Method for producing silica, and method for producing cement clinker and cement composition

Abstract

To provide a method for producing silica capable of producing silica usable in various industries from a silicon-containing waste at a low cost with high safety.SOLUTION: Provided is a method for producing silica, which comprises a slurry preparation step of mixing a silicon-containing waste with an aqueous solution having a sodium hydroxide concentration of 1 to 24 mass% to prepare a slurry containing a silicate, a fractionation step of fractionating an extract liquid containing a silicate and a residue from the slurry, and a crystallization step of bringing the extract liquid into contact with a CO2-containing gas to crystallize silica.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing silica, and a method for producing cement clinker and cement composition.

Background Art

[0002] Silicon-containing wastes such as coal ash, incineration ash, slag, and waste glass are generated in tens of millions of tons annually, and those that cannot be recycled are finally disposed of by landfill. Since silicon contained in large amounts in the waste is an industrially useful component, if silicon can be recovered from these wastes in a reusable form, it is expected to contribute to the reduction of the final disposal amount and the formation of a recycling-oriented society.

[0003]

[0004] As a technique for recovering silica from silicon-containing wastes, for example, Patent Documents 1 and 2 disclose a technique for recovering silica by using coal ash as a raw material, extracting a silica component using a high-concentration aqueous sodium hydroxide solution of 40% by mass or more or 25% by mass or more under heating conditions of 70 to 150°C, and then subjecting the silica crystallization solution obtained by aerating carbon dioxide gas into the extract to solid-liquid separation. 2 O 3 Patent Document 1 aims to produce artificial aggregates from residues rich in alumina content, and as a method for treating residues after extracting silica components from coal ash, a technique of heating and solidifying for molding or adding cement and water for granulation molding is disclosed. Further, Patent Document 2 aims to recover alumina components together with silica components, and discloses a technique of generating Al

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] In conventional silica extraction processes, such as those described in Patent Documents 1 and 2, in order to achieve a high yield of silica, treatment with a high-temperature and high-concentration aqueous sodium hydroxide solution is performed, and there is room for improvement in terms of safety. In addition, when the concentration of sodium hydroxide is increased, there are problems such as a large amount of Na, which can be an interfering factor when crystallizing silica particles, being contained in the extract, and a large amount of components derived from silicon-containing waste other than silica being extracted. Further, when a high-concentration aqueous sodium hydroxide solution is used, there is also a problem that it becomes difficult to use the extraction residue as a cement raw material because a large amount of Na 2 O components remain, making it difficult to convert the extraction residue into a cement raw material.

[0007] The present invention provides a method for producing silica that can be produced from silicon-containing waste at low cost and with high safety, and that can be used in various industries. Further, by suppressing fluctuations in the content of the silica component in the raw material, the present invention provides a method for producing a cement clinker in which the setting of the blending conditions is easy and a stable cement clinker can be produced in terms of quality. Further, by using such a cement clinker, the present invention provides a method for producing a cement composition in which the setting of the blending conditions is easy and a stable cement composition can be produced in terms of quality. MEANS FOR SOLVING THE PROBLEMS

[0008] In one aspect, the present invention provides a method for producing silica, comprising: a slurry preparation step of mixing a silicon-containing waste and an aqueous solution having a sodium hydroxide concentration of 1 to 24% by mass to prepare a slurry containing a silicate; a separation step of separating an extract containing a silicate and a residue from the slurry; and a crystallization step of bringing the extract into contact with a CO 2 -containing gas to crystallize silica particles.

[0009] In the above manufacturing method, an aqueous solution with a lower concentration of silicon-containing waste and sodium hydroxide than before is used to prepare a slurry containing silicate, and silica particles are crystallized by bringing an extract containing silicate obtained from this slurry into contact with a CO 2 -containing gas. Thus, since silicon-containing waste and a low-concentration aqueous sodium hydroxide solution are used as raw materials, silica can be produced at low cost and with high safety. In addition, the silica obtained by this manufacturing method has reduced impurities other than the silicate contained in the extract, and thus can be used in various industries. On the other hand, the residue can be effectively utilized, for example, as a cement raw material.

[0010] In the above separation step, it is preferable to obtain a residue having an Na 2 O content of 0.01 to 5% by mass. Since the Na 2 O content of such a residue is sufficiently reduced, it can be suitably used as a cement raw material.

[0011] In the above slurry preparation step, it is preferable to heat the slurry to 50 to 200 °C to react the silicon-containing waste with sodium hydroxide. Thereby, the extraction rate of silicate from the silicon-containing waste is improved, and the yield of the finally obtained silica can be increased.

[0012] The above manufacturing method preferably has a washing step of washing the solid phase containing the crystallized silica particles after the crystallization step. Thereby, impurities can be reduced and the purity of silica can be increased. It is preferable to wash the solid phase using acid and water in this order. Thereby, the purity and specific surface area of silica can be further increased. The reason for obtaining such an effect is presumed to be the dissolution and removal of sodium carbonate and the reduction of unreacted components, etc. However, the reason for obtaining the effect is not limited to the above content.

[0013] The above silicon-containing waste preferably contains coal ash. By doing so, high-purity silica can be produced. In addition, since the amount of alkali in the residue can be reduced, the residue can be more suitably used as a cement raw material.

