JP2018094514A - Method for recovering phosphorus in treatment water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering phosphorus in treatment water, capable of suppressing an elution of an element other than Ca from steel slag and reducing an amount of used hydrochloric acid, when hydrochloric acid is added to obtain a slurry in which Ca in the steel slag is eluted.SOLUTION: There is provided a method for recovering phosphorus in treatment water, including the steps of: stirring and mixing a predetermined amount of hydrochloric acid in a slag slurry composed of a steel slug and water, and obtaining the slag slurry for recovering phosphorus in which Ca in the steel slug is eluted; stirring and mixing the treatment water containing phosphorus in the slag slurry for recovering phosphorus and leaving it stationary to form a compound containing phosphorus and Ca, and making the compound coagulated and settled as a solid together with a residue of the steel slag; and recovering the precipitated solid matter. In obtaining the slug slurry for recovering phosphorus, hydrochloric acid is added while keeping pH of the slag slurry, which is being added with hydrochloric acid, in a range of 4.5 to 7.0.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for recovering phosphorus in water to be treated.

  Steelmaking slag discharged from steelworks contains elements such as Ca, Fe, Si and Al, and their effective utilization is desired. As a method of reusing steelmaking slag, Patent Document 1 and Patent Document 2 use a hydrochloric acid solution having pH = 2 to 3 and pH = 0 to 1, respectively, and the Ca content and the Fe content contained in the steelmaking slag. A method of separating and reusing at steelworks has been proposed.

  On the other hand, phosphorus is an indispensable element for living organisms, and in recent years there is concern about depletion of phosphorus resources. Therefore, various methods for recovering phosphorus resources are being studied. For example, Patent Document 3 proposes a method for recovering phosphorus from water to be treated containing phosphorus using porous calcium silicate hydrate.

Therefore, the present inventors, as a method for realizing effective utilization of steelmaking slag and recovery of phosphorus resources, a technology for recovering phosphorus from treated water containing phosphorus using steelmaking slag discharged from steelworks. Invented. In this method, first, steelmaking slag and hydrochloric acid are stirred and mixed to obtain a slurry in which Ca in the steelmaking slag is eluted. Thereafter, the slurry from which Ca in the steelmaking slag is eluted is mixed with the waste water containing phosphorus. Thereby, Ca eluted from the steelmaking slag reacts with phosphorus in the waste water to form a compound, and this compound coagulates and settles together with the residue of the steelmaking slag. A solid matter containing phosphorus is obtained by dehydrating and drying the coagulated and precipitated compound. Thereby, phosphorus can be collect | recovered from the to-be-processed water containing phosphorus. Since the collected solid matter contains phosphorus at a high concentration, it can be effectively used as a fertilizer or a fertilizer raw material. However, in this method, when steelmaking slag and hydrochloric acid are stirred and mixed to obtain a slurry from which Ca in steelmaking slag is eluted, there is a problem that components other than Ca, which is a fertilizer component, are eluted. When the amount of SiO ₂ elution in the steelmaking slag increases, the viscosity of the slag slurry increases, which makes it difficult to supply the slag slurry. In addition, there is a problem that the amount of hydrochloric acid used to elute Ca is increased, resulting in an increase in chemical cost.

Japanese Patent No. 5790388 Japanese Patent Laid-Open No. 2006-20296 JP-A-2015-91566

  This invention is made | formed in view of the situation mentioned above, In the collection | recovery method of the phosphorus which collect | recovers phosphorus in to-be-processed water using steelmaking slag, the slurry which added hydrochloric acid and eluted Ca in steelmaking slag In order to provide a method for recovering phosphorus in water to be treated, which can sufficiently dissolve Ca from steelmaking slag while suppressing elution of components other than Ca and reducing the amount of hydrochloric acid to be used. Let it be an issue.

The gist of the present invention is as follows.
(1) To a slag slurry composed of steelmaking slag and water, stir and mix the hydrochloric acid in such an amount that the molar ratio (HCl / CaO) of CaO and hydrochloric acid in the steelmaking slag is 1.00 to 1.50. Obtaining a phosphorus recovery slag slurry from which calcium in the steelmaking slag is eluted;
The compound containing phosphorus and calcium is formed by stirring and mixing the phosphorus recovery slag slurry in the water to be treated containing phosphorus, and then allowing the compound to coagulate and settle as a solid with the steelmaking slag residue. Stages,
Recovering the settled solid matter, and
In the step of obtaining the phosphorus recovery slag slurry, the hydrochloric acid is added while maintaining the pH of the slag slurry during the addition of hydrochloric acid in the range of 4.5 to 7.0. Recovery method.
(2) To the slag slurry composed of steelmaking slag and water, stir and mix the hydrochloric acid in such an amount that the molar ratio (HCl / CaO) of CaO and hydrochloric acid in the steelmaking slag is 1.00 to 1.50. Obtaining a phosphorus recovery slag slurry from which calcium in the steelmaking slag is eluted;
The compound containing phosphorus and calcium is formed by stirring and mixing the phosphorus recovery slag slurry in the water to be treated containing phosphorus, and then allowing the compound to coagulate and settle as a solid with the steelmaking slag residue. Stages,
Recovering the settled solid matter, and
In the step of obtaining the phosphorus recovery slag slurry, an amount of the hydrochloric acid in which the molar ratio (HCl / CaO) of CaO to the hydrochloric acid in the steelmaking slag is less than 1.00 out of the total amount of the hydrochloric acid is added to the slag. After adding to a slurry, the residual amount of the said hydrochloric acid is added, maintaining the pH of the said slag slurry in the range of 4.5-7.0, The collection | recovery method of the phosphorus in to-be-processed water characterized by the above-mentioned.
(3) The method for recovering phosphorus in the water to be treated according to (1) or (2), wherein the solid matter that has been precipitated is dried.
(4) The method for recovering phosphorus in the water to be treated according to any one of (1) to (3), wherein the basicity of the steelmaking slag is in a range of 1 to 7.
(5) The method for recovering phosphorus in the water to be treated according to any one of (1) to (4), wherein a calcium content of the steelmaking slag is in a range of 15 to 55 mass%.
(6) The method for recovering phosphorus in the water to be treated according to any one of (1) to (5), wherein the steelmaking slag has an average particle size of 0.3 mm or less.
(7) When mixing the water to be treated and the slag slurry for phosphorus recovery, the pH of the mixed solution is adjusted to 7.2 to 8.5. (1) to (6) To recover phosphorus in water to be treated.
(8) When the treated water and the phosphorus recovery slag slurry are mixed, the molar ratio (Ca / P) of the amount of calcium in the steelmaking slag and the amount of phosphorus in the treated water is 2 or more and 4 or less. The method for recovering phosphorus in the water to be treated according to any one of (1) to (7).
(9) The method for recovering phosphorus in the water to be treated according to any one of (1) to (8), wherein a solid-liquid ratio of the steelmaking slag, the water, and the hydrochloric acid is 1: 5 or more.
(10) The method for recovering phosphorus in the water to be treated according to any one of (1) to (9), wherein a stirring time after the total amount of the hydrochloric acid is added to the slag slurry is 15 minutes or more.
(11) The method for recovering phosphorus in the water to be treated according to any one of (1) to (10), wherein the stirring time of the water to be treated and the slag slurry for phosphorus recovery is 5 minutes or more.
(12) The method for recovering phosphorus in the water to be treated according to any one of (1) to (11), wherein the water to be treated containing phosphorus includes one or both of domestic wastewater and industrial wastewater.
(13) The method for recovering phosphorus in water to be treated according to any one of (1) to (12), wherein the solid matter is used as a fertilizer.
(14) The method for recovering phosphorus in water to be treated according to any one of (1) to (13), wherein the solid is used as a fertilizer raw material.
(15) The method for recovering phosphorus in the water to be treated according to any one of (1) to (14), wherein the solid is used as a raw material for yellow phosphorus.

  According to the present invention, in the phosphorus recovery method for recovering phosphorus in water to be treated using steelmaking slag, when obtaining a slurry from which Ca in steelmaking slag is eluted, Ca is sufficiently eluted from the steelmaking slag. Thus, elution of components other than Ca can be suppressed, and the amount of hydrochloric acid to be used can be reduced.

The schematic diagram which shows an example of the phosphorus collection | recovery system used for the phosphorus collection | recovery method in the to-be-processed water of this invention. The figure which shows the relationship between the molar ratio (HCl / CaO) of CaO and hydrochloric acid in steelmaking slag in each pH, and the elution amount of the element eluted from steelmaking slag. The figure which shows the relationship between the molar ratio (HCl / CaO) of CaO and hydrochloric acid in steelmaking slag in each pH, and a residue recovery rate. The figure which shows the relationship between elapsed time and the pH of a slurry. Example No. The figure which shows the relationship between elapsed time in 1 and pH and temperature of slurry. Example No. FIG. 3 is a diagram showing the relationship between elapsed time and pH and temperature of slurry in FIG. Example No. 10 is a diagram showing the relationship between elapsed time, pH of slurry, and temperature in FIG. Example No. 15 is a graph showing the relationship between the elapsed time and the pH and temperature of the slurry in FIG. Example No. The figure which shows the relationship between elapsed time, pH of slurry, and temperature in FIG. Example No. 18-No. The figure which shows the relationship between elapsed time in 20 and pH and temperature of slurry.

