JP2007106622A - Treatment method and apparatus for stabilizing gypsum hardened body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method for stabilizing a gypsum hardened body, by which the elution amount of fluorine from the gypsum hardened body, formed by using anhydrous gypsum or hemihydrate gypsum, can be reduced to the environmental standard value or lower by suppressing the addition amount of phosphates and an alkali substance to be minimum; and also to provide a treatment apparatus for stabilizing the gypsum hardened body. <P>SOLUTION: The gypsum hardened body is produced by adding phosphates to a slurry of hemihydrate gypsum or anhydrous gypsum in such a rate that the amount of the phosphates is ≥2 to <15 pts.wt, in terms of the phosphoric acid-equivalent weight converted so that the content of phosphorous becomes the same as that in phosphoric acid, to 1 part by weight of fluorine contained in the slurry, then stirring the resulting mixture, adding an alkali substance to the mixture so that the hydrogen ion concentration index of the mixture becomes ≥6.0 to <8.6, and further stirring the resulting mixture. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a stabilization method and apparatus for hemihydrate gypsum and anhydrous gypsum produced from flue gas desulfurized gypsum and waste gypsum board (recycled gypsum), and more particularly, hemihydrate gypsum or anhydrous gypsum. The present invention relates to a stabilization method and a stabilization processing apparatus for a gypsum hardened body that hardly dissolves fluorine, which is a trace amount of harmful substances contained in the gypsum, and suppresses elution of fluorine into the environment in the hardened gypsum.

  Smoke desulfurization gypsum and waste gypsum board, which is recycled gypsum, often contain a trace amount of environmentally hazardous elements that are designated as environmentally regulated substances, which causes problems during effective use or landfill treatment. In particular, there is a problem when the amount of fluorine eluted added to the soil environmental standards in 2001 exceeds the regulation value.

  In general, gypsum is used in large quantities as gypsum board made from hemihydrate gypsum or anhydrous gypsum, self-leveling material and wall material, cement raw material made from dihydrate gypsum, and soil improver. In particular, gypsum hardened bodies are inexpensive and excellent in fire resistance, so about 4.7 million tons (2003) are used as interior materials for buildings annually, and waste gypsum hardened bodies at the time of building demolition are 860,000 tons ( 2004). Most of the gypsum hardened wastes at the time of building demolition are landfilled together with other industrial waste. Therefore, when the waste gypsum hardened body contains a substance that dissolves into water and contaminates the soil, it becomes a problem of soil contamination.

  The hardened gypsum that was generated as mill material in the factory, as well as scrap and mill material at the construction site, was removed so that deposits such as wallpaper were removed, metal such as nails and screws were removed, and water leakage was controlled. After confirming the above, it is accepted as a raw material in the gypsum hardened product manufacturing factory and is sent to the recycling process. In the recycling process, the waste gypsum is separated into gypsum and paper by primary crushing, secondarily pulverized for particle size adjustment, and taken up as a raw material again.

  However, most of the by-product gypsum such as flue gas desulfurization gypsum which accounts for about 40 to 50% of the raw material for the gypsum hardened body contains fluorine, so that there is a problem that the fluorine is dissolved into the environment.

  In view of such a problem, there is a technique in which a calcium compound such as slaked lime is added to a slurry of hemihydrate gypsum to fix fluorine to calcium gypsum as calcium fluoride. However, the solubility of calcium fluoride as fluorine is about 8 ppm. In the case of fluorine, the amount of elution of fluorine from gypsum is reduced because the elution amount is set to 0.8 mg / L or less as the soil environment standard. This is not a sufficiently effective technology to do this.

  In view of such problems, there are conventional techniques such as the following (1) to (3) as a method for reducing the elution amount of fluorine with respect to gypsum to 0.8 mg / L or less.

(1) An alkali is added to a slurry of dihydrate gypsum or a slurry of hemihydrate gypsum to raise the pH to 9 or higher, and then a phosphoric acid and / or an acid is added to reduce the pH to 1 As described above, a technique of obtaining gypsum by filtering after reducing the eluted fluorine by adjusting the lowered pH to 6 or more (see, for example, Patent Document 1).
(2) A technique in which filtered dihydrate gypsum is washed with weakly acidic wash water containing a sulfuric acid band, and fluorine is eluted and removed in the wash solution (see, for example, Patent Document 2).
(3) Add phosphoric acid and alkaline agent to the filtered dihydrate gypsum and try to reduce the amount of fluorine elution from dihydrate gypsum by mechanical kneading and curing using a kneader together with solid materials such as gypsum. Technology (see, for example, Patent Document 3).

JP 2003-206133 A Japanese Patent Application Laid-Open No. 2004-299962 Japanese Patent Application No. 2004-305833

In the above conventional technique, the following problems remain.
In the techniques of the cited references 1 and 2, when used as a gypsum hardened body using hemihydrate gypsum or anhydrous gypsum as a raw material, it is insufficient to prevent elution of fluorine existing inside the hemihydrate gypsum or anhydrous gypsum. . That is, in the technique of Patent Document 1, an alkali is added to the slurry to raise the pH to 9 or more, and then phosphoric acids and / or acids are added to the slurry to lower the pH of the slurry to nearly 6. Calcium hydrogen phosphate dihydrate that is effective for fixing fluorine to gypsum is not selectively produced, and a large amount of impurities such as apatite compounds are produced, so that fluorine fixation to gypsum becomes insufficient. .

  Further, in the technique of Patent Document 1, since the pH of the gypsum slurry is increased to 9 by adding alkali, a large amount of alkali is necessary, and then phosphoric acid and / or acid is added to bring the pH to around 6. Therefore, in order to neutralize the alkali remaining in the gypsum slurry, more phosphoric acid and / or acid is required, which lowers the purity of gypsum and lowers the purity of the gypsum hardened body.

  In the technique of Patent Document 2, the filtered dihydrate gypsum is washed with weakly acidic wash water containing a sulfuric acid band, and fluorine is eluted in the wash solution to reduce the amount of elution of fluorine. Fluorine eluting in the gypsum crystal is limited to those dissolved with gypsum in the surface layer of gypsum crystals, so when it becomes a fine-grained gypsum produced by hydration from calcined hemihydrate gypsum or anhydrous gypsum, Fluorine eluting from the inside cannot be fixed, and the amount of fluorine elution from the gypsum hardened body exceeds the environmental standard value.

  The technique of Patent Document 3 is a method in which phosphoric acid and an alkaline substance are dispersed on the surface of dihydrate gypsum particles by mechanical kneading to fix fluorine, and a great amount of energy is used in mechanical kneading, and phosphoric acid and alkali are used. Since the dispersion of the substance is insufficient, the fixation of fluorine becomes insufficient when the calcined hemihydrate gypsum is hydrated to form a hardened gypsum.

  The techniques of cited references 1 to 3 are a somewhat effective method for stabilizing fluorine in dihydrate gypsum. However, with hemihydrate gypsum or anhydrous gypsum, it becomes hydrated into fine crystals, so that the internal fluorine comes out on the crystal surface and elutes into the liquid. Therefore, it cannot be said to be effective for reducing the amount of fluorine eluted in the gypsum hardened body which is a hydrated product of hemihydrate gypsum or anhydrous gypsum. From the above, none of the conventional techniques has solved the problem of stabilization in a gypsum hardened body produced by hydrating hemihydrate gypsum or anhydrous gypsum.

