WO2016199896A1 - System for recovering phosphorus from raw water to be treated, method for recovering phosphorus from raw water to be treated, fertilizer, raw material for fertilizer, and raw material for yellow phosphorus - Google Patents

Abstract

Adopted is a system for recovering phosphorus from raw water to be treated, the system being equipped with: a calcium dissolution reactor (1); a steel-slag feeder (3) for supplying steel slag to the calcium dissolution reactor (1); an acid feeder (4) for supplying an acid to the calcium dissolution reactor (1); a phosphorus recovery reactor (2) for recovering phosphorus from phosphorus-containing raw water to be treated, by the action of a steel-slag slurry from the calcium dissolution reactor (1); a raw-water feeder (5) for supplying the phosphorus-containing raw water to the phosphorus recovery reactor (1); a dehydrator (6) for dehydrating solid matter which has flocculated and sedimented inside the phosphorus recovery reactor (1) upon standing after the supply of the raw water and subsequent stirring for mixing; a treated-water discharge device (7) for sending outside a supernatant resulting from the reaction inside the phosphorus recovery reactor (1); and a dryer (8) for drying dehydrated matter having been dehydrated.

Description

Recovery system of phosphorus in treated water, recovery method of phosphorus in treated water, fertilizer, fertilizer raw material and yellow phosphorus raw material

The present invention relates to a system for collecting phosphorus in treated water, a method for collecting phosphorus in treated water, a fertilizer, a fertilizer raw material, and a yellow phosphorus raw material.
This application claims priority on June 11, 2015 based on Japanese Patent Application No. 2015-118263 for which it applied to Japan, and uses the content here.

リ ン Phosphorus is an indispensable element for all living organisms. It is one of the three major nutrients of plants and is an important raw material for fertilizers for agricultural crops. Recently, there is a concern about the exhaustion of phosphorus resources, and recovery of phosphorus resources is required. Phosphorus is one of the causative substances that cause eutrophication in the sea, lakes, and the like, and is often contained in, for example, domestic wastewater discharged from ordinary households. Also, industrial wastewater discharged from business establishments may contain phosphorus. For this reason, it is required to efficiently recover phosphorus from these wastewaters.

As technology for recovering phosphorus from water to be treated containing phosphorus, HAP (hydroxyapatite) crystallization method using crystalline calcium silicate hydrate as a seed crystal, magnesium phosphate from waste water containing phosphorus and ammonia There are a MAP method in which ammonium crystallization is performed, and an aggregation precipitation method using calcium hydroxide or calcium chloride. However, these methods are low in reaction rate, crystallization rate and coagulation sedimentation rate, require complex reaction control using various chemicals, and in crystallization methods such as the MAP method, MAP in pipes, etc. There are various problems such as frequent occurrence of troubles such as precipitation blockage. For this reason, the establishment of a low-cost and simple phosphorus recovery method has been an issue.

Recently, as shown in Patent Documents 1 and 2 and Non-Patent Document 1, a phosphorus recovery technique using amorphous calcium silicate as a phosphorus adsorbent has been proposed. However, the phosphorus adsorbents described in Patent Documents 1 and 2 are, for example, a product obtained by making a silicic acid raw material and a lime raw material into an aqueous slurry and adding an alkali hydroxide to cause a hydrothermal reaction, or sodium silicate. An amorphous calcium silicate hydrate formed by adding Ca (OH) ₂ to an aqueous solution and an unreacted Ca (OH) ₂ aggregate or an alkali-soluble silica in a readily soluble silica raw material Preparation of phosphorous adsorbent, which is a collection of aggregates of amorphous calcium silicate hydrate and Ca (OH) ₂ hydrothermally synthesized by adding slaked lime to silica solution dissolved with NaOH However, the process cost is not reduced. Moreover, the preparation of the amorphous calcium silicate described in Non-Patent Document 1 is complicated, and the reduction of the processing cost does not proceed. Moreover, these techniques are not phosphorus recovery techniques using steel slag, nor are techniques for reusing steel slag as fertilizer.

On the other hand, as shown in Patent Documents 3 and 4, steel-based slag is used as a material for recovering metal ions and phosphorus in water. However, the phosphorus recovery method described in Patent Document 3 activates the slag surface with an alkaline agent to make an adsorbent, and then adsorbs the metal ions and phosphorus by mixing these adsorbents into the water to be treated. In this method, the adsorbed phosphorus is eluted and recovered, and the process is extremely complicated, and the recovery efficiency of metal ions and phosphorus is low.

In Patent Document 4, coal ash and the like are mixed with slag discharged from a steel mill, further slag is further blended, and further, an inorganic acid is added to cause gelation, and then alkali is added to agglomerate and precipitate. And an adsorbent obtained by further mixing coal ash and the like. However, the adsorbent described in Patent Document 4 is only described as being used as a substitute for zeolite.
Furthermore, the invention described in Patent Document 5 is an invention relating to a method for recovering phosphorus from steel slag, and is not a method for recovering phosphorus in waste water.

Also, there is a technique described in Non-Patent Documents 2, 3, 4, and 5 regarding the recovery of phosphorus from steel slag, but it is a technique that uses a large amount of energy and chemicals and has not yet been put into practical use. Moreover, these techniques are not methods for recovering phosphorus in waste water.

JP 2013-6733 A JP 2013-27865 A JP 2002-86139 A Japanese Examined Patent Publication No. 4-17088 JP 2010-270378 A

This invention is made | formed in view of the said situation, The collection | recovery system of the phosphorus in to-be-processed water which can collect | recover phosphorus efficiently from the to-be-processed water containing phosphorus, and the collection | recovery method of the phosphorus in to-be-processed water The issue is to provide.
Moreover, this invention makes it a subject to provide the fertilizer and fertilizer raw material which contain phosphorus, and a yellow phosphorus raw material.

As a result of intensive studies by the present inventors, the phosphorus recovery system shown in FIG. 1 has been devised by paying attention to slag by-produced from an ironworks (hereinafter referred to as “steel slag”). By eluting calcium in steel slag, reacting calcium and phosphorus in the water to be treated to form a compound containing phosphorus and calcium, and coagulating and precipitating this compound together with the residue of steel slag after elution of calcium The present inventors have found that solids containing phosphorus at a high concentration can be efficiently recovered. By using steel slag containing phosphorus as slag, phosphorus in the steel slag is also recovered as a solid. The solid material obtained by coagulation sedimentation is very cohesive and sedimentable and can be separated into solid and liquid by stationary separation. In the present invention, it is not necessary to add a flocculant when the solid is settled. In addition, solid-liquid separation can be easily performed by existing techniques such as centrifugation and membrane filtration. Further, since the recovered solid matter contains a large amount of phosphorus, it can be used as a fertilizer as it is or as a fertilizer raw material.
The present invention is as follows.