[First Embodiment]
The phosphorus recovery method of the present embodiment is a slag slurry composed of steelmaking slag and water, and an amount of hydrochloric acid in which the molar ratio (HCl / CaO) of CaO and hydrochloric acid in the steelmaking slag is 1.00 to 1.50. The step of obtaining a phosphorus recovery slag slurry in which Ca in the steelmaking slag is eluted by stirring and mixing, and stirring and mixing the phosphorus recovery slag slurry in the water to be treated containing phosphorus, A step of forming a compound containing Ca, coagulating and precipitating the compound as a solid together with a steelmaking slag residue, and recovering the precipitated solid, and obtaining a phosphorus recovery slag slurry, Hydrochloric acid is added while maintaining the pH of the slurry in the range of 4.5 to 7.0. Hereinafter, the present embodiment will be described in detail with reference to the phosphorus recovery system shown in FIG.

  First, the phosphorus recovery system 1 shown in FIG. 1 will be described. A phosphorus recovery system 1 shown in FIG. 1 includes a phosphorus recovery reaction tank 2, a phosphorus recovery slag slurry supply unit 3 that supplies a phosphorus recovery slag slurry S 2 to the phosphorus recovery reaction tank 2, and a phosphorus recovery slag slurry supply unit 3. Hydrochloric acid supply part 4 for supplying hydrochloric acid A1 to Ca elution reaction tank 3a, treated water supply part 5 for supplying treated water W2 containing phosphorus to phosphorus recovery reaction tank 2, and hydroxylation for phosphorus recovery reaction tank 2 A pH adjusting device 9 for supplying calcium A2, a dehydrating device 6 for dehydrating the solid S3 settled in the phosphorus recovery reaction tank 2, and a discharge section 7 for discharging the supernatant water W3 in the phosphorus recovery reaction tank 2 to the outside. , Is provided. Further, the phosphorus recovery system 1 shown in FIG. 1 is provided with a drying device 8 for drying the dehydrated product S4 after dehydration.

  The phosphorus recovery reaction tank 2 is provided with a stirring device (not shown). Moreover, the phosphorus collection | recovery reaction tank 2 is connected with the pH adjuster 9 via the caustic soda supply line L14. In the phosphorus recovery reaction tank 2, the phosphorus recovery slag slurry S2 and the water to be treated W2 are sequentially added to the water to be treated W2, and after stirring these, the phosphorus in the water to be treated W2 is allowed to stand. Precipitate as a compound containing phosphorus and Ca.

  The pH adjusting device 9 includes a caustic soda supply line L14 and a sodium hydroxide storage tank 9a. Sodium hydroxide A2 can be supplied to the sodium hydroxide storage tank 9a from the outside. The sodium hydroxide storage tank 9a can supply sodium hydroxide A2 to the phosphorus recovery reaction tank 2 through the caustic soda supply line L14.

  The phosphorus recovery slag slurry supply unit 3 supplies the hydrochloric acid A1 to the Ca elution reaction tank 3a, the slag slurry supply line L1 connecting the Ca elution reaction tank 3a and the phosphorus recovery reaction tank 2, and the Ca elution reaction tank 3a. A hydrochloric acid supply unit 4; The Ca elution reaction tank 3a is provided with a stirrer (not shown). Moreover, in order to supply hydrochloric acid A1 to the Ca elution reaction tank 3a, the steelmaking slag supply line L2 for supplying steelmaking slag S1 from the outside, the water supply line L3 for supplying water W1 from the outside, and And a hydrochloric acid supply line L6. The Ca elution reaction tank 3a is sequentially charged with water W1, steelmaking slag S1, and hydrochloric acid A1, and these are stirred to obtain phosphorus recovery slag slurry S2. The Ca elution reaction tank 3a can supply the phosphorus recovery slag slurry S2 to the phosphorus recovery reaction tank 2 via the slag slurry supply line L1.

  The hydrochloric acid supply unit 4 includes a hydrochloric acid supply line L6 that supplies hydrochloric acid A1 to the Ca elution reaction tank 3a. A hydrochloric acid storage tank (not shown) may be connected to the upstream side of the hydrochloric acid supply line L6. The hydrochloric acid supply unit 4 can supply hydrochloric acid A1 to the Ca elution reaction tank 3a via the acid supply line L6.

  The to-be-processed water supply part 5 is comprised from the raw | natural water storage tank 5a and the raw | natural water supply line L4 which connects the raw | natural water storage tank 5a and the phosphorus collection | recovery reaction tank 2. FIG. A supply line L5 for supplying the treated water W2 from the outside is connected to the raw water storage tank 5a. The to-be-treated water supply unit 5 can supply the to-be-treated water W2 stored in the raw water storage tank 5a to the phosphorus recovery reaction tank 2.

  The discharge section 7 includes a drain line L7 that discharges the supernatant water W3 after the solid matter S3 settles, a drain storage tank 7a that is connected to the tip of the drain line L7, and a discharge line L13 that is connected to the drain storage tank 7a. It consists of and.

  The phosphorus recovery reaction tank 2 is connected to a discharge line L8 that discharges the settled solid matter S3 to the outside. A dehydrator 6 is connected to the end of the discharge line L8. The dehydrator 6 receives the solid S3 that has settled in the phosphorus recovery reaction tank 2 and performs dehydration. The dewatering device 6 is connected to another drainage line L9 for sending the dewatered water W4 dehydrated from the solid S3 to the drainage line L7 of the supernatant water W3. Furthermore, the dehydrator 6 is connected to a transport line L10 for discharging the dehydrated dehydrated material S4 to the outside.

  As for the conveyance line L10, another conveyance line L11 has branched from the middle. A drying device 8 is connected to the end of the branched transfer line L11. The drying device 8 is connected to a discharge line L12 for discharging the dried product S5 after drying.

Next, a method for recovering phosphorus in the water to be treated using the phosphorus recovery system 1 shown in FIG. 1 will be described.
Steelmaking slag S1 used in this embodiment uses steelmaking slag S1 discharged from an ironworks.

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

  Moreover, it is preferable that the Ca content rate of steelmaking slag S1 is the range of 15-55 mass%, and the range of 25-55 mass% is more preferable. If the Ca content in steelmaking slag S1 is too low, the phosphorus recovery rate is lowered, which is not preferable. On the other hand, if the Ca content in the steelmaking slag S1 is too high, the amount of the steelmaking slag S1 residue after elution of Ca is reduced. If the amount of the steelmaking slag S1 residue is reduced, the phosphorus recovery rate is also lowered, which is not preferable.

Table 1 shows an example of components contained in the steelmaking slag S1. As shown in Table 1, the steelmaking slag S1 contains Ca, fertilizer components such as Fe, Al, and Si. In this embodiment, the basicity (CaO / SiO ₂ (weight ratio)) it is preferable to use a steel slag S1 as in the range of 1-7.

  Examples of the water W1 that can be used in the present embodiment include tap water and industrial water.

Examples of hydrochloric acid A1 that can be used in this embodiment include hydrochloric acid and concentrated hydrochloric acid. The concentration of hydrochloric acid or concentrated hydrochloric acid is about 0.5 to 12.0 N, but any concentration may be used. Although a sulfate or nitrate as an acid other than hydrochloric acid, the sulfuric acid would form a gypsum reacts with Ca eluted from steelmaking slag S1 (CaSO ₄₎ is not preferable. Moreover, since nitric acid contains nitrogen, it becomes unpleasant because it causes eutrophication when the treated water W5 after phosphorus recovery is discharged into public water areas.

  The water to be treated W2 used in 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 W2 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 wastewater discharged mainly from urban areas. Urban wastewater 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 in the terminal treatment plant of the public sewer can be suitably used as the treated water W2 in the phosphorus recovery method of the present embodiment. Also, the phosphorus recovery method of the present embodiment is a final treatment. It may be applied when phosphorus is recovered in the field. Furthermore, the to-be-processed water W2 of this embodiment is not restricted to domestic wastewater or industrial wastewater, but can be applied if it contains phosphorus.

  In the phosphorus recovery method of the present embodiment, the molar ratio (HCl / CaO) of CaO and hydrochloric acid A1 in the steelmaking slag S1 to the phosphorus recovery slag slurry S2 composed of the steelmaking slag S1 and the water W1 is 1.00. 1. Stirring and mixing an amount of hydrochloric acid A1 of 1.50 to obtain a phosphorus recovery slag slurry in which Ca in the steelmaking slag S1 is eluted, and stirring the treated water W2 containing phosphorus in the phosphorus recovery slag slurry The mixture is allowed to stand after mixing to form a compound containing phosphorus and Ca, and the compound is coagulated and settled as a solid S3 together with the residue of the steelmaking slag S1, and the collected solid S3 is recovered. In the step of obtaining the phosphorus recovery slag slurry, the hydrochloric acid A1 is added while maintaining the pH of the phosphorus recovery slag slurry S2 in the range of 4.5 to 7.0. To. Hereinafter, each step will be described.

