JP5955653B2 - Method for reducing hexavalent chromium elution amount in fired product and method for producing fired product - Google Patents

Description

  The present invention relates to a method for effectively reducing the hexavalent chromium elution amount of a fired product, and a method for producing a fired product in which the hexavalent chromium elution amount is effectively reduced.

Conventionally, various fired products have been used as materials such as mortar and concrete aggregates, roadbed materials, embankment materials, and backfill materials, and are also used as cement additives by further pulverization. In order to obtain such a calcined product, natural minerals are usually used as raw materials, and in many of these raw materials, simple chromium or trivalent chromium (Cr ³⁺ ) is unavoidable even though the amount is small. Mixed.

  On the other hand, in recent years, with the economic growth and population concentration in urban areas, industrial waste, general waste, etc. are rapidly increasing. In order to promote the consumption of these wastes and the like, for example, Patent Document 1 proposes a calcined product that can use wastes and the like as a raw material. Is likely to be mixed.

JP 2004-2155 A

However, in order to obtain the fired product as described above, a calcination step is inevitably performed, and thus hexavalent chromium (Cr ⁶⁺ ) may be generated from single chromium or trivalent chromium. The generated hexavalent chromium has a higher risk of elution from the obtained calcined product, and the standard value of the amount of elution is determined by JIS K 0058, the Environmental Agency Notification No. 13 or the Environmental Agency Notification No. 46. It has been. Therefore, it is desired to avoid such a risk in order to obtain suitable materials for earthwork materials such as roadbed materials, embankment materials and backfill materials, and aggregates for concrete.

  Therefore, the object of the present invention is to obtain an effect of the amount of hexavalent chromium eluted from the fired product in obtaining a fired product that is suitable for earthwork materials such as roadbed materials, embankment materials and backfill materials, and aggregates for concrete. It is providing the method which can be reduced automatically.

  Therefore, the present inventor has conducted various studies, and in order to obtain a fired product having a specific mineral composition, before firing the raw material, the raw material is prepared so that the mass of the specific metal in the raw material satisfies a specific relationship. As a result, it was found that the amount of hexavalent chromium eluted from the fired product can be effectively reduced, and the present invention has been completed.

That is, in the present invention, by firing the raw material, 2CaO.Al ₂ O ₃ .SiO ₂ (hereinafter referred to as C ₂ AS) per 100 parts by mass of 2CaO.SiO ₂ (hereinafter referred to as C ₂ S). 10 to 100 parts by mass and 3CaO · Al ₂ O ₃ (hereinafter referred to as C ₃ A) content is 20 parts by mass or less.
Firing characterized in that the raw materials are prepared so that the molar amounts of chlorine (Cl), potassium (K) and sodium (Na) in the raw material before firing satisfy the following formulas (1) and (2). The present invention provides a method for reducing the elution amount of hexavalent chromium of a product.
Molar amount of Cl / Molar amount of K ≧ 0.8 (1)
Molar amount of Cl / (Molar amount of Na + Molar amount of K) ≦ 1.0 (2)

Further, the present invention includes a step of firing the raw material for 2CaO · SiO ₂ 100 parts by mass, the _{2CaO · Al 2 O 3 · SiO} 2 containing 10 to 100 parts by weight, and 3CaO · Al ₂ O ₃ Is a method for producing a fired product having a content of 20 parts by mass or less,
Firing characterized in that the raw materials are prepared so that the molar amounts of chlorine (Cl), potassium (K) and sodium (Na) in the raw material before firing satisfy the following formulas (1) and (2). The manufacturing method of a thing is provided.
Molar amount of Cl / Molar amount of K ≧ 0.8 (1)
Molar amount of Cl / (Molar amount of Na + Molar amount of K) ≦ 1.0 (2)

  According to the method for reducing the hexavalent chromium elution amount of the fired product of the present invention, excellent strength development and excellent durability are maintained, and earthwork materials such as roadbed materials, embankment materials and backfill materials and concrete aggregates are used. In a fired product that can be a suitable material, the amount of hexavalent chromium eluted from the fired product can be effectively and easily reduced. Further, according to the method for producing a fired product of the present invention, it becomes a suitable material for earthwork materials such as roadbed materials, embankment materials and backfill materials, and aggregates for concrete, and the amount of elution of hexavalent chromium is effectively reduced. A fired product can be obtained. Therefore, it is a very useful method for consuming a large amount of rapidly increasing waste and the like while ensuring safety.

Hereinafter, the present invention will be described in detail.
The present invention, by firing the raw material for 2CaO · SiO ₂ 100 parts by mass, the _{2CaO · Al 2 O 3 · SiO} 2 containing 10 to 100 parts by weight, and the content of 3CaO · Al ₂ O ₃ In obtaining a fired product having a mass of 20 parts by mass or less,
A raw material is prepared so as to satisfy a specific condition.

In the present invention, the fired product obtained, with respect to 2CaO · SiO ₂ 100 parts by mass, the _{2CaO · Al 2 O 3 · SiO} 2 containing 10 to 100 parts by weight, and the content of 3CaO · Al ₂ O ₃ is 20 parts by mass or less.

The C ₂ S has hydraulic properties, and can react with relaxation in concrete, roadbed, etc., and can increase the strength by densifying the concrete, roadbed, etc. In addition, although the C ₂ AS does not have hydraulic properties, the C ₂ AS is densified by carbonation, and thus can exert an effect of suppressing the neutralization of concrete or increasing the strength of a roadbed or the like.