[1] A calcium elution reaction apparatus that mixes an acid and steel slag and prepares a slag slurry from which calcium in the steel slag is eluted;
A steel slag supply device for supplying the steel slag to the calcium elution reaction device;
An acid supply device for supplying the acid to the calcium elution reaction device;
A phosphorus recovery reaction device that mixes the slag slurry and water to be treated containing phosphorus, reacts calcium in the slag slurry with phosphorus in the water to be treated, and obtains a solid matter containing phosphorus and calcium;
A treated water supply device for supplying the treated water to the phosphorus recovery reactor;
A dehydrator for dehydrating the solid matter produced in the phosphorus recovery reactor after supplying the water to be treated;
A treated water discharge device for sending the supernatant water in the phosphorus recovery reactor after supplying the treated water to the outside of the system;
A system for recovering phosphorus in water to be treated.
[2] The system for recovering phosphorus in water to be treated according to [1], further comprising a drying device that dries the solid matter dehydrated in the dehydrating device.
[3] The system for recovering phosphorus in water to be treated according to [1] or [2], in which molten slag is used instead of the steel slag.
[4] A step of stirring and mixing an acid with steel slag to obtain a slag slurry while eluting calcium in the steel slag;
Stirring and mixing the water to be treated containing phosphorus in the slag slurry, and allowing to stand, thereby forming a compound containing phosphorus and calcium, and coagulating and precipitating the compound as a solid together with the steel slag residue;
A step of recovering the solid matter settled, and a method of recovering phosphorus in the water to be treated.
[5] The method for recovering phosphorus in the water to be treated according to [4], in which the precipitated solid matter is dried.
[6] The method for recovering phosphorus in water to be treated according to [4] or [5], wherein the basicity of the steel slag is in the range of 1 to 7.
[7] The method for recovering phosphorus in the water to be treated according to any one of [4] to [6], wherein a calcium content of the steel slag before addition of hydrochloric acid is in a range of 15 to 55% by mass.
[8] The method for recovering phosphorus in the water to be treated according to any one of [4] to [7], wherein the average particle diameter of the steel slag before addition of hydrochloric acid is 0.3 mm or less.
[9] The treated material according to any one of [4] to [8], wherein the pH of the mixed solution is adjusted to 7.7 to 9.0 when the treated water and the slag slurry are mixed. How to recover phosphorus in water.
[10] When mixing the water to be treated and the slag slurry, the molar ratio (Ca / P) of the amount of calcium in the steel slag and the amount of phosphorus in the water to be treated is 2 or more and 4 or less. The method for recovering phosphorus in the water to be treated according to any one of [4] to [9] to be adjusted.
[11] When the hydrochloric acid is added to the steel slag to obtain the slag slurry, a hydrochloric acid aqueous solution whose concentration is adjusted to 0.5 N or more and 2.0 N or less is used. The method for recovering phosphorus in the water to be treated according to the item.
[12] When the hydrochloric acid is added to the steel slag to obtain the slag slurry, the mixing time is set to 30 minutes or less. The phosphorus in the treated water according to any one of [4] to [11] Collection method.
[13] The method for recovering phosphorus in the water to be treated according to any one of [4] to [12], wherein a stirring and mixing time of the water to be treated and the slag slurry is 5 minutes or more.
[14] The method for recovering phosphorus in the water to be treated according to any one of [4] to [13], wherein the water to be treated containing phosphorus includes one or both of domestic wastewater and industrial wastewater.
[15] The method for recovering phosphorus in the water to be treated according to any one of [4] to [14], in which molten slag is used instead of the steel slag.
[16] A fertilizer containing the solid matter obtained by the method for recovering phosphorus in water to be treated according to any one of [4] to [15].
[17] A fertilizer raw material containing the solid obtained by the method for recovering phosphorus in water to be treated according to any one of [4] to [15].
[18] A yellow phosphorus raw material containing the solid matter obtained by the method for recovering phosphorus in the water to be treated according to any one of [4] to [15].

According to the present invention, phosphorus can be efficiently recovered from water to be treated containing phosphorus.
That is, the phosphorus contained in the water to be treated is coagulated and settled together with the residue of the steel slag after the elution of calcium by the acid and recovered as a solid matter, so that the phosphorus can be efficiently recovered. Here, for example, when using steel slag containing phosphorus, since the phosphorus recovered from the water to be treated and the phosphorus originally contained in the steel slag are contained in the settled solids, the solids Phosphorus is contained in a high concentration therein, and such a solid can be suitably used as a fertilizer, a fertilizer raw material, or a yellow phosphorus raw material. In addition, steel slag discharged from steelworks can be reused as fertilizer. Furthermore, when domestic wastewater or the like is used as water to be treated, phosphorus can be efficiently recovered from steelworks and sewage, which are the two major sources of phosphorus.

The block flow figure showing the phosphorus recovery system which is an embodiment of the present invention. The schematic diagram which shows an example of the phosphorus collection | recovery system which is embodiment of this invention. The graph which shows the relationship between a steel slag residue recovery rate and phosphorus sedimentation rate. The graph which shows the relationship between the amount of hydrochloric acid, the amount of phosphorus collection | recovery per iron and steel slag, the amount of soluble phosphorus, and the amount of soluble phosphorus in recovered phosphorus. The graph which shows the relationship between hydrochloric acid aqueous solution concentration, the amount of phosphorus collection | recovery per steel slag, and a soluble phosphorus content rate. The graph which shows the relationship between the calcium elution reaction time in a steel slag, and a calcium elution rate. The graph which shows the relationship between the particle size of steel slag, a phosphorus removal rate, a phosphorus sedimentation rate, a phosphorus recovery rate, a soluble phosphorus content rate, and the phosphorus concentration of the slag slurry in a supernatant liquid. The graph which shows the relationship between the molar ratio (Ca / P) of the calcium eluted from steel slag, and the phosphorus in to-be-processed water, a phosphorus removal rate, and a soluble phosphorus content rate. The graph which shows the relationship between phosphorus collection | recovery reaction time and phosphorus removal rate. The graph which shows the relationship between pH at the time of phosphorus collection | recovery reaction, and phosphorus collection | recovery rate. The graph which shows the relationship between the phosphorus density | concentration in to-be-processed water and stirring reaction time about Example A and Comparative Example B. FIG. The graph which shows the relationship between phosphorus removal rate and stirring reaction time about Example A and Comparative Example B. The comparison figure of the phosphorus sedimentation rate of Example A and Comparative Example B. The graph which shows the relationship between the sedimentation time of a solid substance, and the aggregate interface height. The graph which shows the relationship between phosphoric acid water concentration, phosphorus removal rate, and soluble phosphorus content rate. The graph which shows the relationship between the kind of steel slag, phosphorus removal rate, phosphorus sedimentation rate, and soluble phosphorus content rate.

Hereinafter, as an example of a system for recovering phosphorus in water to be treated and a method for recovering phosphorus in water to be treated according to the present invention, a method for separating and separating reaction products in a reaction apparatus will be described with reference to FIGS.

1 is provided with a calcium elution reaction apparatus 101, a phosphorus recovery reaction apparatus 102, a solid-liquid separation apparatus 103, a dehydration apparatus 104, and a drying apparatus 105.

The calcium elution reaction apparatus 101 forms slag slurry by mixing steel slag and acid. The formed slag slurry is sent to the phosphorus recovery reactor 102. The phosphorus recovery reactor 102 forms a compound containing phosphorus and calcium by mixing the slag slurry supplied from the calcium elution reactor 101 and the water to be treated supplied from the outside. This compound aggregates with the residue of steel slag to form a solid. The mixture containing the solid is sent to the solid-liquid separator 103.

The solid-liquid separator 103 accepts the mixture obtained in the phosphorus recovery reactor 102 and agglomerates and settles the solid in the mixture. The compound containing phosphorus and calcium and the slurry residue after elution of calcium are agglomerated and precipitated to form a solid, whereby solid-liquid separation is performed. The coagulated and settled solid matter is sent to the dehydrator 104, and the water after separating the solid matter is discharged as phosphorus removal water.

In the dehydrating apparatus 104, the solid matter separated from the solid and liquid is further dehydrated. The phosphorus is finally recovered as a solid containing a high concentration of phosphorus. A part of the dehydrated solid is used as it is for the fertilizer, and another part is sent to the drying device 105. Further, the water that has been dehydrated and separated is discharged as phosphorus-removed water.

In the drying device 105, the solid matter dehydrated in the dehydrating device 104 is further dried. The dried solid becomes a fertilizer or a fertilizer raw material containing a high concentration of phosphorus.

Next, as a specific example of the phosphorus recovery system shown in FIG. 1, the phosphorus recovery system of this embodiment will be described with reference to FIG.

As shown in FIG. 2, the system for recovering phosphorus in the water to be treated according to the present embodiment (hereinafter simply referred to as the present system) elutes the calcium content in the steel slag supply device 3, the acid supply device 4, and the steel slag. A calcium elution reaction apparatus 1 (calcium elution reaction apparatus 101 in FIG. 1), a phosphorus recovery reaction apparatus 2 (phosphorus recovery reaction apparatus 102 and solid-liquid separation apparatus 103 in FIG. 1) for recovering phosphorus in the water to be treated, phosphorus A pH adjusting device 9 for adjusting the pH in the recovery reaction device 2, a dehydration device 6 (dehydration device 104 in FIG. 1) for reducing the water content of the solids coagulated and settled in the phosphorus recovery reaction device 2, and a drying device. 8 (drying device 105 in FIG. 1) and treated water discharging device 7 after removing phosphorus.

The calcium elution reaction apparatus 1 is equipped with a stirring and mixing apparatus (not shown). The calcium elution reaction apparatus 1 is connected to a steel slag storage tank 2a through a slag supply line L1, and is connected to an acid storage tank 4a through an acid supply line L2. The calcium elution reaction apparatus 1 is connected to the phosphorus recovery reaction apparatus 2 via a slag slurry line L3. In the calcium elution reaction apparatus 1, steel slag S1 is charged from the steel slag storage tank 2a, and acid A1 is charged from the acid storage tank 4a, and these steel slag S1 and acid A1 are stirred and mixed for a predetermined time. Thereby, the slag slurry SS which eluted calcium in steel slag S1 is obtained. This slag slurry SS contains an acid solution containing calcium eluted from the steel slag S1 and a steel slag residue, and is supplied to the phosphorus recovery reactor 2 by the slag slurry line L3.