  The object of the present invention is to minimize the addition amount of phosphoric acids and alkaline substances, and to reduce the elution amount of fluorine from a gypsum hardened body produced using anhydrous gypsum or hemihydrate gypsum to an environmental standard value or less. It is providing the stabilization processing method and stabilization processing apparatus of a gypsum hardened body.

  The present invention provides a slurry of hemihydrate gypsum or anhydrous gypsum with 2 parts by weight or more in terms of phosphoric acid equivalent weight so that the content of phosphorus is the same with respect to 1 part by weight of fluorine contained in the slurry. After adding less than 15 parts by weight of phosphoric acid and stirring, an alkaline substance is added and stirred so that the hydrogen ion concentration index (pH) is 6.0 or more and less than 8.6 to prepare a gypsum hardened body. It is the stabilization processing method of the gypsum hardened body characterized by the above-mentioned.

  According to the present invention, for example, in a hydration process during the production of a gypsum hardened body and a process of adding waste gypsum to an aqueous slurry containing soil before ground improvement, a slurry of hemihydrate gypsum or anhydrous gypsum containing fluorine is used. In addition, phosphoric acids are added and stirred, and then an alkaline substance is added and stirred. Hereinafter, the slurry of hemihydrate gypsum or anhydrous gypsum may be referred to as gypsum slurry. The hemihydrate gypsum or anhydrous gypsum contained in the gypsum slurry may be a calcined natural or artificially synthesized gypsum containing fluorine.

  The phosphoric acid may be an acidic phosphate produced by a reaction between phosphoric acid and a cation, or phosphoric acid itself. For example, there are acids such as hypophosphorous acid, phosphorous acid, phosphoric acid, pyrophosphoric acid, polyphosphoric acid, metaphosphoric acid, and calcium hydrogen phosphate and aluminum hydrogen phosphate. In this, the acid which melt | dissolves in water as phosphoric acid treatment water is desirable. Particularly effective is phosphoric acid.

  The alkaline substance may be any alkaline calcium compound. As the alkaline calcium compound, slaked lime (calcium hydroxide), calcium carbonate, dolomite, cement, steel blast furnace slag powder, and the like are applicable.

  First, in the gypsum slurry, 2 parts by weight or more and less than 15 parts by weight of phosphoric acid equivalent weight converted to have the same phosphorus content with respect to 1 part by weight of fluorine contained in the gypsum slurry. By adding and stirring the acids, the gypsum slurry and the phosphoric acid are mixed, and the gypsum slurry can be made acidic. After that, when an alkaline substance is added to and stirred with a gypsum slurry in which phosphoric acids have been stirred, the gypsum slurry and the alkaline substance are mixed, and the solid alkaline substance gradually dissolves into the acidic gypsum slurry. The hydrogen ion concentration index can be gradually increased to a range of 6.0 to 8.6, and calcium hydrogen phosphate dihydrate is easily generated. Conversely, after adding an alkaline substance to the gypsum slurry to make the gypsum slurry alkaline, adding a phosphoric acid to the gypsum slurry to which the alkaline substance has been added and stirring the gypsum slurry, the moment the phosphoric acid is added, Since the hydrogen ion concentration index of the slurry falls to 6.0 to 8.6 and the reaction ends, calcium hydrogen phosphate dihydrate is produced, but a by-product apatite compound is also produced, The amount of calcium hydrogen phosphate dihydrate produced is reduced.

  Calcium hydrogen phosphate dihydrate is sparingly soluble, and this calcium hydrogen phosphate dihydrate is formed in a film shape so as to surround the gypsum particles. Fluorine contained in gypsum reacts with calcium hydrogen phosphate dihydrate to produce calcium fluorophosphate, thereby fixing the fluorine to the gypsum, and the fluorine contained in the hemihydrate gypsum or anhydrous gypsum. The amount of elution from the particles can be reduced.

  The phosphoric acid to be stirred in addition to the gypsum slurry is less than 2 parts by weight in terms of phosphoric acid equivalent so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. In this case, a sufficient amount of calcium hydrogen phosphate dihydrate is not generated, and the amount of fluorine eluted from the gypsum hardened body cannot be reduced to the environmental standard value of 0.8 mg / L or less. Further, the phosphoric acid stirred in addition to the gypsum slurry is 15 parts by weight or more in terms of phosphoric acid equivalent weight converted so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. If this is the case, the hydrogen ion concentration index of the gypsum slurry will be as low as less than 6.0, and the strength of the resulting gypsum hardened body will be low. The phosphoric acid stirred in addition to the gypsum slurry is at least 2 parts by weight in terms of phosphoric acid equivalent weight so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. By selecting less than 15 parts by weight, the elution amount of fluorine in the gypsum hardened body can be reduced to an environmental standard value of 0.8 mg / L or less, and the hydrogen ion concentration index of the gypsum slurry is 6.0. It is prevented that the strength of the resulting gypsum hardened body is lowered due to approaching neutrality.

  If the hydrogen ion concentration index of the gypsum slurry after adding the alkaline substance and stirring is less than 6.0 or more than 8.6, the effect of stabilizing the fluorine is insufficient and the strength of the gypsum hardened body. Becomes lower. Therefore, the ion concentration index of the gypsum slurry after adding the alkaline substance and stirring is 6.0 or more and less than 8.6.

  The amount of phosphoric acid and alkali substance to be stirred in addition to the gypsum slurry is determined by the fluorine content contained in the slurry and the hydrogen ion concentration index of the gypsum slurry after stirring the alkali substance. Thus, by adding phosphoric acids and alkaline substances to the gypsum slurry and stirring, the addition amount of phosphoric acids and alkaline substances is minimized, and from the gypsum hardened body produced using anhydrous gypsum or hemihydrate gypsum. The amount of fluorine elution can be reduced below the environmental standard value.

  Further, the present invention provides a slurry of hemihydrate gypsum or anhydrous gypsum with 2 parts by weight or more in terms of phosphoric acid equivalent weight so that the content of phosphorus is the same with respect to 1 part by weight of fluorine contained in the slurry. In addition, a solution obtained by adding an alkaline substance to a phosphoric acid solution containing less than 15 parts by weight of phosphoric acid and stirring is added and stirred so that the hydrogen ion concentration index is 6.0 or more and less than 8.6. A method for stabilizing a cured gypsum, characterized by producing a cured gypsum.

  According to the present invention, a solution obtained by adding an alkaline substance to the phosphoric acid solution and stirring the slurry of hemihydrate gypsum or anhydrous gypsum has a hydrogen ion concentration index of 6.0 or more and less than 8.6. In the same manner as in the case of preparing a gypsum hardened body after adding the phosphoric acid to the above-described gypsum slurry and stirring, and then stirring with an alkaline substance, the calcium hydrogen phosphate dihydrate is stirred. The object is formed in a film shape so as to surround the gypsum particles, and the fluorine contained in the gypsum reacts with calcium hydrogen phosphate dihydrate to produce calcium fluoride phosphate, whereby fluorine is produced. The amount of fluorine fixed to the gypsum and eluting from the gypsum particles to the outside can be reduced.

