JP2001130903A - Method for recovering phosphate salt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering phosphate salt, capable of efficiently recovering the phosphate salt from incinerated ash, fly ash, etc. at a low cost. SOLUTION: This method for recovering the phosphate salt comprises a dissolving process where a solution containing acid is added to the incinerated ash and/or the incinerated fly ash containing phosphate radicals to adjust a pH of the solution to be 1.6 or less so that the phosphate radicals contained in the ashes is dissolved in the solution containing the acid, a residue-separating process where insoluble residues in the solution containing the acid is separated, and an alkaline component-charging process where an alkaline component is added to the solution separated from the residues so that the pH of the solution is adjusted to be in the range of 1.8-2.2, wherein an iron compound-charging process for charging an iron compound is performed at any time before the alkaline component-charging process is completed and further a recovering process for recovering iron phosphate is performed after the alkaline component- charging process is completed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recovering phosphate groups contained in incinerated ash and incinerated fly ash discharged when incinerating sludge or the like as a phosphate compound.

[0002]

2. Description of the Related Art In recent years, the treatment of sludge and the like generated as residues at municipal sewage or industrial wastewater treatment plants has become an important problem for concerned parties, and has also improved living standards and increased industrial production. And the amount tends to further increase significantly. Most of the sludge, etc.,
At present, it is incinerated into incinerated ash and incinerated fly ash, and is currently discarded. In addition, since the incinerated ash and the like disposed of as the dumped waste contains a phosphoric acid group containing diphosphorus pentoxide (P ₂ O ₅ ) as a main component, the phosphorus is dissolved out of the incinerated ash to form a sea or lake. If aquatic spills are found, algae can form and cause eutrophication of seas and lakes, which can cause serious problems.

[0003] On the other hand, phosphorus is a useful substance depending on the method of its use, and is currently used as a raw material for producing fertilizers for agricultural crops and pharmaceuticals. However, at present, Japan depends on imports for all phosphorus.

[0004] Therefore, it has been conventionally desired to recover phosphate groups contained in incinerated ash such as sludge and reuse them as fertilizers.

Japanese Patent Application Laid-Open No. Hei 9-77506 discloses a method for recovering phosphoric acid from sewage sludge incineration ash, but has a major problem in terms of cost. Also, Japanese Patent Application Laid-Open No. 10-1013
No. 32 also discloses a method for separating and recovering calcium, phosphorus and metal from incinerated ash by acid treatment, but it is difficult to put it to practical use in terms of efficiency and cost.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its main object to provide a method for recovering and reusing phosphorus from incinerated ash such as sludge at low cost. It is assumed that.

[0007]

According to the present invention, in order to achieve the above object, according to the first aspect of the present invention, a solution containing an acid is added to incinerated ash containing phosphate groups and / or fly ash to adjust the pH to 1.6. By the following, a dissolving step of dissolving the phosphate group in the ash in a solution containing the acid, a residue separating step of separating an insoluble residue in the solution containing the acid, and a solution in which the insoluble residue is separated Add alkaline component to pH
Is adjusted to fall within a range of 1.8 to 2.2, and an iron compound input step of inputting an iron compound is performed in any step before the alkali component input step, Further, the present invention provides a method for recovering phosphate, comprising a recovery step of recovering iron phosphate after the alkali component charging step.

[0008] In the method of the present invention, the pH is adjusted to 1.6 or less by adding a solution containing an acid to dissolve the phosphate groups contained in the incinerated ash or incinerated fly ash in the solution. . Next, after removing the insoluble residue in the solution containing the acid, an alkaline component is added so that the pH is in the range of 1.8 to 2.2. At this time, the iron compound is charged at any time before the alkali component charging step. Thus, the p of the solution in which the iron compound is added and the phosphate group dissolves
By setting H in the range of 1.8 to 2.2 as described above, only iron phosphate precipitates and gelates, so that aluminum phosphate which becomes extremely difficult to handle thereafter does not precipitate. Therefore, in the subsequent recovery step, only iron phosphate can be easily recovered with high purity.

[0009] As described above, in the phosphate recovery method of the present invention, phosphate can be easily obtained in the form of iron phosphate with high purity, so that these phosphorus can be reused as fertilizer and the like. It is possible. In addition, it is possible to solve environmental pollution (eg, eutrophication of rivers) due to phosphorus, which has conventionally been a problem when incinerated ash such as sludge is discarded.

In the phosphate recovery method of the present invention, as described in claim 2, an iron compound mixing step may be performed before the residue separation step of separating the insoluble residue,
Further, as described in claim 3, an iron compound charging step may be performed after the residue separation step of separating the insoluble residue.

In the case where the iron compound mixing step is performed before the residue separation step, the amount of the iron compound to be introduced is 0.75 times the theoretical reaction equivalent of the phosphate group contained in the ash. It is preferable that this is the case. Due to the effect of phosphate groups contained in the insoluble residue, iron phosphate can be recovered only at 0.75 of the theoretical reaction equivalent of phosphate groups.
It is because it is about.

In the case where the iron compound charging step is performed after the residue separation step, as described in claim 3, an iron compound equivalent to or more than the theoretical reaction equivalent of the phosphate group in the solution from which the insoluble residue has been separated is charged. Is preferred. in this case,
This is because there is no influence of the insoluble residue.

