JP7165538B2 - Phosphorus recovery material and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a phosphorus recovery material that contains calcium silicate hydrate and magnetic powder, has a low flow rate of magnetic powder, and has a high phosphorus recovery rate, and a method for producing the same.

The HAP method and the MAP method have been conventionally known as methods for recovering phosphorus contained in waste water from facilities such as sewage treatment plants where phosphorus is concentrated. The HAP method is a method in which calcium hydroxide or calcium chloride is added to waste water to crystallize hydroxyapatite [Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ , hydroxyapatite: HAP]. In the MAP method, magnesium ammonium phosphate [NH ₄ MgPO _{4.6H 2} O, Magnesium Ammonium Phosphate: MAP] is crystallized.

The conventional HAP method has the problem that it takes a long time to grow HAP, and the filterability is very poor if the HAP remains as microcrystals. On the other hand, it has been pointed out that the MAP method has a problem of increased removal cost due to scaling to piping.

Calcium silicate hydrate [ _{nCaO.SiO.sub.2.mH.sub.2O} , _Amorphous Calcium Silicate. Hydrates: called CSH) has been proposed. For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2012-050975) describes a phosphorus recovery material composed of aggregates of CSH and slaked lime.

Further, in Patent Document 2 (Japanese Patent Application Laid-Open No. 2017-154047), the Ca/Si molar ratio is 0.5 to 3.5, preferably the Ca/Si molar ratio is 0.8 to 1.5, A phosphorus recovery material containing 50 wt% or more of fine crystalline CSH having a crystallite size of 6.0 nm to 16.0 nm, preferably 6.5 nm to 10.0 nm, and a method of using the phosphorus recovery material, It is described that the phosphorus recovery effect is superior to that of conventional crystalline CSH. In these phosphorus recovery methods using CSH, the reaction between phosphate ions in waste water and calcium ions eluted from CSH is sequential, so the degree of supersaturation of the generated HAP is easily maintained at a low level. It has the advantage of being easy.

On the other hand, in the phosphorus recovery method using CSH, when solid-liquid separation (for example, sedimentation) of the recovered phosphorus is performed in the same manner as the HAP method, the sedimentation time (filtration time) of the product sediment containing phosphorus in the liquid is ) and the like are often rate-determining for the treatment time of the entire process, and there is a problem that the filtration time is long.

As a countermeasure against such long filtration time, it is known to shorten the treatment time by mixing magnetic powder and performing magnetic separation. For example, in Patent Document 3 (Japanese Patent Laid-Open No. 2014-487), a phosphorus recovery material containing calcium silicate and silicon dioxide is further added with a magnetic substance such as magnetite, and HAP sediment that incorporates phosphorus in waste water is produced. Magnetic separation is described.

However, when magnetic powder is mixed with CSH and magnetic separation is carried out, the outflow amount of magnetic powder during magnetic separation greatly varies depending on the range of the Ca/Si molar ratio of CSH, and the Ca/Si molar ratio of CSH is appropriate. It was found that out of the above range, the outflow amount of the magnetic powder increases, which hinders economical treatment.

In addition, the method of Patent Document 3 uses a phosphorus recovery material containing calcium silicate and silicon dioxide, and part or all of the silicon dioxide is amorphous, so that it has an uneven structure or a porous structure. It is intended to increase the phosphorus recovery rate by widening the HAP deposition area when calcium acid (CSH) takes up phosphorus to form hydroxyapatite (HAP) (paragraph [0029]). Therefore, in the manufacturing process, hydrochloric acid is added to the solution to adjust the pH to around 10.5 to generate amorphous porous silicon dioxide (Example 1: paragraphs [0068] to [0076]).
However, since silicon dioxide does not directly participate in the formation of hydroxyapatite (HAP), there is a problem that if the content of silicon dioxide is high, the content of phosphorus in the recovered phosphorus is reduced.

JP 2012-050975 A JP 2017-154047 A JP 2014-487 A

The present invention solves the above-mentioned problems of the conventional phosphorus recovery material, and is a phosphorus recovery material for magnetic separation, which is mainly composed of calcium silicate hydrate (CSH) mixed with magnetic powder. A phosphorus recovery material with a short solid-liquid separation processing time, a small outflow amount of magnetic powder during magnetic separation, a low content of silicon dioxide that is not directly involved in the formation of HAP, and a high phosphorus recovery rate. I will provide a.