  The phosphoric acid to be stirred in addition to the gypsum slurry is less than 2 parts by weight in terms of phosphoric acid equivalent so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. In this case, a sufficient amount of calcium hydrogen phosphate dihydrate is not generated, and the amount of fluorine eluted from the gypsum hardened body cannot be reduced to the environmental standard value of 0.8 mg / L or less. Further, the phosphoric acid stirred in addition to the gypsum slurry is 15 parts by weight or more in terms of phosphoric acid equivalent weight converted so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. If this is the case, the hydrogen ion concentration index of the gypsum slurry will be as low as less than 6.0, and the strength of the resulting gypsum hardened body will be low. The phosphoric acid stirred in addition to the gypsum slurry is at least 2 parts by weight in terms of phosphoric acid equivalent weight so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. By selecting less than 15 parts by weight, the elution amount of fluorine in the gypsum hardened body can be reduced to an environmental standard value of 0.8 mg / L or less, and the hydrogen ion concentration index of the gypsum slurry is 6.0. It is prevented that the strength of the resulting gypsum hardened body is lowered due to approaching neutrality.

  If the hydrogen ion concentration index of the gypsum slurry after stirring the solution obtained by adding an alkaline substance to the phosphoric acid solution containing phosphoric acid and stirring is less than 6.0 or more than 8.6, The stabilizing effect is insufficient and the strength of the gypsum hardened body is lowered. Therefore, the ion concentration index of the gypsum slurry after adding and stirring the solution obtained by adding and stirring the alkaline substance to the phosphoric acid solution containing phosphoric acid is 6.0 or more and less than 8.6.

  As described above, an alkaline substance is added to the phosphoric acid solution and stirred, and the solution is added to the gypsum slurry and stirred to minimize the addition amount of the phosphoric acid and the alkaline substance. The elution amount of fluorine from the gypsum hardened body produced using can be reduced to an environmental standard value or less.

  Further, the present invention provides a slurry of hemihydrate gypsum or anhydrous gypsum with 2 parts by weight or more in terms of phosphoric acid equivalent weight so that the content of phosphorus is the same with respect to 1 part by weight of fluorine contained in the slurry. In addition, calcium hydrogen phosphate dihydrate obtained by adding an alkaline substance to a phosphoric acid solution containing less than 15 parts by weight of phosphoric acid and stirring the resulting mixture has a hydrogen ion concentration index of 6.0 or more and less than 8.6. In addition, the method is a method for stabilizing a gypsum hardened body, which is stirred to prepare a gypsum hardened body.

  According to the present invention, calcium hydrogen phosphate dihydrate obtained by adding and stirring an alkaline substance to a phosphoric acid solution containing the phosphoric acid to a slurry of hemihydrate gypsum or anhydrous gypsum has a hydrogen ion concentration index. By adding and stirring so that it is 6.0 or more and less than 8.6, calcium hydrogen phosphate dihydrate is formed into a film shape so as to surround the gypsum particles, and the fluorine contained in the gypsum Calcium fluorophosphate reacts with calcium hydrogen phosphate dihydrate to generate fluorine, which fixes fluorine to gypsum and elutes fluorine contained in gypsum or anhydrous gypsum from gypsum particles. The amount to be reduced can be reduced.

  The phosphoric acid to be stirred in addition to the gypsum slurry is less than 2 parts by weight in terms of phosphoric acid equivalent so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. In this case, a sufficient amount of calcium hydrogen phosphate dihydrate is not generated, and the amount of fluorine eluted from the gypsum hardened body cannot be reduced to the environmental standard value of 0.8 mg / L or less. Further, the phosphoric acid stirred in addition to the gypsum slurry is 15 parts by weight or more in terms of phosphoric acid equivalent weight converted so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. If this is the case, the hydrogen ion concentration index of the gypsum slurry will be as low as less than 6.0, and the strength of the resulting gypsum hardened body will be low. The phosphoric acid stirred in addition to the gypsum slurry is at least 2 parts by weight in terms of phosphoric acid equivalent weight so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. By selecting less than 15 parts by weight, the elution amount of fluorine in the gypsum hardened body can be reduced to an environmental standard value of 0.8 mg / L or less, and the hydrogen ion concentration index of the gypsum slurry is 6.0. It is prevented that the strength of the resulting gypsum hardened body is lowered due to approaching neutrality.

  In addition, after adding calcium hydrogen phosphate dihydrate obtained by adding an alkaline substance to a phosphoric acid solution containing phosphoric acid and stirring, the hydrogen ion concentration index of the gypsum slurry is less than 6.0 or 8 If it is .6 or more, the stabilizing effect of fluorine is insufficient and the strength of the gypsum hardened body is lowered. Therefore, the hydrogen ion concentration index of the gypsum slurry after adding and stirring calcium hydrogen phosphate dihydrate is 6.0 or more and less than 8.6.

  As previously mentioned, calcium hydrogen phosphate dihydrate is added to gypsum slurry and stirred to produce with anhydrous gypsum or hemihydrate gypsum with minimal addition of phosphates and alkaline substances. The elution amount of fluorine from the gypsum hardened body can be reduced below the environmental standard value.

  Calcium hydrogen phosphate dihydrate is added to the gypsum slurry and stirred to produce a gypsum hardened body compared to the case where calcium hydrogen phosphate dihydrate is produced in the gypsum slurry. Processing time can be shortened.

Further, the present invention provides a slurry of hemihydrate gypsum or anhydrous gypsum with 2 parts by weight or more in terms of phosphoric acid equivalent weight so that the content of phosphorus is the same with respect to 1 part by weight of fluorine contained in the slurry. And phosphoric acid stirring means for adding and stirring less than 15 parts by weight of phosphoric acid;
And an alkaline substance stirring means for adding an alkaline substance and stirring so that the hydrogen ion concentration index of the slurry in which the phosphoric acid is stirred by the phosphoric acid stirring means is 6.0 or more and less than 8.6. This is a device for stabilizing a cured gypsum body.

Further, the present invention provides a slurry of hemihydrate gypsum or anhydrous gypsum with 2 parts by weight or more in terms of phosphoric acid equivalent weight so that the content of phosphorus is the same with respect to 1 part by weight of fluorine contained in the slurry. And a solution generating means for adding an alkaline substance to a phosphoric acid solution containing less than 15 parts by weight of phosphoric acid and stirring to produce a solution;
A gypsum hardened body comprising a solution agitating means for agitating the solution produced by the solution producing means in addition to the slurry so that the hydrogen ion concentration index is 6.0 or more and less than 8.6. This is a stabilization processing apparatus.

Further, the present invention provides a slurry of hemihydrate gypsum or anhydrous gypsum with 2 parts by weight or more in terms of phosphoric acid equivalent weight so that the content of phosphorus is the same with respect to 1 part by weight of fluorine contained in the slurry. And calcium hydrogen phosphate dihydrate generating means for adding an alkaline substance to a phosphoric acid solution containing less than 15 parts by weight of phosphoric acid and stirring to produce calcium hydrogen phosphate dihydrate,
A solution in which calcium hydrogen phosphate dihydrate produced by the calcium hydrogen phosphate dihydrate producing means is added to the slurry and stirred so that the hydrogen ion concentration index is 6.0 or more and less than 8.6. And a stiffening device for stabilizing a gypsum hardened body.

  According to the present invention, the above-described method for stabilizing a gypsum hardened body can be realized. In these apparatuses, in order to realize the above-described method for stabilizing a gypsum hardened body, no special equipment is required, and the apparatus can be manufactured using conventional equipment.

  Further, the present invention provides a phosphoric acid equivalent weight in terms of phosphoric acid equivalent weight so that the content of phosphorus is equal to 1 part by weight of fluorine contained in the powder of hemihydrate gypsum or anhydrous gypsum. A method for producing a gypsum powder that becomes a stabilized gypsum hardened body, comprising adding and mixing a powder of calcium hydrogen phosphate dihydrate containing at least part and less than 15 parts by weight of phosphoric acid.