  First, steelmaking slag S1 is added to water W1 to obtain a slag slurry. In the phosphorus recovery system 1 of FIG. 1, water W1 and steelmaking slag S1 are supplied to the Ca elution reaction tank 3a, and these are stirred and mixed to form slag slurry. In order to stabilize the pH of the slag slurry, stirring is preferably performed for 1 minute or more, more preferably stirring for 5 minutes or more, and further preferably stirring for 10 minutes or more. At this time, during stirring and mixing, f-CaO (free lime) in the steelmaking slag S1 may be eluted, and the pH of the slag slurry may increase to show alkalinity.

  Next, hydrochloric acid A1 is supplied from the hydrochloric acid supply unit 4 to the Ca elution reaction tank 3a, and the slag slurry and hydrochloric acid A1 are stirred and mixed in the Ca elution reaction tank 3a to obtain phosphorus recovery slag slurry S2. At this time, an amount of hydrochloric acid A1 in which the molar ratio (HCl / CaO) of CaO to hydrochloric acid A1 in the steelmaking slag S1 is 1.00 to 1.50 is supplied to the Ca elution reaction tank 3a. Furthermore, hydrochloric acid A1 is supplied while maintaining the pH of the slag slurry in the Ca elution reaction tank 3a in the range of 4.5 to 7.0. The stirring time after supplying hydrochloric acid A1 in such an amount that the molar ratio of CaO to hydrochloric acid A1 (HCl / CaO) in steelmaking slag S1 is 1.00 to 1.50 is preferably 15 minutes or more, and 20 More than minutes are more preferable.

  In the phosphorus recovery reaction tank, when the pH of the slag slurry S2 during supply of hydrochloric acid A1 is in the range of 4.5 to 7.0, Ca elutes preferentially from the steelmaking slag S1, and the elution of components other than Ca is suppressed. Is done. This is mainly due to elution by ion exchange between hydrogen ions supplied to the steelmaking slag S1 and hydroxide ions released from the steelmaking slag S1 in a pH range of 4.5 to 7.0. It is considered that Ca having a large ionization tendency preferentially elutes among the components contained in the slag S1.

On the other hand, if the pH of the slag slurry S2 during supply of hydrochloric acid A1 is less than 4.5, the amount of elution of components other than Ca from the steelmaking slag S1 increases. This is because a large amount of hydrogen ions supplied to the steelmaking slag S1, metal oxides steelmaking slag S1 surface _{(SiO 2, Al 2 O 3} , FeO, Fe 2 O 3 , etc.) react with hydrogen ions This is thought to be due to the collapse and elution from the surface of the steelmaking slag S1. Thereby, since elements other than Ca elute from steelmaking slag S1, and hydrochloric acid A1 supplied for Ca elution is used besides Ca elution, the quantity of hydrochloric acid A1 used for Ca elution increases.

  Further, when the pH of the slag slurry S2 during supply of hydrochloric acid A1 exceeds 7.0, Ca is not sufficiently eluted from the steelmaking slag S1.

  The amount of hydrochloric acid A1 supplied to the Ca elution reaction tank 3a is such that the molar ratio (HCl / CaO) between CaO and hydrochloric acid A1 in the steelmaking slag S1 is 1.00 to 1.50. When the molar ratio (HCl / CaO) between CaO and hydrochloric acid A1 in the steelmaking slag S1 is less than 1.00, Ca in the steelmaking slag S1 cannot be sufficiently eluted, and phosphorus in the treated water is efficiently used. Therefore, it is not possible to secure the amount of Ca elution necessary for the recovery. On the other hand, when the molar ratio (HCl / CaO) of CaO and hydrochloric acid A1 in the steelmaking slag S1 is more than 1.50, the amount of sodium hydroxide A2 used for pH adjustment in the subsequent step increases. This increases the cost of chemicals. In addition, in order to adjust the molar ratio (HCl / CaO) of CaO and hydrochloric acid A1 in the steelmaking slag S1, it is preferable to measure the CaO concentration in the steelmaking slag S1 in advance. It is also preferable to constantly monitor the Ca ion concentration of the phosphorus recovery slag slurry S2 using an ion electrode or the like.

  The solid-liquid ratio between the steelmaking slag S1 and the amount of liquid used for the reaction (the amount of water W1 and hydrochloric acid A1) is adjusted to be 1: 5 (kg: kg) or more. When the CaO concentration in the steelmaking slag S1 is determined, the amount of hydrochloric acid A1 used can be determined from the molar ratio (HCl / CaO) of CaO and hydrochloric acid A1 in the steelmaking slag S1, so that the remaining amount of liquid W1 It can be an amount.

  As an example, a case where the hydrochloric acid A1 is supplied while maintaining the pH of the slag slurry in the Ca elution reaction tank 3a at 5.0 to obtain the phosphorus recovery slag slurry S2 will be described in detail.

  First, in the Ca elution reaction tank 3a, hydrochloric acid A1 is supplied from the hydrochloric acid supply unit 4 while stirring and mixing the slag slurry composed of the water W1 and the steelmaking slag S1 until the pH of the slag slurry decreases to 5.0. When the pH of the slag slurry is lowered to 5.0, the supply of hydrochloric acid A1 is once interrupted. If the stirring and mixing of the slag slurry is continued even after the supply of the hydrochloric acid A1 is interrupted, Ca in the steelmaking slag S1 is eluted and the pH of the slag slurry is increased. Then, since the pH of the slag slurry becomes greater than 5.0, the pH of the slag slurry is lowered to 5.0 by stirring and mixing again while supplying hydrochloric acid A1. When the pH of the slag slurry reaches 5.0, the supply of hydrochloric acid A1 is interrupted and mixed with stirring. Then, Ca in the steelmaking slag S1 elutes, and the pH of the slag slurry rises to more than 5.0. Therefore, stirring and mixing while supplying hydrochloric acid A1, the pH of the slag slurry is lowered to 5.0. Let This operation is repeated until hydrochloric acid A1 is supplied in such an amount that the molar ratio of CaO to hydrochloric acid A1 (HCl / CaO) in steelmaking slag S1 is 1.00 to 1.50. After supplying the entire amount of hydrochloric acid A1, the mixture is stirred and mixed for 15 minutes or longer. As explained above, phosphorus recovery slag slurry S2 is obtained by supplying hydrochloric acid A1 while maintaining the pH of the slag slurry constant.

  Next, the treated water W2 is supplied from the raw water storage tank 5a to the phosphorus recovery reaction tank 2 via the raw water supply line L4, and the phosphorus recovery slag slurry S2 is supplied via the phosphorus recovery slag slurry supply line L2. It supplies to the phosphorus collection | recovery reaction tank 2, stirs and mixes the phosphorus collection | recovery slag slurry S2 and the to-be-processed water W2, and leaves still. What is necessary is just to adjust the mixing ratio of the amount of Ca in steelmaking slag S1, and the amount of phosphorus in the to-be-processed water W2 so that Ca / P ratio may be in the range of 2-4. The adjustment of the Ca / P ratio may be controlled by the mixing ratio of the phosphorus recovery slag slurry S2 and the water to be treated W2. In order to adjust the Ca / P ratio, the Ca concentration in the phosphorus recovery slag slurry S2 and the phosphorus concentration in the water to be treated W2 are preferably measured in advance.

  In order to sufficiently react phosphorus in the treated water W2 and Ca in the phosphorus recovery slag slurry S2, the stirring time of the treated water W2 and the phosphorus recovery slag slurry S2 is preferably 5 minutes or more. . If the stirring time is too short, the reaction between Ca and phosphorus may not proceed sufficiently. Moreover, when stirring time is too long, an apparatus will become large and an installation cost will become high.

By mixing the water to be treated W2 and the phosphorus recovery slag slurry S2 with stirring, phosphorus contained in the water to be treated W2 reacts with Ca in the phosphorus recovery slag slurry S2 eluted from the steelmaking slag S1. Thus, a compound containing phosphorus and Ca is formed. The following compounds can be considered as the compound to be formed. Part of the phosphorus contained in the water to be treated W2 exists as hydrogen phosphate ions (HPO ₄ ²⁻ ), and the hydrogen phosphate ions and Ca ions react to form calcium hydrogen phosphate (CaHPO ₄ ). I guess it will be. At this time, it is considered that Ca further binds 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 stable, the pH of the liquid mixture composed of the phosphorus recovery slag slurry S2 and the water to be treated W2 is adjusted to a range of 7.2 to 8.5. It is preferable to do. When the pH of the mixed solution is less than 7.2, more dihydrogen phosphate ions are present than hydrogen phosphate ions. Since the solubility product of dihydrogen phosphate ion and Ca ion is larger than the solubility product of hydrogen phosphate ion and Ca ion, the precipitation amount of calcium hydrogen phosphate decreases when the pH of the mixed solution is less than 7.2. This may reduce the phosphorus recovery rate. Further, when the pH exceeds 8.5, carbonate ions are generated in the water W2 to be treated, Ca binds to carbonate ions to precipitate calcium carbonate, and phosphorus hardly precipitates, resulting in a decrease in phosphorus recovery rate. Resulting in. The pH in the water to be treated W2 may be adjusted by supplying sodium hydroxide A2 from the pH adjusting device 9 via the caustic soda supply line L14.