The phosphorus recovery reaction apparatus 2 is connected to a pH adjusting device 9 via a caustic soda supply line L5, and is connected to a treated water supply device 5 via a treated water supply line L4. Moreover, the phosphorus collection | recovery reaction apparatus 2 is connected to the dehydration apparatus 6 via the coagulation sediment line L6, and is connected to the treated water discharge apparatus 7 via the treated water line L7. Further, the phosphorus recovery reaction apparatus 2 is provided with a stirring and mixing apparatus (not shown). To-be-treated water W1 is fed from the treated water tank 5a to the phosphorus recovery reactor 2, slag slurry SS is fed from the calcium elution reactor 1, and caustic soda A2 is further fed from the caustic soda storage tank 9a. These are stirred and mixed while adjusting to a predetermined pH with the caustic soda A2, whereby the phosphorus in the water to be treated W1 and the calcium in the slag slurry SS are reacted. The compound produced | generated by reaction produces solid S2 rapidly with the steel slag residue in slag slurry SS.

The steel slag supply device 3 includes a steel slag storage tank 2a, and a steel slag supply line L1 that connects the steel slag storage tank 2a and the calcium elution reactor 1. The steel slag supply device 3 can supply the steel slag S1 stored in the steel slag storage tank 2a to the calcium elution reaction device 1.

The acid supply device 4 includes an acid storage tank 4a and an acid supply line L2 for supplying the acid A1 from the acid storage tank 4a to the calcium elution reaction apparatus 1. The acid supply device 4 can supply the acid A1 to the calcium elution reaction device 1 via the acid supply line L2.

The treated water supply apparatus 5 includes a treated water tank 5a and a treated water supply line L4 that connects the treated water tank 5a and the phosphorus recovery reactor 2. The treated water supply device 5 can supply the treated water W1 stored in the treated water tank 5a to the phosphorus recovery reactor 2.

The pH adjusting device 9 includes a caustic soda storage tank 9a, and a caustic soda supply line L5 connecting the caustic soda storage tank 9a and the phosphorus recovery reactor 2. The pH adjusting device 9 can supply the caustic soda A2 stored in the caustic soda storage tank 9a to the phosphorus recovery reactor 2.

Further, the treated water discharge device 7 includes a treated water line L7 that receives a dephosphorized supernatant W2 that is a supernatant after the solids S2 is coagulated and separated in the phosphorus recovery reaction device 2, and dehydrated water from the dehydrator 6. It consists of a dewatered water line L8 for receiving W3, a treated water line L7, and a treated water tank 7a connected to the tip of the dewatered water line L8.

Further, the dehydrating device 6 is a device that receives the solid matter S2 that has been coagulated and separated in the phosphorus recovery reaction device 2, and dehydrates the solid matter S2. The dehydrator 6 is connected to a dewatered water line L8 for sending dehydrated water W3 dehydrated from the solid S2 to the treated water tank 7a and a dehydrated line L9 for discharging the dehydrated S3 to the outside.

The dehydrated product S3 may be used as a fertilizer as it is, or may be further dried and used as a fertilizer or a fertilizer raw material. When the dehydrated product S3 is further dried, the dehydrated product S3 is fed into the drying device 8 from the middle of the dehydrated product line L9.

Next, a method for recovering phosphorus in the water to be treated using the phosphorus recovery system shown in FIG. 2 will be described. The phosphorus recovery method of the present embodiment shown below is an example of batch processing, but the phosphorus recovery method of the present invention is not limited to batch processing, while continuously flowing water to be treated and slag slurry. Of course, it may be processed.

First, steel slag S1, treated water W1, and acid A1 used in the phosphorus recovery method of the present embodiment will be described. The steel slag S1 is stored in the steel slag storage tank 2a of the phosphorus recovery system shown in FIG. In this embodiment, both blast furnace slag and steelmaking slag can be used as the steel slag S1. In particular, it is preferable to use steel slag having a basicity (CaO / SiO ₂ (weight ratio)) in the range of 1 to 7.

Since blast furnace is charged with calcium ore as a solvent along with iron ore, blast furnace slag contains a relatively high concentration of calcium. In the phosphorus recovery method of this embodiment, since calcium and phosphorus are reacted, a blast furnace slag containing a relatively large amount of calcium is suitable as the steel slag of this embodiment.

Steelmaking slag includes hot metal pretreatment slag generated by hot metal desulfurization and dephosphorization, converter slag generated by decarburization refining of the converter, and casting slag generated by secondary refining. Can also be suitably used in the phosphorus recovery method of the present embodiment because it contains a relatively high concentration of phosphorus. In addition, since calcium is added as a deoxidizer in the secondary refining, the steelmaking slag contains a relatively high concentration of calcium. By using steelmaking slag, a fertilizer or a fertilizer raw material that finally contains a large amount of phosphorus can be obtained.

Moreover, the average particle diameter of the steel slag S1 is preferably 0.3 mm or less, more preferably 0.2 mm or less, and further preferably 0.15 mm or less. However, since the cost increases as the average particle diameter of the steel slag S1 is reduced by pulverization, an optimal value may be determined in consideration of the cost. In addition, if pulverized too much, a large amount of fine residue is generated, and it takes time for solid-liquid separation. Therefore, the particle size of steel slag should be limited to an average particle size that allows smooth solid-liquid separation. . For example, 0.01 mm or more is preferable.

Further, the calcium content of the steel slag S1 before addition of hydrochloric acid is preferably in the range of 15 to 55% by mass, and more preferably in the range of 25 to 55% by mass. If the calcium content in the steel slag S1 is too low, the phosphorus recovery rate decreases, which is not preferable. On the other hand, if the calcium content is too high, the amount of iron slag S1 residue after elution of calcium decreases. In addition, when the quantity of the residue of steel slag S1 decreases, the steel slag residue recovery rate will fall and the phosphorus sedimentation rate will fall. Moreover, the phosphorus sedimentation rate also decreases when the steel slag residue recovery rate is large. Therefore, the steel slag residue recovery rate after addition of hydrochloric acid is preferably 35 to 65%, more preferably 40 to 60%, and even more preferably 45 to 55%. Steel slag that provides such a residue recovery rate may be selected.
Furthermore, in the phosphorus recovery system and phosphorus recovery method of the present invention, molten slag may be used instead of steel slag. Molten slag is slag obtained after processing combustible waste etc. with a gasification melting furnace.

The water to be treated W1 applicable to the phosphorus recovery method of the present embodiment is not particularly limited as long as it contains phosphorus, and the concentration of phosphorus is not particularly limited. As the to-be-processed water W1 of this embodiment, the sewage which flows into a terminal treatment plant from a public sewer is mentioned, for example. Examples of such sewage include urban drainage mainly discharged from urban areas. Urban sewage includes domestic wastewater discharged from ordinary households and wastewater discharged from stores and other facilities. In addition, such sewage may include industrial wastewater discharged from metal refining factories such as steelworks and other factories. In particular, domestic wastewater and industrial wastewater may contain a relatively large amount of phosphorus. Therefore, the sewage treated at the final treatment plant of the public sewer can be suitably used as the treated water W1 in the phosphorus collection method of the present embodiment, and the phosphorus collection method of the present invention can be used at the final treatment plant. You may apply when collect | recovering. Furthermore, the water to be treated of the present invention is not limited to domestic wastewater and industrial wastewater, and any water containing phosphorus can be applied.

Moreover, as acid A1 which can be utilized for the phosphorus collection | recovery method of this embodiment, the aqueous solution of hydrochloric acid is preferable. The concentration of the aqueous hydrochloric acid solution is preferably 0.5 to 2.0N, more preferably 0.7 to 1.6N, and 0.9 to 1.2N because it is easy to handle and requires a certain level of concentration. Further preferred. Although there is sulfuric acid as an acid other than hydrochloric acid, sulfuric acid is not preferable because it reacts with calcium eluted from steel slag to form gypsum (CaSO ₄ ). Moreover, since nitric acid contains nitrogen, it becomes unpleasant because it causes eutrophication when the treated water W4 after phosphorus recovery is discharged into public waters.