The present invention relates to a phosphorus recovery material and a method for producing the same that solves the above problems by the following configurations.
[1] Contains calcium silicate hydrate and magnetic powder, the calcium silicate hydrate has a Ca/Si molar ratio of 1.0 to 1.5 , and the magnetic powder content is 5% by mass or more . The magnetic powder is in a state in which the magnetic powder is incorporated in the calcium silicate hydrate, the content of free silicon dioxide is 5% by mass or less, and the content of slaked lime is 2% by mass or less. A phosphorus recovery material characterized in that the amount of outflow of is suppressed to 20% or less .
[2] The content of calcium silicate hydrate is 55% by mass or more and less than 95% by mass, the content of magnetic powder is 5% by mass or more and less than 45% by mass, and the phosphorus recovery rate is 50% or more . The phosphorus recovery material described in [1].
[3] A Ca/Si molar ratio of 1 by adding a sodium silicate solution to a mixed slurry of slaked lime or quicklime and magnetic powder to form calcium silicate hydrate without adjusting the pH in the presence of dispersed magnetic powder. 0 to 1.5, the content of the magnetic powder is 5% by mass or more, the magnetic powder is incorporated in the calcium silicate hydrate, and the content of free silicon dioxide is 5% by mass. % or less and the content of slaked lime is 2% by mass or less .
[4] A sodium silicate solution is added little by little to a mixed slurry of slaked lime or quicklime and magnetic powder to generate calcium silicate hydrate while the magnetic powder is dispersed without adjusting the pH . A method for producing a phosphorus recovery material.

[Specific explanation]
The present invention will be specifically described below.
The phosphorus recovery material of the present invention contains calcium silicate hydrate and magnetic powder, the calcium silicate hydrate has a Ca/Si molar ratio of 1.0 or more to 1.5 or less , and the magnetic powder content is 5 mass. % or more , the magnetic powder is incorporated in the calcium silicate hydrate, the content of free silicon dioxide is 5% by mass or less, and the content of slaked lime is 2% by mass or less to obtain a magnetic powder. The phosphorus recovery material is characterized in that the outflow of magnetic powder during separation is suppressed to 20% or less .
More specifically, the phosphorus recovery material of the present invention has a calcium silicate hydrate content of 55% by mass or more and less than 95% by mass, and a magnetic powder content of 5% by mass or more and less than 45% by mass. , a phosphorus recovery material having a phosphorus recovery rate of 50% or more .

[Phosphorus recovery material]
The phosphorus recovery material of the present invention contains calcium silicate hydrate (CSH) as a main component. Calcium silicate hydrate (CSH) reacts with phosphorus to form hydroxyapatite (HAP) and has good reactivity with phosphorus, so that the recovery rate of phosphorus can be increased.

Calcium silicate hydrate (CSH) can be produced by mixing a lime slurry of slaked or quicklime with an aqueous sodium silicate solution. A sodium silicate aqueous solution, which is a raw material for calcium silicate hydrate (CSH), is produced by dissolving siliceous raw materials such as siliceous shale, amorphous silica, silica gel, silica fume, opal, and diatomaceous earth in an aqueous sodium hydroxide solution. be able to. Commercially available water glass or the like can also be used.

In the phosphorus recovery material of the present invention, the Ca/Si molar ratio of calcium silicate hydrate (CSH) is in the range of 1.0 to 1.5 . When the phosphorus recovery material of the present invention contains unreacted slaked lime, the above Ca/Si molar ratio is the Ca/Si molar ratio of the entire phosphorus recovery material. If the Ca/Si molar ratio is less than 0.8, the amount of Ca that reacts with phosphorus is small, resulting in a low phosphorus recovery rate. Furthermore, if the Ca/Si molar ratio is in the range of 1.0 or more to 1.5 or less, the content of free silicon dioxide in the phosphorus recovery material can be suppressed to 5% by mass or less, which is preferable.

On the other hand, if the Ca/Si molar ratio is 3.5 or more, the outflow amount of the magnetic powder contained in the phosphorus recovery material increases during magnetic separation, which is not preferable. Specifically, for example, when the Ca/Si molar ratio is 3.5 or more, the outflow amount of the magnetic powder during magnetic separation exceeds 20% by mass. When the Ca/Si molar ratio is 3.5 or more, a large amount of unreacted slaked lime remains in the phosphorus recovery material at 20.6% by mass or more. Due to the repulsive action of electric charges, the binding force between CSH and magnetic powder is weakened. Therefore, the Ca/Si molar ratio is preferably less than 3.5, more preferably 1.5 or less, in order to suppress the outflow of magnetic powder during magnetic separation. As described above, when the Ca/Si molar ratio is less than 3.5, the content of unreacted slaked lime is 21% by mass or less, preferably less than 20.6% by mass. can be done. Furthermore, when the Ca/Si molar ratio is in the range of 1.0 to 1.5 , the amount of slaked lime contained in the phosphorus recovery material of the present invention is 2% by mass or less, preferably 1.6% by mass or less. , and the amount of outflow of the magnetic powder can be further reduced.

In addition, when the phosphorus recovery material is used in a liquid in which phosphorus and carbonic acid coexist, the reaction between Ca and carbonic acid proceeds and the reaction between Ca and phosphorus is suppressed. There is Therefore, when used in a liquid in which phosphorus and carbonic acid coexist, the Ca/Si molar ratio is preferably 1.5 or less.