The content of C ₂ AS in the calcined product in the relative C ₂ S100 parts by mass comprising 10 to 100 parts, preferably 20 to 90 parts by weight, more preferably at 25 to 80 parts by weight . When the content of C ₂ AS is less than 10 parts by mass relative to 100 parts by mass of C ₂ S, the water absorption rate of the calcined product may increase, and the calcined product becomes powdery during cooling (dummy Sting) may occur, and the amount of free lime tends not to decrease even if the firing temperature is raised during firing. On the other hand, if it exceeds 100 parts by mass, the temperature range in which baking can be performed is limited, and it may be difficult to manage production.

The above C ₃ A reduces the water absorption rate of the fired product, and prevents the occurrence of expansion failure when used as an aggregate or roadbed material, thereby reducing the durability of concrete, roadbed, etc. From the viewpoint of suppressing the content, the content should be reduced. Specifically, the content of C ₃ A in the fired product of the present invention is 20 parts by mass or less with respect to expansion failure when used as C ₂ S 100 parts by mass aggregate or roadbed material, Preferably it is 0-10 mass parts.

As a raw material for producing the burned material of such a composition, general Portland cement clinker raw material, i.e., limestone, burnt lime, CaO raw material such as slaked lime, silica, SiO ₂ raw clay such, Al ₂ O clay such as ₃ Raw materials, Fe ₂ O ₃ raw materials such as iron cake and iron cake can be used.

Moreover, in this invention, 1 or more types chosen from an industrial waste, a general waste, a pollutant, and construction generation | occurence | production soil can also be used as a raw material of a baked product, and the effective utilization of a waste can be promoted. Therefore, it is preferable from the viewpoint of natural resources and environmental protection. Here, industrial waste includes, for example, coal ash; raw conslag; various sludges such as sewage sludge, purified water sludge, construction sludge, and iron sludge; boring waste soil, various incineration ash, foundry sand, rock wool, waste glass, blast furnace Secondary ash, construction waste, concrete waste, etc. are listed. Examples of the general waste include sewage sludge dry powder, municipal waste incineration ash, and shells. Examples of contaminants include heavy metal contaminated soil, organic matter contaminated soil, and fluorine contaminated soil. Examples of construction generated soil include soil and residual soil generated from construction sites and construction sites, and waste soil. In the case of using these wastes as raw materials, it can be added the CaO material, SiO ₂ material, Al ₂ O ₃ raw material, a Fe ₂ O ₃ raw material as required.

Depending on the raw material composition of the fired product, in particular, when one or more selected from the above industrial waste, general waste, pollutant and construction generated soil (hereinafter referred to as waste raw material) is used as the raw material, 4CaO · Al ₂ O ₃ · Fe ₂ O ₃ (hereinafter referred to as C ₄ AF) may be produced, but in the fired product of the present invention, preferably a part of C ₂ AS, more preferably C ₂ AS 70 mass% or less of the inside may be substituted with C ₄ AF. When C ₄ AF is substituted beyond this range, the firing temperature range becomes narrow, and the production control may become difficult.
Further, from the viewpoint of avoiding rapid melting during firing, the total content of C ₂ AS and C ₄ AF with respect to 100 parts by mass of C ₂ S is preferably 100 parts by mass or less.

Mineral composition of the burned material of the present invention _{(C 4 AF, C 3 A} , C 2 AS, C 2 S) is, CaO in the raw materials used and the fired product in each of _{SiO 2, Al 2 O 3,} Fe 2 O 3 From the content (% by weight), it can be obtained by the following formula.
C ₄ AF = 3.04 × Fe ₂ O ₃
C ₃ A = 1.61 × CaO−3.00 × SiO ₂ −2.26 × Fe ₂ O ₃
C ₂ AS = −1.63 × CaO + 3.04 × SiO ₂ + 2.69 × Al ₂ O ₃ + 0.57 × Fe ₂ O ₃
C ₂ S = 1.02 × CaO + 0.95 × SiO ₂ -1.69 × Al ₂ O ₃ −0.36 × Fe ₂ O ₃

In the present invention, in order to obtain a fired product, the above raw materials are prepared and fired. When preparing the raw materials, the raw materials are prepared so that the molar amounts of chlorine (Cl), potassium (K) and sodium (Na) in the raw materials before firing satisfy the following formulas (1) and (2). Thereby, the amount of hexavalent chromium eluted from the fired product obtained can be effectively reduced.
Molar amount of Cl / Molar amount of K ≧ 0.8 (1)
Molar amount of Cl / (Molar amount of Na + Molar amount of K) ≦ 1.0 (2)

  In formula (1), the molar amount of Cl / the molar amount of K (molar ratio) is 0.8 or more, preferably 1.0 or more, from the viewpoint of more effectively reducing the amount of hexavalent chromium. is there. If the molar ratio is less than 0.8, the elution amount of hexavalent chromium may not be sufficiently reduced.

  In formula (2), the molar amount of Cl / (the molar amount of Na + the molar amount of K) (molar ratio) is 1.0 or less, preferably 0.8 or less. If the molar ratio exceeds 1.0, a liquid phase is likely to be generated and the firing temperature may be lowered. Therefore, Cl may remain in the fired product more than necessary, or hydrogen chloride in the exhaust gas at the time of firing. Concentration may increase.

