JP5378653B2 - Cement composition and cement-based solidifying material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cement composition which has small elution ratio to the selenium content, and consequently provides suppressed selenium eluted quantity, and to provide a cement based solidifying material. <P>SOLUTION: The cement composition comprises a cement clinker having a selenium content of &le;1.6 mg/kg and gypsum, and in which the content of C<SB>3</SB>A by Vogue type calculation is 0.1 to 4 mass%. Also disclosed is a cement based solidifying material using the same. The cement clinker in the cement composition has selenium content reduced by extracting a part of a selenium-containing waste gas from a cement kiln extending from the suspension pre-heater part of a cement firing apparatus to a rotary kiln hood inlet. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a cement composition containing a cement clinker with a reduced selenium content and a cement-based solidified material. More specifically, the present invention relates to a cement composition and a cement-based solidified material that can reduce the amount of selenium eluted from a hardened cement or solidified soil by reducing the selenium content in the cement clinker.

  Various raw fuels (natural products or various industrial wastes) used in the manufacture of Portland cement usually contain a small amount of harmful heavy metals such as mercury, lead and chromium. As a result, clinker contains heavy metals. Are incorporated in a wide concentration range from 1 mg / kg or less to over 1000 mg / kg. The heavy metals in the clinker dissolve in the water (liquid phase) in the mortar, concrete, or solidified soil together with the hydration reaction of the cement. Many of the dissolved heavy metal ion species are adsorbed by substitution solid solution in the crystal structure of cement hydrate, formation of new hydrate, or hydrated product with particularly low crystallinity, or various additions An agent is added intentionally, and is fixed by reduction, pH adjustment (precipitation as a hydroxide) or coprecipitation with a low crystalline hydrate. For example, hexavalent chromium is reduced to trivalent by adding a reducing agent to make it harmless (for example, see Patent Document 1).

  However, among harmful heavy metals, selenium (Se) is one of the metals that are difficult to suppress or immobilize the eluted ions, and it is necessary to use a large amount of a chelating agent, an aggregating agent, and the like (for example, Patent Document 2). reference).

  In general, selenium mixed in Portland cement is derived from raw materials used and fuel (coal), and sometimes exceeds 1 mg / kg in the cement. When the selenium content in Portland cement increases, the environmental standard (0.01 mg per liter of the test solution) set in the Environmental Agency Notification No. 46 (August 23, 1991) from the solidified soil using cement-based solidified material Selenium in excess of (below) may be eluted.

  Therefore, conventionally, in order to reduce the amount of selenium eluted from hardened cement (mortar, concrete) and solidified soil to a level where there is no problem, the type of raw fuel or the basic unit of raw fuel is limited. A method has been adopted. However, such measures have been problematic in terms of difficulty in securing a stable raw fuel or an increase in manufacturing costs.

JP 2000-102767 A JP 2005-103436 A

  The present invention does not limit the type of raw fuel or the basic unit of raw fuel, the cement clinker with reduced selenium content, and the ratio of elution to the selenium content is small, and as a result, the selenium elution amount can be suppressed. An object is to provide a Portland cement composition and a cement-based solidifying material.

  As a result of intensive studies to achieve the above object, the present inventors have determined that the selenium content in the cement clinker is an appropriate amount, or that selenium is incorporated as extraction dust during the manufacture of the cement clinker. The present inventors have found that the amount of selenium eluted can be reduced and have completed the present invention.

That is, the present invention is a cement composition comprising a cement clinker having a selenium content of 1.6 mg / kg or less, gypsum, and extraction dust containing selenium recovered from the selenium-containing exhaust gas, The selenium content is 1190-5000 mg / kg, the C ₃ A content of the cement composition is 0.1-4 mass%, the C ₄ AF content is 12-18 mass%, and the selenium content is 2.0- It is a cement composition which is 5.0 mg / kg , and a cement-type solidification material using the cement composition. In the cement composition of the present invention, the cement clinker reduces selenium by extracting a part of the selenium-containing exhaust gas from the cement kiln from the suspension preheater part of the cement firing device to the rotary kiln hood inlet.

