JP5626386B2 - CEMENT COMPOSITION, PROCESS FOR PRODUCING THE SAME, AND CEMENT-BASED SOLIDING MATERIAL - Google Patents

Description

  The present invention relates to a cement composition and a cement-based solidifying material including a cement clinker having a reduced selenium content and a washing residue of extraction clinker (extraction dust). 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. Is taken in over 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 the raw material used and fuel (coal), and sometimes exceeds 1 mg / kg in the cement. When the selenium content in Portland cement increases, the environmental standards set in the Environmental Agency Notification No. 46 method (August 23, 1991) from the solidified soil using cement-based solidified material (0.001 per liter of test solution). There is a risk that selenium exceeding 01 mg or less will elute.

  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 provides a cement composition and a cement-based solidifying material capable of suppressing the selenium elution amount as a result of a small elution amount ratio with respect to the selenium content without limiting the type of raw fuel or the basic unit of raw fuel. The purpose is to do.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors set the selenium content in the cement clinker to an appropriate amount, and the extraction clinker incorporating selenium at the time of manufacturing the cement clinker was washed with water and filtered with a water washing residue ( Hereinafter, it was found that the amount of selenium eluted from the cement composition can be reduced by using the “water washing residue”, and the present invention has been completed.

That is, the present invention is a cement composition including a cement clinker, gypsum, and a water residue of extraction clinker, wherein the cement composition has a selenium content of 15.0 mg / kg or less and a C ₃ A amount calculated by the Borg formula. Is a cement composition having 0.1 to 4% by mass and a cement-based solidifying material using the same. 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 suspension preheater part of the cement firing device to the rotary kiln inlet hood. Further, the cement composition of the present invention includes a water washing residue of an extraction clinker containing selenium recovered from the extracted selenium-containing gas, and the selenium content in the cement composition is 15.0 mg / kg or less. .

  The present invention is also directed to a cement firing apparatus provided with a suspension preheater, wherein a portion of the selenium-containing exhaust gas from the cement kiln from the suspension preheater portion to the rotary kiln inlet hood portion is extracted and cooled to cool the selenium-containing exhaust gas. A step of collecting selenium and obtaining an extraction clinker (extraction dust), washing the obtained extraction clinker with water and drying to obtain a washing residue, and then mixing the washing residue with cement clinker and gypsum, the cement composition The manufacturing method of the cement composition including the process made into.

The cement composition according to the present invention includes a cement clinker that reduces selenium by extracting a part 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, gypsum, and extraction A cement composition comprising a clinker washing residue, wherein the cement composition has a selenium content of 15.0 mg / kg or less, a C ₃ A amount of 0.1 to 4% by mass in a Borg calculation, and a C ₃ S amount. Is 55 to 75% by mass, the selenium content of the washing residue with respect to the total mass of the cement composition is 2.5 to 15.0 mg / kg, and the cement clinker has a selenium content of 4.81 mg / kg or less. Yes, the washing residue is characterized in that the selenium content is 10 to 5000 mg / kg.

  The cement composition and the cement-based solidified material according to the present invention extract and separate and remove part of the selenium-containing kiln exhaust gas in the cement firing step, thereby reducing the selenium content in the Portland cement clinker to 6.0 mg / kg or less. The selenium elution amount can be remarkably reduced by using the clinker reduced to selenium and the extracted clinker incorporating selenium with water and the filtered water washing residue.

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 relationship between the selenium content of an extraction clinker and a water washing residue, and a selenium elution amount.

  Below, suitable embodiment of the cement composition and cement-type solidification material which reduced the selenium content based on this invention is described.