The content of calcium silicate hydrate (CSH) in the phosphorus recovery material is preferably in the range of 55% by mass to 95% by mass. If the content of calcium silicate hydrate (CSH) is less than 55% by mass, the effect of recovering phosphorus decreases. On the other hand, when the content of calcium silicate hydrate (CSH) exceeds 95% by mass, the magnetic powder content becomes relatively small, making magnetic separation difficult.

The phosphorus recovery material of the present invention is a phosphorus recovery material for magnetic separation containing calcium silicate hydrate (CSH) and magnetic powder. Magnetic separation is, for example, a method in which a phosphorus recovery material that has reacted with phosphorus to produce hydroxyapatite (HAP) is passed through a magnetic filter, and the phosphorus recovery material is magnetically adsorbed on the filter to separate it from the solution, or HAP is separated from the solution. Various methods using magnetism can be applied, such as a method of attracting the produced phosphorus recovery material to a magnet and pulling it out of the solution for separation. By magnetically separating the phosphorus recovery material of the present invention, the solid-liquid separation time is shorter than general sedimentation separation, and the treatment time can be greatly shortened.

In the phosphorus recovery material of the present invention, the content of the magnetic powder as Fe ₂ O ₃ is preferably in the range of 5% by mass to 45% by mass, more preferably in the range of 8.8% by mass to 42% by mass. If the magnetic powder content is less than 5% by mass, a sufficient magnetic effect cannot be obtained during solid-liquid separation. On the other hand, if the content of the magnetic powder exceeds 45% by mass, the content of calcium silicate hydrate (CSH) becomes relatively small, making it difficult to obtain a sufficient phosphorus recovery effect.

The content of calcium silicate hydrate (CSH) is relatively reduced by containing the magnetic powder in the phosphorus recovery material. When the HAP produced by the reaction of (1) is solid-liquid separated, the HAP is reliably retained and recovered by the magnetism, so that the phosphorus recovery rate can be increased.

In the phosphorus recovery material of the present invention, containing magnetic powder together with calcium silicate hydrate (CSH) means that CSH is generated while magnetic powder is dispersed, and the magnetic powder is taken in and dispersed in CSH. belongs to.

Specifically, CSH is generated in the presence of dispersed magnetic powder, for example, by adding an aqueous sodium silicate solution to a mixed slurry of slaked lime or quicklime and magnetic powder, and generating CSH in the presence of dispersed magnetic powder. It is what I let you do. If the CSH is produced in the presence of magnetic powder dispersed therein, the magnetic powder will be incorporated into the structure of the CSH. The amount of outflow of is remarkably suppressed. Specifically, for example, when the Ca/Si molar ratio of CSH is in the range of 1.0 or more to 1.5 or less , CSH is generated without pH adjustment, and the amount of slaked lime contained in the phosphorus recovery material is reduced to 2. By setting the amount to 20% by mass or less, the outflow amount of the magnetic powder during magnetic separation can be suppressed to 20% by mass or less.

On the other hand, when CSH is mixed with magnetic powder after generating CSH, the magnetic powder is mixed around CSH, and the magnetic powder is not incorporated into the structure of CSH. outflow tends to increase.

The sediment recovered by the phosphorus recovery material of the present invention is hydroxyapatite (HAP) produced by the reaction between calcium silicate hydrate (CSH) and phosphorus in the liquid, and contains a sufficient amount of phosphoric acid. It can be used as a phosphate fertilizer. Generally, when used as a phosphate fertilizer, the standard for by-product phosphate fertilizers requires that the content of citric acid (CP ₂ O ₅ ) be 15% by mass or more.

In the phosphorus recovery material of the present invention, when the content of magnetic powder increases, the content of calcium silicate hydrate (CSH) relatively decreases, so the content of citric acid phosphoric acid contained in the recovered phosphorus decreases. do. In general, when the magnetic powder content exceeds 40% by mass, the citric acid content of the recovered phosphorus tends to fall below 15% by mass. Therefore, when the recovered phosphorus material is used as a phosphate fertilizer, the amount of magnetic powder contained in the recovered phosphorus material is preferably 40% by mass or less.

Magnetic powders contained in the phosphorus recovery material of the present invention include magnetic iron oxides such as magnetite, magnetic iron alloys such as nickel-zinc ferrite, and the like. Commercial products can be used for these magnetic powders. The particle size of the magnetic powder is preferably 20 μm or less, more preferably 5 μm or less. If the particle size of the magnetic powder is larger than 150 μm, it will be difficult to disperse uniformly throughout the phosphorus recovery material, which is not preferable.

The phosphorus recovery material of the present invention has a free silicon dioxide content of 20% by mass or less, preferably 5% by mass or less. Patent Document 3 describes a phosphorus recovery material in which magnetic powder is added to a phosphorus recovery material containing silicon dioxide together with calcium silicate hydrate (CSH), and this phosphorus recovery material is produced by a reaction with phosphorus. It is intended to increase the phosphorus recovery effect by expanding the surface area of HAP by the uneven structure and porous structure of silicon dioxide, but since this silicon dioxide is not directly involved in the formation of HAP, Higher amounts reduce the phosphorus content in the phosphorus recovery.