  The present invention also provides a cement composition for extracting a portion of selenium-containing exhaust gas from a cement kiln and cooling the selenium-containing exhaust gas as bleed dust in a cement firing apparatus equipped with a suspension preheater. It relates to a manufacturing method.

  The cement composition and the cement-based solidified material according to the present invention extract and separate and remove a part of the selenium-containing kiln exhaust gas in the cement firing step, so that the selenium content in the Portland cement clinker is 1.6 mg / kg or less. By using the clinker reduced to selenium and the extracted dust incorporating selenium, the selenium elution amount can be remarkably reduced.

  Hereinafter, preferred embodiments of the Portland cement clinker, the Portland cement composition, and the cement-based solidified material with reduced selenium content according to the present invention will be described.

  In general, the Portland cement clinker is manufactured by an SP system (multistage cyclone preheating system) or an NSP system (multistage cyclone preheating system equipped with a calcining furnace). In these production methods, when a waste material containing a large amount of chloride such as sewage treatment sludge generated at a sewerage treatment facility or municipal waste incineration ash is used as a raw material, a large amount of chloride is taken into the cement clinker. On the other hand, since chloride corrodes the reinforcing bars and steel materials of concrete structures, the content in the cement is regulated. For this reason, as a workaround when using waste containing a large amount of chloride, the chloride is volatilized by high-temperature heat treatment in the kiln firing zone, and backflowed to the raw material preheating part along the flow of combustion gas, In a system that cools, condenses and recirculates by heat exchange, the kiln exhaust gas containing chloride in a volatilized state during the process from the inlet to the raw material preheating section to the inlet to the rotary kiln is used. It is effective to extract and separate a part, collect it after cooling and condensation.

  As an apparatus used in the above method, there is an extraction gas facility such as a chlorine bypass or an alkali bypass. As an example, an extraction gas facility generally used for cement kiln will be described based on the chlorine bypass facility shown in FIG.

  In FIG. 1, 1 is a cement firing kiln, 1a is a firing burner, 2 is a clinker cooler for cooling the clinker fired in the cement firing kiln 1, and 3 is a cement raw material supply side of the cement firing kiln 1 The attached cross-section is a substantially rectangular kiln inlet hood, and the kiln inlet hood 3 constitutes a kiln exhaust gas passage with a part of the calcined raw material receiving passage at the bottom of the kiln kiln. 5 is a suspension preheater (SP) provided with a calcining furnace 5b, 5a is a lowermost cyclone of the suspension preheater 5, 5c is a raw material supply pipe for supplying raw material to the preheater 5, and 4 is a kiln inlet hood. 3 is a rising duct for connecting the upper end of 3 and the suspension preheater 5 to supply the kiln exhaust gas to the suspension preheater 5 via the calcining furnace 5b.

  6 is an exhaust fan of the suspension pre-heater 5, 7 is connected to the lower part of the lowermost cyclone 5 a, and the lower end is connected to the lower part of the side wall of the kiln inlet hood 3 that intersects the side wall on the cement firing kiln 1 side. A chute for feeding high-temperature cement raw material (hereinafter referred to as “calcined raw material”), which is opened and preheated by the suspension preheater 5 and then calcined in the calcining furnace 5b, to the kiln 1 for cement firing, This is a duct for feeding the exhaust gas of the clinker cooler 2 to the calcining furnace 5b.