  Since K and Na in the raw material are usually inevitably mixed into the raw material, Cl is added to the raw material in order to prepare the raw material so as to satisfy the above formulas (1) and (2). As a Cl source used when adding such Cl, organic chlorine compounds such as polyvinyl chloride and polyvinylidene chloride, or waste plastics containing them; inorganic chlorine compounds such as calcium chloride and magnesium chloride, or these are mixed. Waste that is present. Of these, calcium chloride and polyvinyl chloride are preferable from the viewpoint of promoting the volatilization of chlorine.

  In the present invention, it is preferable to further add sulfur as a raw material. Since sulfur tends to form compounds with alkali metals such as K and Na present in the raw material, hexavalent chromium can be prevented from forming compounds with these alkali metals, and more effectively hexavalent chromium. It is possible to reduce the amount of elution. As a sulfur source used when adding such sulfur, from the viewpoint of preventing volatilization of sulfur itself, a compound with a metal other than an alkali metal such as gypsum and iron sulfide is preferable, and from the viewpoint that it can also be used as a CaO source, Gypsum is more preferred.

When preparing the raw materials by adding the above Cl source, etc., if necessary, they may be mixed by crushing, pulverizing, etc., and mixing them, or a crusher or a pulverizer and a mixer may be used. In combination, it may be prepared by performing a two-stage process. When firing using a rotary kiln, which will be described later, since raw materials are rotationally mixed in the rotary kiln, some of the desired CaO raw material, SiO ₂ raw material, Al ₂ O ₃ raw material, Fe ₂ O ₃ raw material, waste, etc. A Cl source or the like may be fed directly to the raw material inlet side of the rotary kiln. In the case of a combustible raw material, it may be supplied by pneumatic feeding from the raw material outlet side or may be supplied as part of the burner fuel.

  1200-1350 degreeC is preferable and the baking temperature at the time of baking has more preferable 1250-1350 degreeC. When the calcination temperature is less than 1200 ° C., alkali metals such as K and Na are not sufficiently volatilized, and the effect of reducing the hexavalent chromium elution amount may be reduced, and the amount of free lime is increased. There is a possibility that expansion failure occurs in earthwork materials. On the other hand, if it exceeds 1350 ° C, the melt may increase and firing may become difficult, and even the added sulfur volatilizes more than necessary, and the desired effect of reducing the elution amount of the desired hexavalent chromium is sufficiently obtained. There is no possibility.

  The firing (heating) time of the raw material is preferably 15 minutes or more, more preferably 30 minutes or more, from the viewpoint of obtaining a sufficient volatilization amount of alkali metals such as K and Na. The upper limit of the heating time is not particularly limited, but is preferably 180 minutes or less, more preferably 120 minutes or less, from an economic viewpoint.

  As the baking (heating) means, either a continuous type or a batch type can be used. A rotary kiln etc. are mentioned as an example of a continuous-type baking (heating) means. Examples of batch-type firing (heating) means include an incinerator, an electric furnace, and a microwave heating device.

  Among these, from the viewpoint of increasing the processing efficiency, a continuous firing (heating) means is preferable, and from the viewpoint of easily providing a heating temperature suitable for volatilization of alkali metals such as K and Na and a residence time of raw materials, More preferred. When the raw material rolls, such as a rotary kiln, the contact rate between the alkali metal and the Cl source is increased and the thermal conductivity is improved, so the residence time of the raw material is higher than when heating under static conditions. Can be shortened.

  In addition, in order to obtain the volatilization amount, to reduce the amount of free lime, or to reduce the water absorption rate, baking is performed by baking at a high temperature or for a long time as long as operation is possible in baking.

[Baking in a reducing atmosphere]
For firing in a reducing atmosphere, an explanation will be given using an internal combustion type device (internal combustion rotary kiln, etc.) and a countercurrent type (combusted at the material outlet side) as an example. It is not something that can be done.
Furthermore, from the viewpoint of enhancing the effect of reducing the hexavalent chromium elution amount, firing may be performed in a reducing atmosphere. Specifically, for example, a method of burning a flammable substance when firing the above-described raw material used can be mentioned. By burning the combustible substance, the periphery of the raw material can be maintained in a reducing atmosphere, and even if hexavalent chromium is generated in the step of firing the raw material, it is reduced to trivalent chromium.

  Examples of such combustible substances include waste solid lump obtained by compressing and / or solidifying waste such as coal, coke, activated carbon, waste wood, waste plastic, heavy oil sludge, and municipal waste.

  When firing in a reducing atmosphere, as a method of supplying a combustible substance, it may be mixed in advance with raw materials used. When a rotary kiln is used as a device used for firing, the inlet side and outlet side of the raw materials used Or you may supply a combustible substance from the middle of a rotary kiln.

  When combustible materials are mixed with raw materials in advance, the amount of combustible materials is preferably as large as possible so long as the combustible materials do not remain in an unburned state in the fired product obtained. Larger is preferable.