For example, in the phosphorus recovery material of Patent Document 3, calcium is added to an alkaline aqueous solution of silicate (sodium silicate aqueous solution, etc.), magnetic powder is added before or after or at the same time, hydrochloric acid is added to adjust the pH, and calcium silicate is added. It is manufactured by a process that produces hydrates (CSH). The silicon dioxide content of the phosphorus recovery material produced by such pH adjustment is approximately 23% by mass to 28% by mass, and contains a large amount of silicon dioxide, about 1/4 of the total amount of the phosphorus recovery material. Since this silicon dioxide is not a component that reacts with phosphorus to form HAP, a large amount of silicon dioxide reduces the phosphorus content of the recovered material.

The phosphorus recovery material of the present invention produces as little free silicon dioxide as possible without pH adjustment such as the addition of hydrochloric acid when producing calcium silicate hydrate (CSH) by the reaction of sodium silicate and calcium. Therefore, the phosphorus recovery material of the present invention has a low content of free silicon dioxide. For example, in the phosphorus recovery material of the present invention, when the Ca/Si molar ratio of CSH is 0.8, Si is slightly larger than Ca, so the content of free silicon dioxide may be 20% by mass. When the Ca/Si molar ratio is in the range of 1.0 to 1.5 or less , the content of free silicon dioxide is generally 5 mass % or less.

〔Production method〕
The phosphorus recovery material of the present invention is obtained by adding a sodium silicate solution to a mixed slurry of slaked lime or quicklime and magnetic powder, preferably by adding the sodium silicate solution little by little, without adjusting the pH, and producing calcium silicate hydrate (CSH ) can be produced by generating According to this method, it is possible to produce a phosphorus recovery material in which the amount of free silicon dioxide is remarkably small and the magnetic powder is uniformly dispersed.

Furthermore, according to the method of adding a sodium silicate solution to a mixed slurry of slaked lime or quicklime and magnetic powder to form calcium silicate hydrate, the calcium silicate hydrate is produced while the magnetic powder is dispersed. Since the magnetic powder is incorporated into the structure of the hydrate, it is possible to obtain a phosphorus recovery material in which the outflow amount of the magnetic powder during magnetic separation is remarkably small.

As described in Patent Document 3, in a method in which a sodium silicate solution is added to the lime slurry and magnetic powder is added before and after the addition, calcium silicate hydrate (CSH) is formed before the magnetic powder is sufficiently dispersed. is generated, and the magnetic powder is not sufficiently incorporated into the calcium silicate hydrate (CSH), so the outflow of the magnetic powder tends to increase during magnetic separation.

In addition, in the production method of Patent Document 3, after adding slaked lime or the like to an alkaline aqueous solution of silicate, hydrochloric acid is added to adjust the pH to 5 to 12, preferably around 10, to generate silicon dioxide. Since such pH adjustment increases the amount of free silicon dioxide, such pH adjustment is not performed in the production method of the present invention. In the production method of the present invention, a sodium silicate solution is added to a mixed slurry of slaked lime or quicklime and magnetic powder, preferably the sodium silicate solution is added little by little to produce calcium silicate hydrate without adjusting the pH. It is possible to obtain a phosphorus recovery material having a free silicon dioxide content of less than 5% by mass.

The phosphorus recovery material of the present invention contains calcium silicate hydrate (CSH) as a main component, and the CSH has good reactivity with phosphorus, so that the phosphorus recovery rate can be increased. Specifically, for example, a phosphorus recovery rate of 50% by mass or more, preferably 55% by mass or more can be obtained.

The phosphorus recovery material of the present invention is a phosphorus recovery material for magnetic separation containing calcium silicate hydrate (CSH) and magnetic powder. Contains from mass % to 42 mass %. By performing magnetic separation on the phosphorus recovery material of the present invention, the processing time can be greatly reduced compared to general sedimentation separation.

In the phosphorus recovery material of the present invention, calcium silicate hydrate (CSH) is produced in the presence of magnetic powder without adjusting the pH . Within the range of 0 to 1.5 , the amount of slaked lime contained in the phosphorus recovery material is 2% by mass or less, and the outflow rate of magnetic powder during magnetic separation can be suppressed to 20% by mass or less.

In addition, the phosphorus recovery material of the present invention has a remarkably low free silicon dioxide content, specifically, a free silicon dioxide content of 5% by mass or less, so relatively calcium silicate hydration The content of substances (CSH) increases, and the phosphorus recovery effect can be enhanced.

Since the phosphorus recovery material using the phosphorus recovery material of the present invention has a high citric acid content, it can be used as a phosphate fertilizer.

The production method of the present invention does not adjust the pH after adding the sodium silicate solution to the mixed powder slurry of slaked lime or quicklime and magnetic powder, so the processing operation is easy and the amount of free silicon dioxide produced is small. .

