JP2018171555A - Recycling method of phosphorus adsorbent in environmental water - Google Patents

Abstract

Kind Code: A1 The present invention solves the above-mentioned problems and regenerates a phosphorus adsorbent that can effectively adsorb phosphorus in environmental water, can be used in a column, and has the ability to adsorb heavy metals and the like. The present invention provides a method for reusing a phosphorus adsorbent, which can be repeatedly reused for adsorption and removal of phosphorus, heavy metals, and the like in environmental water. A method for reusing a phosphorus adsorbent of the present invention is a calcined carbonate compound containing CaO, wherein the content of CaO analyzed using the Rietveld method based on powder X-ray diffraction is 3.7 ≤ Desorption of adsorbed phosphorus, preferably with an eluent, from the phosphorus adsorbent that has adsorbed phosphorus by contacting the phosphorus adsorbent where x ≤ 13.5 (mass%) with environmental water containing phosphorus. or remove the surface by grinding, and the resulting regenerated phosphorus adsorbent is repeatedly brought into contact with environmental water containing phosphorus for reuse. [Selection figure] None

Description

  The present invention relates to a method for reusing a phosphorus adsorbent in environmental water, and in particular, regenerating a phosphorus adsorbent that is excellent in adsorption capacity for heavy metals in addition to phosphorus in environmental water such as rivers and lakes. The present invention relates to a method for reusing a phosphorus adsorbent used for adsorption and removal of phosphorus and heavy metals in water.

The “eutrophication”, which is a typical water pollution problem in lakes, represents a state where nutrients such as nitrogen and phosphorus are accumulated more than necessary and the concentration is high.
As eutrophication progresses, phytoplankton with nutrients such as nitrogen and phosphorus grows abnormally, causing not only mass production of sea lions and mass drowning of seafood, but also impacts on water supply, agricultural and industrial water, and marine resources. For example, there is a possibility of significant influence from the viewpoint of water use, and it is necessary to control phosphorus and nitrogen in lake water to appropriate concentrations.

Many methods of water purification technology for lakes and marshes have been developed and put into practical use.
These methods, for example, can be classified into inflow river countermeasures, in-lake countermeasures, and basin countermeasures, as shown in Table 1 below, which is published in the Ministry of Land, Infrastructure, Transport and Tourism's “Hydraulic Hydraulic and Water Quality Management Technologies”. Is possible.

  For example, a pollution load generated in a river basin flows into a lake through the river and affects the water quality of the lake. Therefore, if the pollution load can be removed in the river, it is considered effective for the conservation and improvement of the lake water quality. Is adopted.

However, as a weak point of the direct purification method, which is a countermeasure against inflow rivers (direct purification), there is a problem that it requires running costs such as operation of the purification device and replacement of sludge treatment media.
The direct purification methods include adsorption method, soil treatment method, vegetation purification method, etc., and the adsorption method attaches microorganisms to a support such as gravel and contacts the microorganisms with organic matter to oxidize the organic matter. Although there is a catalytic oxidation method, such a biological treatment method has problems such as a low removal rate of nitrogen and phosphorus, and a poor treatment stability.
The vegetation purification method and the soil purification method have problems such as requiring a large treatment area for treatment.

Treatment methods specialized in phosphorus can be broadly classified into biological treatment and physicochemical treatment depending on the difference in the underlying mechanism.
Biological treatment method is a promising treatment method because of its cost and simultaneous removal of BOD, nitrogen and phosphorus, but there is a problem of lack of stability of treatment, and future technology development Is expected.

Therefore, at present, physicochemical treatment is used to remove phosphorus from waste water.
Such physicochemical treatment includes coagulation sedimentation method, pressure flotation method, activated sludge method with flocculant addition, crystallization (contact) dephosphorization method, adsorption method, iron contact material phosphorus removal method, etc. A coagulation sedimentation method is used. Most of these physicochemical treatments are treatment methods using calcium salt, magnesium salt, or iron salt as a flocculant or adsorbent.
However, there are problems with the current physicochemical phosphorus removal methods in terms of cost, maintenance, etc., and future technological development is expected.

  The above coagulation sedimentation method using various metal salts such as calcium is generally used at present and has a high phosphorus removal performance and high reliability, while a large amount of sludge is generated. Have the disadvantages of poor concentration and dehydration, and high running costs.