In the phosphorus recovery method of the present embodiment, by adding acid A1 to steel slag S1 to obtain slag slurry SS, the water to be treated W1 containing phosphorus and slag slurry SS are stirred and mixed and allowed to stand, The method includes forming a compound containing phosphorus and calcium, coagulating and sedimenting the formed compound together with the residue of the steel slag S1, and dehydrating the settled solid matter S2. Further, in the phosphorus recovery system of the present embodiment, the dehydrated product S3 may be further dried. Hereinafter, each step will be described.

First, acid A1 is added to steel slag S1 to obtain slag slurry SS. In the phosphorus recovery system of FIG. 2, the steel slag S1 and the acid A1 are supplied from the steel slag supply device 3 and the acid supply device 4 to the calcium elution reaction device 1, and the steel slag S1 and the acid A1 are stirred in the calcium elution reaction device 1. Mix to make slag slurry SS. At this time, calcium contained in the steel slag S1 is eluted by hydrochloric acid. In order to sufficiently dissolve calcium, the steel slag S1 and the acid A1 are preferably stirred and mixed for 1 minute or more, more preferably 2 minutes or more, and even more preferably 5 minutes or more. The upper limit is preferably 60 minutes or less, more preferably 30 minutes or less, still more preferably 20 minutes or less, and most preferably 10 minutes or less. The mixing ratio of the steel slag S1 and the acid A1 depends on the type of the steel slag, but, for example, about 10 L of 0.5 to 2 mol / L hydrochloric acid may be added to 1 kg of the steel slag.

Increasing the amount of hydrochloric acid relative to steel slag increases the amount of calcium eluted, which is advantageous when forming phosphorus as a compound, while reducing the residue of steel slag and coagulating the formed compound. Disadvantageous. The amount of calcium elution is such that when the treated water W1 and the slag slurry SS are mixed, the molar ratio (Ca / P) between the amount of calcium in the steel slag and the amount of phosphorus in the treated water is in the range of 2-4. It may be adjusted so that More preferably, the Ca / P ratio is in the range of 2.5 to 3.5. When the Ca / P ratio is less than 2, the phosphorus removal rate decreases. When the Ca / P ratio is 4 or more, the soluble phosphorus content in the finally obtained dried product S4 decreases. Here, the term “soluble” refers to the property of being dissolved in a 2% aqueous citric acid solution. The term “soluble phosphorus” refers to phosphorus that is dissolved in a 2% aqueous citric acid solution.
Thus, the amount of hydrochloric acid A1 added to the steel slag S1 is an important factor. Depending on the type of the steel slag S1 and the calcium content of the steel slag, for example, the molar amount of hydrochloric acid A1 per 1 kg of the steel slag S1 is preferably in the range of 5 to 20 mol, more preferably 7 to 15 mol. 8 to 12 mol is more preferable.

Next, in the phosphorus recovery reactor 2, the water to be treated W1 containing phosphorus and the slag slurry SS are stirred and mixed, and then allowed to stand. In the phosphorus recovery reactor 2 of FIG. 2, the water to be treated W1 is supplied from the water to be treated supply device 5 to the phosphorus recovery reactor 2, and after stirring and mixing with the slag slurry SS, it is allowed to stand. The mixing ratio of the calcium amount in the steel slag and the phosphorus amount in the treated water W1 may be adjusted so that the Ca / P ratio is in the range of 2-4. The adjustment of the Ca / P ratio may be controlled by the mixing ratio of the slag slurry SS and the water to be treated W1, the amount of hydrochloric acid added when forming the slag slurry SS, and the like. In order to adjust the Ca / P ratio, the calcium concentration in the slag slurry SS and the phosphorus concentration in the water to be treated W1 are preferably measured in advance.

In order to sufficiently react phosphorus in the water to be treated W1 and calcium in the slag slurry SS, the stirring time of the water to be treated W1 and the slag slurry SS is preferably 1 minute or longer, and 5 minutes or longer. Is more preferable. The upper limit is preferably 60 minutes or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less. If the stirring time is too short, the reaction between calcium and phosphorus may not proceed sufficiently. Moreover, when stirring time is too long, the whole apparatus will become large and an installation cost will become high. Therefore, the stirring time is preferably set to an appropriate time.

By mixing the water to be treated W1 and the slag slurry SS with stirring, phosphorus contained in the water to be treated W1 reacts with calcium in the slag slurry SS eluted from the steel slag to contain phosphorus and calcium. A compound forms. The following compounds can be considered as the compound to be formed. Part of the phosphorus contained in the water to be treated W1 exists as hydrogen phosphate ions (HPO ₄ ²⁻ ), and the hydrogen phosphate ions and calcium ions react to form calcium hydrogen phosphate (CaHPO ₄ ). I guess it will be. At this time, it is considered that calcium is further bound to calcium hydrogen phosphate to form Ca ₂ HPO ₄ ²⁺ (triplet).

In order to make hydrogen phosphate ions formed at the time of stirring and mixing stably, the pH of the water W1 to be treated after mixing the slag slurry SS is preferably adjusted to a range of 7.7 to 9.0. The range of 0.0 to 8.7 is more preferable, and the range of 8.2 to 8.5 is still more preferable. When the pH is less than 7.7, more dihydrogen phosphate ions are present than hydrogen phosphate ions. Since the solubility product of dihydrogen phosphate ion and calcium ion is larger than the solubility product of hydrogen phosphate ion and calcium ion, when the pH is less than 7.7, the precipitated amount of calcium hydrogen phosphate decreases and the phosphorus Recovery may be reduced. Further, when the pH exceeds 9, carbonate ions are generated in the water to be treated W1, calcium binds to carbonate ions to precipitate calcium carbonate, phosphorus is difficult to precipitate, and phosphorus recovery rate decreases. End up. The pH in the water to be treated W1 may be adjusted by supplying the caustic soda A2 from the pH adjusting device 9 shown in FIG. 2 through the caustic soda supply line L5.

Further, at the same time as or after the formation of the compound containing phosphorus and calcium, these compounds are agglomerated and precipitated using the residue of the steel slag S1. The residue of the steel slag S1 is negatively charged as a whole because calcium is eluted as a cation. On the other hand, calcium hydrogen phosphate and Ca ₂ HPO ₄ ²⁺ have a low apparent specific gravity, so that they float in the water to be treated, and Ca ₂ HPO ₄ ²⁺ is positively charged. Thus, the negatively charged residue of the steel slag S1 and the floating calcium hydrogen phosphate and Ca ₂ HPO ₄ ²⁺ coexist, thereby generating an electrostatic interaction between them, and the residue of the steel slag S1. In contrast, calcium hydrogen phosphate and compounds such as Ca ₂ HPO ₄ ²⁺ aggregate and finally settle as solid S2. Since it is considered that coagulation sedimentation proceeds by the above mechanism, it is not necessary to add an aggregating agent when the solid matter is settled.

Although the sedimentation time depends on the size of the phosphorus recovery reactor 2, it is preferably 7 minutes or longer, more preferably 10 minutes or longer, and even more preferably 30 minutes or longer. The upper limit is preferably 60 minutes or less, more preferably 50 minutes or less, and even more preferably 40 minutes or less.

Next, a dephosphorization supernatant W2 that is a supernatant after sedimentation of the solid S2 in the phosphorus recovery reactor 2 is sent to the treated water tank 7a through the treated water drain line L7. Thereafter, the dephosphorization supernatant W2 is dephosphorized together with the dehydrated water W3 from the dehydrator 6 and discharged from the treated water tank 7a to the public water area as treated water W4 or sent to another water treatment facility. .

On the other hand, the solid matter S2 that has aggregated and settled at the bottom of the phosphorus recovery reactor 2 is sent to the dehydrator 6 via the aggregated sediment line L6. The solid matter S2 is dehydrated in the dehydrating device 6, and the dewatered water W3 separated at that time is sent to the treated water discharging device 7 via the dehydrated water line L8. Further, the dehydrated product S3 after dehydration is carried out as a fertilizer or a fertilizer raw material by the dehydrated product line L9. Or it is sent to the drying apparatus 8 and is carried out as a fertilizer or a fertilizer raw material after drying.

The dehydrated product S3 transported from the dehydrating device 6 via the dehydrated product line L9 is a solute-soluble phosphorus of 15% by mass or more, which is a standard value for the content of solute-soluble phosphorus, for directing the recovered material for fertilizer use. Contained and used as fertilizer as it is.

Moreover, the dried material S4 carried out from the drying apparatus 8 contains 15% by mass or more of solute-soluble phosphorus, which is a standard value of the solute-soluble phosphorus content, in order to direct the recovered material for fertilizer use as it is. Used as a fertilizer raw material, or as a yellow phosphorus raw material.

