphate crystals are obtained. Thereafter, the phosphate crystals and the treated water are concentrated using a belt concentrator in the same manner as the belt concentration step in step ST11, whereby the phosphate crystals are concentrated, and the waste liquid (Belt concentration step, step ST16).

Next, by performing a drying treatment on the concentrated clean phosphate crystals, moisture contained in the phosphate crystals is removed to the minimum (drying step, step ST17). Thereafter, a granulation process is performed in which the phosphate crystals are pulverized into granules (granulation step, step ST18). Thereby, powdery calcium phosphate 5 is obtained. This calcium phosphate 5 can be effectively used as a raw material for phosphate fertilizer, for example.

As described above, according to the first embodiment, the P alkalinity of the alkaline reaction liquid 1 is equal to or less than the predetermined P alkalinity of ionic silica in which the P alkalinity dependency of ionic silica changes, preferably By reducing the P alkalinity by 1.0 (equivalent / kg) (5000 mg / l) lower than the predetermined P alkalinity of P, more preferably by setting the P alkalinity below P, the amount of extraction of P can be greatly reduced. Without inviting, generation | occurrence | production of soluble Si can be suppressed, generation | occurrence | production of A type zeolite can be suppressed, and the clogging of the filter cloth used for solid-liquid separation after a phosphorus extraction process can be prevented.

Further, according to the first embodiment, even when phosphorus is extracted from various incineration ash having different properties as shown in Table 1, phosphorus, aluminum, and ionic silica are added to the alkaline reaction liquid 1. Since the P alkalinity dependency at the time of elution has the same tendency in any incineration ash, the alkalinity for extracting phosphorus based on the adjustment method of the alkaline reaction liquid in the phosphorus extraction method according to the present invention. By controlling the P alkalinity of reaction liquid 1, that is, the amount of hydroxide ions, incineration ash 2 of all properties suppresses the generation of soluble Si and suppresses generation of A-type zeolite, and after the phosphorus extraction step The clogging of the filter cloth used for the solid-liquid separation can be prevented.

Next, a second embodiment of the present invention will be described. In the second embodiment, the description of the same parts as those in the first embodiment is omitted. FIG. 5 shows a flowchart of the phosphorus recovery method according to the second embodiment of the present invention.

As shown in FIG. 4, first, similarly to the first embodiment, the adjustment of the alkaline reaction liquid 1 (step ST21), the phosphorus extraction step (step ST22), and the solid-liquid separation step (step ST23) are performed, and the processing is performed. Ash and phosphorus extract are separated. Here, in the second embodiment, unlike the first embodiment, each of the phosphorus extraction step and the solid-liquid separation step is performed only once. As described above, when the phosphorus extraction step and the solid-liquid separation step are performed only once, a large amount of P and unreacted NaOH are attached to the water adhering to the treated ash and having a mass about three times that of the treated ash. Remains.

Thereafter, as in the first embodiment, an ash washing step (step ST24) and a solid-liquid separation step (step ST25) by filtration using a filter cloth are performed, and the treated ash and liquid component as solid components are Are separated. Here, in the second embodiment, unlike the first embodiment, the ash washing step and the solid-liquid separation step are each performed only once. As described above, when the phosphorus extraction step and the solid-liquid separation step are performed only once, a large amount of P and unreacted NaOH remain in the adhering water adhering to the treated ash. The liquid component separated by the process and the solid-liquid separation process includes P and unreacted NaOH. Therefore, this liquid component is used as a phosphorus extract.

Thereafter, an acid such as H ₂ SO ₄ is added to the treated ash while adding treated water, and a weak acid washing is performed by adding polyferric sulfate (polytetsu) (weak acid washing step, Step ST26). By adding polytetsu in this weak acid washing step, it becomes possible to perform neutralization washing of the treated ash while suppressing elution of As adhering to the treated ash. Subsequently, a solid-liquid separation process is performed on the mixture of the treated ash and the acidic solution (solid-liquid separation step, step ST27). Thereby, the mixture containing the processed ash is separated into the cleaned processed ash and the discharged waste liquid. Of these, the waste liquid is disposed of by a conventionally known method such as neutralization. In the second embodiment, a part of the waste liquid discharged as necessary can be used as the phosphorus extract.

Next, as in the first embodiment, by performing the drying process (step ST28), a clean treated ash 3 having a minimum moisture content is finally obtained.

Now, with respect to the phosphorus extract separated in the solid-liquid separation process of step ST23 and step ST25, Ca component 4 is added by the phosphate precipitation process to precipitate Ca phosphate (step ST29). In this second embodiment, the amount of Ca (OH) ₂ added is smaller than the amount added in the first embodiment, specifically, the reaction equivalent of 1.3% of the phosphorus extract. Is less than twice.

Thereafter, as in the first embodiment, the solid-liquid separation process (step ST30), the cleaning process using treated water (step ST31), the belt concentration process (step ST32), the drying process (step ST33), and the granulation By performing the process (step ST34), powdered calcium phosphate 5 is obtained.

Next, in the second embodiment, unlike the first embodiment, the regenerated liquid separated in the solid-liquid separation step in step ST30 is mixed with the alkaline reaction liquid 1 before being used in circulation. In addition, a process for removing As contained in the regeneration liquid (As removal process, step ST35) and a process for removing Al contained in the regeneration liquid (Al removal process, step ST36) are performed as necessary.