  Generally, the cement clinker is manufactured by the SP method (multistage cyclone preheating method) or the NSP method (multistage cyclone preheating method 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, an extraction clinker discharging 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, and constitute an extraction clinker storage / dispensing facility 20. The bleed clinker delivered from the bleed clinker storage / delivery facility 20 is received by the bleed clinker carry-out vehicle (bulk vehicle) 23 and then carried out to the bleed clinker storage receiving hopper 33. Thus, the extraction clinker collected and collected by the bag filter 15 of the extraction gas facility 10 and received by the extraction clinker storage receiving hopper 33 is conveyed to the classifier 32 of the cement finishing mill facility 30 and classified, and the coarse powder is The fine powder is returned to the ball mill 31 and collected 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 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”) is preferably 0.05 to 10% by volume. Here, the extraction rate is the percentage (volume%) of the extraction amount (m ³ ) extracted from the cement firing device using the extraction gas equipment with respect to the exhaust gas amount (m ³ ) passing through the kiln inlet hood 3. Say. If the extraction rate is less than 0.05% by volume, the gas containing selenium cannot be extracted sufficiently, and if it exceeds 10% by volume, the fuel consumption deteriorates, the productivity deteriorates due to excessive intake of the calcined raw material, and the imported raw material or Processing of the calcined raw material is required. The extraction rate is more preferably 0.1 to 7% by volume. 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 extraction clinker.
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.

  Selenium condensed and 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. In addition, the extracted clinker including the collected selenium and other heavy metals is extracted through the cushion hopper 21, the double butterfly damper 22 and the extraction clinker carry-out vehicle (bulk vehicle) 23 of FIG. It is carried out to 33. The bleed clinker in the hopper is washed with water in a washing treatment tank 34, filtered with a filter 35 to become a washing residue, sent to the cement finishing mill facility 30, and made into a cement composition. A part of the extraction clinker may be sent to the cement finishing mill facility 30 as it is without being washed with water, and may be used as a cement composition.

  As the 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 condensed can be used. The extraction amount in this case is 0.05 to 5% by mass, preferably 0.1 to 1% by mass with respect to the amount of raw material fed. If the amount is less than 0.05% by mass, selenium cannot be sufficiently collected. If the amount exceeds 5% by mass, productivity deterioration due to excessive extraction of high-temperature gas and processing of the incorporated calcined raw material are required.

The chemical composition of the extraction clinker varies depending on the chemical composition 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 0.1 to 3% by mass. %, K ₂ O is 2 to 60% by mass, preferably 2 to 50% by mass, and Cl is 2 to 50% by mass, preferably 2 to 40% by mass.

  In addition, the selenium content in an appropriate extraction clinker in which the stability of the kiln operation, the heat balance, the economy, etc. are combined is 10 to 5000 mg / kg, preferably 20 to 3000 mg / kg, more preferably 30 to 30% on a mass basis. The range of 2500 mg / kg, particularly preferably 40 to 1000 mg / kg is good.

  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 extraction clinker are cadmium: 200-7000 mg / kg, lead: 500-20000 mg / kg, molybdenum: 20-300 mg / kg, and fluorine: 200-3000 mg / kg.

In this way, in the clinker firing step, selenium-containing gas is extracted using an extraction gas facility, for example, an existing chlorine bypass facility, and selenium is separated and removed as an extraction clinker, and this extraction clinker is clinkered as necessary. Return to. The upper limit of the selenium content in the clinker that does not contain or includes this bleed clinker is 6.5 mg / kg, preferably 6.0 mg / kg, more preferably 5.5 mg / kg, still more preferably 5.0 mg / kg. It is.
Portland cement composition using this clinker, mixed cement and cement-based solidification material (including general soft soil, high organic soil, special soil solidification material (for hexavalent chromium countermeasures)), and solidified soil The amount of elution 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 lower limit of the selenium content in the clinker is preferably lower, but considering the deterioration of fuel consumption due to an increase in the extraction rate, 0.05 mg / kg, preferably 0.2 mg / kg, more preferably 0.5 mg / From the standpoint of industrial and production costs, it is preferable to set kg, more preferably 0.6 mg / kg, particularly preferably 0.7 mg / kg, and most preferably 0.8 mg / kg.

The mineral composition of the cement composition 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 0.2 to 2% by mass, and the amount of C ₄ AF is 12 to 18%. % By mass, preferably 13 to 17% by mass. Here, the C ₃ S amount, the C ₂ S amount, the C ₃ A amount and the C ₄ AF amount in the Borg formula calculation are values calculated by the following equations (1), (2), (3) and (4). is there.
C ₃ S amount (% by mass) = 4.07 × CaO amount−7.60 × SiO ₂ amount−6.72 × Al ₂ O ₃ amount−1.43 × Fe ₂ O ₃ amount−2.85 × SO ₃ Quantity (1)
C ₂ S amount (% by mass) = 2.87 × SiO ₂ amount−0.754 × C ₃ S amount (2)
C ₃ A amount (% by mass) = 2.65 × Al ₂ O ₃ (% by mass) −1.69 × Fe ₂ O ₃ (% by mass) (3)
C ₄ AF amount (mass%) = 3.04 × Fe ₂ O ₃ (mass%) (4)

Fineness of the cement composition is a Blaine specific surface area, 2800~3800cm ² / g, preferably from 3000~3700cm ² / g.