The phosphorus recovery method of the present embodiment described above is an example of recovering phosphorus by batch processing. However, the phosphorus recovery of the present embodiment may be performed by continuous processing.
Specifically, the water to be treated W1 containing phosphorus and the slag slurry SS are continuously charged into the phosphorus recovery reactor 2. In the phosphorus recovery reactor 2, the stage of mixing the water to be treated W1 and the slag slurry SS to form a compound containing phosphorus and calcium, the stage of coagulating and sedimenting the formed compound together with the residue of the steel slag S1, A step of recovering the precipitated solid S2, a step of discharging a dephosphorization supernatant W2 that is a supernatant when the solid S2 is recovered, a step of dehydrating the solid S2 to obtain a dehydrated S3, a solid The step of discharging the dewatered water W3 when the material S2 is dehydrated is continuously performed. Further, a step of drying the dehydrated product S3 may be added.

As described above, according to the phosphorus recovery method and phosphorus recovery system of the present embodiment, calcium is eluted from steel slag and reacted with hydrogen phosphate ions in the water to be treated. Since calcium hydrogen phosphate is agglomerated and precipitated by using calcium oxyhydrogen and the residue after elution of calcium from steel slag, phosphorus in water to be treated W1 can be efficiently recovered with high yield.

In particular, by using the residue of steel slag after calcium elution, calcium hydrogen phosphate can be coagulated and settled in a short time, and the recovery efficiency of phosphorus can be increased. Further, it is not necessary to separately add a flocculant for aggregating calcium hydrogen phosphate, and there is no need for equipment for adding the flocculant. Furthermore, calcium hydrogen phosphate can be generated and aggregated at the same time, so that phosphorus can be recovered in a short time and only one reaction tank is required to recover the phosphorus necessary for recovering phosphorus. The phosphorus recovery reactor 2 can be downsized.

Moreover, according to the phosphorus recovery method of the present embodiment, the formation of slag slurry and the coagulation sedimentation separation of solids can be performed in a short time, and the treatment efficiency of water to be treated and steel slag can be greatly increased.

Also, some steel slag contains a lot of phosphorus discharged from steelworks. According to this embodiment, the phosphorus in the steel slag and the phosphorus in the water to be treated are simultaneously recovered with one apparatus, and the phosphorus content in the aggregated sediment can be increased, and the aggregated sediment is useful. Can be reused as a valuable phosphorus resource. Furthermore, when using sewage treated at a terminal treatment plant (sewage treatment plant) as treated water, phosphorus in sewage that is a cause of eutrophication of the sea or lake can be recovered. Therefore, by applying this embodiment to the recovery of phosphorus in sewage, phosphorus from the steel industry, which is the two largest sources of phosphorus, (from Japan, about 80,000 t-P / Y) and sewage treatment plants It is possible to collect and recycle both phosphorus at the same time (approximately 50,000 t-P / Y emissions in Japan).

In addition, by drying the aggregated and settled solids after dehydration, the volume of the solids can be reduced, and handling of the aggregated and settled solids is facilitated.

Furthermore, since the collected solid substance contains phosphorus in a high concentration, it can be used as a fertilizer, a fertilizer raw material, a yellow phosphorus raw material, or the like as a phosphorus resource.
Moreover, according to this embodiment, since the whole amount of steel slag used for the recovery of phosphorus can be used as fertilizer or fertilizer raw material, steel slag can be effectively used.

Experimental Examples 1 to 11, Example A, and Comparative Example B conducted for examining the relationship between various factors in the embodiment of the present invention will be described below. A model liquid containing 660 mg / L KH ₂ PO ₄ , 1.89 g / L NH ₄ Cl, and 3.36 g / L NaHCO ₃ was prepared as the water to be treated. Steel slag was pulverized by a pulverizer, and the particle size was adjusted by sieving. The calcium content was measured by fluorescent X-ray analysis with an electron microscope.

(Experimental example 1)
In order to investigate the relationship between the steel slag residue recovery rate and the phosphorus sedimentation rate, Experimental Example 1 shown below was performed.
A solid-liquid ratio (kg) of steel slag containing 4% P ₂ O _{5 and} having a calcium content of 40% and a particle size of 0.125 mm and hydrochloric acid having concentrations of 0.5N, 1.0N and 2.0N : L) was mixed at 1:10 and stirred for 60 minutes. Mix the amount of calcium in the slag and the amount of phosphorus in the model solution with a phosphorus concentration of 150 mg / L so that the Ca / P ratio is 3.0, adjust the pH to 8.5, and stir for 60 minutes. After mixing, the mixture was allowed to stand for 5 minutes to coagulate and settle the solid matter. The coagulated and settled solid was centrifuged and collected after drying at 100 ° C., and the slag residue weight, the amount of the supernatant and the total phosphorus concentration in the supernatant were measured. The total phosphorus concentration in the supernatant was measured by the molybdenum blue method. By adjusting the hydrochloric acid concentration and the solid-liquid ratio of the slag slurry and model liquid, nine samples were prepared with a steel slag residue recovery rate ranging from 14 to 92%.

FIG. 3 shows the relationship between the steel slag residue recovery rate obtained by the following equation (1) and the phosphorus sedimentation rate obtained by the following equation (2). According to FIG. 3, the phosphorus sedimentation rate becomes maximum when the steel slag residue recovery rate is around 50%, and the phosphorus sedimentation rate is 70% or more when the steel slag residue recovery rate is in the range of 35 to 65%. Moreover, if the steel slag residue recovery rate is small, the phosphorus sedimentation rate is lowered. On the other hand, it can be seen that the phosphorus sedimentation rate also decreases when the steel slag residue recovery rate is large.

Steel slag residue recovery rate = slag residue weight / input slag weight x 100 ... (1)

Phosphorus sedimentation rate = (phosphorus concentration in model liquid × model liquid volume−total phosphorus concentration in supernatant × supernatant liquid volume) / (phosphorus concentration in model liquid × model liquid volume) × 100 (2)

However, the total phosphorus concentration in the supernatant in the formula (2) is as follows.
Total phosphorus concentration in supernatant = (water-soluble phosphorus amount + phosphorus amount in slag slurry) / supernatant liquid amount

(Experimental example 2)
In order to investigate the relationship between the amount of hydrochloric acid per unit weight of steel slag, the content of soluble phosphorus in the recovered phosphorus, the content of soluble phosphorus and the recovered amount of phosphorus per steel slag, Experimental Example 2 shown below was performed.
Solid-liquid ratio of steel slag containing 4% P ₂ O ₅ , calcium content 40% and particle size 0.125 mm, and hydrochloric acid having concentrations of 0.5N, 1.0N and 2.0N kg: L) were mixed at 1: 5, 1:10 and 1:20 and stirred for 60 minutes. Mix the amount of calcium in the slag and the amount of phosphorus in the model solution with a phosphorus concentration of 150 mg / L so that the Ca / P ratio is 3.0, adjust the pH to 8.5, and stir for 60 minutes. After mixing, the mixture was allowed to stand for 5 minutes to coagulate and settle the solid matter. The aggregated and settled solid was collected, and the amount of the collected solid, the amount of phosphorus in the hydrous solid after sedimentation, and the amount of soluble phosphorus were measured. Five samples were prepared in the range of 2.5 to 40 mol / kg of hydrochloric acid per unit weight of steel slag.
The amount of phosphorus in the water-containing solid after settling was measured by the molybdenum blue method. The amount of ku-soluble phosphorus was determined by measuring the mass of the extract extracted from the solid with a 2% citric acid solution and calculating the amount of ku-soluble phosphorus contained in the extract. In addition, in the measurement of the amount of soluble phosphorus, “Fertilizer test method (2013) National Agriculture, Forestry and Fisheries Consumption Safety Technology Center (http://www.famic.go.jp/ffis/fert/bunseki/sub9_shiken2013.html) It went according to. The calculated amount of soluble phosphorus was used in the following formulas (4) and (5) to obtain the soluble phosphorus content and the soluble phosphorus content in the recovered phosphorus.
In the following experimental examples, measurement and calculation were performed in the same manner as described above.