Further, as described in claim 4, it is preferable that the incinerated ash and / or fly ash is ash discharged when sewage sludge is incinerated. For sewage sludge,
This is because it contains sludge in wastewater from households containing a large amount of phosphorus, and further contains a large amount of phosphorus because, for example, phosphorus in fertilizer used in fields enters sewage. In addition, a considerable amount of sewage sludge discharged during sewage treatment is incinerated, and phosphorus is recovered from incinerated ash and incinerated fly ash discharged during incineration to recycle waste. This is because it can be used.

Further, as set forth in claim 5, in the present invention, the alkali component is an alkali metal hydroxide, an alkaline earth metal hydroxide, an alkali metal carbonate, or an alkaline earth metal. It is preferably one or a mixture of two or more selected from the group consisting of carbonates.
Since the alkaline component is used to adjust the pH of the solution to 1.8 to 2.2, basically any alkaline component may be used as long as it shows alkalinity. It is preferable to use the above-mentioned alkali component because it is easy and a certain degree of purity is secured.

Further, as described in claim 6,
Preferably, the iron compound is an iron compound composed of trivalent iron.
Good. Trivalent iron ion (Fe³⁺) Is phosphate ion
(PO _Four ^3-) And a very stable compound (phosphoric acid)
Iron / FePO_Four) To form a powder (solid).
When the precipitate is separated from the solution, it is easy to separate and collect.
is there.

Further, according to the present invention, as described in claim 7, the iron phosphate recovered by the phosphate recovery method according to any one of claims 1 to 6 includes:
Add an aqueous alkaline solution to adjust the pH to 3.0 or more.
H adjustment step, hydrogen sulfide inflow step in which hydrogen sulfide gas is introduced into the solution after the pH adjustment step to remove iron contained in iron phosphate, and iron sulfide precipitated in the hydrogen sulfide inflow step are removed. The present invention also provides a phosphate recovery method characterized by recovering a phosphate group as a phosphoric acid solution by performing at least a phosphoric acid solution collecting step of obtaining a phosphoric acid solution.

The phosphate recovery method according to any one of claims 1 to 6 is a method for recovering phosphorus in sludge mainly as iron phosphate, and is described in claim 7 above. The method is a method of removing iron from iron phosphate and recovering it as a phosphoric acid solution.

In such a method, an alkaline aqueous solution is charged into the iron phosphate recovered by the phosphate recovery method according to any one of claims 1 to 6,
After the pH is adjusted to 3.0 or higher, hydrogen sulfide gas is introduced, so that iron ions forming iron phosphate and sulfide ions forming hydrogen sulfide gas combine to precipitate as iron sulfide. To remove iron. Then, by removing the precipitate (iron sulfide), it can be recovered as a phosphoric acid solution. By recovering the phosphorus in the phosphate group as a phosphoric acid solution, for example, various phosphate compounds such as calcium phosphate useful as a fertilizer described later can be formed, which is preferable.

Further, as described in claim 8, when the pH adjusting step according to claim 7 is performed and then the hydrogen sulfide inflow step is performed, the pH is adjusted while the hydrogen sulfide gas is flowing. It is also possible to introduce an aqueous alkali solution in order to adjust it to 3.0 or more.

In the present invention, the iron in the iron phosphate is removed by flowing hydrogen sulfide gas. At this time, the pH is adjusted with an aqueous alkali solution before flowing the hydrogen sulfide gas so that the iron is easily removed. I do. Here, when the hydrogen sulfide gas is introduced to precipitate the iron sulfide, phosphoric acid is also generated at the same time, so that the pH of the solution gradually shifts to the acidic side. When the solution shifts to the acidic side, the production of iron sulfide is hindered, and iron may not be removed efficiently. In such a case, the hydrogen sulfide gas continues to flow as described in claim 8 while the p-pulverization is performed by the aqueous alkaline solution.
Maintaining H at 3.0 or more is preferable because it is possible to prevent the pH of the solution from being lowered by the generated phosphoric acid, and to efficiently remove iron when removing it.

Here, as described in claim 9, the alkaline aqueous solution charged in the method according to claim 7 or 8 is a group consisting of sodium hydroxide, calcium hydroxide, or ammonium hydroxide. It is preferably one or a mixture of two or more arbitrarily selected from

The alkaline aqueous solution to be added in the pH adjusting step is used to adjust the pH of the solution to 3.0 or more, and may be any one which exhibits alkalinity. Sodium and the like are preferable because they are inexpensive and easily available.

[0023] Further, as described in claim 10, phosphate is combined with phosphoric acid in the phosphoric acid solution recovered by the phosphate recovery method according to any one of claims 7 to 9 to form phosphate. And a phosphate recovery step of recovering a phosphate generated by phosphoric acid and the compound. I do.