  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 JCAS I-52: 2000 “Method for Quantifying Cement Trace Components by ICP Emission Spectroscopy and Electric Heating Atomic Absorption Spectrometry” In accordance with the above, after the sample was dissolved, it was quantified by electric heating atomic absorption spectrometry. The amount of selenium eluted from cement clinker and cement composition is the Environment Agency Notification No. 13 method (February 17, 1973), and the amount of selenium eluted from the solidified soil is 7 days after solidification. The sample was quantified by the Environment Agency Notification No. 46 method (August 23, 1991).

  The extraction clinker incorporating selenium by the above method is washed with water, made into a water-washed residue separated by solid-liquid separation by filtration, mixed with a cement clinker with reduced selenium content produced during selenium extraction, and made into a cement composition. Effective use can be achieved with simple processing. Specifically, the bleed clinker in the bleed clinker storage receiving hopper 33 of FIG. 1 is washed with water in a washing treatment tank 34, filtered with a filter 35 to obtain a washing residue, and ground with a cement clinker and gypsum in a finishing mill 30. And a cement composition is obtained. The amount of water used for washing is 5 to 20 times, preferably 7 to 15 times, and more preferably 8 to 13 times the mass of the extraction clinker. If there is a lot of water in the washing residue, dry using the exhaust gas from the kiln.

Chemical components of the washing residue, the chemical components of the bleed clinker varies by washing with water conditions, etc., Na ₂ O from 0.1 to 2% by weight, preferably from 0.2 to 1 wt%, _{K 2} O is 0.1 It is 10% by mass, preferably 0.5-6% by mass, and Cl is 0.2-5% by mass, preferably 0.5-2% by mass. If it is below these upper limit values, there is not much alkali amount and a normal cement composition can be obtained. Further, the upper limit of the selenium content in the washing residue is 5000 mg / kg, preferably 4000 mg / kg, particularly preferably 3000 mg / kg, more preferably 1000 mg / kg, and most preferably 500 mg / kg. The lower limit is 10 mg / kg, preferably 50 mg / kg, particularly preferably 100 mg / kg, more preferably 150 mg / kg, most preferably 200 mg / kg. Within these ranges, the selenium elution amount from the solidified soil can satisfy the environmental standard value even if added to the clinker.

The upper limit of the selenium content of the cement composition obtained by the above method is 15.0 mg / kg, preferably 14.0 mg / kg, particularly preferably 13.0 mg / kg. The lower limit is 1.3 mg / kg, preferably 2.0 mg / kg, particularly preferably 3.0 mg / kg, more preferably 4.0 mg / kg, most preferably 5.0 mg / kg.
The upper limit of the selenium content of the extraction clinker (extraction dust) with respect to the total mass of the cement composition is 9.5 mg / kg, preferably 8.0 mg / kg, particularly preferably 7.0 mg / kg, more preferably 6.0 mg / kg. kg, most preferably 5.0 mg / kg. The lower limit is 0.1 mg / kg, preferably 0.2 mg / kg, particularly preferably 0.4 mg / kg, more preferably 0.6 mg / kg, most preferably 0.7 mg / kg.
The upper limit of the selenium content of the water washing residue relative to the total mass of the cement composition is 15.0 mg / kg, preferably 14.0 mg / kg, particularly preferably 13.0 mg / kg, more preferably 12.0 mg / kg, most preferably Is 11.0 mg / kg. The lower limit is 1.3 mg / kg, preferably 2.0 mg / kg, particularly preferably 2.5 mg / kg, more preferably 3.0 mg / kg, most preferably 4.0 mg / kg.
If it is the said range, it is possible to obtain the cement composition which can be satisfied in terms of the stability of the kiln operation, the heat balance, the economical efficiency, etc., and the amount of selenium elution from the solidified soil.
This is based on a new finding that the selenium compound in the water washing residue is different from the selenium compound and the extraction clinker in the Portland cement clinker discharged from the kiln. That is, even if the selenium content in the cement composition is the same, the selenium elution amount per unit mass of the selenium in the cement clinker, the selenium in the extraction clinker, and the selenium in the water washing residue is such that it is the latter. This is because it is reduced. That is, the selenium elution amount is in the order of cement clinker> extraction clinker> water washing residue. The selenium content of the water washing residue and the extraction clinker and the selenium elution amount from these powders are shown in FIG.