  The extraction gas facility 10 for a cement kiln has an exhaust gas cooling port 3a that is open on the side wall located on the kiln side of the rising portion of the kiln inlet hood 3 and an exhaust gas cooling unit that is communicated with the inside and fixed to the side wall. The exhaust gas extraction pipe 11 also serving as a means, the lump removal device (chamber) 12 connected to the exhaust gas outlet of the exhaust gas extraction tube 11, the exhaust gas outlet of the lump removal device 12 and the exhaust gas duct 13a communicate the exhaust gas inlet. The bag filter (dust collecting means) 15, the exhaust fan 16 communicated with the exhaust gas outlet of the bag filter 15 through the duct 13b, the gas outlet of the exhaust fan 16, and the exhaust gas of the clinker cooler 2 are sent to the calcining furnace 5b. Upstream from the exhaust gas inlet of the bag filter 15 of the exhaust gas duct 13a and the duct 13c for exhausting the extracted gas connecting the duct 8 A cool air inlet tube 14 with a damper 14a which is connected to a location, and a cooling fan 11a of the exhaust gas extraction pipe 11 connected with an air supply duct.

  Note that the extraction gas exhaust duct 13c connects the gas outlet of the exhaust fan 16 and the duct 8 for sending the cooler exhaust gas to the calcining furnace 5b to exhaust the extraction gas instead of exhausting the extraction gas. A mode in which the furnace 5b is directly connected, a mode in which the gas outlet of the exhaust fan 16 and the rising duct 4 are connected, or a mode in which the clinker cooler 2 is returned to the cooling fan 2a may be employed.

  On the other hand, a lower hopper 15 a, a dust discharge screw conveyor 15 b, a cushion hopper 21, and a double butterfly damper 22 are provided at the lower part of the bag filter 15 to constitute a dust storage / discharge device 20. The dust delivered from the dust storage / delivery facility 20 is received by a dust delivery vehicle (bulk vehicle) 23 and then delivered to a dust storage receiving hopper 33. Thus, the dust collected and collected by the bag filter 15 of the extraction gas facility 10 and received by the dust storage receiving hopper 33 is conveyed to the classifier 32 of the cement finishing mill facility 30 and classified, and the coarse powder is ball mill 31. The fine powder is recovered as a cement product together with the classified cement fine powder.

The present inventors use this kiln exhaust gas extraction technology not only to remove chlorides in the raw material, but also to be effective for extraction of volatile heavy metals, particularly for extraction and separation of selenium. I found it. That is, in the extracted gas, in addition to the generally known chlorine, potassium, sulfur, and the like, heavy metals such as selenium, cadmium, lead, molybdenum, fluorine, and zinc are included in the form of gas. it is conceivable that. Further, the extracted gas may contain a cement raw material or a calcined raw material thereof. The selenium content remaining in the portulan cement clinker varies depending on the flow of gas unique to each cement kiln, the site to be extracted, and the ratio of the extracted gas. When gas containing selenium is extracted, a portion with a high selenium content in the exhaust gas is suitable for the extraction position. Specifically, the portion from the suspension pre-heater 5 portion of the cement firing device to the rotary kiln inlet hood 3 portion is preferable. When the existing extraction gas equipment is used as it is, the rising duct 4 portion or the kiln inlet hood 3 Part is preferred. Also, considering the vaporization temperature of SeO ₂ at 1 atm of about 320 ° C., the upper stage of the suspension preheater where the extraction gas temperature is lowered, specifically the lowest stage, from the point of heat loss generation of the kiln due to high temperature gas extraction It is more preferable that the exhaust gas extraction port is newly provided at each of the cyclone junction ducts 5f between the cyclone 5a and the extraction fan 6, particularly the outlet 5g of the uppermost cyclone 5e where the gas temperature is close to 300 ° C. When the extraction gas temperature is low, the cooling part for protecting the extraction pipe from heat is unnecessary, and the shape of the external air, which is a feature of the conventional chlorine bypass device, flows as a swirl flow on the inner wall of the extraction pipe (as shown in FIG. 1). Or a double tube shape in which a portion through which the cooling gas passes is provided around the bleed tube, it can be a simple cylindrical bleed tube.