[0014] CO 2 The contained gas preferably includes exhaust gas generated in a factory. By doing so, silica can be produced at an even lower manufacturing cost.

[0015] In the above manufacturing method, it is preferable to use the above residue as a cement raw material. Since an aqueous solution with a low concentration of sodium hydroxide is used when preparing the slurry, Na remaining in the residue 2 O can be reduced. By doing so, the residue can be suitably used as a cement raw material. By effectively utilizing the residue in this way, the manufacturing cost of silica can be further reduced.

[0016] In one aspect, the present invention provides a method for manufacturing cement clinker, which includes a slurry preparation step of mixing a silicon-containing waste and an aqueous solution with a sodium hydroxide concentration of 1 to 24% by mass to prepare a slurry containing silicate, a separation step of separating an extract containing silicate and a residue from the slurry to obtain a residue with an Na 2 O content of 0.01 to 5% by mass, and a firing step of using the residue as a raw material for cement.

[0017] In the above manufacturing method, a slurry containing silicate is prepared using a silicon-containing waste and an aqueous solution with a lower sodium hydroxide concentration than before, and the residue obtained from this slurry is used as a raw material for cement. Thus, since a silicon-containing waste and a low-concentration aqueous sodium hydroxide solution are used as raw materials, fluctuations in the content of the silica component can be suppressed more than when using the silicon-containing waste as a raw material as it is. Therefore, it is easy to set the blending conditions, and a cement clinker with stable quality can be produced. Also, the residue is Na 2Since the content of O is sufficiently reduced, the generation of volatile components of the alkali components is suppressed when introduced into the cement kiln. As a result, the generation and precipitation of volatile components are reduced, and the load on the cement kiln is alleviated. Therefore, cement clinker can be stably produced.

[0018] In one aspect, the present invention provides a method for producing a cement composition, which includes a blending step of blending the cement clinker obtained by the above-described production method and gypsum. This production method uses the cement clinker obtained by the above-described production method. Therefore, it is easy to set the blending conditions, and a cement composition with stable quality can be produced.

[0019] In one aspect, the present invention provides a method for producing a cement composition, which includes a slurry preparation step of mixing a silicon-containing waste and an aqueous solution with a sodium hydroxide concentration of 1 to 24% by mass to prepare a slurry containing silicate, a separation step of separating an extract containing silicate and a residue from the slurry to obtain a residue with an Na 2 O content of 0.01 to 5% by mass, and a blending step of blending the residue, the cement clinker, and gypsum. This production method can effectively utilize the residue obtained from the silicon-containing waste as a new option for the blending raw materials of the cement composition. And it can suppress the variation in the content of the silica component of the raw materials compared to the case of directly using the silicon-containing waste as a raw material. Therefore, it is easy to set the blending conditions, and a cement composition with stable quality can be produced.

Effects of the Invention

[0020] According to the present invention, it is possible to provide a method for producing silica that can be used in various industries, which can be produced from silicon-containing waste at low cost and with high safety. Further, by suppressing fluctuations in the content of the silica component in the raw material, it is possible to provide a method for producing cement clinker that is easy to set blending conditions and can produce cement clinker that is stable in terms of quality. Further, by using such cement clinker, it is possible to provide a method for producing a cement composition that is easy to set blending conditions and can produce a cement composition that is stable in terms of quality. Furthermore, the effective utilization amount of silicon-containing waste can be increased.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings as appropriate. However, the following embodiments are examples for explaining the present invention and are not intended to limit the present invention to the following contents.

[0023] A method for producing silica according to an embodiment includes a slurry preparation step of mixing a silicon-containing waste and an aqueous solution having a sodium hydroxide concentration of 1 to 24% by mass to prepare a slurry containing a silicate, a separation step of separating an extract containing a silicate and a residue from the slurry, and a crystallization step of bringing the extract into contact with a CO 2 -containing gas to crystallize silica. FIG. 1 is a diagram showing an example of the production method of the present embodiment.

[0024] In the slurry preparation step, as raw materials, an aqueous solution with a concentration of 1 to 24% by mass of silicon-containing waste and sodium hydroxide is used. The silicon-containing waste may contain at least one selected from the group consisting of coal ash, incineration ash, slag, and waste glass. Among these, from the viewpoints of improving the purity of silica and reducing the amount of alkali in the residue, it is preferable that the silicon-containing waste contains coal ash. The coal ash is not particularly limited as long as it is produced by the combustion of coal.

[0025] The coal ash may be, for example, ash generated when pulverized coal is burned in a coal-fired power plant. More specifically, fly ash recovered by an electrostatic precipitator or the like, and clinker ash dropped and collected from a combustion boiler may be mentioned. In particular, fly ash is composed of fine particles and has high reactivity with an aqueous sodium hydroxide solution, and also has a low content of impurities such as calcium, sodium, and heavy metals. Therefore, it is preferable that the silicon-containing waste contains fly ash.

[0026] The silicon content of the silicon-containing waste is preferably 30 to 80% by mass, more preferably 40 to 80% by mass, and even more preferably 60 to 80% by mass in terms of SiO 2 conversion. If the silicon content is within the above range, the silicate component required for the production of silica can be sufficiently ensured. Also, since the silicon content in the residue can be maintained at a certain level, it can be suitably used as a cement raw material.