  According to the present invention, by adjusting the amount of calcium hydrogen phosphate dihydrate powder added and mixed so that the fluorine elution amount does not exceed the environmental standard value, the fluorine elution amount is A gypsum hardened body having a value lower than that can be easily produced.

Further, the present invention provides a phosphoric acid equivalent weight in terms of phosphoric acid equivalent weight so that the content of phosphorus is equal to 1 part by weight of fluorine contained in the powder of hemihydrate gypsum or anhydrous gypsum. Calcium hydrogen phosphate dihydrate producing means for obtaining calcium hydrogen phosphate dihydrate by adding an alkaline substance to a phosphoric acid solution containing at least part and less than 15 parts by weight of phosphoric acid, followed by stirring;
A gypsum that becomes a stabilized gypsum hardened body, characterized by comprising a mixing means for adding and mixing calcium hydrogen phosphate dihydrate produced by the calcium hydrogen phosphate dihydrate producing means to the powder. This is a powder production apparatus.
According to the present invention, the above-described method for producing gypsum powder can be realized.

  According to the present invention, the amount of phosphoric acid or phosphoric acid solution and alkaline substance used in the stabilization treatment is reduced by producing calcium hydrogen phosphate dihydrate for stabilizing fluorine in the gypsum slurry. As a minimum, it is possible to produce a stabilized gypsum hardened body whose fluorine elution amount is lower than the environmental standard value.

  According to the present invention, the amount of phosphoric acid or phosphoric acid solution used for the stabilization treatment and the amount of alkaline substance is minimized by supplying pre-synthesized calcium hydrogen phosphate dihydrate to the gypsum slurry. Thus, it is possible to produce a stabilized gypsum hardened body whose fluorine elution amount is lower than the environmental standard value. By stirring the calcium hydrogen phosphate dihydrate into the gypsum slurry, the treatment time can be shortened compared to when calcium hydrogen phosphate dihydrate is produced in the gypsum slurry. .

  Moreover, according to this invention, the stabilization processing method of the gypsum hardened body mentioned above is realizable. In these apparatuses, in order to realize the above-described gypsum stabilization treatment method, no special equipment is required, and the apparatus can be manufactured using conventional equipment.

Further, according to the present invention, by adjusting the amount of calcium hydrogen phosphate dihydrate powder mixed so that the amount of fluorine eluted does not exceed the environmental standard value, the amount of fluorine eluted is the environmental standard value. It is possible to easily produce a gypsum hardened body that is less than.
Moreover, according to this invention, the manufacturing method of the gypsum powder mentioned above is realizable.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below, but the present invention is not limited to the following embodiment, and can be implemented with appropriate modifications.

  FIG. 1 is a diagram schematically showing a stabilization processing apparatus 1 according to a first embodiment of the present invention. First, the gypsum referred to below will be explained. The gypsum may be either natural or artificially synthesized. There are various types of gypsum synthesized, for example, titanium gypsum by-produced in the production of phosphoric acid, and waste gypsum (recycled gypsum) separated from paper from gypsum board for the purpose of recycling such as construction waste. Since the present invention is for reducing the amount of fluorine eluted from the gypsum hardened body, it is generally used for byproduct gypsum containing fluorine. However, natural gypsum can be similarly applied if it contains fluorine.

Raw gypsum hardened body, i.e. hemihydrate gypsum as the processing target _{(CaSO 4 · 1 / 2H 2} O) or anhydrite (CaSO ₄₎ is a dihydrate gypsum containing fluorine _(CaSO 4 · _2H 2 O) The particle size is adjusted by firing and pulverization. The particle size of the hemihydrate gypsum or anhydrous gypsum is selected to be 150 μm (micrometer) or less. The method for converting the dihydrate gypsum into hemihydrate gypsum or anhydrous gypsum may be any one heated in a furnace or one heated in a circulation type furnace such as a kiln. The heating temperature may be usually 110 to 300 ° C.

  The stabilization processing apparatus 1 includes a slurry stirring tank 2, a phosphoric acid stirring means 3, and an alkaline substance stirring means 4. The slurry agitation tank 2 contains a slurry of hemihydrate gypsum or anhydrous gypsum, and agitates the slurry of hemihydrate gypsum or anhydrous gypsum. Hereinafter, the slurry of hemihydrate gypsum or anhydrous gypsum is referred to as gypsum slurry. The phosphoric acid supply means 3 adds phosphoric acid to the gypsum slurry and stirs it. The alkaline substance stirring means 4 adds and stirs an alkaline substance to a gypsum slurry in which phosphoric acids are stirred.

First, hemihydrate gypsum or anhydrous gypsum is placed in the slurry agitation tank 2, and water (H ₂ O) is supplied to the slurry agitation tank 2 and agitated. The slurry agitation tank 2 is provided with an agitation device for agitating the gypsum slurry, whereby the hemihydrate gypsum or anhydrous gypsum and water are agitated. The water which makes a slurry of hemihydrate gypsum or anhydrous gypsum supply the quantity which becomes a required quantity from the supply amount of hemihydrate gypsum or anhydrous gypsum. The concentration of gypsum slurry is on the order of 20 to 30 weight percent (wt%).

  The phosphoric acid stirring means 3 includes a phosphoric acid stirring tank 5 and a phosphoric acid supply unit 6. The gypsum slurry stirred in the slurry stirring tank 2 is accommodated in the phosphoric acid stirring tank 5. After the gypsum slurry is stored in the phosphoric acid stirring tank 5, a phosphoric acid solution or phosphoric acid powder is supplied to the phosphoric acid stirring tank 5 by the phosphoric acid supply unit 6. The phosphoric acid stirring tank 5 is provided with a stirring device for stirring the phosphoric acid solution or the phosphoric acid powder supplied from the phosphoric acid supply unit 6 to the gypsum slurry. Phosphoric acids are added to the gypsum slurry by the phosphoric acid stirring means 3 and stirred to mix them.

  The phosphoric acid may be an acidic phosphate produced by a reaction between phosphoric acid and a cation, or phosphoric acid itself. For example, there are acids such as hypophosphorous acid, phosphorous acid, phosphoric acid, pyrophosphoric acid, polyphosphoric acid, metaphosphoric acid, and calcium hydrogen phosphate and aluminum hydrogen phosphate. In this, the acid which melt | dissolves in water as phosphoric acid treatment water is desirable. Particularly effective is phosphoric acid.

  The alkaline substance stirring means 4 includes an alkaline substance stirring tank 7 and an alkaline substance supply unit 8. The gypsum slurry in which phosphoric acids are stirred in the phosphoric acid stirring tank 5 is accommodated in the alkaline substance stirring tank 7. After the gypsum slurry is stored in the alkaline substance stirring tank 7, the alkaline substance is supplied to the alkaline substance stirring tank 7 by the alkaline substance supply unit 8. The alkaline substance stirring tank 7 is provided with a stirring device for stirring the alkaline substance supplied from the alkaline substance supply unit 8 to the gypsum slurry in which phosphoric acids are stirred. The alkaline substance stirring means 4 adds and stirs the alkaline substance to the gypsum slurry mixed with the phosphoric acids and mixes them.

  The alkaline substance may be any alkaline calcium compound. As the alkaline calcium compound, slaked lime (calcium hydroxide), calcium carbonate, dolomite, cement, steel blast furnace slag powder, and the like are applicable.