In addition, at the same time as or after the formation of the compound containing phosphorus and Ca, these compounds are agglomerated and precipitated using the residue of the steelmaking slag S1. The residue of the steelmaking slag S1 is negatively charged as a whole because Ca is eluted as a cation. On the other hand, calcium hydrogen phosphate and Ca ₂ HPO ₄ ²⁺ have a small apparent specific gravity, so that they float in the water W2 to be treated, and Ca ₂ HPO ₄ ²⁺ is positively charged. In this way, the negatively charged residue of the steelmaking 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 steelmaking slag S1. In contrast, calcium hydrogen phosphate and compounds such as Ca ₂ HPO ₄ ²⁺ aggregate and finally settle as solid S3. Since it is considered that coagulation sedimentation proceeds by the above mechanism, it is not necessary to add a coagulant when the solid S3 is sedimented.

  Although depending on the size of the phosphorus recovery reaction tank 2, the sedimentation time is preferably 7 minutes or more, more preferably 10 minutes or more, and still more preferably 30 minutes or more. The upper limit is preferably 60 minutes or less, more preferably 50 minutes or less, and even more preferably 40 minutes or less.

  Next, in the phosphorus recovery reaction tank 2, the supernatant water W3, which is the supernatant after sedimentation of the solid S3, is sent to the drainage storage tank 7a via the drainage line L7. Thereafter, the supernatant water W3 is discharged into the public water area as the treated water W5 from the drainage storage tank 7a together with the dehydrated water W4 from the dehydrator 6, or is sent to another water treatment facility.

  On the other hand, the solid S3 that has aggregated and settled at the bottom of the phosphorus recovery reaction tank 2 is sent to the dehydrator 6 via the discharge line L8. The solid material S3 is dehydrated in the dehydrating device 6, and the dehydrated water W4 separated at that time is sent to the drainage storage tank 7a via the drainage line L9. The sedimented solid matter S3 may be dehydrated by using filtration, centrifugation, pressure dehydration (roller breath, filter press, screw press), multiple disk rotation dehydration, multiple vibration filter, or the like.

  The dehydrated product S4 after the dehydration is discharged out of the system by the transfer line L10 or is sent to the drying device 8 via the transfer line L11. Carried out as fertilizer or fertilizer raw material. Or it is sent to the drying apparatus 8 and dried. The drying treatment of the dehydrated product S4 may be natural drying by leaving it in a room temperature environment. In a room temperature environment, for example, if it is left for about 12 hours, it will be sufficiently dried. The dehydrated product S4 sent to the drying device 8 is dried and then discharged out of the system as a dried product S5.

  The dehydrated matter S4 carried out from the dehydrating apparatus 6 contains 15% by mass or more of kurea-soluble phosphorus, which is the standard value of the kurea-soluble phosphorus content for directing the recovered material for fertilizer use, and is used as it is as a fertilizer. It is done. Moreover, it contains many elements such as Fe, Si, Mn, Mg, etc., which are fertilizer active ingredients. 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.

  Moreover, the dried product S5 carried out from the drying device 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. Moreover, it contains many components such as Ca, Fe, Mg, Mn, and Si, which are fertilizer active components.

  As described above, according to the method for recovering phosphorus in the water to be treated according to the present embodiment, the molar ratio (HCl / CaO) between CaO and hydrochloric acid in the steelmaking slag is 1.00 to 1.50. In the step of obtaining a phosphorus recovery slag slurry in which hydrochloric acid is stirred and mixed to elute Ca in the steelmaking slag, hydrochloric acid is added while maintaining the pH of the slag slurry in the range of 4.5 to 7.0, Ca in the steelmaking slag can be sufficiently eluted, elution of components other than Ca can be suppressed, and a large amount of fertilizer components can remain in the collected solid matter. In addition, the amount of hydrochloric acid to be used can be reduced, and the chemical cost can be reduced. Furthermore, when the amount of hydrochloric acid to be used is reduced, the amount of sodium hydroxide used for pH adjustment can be reduced when the water to be treated and the slag slurry for phosphorus recovery are stirred and mixed. The chemical cost can be further reduced.

Also, Ca is eluted from the steelmaking slag, and this is reacted with hydrogenphosphate ions in the water to be treated to form calcium hydrogenphosphate. Further, using the residue after the calcium is eluted from the steelmaking slag, calcium hydrogenphosphate is used. As a result, the phosphorus in the water to be treated can be efficiently recovered with high yield.
In particular, by utilizing the steelmaking slag residue after elution of Ca, calcium hydrogenphosphate 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 simultaneously, phosphorus can be recovered in a short time, and only one reaction tank is required to recover phosphorus, and the phosphorus recovery reaction tank 2 can be made compact. Can be

  Moreover, since elution of components other than Ca in steelmaking slag can be suppressed, atomization of the steelmaking slag residue in phosphorus recovery slag slurry can be prevented. Furthermore, the amount of residue of the steelmaking slag in the phosphorus recovery slag slurry can be increased, and the residue recovery rate represented by the following formula (1) is 80% or more. Therefore, phosphorus in the for-treatment water can be recovered more efficiently.

  Steelmaking slag residue recovery rate = (steelmaking slag residue weight (g) / input steelmaking slag weight (g)) × 100 (1)

  Further, in the phosphorus recovery method of the present embodiment, the hydrochloric acid consumption rate represented by the following formula (2) is 85% or more, and the hydrochloric acid consumption rate is increased by 10 to 30% compared to the conventional method invented by the present inventors. Can be made. Therefore, the amount of hydrochloric acid used when Ca is eluted from the steelmaking slag can be greatly reduced. In addition, the amount (mol) of hydrochloric acid used for Ca elution in the following formula (2) is represented by the following formula (3), and the added Cl amount (mol) is represented by the following formula (4).

  Hydrochloric acid consumption rate (%) = (amount of hydrochloric acid used for Ca elution (mol) / amount of added Cl (mol)) × 100 (2)

The amount of hydrochloric acid used for Ca elution (mol) = the amount of Ca in the filtrate (g / L) × (the amount of water + the amount of hydrochloric acid) (L) /40.0784×2 (3)
The amount of added Cl (mol) = the amount of added hydrochloric acid (L) × the concentration of hydrochloric acid (mol / L) (4)

  Some steelmaking slag contains a large amount of phosphorus discharged from steelworks. According to this embodiment, the phosphorus in the steelmaking 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 (about 80,000 t-P / Y discharge in Japan) and sewage treatment plants are the two major sources of phosphorus. It is possible to simultaneously collect and recycle both phosphorus (of about 50,000 t-P / Y in Japan).

  Further, by drying the aggregated and settled solid matter after dehydration, the volume of the solid matter can be reduced, and handling of the aggregated and settled solid matter becomes easy.

Furthermore, since the collect | recovered solid substance contains the element and phosphorus which are fertilizer components in steelmaking slag in high concentration, it can be used suitably as a fertilizer, a fertilizer raw material, or a yellow phosphorus raw material.
Moreover, according to this embodiment, since the whole quantity of the steelmaking slag used for the collection | recovery of phosphorus can be utilized as a fertilizer or a fertilizer raw material, steelmaking slag can be used effectively.

[Second Embodiment]
Next, a second embodiment will be described with reference to the phosphorus recovery system shown in FIG. In the following description, the description overlapping with the first embodiment is omitted.

  In the phosphorus recovery method of the present embodiment, the molar ratio (HCl / CaO) of CaO and hydrochloric acid A1 in the steelmaking slag S1 is 1.00 to 1.50 in the slag slurry composed of the water W1 and the steelmaking slag S1. A step of obtaining a phosphorus recovery slag slurry S2 in which Ca in the steelmaking slag S1 is eluted, and a water W2 containing phosphorus in the phosphorus recovery slag slurry S2 with stirring. And then allowing the compound containing phosphorus and Ca to form, coagulating and precipitating the compound together with the residue of the steelmaking slag S1 as a solid S3, and recovering the precipitated solid S3. And in the stage of obtaining a phosphorus recovery slag slurry, the molar ratio (HCl / CaO) of CaO to hydrochloric acid A1 in the steelmaking slag S1 is less than 1.00 out of the total amount of hydrochloric acid A1. The amount of hydrochloric acid A1 was added to the slag slurry that is characterized by adding the remaining amount of hydrochloric A1 while maintaining the pH of the slag slurry in the range of 4.5 to 7.0. Hereinafter, each stage will be described in detail.

  First, water W1 and steelmaking slag S1 are supplied to the Ca elution reaction tank 3a, and these are stirred and mixed to form slag slurry.

  Next, hydrochloric acid A1 is supplied from the hydrochloric acid supply unit 4 to the Ca elution reaction tank 3a, and the slag slurry and hydrochloric acid A1 are stirred and mixed in the Ca elution reaction tank 3a to obtain a phosphorus recovery slag slurry S2. At this time, out of the amount of hydrochloric acid A1 in which the molar ratio (HCl / CaO) of CaO to hydrochloric acid A1 in steelmaking slag S1 is 1.00 to 1.50, the mole of CaO and hydrochloric acid A1 in steelmaking slag S1 An amount of hydrochloric acid A1 with a ratio (HCl / CaO) of less than 1.00 is supplied to the phosphorus recovery reaction tank 2 without adjusting the pH. The amount of hydrochloric acid added at this time is preferably such that the molar ratio of CaO to hydrochloric acid A1 (HCl / CaO) in steelmaking slag S1 is 0.75, and is 0.70. Is more preferable. The pH at the time of supplying hydrochloric acid A1 is not particularly controlled. However, since the elution amount of components other than Ca increases when the pH is less than 4.5, hydrochloric acid A1 is added so that the pH does not become less than 4.5. It is preferable to do. Thereafter, the remaining amount of hydrochloric acid A1 is supplied while maintaining the pH of the slag slurry in the Ca elution reaction tank 3a in the range of 4.5 to 7.0. After the total amount of hydrochloric acid A1 is added, the mixture is stirred and mixed for 15 minutes or longer to obtain phosphorus recovery slag slurry S2.