[0027] The chemical composition of the silicon-containing waste, based on the dry mass, is preferably such that Al 2 O 3 is 1 to 40% by mass, Fe 2 O 3 is 0 to 5% by mass, CaO is 0 to 5% by mass, MgO is 0 to 5% by mass, SO 3 is 0 to 5% by mass, Na 2 O is 0 to 5% by mass, and K 2 O is 0 to 5% by mass. With a silicon-containing waste having such properties, the impurities precipitated during silica crystallization are reduced, and high-purity silica can be easily obtained.

[0028] The average particle size of the silicon-containing waste is preferably 0.1 to 100 μm, more preferably 0.5 to 50 μm, and even more preferably 1 to 10 μm. If the particle size of the silicon-containing waste is within the above range, the silicate component can be efficiently extracted. The above average particle size is the median diameter (D50) determined by the laser diffraction / scattering method.

[0029] An aqueous solution of sodium hydroxide with a concentration of 1 to 24% by mass (sodium hydroxide aqueous solution) may use the industrially produced sodium hydroxide aqueous solution as it is, or a solution prepared by mixing a sodium hydroxide aqueous solution and water to a predetermined concentration may be used. Also, solid sodium hydroxide in the form of granules or powder may be mixed with water and adjusted to an aqueous solution of a predetermined concentration before use.

[0030] The concentration of sodium hydroxide in the sodium hydroxide aqueous solution is 1 to 24% by mass. From the viewpoint of sufficiently extracting the silicate component, this sodium hydroxide concentration is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. On the other hand, from the viewpoints of suppressing the extraction of impurities such as Ca and increasing the purity of silica, and suppressing the residual Na derived from the sodium hydroxide aqueous solution in the residue for suitable use as a cement raw material, the sodium hydroxide concentration is preferably 20% by mass or less, more preferably 18% by mass or less.

[0031] In the slurry preparation step, the above-mentioned raw materials are mixed to prepare a slurry containing silicate. In this slurry preparation step, by setting the concentration of sodium hydroxide in the aqueous sodium hydroxide solution mixed with the silicon-containing waste within the above-mentioned range, it is possible to extract silicate with high purity while suppressing the extraction of impurities such as Ca. The reason for this is not clear, but for example, when heating the silicon-containing waste in an aqueous solution containing sodium hydroxide at a concentration exceeding 24% by mass, the amount of Na in the aqueous solution becomes excessive, and substitution between Ca in the Ca-containing mineral contained in the silicon-containing waste and Na in the aqueous solution easily occurs. As a result, the extraction rate of Ca increases. On the other hand, when the concentration of the aqueous sodium hydroxide solution is 24% by mass or less, the amount of Na in the aqueous solution becomes an appropriate amount, and substitution between the Ca-containing mineral and Na in the aqueous solution is suppressed. As a result, it is presumed that the extraction rate of Ca decreases.

[0032] The mixing ratio of the aqueous sodium hydroxide solution to the silicon-containing waste when preparing the slurry, that is, the liquid / solid ratio, is preferably 1 to 20, more preferably 1 to 5, and even more preferably 2 to 3 on a mass basis. If the liquid / solid ratio is within the above range, it becomes easier to adjust the molar ratio of Na contained in sodium hydroxide and Si contained in the silicon-containing waste to a range of 1.0 to 2.0 while ensuring the fluidity of the slurry. As a result, it is possible to suppress the amount of Na in the extract from becoming excessive, and it becomes easier to obtain high-purity silica.

[0033] The slurry is preferably heated from the viewpoint of promoting the reaction between the silicon-containing waste and sodium hydroxide. The heating of the slurry may be carried out while mixing and stirring the slurry and, if necessary, while applying pressure. The temperature of the slurry is preferably 50 to 200°C. As a result, silicate can be sufficiently extracted from the silicon-containing waste. From the viewpoint of further promoting the extraction of silicate, the temperature of the slurry is preferably 65°C or higher, more preferably 80°C or higher. On the other hand, from the viewpoint of simplifying the equipment, the temperature of the slurry is preferably 150°C or lower, more preferably 100°C or lower.

[0034] In the above temperature range, the slurry is preferably heated for 0.5 to 4 hours, more preferably for 1 to 3.5 hours, and even more preferably for 2 to 3.5 hours. By doing so, silicate can be efficiently and sufficiently extracted from the silicon-containing waste.

[0035] In the separation step, an extract containing silicate and a residue are separated from the slurry. The slurry may be separated into an extract containing silicate and a residue which is a solid content. For example, the slurry may be separated into an extract and a residue using a known dehydrator. Examples of the dehydrator include a filter press, a belt press, a roll press, a centrifugal dehydrator, and a ceramic filter. However, the separation means is not limited to these.

[0036] The extraction rate of silicate extracted into the extract from the silicon-containing waste is preferably 5 to 60%, more preferably 10 to 50%, and even more preferably 15 to 40%. If the extraction rate of silicate is within the above range, sufficient silicate required for silica production can be ensured and the yield of high-purity silica can be increased. In addition, since the residue also contains a certain amount of silicate, the residue can be suitably used as a cement raw material. In this specification, the extraction rate of silicate is a value obtained by dividing the silicon content in the extract in which silicate is extracted by the silicon content in the fly ash. Details of the derivation method will be described in the examples below.