The details of supplying the combustible substance on the inlet side of the raw material used in the rotary kiln or in the middle of the rotary kiln are as follows.
In this case, the combustible substance is preferably one that can maintain the reducing atmosphere for a long time. Specifically, for example, a combustible substance having a slower combustion speed than the main fuel of the rotary kiln or a combustion speed similar to that of the main fuel and having coarser grains than the main fuel can be mentioned. Specific examples include petroleum coke, coal coke, and anthracite. It is preferable that the burning speed is low because the combustible substance can be made finer.

  The average particle size of the combustible material is preferably 0.5 to 20 mm, more preferably 1 to 5 mm. If the average particle size is less than 0.5 mm, there is a possibility that the reducing atmosphere cannot be maintained for a long time because there is a risk of burning out at an extremely early stage during combustion. When the average particle size exceeds 20 mm, a large amount of unburned combustible material remains in the obtained fired product, so that the supplied combustible material may be wasted, and the remaining unburned carbon is AE. By adsorbing the agent, for example, when the fired product is used as a concrete aggregate, the air entrainment of the mortar concrete deteriorates, or when compacted, unburned carbon appears on the surface, and the appearance of the mortar concrete is Problems such as deterioration may occur.

  The amount of the combustible material is preferably 5 to 40 kg, more preferably 10 to 40 kg, and further preferably 12 to 40 kg per 1000 kg of the fired product to be obtained. If the amount is less than 5 kg, the reduction effect may be small. If the amount exceeds 40 kg, a large amount of unburned combustible material remains in the obtained fired product, and the air entrainment and appearance of the mortar concrete deteriorate when the fired product is used as a concrete aggregate. There is a case.

  When firing in a reducing atmosphere, in the case where the combustible substance is supplied in the middle of the rotary kiln, it is preferable to supply the combustible substance in the middle from the position where the temperature is highest in the rotary kiln to the inlet side of the raw material used. .

The oxygen (O ₂ ) concentration in the furnace when burning the combustible material is preferably 5% by mass or less, more preferably 3% by mass or less, from the viewpoint that the combustible material is not immediately lost. .

In the case of firing in a reducing atmosphere, the case where a combustible substance is supplied from the outlet side of the raw material used will be described.
The combustible substance can be easily pumped from the outlet side of the used raw material into the furnace using air. A dedicated inlet may be provided on the exit side of the rotary kiln. Further, a coarse combustible substance (having an average particle diameter of about 1 to 10 mm) may be dropped as part of the fuel of the main burner.

  The combustible substance is preferably one that can be in a reduced state stronger than the case where the combustible substance is supplied on the inlet side of the raw material used or in the middle of the rotary kiln. Specifically, for example, a combustible material having a higher combustion speed than the main fuel of a rotary kiln can be used. Examples of the combustible material having a high combustion rate include the above-described solid waste lump.

  In this case, the average particle diameter of the combustible substance is preferably 0.1 to 10 mm, and more preferably 1 to 5 mm. If the average particle size is less than 0.1 mm, the reducing atmosphere may not be maintained because it burns out at an extremely early stage during firing. If the average particle size exceeds 10 mm, a large amount of unburned combustible material remains in the obtained fired product, and the supplied combustible material is wasted, and the fired product is used as a concrete aggregate. However, the air entrainment and appearance of mortar concrete may deteriorate. In addition, the time which can maintain a reducing atmosphere can be adjusted with the average particle diameter of a combustible substance.

  The amount of heat of the combustible substance can be used so as to be usually 2 to 40% with respect to the amount of heat of the whole fuel used for the main burner. If the amount of heat of the combustible substance is less than 2%, the reduction effect may be small. When the amount of heat of the combustible material exceeds 40%, a large amount of unburned combustible material remains in the obtained fired product, and the supplied combustible material is wasted, and the fired product is used as a concrete aggregate However, the air entrainment and appearance of mortar concrete may deteriorate.

  Compared to the case where the combustible substance is supplied from the inlet side of the raw material used or in the middle of the rotary kiln, when the raw material is supplied from the outlet side, the reducing atmosphere in the rotary kiln is part of the furnace. In addition to maintaining the reducing atmosphere for a long time, the supply position of the combustible substance (falling position) should be higher than the position where the maximum temperature is reached in the rotary kiln so that the reducing atmosphere is in a high temperature range where the reduction reaction rate is high. It is preferable to adjust to the inlet side. The supply position is preferably deeper than the point of 4D from the exit of the kiln, where D is usually the inner diameter of the kiln. Moreover, when the position which becomes the highest temperature in a kiln becomes the exit side more according to setting conditions, such as a main burner, a back | inner side is preferable from the point of 3D from the exit of a kiln. The supply position (falling position) is preferably adjusted by the angle of the inlet of the combustible substance, the position of the inlet, the speed at which the combustible substance is introduced, and the particle size and density of the combustible substance.

  Furthermore, as another method for firing in a reducing atmosphere, there is a method in which a flame is brought into direct contact with a raw material used. Specifically, in an internal combustion type apparatus (internal combustion rotary kiln or the like), firing is performed so that the raw material used during firing (heating) and the flame of the burner are in direct contact (hereinafter also referred to as “flame film firing”). As a method of performing flame film baking using an internal combustion type rotary kiln, (a) a main burner for heating is installed at the lower part, and the flame is baked (heated) so as to lick the raw materials used, (b) Adjust the air speed to diverge the flame and fire (heat) so that the flame licks the raw materials used. (C) Extend the flame by turning down the angle of the main burner and use the flame Examples of the method include firing (heating) so as to lick the raw material. Moreover, you may install the auxiliary burner for flame film baking other than the main burner for heating. By adjusting each condition, the reduction effect improves as the contact time between the raw material used and the flame becomes longer. Even if chromium is contained in the raw material used, the formation of hexavalent chromium can be prevented, and even if hexavalent chromium is produced in the process of firing the raw material used, it is reduced to trivalent chromium. The

  From the viewpoint of generating more flame film, the oxygen concentration at the time of flame film baking is preferably 5% by mass or less, more preferably 3% or less.