  Below, as an example, among the hydrochloric acid A1 in an amount such that the molar ratio (HCl / CaO) between CaO and hydrochloric acid A1 in the steelmaking slag S1 is 1.00 to 1.50, the slag slurry contains the steelmaking slag S1. After adding hydrochloric acid A1 in such an amount that the molar ratio of CaO to hydrochloric acid A1 (HCl / CaO) is 0.70, the remaining amount of hydrochloric acid A1 is added while maintaining the pH of the slag slurry at 5.0, The case where the phosphorus collection | recovery slag slurry S2 is obtained is demonstrated in detail.

  First, in the Ca elution reaction tank 3a, while stirring and mixing the slag slurry composed of the water W1 and the steelmaking slag S1, among the hydrochloric acid having an HCl / CaO ratio of 1.00 to 1.50, in the steelmaking slag S1 Hydrochloric acid A1 in an amount such that the molar ratio of CaO to hydrochloric acid A1 (HCl / CaO) is 0.70 is supplied from the hydrochloric acid supply unit 4. At this time, hydrochloric acid A1 is supplied without adjusting the pH of the slag slurry. Then, the pH of the slag slurry is reduced to less than 5.0, but when stirring and mixing is continued, Ca in the steelmaking slag S1 is eluted and the pH of the slag slurry is increased. When the pH of the slag slurry exceeds 5.0, the mixture is stirred and mixed while supplying hydrochloric acid A1, and the pH of the slag slurry is lowered to 5.0. When the pH of the slag slurry reaches 5.0, the supply of hydrochloric acid A1 is interrupted and mixed with stirring. Then, Ca in the steelmaking slag S1 elutes, and the pH of the slag slurry rises to over 5.0. Therefore, stirring and mixing is performed again while supplying hydrochloric acid A1, and the pH of the slag slurry is adjusted to 5.0. To lower. Such an operation is repeated until the supply of the remaining amount of hydrochloric acid A1 is completed. After supplying the entire amount of hydrochloric acid A1, the mixture is stirred and mixed for 15 minutes or longer. As described above, among hydrochloric acid in an amount such that the HCl / CaO ratio is 1.00 to 1.50, the molar ratio (HCl / CaO) between CaO and hydrochloric acid A1 in the steelmaking slag S1 is 0.70. After supplying an amount of hydrochloric acid A1 without adjusting the pH, the remaining amount of hydrochloric acid A1 is supplied while maintaining the pH of the slag slurry constant, thereby obtaining phosphorus recovery slag slurry S2.

  Next, the treated water W2 is supplied from the raw water storage tank 5a to the phosphorus recovery reaction tank 2 via the raw water supply line L4, and the phosphorus recovery slag slurry S2 is supplied via the phosphorus recovery slag slurry supply line L2. It supplies to the phosphorus collection | recovery reaction tank 2, stirs and mixes the phosphorus collection | recovery slag slurry S2 and the to-be-processed water W2, and leaves still. The solid S3 that has aggregated and settled at the bottom of the phosphorus recovery reaction tank 2 is sent to the dehydrator 6. In the dehydrator 6, the solid S3 is dehydrated, and the dewatered water W4 separated at that time is sent to the drainage storage tank 7a. Further, the dehydrated product S4 after dehydration is carried out as fertilizer or a fertilizer raw material. Or after sending to the drying apparatus 8 and drying, it is carried out as a fertilizer or a fertilizer raw material. On the other hand, the supernatant water W3, which is the supernatant after sedimentation of the solid matter S3, is sent to the drainage storage tank 7a via the discharge line L7. Thereafter, the supernatant water W3 is discharged as dephosphorized water together with the dewatered water W4 from the dewatering device 6 into the public water area as the treated water W5 from the drainage storage tank 7a, or sent to another water treatment facility.

  As described above, according to the method for recovering phosphorus in the water to be treated according to the present embodiment, the molar ratio (HCl / CaO) between CaO and hydrochloric acid in the steelmaking slag is 1.00 to 1.50. In the step of obtaining a phosphorus recovery slag slurry in which hydrochloric acid is stirred and mixed to elute calcium in the steelmaking slag, the molar ratio (HCl / CaO) of CaO and hydrochloric acid in the steelmaking slag is 1. After adding an amount of hydrochloric acid that is less than 00 to the slag slurry, the remaining amount of hydrochloric acid is added while maintaining the pH of the slag slurry in the range of 4.5 to 7.0. Elution of components can be suppressed, Ca can be sufficiently eluted, and a large amount of fertilizer components can remain in the collected solid matter. In addition, the amount of hydrochloric acid to be used can be reduced, and the chemical cost can be reduced. Furthermore, when the amount of hydrochloric acid to be used is reduced, the amount of sodium hydroxide used for pH adjustment can be reduced when the water to be treated and the slag slurry for phosphorus recovery are stirred and mixed. The chemical cost can be further reduced.

  In addition, in the stage of obtaining the phosphorus recovery slag slurry, the amount of hydrochloric acid whose HCl / CaO ratio is less than 1.00 out of the amount of hydrochloric acid whose HCl / CaO ratio is 1.00 to 1.50 is adjusted to pH. Therefore, the time required for adding hydrochloric acid can be shortened compared to the first embodiment.

  Experimental examples 1 to 5 performed for examining the relationship between various factors in the embodiment of the present invention will be described below.

[Experimental Example 1]
20 g of steelmaking slag having a particle size of less than 0.125 mm and water were stirred and mixed for 10 minutes to obtain a slag slurry. Thereafter, 2 mol / L hydrochloric acid was added while maintaining the pH of the slag slurry at 1.5, 3.0, 4.0, 5.0, and 5.5, respectively. After adding hydrochloric acid in such an amount that the molar ratio of CaO to hydrochloric acid (HCl / CaO) in steelmaking slag was 0.70 to 1.90, the mixture was stirred and mixed for 30 minutes to obtain a slag slurry for phosphorus recovery. The amount of water was adjusted so that the solid-liquid ratio of the steelmaking slag, the amount of water and the amount of hydrochloric acid was 1:10.
Further, 20 g of steelmaking slag and 200 mL of 1 mol / L hydrochloric acid were mixed with stirring to obtain a slag slurry for phosphorus recovery.

  The phosphorus recovery slag slurry obtained by the above steps was filtered and separated into a steelmaking slag residue and liquid. And the amount of Ca, Si, and Al contained in the residue of steelmaking slag was measured with the ICP emission spectroscopic analyzer. The amounts of Ca, Si, and Al obtained by measurement are shown in FIGS. 2 (a) to 2 (c), respectively.

As shown in FIG. 2 (a), when the pH of the slag slurry is maintained at 4.5 or more, the molar ratio (HCl / CaO) between CaO and hydrochloric acid in the steelmaking slag is in the range of 1.00 to 1.50. , The Ca elution amount is increased.
Moreover, when FIG.2 (b) and FIG.2 (c) are seen, when the pH of slag slurry is maintained at 4.5 or more, the molar ratio (HCl / CaO) of CaO and hydrochloric acid in steelmaking slag is 1. Si and Al are hardly eluted in the range of 0.001 to 1.50. On the other hand, when the pH of the slag slurry is maintained below 4.5 and when steelmaking slag and hydrochloric acid are directly mixed, the elution amounts of Si and Al are increased.

  From the above, it can be seen that by maintaining the pH during addition of hydrochloric acid at 4.5 or more, the amount of Ca eluted from the steelmaking slag increases, and the amount of elements other than Ca can be reduced. Therefore, the amount of hydrochloric acid used for Ca elution can be reduced.

[Experiment 2]
20 g of steelmaking slag having a particle size of less than 0.125 mm and water were stirred and mixed for 10 minutes to obtain a slag slurry. Thereafter, 2 mol / L hydrochloric acid was added while maintaining the pH of the slag slurry at 1.5, 2.0, 3.0, 4.0, 4.5, 5.0, 5.5. Hydrochloric acid was added until the molar ratio of CaO to hydrochloric acid (HCl / CaO) in the steelmaking slag became 0.70 to 1.96, and then stirred and mixed for 30 minutes to obtain a slag slurry for phosphorus recovery. The amount of water was adjusted so that the solid-liquid ratio between the amount of water and hydrochloric acid and the steelmaking slag was 1:10.
Further, 20 g of steelmaking slag and 200 mL of 1 mol / L hydrochloric acid were mixed with stirring to obtain a slag slurry for phosphorus recovery.