[0037] The ratio (residual rate) of the silicate contained in the silicon-containing waste remaining in the residue is preferably 40 to 95%, more preferably 50 to 90%, and even more preferably 60 to 85%. If the residual rate of silicate is within the above range, sufficient silicate required for silica production can be ensured and the yield of silica can be increased. In addition, since the residue also contains a certain amount of silicate, the residue can be suitably used as a cement raw material. When the slurry is separated into two, an extract and a residue, the residual rate of silicate in the residue can be obtained by subtracting the above-mentioned extraction rate of silicate from 100 (%).

[0038] The extraction rate of Ca extracted from the silicon-containing waste into the extract of the slurry is preferably 0.1 to 5%, more preferably 0.1 to 2%, and still more preferably 0.1 to 1%. If the extraction rate of Ca is within the above range, the amount of calcium carbonate precipitated during silica crystallization can be reduced, and the purity of silica can be increased. In this specification, the extraction rate of Ca is a value obtained by dividing the calcium content in the extract from which the silicate has been extracted by the calcium content in the coal ash. Details of the derivation method will be described in the examples below.

[0039] From the viewpoint of obtaining silica having a sufficiently high purity, the Na concentration of the extract is preferably 300 g / L or less, more preferably 200 g / L or less, and still more preferably 100 g / L or less. The lower limit of the Na concentration may be, for example, 10 g / L.

[0040] The content of Na in the residue in terms of Na 2 O conversion (Na 2 O content) is preferably 0.01 to 5% by mass, more preferably 0.01 to 3% by mass, and still more preferably 0.01 to 1% by mass. If the Na 2 O content in the residue is within the above range, the residue can be suitably used as a cement raw material. In this embodiment, since a low-concentration aqueous sodium hydroxide solution is used in the slurry preparation step, the Na 2 O content of the residue can be smoothly adjusted to the above range.

[0041] The content of Si in the residue in terms of SiO 2 conversion (SiO 2 content) is preferably 20% by mass or more, more preferably 30% by mass or more, and still more preferably 35% by mass or more. If the SiO 2 content in the residue is within the above range, the residue can be suitably used as a cement raw material. The SiO 2 content in the residue is preferably 70% by mass or less, more preferably 60% by mass or less. The SiO 2If the content is within the above range, the yield of SiO 2 can be made sufficiently large. The SiO 2 content of the residue is determined by converting the Si content to SiO 2 .

[0042] In the crystallization step, silica particles are crystallized by bringing the extract into contact with a CO 2 -containing gas. Before contacting with the CO 2 -containing gas, the extract obtained in the fractionation step may be diluted with water, and the diluted extract may be brought into contact with the CO 2 -containing gas. Examples of the dilution water include tap water, industrial purified water, industrial wastewater, and water for washing and filtering the residue, but are not limited thereto. By diluting the extract and appropriately changing the concentration of the silicate, the primary particle diameter of the silica particles to be crystallized can be adjusted. The method of contacting the extract with the CO 2 -containing gas is not particularly limited. For example, the CO 2 -containing gas may be bubbled and aerated through the extract, or a countercurrent contact may be made between the descending extract and the ascending CO 2 -containing gas using a contact tower or the like.

[0043] The aeration flow rate of the CO 2 -containing gas is preferably 1 to 30 L / min, more preferably 5 to 20 L / min, and even more preferably 10 to 15 L / min per liter of the extract. If the aeration flow rate is within the above range, silica particles having a fine and high specific surface area can be crystallized. Also, the primary particle diameter of the silica particles can be adjusted to a desired value by appropriately changing the aeration flow rate within the above range.

[0044] The CO 2 -containing gas used in the crystallization step preferably contains exhaust gas discharged from the factory from the viewpoint of cost reduction. As the exhaust gas discharged from the factory, it is preferable to contain at least one selected from the group consisting of, for example, boiler exhaust gas, cement kiln exhaust gas, chlorine bypass exhaust gas, and synthetic gas exhaust gas from a chemical factory. The CO 2 -containing gas is CO 2From the perspective of improving purity, industrial gas may be included.

[0045] CO 2 CO in the contained gas 2 The concentration is preferably 10 to 100%, more preferably 10 to 98%, and still more preferably 30 to 90%. CO 2 CO with a concentration within the above range 2 If the contained gas is used, it becomes easier to produce high-purity silica. In the crystallization step, silica particles are generated, and the extract becomes slurry-like (silica-containing slurry). The contact between the extract and the CO 2 contained gas is preferably carried out until the pH of the extract (silica-containing slurry) preferably becomes 7 to 12, more preferably 8 to 10. Thereby, silica can be sufficiently crystallized, and the yield of silica can be increased. Solid-liquid separation of the obtained silica-containing slurry may be performed to recover silica. Thereby, powdery silica can be obtained. The sodium carbonate component may be recovered from the alkaline solution from which silica has been recovered by the above solid-liquid separation and reused as part of the raw material in the extraction step.

[0046] The above method for producing silica may have a washing step of washing the solid phase containing the crystallized silica particles after the crystallization step. The washing may be performed by solvent substitution of the silica-containing slurry. Specifically, solid-liquid separation and addition of the washing liquid may be repeated. The solid-liquid separation may be performed by centrifugation or filtration.