The amount of hydrochloric acid per unit weight of steel slag, the amount of phosphorus recovered per steel slag determined by the following equation (3), the content of soluble phosphorus determined by the following equation (5), and the amount of phosphorus recovered by the following equation (6) FIG. 4 shows the relationship of the content of soluble phosphorus. According to FIG. 4, the amount of phosphorus recovered per steel slag and the soluble phosphorus content are maximum when the value of the amount of hydrochloric acid per unit weight of steel slag is around 10 mol / kg. If the amount of hydrochloric acid per unit weight of steel slag is less than 10 mol / kg, the recovered amount of phosphorus, the content of soluble phosphorus in the recovered phosphorus, and the content of soluble phosphorus will decrease. Moreover, when the amount of hydrochloric acid per steel slag unit weight becomes larger than 10 mol / L, it turns out that the collection | recovery amount of phosphorus, the soluble phosphorus content rate in a recovery phosphorus, and a soluble phosphorus content rate fall. Further, the content of the soluble phosphorus in the recovered phosphorus takes a value of almost 100% within the range of the amount of hydrochloric acid per unit weight of the steel slag of 10 to 25 mol / L, and the content of the soluble phosphorus is 5 to 40 mol / L. In the range of 15% or more.

・ Phosphorus recovery amount per steel slag = Phosphorus recovery amount / Input slag amount (3)

However, the phosphorus recovery amount in the formula (3) is the phosphorus amount in the recovered water-containing solid material after settling.

Ku-soluble phosphorus content = ku-soluble phosphorus amount / amount of collected solid x 100 (4)

Quantitative phosphorus content in recovered phosphorus = amount of soluble phosphorus / total amount of recovered phosphorus x 100 ... (5)

(Experimental example 3)
Next, in order to investigate the relationship between the concentration of aqueous hydrochloric acid, the amount of phosphorus recovered per steel slag, and the content of soluble phosphorus, the following Experimental Example 3 was performed.
Solid-liquid ratio of steel slag containing 4% P ₂ O ₅ , calcium content 40% and particle size 0.125 mm, and hydrochloric acid having concentrations of 0.5N, 1.0N and 2.0N kg: L) were mixed at 1: 5, 1:10 and 1:20, and stirred and mixed for 60 minutes. Mix the amount of calcium in the slag and the amount of phosphorus in the model solution with a phosphorus concentration of 150 mg / L so that the Ca / P ratio is 3.0, adjust the pH to 8.5, and stir for 60 minutes. After mixing, the mixture was allowed to stand for 5 minutes to coagulate and settle the solid matter. The coagulated and settled solid was collected, and the amount of phosphorus and the amount of soluble phosphorus in the hydrous solid after sedimentation were measured in the same manner as in Experimental Example 2.

FIG. 5 shows the relationship between the concentration of the hydrochloric acid aqueous solution, the amount of phosphorus recovered per steel slag determined by the equation (3), and the content of soluble phosphorus determined by the equation (4). According to FIG. 5, the phosphorus recovery amount and the soluble phosphorus content are maximized when the hydrochloric acid aqueous solution concentration is around 1N. When the hydrochloric acid aqueous solution concentration is higher than 1N, the phosphorus recovery amount and the soluble phosphorus content gradually decrease, whereas when the hydrochloric acid aqueous solution concentration is lower than 1N, the phosphorus recovered amount and the soluble phosphorus content rapidly increase. It is falling. In practical use, the optimum value is determined by comprehensively considering the value of the collected phosphorus, the procurement cost of slag and hydrochloric acid, etc.

(Experimental example 4)
In order to investigate the relationship between the calcium elution reaction time and the calcium elution rate when stirring and mixing steel slag and hydrochloric acid, Experimental Example 4 shown below was performed.
Mixing steel slag containing 4% P ₂ O ₅ with a calcium content of 40% and a particle size of 0.125 mm, and hydrochloric acid with a concentration of 1.0 N so that the solid-liquid ratio is 1:10. The mixture was stirred for 60 minutes, and the amount of calcium elution at each time was measured.

The relationship between calcium elution reaction time and calcium elution rate is shown in FIG. Calcium elution rapidly proceeds with the optimum value (10 mol / kg) of the amount of hydrochloric acid per unit weight of slag shown in Experimental Example 2 and the optimal value (1N) of the aqueous hydrochloric acid concentration shown in Experimental Example 3; The calcium elution rate is almost saturated in about 2 minutes, and is completely saturated in 5 minutes. Therefore, the mixing time of the steel slag and hydrochloric acid depends on the mixing ratio and hydrochloric acid concentration, but is preferably 1 minute or longer, more preferably 2 minutes or longer, and 5 minutes or longer is sufficient.

(Experimental example 5)
Next, in order to investigate the relationship between the particle size of steel slag, the phosphorus removal rate, the phosphorus sedimentation rate, the phosphorus recovery rate, the soluble phosphorus content, and the phosphorus concentration in the supernatant liquid slag slurry, Experimental Example 5 shown below is performed. went.
Steel slag containing 4% P ₂ O ₅ with a calcium content of 40% and particle sizes of 0.125 mm, 0.3 mm, and 0.5 mm, and concentrations of 0.5 N, 1.0 N, and 2.0 N Hydrochloric acid was mixed at a solid-liquid ratio of 1:10 and stirred for 60 minutes. Mix the amount of calcium in the slag and the amount of phosphorus in the model solution with a phosphorus concentration of 150 mg / L so that the Ca / P ratio is 3.0, adjust the pH to 8.5, and stir for 60 minutes. After mixing, the mixture was allowed to stand for 5 minutes to coagulate and settle the solid matter. The water-soluble phosphorus concentration in the supernatant was measured. Further, in the same manner as in Experimental Example 2, the amount of phosphorus in the collected solid and the amount of soluble phosphorus in the solid were measured.

The particle size of steel slag, the phosphorus removal rate determined by the following equation (6), the phosphorus sedimentation rate determined by the above equation (2), the phosphorus recovery rate determined by the following equation (7), and the above equation (4) FIG. 7 shows the relationship between the soluble phosphorus content and the phosphorus concentration in the supernatant slag slurry. According to FIG. 7, the phosphorus removal rate does not depend on the slag particle size, but when the slag particle size is smaller than 0.3 mm, the phosphorus sedimentation rate and the phosphorus recovery rate increase rapidly, and the phosphorus concentration in the supernatant liquid slag slurry is It drops rapidly (ie, it tends to settle). On the other hand, when it is larger than 0.3 mm, the phosphorus sedimentation rate and the phosphorus recovery rate are relatively slowly lowered, and the phosphorus concentration in the supernatant liquid slag slurry is gradually increased. The soluble phosphorus content in solids decreases as the slag particle size decreases, but at any particle size, the soluble phosphorus content is 15% by mass, which is the standard value when used as a fertilizer as it is. The above numerical values are shown. Therefore, it is found that it is preferable to finely pulverize the slag particle size to 0.3 mm or less in order to allow the removed phosphorus to settle and recover efficiently.

Phosphorus removal rate = (Phosphorus concentration in model solution−Water-soluble phosphorus concentration in supernatant) / Phosphorus concentration in model solution × 100 (6)

Phosphorus recovery rate = total phosphorus amount in hydrous solids after settling / (phosphorus concentration in model liquid x model liquid amount + phosphorus amount in input slag) x 100 ... (7)

(Experimental example 6)
Next, in order to investigate the relationship between the Ca / P ratio, the phosphorus removal rate, and the soluble phosphorus content, Experimental Example 6 below was performed.
Steel slag containing 4% P ₂ O _{5 and} having a calcium content of 40% and a particle size of 0.125 mm was mixed with hydrochloric acid having a concentration of 1N so that the solid-liquid ratio was 1:10. Stir for minutes. The amount of calcium in the slag and the amount of phosphorus in the model solution having a phosphorus concentration of 150 mg / L so that the Ca / P ratio is 2.0, 2.5, 3.0, 3.5, and 4.0. After adjusting the pH to 8.5, stirring and mixing for 60 minutes, the mixture was allowed to stand for 5 minutes to coagulate and settle the solid matter. In the same manner as in the other experimental examples, the amount of solid matter that was coagulated and precipitated, the amount of soluble phosphorus, and the concentration of water-soluble phosphorus in the supernatant were measured. The phosphorus concentration in the model solution was fixed, the amount of slag used and the amount of hydrochloric acid used were adjusted, and the Ca / P ratio was changed.

FIG. 8 shows the relationship between the Ca / P ratio, the phosphorus removal rate determined by the equation (6), and the soluble phosphorus content determined by the equation (4). As the Ca / P ratio increases, the phosphorus removal rate increases while the soluble phosphorus content decreases. It can be seen that the Ca / P ratio is preferably in the range of 2-4. Moreover, in order to direct the recovered material for fertilizer use as it is, it is understood that the soluble phosphorus content is required to be 15% by mass or more and that the Ca / P ratio is preferably about 3 in order to secure the phosphorus removal rate.