In order to solve the above problem, it is not a method of directly adding and processing a powdery flocculant or adsorbent to the target system, but it can be used in a column. As a technique for reusing a column, for example, JP-A-2008-6404 (Patent Document 1) describes the removal of the phosphorus component in the phosphorus-containing wastewater in the treatment of the phosphorus-containing wastewater, which uses a specific composite metal hydroxide as an adsorbent for the phosphorus component, In each of the step of desorbing the phosphorus component from the composite metal hydroxide after adsorbing the phosphorus component and the step of regenerating the phosphorus component adsorption capacity of the composite metal hydroxide, the composite metal hydroxide is converted into a composite metal hydroxide after each step. On the other hand, it is disclosed that the washing process is performed until the pH of the washed water becomes 11 or less.
However, the above technique is not suitable for environmental water from the viewpoint of cost.

Furthermore, environmental water such as rivers and lakes may contain heavy metals, metalloids such as arsenic, selenium, and boron, and halogens such as fluorine, in addition to phosphorus. It is also desirable to have adsorption capacity for heavy metals.
Here, in addition to heavy metals, metalloids such as arsenic, selenium, and boron and halogens such as fluorine are collectively referred to as “heavy metal”.
In addition, quick lime is widely used as a calcium salt in the coagulation sedimentation method, crystallization (contact) dephosphorization method, and adsorption method. However, quick lime has a certain degree of solubility, so the adsorbent is dissolved in the solution. It is not suitable for repeated use.Furthermore, quick lime exhibits adsorption performance for insolubilization of heavy metals such as lead and cadmium, but it has low adsorption capacity for metalloids such as arsenic and selenium. Hokkaido Institute of Health Rep. Hokkaido Inst. Pub. Health, 62, 35-41 (2012) ”(Non-patent Document 1) and“ Niigata Prefectural Institute of Health and Environmental Science Vol. 25, 93-95 (2010) ”( Non-patent document 2).

  Accordingly, in view of the above situation, it is desirable that a low-cost phosphorus adsorbent that can be used and reused in a column and that has adsorption ability not only for phosphorus but also for heavy metals and the like can be regenerated and reused. ing.

Japanese Patent Laid-Open No. 2008-6404

Hokkaido Institute of Public Health Rep. Hokkaido Inst. Pub. Health, 62, 35-41 (2012) Annual report of Institute for Health and Environmental Sciences, Niigata Volume 25 93-95 (2010)

  An object of the present invention is to regenerate a phosphorus adsorbent that can solve the above-mentioned problems, can effectively adsorb phosphorus in environmental water, can be used in a column, and has an adsorption capacity for heavy metals and the like. Another object of the present invention is to provide a method for reusing a phosphorus adsorbent that can be reused for adsorption and removal of phosphorus, heavy metals, and the like repeatedly in environmental water.

  The present invention was specified based on the knowledge that the CaO content in the calcined carbonate compound containing CaO is closely related to the adsorption removal rate of phosphorus in the environmental water and the adsorbent residual rate after adsorbing phosphorus. It has been found that a phosphorus adsorbent can be reused by applying a conventional method of desorbing phosphorus, heavy metals, etc., and has arrived at the present invention.

(1) The method for reusing a phosphorus adsorbent of the present invention is a calcined carbonate compound containing CaO, and the content of CaO analyzed using the Rietveld method by powder X-ray diffraction is 3.7 ≦ x Regenerated phosphorus adsorption obtained by desorbing the adsorbed phosphorus from the phosphorus adsorbent that adsorbs phosphorus by bringing the phosphorus adsorbent ≦ 13.5 (mass%) into contact with environmental water containing phosphorus This is a method for reusing a phosphorus adsorbent, wherein the agent is repeatedly brought into contact with environmental water containing phosphorus and reused.
(2) In the method for reusing a phosphorus adsorbent of (1) above, the phosphorus adsorbent adsorbing phosphorus further adsorbs heavy metals in the environmental water and desorbs the adsorbed heavy metals for reuse. It is characterized by doing.

(3) In the method for reusing a phosphorus adsorbent according to (1) or (2) above, the phosphorus adsorbent further contains a ferrous compound.
(4) The method for recycling a phosphorus adsorbent according to any one of (1) to (3) above, wherein the calcined carbonate compound is calcined dolomite.
(5) In the method for reusing a phosphorus adsorbent as described in any one of (1) to (4) above, adsorbed phosphorus and heavy metals are removed by eluent or ground to remove. It is characterized by doing.

  The method for reusing a phosphorus adsorbent of the present invention can repeatedly use a phosphorus adsorbent that is excellent in adsorption removal performance of phosphorus and heavy metals in environmental water, and rivers and lakes satisfy environmental standard values. It is possible to repeatedly exhibit an effective effect, and by applying a known desorption method such as phosphorus or heavy metal, it is possible to desorb adsorbed phosphorus or heavy metal, which can be reused. . Therefore, it becomes economically useful.