By adding an appropriate compound to the phosphoric acid solution recovered according to any one of claims 7 to 9, the compound reacts with phosphoric acid, and as a result, a phosphoric acid compound is obtained. Phosphorus can be recovered. That is, according to a series of inventions described from claim 1,
Phosphorus can be recovered as iron phosphate from incinerated ash and / or incinerated fly ash containing phosphate groups. Phosphorus can be recovered as a phosphoric acid solution, and further recovered as a phosphate compound other than iron phosphate. It is also possible. Therefore, the method of recovering phosphorus can be selected depending on the use of the recovered phosphorus, which is preferable.

Further, as described in claim 11, in the method according to claim 10, the compound mixed in the compound mixing step forms a calcium compound capable of forming calcium phosphate, magnesium phosphate. It is preferably a magnesium compound which can be used, or one or more mixtures selected from the group consisting of aqueous ammonia solution and ammonia gas.

The phosphate recovered according to the present invention is suitable for use as a fertilizer, but most of the soil in Japan is acidic soil. This is because iron acid is more suitable as a fertilizer when it is used as calcium phosphate, magnesium phosphate, or ammonium phosphate.

[Detailed Description of the Invention] (First Embodiment) Hereinafter, a method for recovering phosphorus in a phosphate group as iron phosphate in the phosphate recovery method of the present invention will be described for each step.

First, a dissolving step for dissolving phosphate groups contained in incinerated ash and the like will be described. In the dissolution step of the present invention, the pH is adjusted to 1.6 or less by adding a solution containing an acid to incinerated ash containing phosphate groups and / or fly ash (hereinafter sometimes referred to as incinerated ash). Thereby, the phosphate groups in the ash are dissolved in the solution containing the acid.

The phosphate group referred to in the present invention means phosphoric acid,
Alternatively, it is a generic term for a compound that can be a phosphoric acid compound, that is, a compound containing a phosphorus element (P), and the chemical structure and the like are not particularly limited. For example, incinerated ash and the like contain a large amount of the phosphorus element (P) as phosphorus pentoxide (P ₂ O ₅ ).

The incinerated ash and / or fly ash to which the present invention is applied is not particularly limited, and may be any as long as it contains a phosphate group.
Above all, incineration ash and incineration fly ash obtained by incineration of sewage sludge discharged from sewage treatment plants and the like are particularly preferably applied because they contain a large amount of phosphorus. That is, since such sewage sludge contains sewage sludge discharged from homes, for example, contains a large amount of phosphorus and the like contained in detergents and the like,
Furthermore, phosphorus from fertilizer used in fields and the like invades sewage. Therefore, such sewage sludge contains a large amount of phosphorus and is suitably applied to the present invention. In addition, such sewage sludge is discarded because it has no use and is preferably reused.

In this dissolving step, the phosphate group is dissolved in a solution containing an acid. That is, by adding a solution containing an acid to the incineration ash or the like, the phosphate group contained as a solid in the incineration ash or the like is dissolved and extracted in the acid-containing solution. Acids that can be used in this step include:
There is no particular limitation, and any acid may be used. Among them, hydrochloric acid, nitric acid, sulfuric acid, etc. are easily available,
It is also preferable because it is relatively inexpensive.

In the dissolving step of the present invention, the pH of the solution containing the acid is adjusted to 1.6 or less. It has a pH of 1.
If the value is larger than 6, the phosphate groups contained in the incineration ash and the like are not completely dissolved, so that the phosphate cannot be efficiently recovered. In this step, p
Although H is not particularly limited as long as it is 1.6 or less, since a large amount of acid is required to lower the pH, the pH is preferably about 1.4 to 1.6 in consideration of the cost. It is suitable.

Next, a description will be given of a residue separation step for separating insoluble residues that have not been dissolved in the solution containing an acid in the above-mentioned dissolution step.

Various metals and compounds are contained in incinerated ash and the like, and as described above, even if the pH is adjusted to 1.6 or less with an acid, an insoluble residue that does not dissolve remains. Such an insoluble residue must be removed in advance because it causes a problem when iron phosphate is recovered in a recovery step described later. Therefore,
In the present invention, the residue separation step is performed after the dissolution step.

The method for separating the insoluble residue is not particularly limited. For example, filtration is the most commonly used method.

In the phosphate recovery method of the present invention, after the above-described residue separation step, an alkali component is added to the solution from which the insoluble residue has been separated, and the pH is adjusted within the range of 1.8 to 2.2. Perform the alkali component charging step,
In the present invention, it is necessary to perform an iron compound charging step of charging an iron compound in any step before the alkali component charging step.

The iron compound charging step in the present invention means that the phosphate contained in the incinerated ash is recovered in the form of a solution containing an acid in which the phosphate group is dissolved in order to recover the phosphate as iron phosphate which can be easily separated and recovered. The purpose is to supply iron ions by feeding an iron compound into the iron.

The iron compound charging step may be performed at any time as long as it is before the alkali component charging step as described above. Specifically, the iron compound charging step may be performed before the residue separation step, and may be performed after the residue separation step. Can be mentioned.

Hereinafter, the case where the iron compound charging step is performed before the residue separation step and the case where the iron compound charging step is performed after the residue separation step will be described separately.

First, the case where the iron compound charging step is performed before the residue separation step will be described with reference to the flowchart shown in FIG. As shown in FIG. 1, first, a solution containing an acid and an iron compound are added to incineration ash containing a phosphate group, and the pH is set to 1.
By adjusting the value to 6 or less, the phosphate groups contained in the incineration ash and the like are dissolved.