(Experimental example 7)
Next, in order to examine the relationship between the phosphorus recovery reaction time and the phosphorus removal rate, Experimental Example 7 shown below was performed.
Steel slag containing 4% P ₂ O _{5 and} having a calcium content of 40% and a particle size of 0.125 mm and hydrochloric acid having a concentration of 1N are mixed so that the solid-liquid ratio is 1:10. Stir for 60 minutes. Mix the amount of calcium in the slag and the amount of phosphorus in the model solution with a phosphorus concentration of 150 mg / L so that the Ca / P ratio is 3.0, adjust the pH to 8.5, and stir for 60 minutes. After mixing, the mixture was allowed to stand for 5 minutes, the supernatant liquid at each time was collected, and the water-soluble phosphorus concentration in the supernatant liquid was measured.

FIG. 9 shows the relationship between the phosphorus recovery reaction time and the phosphorus removal rate determined by the above equation (6). It can be seen that phosphorus in the model solution reacts quickly with the slag slurry, the phosphorus removal rate reaches 85% or more after 5 minutes reaction, and the phosphorus removal rate reaches the maximum value after 20 minutes reaction. Therefore, it can be seen that the stirring time is preferably 5 minutes or more.

(Experimental example 8)
Next, Experimental Example 8 shown below was performed in order to investigate the relationship between the pH at the time of stirring and mixing the slag slurry and the model liquid and the phosphorus recovery rate.
Steel slag containing 4% of P ₂ O ₅ , calcium content of 40% and particle size of 0.125 mm, and hydrochloric acid having a hydrochloric acid concentration of 1N are mixed so that the solid-liquid ratio is 1:10. Stir for 60 minutes. The amount of calcium in the slag and the amount of phosphorus in the model solution having a phosphorus concentration of 150 mg / L are mixed so that the Ca / P ratio is 3.0, and the pH is not adjusted from 7.4 to 8.0. 8.5 and 9.0, and after stirring and mixing for 60 minutes, the mixture was allowed to stand for 5 minutes to coagulate and settle the solid matter. The pH at the time of stirring and mixing was changed by adding a 5 mol / L NaOH aqueous solution. The coagulated and settled solid was collected and the amount of phosphorus in the solid was measured.

FIG. 10 shows the relationship between the pH and the phosphorus recovery rate determined by the equation (7). There is a maximum value of phosphorus recovery near pH 8.4. It can be seen that when the pH is in the range of 7.7 to 9.0, the phosphorus recovery rate is greater than 70%, and in the range of 8.0 to 8.7, the phosphorus recovery rate is greater than 80%.

Next, in order to investigate whether the residue of steel slag contributed to coagulation sedimentation, the following Example A and Comparative Example B were performed.
(Example A)
₅ % of a 1.3 mol / L hydrochloric acid aqueous solution was added to 0.5 g of steel slag having a mass percentage of 4% P ₂ O ₅ , a calcium content of 40%, and a particle size of 0.125 mm. By vigorously stirring for a minute, a slag slurry from which calcium in the steel slag was eluted was obtained. The slag slurry contained steel slag residues.
Then, as a model solution, a model solution containing KH ₂ PO ₄ at a concentration of 392 mg / L, NH ₄ Cl at a concentration of 1.86 g / L, and NaHCO ₃ at a concentration of 3.36 g / L was prepared. .
To 500 ml of this model solution, the entire amount of the slag slurry prepared above is added, and immediately after the addition, the pH is adjusted to 8.5 using a 1 mol / L NaOH aqueous solution, and 0 minutes, 5 minutes, 20 minutes and 60 minutes. In each stirring time, 2 ml of the liquid was sampled and filtered through a syringe filter having a pore size of 0.22 μm. The water-soluble phosphorus concentration in the filtrate after filtration was measured by the molybdenum blue method. And the phosphorus removal rate was calculated | required by following formula (8) from the water-soluble phosphorus density | concentration in a filtrate. The results are shown in Table 1, FIG. 11 and FIG.

Phosphorus removal rate (%) = {(PO ₄ −P) ₀ − (PO ₄ −P) _x } / (PO ₄ −P) ₀ × 100 (8)

However, (PO ₄ -P) ₀ and (PO ₄ -P) _x in the formula (8) are as follows.
(PO ₄ -P) ₀ : Concentration of water-soluble phosphorus in the filtrate with stirring 0 minutes (PO ₄ -P) _x : Concentration of water-soluble phosphorus in the filtrate with stirring time x minutes (where x is 5 minutes, 20 Min, 60 min)

Further, the entire amount (about 500 ml) of the stirring liquid stirred for 60 minutes was quickly transferred to a graduated cylinder and coagulated and settled for 5 minutes, and then 400 ml of the supernatant liquid was taken out by siphon. The total phosphorus amount in the removed supernatant was measured. Then, by subtracting the phosphorus amount in the supernatant liquid from the phosphorus amount in the model liquid, the phosphorus amount in 100 ml of the residual liquid containing the sediment left in the graduated cylinder was calculated. Furthermore, the precipitation rate of phosphorus was calculated | required based on following formula (9). The results are shown in Table 2 and FIG.

Phosphorus sedimentation rate (%) = phosphorus amount in 100 ml of residual liquid / phosphorus amount in model solution × 100 (9)

(Comparative Example B)
In the same manner as in Example A, a slag slurry from which calcium in the steel slag was eluted was obtained, and the residue of the steel slag was removed from the slag slurry to obtain a supernatant.
A model solution was prepared in the same manner as in Example A.
To the 500 ml of this model solution, the supernatant of the slurry prepared previously is added, and immediately after the addition, the pH is adjusted to 8.5 using a 1 mol / L NaOH aqueous solution, and 0 minutes, 5 minutes, 20 minutes and 60 minutes. Stir at the level of. Thereafter, in the same manner as in Example A, the phosphorus concentration, phosphorus removal rate, and phosphorus precipitation rate were determined. The results are shown in Tables 1 and 2 and FIGS.

As shown in Table 1 and FIGS. 11 to 13, it can be seen that Example A has a higher phosphorus removal rate than Comparative Example B. This is because in Example A, the residue of iron and steel slag was contained, so that the calcium phosphate coagulation sedimentation was performed efficiently. Further, as shown in Table 2 and FIG. 13, in Comparative Example B, the phosphorus precipitation rate was about 39%, whereas in Example A, the phosphorus precipitation rate reached 69%. Thus, in Example A, it can be seen that phosphorus can be coagulated and settled in a relatively short time.

(Experimental example 9)
Next, Experimental Example 9 was performed in order to investigate the relationship between the solid sedimentation time and the solid interface height.
Steel slag containing 4% P ₂ O _{5 and} having a calcium content of 40% and a particle size of 0.125 mm was mixed with hydrochloric acid having a concentration of 1N so that the solid-liquid ratio was 1:10. Stir for minutes. The amount of calcium in the slag and the amount of phosphorus in the model solution having a phosphorus concentration of 150 mg / L are mixed so that the Ca / P ratio is 3.0, the pH is adjusted to 8.5, and the inner diameter is 64 mm. The mixture was stirred and mixed in a 1000 mL graduated cylinder for 60 minutes and allowed to stand. The interface height of the aggregated solid was taken at three levels, and the interface height at each level was measured every minute. The results are shown in FIG.

According to FIG. 14, the aggregates settled rapidly at any level, and the sedimentation was completed in about 7 minutes. Although the sedimentation time in the actual machine depends on the size of the phosphorus recovery reactor 2, 30 minutes or more is considered sufficient.

(Experimental example 10)
Next, in order to investigate the relationship between phosphorus concentration, phosphorus removal rate, and soluble phosphorus content, Experimental Example 10 shown below was performed.
Mix steel slag containing 4% P ₂ O ₅ with a calcium content of 40% and a particle size of 0.125 mm or less, and hydrochloric acid with a concentration of 1 N so that the solid-liquid ratio is 1:10. For 60 minutes. The amount of calcium in the slag and the amount of phosphorus in the synthetic phosphoric acid water with the phosphorus concentrations of 50 mg / L, 150 mg / L, 300 mg / L and 600 mg / L are mixed so that the Ca / P ratio is 3.0. The pH was adjusted to 8.5, and the mixture was stirred and mixed for 60 minutes, and then allowed to stand for 5 minutes to coagulate and sediment the solid matter. The water-soluble phosphorus concentration in the supernatant and the amount of soluble phosphorus in the collected solid were measured. A similar experiment was also conducted using actual sewage as the treated water. Sewage with phosphorus concentrations of 109 mg / L and 291 mg / L was used.