A graph showing the relationship between the amount of magnetic powder added and the phosphorus recovery rate. A graph showing the relationship between the amount of magnetic powder added and the outflow rate of magnetic powder. A graph showing the relationship between the Ca/Si molar ratio and the outflow rate of the magnetic powder.

Examples of the present invention are shown below. In addition, % of addition amount or content is mass %.
[Example 1: Preparation of sodium silicate solution]
A sodium silicate solution was prepared by dissolving amorphous silica in an aqueous sodium hydroxide solution. Table 1 shows the conditions for producing the sodium silicate solution. The amounts of NaOH and amorphous silica shown in Table 1 were mixed with water to form a suspension, and the liquid volume was adjusted to 1 kg. , reacted for 1 hour to prepare level 1 to level 4 sodium silicate solutions. The amorphous silica used contained 47.7% by mass of SiO ₂ and 49.7% by mass of water.
The Level 1 solution did not become completely clear after heating for 1 hour and was very viscous. It was completely dissolved when heated for 1.5 hours. Level 2 was completely dissolved at 80°C for 1 hour, but the viscosity was very high. Levels 3 and 4 both dissolved completely and had low viscosity. The solutions of levels 1 and 2 have a high Si/Na molar ratio and are therefore advantageous as silicic acid sources for CSH synthesis. board.

[Example 2: Production of phosphorus recovery materials A1 to A6]
Slaked lime (manufactured by Yakusen Lime Co., Ltd., conforming to JIS R 9001:2006 special issue) and magnetic powder (magnetite: Fe ₃ O ₄ manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed to form a slurry. Next, 96 g of water was added to 67.5 g of the sodium silicate solution (Na ₂ SiO ₃ ) of level 3 prepared in Example 1 to dilute it to a sodium silicate solution of 49.5 mg-SiO ₂ /L. . This diluted sodium silicate solution was added little by little over 3 minutes at room temperature to the mixed slurry of slaked lime and magnetic powder so that the Ca/Si molar ratio was finally 1, and the reaction was continued for 1 hour from the start of the addition. let me During this time, stirring was continued using a stirring blade so that the inside of the reaction vessel was uniform. Thus, a phosphorus recovery material comprising m-CSH (Magnetic CSH: Magnetic CSH) in which CSH was generated in the presence of magnetic powder was produced. Phosphorus recovery materials (A1 to A6) with different contents of magnetic powder were produced. These production conditions are shown in Tables 2A1-A6.

[Example 3: Production of phosphorus recovery materials A7 to A11]
The amount of magnetic powder in the mixed slurry of slaked lime and magnetic powder was 5 g, and the amount of sodium silicate solution and the amount of dilution water were adjusted so that the Ca/Si molar ratio of CSH was 0.8 to 3.5. In the same manner as in Example 2, phosphorus recovery materials (A7 to A11) composed of magnetic CSH (m-CSH) produced by dispersing CSH in magnetic powder were produced. These production conditions are shown in Tables 2A7-A11. The content of slaked lime was obtained by the method (glycerin-alcohol method (method B)) defined in the method for determining free calcium oxide in the standard test method of the Japan Cement Association (JCAS, 1997). At this time, 50 mL of the slurry was suction-filtered for the sample used for the analysis, washed with the same amount of ethanol (50 mL) as the slurry, dried at 150° C. for 3 hours, pulverized well, and subjected to the test. The slaked lime content of each phosphorus recovery material is shown in Table 2A7-A11 and A4 where the Ca/Si molar ratio of CSH is 1.

[ Comparative Example : Production of phosphorus recovery materials B1 to B8]
After generating CSH in the same manner as in Examples 2 and 3 except that the same slaked lime as in Example 2 was used and a slurry containing no magnetic powder was used in advance, a predetermined amount of magnetic powder was added and the magnetic powder was mixed. Phosphorus recovery materials (B2 to B8) made of CSH were produced. These manufacturing conditions are shown in Table 2. Table 2 shows a sample of CSH with a Ca/Si molar ratio of 1, which was not mixed with magnetic powder, as B1.

[Comparative Examples: C1, C2]
Based on Examples 2 and 5 of Patent Document 3, an aqueous sodium silicate solution (water glass) was used as a raw material, and the same magnetite (Fe ₃ O ₄ ) manufactured by Fuji Film Wako Pure Chemical Industries, Ltd. as in this example was used, and the following procedures were performed. prepared a phosphorus recovery material containing magnetic powder. A 1.6N NaOH aqueous solution and magnetic powder were added to water glass, and after stirring well, slaked lime was added and the mixture was stirred well at 500 rpm for 3 minutes. Thereafter, 2.9 mol/L hydrochloric acid was added at a rate of 10 mL/min up to pH 12.5 and 1 to 2 mL/min up to pH 10.5 to adjust the pH to finally pH 10.5±1. In this manner, phosphorus recovery materials (C1 and C2) having different amounts of magnetic powder were produced. Production conditions are shown in Tables 2C1 and 2C2.