In addition, the method of using the phosphorus adsorbent of the present invention does not depend on the difference in composition depending on the production area of the dolomite ore used as a raw material, the setting of the baking conditions such as the baking temperature, etc., and the phosphorus adsorption having excellent phosphorus adsorption performance The agent can be regenerated and reused, and can be reused in the column.
Furthermore, even if the phosphorus adsorbent is reused, the phosphorus adsorption performance is effectively exhibited, and the adsorbent residual rate after phosphorus adsorption can be kept high.

It is a figure which shows the relationship between CaO content in baking dolomite, phosphoric acid adsorption removal rate, and CaO content in baking dolomite, and adsorption agent residual rate. It is the elements on larger scale of FIG. 1 in case CaO content is 2-16 mass%.

The present invention is illustrated by the following embodiments, but is not limited thereto.
The method for reusing a phosphorus adsorbent of the present invention is a calcined carbonate compound containing CaO, and the content of CaO analyzed using the Rietveld method by powder X-ray diffraction is 3.7 ≦ x ≦ 13. The phosphorus adsorbent obtained by desorbing adsorbed phosphorus from the phosphorus adsorbent that adsorbs phosphorus by bringing phosphorus adsorbent 5 (mass%) into contact with environmental water containing phosphorus, This is a method for reusing a phosphorus adsorbent that is repeatedly brought into contact with environmental water containing phosphorus. As a method for desorbing the adsorbed phosphorus, a chemical method such as desorption with an eluent or a physical method such as grinding the surface can be applied.
This makes it possible to efficiently recover phosphorus, heavy metals, and the like by repeatedly using the adsorbent.

  The phosphorus adsorbent used in the present invention quantifies the CaO phase contained in the calcined carbonate compound by having a correlation between the content of the CaO phase in the calcined carbonate compound and the phosphorus adsorption removal rate, By setting the content within the above range, the calcined carbonate compound adsorbs excellent phosphorus, heavy metals, etc. regardless of the difference in composition depending on the production area of the carbonate compound as the raw material and the setting of firing conditions such as the firing temperature. It is an adsorbent having performance and an excellent adsorbent residual rate after adsorption of phosphorus, heavy metals and the like.

The calcined carbonate compound is not particularly limited as long as it contains CaO. For example, calcined limestone and calcined dolomite can be used, but calcined dolomite is preferably used from the viewpoint of cost and environmental load.
The raw material dolomite used as a raw material of a baked dolomite is not specifically limited, Arbitrary raw material dolomite which can be obtained on the market can be used, and a production area and a composition of raw material dolomite are not ask | required.

Dolomite has a double salt structure in which the molar ratio of limestone CaCO ₃ and magnesite MgCO ₃ is 1: 1, and Ca ²⁺ ions and Mg ²⁺ ions are alternately layered with CO ₃ ^2- groups in between. In general, the magnesium carbonate is 10 to 45% by mass.
Dolomite is present in large quantities in Japan, and an adsorbent using dolomite is advantageous from the viewpoint of cost and environmental load.

Dolomite is calcined, and the following formula (1):
CaMg (CO ₃ ) ₂ → MgO + CaO + 2CO ₂ (1)
The decomposition reaction represented by is shown.
It is considered that CaO is formed by the thermal decomposition by firing dolomite and exhibits adsorption performance such as phosphorus and heavy metals.

The phosphorus adsorbent used in the present invention has a CaO content of 3 by analyzing the content of the CaO phase in the calcined carbonate compound, for example, calcined dolomite obtained by calcining dolomite, by the Rietveld method using powder X-ray diffraction. If it is a calcined dolomite that satisfies .ltoreq.7.ltoreq.x.ltoreq.13.5 (mass%), preferably 12.1.ltoreq.x.ltoreq.13.5 (mass%), it exhibits excellent phosphorus adsorption performance.
When the CaO content is less than 3.7% by mass, the phosphorus adsorption performance decreases, and when it is more than 13.5% by mass, the adsorbent residual rate after phosphorus adsorption decreases.