  A gypsum hardened body is produced by stirring the gypsum slurry in which the phosphoric acids have been stirred in the alkaline substance stirring tank 7 and the alkali substance, followed by curing. In the curing treatment, a gypsum slurry in which phosphoric acids and an alkaline substance are stirred is allowed to stand. By standing, hemihydrate gypsum or anhydrous gypsum contained in gypsum slurry is hydrated and individualized.

A method for supplying the amounts of phosphoric acids and alkaline substances in the present embodiment will be described below. First, the phosphoric acid supply means 3 is 2 parts by weight or more in equivalent weight of phosphoric acid converted so that the content of phosphorus is equal to 1 part by weight of fluorine contained in the slurry of gypsum in the gypsum slurry. Further, less than 15 parts by weight of phosphoric acid is added and stirred. This can make the gypsum slurry acidic. Thereafter, when an alkaline substance is added to and stirred with a gypsum slurry in which phosphoric acids have been stirred, the solid alkaline substance gradually dissolves into the acidic gypsum slurry, and the hydrogen ion concentration index is 6.0. It can be gradually raised to a range of ˜8.6, and calcium hydrogen phosphate dihydrate (CaHPO ₄ .2H ₂ O) is easily generated.

Calcium hydrogen phosphate dihydrate is sparingly soluble, and this calcium hydrogen phosphate dihydrate is formed in a film shape so as to surround the gypsum particles. Fluorine contained in gypsum reacts with calcium hydrogen phosphate dihydrate to produce calcium fluorophosphate (Ca ₁₀ F ₂ (PO ₄ ) ₆ ), whereby fluorine is fixed to gypsum, It is possible to reduce the amount of fluorine eluted from the gypsum particles to the outside from the gypsum or anhydrous gypsum.

  The phosphoric acid to be stirred in addition to the gypsum slurry is less than 2 parts by weight in terms of phosphoric acid equivalent so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. In this case, a sufficient amount of calcium hydrogen phosphate dihydrate is not generated, and the amount of fluorine eluted from the gypsum hardened body cannot be reduced to the environmental standard value of 0.8 mg / L or less. Further, the phosphoric acid stirred in addition to the gypsum slurry is 15 parts by weight or more in terms of phosphoric acid equivalent weight converted so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. If this is the case, the hydrogen ion concentration index of the gypsum slurry will be as low as less than 6.0, and the strength of the resulting gypsum hardened body will be low. The phosphoric acid stirred in addition to the gypsum slurry is at least 2 parts by weight in terms of phosphoric acid equivalent weight so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. By selecting less than 15 parts by weight, the elution amount of fluorine in the gypsum hardened body can be reduced to an environmental standard value of 0.8 mg / L or less, and the hydrogen ion concentration index of the gypsum slurry is 6.0. It is prevented that the strength of the resulting gypsum hardened body is lowered due to approaching neutrality.

  When adding phosphoric acids for lowering the pH of gypsum slurry to the gypsum slurry, the phosphoric acid supply unit 6 may add the phosphoric acids as they are, or may be diluted with water or the like. It is necessary to sufficiently stir after the addition of phosphoric acids. For example, the stirring time is selected to be about 5 minutes.

  The alkaline substance supply unit 8 detects the pH of the gypsum slurry in the alkaline substance agitation tank 7 and supplies the alkaline substance to the gypsum slurry so that the pH is 6.0 or more and less than 8.6. . The pH of the gypsum slurry is detected by a pH measuring device. If the hydrogen ion concentration index of the gypsum slurry after stirring the alkaline substance is less than 6.0 or more than 8.6, the effect of stabilizing the fluorine is insufficient and the strength of the gypsum hardened body is lowered. . Therefore, the ion concentration index of the slurry of gypsum after stirring the alkaline substance is 6.0 or more and less than 8.6.

  The amount of phosphoric acids to be stirred in addition to the gypsum slurry is determined by the fluorine content contained in the slurry and the hydrogen ion concentration index of the gypsum slurry after stirring the alkaline substance. Fluorine elution from gypsum hardened gypsum produced using anhydrous gypsum or hemihydrate gypsum by adding phosphoric acids and alkaline substances to the gypsum slurry and stirring to minimize the addition of phosphoric acids and alkaline substances The amount can be below the environmental standard value.

  The supply amount of phosphoric acid is basically controlled by the hydrogen ion concentration index of the gypsum slurry, but when the properties of the gypsum slurry and the supplied phosphoric acid are stable, a fixed ratio to the gypsum slurry. You may supply with. The amount of the alkaline substance is supplied at a necessary ratio with respect to the amount of phosphoric acids. When phosphoric acid is used as the phosphoric acid and slaked lime is used as the alkaline substance, the amount of slaked lime is desirably supplied on the basis of 1/2 amount of phosphoric acid. That is, the slaked lime is 1/2 part by weight with respect to 1 part by weight of phosphoric acid.

  In the present embodiment, each process from the gypsum slurry to the production of the gypsum hardened body is performed at a room temperature of about 20 ° C to 30 ° C.

  In the present embodiment, the slurry agitation tank 2, the phosphoric acid agitation tank 5 and the alkaline substance agitation tank 7 are realized by separate agitation tanks, but this does not prevent the functions from being separately used in the same agitation tank. In other embodiments of the present invention, the slurry stirring tank 2, the phosphoric acid stirring tank 5, and the alkaline substance stirring tank 7 may be realized by one stirring tank.

  FIG. 2 is a diagram systematically showing the stabilization processing apparatus 10 according to the second embodiment of the present invention. In the present embodiment, the same components as those of the stabilization processing device 1 of the first embodiment described above may be denoted by the same reference numerals, and the description thereof may be omitted. In the present embodiment, the gypsum slurry, phosphoric acid and alkaline substance are the same as those in the above-described embodiment.

  The stabilization processing apparatus 10 includes a slurry stirring tank 2 and a solution stirring means 11. The solution stirring means 11 includes a first stirring tank 12, a second stirring tank 13, a phosphoric acid supply unit 6, and an alkaline substance supply unit 8. The first stirring tank 12 contains gypsum slurry stirred in the slurry stirring tank 2.

  The phosphoric acid supply unit 6 has a phosphoric acid equivalent weight of 2 parts by weight or more and less than 15 parts by weight with respect to 1 part by weight of fluorine contained in the gypsum slurry. The phosphoric acid solution containing acids or the phosphoric acid powder and water are supplied to the second stirring tank 13. The alkaline substance supply unit 8 supplies an alkaline substance to the second stirring tank 13. The second stirring tank 13 is provided with a stirring device for stirring the phosphoric acid solution supplied from the phosphoric acid supply unit 6 or the phosphoric acid powder and water, and the alkaline substance supplied from the alkaline substance supply unit 8. It is done. In the second stirring tank 13, the phosphoric acids supplied from the phosphoric acid supply unit 6 and the alkaline substance supplied from the alkaline substance supply unit 8 are added and mixed to react with each other, thereby hydrogen phosphate. A solution containing calcium dihydrate is produced.

  The solution generated in the second stirring tank 13 is supplied to a gypsum slurry stored in the first stirring tank 12. The first stirring tank 12 is provided with a stirring device for stirring the gypsum slurry and the solution supplied from the second stirring tank 13, and the gypsum slurry and the solution supplied from the second stirring tank 13 are added. And stirred and mixed.