  Furthermore, you may use together combustion of the combustible substance mentioned above, and / or flame film baking.

  Moreover, it is good also as reducing atmosphere by adjusting the atmosphere at the time of baking (heating). For example, as another method of firing the raw material used in a reducing atmosphere, a method of burning the fuel used for firing with an air amount smaller than the theoretical air amount can be given.

  Specifically, in an internal combustion type apparatus (such as an internal combustion rotary kiln), the air ratio in the furnace (ratio of the supply air amount to the theoretical air amount) is 0.8 to 1.0, and the oxygen concentration in the furnace is The fuel is burned at 1% by mass or less or at a carbon monoxide concentration of 0.1 to 1.0% by mass. If the air ratio is less than 0.8 or the carbon monoxide concentration exceeds 1.0% by mass, combustion necessary for firing may be difficult. When the air ratio exceeds 1.0, when the oxygen concentration exceeds 1% by mass, or when the carbon monoxide concentration is less than 0.1% by mass, the reduction effect may be reduced.

  The fuel used for heating (firing) includes heavy oil, pulverized coal, regenerated oil, LPG, NPG, and flammable substances as the main fuel (burner fuel), and the particle size is adjusted so that it burns in space. Used.

  Furthermore, from the viewpoint of enhancing the effect of reducing the hexavalent chromium elution amount, in addition to firing in the reducing atmosphere, a combustible substance may be added to the high-temperature fired product. Specifically, for example, a high-temperature holding process is performed by filling and standing in a hot stove or a simple container, or a combustible substance is mixed in a cooling process using an air quenching cooler or a rotary cooler. Among these, it is preferable to use a rotary type device from the viewpoint of being in contact with oxygen and having a high degree of mixing of combustible materials. The method for charging the combustible substance is not particularly limited, but when a rotary kiln is used as an apparatus used for firing, the combustible substance can be dropped and dropped into the outlet.

  The higher the temperature of the fired product when the combustible material is charged, the higher the effect, and preferably 800 ° C. or higher, more preferably 1000 ° C. or higher. The longer the cooling time after introducing the combustible substance, the higher the effect, and it is preferably 1 minute or more, more preferably 3 minutes or more, to decrease to 600 ° C. from the introduction. The amount of combustible material used can be 2 to 20% of the heat quantity of the main fuel (burner fuel). If the input amount is too large, a large amount of combustible material may remain, and if the input amount is too small, the reduction effect may be reduced.

  Since the reduction time is short and the reduction temperature is low, the combustible substance is preferably one that can be in a stronger reduction state. For example, coal solids such as coal, coke, activated carbon, waste wood, waste plastic, heavy oil sludge, and municipal solid waste are compressed and / or solidified, and the combustible material has a high burning rate. Waste solid lump obtained by compressing and / or solidifying waste wood, waste plastic, heavy oil sludge, and waste such as municipal waste is preferable.

The average particle size of the combustible material is preferably 0.1 to 10 mm, more preferably 1 to 5 mm. If the average particle size of the combustible material exceeds 10 mm, a large amount of combustible material may remain in the fired product after cooling. Further, when the average particle size is less than 0.1 mm, the reduction reduction effect is reduced, and there is a possibility that the air is scattered due to the wind speed of the cooling air when being charged.
What is necessary is just to adjust the above-mentioned conditions so that the reduction effect of hexavalent chromium is large, the flammable substance is prevented from being scattered by the wind speed of air, and the combustible substance does not remain.

  The position where the flammable substance is supplied is that the raw material used comes out of the firing process from the viewpoint of maintaining the reduced state for a long time because the reduced state is a part of the furnace, and the reduced state at a higher volatility. It is preferred to mix immediately.

[Melting of fired product]
Moreover, after passing the process of baking a raw material, you may obtain a melt by further heating and melting the obtained fired product. By converting the calcined product into a melt, the hexavalent chromium contained in the calcined product is sealed in the glass, and when used for earthwork materials, etc., the amount of hexavalent chromium eluted can be reduced more effectively. it can. The fired product is further heated and melted, and then cooled to obtain a granular melt. Since the obtained granular melt has a low water absorption and high strength, it can be suitably used as an aggregate for concrete. The melt may be cooled rapidly or slowly. In addition, there may be a lot of alkali elution from the fired product (high pH), but the alkali elution further decreases (pH decreases) due to the vitrification of minerals and the amount of free lime (f.CaO). The load on the environment can also be reduced.

  In order to melt the fired product, it is preferable to directly melt the fired product in a high-temperature state obtained by the firing process (for example, the fired product immediately after coming out of the kiln) from the viewpoint of energy cost.

  The particle size of the fired product to be melted is not particularly limited, but from the viewpoint of shortening the melting time, the fired product is preferably coarsely pulverized to a diameter of 40 mm or less, more preferably 20 mm or less.