Here, the phosphorus adsorption mechanism by calcination dolomite is guessed.
Specifically, dolomite is thermally decomposed in two stages by the following thermal decomposition reaction to produce CaO.
CaMg (CO ₃ ) ₂ → CaCO ₃ + MgO + CO ₂ about 750-800 ° C.
CaCO ₃ + MgO + CO ₂ → CaO + MgO + 2CO ₂ About 800 over −1000 ° C.
In addition, the produced CaO reacts with phosphorus, and hardly soluble hydroxyapatite is produced according to the following reaction formula.
5Ca ²⁺ + 4OH ⁻ + HPO ₄ ²⁻ → Ca ₅ (OH) (PO ₄ ) ₃ + 3H ₂ O
Here, when comparing the solubility of Ca (OH) ₂ which is considered to be formed by hydration of CaCO ₃ and CaO, Ca (OH) ₂ is higher by about two orders of magnitude (25 ° C .: CaCO ₃ ... 0.015 g / l, Ca (OH) ₂ ... 1.7 g / l). The higher the degree of firing, the higher the proportion of CaO phase generated, and at the same time the proportion of Ca ²⁺ present in the solution.
Therefore, it is considered that under the firing conditions with a low degree of firing, for example, with a low firing temperature or a short firing time, the amount of CaO produced is not sufficient, and the reaction does not proceed and hydroxyapatite is not produced.

Hydroxyapatite, which is considered to be produced by reaction of phosphorus and calcium, is a hardly soluble compound, while CaO has a certain degree of solubility. For this reason, when an excessive amount of CaO phase is present in the phosphorus adsorbent with respect to the inflowing phosphorus load, it is considered that dissolution of excess CaO phase that does not react with phosphorus occurs.
When the degree of firing is too high, for example, it is considered that the phosphorus adsorbent residual rate decreases under firing conditions where the firing temperature is high or the firing time is long.

In the phosphorus adsorbent, it is thought that only the vicinity of the surface of the phosphorus adsorbent can contribute to phosphorus adsorption when it comes into contact with environmental water, and the degree of firing is increased until CaO is generated inside the phosphorus adsorbent. Even so, it is considered that these CaOs can hardly contribute to phosphorus adsorption.
Therefore, it is thought that the baked dolomite whose CaO content exceeds 13.5 (mass%) is not suitable for use in a column, for example.

In general, there is a method of measuring the degree of firing of pyrolyzed minerals by TG-DSC (thermogravimetry / differential scanning calorimetry), but in the case of dolomite, two peaks, Ca and Mg, are measured in a nitrogen atmosphere. Are not suitable for quantification of each component contained in the baked dolomite.
On the other hand, unlike the TG-DSC method, the Rietveld method based on powder X-ray diffraction can accurately analyze the amount of CaCO ₃ phase, MgO phase, and CaO phase contained in the calcined dolomite. Thus, it is possible to accurately determine the CaO phase produced in the process.

The phosphorus adsorbent used in the present invention can adsorb and remove not only phosphorus but also heavy metals from environmental water.
Here, examples of heavy metals contained in “heavy metal etc.” that can be adsorbed and removed include one or more kinds of chromium, lead, arsenic, cadmium, etc., and examples of semimetals include arsenic, selenium. Boron and the like can be exemplified, and examples of the halogen include chlorine and fluorine. However, the halogen is not limited to these heavy metals, metalloids and halogens.

A suitable phosphorus adsorbent for use in the present invention is a phosphorus adsorbent obtained by further adding a ferrous compound to a calcined carbonate compound such as the calcined dolomite. By containing the ferrous compound in the adsorbent, the adsorption removal rate of heavy metals and the like can be further improved.
Examples of the ferrous compound mixed with the calcined carbonate compound include ferrous chloride and ferrous sulfate.

The content of the residual CaO phase is preferably 5: 5 by mass ratio with respect to the calcined carbonate compound such as calcined dolomite whose content of the residual CaO phase is 3.7 ≦ x ≦ 13.5 (mass%). ~ 9: 1, more preferably 9: 1.
By containing a ferrous compound in such a content range, it is possible to more effectively adsorb and insolubilize heavy metals etc. by its reduction, coprecipitation, adsorption action, heavy metals etc. from environmental waters such as rivers and lakes, It becomes possible to remove more effectively.

Moreover, as a manufacturing method of the phosphorus adsorbent used for this invention, when baking the carbonate compound containing Ca, content of the CaO phase in the baking carbonate compound analyzed using the Rietveld method by powder X-ray diffraction However, it can manufacture by baking so that it may become 3.7 <= x <= 13.5 (mass%).
As described above, examples of the carbonate compound containing Ca as a raw material include limestone and dolomite.