  After the solution supplied from the second stirring tank 13 is added to the gypsum slurry in the first stirring tank 12 and stirred, a hardened gypsum body is produced by curing.

  To a slurry of hemihydrate gypsum or anhydrous gypsum, a solution obtained by adding an alkaline substance to the phosphoric acid solution and stirring is added and stirred so that the hydrogen ion concentration index is 6.0 or more and less than 8.6. Thus, after adding the phosphoric acids to the above-described gypsum slurry and stirring the mixture, the alkaline substance is added and stirred to prepare the gypsum hardened body. Formed in a film shape so as to surround the particles, fluorine contained in gypsum reacts with calcium hydrogen phosphate dihydrate to produce calcium fluorophosphate, thereby fixing fluorine to gypsum. In addition, the amount of fluorine contained in hemihydrate gypsum or anhydrous gypsum to the outside from the gypsum particles can be reduced.

  The phosphoric acid to be stirred in addition to the gypsum slurry is less than 2 parts by weight in terms of phosphoric acid equivalent so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. In this case, a sufficient amount of calcium hydrogen phosphate dihydrate is not generated, and the amount of fluorine eluted from the gypsum hardened body cannot be reduced to the environmental standard value of 0.8 mg / L or less. Further, the phosphoric acid stirred in addition to the gypsum slurry is 15 parts by weight or more in terms of phosphoric acid equivalent weight converted so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. If this is the case, the hydrogen ion concentration index of the gypsum slurry will be as low as less than 6.0, and the strength of the resulting gypsum hardened body will be low. The phosphoric acid stirred in addition to the gypsum slurry is at least 2 parts by weight in terms of phosphoric acid equivalent weight so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. By selecting less than 15 parts by weight, the elution amount of fluorine in the gypsum hardened body can be reduced to an environmental standard value of 0.8 mg / L or less, and the hydrogen ion concentration index of the gypsum slurry is 6.0. It is prevented that the strength of the resulting gypsum hardened body is lowered due to approaching neutrality.

  If the hydrogen ion concentration index of the gypsum slurry after adding and stirring the solution obtained by adding an alkaline substance to the phosphoric acid solution containing phosphoric acid and stirring is less than 6.0 or 8.6 or more, The effect of stabilizing fluorine is insufficient, and the strength of the gypsum hardened body is lowered. Therefore, the ion concentration index of the gypsum slurry after stirring the solution obtained by adding an alkaline substance to the phosphoric acid solution containing phosphoric acid and stirring is set to 6.0 or more and less than 8.6.

  As described above, an alkaline substance is added to the phosphoric acid solution and stirred, and the solution is added to the gypsum slurry and stirred to minimize the addition amount of the phosphoric acid and the alkaline substance. The elution amount of fluorine from the gypsum hardened body produced using can be reduced to an environmental standard value or less.

  In the present embodiment, each process from the gypsum slurry to the production of the gypsum hardened body is performed at a room temperature of about 20 ° C to 30 ° C.

  In the present embodiment, the slurry agitation tank 2 and the first agitation tank 12 are realized by separate agitation tanks, but this does not prevent the functions from being divided and used in the same agitation tank. In another embodiment, the slurry agitation tank 2 and the first agitation tank 12 may be realized by a single agitation tank.

  FIG. 3 is a diagram systematically illustrating the stabilization processing apparatus 20 according to the third embodiment of the present invention. In the present embodiment, the same components as those in the stabilization processing devices 1 and 10 of the first and second embodiments described above may be denoted by the same reference numerals, and the description thereof may be omitted. In the present embodiment, the gypsum slurry, phosphoric acid and alkaline substance are the same as those in the above-described embodiment.

  The stabilization processing device 20 includes a slurry stirring tank 2 and a solution stirring means 21. The solution stirring means 21 includes a first stirring tank 12, a second stirring tank 13, a phosphoric acid supply unit 6, an alkaline substance supply unit 8, and a filter 22.

  The solution stirred in the second stirring tank 13 is supplied to the filter 22. The filter 22 filters the solution produced by stirring in the second stirring tank 13 and separates it into solid content and filtered water. The solid content includes calcium hydrogen phosphate dihydrate. In the second embodiment described above, the solution stirred in the second stirring tank 13 is supplied to the first stirring tank 12, but in this embodiment, the solution stirred in the second stirring tank 13 is filtered. Only the solid content obtained in this manner is supplied to the first stirring tank 12.

  A method for producing calcium hydrogen phosphate dihydrate will be described. First, 10 parts by weight of phosphoric acid is added to 10,000 parts by weight of water in the second stirring tank 13 and sufficiently stirred. To this, 5 parts by weight of slaked lime is added and further stirred at room temperature for 30 minutes. Next, in the filter 22, this slurry is suction filtered through a membrane filter having a pore diameter of 0.45 μm, and the filtrate is dried at 45 ° C. for 24 hours to obtain calcium hydrogen phosphate dihydrate.

  The gypsum hardened body is produced by adding the calcium hydrogen phosphate dihydrate supplied from the filter 22 to the slurry of gypsum in the first stirring tank 12 and stirring, followed by curing.

  Calcium hydrogen phosphate dihydrate obtained by adding an alkaline substance to a phosphoric acid solution containing phosphoric acid in a slurry of hemihydrate gypsum or anhydrous gypsum and stirring it, a hydrogen ion concentration index of 6.0 or more, and By stirring so as to be less than 8.6, calcium hydrogen phosphate dihydrate is formed into a film shape surrounding gypsum particles, and fluorine contained in gypsum and calcium hydrogen phosphate dihydrate Fluorine is fixed to gypsum by reacting with the product to generate calcium fluorophosphate, and the amount of fluorine contained in the gypsum or anhydrous gypsum can be reduced from the gypsum particles to the outside. .

  The phosphoric acid to be stirred in addition to the gypsum slurry is less than 2 parts by weight in terms of phosphoric acid equivalent so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. In this case, a sufficient amount of calcium hydrogen phosphate dihydrate is not generated, and the amount of fluorine eluted from the gypsum hardened body cannot be reduced to the environmental standard value of 0.8 mg / L or less. Further, the phosphoric acid stirred in addition to the gypsum slurry is 15 parts by weight or more in terms of phosphoric acid equivalent weight converted so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. If this is the case, the hydrogen ion concentration index of the gypsum slurry will be as low as less than 6.0, and the strength of the resulting gypsum hardened body will be low. The phosphoric acid stirred in addition to the gypsum slurry is at least 2 parts by weight in terms of phosphoric acid equivalent weight so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. By selecting less than 15 parts by weight, the elution amount of fluorine in the gypsum hardened body can be reduced to an environmental standard value of 0.8 mg / L or less, and the hydrogen ion concentration index of the gypsum slurry is 6.0. It is prevented that the strength of the resulting gypsum hardened body is lowered due to approaching neutrality.

  In addition, after adding calcium hydrogen phosphate dihydrate obtained by adding an alkaline substance to a phosphoric acid solution containing phosphoric acid and stirring, the hydrogen ion concentration index of the gypsum slurry is less than 6.0 or 8 If it is .6 or more, the stabilizing effect of fluorine is insufficient and the strength of the gypsum hardened body is lowered. Therefore, the ion concentration index of the gypsum slurry after stirring the calcium hydrogen phosphate dihydrate is 6.0 or more and less than 8.6.

  As previously mentioned, calcium hydrogen phosphate dihydrate is added to gypsum slurry and stirred to produce with anhydrous gypsum or hemihydrate gypsum with minimal addition of phosphates and alkaline substances. The elution amount of fluorine from the gypsum hardened body can be reduced below the environmental standard value.