The extraction gas temperature of the exhaust gas extraction port 3a is preferably 300 to 1300 ° C. If the extraction gas temperature is less than 300 ° C., only a part of selenium may be volatilized. If the extraction gas temperature exceeds 1300 ° C., it is necessary to install a refractory brick or the like to ensure the heat resistance of the extraction port portion. . Since the temperature at which SeO ₂ vaporizes at 1 atmosphere is about 320 ° C., the extraction gas temperature is more preferably 320 to 1200 ° C. Moreover, from the point which prevents the heat loss of the kiln by high temperature gas extraction, 320-800 degreeC of extraction gas temperature is especially preferable, and 320-400 degreeC is especially preferable.

  The extraction rate (hereinafter simply referred to as “extraction rate”) for the exhaust gas passing through the rising duct 4 or the kiln inlet hood 3 is preferably 0.05 to 10%. If it is less than 0.05%, the gas containing selenium cannot be sufficiently extracted, and if it exceeds 10%, the fuel consumption deteriorates, the productivity deteriorates due to excessive intake of the calcined raw material, and the processing of the imported raw material or calcined raw material Is required. The extraction rate is more preferably 0.1 to 7%. Note that, as conventionally performed, the extraction rate is controlled from the kiln by the opening of a damper installed upstream of the exhaust fan 16 with respect to the air volume at the extraction position calculated from the theoretical value and the actual measurement value. The amount of the exhaust gas flowing into the exhaust gas extraction port 3a (extraction amount) is adjusted.

The extraction gas is cooled to 350 ° C. or less, preferably 320 ° C. or less, more preferably 300 ° C. or less, and particularly preferably 250 ° C. or less in the portion of the lump removal device 12. If it exceeds 350 ° C., the selenium contained in the exhaust gas is not sufficiently cooled and is not sufficiently taken into the extracted dust.
The extraction gas is cooled by mixing the cooling air from the cooling fan 11a with the extraction gas in the exhaust gas extraction pipe 11, and sequentially measuring the mixed gas temperature with a thermometer installed in the vicinity of the exhaust gas extraction port 3a. Also adjust the amount.

The selenium solidified by cooling is collected by the bag filter 15 of the extraction gas equipment. The extracted gas from which selenium and other heavy metals are collected and removed is returned to the calcining furnace 5b through the duct 13c. Further, the collected exhaust dust containing selenium and other heavy metals is transferred to the dust storage receiving hopper 33 via the cushion hopper 21, the double butterfly damper 22 and the dust carrying vehicle (bulk vehicle) 23 of FIG. After carrying out, it is sent to the cement finishing mill equipment 30, and dust fine powder is made into a cement composition with classified cement fine powder.

As a selenium collection method, in addition to the above method, a method of extracting a part of the calcined raw material from the lowest cyclone 5a where selenium is relatively easily aggregated can be used. The extraction amount in this case is 0.05 to 5%, preferably 0.1 to 1% with respect to the raw material feed amount. If it is less than 0.05%, selenium cannot be sufficiently collected, and if it exceeds 5%, productivity deterioration due to excessive incorporation and treatment of the incorporated calcined raw material are required.

The chemical component of the extraction dust varies depending on the chemical component of the raw material, the cement clinker manufacturing plant, the position of the extraction gas installation, the extraction method, etc., but Na ₂ O is 0.1 to 5% by mass, preferably 1 to 3% by mass, K ₂ O 2 to 60 wt%, preferably from 30 to 50 wt%, Cl 2 to 50% by weight, preferably from 30 to 40 wt%.

  In addition, the selenium content in the extracted bleed dust combined with the stability of the kiln operation, the heat balance, the economy and the like is preferably in the range of 50 to 5000 mg / kg on a mass basis. From the point of elution characteristics of selenium, the range of 200 to 2000 mg / kg is more preferable.