The acid added for dissolving the phosphate groups in the incineration ash is not particularly limited, and may be any acid as described above.

The iron compound is added because the amount of the iron compound contained in the incineration ash and the like is very small, so that all the phosphate ions (PO ₄ ^3- ) in the solution are efficiently recovered as iron phosphate. Because you can't.

Here, the iron compound to be added is not particularly limited and may be any compound. Generally, iron compounds can be roughly classified into divalent iron compounds and trivalent iron compounds according to the valence of iron forming the compound. In the method of the present invention, as the divalent iron compound, for example, ferrous sulfate (FeSO ₄ ) or ferrous chloride (FeC ₄ )
l ₂ ) and the like, and as the trivalent iron compound, for example, ferric sulfate (Fe ₂ (SO ₄ ) ₃ ) or ferric chloride
Iron (FeCl ₃ ) or the like can be used. Among them, when phosphate ions (PO ₄ ^3- ) in the solution are formed and iron phosphate is formed, iron which is mixed in the iron compound mixing step of the present invention due to the stability of iron phosphate, ease of recovery, etc. The compound is preferably a trivalent iron compound, of which ferric chloride (FeCl ₃ ) is particularly preferably used.

When the iron compound charging step is performed before the residue separation step (see FIG. 1), the amount of the iron compound added in the iron compound mixing step is determined by the theoretical reaction equivalent of phosphate groups contained in incinerated ash and the like. It is preferably 0.75 times or more of the following. This is an experimentally determined value. If the iron compound is present at 0.75 times or more the theoretical reaction equivalent of the phosphate group, phosphorus and the iron compound may form a complex in the subsequent alkali component charging step. Because it can be. Here, it can be considered that an iron compound is usually required in the same amount as the theoretical reaction equivalent of the phosphate group. However, incineration ash of sludge, etc., contains trivalent iron in addition to phosphate group. This is because these metals also form a complex with phosphorus, so that the amount of the iron compound to be added should be 0.75 times or more the theoretical equivalent of the phosphate group.

Next, a residue separation step is performed as shown in FIG. This step is a step for separating insoluble residues remaining as a solid in the solution without dissolving when the incinerated ash or the like is dissolved in the above-described dissolving step. Note that the insoluble residue does not necessarily contain a large amount of a phosphate group which is a target of the phosphate in the present invention and may be removed.

Next, according to the method of the present invention, an alkaline component is added to the solution from which the insoluble residue has been separated, and the pH is 1.8 to 1.8.
An alkali component feeding step of adjusting the content to the range of 2.2 is performed.

The reason for adding the alkali component is to increase the pH adjusted to 1.6 or less in the dissolving step so that the pH falls within the range of 1.8 to 2.2.

Here, the reason why the lower limit of the pH of the solution is set to 1.8 will be described.

First, as described above, the phosphate group dissolves when the pH becomes 1.6 or less. The dissolved phosphate radical will be present as phosphate ion (PO ₄ ^3-) in solution, the phosphate ions (PO ₄ ^3-), like present in solution trivalent iron ions (Fe ³⁺ ) to form iron phosphate (FePO ₄ ).

However, the solubility of iron phosphate (FePO ₄ ) is pH-dependent, and precipitation does not occur when the pH is 1.6, but when the pH is gradually increased by adding an alkali component, the solubility is gradually increased. Begin to precipitate. The iron phosphate (FePO)
_The pH at which ₄ ) begins to precipitate is about 1.7, and a pH of 1.8 or more is required to recover iron phosphate efficiently. For this reason, the lower limit of the pH of the solution was set to 1.8.

Next, the reason why the upper limit of the pH of the solution is set to 2.2 will be described. The sludge incineration ash contains various metals such as iron (Fe), copper (Cu), and aluminum (Al) in addition to phosphorus. It is possible to react with (PO ₄ ^3- ) to form phosphate in solution. here,
As long as the purpose is to finally recover phosphorus, a salt with any metal is basically good, however, iron phosphate formed by iron (Fe) and phosphate ions is For example, aluminum phosphate formed by aluminum (Al) and phosphate ions (PO ₄ ^3- ) is easy to recover when precipitated because of being solid.
Its shape is a gel, and the precipitate cannot be collected efficiently.

Therefore, when recovering phosphate, it is preferable to recover it as iron phosphate. Here, considering the pH dependency of the solubility of the phosphate formed by each metal and phosphate ion (PO ₄ ^3- ), the upper limit of the pH at which only iron phosphate precipitates is 2.2. Experimental results have shown that aluminum phosphate precipitates at a pH higher than this. Therefore, the upper limit of the pH is 2.2.
It was decided.

FIG. 2 shows the pH dependence of the solubility of each phosphate obtained by calculation in a single system.

The single system refers to a state in which only one kind of metal (for example, Fe, Al, etc.) is present in the solution.
The curves shown in FIG. 2 are the solubility curves of the respective metal phosphates. From the difference in solubility between iron phosphate (FePO ₄ ) and aluminum phosphate (AlPO ₄ ), it can be seen that iron phosphate (FePO ₄ ) precipitates at a lower pH value.