  The temperature at which the carbonate compound is fired is not particularly limited, and can be usually fired at a temperature at which dolomite is fired to produce fired dolomite, for example, 650 to 1000 ° C., but the content of the CaO phase is 3. Firing is performed in consideration of the firing time so that 7 ≦ x ≦ 13.5 (mass%). If the content of the CaO phase in the fired carbonate compound after firing is within the above range, the firing time is not limited.

  For example, in the process of calcining dolomite as an example of a carbonate compound, by selecting a calcined dolomite with a CaO phase content in a range of 3.7 ≦ x ≦ 13.5 (mass%), The phosphorus adsorbent used in the present invention can be obtained.

  The phosphorus adsorbent is adjusted so that the content of the CaO phase in the calcined carbonate compound, for example, calcined dolomite, using the Rietveld method by powder X-ray diffraction is 3.7 ≦ x ≦ 13.5 mass%) By doing so, it is possible to easily manage the quality of the phosphorus adsorbent so as to have excellent adsorption performance such as phosphorus and heavy metals.

Preferably, by adding a ferrous compound to the calcined dolomite that is the phosphorus adsorbent thus obtained, not only phosphorus but also heavy metals can be adsorbed more effectively simultaneously. It becomes possible to produce a phosphorus adsorbent used in the above.
Examples of the ferrous compound include ferrous sulfate and ferrous chloride.
As described above, the composition is preferably 5: 5 to 9: 1 in a mass ratio with respect to the calcined dolomite in which the content of the residual CaO phase is 3.7 ≦ x ≦ 13.5 (mass%). More preferably, the mixture is mixed at 9: 1, and the mixing method is not particularly limited as long as it can be uniformly mixed.

By bringing the phosphorus adsorbent used in the present invention into contact with environmental water such as rivers and lakes, phosphorus contained in environmental water can be removed, and heavy metals contained in environmental water can also be adsorbed and removed. It becomes possible.
The method for contacting the phosphorus adsorbent with the environmental water is not particularly limited, and any known method can be applied. For example, the column is filled with the phosphorus adsorbent and the column is filled with a river or a lake. Examples thereof include a method of passing environmental water using a pump or the like, a method of charging and stirring a phosphorus adsorbent into environmental water such as a river or a lake. For example, when it is introduced into environmental water such as a river or a lake, it is possible to add a flocculant and collect it by a solid-liquid separation method.

By using the column filled with a phosphorus adsorbent, it is possible to continuously remove phosphorus, heavy metals, and the like from the environmental water, thereby saving space.
A plurality of the columns can be used, and the columns can be used directly or in parallel.

  The phosphorus adsorbent used in the present invention can be applied depending on the use, whether it is used in powder form or in bulk form. For example, those that are packed in a column or laid on the riverbed maintain a solid state. In order to be expected, a lump-like one is preferably used.

  The contact ratio between the phosphorus adsorbent and the environmental water can be arbitrarily set so that the solid-liquid ratio reaches the environmental standard, which is a target value that depends on each river or lake. Although it does not specifically limit as temperature at the time of making environmental waters, such as a river and lakes, etc. containing phosphorus etc. contact, For example, the range of 0-50 degreeC can be illustrated.

The pH of the reaction system when bringing the phosphorus adsorbent used in the present invention into contact with environmental water such as rivers and lakes containing phosphorus is not particularly limited, but is preferably about pH 10 to 13.
Since the phosphorus adsorbent used in the present invention can make the pH of the aqueous solution alkaline, for example, heavy metals such as cadmium can be precipitated and removed in the form of hydroxide, and lead, arsenic, selenium, It becomes possible to effectively adsorb and remove heavy metals such as chromium.

After the phosphorus adsorbent having the above structure adsorbs phosphorus, heavy metal, etc., a known desorption method, for example, a chemical desorption method such as a desorption method using an eluent or the like, phosphorus, etc. are adsorbed on the surface. By applying a physical desorption method such as grinding the surface of the phosphorus adsorbent, it is possible to remove adsorbed phosphorus, heavy metals, and the like.
Regenerated phosphorus adsorbent that effectively adsorbs phosphorus, heavy metals, etc. contained in environmental water by repeatedly contacting the phosphorus adsorbent regenerated by these chemical and physical desorption methods with environmental water containing phosphorus. Can be reused as

Specifically, as an example of a chemical desorption method, a phosphorus adsorbent that adsorbs phosphorus, heavy metals, etc. is washed and eluted with an eluent to elute and desorb adsorbed phosphorus, heavy metals, etc. There is a way to play it so that it can be reused.
For example, phosphorus and heavy metals adsorbed on the adsorbent can be eluted using inorganic acids, organic acids, organic solvents, or inorganic solvents. Examples of inorganic acids include hydrochloric acid, sulfuric acid, nitric acid, and organic acids. , Formic acid, acetic acid, oxalic acid, citric acid, inorganic solvents include sodium hydroxide solution, potassium hydroxide solution, sodium chloride solution, potassium chloride solution, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, etc. be able to.
The adsorbent after elution can be reused by being packed in a column after washing with pure water.