  In this case, heavy metals that are volatilized and extracted include cadmium, lead, molybdenum, fluorine, and zinc in addition to selenium. Examples of the content of these heavy metals in the extracted dust are cadmium: 200 to 7000 mg / kg, lead: 500 to 20000 mg / kg, molybdenum: 20 to 300 mg / kg, and fluorine: 200 to 3000 mg / kg.

In this way, in the clinker firing step, the selenium content in the clinker is 1.6 mg / kg by separating and removing selenium by extracting the selenium-containing gas using an extraction gas facility, for example, an existing chlorine bypass facility. In the following, it is preferably 1.5 mg / kg or less, more preferably 1.0 mg / kg or less.
With this low selenium content clinker, cement composition, mixed cement and cement-based solidified material (including general soft soil, high organic soil, special soil solidified material (for hexavalent chromium countermeasures)), and solidification treatment The amount of selenium eluted from the soil can be greatly reduced. In particular, the selenium elution amount can achieve an environmental standard (0.01 mg / L) or less for soil contamination in almost all soils. Further, the selenium content in the clinker is preferably lower, but considering the deterioration of fuel consumption due to an increase in the extraction rate, it is 0.05 mg / kg or more, preferably 0.2 mg / kg or more, particularly preferably 0.6 mg / kg. More than kg is more preferable in terms of industrial and production costs.

The cement composition corresponds to a sulfate-resistant cement, and the mineral composition thereof has a C ₃ S amount of 55 to 75% by mass, preferably 58 to 70% by mass, calculated by the Borg formula. The amount of C ₂ S is 5 to 25% by mass, preferably 10 to 20% by mass, the amount of C ₃ A is 0.1 to 4% by mass, preferably 0.1 to 2% by mass, and the amount of C ₄ AF is 12 to 12%. 18 mass%, preferably 13-17 mass%. Here, the C ₃ S amount, C ₂ S amount, C ₃ A amount and C ₄ AF amount in the Borg calculation are values calculated by the following equations (1), (2), (3) and (4). is there.
C ₃ S amount (mass%) = 4.07 × CaO (mass%) − 7.60 × SiO ₂ (mass%) − 6.72 × Al ₂ O ₃ (mass%) − 1.43 × Fe ₂ O ₃ (mass%)-2.85 × SO ₃ (mass%) (1)
C ₂ S amount (mass%) = 2.87 × SiO ₂ (mass%) − 0.754 × C ₃ S (mass%)
(2)
C ₃ A amount (mass%) = 2.65 × Al ₂ O ₃ (mass%) − 1.69 × Fe ₂ O ₃ (mass%) (3)
C ₄ AF amount = 3.04 × Fe ₂ O ₃ (mass%) (4)

  The fineness of the cement composition is 2800-3800 cm2 / g, preferably 3000-3700 cm2 / g, in terms of Blaine specific surface area.

  In addition to selenium, cadmium, lead, molybdenum, fluorine, and zinc are used for extraction and separation operations at high temperatures, in addition to reducing the content of clinker, and cement using clinker that reduces heavy metals. By treating with a solidified material, it has the effect of suppressing the elution of these heavy metals from the solidified soil. In addition, selenium in cement clinker decreases for a long period of time, in contrast to the amount of elution from solidified soil, such as hexavalent chromium and cadmium, significantly decreasing with age. Although it has a tendency, it has the characteristic of not changing greatly.

The allowable content of selenium in various cements and cement-based solidification materials is that the amount of selenium eluted from the solidified soil is generally greater than the amount of selenium eluted from the hardened cement (for example, mortar or hardened concrete). It is often determined by the amount of elution from the treated soil.

  The selenium content of the cement clinker or cement composition of the present invention is quantified by the cement association standard test method CAJS I-52: 2000 “Method for quantifying cement minor components by ICP emission spectroscopic analysis and electric heating atomic absorption spectrometry”. In accordance with the above, after the sample is dissolved, it is quantified by electric heating atomic absorption spectrometry. The amount of selenium eluted from cement clinker and cement composition is the Method No. 13 of the Environment Agency, and the amount of selenium eluted from the solidified soil is the method of the Method No. 46 of the Environment Agency by using a sample 7 days after solidification. It is determined by.