The pH at which iron phosphate (FePO ₄ ) precipitates in FIG. 2 shows a value considerably different from that in the case of the present invention described above. This is because FIG. 2 shows the calculated solubility in a single system, whereas in the case of the present invention, various metals are contained because sludge or the like is used in the present invention. It is considered that there is a large difference.

The alkaline component that can be used in the present invention is not particularly limited and may be any. Among them, an alkali metal hydroxide, an alkaline earth metal hydroxide, an alkali metal carbonate, and a mixture of one or more selected from the group consisting of alkaline earth metal carbonates are preferable, For example, potassium hydroxide (KOH), magnesium hydroxide (Mg (O
H) ₂ ), calcium hydroxide (Ca (OH) ₂ ), sodium carbonate (Na ₂ CO ₃ ), potassium carbonate (K ₂ CO ₃ ),
Magnesium carbonate (MgCO ₃ ), calcium carbonate (C
aCO ₃ ) can be preferably used.

Next, an iron phosphate recovering step is performed for recovering the iron phosphate precipitated by performing the alkaline component charging step.

Here, the method for recovering iron phosphate is not particularly limited, and can be recovered by, for example, filtration.

Next, a case where the iron compound charging step is performed after the residue separation step will be described with reference to FIG.

As in the example shown in FIG. 1, a solution containing an acid is first added to incinerated ash or the like containing a phosphate group to adjust the pH to 1.6 or less, so that the phosphate group contained in the incinerated ash or the like is adjusted. Dissolve. Here, in this dissolving step, the difference from the dissolving step in the example shown in FIG. 1 is that, in the dissolving step in the example shown in FIG. However, in the method shown in FIG. 3, the iron compound is added after the residue separation step, and is not added here.

The other conditions, such as the type of acid, are the same as in the example shown in FIG. 1 described above, and a description thereof will be omitted.

Next, a residue separation step is performed as shown in FIG. This step is for separating the insoluble residue remaining as a solid in the solution without dissolving when the incinerated ash or the like is dissolved in the above-described dissolving step. The residue separating step shown in FIG. Is performed in the same manner as described above.

Next, an iron compound charging step of adding an iron compound to the solution from which the insoluble residue has been removed in the residue separation step is performed. The iron compound is added, as in the example shown in FIG. 1 described above, since the amount of the iron compound contained in the incineration ash or the like is very small, all the phosphate ions (PO ₄ ^3- ) in the solution are efficiently removed. This is for recovering as iron phosphate.

Further, in the example shown in FIG. 1, the iron compound is preferably 0.75 times or more the theoretical reaction amount of the phosphate group, whereas in the method shown in FIG. It is preferable that the reaction amount is not less than the theoretical reaction amount. The reason is as follows.

In the example shown in FIG. 1, since the iron compound is mixed before the insoluble residue is separated as described above, that is, in a state where the insoluble residue is still contained in the solution, the phosphate group is incorporated into the insoluble residue. In contrast, in the method shown in FIG. 3, since the iron compound is mixed in after the insoluble residue separation step, the phosphate group is not taken into the insoluble residue, and the phosphate group is not removed. An iron compound in excess of the theoretical reaction amount is required.

Here, other conditions such as the iron compound to be added are the same as those in the example shown in FIG.

Next, in the method shown in FIG. 3, an alkali component is added to the solution after the iron compound charging step is completed, and the pH is set to 1.8.
After performing the alkali component charging step of adjusting the content to fall within the range of ~ 2.2, iron phosphate is recovered in the recovery step.
These alkali component charging step and recovery step are performed in the same manner as in the example shown in FIG. 1 described above. (Second Embodiment) Next, a method for recovering phosphorus in a phosphate group by converting the iron phosphate recovered by the method described above into a phosphoric acid solution or a phosphate compound other than iron is shown in the flowchart of FIG. Each step will be described with reference to FIG.

First, the pH adjustment step will be described.

The pH adjusting step is a step in which an alkaline aqueous solution is added to the iron phosphate recovered by the method described above (see FIGS. 1 and 3) to adjust the pH of the solution to 3.0 or more. After that, when a hydrogen sulfide inflow step is performed to remove iron, the process is performed so that most of the iron in the system can be removed (to prevent iron from remaining in the solution).

The alkaline aqueous solution used in the pH adjusting step is
There is no particular limitation, and any alkaline aqueous solution may be used as long as the pH of the solution can be adjusted to 3.0 or more. Among them, one or two or more mixtures arbitrarily selected from the group consisting of sodium hydroxide, potassium hydroxide, and ammonium hydroxide are preferable. This is because these alkaline aqueous solutions are relatively inexpensive and easily available.

This pH adjustment step is preferably performed also during the subsequent hydrogen sulfide inflow step. As will be described later, when iron is precipitated as iron sulfide in the hydrogen sulfide inflow step, phosphoric acid is generated at the same time, so that the pH of the solution is shifted to the acidic side. It is also preferable to adjust the pH by introducing an aqueous alkali solution. Here, a method for adjusting the pH using an alkaline aqueous solution during the hydrogen sulfide inflow step is not particularly limited. The present invention is not limited thereto, and may be performed only once during the hydrogen sulfide inflow step. And it can be performed continuously during the hydrogen sulfide inflow step.