  The phosphorus recovery slag slurry obtained by the above method was filtered and separated into a steelmaking slag residue and liquid. The amount of residual steelmaking slag was measured, and the residue recovery rate was determined by the following formula (1). The result is shown in FIG. In addition, in the test example described as "Reaction method A" in FIG. 3, the slag slurry for phosphorus collection | recovery was obtained by stirring and mixing hydrochloric acid and steelmaking slag. Further, in the test example described as “Reaction Method B” in FIG. 3, hydrochloric acid is added to a slag slurry obtained by stirring and mixing water and steelmaking slag while maintaining a constant pH for phosphorus recovery. A slag slurry was obtained.

  Residue recovery rate (%) = (residue amount of steelmaking slag (g) / slag amount mixed with water (g)) × 100 (1)

  Referring to FIG. 3, when the pH of the slag slurry is maintained at 4.5 or higher, the residue recovery rate is 80% or higher. On the other hand, the residue recovery rate is low when the pH of the slag slurry is maintained below 4.5 and when the steelmaking slag and hydrochloric acid are directly mixed.

  From the above, it can be seen that by maintaining the pH during addition of hydrochloric acid at 4.5 or more, the residue recovery rate of steelmaking slag can be increased. Therefore, it becomes possible to collect | recover phosphorus in to-be-processed water efficiently.

[Experiment 3]
20 g of steelmaking slag having a particle size of less than 0.125 mm and 100 mL of water were stirred and mixed for 10 minutes to obtain a slag slurry. Thereafter, 85 mL of 2 mol / L hydrochloric acid was added while adjusting the pH of the slag slurry to 4.5. After adding the entire amount of hydrochloric acid, the mixture was stirred and mixed to obtain a slag slurry for phosphorus recovery.

  FIG. 4 shows the relationship between the elapsed time in the stage of obtaining the slag slurry and the stage of obtaining the phosphorus recovery slag slurry and the pH of the slag slurry. According to FIG. 4, it can be seen that the increase in pH becomes moderate in about 15 minutes after the addition of the total amount of hydrochloric acid. From this, it can be seen that when the total amount of hydrochloric acid is added and stirred for about 15 minutes, the total amount of added hydrochloric acid is consumed for the reaction with the steelmaking slag. Therefore, it turns out that it is preferable that the stirring time after adding the whole quantity of hydrochloric acid shall be 15 minutes or more.

[Experimental Example 4]
A slag slurry for phosphorus recovery was obtained under the conditions shown in Table 2. In the test example described as “Reaction Method A” in Table 2, slag slurry for phosphorus recovery was obtained by stirring and mixing hydrochloric acid and steelmaking slag. In the test example described as “Reaction Method B” in Table 2, hydrochloric acid was added to a slag slurry obtained by stirring and mixing water and steelmaking slag while maintaining a constant pH, and a slag slurry for phosphorus recovery was added. Obtained. In the test example described as “Reaction Method C” in Table 2, the molar ratio of CaO and hydrochloric acid in the steelmaking slag without adjusting the pH to the slag slurry obtained by stirring and mixing water and steelmaking slag ( After adding an amount of hydrochloric acid such that (HCl / CaO) was less than 1.00, the remaining amount of hydrochloric acid was added while maintaining the pH of the slurry to obtain a slag slurry for phosphorus recovery. In addition, No. 1-No. 13, no. 15-No. The hydrochloric acid used in No. 17 is dilute hydrochloric acid. The hydrochloric acid used in 14 is concentrated hydrochloric acid.

  Moreover, the phosphorus collection | recovery slag slurry obtained on the conditions shown in Table 2 was filtered, and it solid-liquid-separated into the residue and liquid component of steelmaking slag. Then, the amount of Ca contained in the liquid was measured with an ICP emission spectroscopic analyzer. The hydrochloric acid consumption rate was calculated | required using Ca amount in the measured liquid component, and following formula (2). However, in the following formula (2), the hydrochloric acid amount (mol) used for Ca elution is represented by the following formula (3), and the added Cl amount (mol) is represented by the following formula (4). The obtained results are shown in Table 2.

  Hydrochloric acid consumption rate (%) = (amount of hydrochloric acid used for Ca elution (mol) / amount of added Cl (mol)) × 100 (2)

The amount of hydrochloric acid used for Ca elution (mol) = the amount of Ca in the filtrate (g / L) × (the amount of water + the amount of hydrochloric acid) (L) /40.0784×2 (3)
The amount of added Cl (mol) = the amount of added hydrochloric acid (L) × the concentration of hydrochloric acid (mol / L) (4)

  Here, as an example, No. 2 shown in Table 2 is used. 1, no. 3, no. 10, no. 15, no. Each of the 16 conditions will be described in detail with reference to FIGS. 5 to 9 are diagrams showing the relationship between the elapsed time in the stage of obtaining the slag slurry and the stage of obtaining the phosphorus recovery slag slurry and the pH of the slag slurry. 5, FIG. 6, FIG. 7, FIG. 8, and FIG. 1, no. 3, no. 10, no. 15, no. 16 corresponds.

  No. corresponding to FIG. In No. 1, 200 mL of 1 mol / L hydrochloric acid was added to 20 g of steelmaking slag, and a slag slurry for phosphorus recovery was obtained by stirring and mixing for 30 minutes. As can be seen from FIG. 5, the pH decreases to about 0 when hydrochloric acid is added, and then increases with the passage of time. As a result, looking at Table 2, the hydrochloric acid consumption rate is 76%. In this way, No. 1 corresponding to FIG. In No. 1, the entire amount of hydrochloric acid is charged at once, and the pH of the slag slurry during the addition of hydrochloric acid is not maintained in the range of 4.5 to 7.0, so the hydrochloric acid consumption rate is low.

  No. corresponding to FIG. In No. 3, 100 mL of water and 20 g of steelmaking slag were stirred and mixed for 10 minutes to obtain a slag slurry, and then 100 mL of 2 mol / L hydrochloric acid was added while adjusting the pH to 3.0. Hydrochloric acid was added until the molar ratio of CaO to hydrochloric acid in the steelmaking slag (HCl / CaO) was 1.40, and the mixture was stirred and mixed for 30 minutes to obtain a slag slurry for phosphorus recovery. Referring to FIG. 6, it can be seen that when water and steelmaking slag are stirred and mixed, the pH increases and becomes alkaline, and then when hydrochloric acid is added, the pH decreases. Moreover, it turns out that hydrochloric acid is added, adjusting pH of slag slurry to 3.0. As a result, referring to Table 2, the hydrochloric acid consumption rate is 78%. In this way, No. 1 corresponding to FIG. In No. 3, since the pH of the slag slurry during the addition of hydrochloric acid is not maintained in the range of 4.5 to 7.0, the hydrochloric acid consumption rate is low.

  No. corresponding to FIG. In No. 10, 130 mL of water and 20 g of steelmaking slag were stirred and mixed for 10 minutes to obtain a slag slurry, and then 70 mL of 2 mol / L hydrochloric acid was added while adjusting the pH to 5.0. Hydrochloric acid was added until the molar ratio of CaO to hydrochloric acid in the steelmaking slag (HCl / CaO) was 1.00, and then stirred and mixed for 30 minutes to obtain a slag slurry for phosphorus recovery. Referring to FIG. 7, it can be seen that when water and steelmaking slag are stirred and mixed, the pH increases and becomes alkaline, and then when hydrochloric acid is added, the pH decreases. Moreover, it turns out that hydrochloric acid is added, adjusting pH of slag slurry to 5.0. As a result, looking at Table 2, the hydrochloric acid consumption rate is 97%. In this way, No. 1 corresponding to FIG. In No. 10, since the pH of the slag slurry during hydrochloric acid addition is maintained in the range of 4.5 to 7.0, the hydrochloric acid consumption rate is high.

  No. corresponding to FIG. In No. 15, 130 mL of water and 20 g of steelmaking slag were stirred and mixed for 10 minutes to obtain a slag slurry, and then 70 mL of 2 mol / L hydrochloric acid was added while adjusting the pH to 5.5. Hydrochloric acid was added until the molar ratio of CaO to hydrochloric acid in the steelmaking slag (HCl / CaO) was 1.00, and then stirred and mixed for 30 minutes to obtain a slag slurry for phosphorus recovery. Referring to FIG. 8, it can be seen that when water and steelmaking slag are stirred and mixed, the pH increases and becomes alkaline, and then when hydrochloric acid is added, the pH decreases. Moreover, it turns out that hydrochloric acid is added, adjusting pH of slag slurry to 5.5. As a result, looking at Table 2, the hydrochloric acid consumption rate is 97%. In this way, No. 1 corresponding to FIG. In No. 15, since the pH of the slag slurry during the addition of hydrochloric acid is maintained in the range of 4.5 to 7.0, the hydrochloric acid consumption rate is high.