Further, as an example of the physical desorption method, there is a method in which the surface of a phosphorus adsorbent that adsorbs phosphorus, heavy metal, or the like is ground and regenerated so that it can be reused.
It is considered that phosphorus, heavy metals, etc. are adsorbed on the surface of the phosphorus adsorbent. Therefore, by surface grinding of the phosphorus adsorbent using means such as a ball mill and an automatic sieve, the surface of the phosphorus adsorbent is Make it a fresh surface.
As a result, the phosphorus adsorbent can be reused.

By applying the above chemical or physical desorption method, the phosphorus adsorbent can be reused many times, which is economically useful.
Thus, the phosphorus adsorbent regenerated by desorbing the adsorbed phosphorus and heavy metals has excellent adsorption removal performance for phosphorus and heavy metals in the environmental water, similar to the fresh phosphorus adsorbent. .

The invention is illustrated by the following examples and comparative examples.
(Examples 1-5 and Comparative Examples 1-12)
(1) Preparation of baked dolomite Using dolomite (production area: Tochigi (Kuzuu district), particle size: 3-7 mm), each baking time (5-300 minutes) shown in Table 2 below at a baking temperature of 800 ° C or 750 ° C. ) To prepare each baked dolomite. For comparison, unburned dolomite was also prepared. Hereinafter, calcined dolomite and uncalcined dolomite are referred to as calcined dolomite or the like.

(2) Powder X-ray diffraction and Rietveld analysis of each baked dolomite etc. Using a planetary mill, the average particle size of 50 ± 10 μm is obtained by using the planetary mill for the massive baked dolomite etc. obtained in (1) above. It grind | pulverized to a grade (300 rpm, 10 min), and powder, such as each baked dolomite, was used as the phosphorus adsorbent. Each obtained phosphorus adsorbent powder was subjected to powder X-ray diffraction and Rietveld analysis under the following conditions, and quantitative measurement of each phase shown in Table 2 was performed.

・ Powder X-ray diffraction measurement and Rietveld analysis conditions Equipment: PANalytical X'Pert Pro MPD
Rietveld analysis software: PANalytical High Score Plus
Measurement conditions: tube Cu-Kα, tube voltage 45 kV, current 40 mA
Divergence slit variable (12 mm)
Anti-scatter slit (incident side) None
Solar slit (incident side) 0.04 rad.
No light receiving slit
Anti-scatter slit (light receiving side) variable (12 mm)
Solar slit (light receiving side) 0.04 rad
Scanning range 2θ = 20 to 70 °,
Scanning step 0.008 °,
Counting time Adjusted so that the number of counts of the strongest line is 10000 ± 1000 cps Each measurement was considered to be successful when Goodness of fit ≦ 7, and the results are shown in Table 2 below.

(3) Preparation of simulated environmental water A Simulated environmental water A was prepared by blending the reagents shown in Table 3 below such that the various ions shown in Table 3 had the predetermined concentrations shown in Table 3.

(4) Phosphorus adsorption test (calculation of phosphorus adsorption removal rate and adsorbent residual rate)
To a 50 ml conical tube, each calcined dolomite having a composition shown in Table 2 obtained in (1) above (particle size 3 to 7 mm) and simulated environmental water A obtained in (3) above were fixed. It added so that liquid ratio (mass ratio) might be set to 1: 100, and it stirred for 30 minutes each.
Subsequently, suction filtration was performed using a 0.45 μm membrane filter, and the phosphorus concentration in the filtrate was quantified by ICP-AES (ICP emission spectroscopy, measuring apparatus: ARCOS FHX22 manufactured by SPECTRO), and the following formula 1 The adsorption removal rate was calculated. The results are shown in Table 4 and FIGS.
Further, the adsorbent residual rate after the adsorption test is calculated from the following formula 2, and the pH and oxidation-reduction potential (ORP) of the filtrate are calculated from a desktop pH meter manufactured by Horiba, Ltd .: F-73. (PH electrode: 9615S-10D, ORP electrode: 9300-10D). The results are also shown in Table 4 and FIGS.