The extracted dust from which selenium is taken in by the above method can be returned to the cement raw material after chelating by the method described in Patent Document 2 (Japanese Patent Laid-Open No. 2005-103476). By mixing with a cement clinker whose amount is reduced to 1.6 mg / kg or less to obtain a cement composition, effective use can be achieved without any special treatment.
Specifically, the extracted dust collected by the bag filter 15 of FIG. 1 is pulverized with a cement clinker and gypsum by a finishing mill 30 to obtain a cement composition.

  The selenium content of the cement composition obtained by the above method is preferably 5.0 mg / kg or less, and more preferably 4.0 mg / kg or less. This is based on the new finding that the selenium compound in the bleed dust collected by bleed has different elution characteristics from the selenium compound in the Portland cement clinker discharged from the kiln. In other words, even if the selenium content in the cement composition is the same, the selenium elution amount per unit mass of the selenium in the Portland cement clinker and the selenium in the extracted / collected extracted dust is the latter. This is because it is greatly reduced.

The reason for the above phenomenon is not clear, but is presumed to be due to the following mechanism. That is, when the clinker calcined near 1200 ° C. comes into contact with water, C ₃ S, C ₂ S, C ₃ A, and C ₄ AF in the clinker mineral quickly start a hydration reaction. While the selenium contained therein is also eluted in the liquid phase along with this hydration reaction, the extracted dust heated only at about 800 ° C is a calcined raw material and hydrated because almost no clinker mineral is generated. The reaction does not proceed, so it is considered that selenium in the extracted dust is difficult to elute into the liquid phase.

  The extraction dust can be added to a normal clinker as described above, but an appropriate amount is added to a Portland cement clinker whose selenium content is reduced to 1.6 mg / kg or less, and the selenium content in the cement composition is 5%. When the amount is not more than 0.0 mg / kg, the effect of reducing the amount of selenium eluted can be improved.

The cement-based solidified material of the present invention, in which gypsum is added to this cement composition, is composed of general soft soil, highly organic soil, highly hydrous ultra-soft soil, volcanic ash cohesive soil, special soil (soil that is easy to dissolve hexavalent chromium). Targets application to solidification. The total amount of gypsum added at the time of preparing the cement composition and the gypsum added at the time of preparing the cement-based solidified material is 5 to 15% by mass with respect to the cement-based solidified material, based on SO ₃ , Preferably it is 6-12 mass%. The cement-based solidified material may contain one or more of blast furnace slag, fly ash, alumina cement, magnesia, quicklime, and slaked lime in addition to gypsum. The amount of cement-based solidifying material added to the target soil is 50 to 400 kg / m ³ , preferably 100 to 300 kg / m ³ . When it is within this range, an appropriate solidification strength can be obtained.

  Hereinafter, the present invention will be described in more detail with reference to examples and drawings. However, these descriptions are merely examples and do not limit the scope of the present invention.

The cement clinker, extraction dust, cement, cement-based solidified material and sample soil used are as follows.

As the cement clinker, a total of five types of clinker (K1 to K5) with different selenium contents obtained by changing the presence / absence of bleed and the bleed rate in an actual machine manufacturing plant were used as samples. Here, the extraction position of the exhaust gas in the factory was the inlet hood part, and the extraction temperature was 1150 to 1200 ° C. Table 1 shows the extraction rate. To these clinker, gypsum mixed with dihydric gypsum and hemihydrate gypsum at a mass ratio of 2: 8 was added in an internal ratio so that it would be 1.9% based on SO _{3 in} the cement. Was pulverized so as to have a brain specific surface area of 3250 ± 50 cm ² / g to obtain a cement composition. The trial cement composition was measured for the amount of selenium eluted from the powder according to the Environment Agency Notification No. 13 method (February 17, 1973). The results are shown in Table 1.