[Example 5: Measurement of the amount of free _SiO2 ]
For each of the phosphorus recovery materials A2, A4, A6, A7, A10, B1, B3, B4, B7 and C1, C2 in Table 2, the content of free silicon dioxide was measured according to the following procedure.
2M hydrochloric acid was added to the phosphorus recovery material to elute silicon dioxide. If hydrochloric acid is added as it is, silica gel will precipitate. CaCl ₂ .2H ₂ O was added to the solution and slurried with a small amount of water. Then, the slurry was washed into a 200 mL beaker with about half of 200 mL of 2M hydrochloric acid prepared in advance, and the remaining 2M hydrochloric acid was added and stirred for 10 minutes. Immediately after stirring, the mixture was filtered and sucked (Advantech Toyo Co., Ltd. No. 5C filter paper was used), the filter paper was placed in a platinum crucible and incinerated, and the weight was measured after ignition at 1000°C. After igniting and measuring the weight, add 1 to 2 drops of (1+5) sulfuric acid to moisten the solid content in the platinum crucible, add 5 mL of hydrofluoric acid, heat and evaporate, and heat again at 1000 ° C. It was heated and weighed. The content (%) of free silicon dioxide was determined by the formula: [(Weight after ignition--Weight after ignition after addition of hydrofluoric acid)/amount of sample taken].times.100. Table 2 shows the results.

[Example 6: Phosphorus recovery test]
Using 5 L of simulated waste water (KH ₂ PO ₄ : 0.392 g/L, NH ₄ Cl: 1.89 g/L), each phosphorus recovery material (A1 to A11, B1 to B8, C1, C2) were added to the simulated effluent. As comparative samples, a phosphorus recovery test was conducted by adding slaked lime alone and a mixed sample of slaked lime and magnetic powder to the simulated waste water. Slaked lime alone and mixed samples of slaked lime and magnetic powder were thoroughly stirred with a small amount of water to form a slurry, and then added to the simulated waste water. After the addition, the mixture was allowed to react at room temperature for 1 hour. After the reaction, magnetic separation was performed to examine the phosphorus removal rate and phosphorus recovery rate. These results are shown in Table 3. FIG. 1 shows the relationship between the amount of magnetic powder added and the phosphorus recovery rate. Similarly, the relationship between the amount of magnetic powder added and the outflow rate of magnetic powder is shown in FIG. FIG. 3 shows the relationship between the Ca/Si molar ratio and the outflow rate of the magnetic powder.

Magnetic separation was carried out by putting a cylindrical neodymium magnet with a diameter of 30 mm and a thickness of 15 mm (maximum magnetic flux density of 0.5 T) in a polyethylene bag with a thickness of 0.04 mm into this solution and moving it slowly while immersing it for about 20 seconds. It was carried out by pulling up from the liquid. This operation was repeated three times for samples containing magnetic powder. The collected material was transferred onto a filter paper, filtered by suction, and then dried at 100° C. until it had a constant weight.
Since the comparative samples (B1 and D1) containing no magnetic powder could not be subjected to magnetic separation, the sediment was filtered by suction after the phosphorus recovery reaction, and dried at 100° C. to a constant weight.

Suspended solids (SS) and phosphorus recovery were determined as follows. About 250 to 300 ml of the liquid after magnetic separation (hereinafter referred to as effluent) was uniformly divided into two beakers. . Add (1 + 1) hydrochloric acid to the other fractionated liquid to adjust the pH to 1, filter this with the above No. 5B filter paper, determine the phosphorus concentration (total amount of phosphorus in the effluent), The P recovery rate (%) was determined by the formula (total amount of phosphorus/initial amount of phosphorus)×100.

The phosphorus removal rate was obtained by suction-filtrating the effluent water after magnetic separation with the above No. 5B filter paper, analyzing the phosphorus in the filtrate, and calculating the formula (1 - amount of phosphorus in filtrate/initial amount of phosphorus) x 100. The P removal rate (%) was determined by
The magnetic powder recovery rate (%), which is an index of magnetic powder leakage, was obtained by the formula (1-magnetic powder concentration in outflow water/initial magnetic powder concentration)×100. The initial magnetic powder concentration is the magnetic powder concentration before magnetic separation.

As a method for analyzing each component, the total amount of phosphoric acid (T-P ₂ O ₅ ) and citric acid (C-P ₂ O ₅ ) in the material collected by suction filtration and the material collected by magnetic separation were analyzed by the fertilizer analysis method. Analyzed by the prescribed ammonium vanadomolybdate method.

Phosphorus in the filtrate after suction filtration to determine the phosphorus removal rate and in the effluent water was analyzed according to the molybdenum blue spectrophotometry method specified in the standard (JIS K 0102 "Factory wastewater test method"), and the effluent water SS ( Suspended solids) was analyzed for suspended solids specified in the standard (JIS K 0102 "Factory wastewater test method"). Regarding the magnetic powder concentration, assuming that the dissolved iron in iron is zero, the suspended components after the SS analysis are decomposed with aqua regia, and the diluted solution is subjected to the Fe frame specified in the standard (JIS K 0102 "Factory wastewater test method"). Analyzed by atomic absorption spectroscopy.