Next, the hydrogen sulfide inflow step will be described.

In the method of the present invention, a hydrogen sulfide inflow step of flowing hydrogen sulfide into the solution after the pH adjustment step is performed. This is a step performed to precipitate and remove iron contained in the phosphate. Iron phosphate was dissolved by the pH adjustment step is made in the solution with iron ions (Fe ³⁺⁾ and phosphate ions (PO ₄ ^3-). By flowing hydrogen sulfide gas (H ₂ S) in such a state, iron ions (Fe ³⁺ ) in the solution are reduced to iron ions (Fe ²⁺ ),
Since it combines with sulfur (S ²⁻ ) in hydrogen sulfide gas (H ₂ S) and precipitates as iron sulfide (FeS), iron can be removed from the solution.

In the method of the present invention, subsequently, an iron separation step for removing a precipitate (iron sulfide) generated in the hydrogen sulfide inflow step is performed.

The method used in this step is not particularly limited, and any method may be used as long as iron sulfide as a precipitate can be removed from the solution.
For example, a filtration method or a sedimentation separation method is generally used, and is preferable because it is simple and the like.

By performing the above steps (iron separation step), phosphorus in the phosphate groups can be recovered as a phosphoric acid solution.

When phosphorus in the phosphate group is recovered as a phosphate compound other than iron, the solution (phosphoric acid solution) that has undergone the iron separation step is combined with phosphoric acid to form phosphate. A compound mixing step of mixing the compound is performed.

In the solution (phosphate solution) after the removal of iron, phosphate ions separated from iron ions are present, and the phosphate ions bind to the compound mixed in the compound mixing step. To form phosphate. Here, the compounds to be mixed are preferably those listed below. 1) a calcium compound capable of forming calcium phosphate; 2) a magnesium compound capable of forming magnesium phosphate; 3) an ammonia compound or ammonia gas capable of forming ammonium phosphate. One or more mixtures.

Among the calcium compounds described in 1) above, calcium oxide (CaO), calcium carbonate (CaCO ₃ ), calcium hydroxide (Ca (OH) ₂ ),
Calcium chloride (CaCl ₂ ) is particularly preferred. Among the magnesium compounds described in 2) above, magnesium oxide (MgO), magnesium carbonate (MgCO ₃ ),
Magnesium hydroxide (Mg (OH) ₂ ) and magnesium chloride (MgCl ₂ ) are particularly preferred. And the above 3)
Among the ammonia compounds described in (1), ammonium hydroxide (NH ₄ OH) and ammonium chloride (NH ₄ Cl) are preferable.

The compounds 1) to 3) are preferable because phosphates (calcium phosphate, magnesium phosphate, or ammonium phosphate) generated when reacted with phosphoric acid are particularly preferable when these are used as fertilizers. It is.

When the aqueous alkali solution used in the above-mentioned pH adjustment step is ammonium hydroxide, ammonium hydroxide is present in the solution. (Or gas). This is because the amount of the ammonia aqueous solution mixed can be saved by the amount of the ammonium ions present in the solution.

In the method of the present invention, a phosphate compound can be efficiently recovered by each of the steps described above. Further, the final method of recovering the phosphate compound is not particularly limited, and the same method (for example, filtration) as in the case of recovering iron phosphate can be used.

The phosphate recovery method described above is an example of the method of the present invention, and the present invention is not limited to this. The technical idea and the technical concept described in the claims of the present invention are not limited thereto. Any components having substantially the same configuration and exhibiting the same function and effect are included in the technical scope of the present invention.

The iron phosphate and the like recovered by the method of the present invention can be used for producing fertilizers for agricultural crops, pharmaceuticals, and the like.

[0085]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, some numerical values are limited. The following is an example which is the basis of the numerical values.

Example 1 Table 1 shows components contained in a solution obtained by dissolving hopper ash at pH 1.6 and 2.0 using sulfuric acid, respectively.

[0087]

[Table 1]

As shown in Table 1, when the pH was 2.0, diphosphorus pentoxide (P ₂ O ₅ ) dissolved in the solution was 1.89.
g, whereas when the pH is 1.6, the phosphorus pentoxide (P ₂ O ₅ ) dissolved in the solution is 11.8 g. This indicates that the pH needs to be 1.6 or less in order to dissolve phosphate groups contained in incinerated ash and the like.

(Embodiment 2) In this embodiment, first, incineration fly ash of sewage sludge is dissolved with sulfuric acid, and then iron chloride (FeCl ₃ ) is charged as a trivalent iron compound to separate insoluble residues. Sodium hydroxide (NaO) as an alkaline component
H) to adjust the pH of the solution,
The formation of precipitate (iron phosphate) for each H was confirmed. In addition, as a condition when the precipitate is generated, the temperature is normal temperature,
The reaction time (the time until the formation of a precipitate was confirmed) was 1 hour, and stirring was continued with a magnetic stirrer during the reaction time.

The results are shown in Table 2 below.