The reason for the above phenomenon is not clear, but is presumed to be due to the following mechanism.
That is, the clinker calcined near 1200 ° C. is contained in the clinker because C ₂ S, C ₃ A, and C ₄ AF in the clinker mineral quickly start a hydration reaction when contacted with water. While selenium and the like are also eluted in the liquid phase with this hydration reaction, the extraction clinker heated only at about 800 ° C. is a calcined raw material, and since the clinker mineral is not generated so much, the hydration reaction does not proceed. Therefore, it is considered that selenium in the extraction clinker is difficult to elute into the liquid phase.
Further, the water washing residue obtained by washing the extraction clinker with water is considered to be in a state in which selenium is not easily eluted from the water washing residue because of some hydration.

  Although the water washing residue of the extraction clinker can be added to a normal clinker as described above, an appropriate amount is added to a Portland cement clinker whose selenium content is reduced to 6.0 mg / kg or less, and the selenium content in the cement composition It is also possible to use it in an amount of 15.0 mg / kg or less.

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 elute 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. When blast furnace slag fine powder is used, it is added in an amount of 20 to 40% by mass, preferably 30 to 40% by mass, with respect to the cement composition.
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.

(1) Preparation of trial cement Portland cement clinker was sampled from a total of four types of clinker (K1 to K4) with different selenium contents obtained experimentally by changing the presence / absence of extraction and the extraction rate. Among these, K3 and K4 contain extraction clinker (extraction dust). The exhaust gas extraction positions were all in the inlet hood, and the extraction temperature was 1100 to 1250 ° C. Table 1 shows the selenium content and the extraction rate. Gypsum prepared by mixing dihydric gypsum and hemihydrate gypsum in a mass ratio of 2: 8 to these clinker is divided in proportion so as to be 1.9 ± 0.25 mass% based on SO _{3 in} the cement. It was added and pulverized with a test ball mill to a Blaine specific surface area of 3250 ± 150 cm ² / g to obtain trial cements (SR1 to SR4). The Blaine specific surface area of the trial cement was measured according to JIS R 5201: 1997 “Cement physical test method”. The mineral composition was measured according to JIS R 5202: 1999 “Chemical analysis method of Portland cement”. The results are shown in Table 2.

(2) Preparation of cement composition A predetermined amount of trial cement and extraction clinker or washing residue were mixed to prepare a cement composition. As the extraction clinker, D1 to D3 obtained experimentally in an actual cement manufacturing plant were used. Table 4 shows the extraction rate, selenium content, and selenium elution amount of the extraction clinker. About 100 g of each of the extraction clinkers D1 to D3 was put into a beaker containing 10 times the amount of tap water based on the mass ratio, and the residue was washed with a magnetic stirrer for 2 hours, and then filtered with 5 types A filter paper. After drying with a dryer at 105 ° C., the mixture was allowed to stand overnight in a desiccator until it reached room temperature.
Three kinds of water washing residues S1 to S3 obtained by such a method were used to change the selenium content in the cement composition. Table 5 shows the selenium content, selenium elution amount, and other chemical components of the water washing residue. The amount of selenium eluted in Table 5 was determined by the Environmental Agency Notification No. 13 method (February 17, 1973), ig. loss-f. CaO was measured according to JISM 8853: 1998 “aluminosilicate material for ceramics” and Cl was measured according to JIS R 5202 “Chemical analysis method of cement”.
Moreover, the comparison of the selenium elution amount of Tables 4 and 5 is shown in FIG. It can be seen that the washing residue is less likely to elute selenium than the extraction clinker.
Table 6 shows the extraction clinker, the addition amount of the washing residue, and the selenium content of the cement composition obtained.