[0047] It is preferable to use water for washing, and it is preferable to use an acid and water. When washing with an acid and water, it is particularly preferable to wash with water after washing with the acid. By washing with water after washing with the acid, impurities can be removed with a smaller amount of washing. In addition, silica with higher purity and higher specific surface area can be produced. The factors include that salts such as carbonates crystallized together with silica particles are easily dissolved by the acid and are easily removed by subsequent washing with water, the amount of crystallization of silica particles increases due to the reaction of unreacted silicate with the acid, and pores blocked by the removal of impurities are exposed.

[0048] The acid used for washing may contain at least one selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. These can be used alone or in combination. Among these, from the viewpoint of further increasing the purity of silica, it is preferable to use hydrochloric acid for washing. In this specification, dilute hydrochloric acid is also included in hydrochloric acid.

[0049] In the washing step, the purity of silica can be improved by repeatedly performing solvent substitution in which solvent addition and solid-liquid separation are carried out. The number of repetitions of solvent substitution is preferably 3 or more times, more preferably 4 or more times, and still more preferably 5 or more times. By increasing the number of repetitions in this way, the main impurities in silica can be removed, and high-purity silica can be recovered.

[0050] The SiO 2 purity of the silica produced by the method for producing silica of this embodiment is preferably 85% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and particularly preferably 97% by mass or more, based on the dry mass. The silica may be in powder form. Such high-purity silica powder can be suitably used as raw materials for, for example, filler materials, paints, adhesives, abrasives, and fine ceramics. However, its uses are not limited to those described above.

[0051] The BET specific surface area of the silica powder produced by the method for producing silica of this embodiment is preferably 30 m 2 / g or more, more preferably 200 m 2 / g or more, and still more preferably 400 m 2 / g or more. Such high-specific-surface-area silica can be suitably used as filler materials, adsorbent materials, moisture-absorbing materials, admixtures for concrete, antiblocking materials, and the like.

[0052] As shown in Fig. 1, the method for producing silica according to this embodiment may have a firing step of introducing the residue separated from the slurry, as one of the cement raw materials, into a cement kiln such as a rotary kiln. The residue separated from the slurry in the separation step contains Si and Al and has a low content of Na 2 O. Since the content of Na 2 O is low, the volatiles generated during firing in the cement kiln can be reduced. Therefore, the dust generated during firing is reduced, and the equipment load can be alleviated. Accordingly, cement clinker can be stably produced.

[0053] Other cement raw materials (such as limestone, silica stone, clay, construction-generated soil, blast furnace slag, and steelmaking slag) may be introduced into the cement kiln together with the residue. In the cement kiln, the cement raw materials are fired to obtain cement clinker. The cement clinker may be ground while being mixed with gypsum in, for example, a grinder (finishing mill), etc. Thereby, cement (cement composition) is obtained. Fly ash, slag powder, etc. may be blended as necessary. The obtained cement composition may be Portland cement or blended cement.

[0054] According to the method for producing silica of this embodiment, silica can be produced with high safety. In addition, the setting of the blending conditions is easy, and cement clinker and cement composition having stable quality can be produced.

[0055] In the example of Fig. 1, an example of producing cement clinker and cement together with silica has been described, but it is not essential to produce cement clinker and cement. For example, as shown in Fig. 2, only silica may be produced. In this case, the residue may be used for other purposes.

[0056] A method for manufacturing cement clinker according to an embodiment includes a slurry preparation step of mixing a silicon-containing waste and an aqueous solution with a sodium hydroxide concentration of 1 to 24% by mass to prepare a slurry containing silicate, a separation step of separating an extract containing silicate and a residue from the slurry to obtain a residue with an Na 2 O content of 0.01 to 5% by mass, and a firing step of using the residue as a raw material for a cement kiln. The slurry preparation step, separation step, and firing step in this manufacturing method can be performed in the same manner as the slurry preparation step and separation step in the above-described silica manufacturing method. Therefore, the description content of the above-described silica manufacturing method is also applicable to the cement clinker manufacturing method according to this embodiment, and duplicate descriptions are omitted.

[0057] The extract containing silicate obtained in the separation step of the cement clinker manufacturing method of this embodiment can be suitably used as a raw material for manufacturing silica. Therefore, silica may be manufactured by the above-described crystallization step and washing step. However, manufacturing silica is not essential, and the extract containing silicate may be used for other purposes. Thus, in the cement clinker manufacturing method of this embodiment, silica may be manufactured together with the cement clinker, or the cement clinker may be manufactured without manufacturing silica.

[0058] In the cement clinker manufacturing method of this embodiment, since a residue with an Na 2 O content of 0.01 to 5% by mass is used as a cement raw material, it is possible to reduce the volatile matter generated when firing the cement raw material in a cement kiln in the firing step. Therefore, the dust generated during firing is reduced, and the equipment load can be reduced. Thus, cement clinker can be stably manufactured.