  From the viewpoint of lowering the melting temperature, it is preferable that the Si source, Fe source or Al source is added to the fired product in advance before melting, and in particular, from the viewpoint of fluidity of the melt, it is preferable to add the Si source.

As Si sources that can be added, SiO ₂ raw materials and waste such as silica, clay, coal ash, steel slag, construction generated soil, etc. As Fe sources, Fe ₂ O ₃ raw materials such as iron cake and iron cake, Examples of waste and Al sources include Al ₂ O ₃ raw materials and waste such as aluminum dross and red mud.

When used as a coarse aggregate of concrete aggregate, the amount of Si source or the like to be added is determined from the viewpoint of enhancing the adhesiveness to the cement paste with a hydraulic modulus (HM = CaO mass% / (SiO ₂ mass% + Al ₂ O ₃ % by mass + Fe ₂ O ₃ % by mass) is preferably set to an amount of 1.0 or more, and when used as a fine aggregate or earthwork material for concrete aggregate, when used as a coarse aggregate In comparison with the above, a larger amount of Si source or Fe source can be added. However, from the viewpoint of economy and melt fluidity, the hydraulic modulus (HM = CaO mass% / (SiO ₂ mass% + Al ₂ (O ₃ mass% + Fe ₂ O ₃ mass%) is preferably an amount that results in a composition of 0.5 or more.

  When no Si source or the like is added, the melting temperature is preferably 50 ° C. or more higher than the firing temperature and more preferably 100 ° C. or more from the viewpoint of reducing hexavalent chromium elution and water absorption. Moreover, when adding Si source etc., it is preferable to set it as 1300 degreeC or more from a viewpoint of the reduction effect of hexavalent chromium elution amount or a water absorption rate, and it is more preferable to set it as 1350 degreeC or more.

  As the melting furnace, an existing melting furnace such as a coke bed furnace, a swirling melting furnace, a surface melting furnace, or a rotary kiln may be used. In addition, when a rotary kiln is a melting furnace, it can also serve as baking when passing the temperature range before melting.

[Adding drugs]
Furthermore, from the viewpoint of enhancing the effect of reducing the hexavalent chromium elution amount, a drug may be used in addition to the above method. An example of such a drug is a reducing agent. By using this, hexavalent chromium can be reduced to trivalent chromium and insolubilized in an alkaline form. Specific examples of such a reducing agent include sulfites such as sodium sulfite, iron (II) salts such as iron (II) sulfate and iron (II) chloride, sodium thiosulfate, and iron powder. What is necessary is just to add and mix these reducing agents to the baked material after passing through a baking process.

Examples of other agents include adsorbents. By using this, hexavalent chromium can be adsorbed and insolubilized, and elution of hexavalent chromium can be suppressed. Specific examples of such adsorbents include zeolites, Schwermannite, clay minerals, layered double hydroxides such as hydrotalcite compounds such as Mg-Al and Mg-Fe, and Ca-Al hydroxides. Products, Ca-Al compounds such as ettringite and monosulfate, hydrous oxides such as iron oxide (hematite) and bismuth oxide, magnesium compounds such as magnesium hydroxide, lightly burned magnesium, and calcined dolomite, magnesium oxide, iron sulfide and iron Examples thereof include iron compounds such as powder, chebermanite and Fe (OH) ₂ , one or a mixture of two or more of silicon oxide, aluminum oxide and iron oxide, or a fired product, and a compound containing cerium and a rare earth element.

  The dosage of these chemicals is such that the amount of metal salt per 100 kg of the calcined product is preferably 0.01 to 10 kg, more preferably 0.1 to 7 kg, and still more preferably 0.2 to 5 kg. The concentration, the spray amount of the aqueous solution, and the input amount of the fired product into the aqueous solution are adjusted. If the amount of drug input is too small, the effect of reducing the hexavalent chromium elution amount may be reduced. If the amount of drug input is too large, the effect of reducing the hexavalent chromium elution amount is saturated, resulting in high costs. There is a risk of becoming.

  What is necessary is just to mix, spray, or submerge what made the chemical | medical agent into the powder form, the slurry, or the aqueous solution. The temperature at this time is preferably 800 ° C. or lower, more preferably 600 ° C. or lower, and further preferably 400 ° C. or lower. The temperature at the time of charging the drug by submerging is preferably 100 ° C. or higher, more preferably 150 ° C. or higher. By using a temperature of 100 ° C. or higher when the drug is added, when the resulting fired product is used for aggregates with pores, it is effective because it absorbs water well, penetrates the drug, and adheres to the surface. It is. If the temperature when the chemical is added is too high, cracks or the like may occur in the fired product, which may cause atomization or decrease in strength.

Furthermore, from the viewpoint of enhancing the effect of reducing the hexavalent chromium elution amount, washing with water may be performed in addition to the above method. Specifically, such washing with water is
1) A method of spraying a liquid with a sprinkler or the like on a fired product in a container or on a belt conveyor,
2) Supplying the fired product to a container and immersing it in a liquid, or supplying a liquid and replacing it,
3) A method of replacing the fired product while being immersed in a liquid (such as a trommel),
This is a method of cleaning by, for example The cleaning liquid may be simple water or an aqueous solution of the above drug. The liquid after washing may be reused, or may be discarded after water treatment. The washing time, the number of washings, and the amount of the washing solution are not particularly limited, and may be carried out until the hexavalent chromium elution amount satisfies the reference value.