Adsorption removal rate (%) = (Ci−Cf) / Ci × 100 (1)
Ci = Phosphate initial concentration in simulated environmental water A before adsorption test (mg / l)
Cf = phosphoric acid concentration (mg / l) in filtrate of simulated environmental water A after adsorption test
Adsorbent residual rate (%) = Af / Ai × 100 (2)
Ai = initial adsorbent mass (g) before adsorption test,
Af = mass of adsorbent after adsorption test (g)
However, the adsorbent weight Af after the adsorption test was only the weight remaining on the sieve with a notary mesh opening of 2.8 mm defined in JIS Z 8801-1-2000.

  When the calcined dolomite of Examples 1 to 5 (calcining time 60 to 100 minutes) having a CaO content of 3.7 to 13.5 (mass%) was used as the adsorbent, the phosphate adsorption removal rate and the adsorption The residual ratio of the agent was 98% or more. On the other hand, the calcined dolomite having the CaO content of Comparative Examples 1 to 7 was 0 to 2.6% by mass, and the phosphoric acid adsorption removal rate was not sufficient. It can be seen that calcined dolomite having a CaO content of 8 to 12 exceeding 13.5 (% by mass) had a sufficient phosphate adsorption removal rate, but the adsorbent residual rate was lowered.

  Further, each baked dolomite adsorbing phosphorus is washed with pure water, and then immersed in a 0.1 mol / l sodium carbonate solution and stirred to remove the adsorbed phosphorus and regenerate the regenerated phosphorus adsorbent. The phosphorus adsorption test was performed again. The results of the measured adsorption removal rate and adsorbent residual rate were substantially the same as those shown in Table 4.

  In addition, each baked dolomite that has adsorbed phosphorus is collected, and the surface of each baked dolomite that has adsorbed phosphorus is ground using an automatic sieving machine or ball mill means to remove the surface on which phosphorus is adsorbed. Then, the above phosphorus adsorption test was performed again on the regenerated phosphorus adsorbent with the adsorbent surface being a fresh surface. The results of the measured adsorption removal rate and adsorbent residual rate were substantially the same as those shown in Table 4.

(5) Phosphoric acid adsorption test under conditions where the solid-liquid ratio was changed Using the calcined dolomite of Examples 1 and 3 and the simulated environmental water A of (3), the solid-liquid ratio (mass ratio) was 1: The phosphorus adsorption test similar to the above (4) was carried out by changing to 50, 1:30, 1:20, and 1:10.
The results are shown in Table 5 below. The phosphate ion concentration is the total phosphorus concentration.

The target concentration of phosphorus reduction in rivers and lakes varies depending on each river and lake.
For example, the target value for total phosphorus in the Lake Water Quality Conservation Plan for Kasumigaura (6th period) is set at 0.084 mg / l, and phosphorus adsorption is performed so that the solid-liquid ratio meets the standard. It is possible to charge the agent.
In Table 5, the target value in Kasumigaura is exemplified as an example of the phosphorus reduction target value. However, the amount of phosphorus adsorbent added is not limited to Kasumigaura and can be arbitrarily set according to the target standard of rivers and lakes. Thus, the phosphorus concentration can be reduced to the target concentration.

  Further, each baked dolomite adsorbing phosphorus is washed with pure water, and then immersed in a 0.1 mol / l sodium carbonate solution and stirred to remove the adsorbed phosphorus and regenerate the regenerated phosphorus adsorbent. The phosphorus adsorption test was performed again. The results of the measured adsorption removal rate were substantially the same as those shown in Table 5.

  In addition, each baked dolomite that has adsorbed phosphorus is collected, and the surface of each baked dolomite that has adsorbed phosphorus is ground using an automatic sieving machine or ball mill means to remove the surface on which phosphorus is adsorbed. Then, the above phosphorus adsorption test was performed again on the regenerated phosphorus adsorbent having the fresh adsorbent surface. The results of the measured adsorption removal rate were substantially the same as those shown in Table 5.

(6) Phosphoric acid and arsenic adsorption test The phosphoric acid and arsenic adsorption test in the environmental water was carried out by preparing the following simulated environmental water B. Specifically, as simulated environmental water B, simulated environmental water B was prepared by blending the reagents shown in Table 6 below so that various ions shown in Table 6 had predetermined concentrations shown in Table 6.

In the phosphoric acid and arsenic adsorption test, each calcined dolomite having the composition shown in Table 2 obtained in (1) above (firing time 0, 60, 80, 100, 300 minutes: particle size 3 to 7 mm) The sample was poured into simulated environmental water B shown in Fig. 6 and shaken for 30 minutes each (solid-liquid ratio (mass ratio) was 1: 100).
Moreover, the same test was done also about the adsorption agent which added 10 mass% of ferrous sulfate monohydrate to each baking dolomite internally.