Next, the cement-based solidified material is prepared so that natural anhydrous gypsum (brane specific surface area of 4030 cm ² / g) is added to the trial cement (samples SR3, 4 and 5) so as to be 10% by mass based on SO ₃ in the solidified material. Added in percent. That is, the total amount of the gypsum added at the time of preparing the trial cement and the gypsum added at the time of preparing the solidified material is added in an internal ratio so that the total amount of the gypsum added to the solidified material is 10% by mass on the SO ₃ basis, Adjusted. In this case, the selenium content in the Portland cement composition was changed by using two kinds of D1 and D2 obtained experimentally in an actual cement manufacturing plant as the extraction dust. The selenium contents of D1 and D2 were 74.2 and 1190 mg / kg, respectively. Table 4 shows the extraction rate of the extracted dust.

As the solidified soil, 200 kg / m ³ of the above cement-based solidified material was added to Kurobo produced in Kyushu (natural water content 150 mass%), scraped off with a soil mixer for 2 minutes, and stirred and mixed for 2 minutes at low speed. The solidified soil thus obtained is divided into three layers in a φ5 × 10 cm mold, and a cylindrical specimen is prepared by tapping filling while removing air bubbles for each layer. Sealed and cured until. The cylindrical specimen was crushed to 2 mm or less, and the elution amount of selenium was measured according to the Environmental Agency Notification No. 46 method (August 23, 1991).

[ Examples 3 and 4 , Comparative Example 1, Reference Examples 1 and 2 ]
Table 1 shows the selenium content of a trial cement made of cement clinker that does not contain extraction dust and the selenium elution amount from cement powder, and the brain ratio measured in accordance with JIS R 5201: 1997 “Physical Test Method for Cement” Table 2 shows the surface area and the mineral composition measured according to JIS R 5202: 1999 “Chemical analysis method of Portland cement”. Table 3 shows main chemical components of the cements L3 and L5. Table 4 shows chemical components of the extracted dust. Ig. loss-f. CaO was measured according to JIS M 8853: 1998 “aluminosilicate material for ceramics”, and Cl was measured according to JIS R 5202 “Chemical analysis method of cement”.

  Moreover, the X-ray-diffraction measurement result of extraction dust is shown in FIG. For X-ray diffraction, RINT-2500V manufactured by Rigaku Corporation was used as an apparatus, and the measurement conditions were as follows.

Tube: Cu, tube current: 130 mA, tube voltage: 50 kV, sampling width: 0.02 °, scanning speed: 4 ° / min, wavelength: 1.5405 mm, measurement diffraction angle range (2θ): 5 ° to 70 °

  As shown in Table 1, in cement containing no bleed dust, cement using clinker having a selenium content of 1.6 mg / kg or less (Examples 1 to 4) had a selenium elution amount of 0. It was at a low level of 01 mg / L or less. However, from the cement (Comparative Example 1) having a selenium content exceeding 1.6 mg / kg, the selenium elution amount exceeded 0.01 mg / L.

[Examples 9 to 11, Examples 15 and 16, Comparative Examples 2 to 6, Reference Examples 3 to 9 ]
Cement-based solidification material (No. 1-16) adjusted with or without extraction dust D1 and D2 added to trial cements SR3 and SR4, and cement-based solidification material adjusted by adding anhydrous gypsum to SR5 Table 5 and FIG. 3 show the amount of selenium eluted from the solidified soil obtained by treating (black) using (No. 17).

  As shown in FIG. 3, the amount of selenium eluted from the solidified soil increased as the selenium content in the Portland cement composition increased in both cases where extraction dust was added and in the case where no extraction dust was added. In the test range shown in FIG. 3, when extraction dust was added, if the selenium content in the Portland cement composition was about 5.0 mg / kg or less, the soil environment standard was generally satisfied. In addition, reducing selenium in the Portland cement clinker is more effective in suppressing elution, and when the selenium content of the extracted dust becomes excessive, selenium from the solidified soil slightly increases.