(3) Preparation of cement-based solidified material The cement-based solidified material is internally divided so that anhydrous gypsum hydrofluoric acid (brane specific surface area 4030 cm ² / g) is 8% by mass based on SO ₃ in the solidified material. 9 kinds of solidifying materials (No. 1 to 9) were prepared. 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 was added in an internal ratio so that the total amount of the gypsum added to the solidified material was 8% by mass on the SO ₃ basis. Was prepared.

(4) Evaluation solidification soil selenium elution amount, Chiba occurring Kanto loam above the cement solidifying material 200 kg / m ³ was added to (natural water content 108 wt%), were mixed and stirred at a low speed for 2 minutes with soil mixer After scraping off, the mixture was further stirred at low speed for 2 minutes. 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, and the age is 7 days at 20 ° C. Sealed and cured until. The cylindrical specimen was crushed to 2 mm or less, and the selenium elution amount was measured in accordance with the Environmental Agency Notification No. 46 method (August 23, 1991). The results are shown in Table 6.

  As shown in Table 6, the cement composition to which the water washing residue was added had a selenium content of the cement composition of 15.0 mg / kg or less, so that the amount of selenium eluted from the solidified soil was 46 No. method (August 23, 1991) environmental standard was 0.01 mg / L or less (Examples 1 to 7). On the other hand, the selenium content of the cement composition as high as 15.6 mg / kg (Comparative Example 1) could not satisfy the environmental standards. In the case where no washing residue was added (Comparative Example 2), the selenium content of the cement composition was 4.7 mg / kg, which was much lower than other cement compositions in order to satisfy the environmental standards. It was.

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 extraction clinker 14: Cold air intake pipe 15: Bag filter (dust collector)
15a: Bag filter lower hopper 15b: Extraction clinker discharge screw conveyor 16: Exhaust (attraction) fan 20: Extraction clinker storage / discharge facility 21: Cushion hopper 22: Butterfly damper 23: Extraction clinker unloading vehicle 30: Finishing mill facility 31: Ball mill 32: Classifier 33: Extraction clinker storage receiving hopper 34: Washing treatment tank 35: Filter

Claims (8)

Cement composition including cement clinker that reduces selenium by extracting a part of the selenium-containing exhaust gas from the cement kiln from the suspension preheater part of the cement kiln to the rotary kiln inlet hood, gypsum, and water washing residue of the extraction clinker A thing,
The cement composition selenium content of 15.0 mg / kg or less, _{C 3} A content is 0.1 to 4 mass% of Borg type calculation, a _{C 3} S content is 55 to 75 wt%, the cement composition The selenium content of the washing residue with respect to the total mass of is 2.5 to 15.0 mg / kg,
The cement clinker has a selenium content of 4.81 mg / kg or less,
Cement composition characterized in that the water washing residue has a selenium content of 10 to 5000 mg / kg. The cement composition according to claim 1, wherein the cement composition has a selenium content of 3.0 to 15.0 mg / kg.   The rinsing clinker that collects selenium from the selenium-containing exhaust gas is obtained by extracting a part of the selenium-containing exhaust gas from the cement kiln from the suspension pre-heater part of the cement firing device to the rotary kiln inlet hood, and cooling the rinsing residue. The cement composition according to claim 1 or 2, which has been washed with water and filtered.   Furthermore, the cement composition of any one of Claims 1-3 containing an extraction clinker.   A cement-based solidifying material comprising the cement composition according to any one of claims 1 to 4 and gypsum. In cement firing equipment with suspension preheater,
Extracting a portion of the selenium-containing exhaust gas from the cement kiln from the suspension preheater to the rotary kiln inlet hood, cooling it, collecting selenium from the selenium-containing exhaust gas, and obtaining an extraction clinker;
The obtained extraction clinker is washed with water and dried to obtain a water washing residue, and then the water washing residue is mixed with cement clinker and gypsum to obtain a cement composition according to any one of claims 1 to 4. The manufacturing method of the cement composition characterized by including.   The method for producing a cement composition according to claim 6, wherein an extraction rate of the exhaust gas is 0.05 to 10% by volume, and a temperature of the exhaust gas to be extracted is 300 to 1300 ° C.   The method for producing a cement composition according to claim 6 or 7, wherein the extraction clinker and 5 to 20 times the amount of water with respect to the extraction clinker are mixed and washed with water.

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