  Note that the alkali metal salt volatilized in the exhaust gas can be recovered by a dust collector or a scrubber after being cooled to be solid. In addition, when a preheater is attached to the kiln, a part of the exhaust gas containing a high concentration of volatilized alkali metal salt is extracted and cooled to recover the solid alkali salt. . The recovered alkali metal salt can be subjected to further volume reduction treatment by being subjected to treatment such as washing or adsorption as necessary.

  The amount of free lime in the fired product or melt thus obtained is preferably 1.0% by mass or less, more preferably 0.8% by mass or less. If a large amount of free lime is present in the fired product or melt, expansion failure may occur when used as an aggregate or roadbed material, but the fired product or melt obtained in the present invention is effective. Can be prevented.

  The water absorption rate of the obtained fired product or melt is preferably 5% or less, more preferably 3% or less, and even more preferably 2% or less. When the water absorption is 5% or less, hexavalent chromium is contained in the mineral, and the amount of elution is reduced. Moreover, since a high intensity | strength granular material is obtained as a baked material or a molten material, it can be used conveniently as an aggregate for concrete. The water absorption means a value measured according to “JIS A 1110 (Coarse aggregate density and water absorption test method)”.

Moreover, the absolute dry density of the fired product or melt obtained is preferably 2.0 to 3.0 g / cm ³ , more preferably 2.3 to 3.0 g / cm ³ , and still more preferably 2 0.5-3.0 g / cm ³ . When the absolute dry density of the fired product or the melt is less than 2.0 g / cm ³ , for example, when used as an aggregate of concrete, the strength of the concrete may be reduced.

  In addition, what is necessary is just to adjust and use the particle size of the baked material and melt obtained by sieving etc. according to a use and considering compaction property etc. Especially, from a viewpoint of using suitably as the above-mentioned civil engineering / harbor material, it is preferably 0.1 to 100 mm, and particularly when used as a coarse aggregate, for example, by adjusting the particle size to 5 mm or more by sieving or the like. It is good.

  The fired product and melt of the present invention can be used as a concrete aggregate, or a civil engineering material such as a roadbed material and a backfill material. As an aggregate for concrete, it can be used for both fine aggregate and coarse aggregate.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

[Examples 1-9, Comparative Examples 1-5]
Using the raw materials having the composition shown in Table 1, blending was performed at the ratio shown in Table 2 so that the content in the raw material before firing would be the amount shown in Table 3. The raw material contained no chlorine. As limestone, commercially available limestone fine powder (Blaine specific surface area 3350 cm ² / g) was used, and reagents were used as CaCl ₂ and CaSO ₄ . Raw consludge, sewage sludge incineration ash, and construction generated soil were crushed in advance by a disk mill. As industrial raw materials, commercially available silica fine powder (# 200), alumina powder (reagent), and iron oxide powder (reagent) were used. In addition, the raw material of Comparative Example 2 and 3, 100 parts by weight of raw material to, was added 1.5 parts by mass over Na ₂ SO ₄ reagent.

Next, the obtained mixture was hand-granulated to a diameter of about 1 cm and fired in the air using a box-type electric furnace. Specifically, the mixture was charged when the temperature in the electric furnace reached 800 ° C., the temperature was raised to the temperature shown in Table 3 in 45 minutes, and the temperature was maintained for 15 minutes to obtain a fired product. The resulting fired product of the mineral composition _{(C 2 S, C 2 AS} , C 4 AF, C 3 A) of CaO in use in the raw material, the content of _{SiO 2, Al 2 O 3,} Fe 2 O 3 ( mass %) By the above formula and shown in Table 2.

In addition, each amount of SO ₃ , K ₂ O, and Na ₂ O was measured by fluorescent X-ray analysis (XRF), and the Cl amount was measured using a wet method to determine the volatility (mass%). . The amount of free lime (f.CaO) was determined according to the Cement Association Standard Test Method I-01-1997. The water absorption rate (%) was determined according to JIS A 1110. The elution amount of hexavalent chromium was determined according to JIS K 0058-1 (solid, water solid content ratio 10).
The results are shown in Table 3.

The calcined products of Examples 1 to 9 satisfying the requirements of Cl / K ≧ 0.8 and Cl / (Na + K) ≦ 1.0 had a hexavalent chromium elution amount of 0.05 mg / L or less. In particular, in Examples 3 to 4, in which the K ₂ O amount is as low as 0.1% or less and the SO ₃ amount is as high as 0.6% or more, the elution amount of hexavalent chromium was as low as 0.01 mg / L. It was. In Example 9, in which the amount of SO ₃ was higher than that in Example 8, the water absorption was higher than that in Example 8. Therefore, although the hexavalent chromium insolubilizing effect due to vitrification was small, the elution amount of hexavalent chromium was in Example It is 0.03 mg / L which is the same as 8, and it can be seen that there is a reduction effect of the hexavalent chromium elution amount.

On the other hand, in Comparative Example 4 in which no CaCl ₂ was added, the elution amount of hexavalent chromium was as high as 0.16 mg / L. Further, Comparative Example 5 in which Cl / (Na + K)> 1.0 was melted at a low temperature and the firing temperature could not be raised.