Specifically, each baked dolomite and the simulated environmental water B were blended in a 50 ml conical tube so that the solid-liquid ratio (mass ratio) was 1: 100, and each was shaken for 30 minutes.
Subsequently, suction filtration was performed using a 0.45 μm membrane filter, and the phosphoric acid concentration in the filtrate was quantified by ICP-AES (ICP emission spectroscopy, measuring device: ARCOS FHX22 manufactured by SPECTRO), and the filtrate The arsenic concentration in the solution was quantified according to JIS K 0102: 2013 61.3 (measuring device: ARCOS FHX22, manufactured by SPECTRO, hydride generator TEGXYNE CETAC, HGX-200), and from the following formula (3), respectively. The adsorption removal rate was calculated.
Table 7 shows the results of each of the massive calcined dolomite and Table 8 shows the results of the adsorbent obtained by adding ferrous sulfate monohydrate to the massive calcined dolomite.
The pH and oxidation-reduction potential (ORP) of the filtrate were measured with a desktop pH meter: F-73 (pH electrode: 9615S-10D, ORP electrode: 9300-10D) manufactured by Horiba, Ltd. . These results are also shown in Tables 7 and 8.

Adsorption removal rate (%) = (Ci−Cf) / Ci × 100 (3)
Ci = initial concentration of phosphoric acid or arsenic in simulated environmental water B before adsorption test (mg / l)
Cf = phosphoric acid or arsenic concentration (mg / l) in filtrate of simulated environmental water B after adsorption test

  From the results of Tables 7 and 8 above, in the calcined dolomite having a CaO content of 3.7 ≦ x ≦ 13.5 (mass%), the bulk dolomite alone had an arsenic adsorption removal rate of 62 to 68%. By adding monoiron monohydrate, it was improved to about 98%. For heavy metals such as arsenic, it is possible to further improve the adsorption performance by using ferrous sulfate monohydrate together.

  Also, each baked dolomite that adsorbs phosphorus and arsenic is washed with pure water, then immersed in a 0.1 mol / l sodium carbonate solution and stirred to regenerate by desorbing the adsorbed phosphorus and arsenic. The phosphoric acid adsorbent was again subjected to the phosphoric acid and arsenic adsorption test. The results of the measured adsorption removal rate were substantially the same as those shown in Tables 7 and 8.

  Also, each baked dolomite that adsorbs phosphorus and arsenic is collected, and the surface of each baked dolomite that adsorbs phosphorus and arsenic is ground using an automatic sieving machine or ball mill means to adsorb phosphorus and arsenic. The phosphorus and heavy metal adsorption tests were again performed on the regenerated phosphorus adsorbent with the adsorbent surface removed and the adsorbent surface fresh. The results of the measured adsorption removal rate were substantially the same as those shown in Tables 7 and 8.

The method for reusing a phosphorus adsorbent according to the present invention can be applied to repeated use by regenerating a phosphorus adsorbent that efficiently adsorbs and removes harmful phosphorus and heavy metals contained in environmental water such as rivers and lakes. It becomes possible.

Claims (5)

  A phosphorous adsorbent, which is a calcined carbonate compound containing CaO, and the content of CaO analyzed using the Rietveld method by powder X-ray diffraction is 3.7 ≦ x ≦ 13.5 (mass%); The adsorbed phosphorus is desorbed from the phosphorus adsorbent that has adsorbed phosphorus by bringing it into contact with environmental water containing phosphorus, and the regenerated phosphorus adsorbent obtained is repeatedly reused by contacting it with environmental water containing phosphorus. A method for reusing a phosphorus adsorbent, comprising:   2. The method of reusing a phosphorus adsorbent according to claim 1, wherein the phosphorus adsorbent adsorbing phosphorus further adsorbs heavy metals in environmental water and desorbs the adsorbed heavy metals for reuse. A method for reusing a phosphorus adsorbent, which is characterized.   3. The method for reusing a phosphorus adsorbent according to claim 1, wherein the phosphorus adsorbent further contains a ferrous compound.   The method for reusing a phosphorus adsorbent according to any one of claims 1 to 3, wherein the calcined carbonate compound is a calcined dolomite. The method for reusing a phosphorus adsorbent according to any one of claims 1 to 4, wherein the adsorbed phosphorus and heavy metal are removed by eluent or the surface is ground to remove. , Reuse method of phosphorus adsorbent.

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