  No. corresponding to FIG. In No. 16, 128 mL of water and 20 g of steelmaking slag were stirred and mixed for 10 minutes, and 50 mL of 2 mol / L hydrochloric acid was added without adjusting the pH of the slag slurry. After adding 50 mL of 2 mol / L hydrochloric acid at which the molar ratio of CaO to hydrochloric acid (HCl / CaO) in steelmaking slag becomes 0.70, the addition of hydrochloric acid was once stopped, and the pH of the slag slurry was 5.1 to 5.1. Stir and mix until it rises to 7. After confirming that the pH of the slag slurry was raised to 5.1-7, 22 mL of 2 mol / L hydrochloric acid was added while adjusting the pH of the slag slurry to be pH = 5. Hydrochloric acid was added until the molar ratio of CaO to hydrochloric acid in the steelmaking slag (HCl / CaO) reached 1.00 in total, and then stirred and mixed for 30 minutes to obtain a slag slurry for phosphorus recovery. Referring to FIG. 9, it can be seen that when water and steelmaking slag are stirred and mixed, the pH increases and becomes alkaline, and then when hydrochloric acid is added, the pH decreases. Moreover, it turns out that the pH of slag slurry is set to 4.5 immediately after adding hydrochloric acid of the quantity from which the molar ratio (HCl / CaO) of CaO and hydrochloric acid in steelmaking slag becomes 0.70. Furthermore, when adding the residual amount of hydrochloric acid, it turns out that hydrochloric acid is added, adjusting the pH of slag slurry to 5.0. As a result, referring to Table 2, the hydrochloric acid consumption rate is 90%. In this way, No. 1 corresponding to FIG. 16, the pH was less than 5.0 when hydrochloric acid having a molar ratio (HCl / CaO) of 0.70 was added without adjusting the pH of the slag slurry. When adding, since the pH of the slag slurry during the addition of hydrochloric acid is maintained in the range of 4.5 to 7.0, the hydrochloric acid consumption rate is high. Further, No. 1 corresponding to FIG. Compared with 10, it can be seen that the time required for the addition of hydrochloric acid can be shortened.

Further, according to Table 2, No. which is an example of the present invention. 5, no. 9, no. 10, no. 14, no. 15, no. 16, the hydrochloric acid consumption rate is 85% or more.
On the other hand, No. which is a comparative example. In No. 1, hydrochloric acid is directly added to steelmaking slag to obtain a slag slurry. Since the method of adding hydrochloric acid is not the method of the present invention, the consumption rate of hydrochloric acid is low.
No. 2-No. 4, no. In No. 8, since the pH when adding hydrochloric acid to the slag slurry was low, hydrochloric acid was used for elution other than Ca elution, and the hydrochloric acid consumption rate was low.
No. 11-No. No. 13 has a hydrochloric acid consumption rate of 85% or more, but as shown in Table 3, the amount of Ca (g / L) in the filtrate is less than that of the present invention example, and it is 11000 mg / L or less, and the treatment The amount of elution was insufficient to recover phosphorus in water. This is because Ca was not sufficiently eluted because the molar ratio of CaO to hydrochloric acid (HCl / CaO) in the steelmaking slag was low.

In Table 2, No. 7, no. 8, no. 10, no. 13, no. 14, no. 15, no. The phosphorus recovery slag slurry obtained under the conditions shown in No. 16 was filtered, and solid-liquid separation was performed into a steelmaking slag residue and liquid. And the amount of Ca, Si, and Al contained in the liquid was measured with an ICP emission spectroscopic analyzer. Table 3 shows the measurement results.
In addition, No. For No. 16, a part of the slag slurry was sampled immediately after the addition of hydrochloric acid in such an amount that the molar ratio of CaO to hydrochloric acid in the steelmaking slag (HCl / CaO) was 0.70. 16-1), and the result (No. 16-2) of collecting and measuring the phosphorus recovery slag slurry obtained by adding the remaining amount of hydrochloric acid while adjusting the pH and stirring and mixing. Yes.
In Table 3, No. In No. 17, a slag slurry for phosphorus recovery was obtained under the following conditions. 130 mL of water and 20 g of steelmaking slag were stirred and mixed for 10 minutes to obtain a slag slurry, and then 70 mL of 2 mol / L hydrochloric acid was added while adjusting the pH to 3.5. Hydrochloric acid was added until the molar ratio of CaO to hydrochloric acid in the steelmaking slag (HCl / CaO) was 1.00, and then stirred and mixed for 30 minutes to obtain a slag slurry for phosphorus recovery. The results obtained by collecting and measuring the slag slurry for phosphorus recovery at this time are No. 1 in Table 3. 17.

  According to Table 3, as for the present invention example (No.10 and No.14, No.15 and No.16), Ca elution amount is a comparative example (No.7, No.8, No.11-No.13, It can be seen that there are many compared to No. 17). Moreover, it turns out that the example of this invention has few elution amounts of Si and Al compared with a comparative example. Moreover, even if the hydrochloric acid used in the stage of obtaining the phosphorus recovery slag slurry is dilute hydrochloric acid or concentrated hydrochloric acid, the amount of hydrochloric acid used for Ca elution can be reduced and the elution of elements other than Ca can be suppressed. I understand that. Further, it can be seen that even when the pH of the slag slurry is controlled to pH 5.5, the amount of hydrochloric acid used for Ca elution is reduced and elution of elements other than Ca can be suppressed.

  No. 7, no. 8 and no. It can be seen that No. 17 has a high pH during the addition of hydrochloric acid, so that the elution amount of Si and Al is increased.

  No. 11-No. No. 13, since the molar ratio of CaO to hydrochloric acid in steelmaking slag (HCl / CaO) was 0.70, the elution amount of Si and Al was reduced, but the Ca elution amount was 11000 mg / L or less. It can be seen that the amount of elution is insufficient to recover phosphorus in the water to be treated. From this, it can be seen that when the molar ratio of CaO to hydrochloric acid in the steelmaking slag (HCl / CaO) is less than 1.0, Ca cannot be sufficiently eluted.

No. 16-1 is a measurement result obtained by sampling a part of the slag slurry immediately after adding an amount of hydrochloric acid in which the molar ratio of CaO to hydrochloric acid in the steelmaking slag (HCl / CaO) is 0.70. However, it can be seen that the elution amount of Si and Al is reduced. However, it can be seen that Ca is not sufficiently eluted at this stage.
Then, while maintaining pH at 5.0, it is a measurement result about the slag slurry for phosphorus collection | recovery obtained by adding the residual amount of hydrochloric acid. When 16-2 is seen, it turns out that the elution amount of Ca is increasing, suppressing the elution amount of Si and Al.
In addition, No. The residue recovery rate of 16-2 was 85%, which was as high as the example of the present invention shown in FIG.

[Experimental Example 5]
In order to confirm the change with time of pH of the slag slurry when the hydrochloric acid was added in two stages to produce the slag slurry, the following experiment was conducted. For this experiment, No. 18-No. 20 and FIG.
FIG. 10 is a diagram showing the relationship between the elapsed time and the pH of the slag slurry in the stage of obtaining the phosphorus recovery slag slurry while adding hydrochloric acid after the steelmaking slag is added to water and stirred for 10 minutes.

In Table 4 corresponding to FIG. 18-No. In No. 20, 26 mL of water and 4 g of steelmaking slag were stirred and mixed for 5 minutes, and 15 mL of 2 mol / L hydrochloric acid was added so that the molar ratio of CaO to hydrochloric acid in the steelmaking slag (HCl / CaO) was 0.70. After adding hydrochloric acid and stirring for 5 minutes, 4 mL of 2 mol / L hydrochloric acid was added every 1 minute over 15 minutes. Hydrochloric acid was added until the molar ratio of CaO to hydrochloric acid in the steelmaking slag (HCl / CaO) reached 1.00 in total, and then stirred and mixed for 15 minutes to obtain a slag slurry for phosphorus recovery. In addition, No. In No. 21, a phosphorus recovery slag slurry was obtained by adding a necessary amount of hydrochloric acid to steelmaking slag at a time and stirring and mixing.
When FIG. 10 is seen, when adding hydrochloric acid in such an amount that the molar ratio of CaO to hydrochloric acid (HCl / CaO) in steelmaking slag becomes 0.70, the pH is 4.5 to You can see that it is about 6.
Furthermore, when adding the remaining hydrochloric acid, it turns out that hydrochloric acid is added, adjusting the pH of a slag slurry to 4.5 or more.

In order to investigate the relationship between the amount of NaOH to be used, the content of soluble phosphorus in the recovered phosphorus, and the content of soluble phosphorus, the following experimental examples were conducted.
The phosphorus recovery slag slurry produced above and the phosphorus amount in the model liquid having a phosphorus concentration of 150 mg / L are mixed so that the Ca / P ratio is 3.0, so that the pH shown in Table 4 is obtained. After adjusting and stirring and mixing for 20 minutes, the mixture was allowed to stand for 5 minutes to coagulate and settle the solid matter. Coagulated and settled solids were collected, the amount of collected solids, the phosphorus content in the hydrated solids after sedimentation, and the amount of solute phosphorus measured, and the phosphorus content in the hydrated solids after sedimentation was molybdenum. It was measured by the blue method. The amount of ku-soluble phosphorus was determined by measuring the mass of the extract extracted from the solid with a 2% aqueous 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.
Further, the NaOH reduction rate (wt%), the soluble phosphorus content (wt%), and the soluble phosphorus content (gC—P ₂ O ₅ / kg slag) are obtained by the following formulas (5) to (7), respectively. It was.