[0059] The manufacturing method of the cement composition according to one embodiment includes a blending step of blending cement clinker and gypsum after the firing step in the above-described manufacturing method of cement clinker. The blending may be performed while grinding the cement clinker using an ordinary grinder (finishing mill). The resulting cement composition may be Portland cement or blended cement. According to the manufacturing method of the cement composition of the present embodiment, it is easy to set the blending conditions, and a cement composition stable in terms of quality can be manufactured.

[0060] The manufacturing method of the cement composition according to another embodiment includes a slurry preparation step of mixing a silicon-containing waste and an aqueous solution having a sodium hydroxide concentration of 1 to 24% by mass to prepare a slurry containing silicate, and separating an extract containing silicate and a residue from the slurry to obtain a residue having an Na 2 O content of 0.01 to 5% by mass, and a blending step of blending the residue, cement clinker, and gypsum. The slurry preparation step and the separation step may be the same as the slurry preparation step and the separation step in the above-described manufacturing method of silica. Therefore, the description content in the manufacturing method of silica is also applicable to this manufacturing method of the cement composition. Duplicate descriptions are omitted here.

[0061] The cement clinker blended in the blending step may be the cement clinker obtained by the above-described manufacturing method of cement clinker, or the cement clinker obtained by a manufacturing method different from the above-described manufacturing method of cement clinker. The blending may be performed by mixing the residue and gypsum while grinding the cement clinker using an ordinary grinder (finishing mill). The resulting cement composition may be Portland cement or blended cement.

[0062] The extract containing silicate obtained in the separation step can be suitably used as a raw material for producing silica. Therefore, silica may be produced by the above-described crystallization step and washing step. However, it is not essential to produce silica, and the extract containing silicate may be used for other purposes. Thus, in the method for producing the cement composition of the present embodiment, silica may be produced together with the cement composition, or the cement composition may be produced without producing silica.

[0063] According to the method for producing the cement composition of the present embodiment, the residue can be effectively utilized as a new option for the blending raw materials of the cement composition. Therefore, it is easy to set the blending conditions, and a cement composition having stable quality can be produced.

[0064] As described above, the embodiments of the present invention have been described, but the present invention is not limited to the above embodiments at all.

Examples

[0065] The content of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0066] [1: Extraction of Silicate from Silicon-Containing Waste] A plurality of experiments were conducted in which at least one of the concentration of the sodium hydroxide aqueous solution mixed with the silicon-containing waste, the heating temperature when preparing the slurry, and the heating time was different. As a result, the influence of each condition on the extraction rates of Si and Ca from the silicon-containing waste, the Na concentration in the extract, and the Na 2 content in the residue was examined. The specific procedure and results will be described below.

[0067] As the silicon-containing waste, coal ash (produced by Ube Industries, Ltd., fly ash) generated from a coal-fired power plant that burns pulverized coal was used. The loss on ignition and chemical components of the coal ash used are shown in Table 1. The values shown in Table 1 are the values measured by the following method.

[0068] · Loss on ignition of coal ash: Measured in accordance with the loss on ignition measurement method specified in JIS R 5202 "Chemical analysis methods for cement". · SiO content of coal ash 2 、Al 2 O 3 、Fe 2 O 3 、CaO, MgO, SO 3 、Na 2 O、K 2 O content: Measured in accordance with JIS M 8853 "Chemical analysis methods for aluminosilicate raw materials for ceramics".

[0069]

Table 1

[0070] (Example 1) Sodium hydroxide (manufactured by Fujifilm Wako Pure Chemical Corporation, reagent grade 1, granular) and distilled water were mixed to prepare a 3.7 mass% aqueous sodium hydroxide solution. 50 g of coal ash and 550 g of an aqueous sodium hydroxide solution with a concentration of 3.7 mass% were weighed. These were mixed at 200 rpm using a stirrer (manufactured by Shin-Tong Science Co., Ltd., Three-One Motor type 600G) in a container adjusted to 80°C and reacted for 1 hour. The mass ratio of the aqueous sodium hydroxide solution to the coal ash was as shown in the "liquid / solid ratio" in Table 2. The slurry thus obtained was filtered using a commercially available filter paper (circular quantitative filter paper No. 5C) and a suction filtration device (manufactured by Advantec Toyo Co., Ltd.) to separate it into an extract and a residue (solid content).

[0071] The concentrations of Si and Ca contained in the extract were quantified using an ICP emission spectroscopic analyzer (manufactured by Hitachi High-Tech Science Corporation, model: PS3520UVDDII). The concentration of Na contained in the extract was quantified using an atomic absorption spectrophotometer (manufactured by Shimadzu Corporation, model: AA-7000). The extraction rates of (1) silicate, (2) Ca, and (3) the Na O content in the residue were determined by the following calculation formulas. In addition, the Na in (3) 2 O 2The mass of O was determined by converting the quantitative analysis results of Na. The results are shown in Table 2.

[0072] (1) Extraction rate of silicate (%) = Si (g) in the extract / {mass of coal ash (g) × Si content of coal ash (mass%)} × 100 (2) Extraction rate of Ca (%) = Ca (g) in the extract / {mass of coal ash (g) × Ca content of coal ash (mass%)} × 100 (3) Na in the residue 2 O content (mass%) = {Na 2 O (g) at the time of raw material blending - Na 2 O (g) contained in the extract} / mass of the residue (g) × 100

[0073] (Examples 2 to 4, and Comparative Example 1) Experiments were conducted in the same manner as in Example 1 except that the concentration of the sodium hydroxide aqueous solution was changed as shown in Table 2, and an extract and a residue were obtained. In the same manner as in Example 1, each measurement and calculation was performed to determine the extraction rates of silicate and Ca, and the Na 2 O content in the residue. The results are shown in Table 2.