[0091]

[Table 2]

The legends shown in Table 2 are as follows. -: No precipitate was formed. Δ: A precipitate was formed, but disappeared when observed the next day. (The stirring was continued until the next day.) ：: A precipitate was formed.

From Table 2, it can be seen that no precipitate is formed at a pH of 1.6 or less, regardless of whether the concentration of sodium hydroxide used as the alkali component is 10% or 20%. It turns out that it is not possible to recover them. In addition, when the pH was 1.7, when 10% sodium hydroxide was used, it was found that the precipitation was incomplete, and in order to efficiently and surely collect the precipitate, that is, iron phosphate, Indicates that the pH is preferably 1.8 or more.

Example 3 In this example, the components of the precipitate (precipitated at pH 2.0) produced in Example 1 were examined. The results are shown in Table 3 below.

[0095]

[Table 3]

Table 3 shows that most of the precipitated components are phosphorus and iron, and almost no aluminum component is contained. Therefore, it can be seen that the present invention can recover phosphate groups with relatively high purity as iron phosphate.

(Embodiment 4) In the present invention, iron in iron phosphate is precipitated as iron sulfide by flowing hydrogen sulfide gas after the iron phosphate once recovered is made into a suspension.
An iron separation step of recovering iron from the solution is performed. In the present example, the following experiment was performed in order to confirm whether or not iron sulfide can be generated by flowing hydrogen sulfide gas to separate iron.

By performing the above first embodiment, iron phosphate (solid) was obtained, and this iron phosphate was dispersed in distilled water to produce a solution containing iron phosphate.

The solution was placed in absorption bottle 1 as shown in FIG.
, And hydrogen sulfide gas was introduced into the solution from the hydrogen sulfide gas inflow pipe 2. At this time, the solution was a magnetic stirrer 3
Continuously stirred. Reference numeral 4 in the drawing denotes a rotor, reference numeral 5 denotes a gas exhaust pipe, and reference numeral 6 denotes a diffuser balloon.

The experimental conditions were as follows: a solution containing iron phosphate was produced by using 20 g of iron phosphate (solid) used, 200 ml of distilled water, and NaOH (adjusting to pH 4) for adjusting pH. The used hydrogen sulfide gas is a mixed gas of hydrogen sulfide gas and nitrogen gas, and the ratio is 10% of hydrogen sulfide gas and 90% of nitrogen gas.

The experiment was conducted according to the above-described experimental procedures and experimental conditions with the nitrogen gas inflow time being 1 hour, 3 hours, and 5 hours. Table 4 below shows the results.

[0102]

[Table 4]

As can be seen from Table 4, it is clear that iron sulfide (FeS) is produced in each case. It was also confirmed that the solution turned black in less than 15 minutes after the introduction of the hydrogen sulfide gas (the pH of the solution was 3.5 at this time).
Met. ). Table 4 also revealed that a reaction time of 1 hour was sufficient.

(Example 5) In the present invention, calcium phosphate or the like is formed by dissolving phosphate groups from iron phosphate once recovered, but iron in iron phosphate is precipitated as iron sulfide to release phosphate groups. At that time, the pH is set to 3.0 or more. In the present embodiment, various concentrations of hydrogen sulfide gas are introduced into the suspension containing iron phosphate, and the pH at which iron sulfide is efficiently generated is adjusted.
An experiment was performed to determine The method and results of the experiment are described below.

<Experimental Method> The experiment was performed using the experimental apparatus described in Example 4 above. The components of the suspension containing iron phosphate were iron phosphate: 20 g and distilled water: 200 ml. The concentration of the hydrogen sulfide gas flowing into the suspension is generated by mixing the hydrogen sulfide gas and the nitrogen gas, and is 100%, 10%, 1%, 0.1%,
Five kinds of hydrogen sulfide gas of 0.01% were prepared. The suspension containing the iron phosphate is white, and the color of the solution changes to black when the iron sulfide is generated by flowing hydrogen sulfide gas. Therefore, the formation of the iron sulfide is easily confirmed by the color of the solution. It is possible.

While the above five kinds of hydrogen sulfide gases are flowing into the suspension, the pH of the suspension is gradually increased by gradually adding a NaOH solution, so that the suspension changes from white to black. The pH of the suspension was measured. The pH measured in this experiment is p that efficiently produces iron sulfide in hydrogen sulfide gas at each concentration.
H.

<Experimental Results> The experimental results are shown in FIG.

As can be seen from FIG. 6, as the concentration of hydrogen sulfide gas flowing into the suspension decreases, the pH at which the color of the suspension changes from white to black, that is, iron sulfide is efficiently produced. The pH was found to be high.

From the results of this experiment, the relationship between the pH of the suspension and the concentration of the inflowing hydrogen sulfide gas (assumed to be X%) is obtained as an empirical formula: (pH of the suspension) = 4.0− 0.5 logX. Therefore, in the present invention, the concentration of the hydrogen sulfide gas flowing in the hydrogen sulfide inflow step is measured in advance and substituted into the empirical formula, so that the pH should be adjusted in the pH adjustment step in order to efficiently generate iron sulfide. The value of the pH can be determined.