As shown in Tables 2 and 3, the phosphorus recovery materials ( A3 to A6, A8 to A10 ) of the present invention have free The silicon dioxide content is 5% by mass or less, and the phosphorus recovery rate is 50% or more, preferably 55% or more. On the other hand, the free silicon dioxide contents of Comparative Samples C1 and C2 were 28.5% by mass and 23.5% by mass, both exceeding 20% by mass, and the phosphorus recovery rate did not reach 30%.

Further, as shown in Tables 2 and 3, when the Ca/Si molar ratio of CSH is in the range of 0.8 or more to less than 3.5, the outflow amount of magnetic powder during magnetic separation is Although it is less than 35%, if the CSH is generated in the presence of magnetic powder and the Ca/Si molar ratio of the CSH is in the range of 1.0 or more to 1.5 or less, the content of the magnetic powder is 8% by mass or more (8.8% by mass or more for A3 to A10) , the outflow rate of the magnetic powder during magnetic separation is suppressed to 20% or less.

The phosphorus recovery material of the present invention has a maximum phosphorus recovery rate of 85.9%, and exhibits a high phosphorus recovery rate even when the magnetic powder content is clearly lower than that of the comparative samples D2 to D4. In Comparative Samples D2 to D4, only a small amount of recovered phosphorus adsorbed on the magnetic powder was pulled up. There is little benefit from Among Samples A2 to A10 of the present invention, even Sample A2, which has the lowest magnetic powder content, has a remarkably low SS content in the outflow water, which is about 50% of that of Comparative Sample D2. %, and roughly half of the phosphorus is recovered. Thus, the phosphorus recovery material of the present invention has a much higher magnetic separation effect than Comparative Samples D2-D4.

As shown in Table 3, the total amount of phosphoric acid (T-P ₂ O ₅ ), the amount of citric acid (C-P ₂ O ₅ ), and the ratio of the amount of citric acid to the total amount of phosphoric acid ( C/T-P), the C-P ₂ O ₅ of samples A3 to A5 of the present invention, excluding A6, which has a high magnetic powder content, is 15.0, the standard for by-product phosphate fertilizers stipulated by the Fertilizer Regulation Law. % or more satisfied.

As shown in Table 3 and FIG. 2, the magnetic powder concentration in the effluent of the phosphorus recovery material of the present invention is as low as less than 20 mg/L, except for A6, and does not change significantly. On the other hand, in Comparative Samples D2 to D4, when the amount of magnetic powder is large, the concentration of magnetic powder in the outflow water also increases. As described above, the phosphorus recovery material containing the magnetic powder of the present invention has better magnetic separation performance than the comparative sample using slaked lime, so that the phosphorus recovery rate is high.

Also, as shown in Table 3 and FIG. 3, when the Ca/Si molar ratio of CSH is in the range of 0.8 to 1.5, the amount of SS in the effluent is 49.5 mg/L to 275 mg/L. Therefore, when the Ca/Si molar ratio is 3.5, the amount of SS in the effluent is 356 mg/L to 402 mg/L, which is a sharp increase of about 7 to about 2 times. The SS in the effluent is mainly magnetic powder, and by controlling the Ca/Si molar ratio of CSH in the range of 0.8 to 1.5, the outflow of magnetic powder can be greatly suppressed.

[Comparison of solid-liquid separation time]
In the phosphorus recovery test of Example 6, the time required for magnetic separation of the phosphorus recovery materials A1 to A11, the time required for sedimentation separation of B1, and the time required for suction filtration of B1 were compared. The magnetic separation of the phosphorus recovery materials A1 to A11 was carried out, as shown in Example 6, by immersing a cylindrical neodymium magnet in the solution after reaction for about 20 seconds and pulling it out of the solution, which was repeated three times. This operation (20 seconds x 3 times = 1 minute) was defined as the time required for magnetic separation. On the other hand, for the phosphorus recovery material B1, the sedimentation separation time and the suction filtration time were measured, and the time required to filter all 5 L of the solution was taken as the required time. Suction filtration was performed using Advantech Toyo Co., Ltd. No. 5B filter paper (110 mm diameter) was used.
The suction filtration of B1 took 17 minutes to filter all 5 L of solution. In addition, when solid-liquid separation is performed with a filter cloth or the like by gravity settling, filtration is performed after gravity settling (concentration). Depending on the particle size, some CSH settles in about 5 minutes, while others continue to settle even after 30 minutes. The required time was 30 minutes. On the other hand, magnetic separation enables solid-liquid separation without requiring a sedimentation time, and the sedimentation time is 0 minutes. The results are shown in Table 4.