Further, as shown in FIG. 3, even if the selenium content in the Portland cement composition is the same 2.0 mg / kg, the clinker containing more selenium (Δ mark in FIG. 3) The amount of selenium eluted is larger than that containing less selenium (circles in FIG. 3). That is, it is understood that selenium is less likely to elute when the selenium content in the extracted dust is increased.

It is a figure which shows the systematic diagram of one Embodiment which bleeds selenium using an extraction gas installation. It is a figure which shows the X-ray-diffraction measurement result of dust D1 and D2. It is a figure which shows the relationship between the selenium content in a cement composition, and the selenium elution amount from solidification soil.

Explanation of symbols

1: Kiln for cement firing 1a: Burner for firing 2: Clinker cooler 2a: Cooling fan for clinker cooler 3: Kiln inlet hood 3a: Exhaust gas extraction port 4: Rising duct 5: SP (suspension preheater)
5a: lowermost cyclone 5b: calcining furnace 5c: raw material supply pipe 5e: uppermost cyclone 5f: cyclone junction duct 5g: uppermost cyclone outlet 6: exhaust fan 7: chute 8: cooler exhaust gas supply duct 10: extraction gas equipment 11: Exhaust gas extraction pipe 11a: Cooling fan 12: Lump removal devices 13a, 13b, 13c: Exhaust gas duct 14: Cold air intake pipe 15: Bag filter (dust collector)
15a: Bag filter lower hopper 15b: Dust discharging screw conveyor 16: Exhaust (attraction) fan 20: Dust storage / dispensing equipment 21: Cushion hopper 22: Butterfly damper 23: Dust delivery vehicle 30: Finishing mill equipment 31: Ball mill 32: Classifier 33: Dust storage receiving hopper

Claims (9)

A cement composition comprising a cement clinker having a selenium content of 1.6 mg / kg or less, gypsum, and extraction dust containing selenium recovered from a selenium-containing exhaust gas,
The selenium content in the extracted dust is 1190-5000 mg / kg,
_{C 3} A content is 0.1 to 4 mass% of the Borg type Calculation said cementitious _composition, the _C 4 AF weight 12 to 18% by weight and selenium content of 2.0~5.0mg / kg Cement composition characterized. The cement composition according to claim 1, wherein the selenium content in the cement clinker is 0.6 to 1.6 mg / kg. The cement according to claim 1 or 2 , wherein the cement clinker is obtained by extracting a part of the selenium-containing exhaust gas from the cement kiln in the cement kiln from the suspension preheater part to the rotary kiln inlet hood part to reduce selenium. Composition. The extracted dust is extracted dust in which a portion of the selenium-containing exhaust gas from the cement kiln from the suspension pre-heater section of the cement firing device to the rotary kiln inlet hood is extracted and cooled to collect selenium from the selenium-containing exhaust gas. The cement composition according to any one of claims 1 to 3, wherein: The cement composition according to any one of claims 1 to 4, wherein the amount of the extraction dust added is 0.034 to 0.35 mass% with respect to the cement composition. A cement-based solidifying material comprising the cement composition according to any one of claims 1 to 5 . In the cement firing apparatus provided with the suspension preheater, a part of the selenium-containing exhaust gas from the cement kiln from the suspension preheater part to the rotary kiln inlet hood part is extracted, cooled, and selenium is extracted from the selenium-containing exhaust gas as extraction dust. A method for producing a cement composition, wherein the cement composition according to any one of claims 1 to 5 is collected by mixing and extracting dust dust, cement clinker and gypsum.   The method for producing a cement composition according to claim 7, wherein an extraction rate of the exhaust gas is 0.1 to 10% and an extraction gas temperature is 300 to 1300 ° C. A method for producing a cement-based solidified material, comprising producing a cement-based solidified material using the cement composition obtained by the production method according to claim 7 or 8.

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