  In the present embodiment, by adding calcium hydrogen phosphate dihydrate to the gypsum slurry and stirring, compared to the case where calcium hydrogen phosphate dihydrate is generated in the gypsum slurry, The processing time which produces a gypsum hardened body can be shortened.

  Moreover, in the stabilization processing apparatus 20, you may use the filtered water produced | generated by the filter 22 by supplying to the slurry stirring tank 2 as water of a hydration process. In this case, the filtered water from the filter 22 is supplied so that it becomes a required amount with respect to the amount of gypsum slurry.

  In the present embodiment, each process from the gypsum slurry to the production of the gypsum hardened body is performed at a room temperature of about 20 ° C to 30 ° C.

  FIG. 4 is a diagram schematically showing a gypsum powder manufacturing apparatus 30 according to a fourth embodiment of the present invention. In the present embodiment, the same components as those of the stabilization processing devices 10 and 20 of the second and third embodiments described above may be denoted by the same reference numerals, and the description thereof may be omitted. In the present embodiment, the gypsum slurry, phosphoric acid and alkaline substance are the same as those in the above-described embodiment.

  The gypsum powder production apparatus 30 includes a calcium hydrogen phosphate dihydrate production means 31 and a mixing means 32. The calcium hydrogen phosphate dihydrate generating means 31 includes a stirring tank 34, a phosphoric acid supply unit 6, an alkaline substance supply unit 8, a filter 22 and a dryer 33. The stirring tank 34 has the same configuration as the second stirring tank 13 described above.

  The solid substance of calcium hydrogen phosphate dihydrate obtained by the filter 22 is fed to the dryer 33. The dryer 33 dries the given calcium hydrogen phosphate dihydrate solid and supplies it to the mixing means 32.

  The mixing means 32 adds and mixes the hemihydrate gypsum powder or anhydrous gypsum powder and the dried calcium hydrogen phosphate dihydrate supplied from the dryer 33. This produces hemihydrate gypsum powder or anhydrous gypsum powder that stabilizes when it becomes a gypsum hardened body.

  Calcium hydrogen phosphate dihydrate mixed with hemihydrate gypsum powder or anhydrous gypsum powder contains phosphorus content with respect to 1 part by weight of fluorine contained in hemihydrate gypsum powder or anhydrous gypsum powder. 2 parts by weight or more and less than 15 parts by weight of phosphoric acid in terms of equivalent weight of phosphoric acid converted so as to be the same. The gypsum hardened body whose fluorine elution amount is lower than the environmental standard value by adjusting the amount of calcium hydrogen phosphate dihydrate powder mixed so that the fluorine elution amount does not exceed the environmental standard value. Can be easily manufactured.

  In the present embodiment, the step of stirring the phosphoric acid solution and the alkaline substance and filtering the solution is performed at a room temperature of about 20 ° C to 30 ° C.

Hereinafter, the present invention will be described in detail by way of examples.
In the following examples, as the raw hemihydrate gypsum or anhydrous gypsum, hemihydrate gypsum obtained by calcining the exhausted gypsum generated from the flue gas desulfurization apparatus was used. The analytical values of desulfurized gypsum are shown in Table 1. Table 1 shows the fluorine content in the desulfurized gypsum (dihydrate gypsum), the fluorine elution amount, and the hydrogen ion concentration index of the fluorine eluate.

  In Table 1, the fluorine content in gypsum is that in gypsum dried at 45 ° C. for 24 hours. The fluorine elution amount was in accordance with the dissolution test (Environmental Agency Notification No. 46).

  Fluorine content such as gypsum is adjusted to pH = 5.0 to 5.5 using a distillate of steam distillation and adding a buffer solution (total ionic strength adjusting solution) according to JIS R 9101. The potential was measured using a fluoride ion electrode.

  In the dissolution test, the amount of fluorine elution from gypsum is 50 mL or more in a pure water solvent (pH = 5.8 to 6.3) with a sample of 50 g or more in a 1 L polyethylene container. Shake horizontally (shaking width 4 cm to 5 cm, room temperature about 20 ° C.) for 6 hours about 200 times per minute, let stand for 10-30 minutes, centrifuge at about 3000 rpm for 20 minutes, and supernatant The liquid was suction filtered using a membrane filter having a filter paper pore diameter of 0.45 μm. The fluorine concentration in the filtrate was measured with a fluorine ion electrode. The ion electrode method was in accordance with JIS R 9101.

  The hemihydrate gypsum used for the test was prepared by the following method. An appropriate amount of the above drained gypsum was taken, kneaded with a kneader, and dried at 45 ° C. overnight (24 hours or more). Then, after baking at 170 degreeC with a dryer for 2 hours, it took out and was cured in air at room temperature for 24 hours or more to make a half-water gypsum. When adjusted from dihydrate gypsum to hemihydrate gypsum, the water loss was 20.8%.

Example 1
After adding a predetermined amount of phosphoric acid (1.0 g) and slaked lime (0.5 g) to distilled water (142 g) with a standard mixed water amount (71 wt% with respect to gypsum), hemihydrate gypsum (about 200 g) Was left to stand for 1 day to obtain a gypsum hardened body. The produced gypsum hardened body was dried at 45 ° C. for 24 hours or more, then pulverized and sieved with a 2 mm mesh, and an elution test (Environment Agency Notification No. 46) was conducted. When the eluate of the cured gypsum was pH 7.2, the fluorine elution amount was 0.6 [mg / L].

(Example 2)
First, a predetermined amount of phosphoric acid (1.6 g) is added to a beaker with distilled water (142 g) having a standard mixed water amount (71 wt% with respect to gypsum), and the pH is stabilized. Next, a predetermined amount of slaked lime (0.8 g) was taken into a beaker and a solution with a stabilized pH was used. To this solution, hemihydrate gypsum (about 200 g) was added and allowed to stand for 1 day to obtain a gypsum hardened body. The cured gypsum body was dried at 45 ° C. for 24 hours or more, then pulverized and sieved with a 2 mm mesh, and an elution test (Environment Agency Notification No. 46) was performed. Here, the converted concentrations of phosphoric acid and slaked lime were calculated based on dihydrate gypsum. Table 2 shows the processing conditions and the results of the dissolution test. The pH of the eluate of the cured gypsum was 7.3, and the fluorine elution amount was 0.2 [mg / L].

  Table 2 shows the pre-treatment conditions for the cured gypsum and the results of the elution test for the cured gypsum in this example.

(Example 3)
A standard amount of water (71% with respect to gypsum) of distilled water (142 g) is placed in a beaker and calcium hydrogen phosphate dihydrate (reagent) is stirred in a predetermined amount (0.8 g) to stabilize the pH. To this solution, hemihydrate gypsum (about 200 g) was added, stirred, and allowed to stand for 1 day to obtain a gypsum hardened body. The cured gypsum body was dried at 45 ° C. for 24 hours or more, then pulverized and sieved with a 2 mm mesh, and an elution test (Environment Agency Notification No. 46) was performed. The pH of the eluate of the cured gypsum was 7.4, and the fluorine elution amount was 0.6 [mg / L].

(Comparative Example 1)
A gypsum hardened body was produced by adding the phosphoric acid and slaked lime to the gypsum slurry by one method of the example. The cured gypsum body was dried at 45 ° C. for 24 hours or more, then pulverized and sieved with a 2 mm mesh, and an elution test (Environment Agency Notification No. 46) was performed. The pH of the eluate of the cured gypsum body was 8.5, and the fluorine elution amount was 3.9 [mg / L].