NaOH reduction rate (wt%) = (NaOH usage amount (mL) of Comparative Example No. 21−NaOH usage amount (mL) of Invention Examples No. 18 to 20)
÷ Amount of NaOH used in Comparative Example 23 (mL) (5)

  Cu-soluble phosphorus content (wt%) = Cu-soluble phosphorus amount (g) ÷ recovered solid amount (g) × 100 (6)

Cu-soluble phosphorus content (gC—P ₂ O ₅ / kg slag) = Cu-soluble phosphorus amount (g) ÷ Slag usage (kg) (7)

According to Table 4, in any of the test examples, the recovered material shows 15% by mass or more which is a standard value of the content of soluble phosphorus for direct application to fertilizer, and can be used as it is as a fertilizer. The soluble phosphorus content in the recovered product was compared with that in Comparative Example No. It can be seen that the present invention examples (No. 18 to No. 20) have a higher content of soluble phosphorus than 21.
In addition, the inventive examples (No. 18 to No. 20) are comparative example Nos. It can be seen that the amount of NaOH aqueous solution used for adjusting the pH of the water to be treated can be greatly reduced compared to 21.
In practical use, the optimum value is determined by comprehensively taking into account the value of the collected phosphorus, the cost of procurement of steelmaking slag, hydrochloric acid, NaOH (caustic soda), and the like.

The gist of the present invention is as follows.
(1) To a slag slurry composed of steelmaking slag and water, stir and mix the hydrochloric acid in such an amount that the molar ratio (HCl / CaO) of CaO and hydrochloric acid in the steelmaking slag is 1.00 to 1.50. Obtaining a phosphorus recovery slag slurry from which calcium in the steelmaking slag is eluted;
The compound containing phosphorus and calcium is formed by stirring and mixing the phosphorus recovery slag slurry in the water to be treated containing phosphorus, and then allowing the compound to coagulate and settle as a solid with the steelmaking slag residue. Stages,
Recovering the settled solid matter, and
In the step of obtaining the phosphorus recovery slag slurry, the hydrochloric acid is added while maintaining the pH of the slag slurry during the addition of hydrochloric acid in the range of 4.5 to 7.0. Recovery method.
(2) To the slag slurry composed of steelmaking slag and water, stir and mix the hydrochloric acid in such an amount that the molar ratio (HCl / CaO) of CaO and hydrochloric acid in the steelmaking slag is 1.00 to 1.50. Obtaining a phosphorus recovery slag slurry from which calcium in the steelmaking slag is eluted;
The compound containing phosphorus and calcium is formed by stirring and mixing the phosphorus recovery slag slurry in the water to be treated containing phosphorus, and then allowing the compound to coagulate and settle as a solid with the steelmaking slag residue. Stages,
Recovering the settled solid matter, and
In the step of obtaining the phosphorus recovery slag slurry, an amount of the hydrochloric acid in which the molar ratio (HCl / CaO) of CaO to the hydrochloric acid in the steelmaking slag is less than 1.00 out of the total amount of the hydrochloric acid is added to the slag. After adding to a slurry, the residual amount of the said hydrochloric acid is added, maintaining the pH of the said slag slurry in the range of 4.5-7.0, The collection | recovery method of the phosphorus in to-be-processed water characterized by the above-mentioned.
(3) The method for recovering phosphorus in the water to be treated according to (1) or (2), wherein the solid matter that has been precipitated is dried.
(4) The method for recovering phosphorus in the water to be treated according to any one of (1) to (3), wherein the basicity of the steelmaking slag is in a range of 1 to 7.
(5) The method for recovering phosphorus in the water to be treated according to any one of (1) to (4), wherein a calcium content of the steelmaking slag is in a range of 15 to 55 mass%.
(6) The method for recovering phosphorus in the water to be treated according to any one of (1) to (5), wherein the steelmaking slag has an average particle size of 0.3 mm or less.
(7) When mixing the water to be treated and the slag slurry for phosphorus recovery, the pH of the mixed solution is adjusted to 7.2 to 8.5. (1) to (6) To recover phosphorus in water to be treated.
(8) When the treated water and the phosphorus recovery slag slurry are mixed, the molar ratio (Ca / P) of the amount of calcium in the steelmaking slag and the amount of phosphorus in the treated water is 2 or more and 4 or less. The method for recovering phosphorus in the water to be treated according to any one of (1) to (7).
(9) The method for recovering phosphorus in the water to be treated according to any one of (1) to (8), wherein a solid-liquid ratio of the steelmaking slag, the water, and the hydrochloric acid is 1: 5 or more.
(10) The method for recovering phosphorus in the water to be treated according to any one of (1) to (9), wherein a stirring time after the total amount of the hydrochloric acid is added to the slag slurry is 15 minutes or more.
(11) The method for recovering phosphorus in the water to be treated according to any one of (1) to (10), wherein the stirring time of the water to be treated and the slag slurry for phosphorus recovery is 5 minutes or more.
(12) The method for recovering phosphorus in the water to be treated according to any one of (1) to (11), wherein the water to be treated containing phosphorus includes one or both of domestic wastewater and industrial wastewater.
(13) The method for recovering phosphorus in water to be treated according to any one of (1) to (12), wherein the solid matter is used as a fertilizer.
(14) The method for recovering phosphorus in water to be treated according to any one of (1) to ( 12 ), wherein the solid matter is used as a fertilizer raw material.
(15) The method for recovering phosphorus in the water to be treated according to any one of (1) to ( 12 ), wherein the solid is used as a raw material for yellow phosphorus.

Claims (15)

The steelmaking slag is prepared by stirring and mixing the hydrochloric acid in an amount such that the molar ratio (HCl / CaO) between CaO and hydrochloric acid in the steelmaking slag is 1.00 to 1.50. Obtaining a phosphorus recovery slag slurry from which calcium in the solution is eluted;
The compound containing phosphorus and calcium is formed by stirring and mixing the phosphorus recovery slag slurry in the water to be treated containing phosphorus, and then allowing the compound to coagulate and settle as a solid with the steelmaking slag residue. Stages,
Recovering the settled solid matter, and
In the step of obtaining the phosphorus recovery slag slurry, the hydrochloric acid is added while maintaining the pH of the slag slurry during the addition of hydrochloric acid in the range of 4.5 to 7.0. Recovery method. The steelmaking slag is prepared by stirring and mixing the hydrochloric acid in an amount such that the molar ratio (HCl / CaO) between CaO and hydrochloric acid in the steelmaking slag is 1.00 to 1.50. Obtaining a phosphorus recovery slag slurry from which calcium in the solution is eluted;
The compound containing phosphorus and calcium is formed by stirring and mixing the phosphorus recovery slag slurry in the water to be treated containing phosphorus, and then allowing the compound to coagulate and settle as a solid with the steelmaking slag residue. Stages,
Recovering the settled solid matter, and
In the step of obtaining the phosphorus recovery slag slurry, an amount of the hydrochloric acid in which the molar ratio (HCl / CaO) of CaO to the hydrochloric acid in the steelmaking slag is less than 1.00 out of the total amount of the hydrochloric acid is added to the slag. After adding to a slurry, the residual amount of the said hydrochloric acid is added, maintaining the pH of the said slag slurry in the range of 4.5-7.0, The collection | recovery method of the phosphorus in to-be-processed water characterized by the above-mentioned.   The method for recovering phosphorus in water to be treated according to claim 1 or 2, wherein the solid matter that has been precipitated is dried.   The method for recovering phosphorus in water to be treated according to any one of claims 1 to 3, wherein the steelmaking slag has a basicity in the range of 1 to 7.   The method for recovering phosphorus in water to be treated according to any one of claims 1 to 4, wherein a calcium content of the steelmaking slag is in a range of 15 to 55 mass%.   The method for recovering phosphorus in water to be treated according to any one of claims 1 to 5, wherein an average particle diameter of the steelmaking slag is 0.3 mm or less.   The to-be-processed method as described in any one of Claims 1 thru | or 6 which adjusts pH of a liquid mixture to 7.2-8.5 when mixing the said to-be-processed water and the said slag slurry for phosphorus collection | recovery. How to recover phosphorus in water.   When the treated water and the phosphorus recovery slag slurry are mixed, the molar ratio (Ca / P) of the calcium amount in the steelmaking slag and the phosphorus amount in the treated water is 2 or more and 4 or less. The method for recovering phosphorus in the water to be treated according to any one of claims 1 to 7 to be adjusted.   The method for recovering phosphorus in water to be treated according to any one of claims 1 to 8, wherein a solid-liquid ratio of the steelmaking slag, the water, and the hydrochloric acid is 1: 5 or more.   The method for recovering phosphorus in the water to be treated according to any one of claims 1 to 9, wherein a stirring time after the total amount of the hydrochloric acid is added to the slag slurry is 15 minutes or more.   The recovery method of phosphorus in to-be-processed water as described in any one of Claims 1 thru | or 10 which makes stirring time of the said to-be-processed water and the said phosphorus collection | recovery slag slurry 5 minutes or more.   The method for recovering phosphorus in water to be treated according to any one of claims 1 to 11, wherein the water to be treated containing phosphorus includes one or both of domestic wastewater and industrial wastewater.   The method for recovering phosphorus in water to be treated according to any one of claims 1 to 12, wherein the solid matter is fertilizer.   The method for recovering phosphorus in water to be treated according to any one of claims 1 to 13, wherein the solid material is used as a fertilizer raw material.   The method for recovering phosphorus in water to be treated according to any one of claims 1 to 14, wherein the solid material is a yellow phosphorus raw material.

Images