Specifically, the As removal step is performed when the concentration of As contained in the regenerated liquid that has been subjected to solid-liquid separation in Step ST30 becomes a predetermined value (for example, 10 mg / l) or more. In this As removal step, after adding slaked lime to the regenerated liquid to adsorb As, the As is removed from the regenerated liquid by performing solid-liquid separation. Here, about the addition amount of the slaked lime added to a reproduction | regeneration liquid, it determines suitably according to the density | concentration of As.

In addition, the Al removal step is performed when the concentration of Al contained in the regenerated liquid that has been subjected to solid-liquid separation in Step ST30 becomes a predetermined value (for example, 10,000 mg / l) or more. In this Al removal step, Al is removed by adding soluble Si to the regenerating solution.

As described above, according to the second embodiment, each of the phosphorus extraction step and the subsequent solid-liquid separation step is performed only once, and each of the ash washing step and the subsequent solid-liquid separation step is 1 each. By using the liquid separated by performing only once as the phosphorus extract, the number of steps can be reduced without reducing the amount of P extracted. Moreover, it becomes possible to suppress the elution of As from the treated ash by adding polytetsu in the weak acid washing step.

The embodiments of the present invention have been specifically described above, but the present invention is not limited to the above-described embodiments, and various modifications based on the technical idea of the present invention are possible. For example, the numerical values given in the above embodiment are merely examples, and different numerical values may be used as necessary.

In the above-described second embodiment, the As removal step is performed when the concentration of As exceeds a predetermined value with respect to the regenerated solution separated by solid-liquid separation after depositing Ca phosphate. However, when the concentration of As exceeds a predetermined value, the addition amount of Ca (OH) ₂ added in the phosphate precipitation step of step ST29 is increased to 1.3 times 1.5 times the reaction equivalent or more. The amount of Ca may be increased by less than double.

In the embodiment described above, the P alkalinity dependency per unit mass of the incinerated ash is adopted as an example of the hydroxide ion amount dependency per unit mass of the incinerated ash. As another example of the dependence of the amount of hydroxide ions, the elution of P, Al, and Si can be controlled based on the dependence of the incineration ash on the liquid-solid ratio.

Further, in the above-described embodiment, as a method for deriving the predetermined P alkalinity, a straight line is applied from the largest measured value to the smaller measured value among the measured values of P alkalinity, and on the other hand A straight line is applied sequentially from the smallest measured value of the measured values of P alkalinity to the measured value of the larger side, and the P alkalinity at the intersection of the two straight lines is defined as the predetermined P alkalinity. A derivation method may be adopted.

DESCRIPTION OF SYMBOLS 1 Alkaline reaction liquid 2 Incineration ash 3 Processed ash 4 Ca component 5 Calcium phosphate

Claims

A phosphorus extraction step of mixing the drug and incinerated ash containing at least silicon, aluminum and phosphorus to extract phosphorus in the drug;
A method for extracting phosphorus from incinerated ash, comprising: a solid-liquid separation step of separating a liquid mixture of a solution containing phosphorus and an insoluble component into a liquid component and a solid component using a filter medium,
Based on the dependence of the amount of hydroxide ions per unit mass of the incinerated ash in the elution concentration of ionic silica eluted from the incinerated ash on the chemical, the unit concentration of the incinerated ash per unit mass of the ionic silica Measure the amount of hydroxide ions per unit mass of the incinerated ash, the tendency of which depends on the amount of hydroxide ions of
The method for extracting phosphorus from incinerated ash, wherein the amount of hydroxide ions per unit mass of the incinerated ash in the medicine is made equal to or less than a predetermined amount of hydroxide ions of the ionic silica.
A phosphorus extraction step of mixing the drug and incinerated ash containing at least silicon, aluminum and phosphorus to extract phosphorus in the drug;
A method for extracting phosphorus from incinerated ash, comprising: a solid-liquid separation step of separating a liquid mixture of a solution containing phosphorus and an insoluble component into a liquid component and a solid component using a filter medium,
Based on the P alkalinity dependence of the elution concentration of ionic silica eluted from the incinerated ash into the chemical, the P alkalinity of which the tendency of the elution concentration of the ionic silica depends on the P alkalinity is changed. Measure in advance as the predetermined P alkalinity,
The method for extracting phosphorus from incinerated ash, wherein the P alkalinity of the drug is made equal to or less than a predetermined P alkalinity of the ionic silica.
Based on the P alkalinity dependency of the elution concentration of phosphorus extracted from the incinerated ash to the chemical, the predetermined P alkalinity of phosphorus in which the tendency of the phosphorus elution concentration to depend on the P alkalinity changes is measured in advance, The method for extracting phosphorus from incinerated ash according to claim 2, wherein the P alkalinity of the chemical is set to a P alkalinity which is 1.0 (equivalent / kg) lower than a predetermined P alkalinity of the phosphorus.
Based on the P alkalinity dependency of the elution concentration of phosphorus extracted from the incinerated ash to the chemical, the predetermined P alkalinity of phosphorus in which the tendency of the phosphorus elution concentration to depend on the P alkalinity changes is measured in advance, The method for extracting phosphorus from incinerated ash according to claim 2 or 3, wherein the P alkalinity of the drug is set to be equal to or less than a predetermined P alkalinity of the phosphorus.