FIG. 15 shows the relationship between the phosphorus concentration, the phosphorus removal rate determined by the equation (6), and the soluble phosphorus content determined by the equation (4). When the phosphorus concentration is 50 to 600 mg / L, the soluble phosphorus content is 15% by mass or more. Since the standard value of the content of soluble phosphorus when using the coagulated and settled solid as it is as a fertilizer is 15% by mass or more, it is understood that any phosphorus concentration used in this example is effective. Furthermore, looking at the results of experiments using actual sewage, both the phosphorus removal rate and the soluble phosphorus content are close to the results of the model solution, so the treated water is effective for a wide range of sewage in the sewage treatment plant. I believe that.

(Experimental example 11)
In Experimental Examples 1 to 10, Example A and Comparative Example B, steel slag containing 4% by mass of P ₂ O ₅ and having a calcium content of 40% is used as the steel slag. Then, in order to investigate the relationship between phosphorus removal rate, phosphorus sedimentation rate, and soluble phosphorus content using steel slag having different chemical components, Experimental Example 11 shown below was performed. The experiment was also conducted in the waste melting furnace slag.
The steel slag used in Experimental Example 11 is as follows. These are typical steel slag by-produced in steelworks. Moreover, molten slag is slag obtained after processing combustible waste etc. with a gasification melting furnace.

Steel slag A containing 0% P ₂ O ₅ by mass%, a calcium content of 42%, a basicity of 1.8, and a particle size of 0.125 mm.
Steel slag B containing 0% P ₂ O ₅ by mass%, a calcium content of 28%, a basicity of 5.6, and a particle size of 0.125 mm.
Steel slag C containing 4% P ₂ O ₅ by mass%, having a calcium content of 40%, a basicity of 2.0, and a particle size of 0.125 mm.
Steel slag D containing 2% P ₂ O ₅ by mass%, having a calcium content of 50%, a basicity of 3.8, and a particle size of 0.125 mm.
Steel slag E containing 0% P ₂ O ₅ by mass%, a calcium content of 33%, a basicity of 6.6, and a particle size of 0.125 mm.
A molten slag containing 0% P ₂ O ₅ by mass%, a calcium content of 37%, a basicity of 1.2, and a particle size of 0.125 mm.

These steel slag and hydrochloric acid having a concentration of 1N were mixed at a solid-liquid ratio of 1:10 and stirred for 60 minutes. Mix the amount of calcium in the slag and the amount of phosphorus in the model solution with a phosphorus concentration of 150 mg / L so that the Ca / P ratio is 3.0, adjust the pH to 8.5, and stir for 60 minutes. After mixing, the mixture was allowed to stand for 5 minutes to coagulate and settle the solid matter. The phosphorus concentration in the supernatant and the amount of phosphorus in the coagulated sediment were measured. FIG. 16 shows the phosphorus removal rate, phosphorus sedimentation rate, and soluble phosphorus content of each steel slag.

In any steel slag used in Experimental Example 11, the phosphorus removal rate is 85% or more, which indicates that any steel slag by-produced in the steelworks can be applied to this system. In addition, this system is considered effective for phosphorus removal rate. In addition, if the content of soluble phosphorus satisfies 15% by mass or more, the recovered product can be directly used for fertilizer, and those having a soluble phosphorus content of less than 15% by mass can also be used in blended fertilizers and the like. . That is, when the collected material is used as it is as a fertilizer, it may be determined by comprehensively considering the application location, the value of collected phosphorus, the procurement cost of steel slag and hydrochloric acid, and the like.

According to the present invention, phosphorus can be efficiently recovered from water to be treated containing phosphorus.
That is, the phosphorus contained in the water to be treated is coagulated and settled together with the residue of the steel slag after the elution of calcium by the acid and recovered as a solid matter, so that the phosphorus can be efficiently recovered. Here, for example, when using steel slag containing phosphorus, since phosphorus in steel to be treated and phosphorus in steel slag can be recovered at the same time, since phosphorus is contained in a high concentration, fertilizer, fertilizer raw material or yellow phosphorus It can be suitably used as a raw material.

DESCRIPTION OF SYMBOLS 1 Calcium elution reaction apparatus 2 Phosphorus recovery reaction apparatus 3 Steel slag supply apparatus 4 Acid supply apparatus 5 To-be-processed water supply apparatus 6 Dehydration apparatus 7 Treated water discharge apparatus 8 Drying apparatus 9 pH adjustment apparatus

Claims (18)

1. A calcium elution reaction apparatus that mixes an acid and steel slag, and prepares a slag slurry from which calcium in the steel slag is eluted;
   A steel slag supply device for supplying the steel slag to the calcium elution reaction device;
   An acid supply device for supplying the acid to the calcium elution reaction device;
   A phosphorus recovery reaction device that mixes the slag slurry and water to be treated containing phosphorus, reacts calcium in the slag slurry with phosphorus in the water to be treated, and obtains a solid matter containing phosphorus and calcium;
   A treated water supply device for supplying the treated water to the phosphorus recovery reactor;
   A dehydrator for dehydrating the solid matter produced in the phosphorus recovery reactor after supplying the water to be treated;
   A treated water discharge device for sending the supernatant water in the phosphorus recovery reactor after supplying the treated water to the outside of the system;
   A system for recovering phosphorus in water to be treated.
2. The system for recovering phosphorus in water to be treated according to claim 1, further comprising a drying device for drying the solid matter dehydrated in the dehydrating device.
3. The system for recovering phosphorus in water to be treated according to claim 1 or 2, wherein molten slag is used in place of the steel slag.
4. A step of stirring and mixing an acid with steel slag to obtain a slag slurry while eluting calcium in the steel slag;
   Stirring and mixing the water to be treated containing phosphorus in the slag slurry, and allowing to stand, thereby forming a compound containing phosphorus and calcium, and coagulating and precipitating the compound as a solid together with the steel slag residue;
   A step of recovering the solid matter settled, and a method of recovering phosphorus in the water to be treated.
5. The method for recovering phosphorus in water to be treated according to claim 4, wherein the precipitated solid matter is dried.
6. The method for recovering phosphorus in water to be treated according to claim 4 or 5, wherein the basicity of the steel slag is in the range of 1 to 7.
7. The method for recovering phosphorus in water to be treated according to any one of claims 4 to 6, wherein a calcium content of the steel slag before addition of hydrochloric acid is in the range of 15 to 55 mass%.
8. The method for recovering phosphorus in water to be treated according to any one of claims 4 to 7, wherein an average particle diameter of the steel slag before addition of hydrochloric acid is 0.3 mm or less.
9. The phosphorus in the water to be treated according to any one of claims 4 to 8, wherein the pH of the liquid mixture is adjusted to 7.7 to 9.0 when the water to be treated and the slag slurry are mixed. Recovery method.
10. When mixing the water to be treated and the slag slurry, the molar ratio (Ca / P) of the amount of calcium in the steel slag and the amount of phosphorus in the water to be treated is adjusted to 2 or more and 4 or less. The method for recovering phosphorus in the water to be treated according to any one of claims 4 to 9.
11. 11. The aqueous hydrochloric acid solution having a concentration adjusted to 0.5 N or more and 2.0 N or less is used when the hydrochloric acid is added to the steel slag to obtain the slag slurry. To recover phosphorus in water to be treated.
12. The method for recovering phosphorus in water to be treated according to any one of claims 4 to 11, wherein when the hydrochloric acid is added to the steel slag to obtain the slag slurry, the mixing time is 30 minutes or less.
13. The method for recovering phosphorus in water to be treated according to any one of claims 4 to 12, wherein a stirring and mixing time of the water to be treated and the slag slurry is 5 minutes or more.
14. The method for recovering phosphorus in water to be treated according to any one of claims 4 to 13, wherein the water to be treated containing phosphorus includes one or both of domestic wastewater and industrial wastewater.
15. The method for recovering phosphorus in water to be treated according to any one of claims 4 to 14, wherein molten slag is used in place of the steel slag.
16. A fertilizer containing the solid matter obtained by the method for recovering phosphorus in water to be treated according to any one of claims 4 to 15.
17. A fertilizer raw material containing the solid matter obtained by the method for recovering phosphorus in water to be treated according to any one of claims 4 to 15.
18. The yellow phosphorus raw material which contains the said solid substance obtained by the collection | recovery method of the phosphorus in the to-be-processed water as described in any one of Claims 4 thru | or 15.

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