[0074] From the results of Examples 1 to 4 and Comparative Example 1, it was confirmed that the higher the concentration of sodium hydroxide in the sodium hydroxide aqueous solution, the higher the extraction rate of silicate. However, it was confirmed that the higher the sodium hydroxide concentration, the higher the concentration of Na contained in the extract. Also, in Comparative Example 1 where the sodium hydroxide concentration was 40 mass%, the extraction rate of Ca was also extremely high. The Ca component precipitates as CaCO 3 during crystallization, which is a factor in reducing the purity of the obtained silica. Therefore, it is preferable that the extraction rate of CaO is low.

[0075] In Examples 1 to 3 using a sodium hydroxide aqueous solution with a low sodium hydroxide concentration (24 mass% or less), the Na 2 O content in the residue was sufficiently low.

[0076] (Examples 5 to 8) Examples 5 and 6 are those in which the heating temperature during slurry preparation was changed compared to Example 4, and Examples 7 and 8 are those in which the heating time during slurry preparation was changed compared to Example 4. Under the same conditions as in Example 4, slurry preparation and separation operations were performed to obtain the extracts and residues of Examples 5 to 8. Also in Examples 5 to 8, in the same manner as in Example 4, each measurement and calculation was performed to obtain the extraction rates of silicate and Ca, the Na concentration in the extract, and Na 2 O content in the residue. The results are shown in Table 2.

[0077] From Examples 4 to 8, it was confirmed that under the condition of a constant sodium hydroxide concentration, by changing the heating temperature and / or heating time of the slurry, the extraction rate of silicate can be adjusted while suppressing the Na concentration and Ca extraction rate in the extract.

[0078]

Table 2

[0079] [2. Extraction of silicate, crystallization, recovery, and washing of silica] In this experiment, the washing method of the solid phase (solid content) containing silica crystallized and recovered from the extract was changed, and the effects on the purity and BET specific surface area of the obtained silica were examined.

[0080] (Example 9) Fly ash similar to the fly ash used in Examples 1 to 8 and Comparative Example 1 was prepared. 200 g of this fly ash and 500 g of an aqueous sodium hydroxide solution with a sodium hydroxide concentration of 16% by mass prepared in the same manner as in Example 1 were mixed, and using a stirrer, the reaction was carried out while stirring at 95 °C for 3.5 hours. The slurry thus obtained was filtered using a commercially available filter paper (circular quantitative filter paper No. 5C) and a suction filtration device (manufactured by Advantec Toyo Co., Ltd.) to separate it into an extract and a residue (solid content).

[0081] The extraction rate of silicate determined by the above calculation formula was 34%, and the extraction rate of Ca was 0.7%. Also, SiO of the residue determined by the following calculation formula 2The content was 45.2 mass%. The mass of SiO 2 was determined by converting the quantitative analysis result of Si in the extract into SiO 2 . The SiO 2 content (mass%) in the residue = {SiO 2 (g) at the time of raw material blending - SiO 2 (g) contained in the extract} / mass of the residue (g) × 100

[0082] After the reaction was completed, 0.3 L of the extract containing the silicate component was diluted with distilled water so that the liquid volume became 1 L, and the diluted solution was transferred to a crystallization reaction tank. While mixing at 450 rpm using a stirrer, carbon dioxide gas (manufactured by Air Liquide Japan, CO 2 concentration: 99.5 volume% or more) was bubbled at 15 L / min and reacted until the pH reached 9. As a result, silica particles were crystallized to obtain a silica-containing slurry containing silica particles.

[0083] After the reaction was completed, the silica-containing slurry was separated into solid and liquid by centrifugation. In order to wash the solid phase (solid content) containing silica particles, the liquid phase of the silica-containing slurry was replaced with distilled water and stirred, and then solid-liquid separation was performed again by centrifugation. Such replacement of the distilled water by centrifugation was performed 6 times in total to wash the solid phase containing silica particles (water washing). After repeating the water washing 6 times, it was dried to obtain a solid content.

[0084] The solid content obtained by drying using a planetary mill (manufactured by Ito Seisakusho, model LA-PO.1) was crushed at 340 rpm for 8 minutes and recovered as powdery silica. The SiO 2 content (purity) and BET specific surface area of this silica powder were as shown in Table 3.

[0085] The SiO 2 purity of the silica powder was determined by the following procedure. The insoluble Si in the silica powder was quantified by the perchloric acid dehydration gravimetric method. Also, the acid-soluble Si was quantified using an ICP emission spectroscopic analyzer (manufactured by Hitachi High-Technologies Corporation, model: PS3520UVDDII). The respective quantified values were added together to obtain the SiO 2The purity was determined. The BET specific surface area of the silica powder was determined by the following procedure. The silica powder was heated in a nitrogen atmosphere at 110 °C for 30 minutes. Thereafter, it was measured using a specific surface area and pore size distribution measuring apparatus (manufactured by MicrotracBEL Corp., apparatus name: BEL-SORP-mini).