(Comparative Example 2)
Phosphoric acid (0.6 wt%) and slaked lime (0.3 wt%) were mechanically kneaded into dihydrate gypsum, and then dried at 45 ° C. for 24 hours or more. This dihydrate gypsum was subjected to a dissolution test (Environment Agency Notification No. 46). The pH of the dihydrate gypsum eluate was 6.4, and the fluorine elution amount was 0.2 [mg / L] or less. Next, this dihydrate gypsum was baked in a dryer at 170 ° C. for 2 hours, and then hemihydrate gypsum was cured at room temperature for 24 hours or more. Hemihydrate gypsum (about 200 g) was put into a beaker of distilled water (142 g) with a standard water mixture (71% with respect to gypsum), kneaded and allowed to stand for 1 day to obtain a gypsum hardened body. The cured gypsum body was dried at 45 ° C. for 24 hours or more, then pulverized and sieved with a 2 mm mesh, and an elution test (Environment Agency Notification No. 46) was performed. The eluate of the gypsum hardened body had a pH of 7.5 and a fluorine elution amount of 1.2 [mg / L].

  As described above, in this example, it was possible to suppress the fluorine elution amount from the produced gypsum hardened body to 0.8 [mg / L] or less, which is the environmental standard value.

  In the procedure of Example 2 described above, slaked lime, which is an alkaline substance, is added in an amount about half that of phosphoric acid, and the pH of the solution after adding the alkaline substance is about 8.3. From the result of measuring the elution amount of fluorine by conducting an elution test (Environment Agency Notification No. 46) on a hardened gypsum body dried at 45 ° C. for 24 hours or more, then pulverized and sieved with a 2 mm mesh The phosphoric acid equivalent of 2 parts by weight or more and less than 12 parts by weight in terms of phosphoric acid equivalent so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. In addition, by stirring, the elution amount of fluorine can be reliably reduced below the environmental standard value, and converted so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in the gypsum slurry. Phosphoric acid It was found that the amount of fluorine eluted can be more reliably reduced below the environmental standard value by adding 2 parts by weight or more and less than 15 parts by weight of phosphoric acid to the gypsum slurry and stirring. .

It is a figure which shows systematically the stabilization processing apparatus 1 of the 1st Embodiment of this invention. It is a figure which shows systematically the stabilization processing apparatus 10 of the 2nd Embodiment of this invention. It is a figure which shows systematically the stabilization processing apparatus 20 of the 3rd Embodiment of this invention. It is a figure which shows systematically the manufacturing apparatus 30 of the gypsum powder of the 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,10,20 Stabilization processing apparatus 2 Slurry stirring tank 3 Phosphoric acid stirring means 4 Alkaline substance stirring means 5 Phosphoric acid stirring tank 6 Phosphoric acid supply part 7 Alkaline substance stirring tank 8 Alkaline substance supply part 11, 21 Solution stirring means 12 1st stirring tank 13 2nd stirring tank 22 Filtration machine 30 Gypsum powder production apparatus 31 Calcium hydrogen phosphate dihydrate generating means 32 Mixer 33 Dryer 34 Stirring tank

Claims (8)

  In a slurry of hemihydrate gypsum or anhydrous gypsum, 2 parts by weight or more and less than 15 parts by weight in terms of phosphoric acid equivalent so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in this slurry After adding and stirring the phosphoric acid, an alkali substance is added and stirred so that the hydrogen ion concentration index is 6.0 or more and less than 8.6 to produce a gypsum hardened body. Body stabilization treatment method.   In a slurry of hemihydrate gypsum or anhydrous gypsum, 2 parts by weight or more and less than 15 parts by weight in terms of phosphoric acid equivalent so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in this slurry A solution obtained by adding an alkaline substance to a phosphoric acid solution containing the above phosphoric acid and stirring is added so that the hydrogen ion concentration index is 6.0 or more and less than 8.6, and the mixture is stirred to obtain a gypsum cured product. A method for stabilizing a gypsum hardened body, characterized by being produced.   In a slurry of hemihydrate gypsum or anhydrous gypsum, 2 parts by weight or more and less than 15 parts by weight in terms of phosphoric acid equivalent so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in this slurry Calcium hydrogen phosphate dihydrate obtained by adding an alkaline substance to a phosphoric acid solution containing the phosphoric acid and stirring the mixture is added so that the hydrogen ion concentration index is 6.0 or more and less than 8.6. A method for stabilizing a gypsum hardened body, comprising stirring to produce a gypsum hardened body. In a slurry of hemihydrate gypsum or anhydrous gypsum, 2 parts by weight or more and less than 15 parts by weight in terms of phosphoric acid equivalent so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in this slurry Phosphoric acid stirring means for adding and stirring the phosphoric acid,
And an alkaline substance stirring means for adding an alkaline substance and stirring so that the hydrogen ion concentration index of the slurry in which the phosphoric acid is stirred by the phosphoric acid stirring means is 6.0 or more and less than 8.6. Stabilizer for gypsum hardened body. In a slurry of hemihydrate gypsum or anhydrous gypsum, 2 parts by weight or more and less than 15 parts by weight in terms of phosphoric acid equivalent so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in this slurry Solution generation means for adding an alkaline substance to a phosphoric acid solution containing phosphoric acid and stirring to produce a solution;
A gypsum hardened body comprising a solution agitating means for agitating the solution produced by the solution producing means in addition to the slurry so that the hydrogen ion concentration index is 6.0 or more and less than 8.6. Stabilization processing equipment. In a slurry of hemihydrate gypsum or anhydrous gypsum, 2 parts by weight or more and less than 15 parts by weight in terms of phosphoric acid equivalent so that the phosphorus content is the same with respect to 1 part by weight of fluorine contained in this slurry Calcium hydrogen phosphate dihydrate generating means for adding an alkaline substance to a phosphoric acid solution containing the phosphoric acid and stirring to generate calcium hydrogen phosphate dihydrate;
A solution in which calcium hydrogen phosphate dihydrate produced by the calcium hydrogen phosphate dihydrate producing means is added to the slurry and stirred so that the hydrogen ion concentration index is 6.0 or more and less than 8.6. And a stiffening device for stabilizing a gypsum hardened body.   More than 2 parts by weight and 15 parts by weight in equivalent weight of phosphoric acid converted so that the content of phosphorus is equal to 1 part by weight of fluorine contained in the powder of hemihydrate gypsum or anhydrous gypsum A method for producing a gypsum powder that becomes a stabilized gypsum hardened body, comprising adding and mixing a powder of calcium hydrogen phosphate dihydrate containing less than part of phosphoric acid. 2 parts by weight or more in the equivalent weight of phosphoric acid converted so that the content of phosphorus is equal to 1 part by weight of fluorine contained in the powder of hemihydrate gypsum or anhydrous gypsum, and 15 A calcium hydrogen phosphate dihydrate production means for adding calcium substance to a phosphoric acid solution containing less than parts by weight of phosphoric acid and stirring to obtain calcium hydrogen phosphate dihydrate;
A gypsum powder that becomes a stabilized gypsum hardened body, characterized in that it comprises a mixing means for mixing calcium hydrogen phosphate dihydrate produced by the calcium hydrogen phosphate dihydrate producing means with the powder. Manufacturing equipment.

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