However, p calculated by the above empirical formula
The value of H is a value obtained using a suspension containing no impurities, as is clear from the present experimental method. Therefore, the calculated pH value is a value for efficiently producing iron sulfide. Is a reference value. Therefore, if the pH is adjusted to 3.0 or more in the pH adjusting step of the method of the present invention, even if the pH value is different from the pH value obtained by the above empirical formula, iron sulfide is reduced by the subsequent hydrogen sulfide inflow step. It is possible to remove the precipitate. However, in order to efficiently produce iron sulfide, it is preferable to adjust the pH to be equal to or higher than the pH determined by the above empirical formula, and when expressed using the above formula, (pH to be adjusted) ≧ 4.0−0.5 logX (X is the concentration (%) of hydrogen sulfide gas).

[0111]

According to the phosphate recovery method of the present invention as described above, phosphorus useful for the production of agricultural fertilizers and the production of pharmaceuticals from waste such as incineration ash such as sludge can be converted into a phosphate compound at low cost. Can be collected and reused.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating the method of the present invention.

FIG. 2 shows the solubility curves of various phosphates in a single system.

FIG. 3 is a flowchart illustrating the method of the present invention.

FIG. 4 is a flowchart illustrating the method of the present invention.

FIG. 5 is a schematic sectional view of an experimental apparatus used in the examples.

FIG. 6 is a diagram showing the results of an experiment performed in Example 5.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Absorption bottle, 2 ... Hydrogen sulfide gas inlet, 3 ... Magnet stirrer, 4 ... Rotor, 5 ... Gas exhaust pipe, 6 ... Balloon.

Claims (11)

[Claims] The pH of the incinerated ash and / or fly ash containing a phosphate group is adjusted to a pH of 1.6 or less by adding a solution containing an acid to the incinerated ash and / or the fly ash. A dissolving step of dissolving, a residue separating step of separating an insoluble residue in the solution containing the acid, and adding an alkali component to the solution from which the insoluble residue is separated,
an alkali component charging step of adjusting the pH to be in the range of 1.8 to 2.2, and wherein the iron compound charging step of charging the iron compound is performed in any of the steps before the alkali component charging step. A method of recovering a phosphate, further comprising a recovery step of recovering iron phosphate after the alkali component charging step. 2. An iron compound mixing step is performed before the residue separation step of separating the insoluble residue, and the amount of the iron compound to be charged is 0.75 times the theoretical reaction equivalent of the phosphate group contained in the ash. The method for recovering phosphate according to claim 1, wherein: 3. An iron compound mixing step is performed after the residue separation step of separating the insoluble residue, and the amount of the iron compound to be introduced is equal to or more than the theoretical reaction equivalent of the phosphate group in the solution from which the insoluble residue is separated. The method for recovering phosphate according to claim 1, wherein: 4. The incinerated ash and / or fly ash,
The phosphate recovery method according to any one of claims 1 to 3, wherein the wastewater is incinerated ash and / or fly ash discharged when sewage sludge is incinerated. 5. The alkali component is one or more selected from the group consisting of an alkali metal hydroxide, an alkaline earth metal hydroxide, an alkali metal carbonate, and an alkaline earth metal carbonate. The phosphate recovery method according to any one of claims 1 to 4, wherein the mixture is a mixture of the following. 6. The phosphate recovery method according to claim 1, wherein the iron compound is an iron compound composed of trivalent iron. 7. An alkaline aqueous solution is added to the iron phosphate recovered by the phosphate recovery method according to any one of claims 1 to 6, to adjust the pH to 3.0 or more. PH adjusting step, a hydrogen sulfide inflow step of flowing hydrogen sulfide gas into the solution after the pH adjustment step to remove iron contained in iron phosphate, and iron sulfide precipitated by the hydrogen sulfide inflow step. A phosphoric acid solution collecting step of obtaining a phosphoric acid solution by removing the phosphoric acid solution, wherein a phosphate group is collected as a phosphoric acid solution by performing at least: 8. In the case where the pH adjusting step according to claim 7 is performed and then the hydrogen sulfide inflow step is performed, the pH is adjusted to 3. even while the hydrogen sulfide gas is flowing.
The method for recovering phosphate according to claim 7, wherein an alkaline aqueous solution is added to adjust to 0 or more. 9. The alkaline aqueous solution charged in the method for recovering phosphoric acid according to claim 7 or 8, wherein the alkaline aqueous solution is selected from the group consisting of sodium hydroxide, calcium hydroxide, and ammonium hydroxide. The phosphate recovery method according to claim 7 or 8, wherein the mixture is a mixture of two or more. 10. The phosphoric acid solution recovered by the phosphate recovery method according to any one of claims 7 to 9,
A compound mixing step of mixing a compound capable of forming a phosphate by binding to phosphoric acid; and a phosphate recovering step of recovering a phosphate generated by the phosphoric acid and the compound. Phosphate recovery method. 11. The compound mixed in the compound mixing step is a calcium compound capable of forming calcium phosphate, a magnesium compound capable of forming magnesium phosphate, or an ammonia compound capable of forming ammonium phosphate. The method for recovering phosphate according to claim 10, wherein the phosphate recovery method is one or a mixture of two or more selected from the group consisting of ammonia gas.