As shown in this result, the processing time for solid-liquid separation by magnetic separation in A1 to A11 is about 1/47 of the processing time for B1, and the solid-liquid separation time can be greatly shortened. By the way, assuming that the flow rate of wastewater is 250 L/h (= 4.2 L/min), the hydraulic retention time (HRT) in the solid-liquid separation process is calculated as 47 minutes for solid-liquid separation in B1, about 196 L of volume is required for total processing. If magnetic separation is performed at the same flow rate, the HRT is 1 minute, so if there is a volume of about 4 L, the same treatment can be performed. Thus, the advantage of shortening the solid-liquid separation time is very large. Even if the sedimentation time of B1 is ignored, the solid-liquid separation time of A1 to A11 is 1/17 of B1, and the solid-liquid separation time is sufficiently short.

式[１]において、Ｆｍ：磁性粒子にかかる磁気力、Ｖ：分離対象物質の体積、μ₀：真空の透磁率、χ_ｐ、χ_ｆ：それぞれ粒子と流体（水）の磁化率、Ｈ：磁界度、grad Ｈ：磁気勾配である。
マグネタイトのような強磁性体では、粒子に働く磁気力は水に働く磁気力よりも格段に大きいため水に働く磁気力は無視できる。さらに、χ_ｐは一定では無いので、「磁化の強さ」をＭとして表すことによって、強磁性粒子に働く磁気力は粒子の体積と磁化の強さと磁気勾配の積から次式[２]のように近似できる。

As a formula related to magnetic separation, the magnetic force when the substance to be separated is assumed to be spherical is represented by the following formula [1] (Watanabe "Magnetic Separation Mechanism and Application of Wastewater and Sewage Treatment”).

In formula [1], Fm: magnetic force applied to magnetic particles, V: volume of substance to be separated, μ ₀ : vacuum magnetic permeability, χ _p , χ _f : magnetic susceptibility of particles and fluid (water), respectively, H: Magnetic field intensity, grad H: Magnetic gradient.
In ferromagnetic materials such as magnetite, the magnetic force acting on particles is much larger than that acting on water, so the magnetic force acting on water can be ignored. Furthermore, since χ _p is not constant, by expressing the "strength of magnetization" as M, the magnetic force acting on the ferromagnetic particles is given by the following equation [2] from the product of the volume of the particles, the strength of magnetization, and the magnetic gradient: can be approximated as

As shown in the formula [2], it can be seen that the larger the particle size of the magnetic particles, the greater the magnetic force that acts. When this is applied to the results in Table 3, the phosphorus recovery materials (A2 to A6) of the present invention have a large volume V because the magnetic powder is incorporated into the structure of CSH, and the magnetic separation performance is high. The magnetic force applied is large). On the other hand, in Comparative Samples D2 to D4, since the magnetic powder was dispersed together with the slaked lime slurry, the magnetic force acting on the particles was reduced and the magnetic powder flowed out. Specifically, for example, the average particle diameter (median diameter) of the phosphorus recovery material of the present invention is 25 μm, and the average particle diameter of the magnetic powder is 2.5 μm. The volume ratio of formula [2] is 25 ³ /2.5 ³ =1000. On the other hand, the content of magnetic powder is 20/100=1/5, taking an A4 sample as an example. Therefore, assuming a constant magnetic field on the particles, the magnetic force is 1000/5=200 times higher in the phosphorus recovery material of the invention. As described above, the phosphorus recovery material of the present invention has a high magnetic separation effect because the magnetic powder is incorporated into the CSH.

Claims (4)

A magnetic powder containing calcium silicate hydrate and magnetic powder, wherein the Ca/Si molar ratio of the calcium silicate hydrate is 1.0 or more and 1.5 or less , and the content of the magnetic powder is 5% by mass or more . is incorporated in the calcium silicate hydrate, the content of free silicon dioxide is 5% by mass or less, and the content of slaked lime is 2% by mass or less, and the outflow amount of magnetic powder during magnetic separation is suppressed to 20% or less . The content of calcium silicate hydrate is 55% by mass or more and less than 95% by mass, the content of magnetic powder is 5% by mass or more and less than 45% by mass, and the phosphorus recovery rate is 50% or more . Phosphorus recovery material as described. A Ca/Si molar ratio of 1.0 or more by adding a sodium silicate solution to a mixed slurry of slaked lime or quicklime and magnetic powder to form calcium silicate hydrate without adjusting the pH while the magnetic powder is dispersed. ~1.5 or less, the content of the magnetic powder is 5% by mass or more, the magnetic powder is incorporated in the calcium silicate hydrate, and the content of free silicon dioxide is 5% by mass or less. A method for producing a phosphorus recovery material, comprising producing a phosphorus recovery material having a slaked lime content of 2% by mass or less . 4. The phosphorus recovery material according to claim 3, wherein a sodium silicate solution is added little by little to a mixed slurry of slaked lime or quicklime and magnetic powder to form calcium silicate hydrate while the magnetic powder is dispersed without adjusting the pH. manufacturing method.

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