[0086] [Example 10] Silica particles were crystallized in the same procedure as in Example 9 to obtain a silica-containing slurry containing silica particles. After obtaining the silica-containing slurry, the silica-containing slurry was separated into solid and liquid by centrifugation. In order to wash the solid phase containing silica particles, the liquid phase of the silica-containing slurry was replaced with dilute hydrochloric acid (HCl concentration: 9.5 to 10.5 w / v%) and stirred (acid washing). Thereafter, the solid content was washed by performing a total of 5 replacements with distilled water by centrifugation (water washing). Washing, drying, and pulverization were performed in the same procedure as in Example 9 except that the first washing was performed with dilute hydrochloric acid instead of distilled water to obtain silica powder. The SiO of this silica powder 2 The purity and BET specific surface area were measured in the same manner as in Example 9. The results are shown in Table 3.

[0087] [Table 3]

[0088] In Examples 9 and 10, silica powder having a sufficiently high purity could be obtained. Compared with Example 9 in which the solid phase containing silica was washed only with water, in Example 10 in which washing was performed using a combination of an acid and water, silica powder having a higher purity and a higher specific surface area could be produced. As factors for this, it is presumed that sodium carbonate precipitated inside the pores of the silica particles by the crystallization reaction was dissolved by the acid and removed by washing, and that unreacted sodium silicate present in the silica-containing slurry reacted with hydrochloric acid, and porous gel-like silica was formed on the surface of the silica particles crystallized by aeration of carbon dioxide gas. [Industrial Applicability]

[0089] According to the silica production method of the present invention, by using an aqueous sodium hydroxide solution of low concentration, silica having high-quality properties can be recovered from silicon-containing waste safely and at low cost. As a result, it is possible to lead to an increase in the effective utilization amount of silicon-containing waste.

Claims

1. A slurry preparation step of mixing a silicon-containing waste and an aqueous solution having a sodium hydroxide concentration of 1 to 16% by mass to prepare a slurry containing a silicate; A separation step of separating an extract containing the silicate from the slurry and a residue having a content of Si in terms of SiO ２ of 30% by mass or more; The extraction liquid and CO ２ A crystallization step of bringing the gas containing the same into contact to crystallize silica particles; A washing step of washing a solid phase containing the crystallized silica particles; In the washing step, solid-liquid separation of the silica-containing slurry containing the solid phase and addition of a washing liquid are repeatedly performed for washing, and the SiO of silica in the solid phase ２ A method for producing silica that increases the purity.

2. The method for producing silica according to claim 1, wherein the extraction rate of the silicate extracted into the extract in the separation step is 5 to 40%.

3. In the separation step, the residue having a content of Na in terms of Na ２ O of 0.01 to 5% by mass is obtained from the slurry, and the method for producing silica according to claim 1 or 2. ２ ​

4. In the slurry preparation step, the method for producing silica according to any one of claims 1 to 3, wherein the slurry is heated to 50 to 200 ° C to react the silicon-containing waste with the sodium hydroxide.

5. The method for producing silica according to any one of claims 1 to 4, wherein the washing of the solid phase repeatedly performed in the washing step includes washing with an acid and then washing with water.

6. The method for producing silica according to any one of claims 1 to 5, wherein the silicon-containing waste contains coal ash.

7. The foregoing CO ２ The method for producing silica according to any one of claims 1 to 6, wherein the gas containing the gas generated in the factory contains exhaust gas generated in the factory.

8. The method for producing silica according to any one of claims 1 to 7, wherein the residue is used as a cement raw material.

9. The SiO of the silica obtained through the washing step ２ The method for producing silica according to any one of claims 1 to 8, wherein the purity is 85% by mass or more.

10. A slurry preparation step of mixing a silicon-containing waste and an aqueous solution having a sodium hydroxide concentration of 1 to 24% by mass to prepare a slurry containing a silicate; The extract containing the silicate and the residue are separated from the slurry, and the residue having a Na content in terms of Na ２ O conversion of 0.01 to 5% by mass and an Si content in terms of SiO ２ conversion of 30% by mass or more is obtained; a separation step A firing step of introducing the residue as a raw material for cement into a cement kiln to obtain a cement clinker; a method for producing a cement clinker.

11. A method for producing a cement composition, comprising a blending step of blending the cement clinker obtained by the production method of claim 10 and gypsum to obtain a cement composition.

12. A slurry preparation step of mixing a silicon-containing waste and an aqueous solution having a sodium hydroxide concentration of 1 to 24% by mass to prepare a slurry containing a silicate; Separate an extract containing the silicate and a residue from the slurry, and obtain the residue in which the content in terms of Na ２ O is 0.01 to 5% by mass and the content in terms of SiO ２ of Si is 30% by mass or more. A separation step ２ wherein the content in terms of Na ２ O is 0.01 to 5% by mass and the content in terms of SiO ２ of Si is 30% by mass or more ２ and a separation step of obtaining the residue A blending step of blending the residue, the cement clinker, and gypsum; a method for producing a cement composition.

13. In the blending step, the method for producing a cement composition according to claim 12, wherein the residue, the cement clinker, and the gypsum are blended to obtain Portland cement or blended cement.

Images