On the other hand, Comparative Example 2 in which the content of C ₂ AS with respect to 100 parts by mass of C ₂ S is less than 10 parts by mass is f. The amount of CaO was 1.5%, which caused expansion and destruction. Further, Comparative Example 3 in which the content of C ₂ AS and C ₄ AF with respect to 100 parts by mass of C ₂ S exceeded 100 parts by mass was rapidly melted and the firing temperature could not be increased. In Comparative Example 1 in which the content of C ₂ AS with respect to 100 parts by mass of C ₂ S exceeds 20 parts by mass, the water absorption was 6% higher than the others.

[Examples 10 to 11]
The fired product obtained in Example 2 was melted to produce a melt. In Example 10, the fired product obtained in Example 2 was heated at 1450 ° C. for 1 hour. In Example 11, 0.8 parts by mass of the fired product obtained in Example 2 was roughly pulverized to a diameter of 2 mm or less, 0.2 parts by mass of silica powder was added (hydraulic modulus 0.8), and 1 at 1350 ° C. Heated for hours.
The pH was determined by measuring the immersion water used for measuring the elution amount of hexavalent chromium with a pH meter of a glass electrode.
The results are shown in Table 4 including the fired product obtained in Example 2.

  From the results of Table 4, it can be seen that in Example 10 in which the obtained fired product was melted, f.CaO was not detected and the pH was reduced. Moreover, since the elution amount of hexavalent chromium is reduced by half and the water absorption rate is reduced to 1.0%, it can be seen that it is useful as an aggregate for concrete having excellent performance.

  Furthermore, in Example 11 to which the Si source was added, it can be seen that the melting temperature can be lowered, and further, all of the hexavalent chromium elution amount, the water absorption rate, and the pH can be further reduced.

  As described above, it is obvious that the fired product and melt obtained by the firing method of the present invention can be used as earthwork material or aggregate of safe and good quality.

Claims (12)

By firing the raw material for 2CaO · SiO ₂ 100 parts by mass, the _{2CaO · Al 2 O 3 · SiO} 2 containing 10 to 100 parts by weight, the content of 3CaO · Al ₂ O ₃ is 20 parts by mass or less And a calcined product having a total content of 2CaO · Al ₂ O ₃ · SiO ₂ and 4CaO · Al ₂ O ₃ · Fe ₂ O ₃ of 100 parts by mass or less,
Calcium chloride and gypsum are added so that the molar amounts of chlorine (Cl), potassium (K) and sodium (Na) in the raw material before firing satisfy the following formulas (1) and (2), A method for reducing the amount of elution of hexavalent chromium in a fired product, characterized by comprising blending.
Molar amount of Cl / Molar amount of K ≧ 1.0 (1)
Molar amount of Cl / (Molar amount of Na + Molar amount of K) ≦ 0.8 (2)   The method for reducing the amount of elution of hexavalent chromium in a fired product according to claim 1, wherein the water absorption of the fired product is 5% or less.   The method for reducing the amount of elution of hexavalent chromium in a fired product according to claim 1 or 2, wherein the raw material is at least one selected from industrial waste, general waste, contaminants and construction generated soil.   The method for reducing the hexavalent chromium elution amount of the fired product according to any one of claims 1 to 3, wherein the firing temperature is 1200 to 1350 ° C.   The amount of free lime in a baked product is 1 mass% or less, The hexavalent chromium elution amount reduction method of the baked product of any one of Claims 1-4.   The method for reducing a hexavalent chromium elution amount of a fired product according to any one of claims 1 to 5, wherein the raw material is fired in a reducing atmosphere.   The method for reducing the hexavalent chromium elution amount of the fired product according to any one of claims 1 to 6, wherein the fired product obtained is further melted after the step of firing the raw material.   The amount of elution of hexavalent chromium in the fired product according to any one of claims 1 to 7, wherein after the step of firing the raw material, a chemical is further added to the obtained fired product to insolubilize hexavalent chromium. Reduction method. Comprising the step of firing the raw material for 2CaO · SiO ₂ 100 parts by mass, the _{2CaO · Al 2 O 3 · SiO} 2 containing 10 to 100 parts by weight, the content of 3CaO · Al ₂ O ₃ is 20 parts by weight hereinafter der is, and a process for the preparation of _{2CaO · Al 2 O 3 · SiO} 2 and _{4CaO · Al 2 O 3 · Fe} 2 total content burned material Ru der 100 parts by mass or less of O _3,
Calcium chloride and gypsum are added so that the molar amounts of chlorine (Cl), potassium (K) and sodium (Na) in the raw material before firing satisfy the following formulas (1) and (2), A method for producing a fired product, characterized by being formulated.
Molar amount of Cl / Molar amount of K ≧ 1.0 (1)
Molar amount of Cl / (Molar amount of Na + Molar amount of K) ≦ 0.8 (2)   The method for producing a fired product according to claim 9, wherein the raw material is fired in a reducing atmosphere.   A method for producing a granular melt obtained by encapsulating hexavalent chromium in glass, wherein the fired product obtained by the production method according to claim 9 or 10 is melted and then cooled.   The method for producing a fired product according to claim 9 or 10, wherein after the step of firing the raw material, a chemical is added to the obtained fired product to insolubilize hexavalent chromium.