JP2008179502A - Cementitious composition reduced in content of water-soluble hexavalent chromium and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cementitious composition having a reduced content of water-soluble Cr(VI) and good quality, and to provide a method for producing the same. <P>SOLUTION: The cementitious composition reduced in the content of water-soluble hexavalent chromium comprises cement clinker and gypsum, wherein the K<SB>2</SB>O content (mass%) and the total Cr content (mass%) in the cement clinker satisfies the relation: total Cr content×10<SP>4</SP>≤-222×K<SB>2</SB>O content+225. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

In the present invention, the amount of water-soluble hexavalent chromium (hereinafter sometimes referred to as “water-soluble Cr (VI)”) that may be eluted during the hydration process of cement is 20 mg / kg (20 × 10 ⁻⁴ mass%). ) The following relates to a reduced water-soluble hexavalent chromium-reducing cement composition and a method for producing the same.

  Cement clinker is manufactured by firing various materials such as limestone, clay, silica, and iron materials at a high temperature in a rotary kiln. However, in cement clinker produced under such high temperature conditions, chromium as a minor component contained in the raw material may be present in a significant amount in the form of harmful water-soluble Cr (VI).

In recent years, due to increasing environmental considerations, when cement is used as a soil conditioner for fixing harmful metals, the amount of water-soluble Cr (VI) eluted from the solidified improved soil is the soil environment standard value (0. In September 1998, the guidelines for setting the water-soluble Cr (VI) content in cement to 20 mg / kg (20 × 10 ⁻⁴ mass%) or less were established in the cement industry with the aim of satisfying the requirement of 0.5 mg / L or less) From then on, management is based on this.

  Further, as described in Non-Patent Document 1, the water-soluble Cr (VI) in the cement clinker is present in the form of a highly soluble chromate salt, for example, an alkali metal salt such as sodium chromate or potassium chromate. It is said. However, Non-Patent Document 1 does not disclose a method for controlling / reducing water-soluble Cr (VI).

Heretofore, several methods have been disclosed regarding water-soluble Cr (VI) elution prevention methods. For example, in Patent Document 1, for the prevention of water-soluble Cr (VI) elution from a solidified product using cement, a predetermined amount of slag is added to cement that defines the total amount of C ₃ S and C ₃ A in the cement. Thus, even when volcanic ash cohesive soil or the like is used as the soil to be treated, an elution prevention method is disclosed that can provide high solidification strength. However, in this method, it is necessary to newly add slag to the cement, and the manufacturing process is complicated. In addition, there is a case where strength development is inferior by mixing slag having low reactivity.

On the other hand, in Patent Document 2, a combustible resin such as plastic is put into a kiln when cement clinker is fired to prevent the formation of water-soluble Cr (VI) in the cement clinker by using the inside of the kiln as a reducing atmosphere. A method for reducing water-soluble Cr (VI) therein is disclosed. However, in the method of introducing the combustible resin into the kiln, it is difficult to make the atmosphere in the kiln uniform, and the firing state varies, so the amount of water-soluble Cr (VI) in the produced cement clinker and f.CaO There was a problem that quality fluctuations such as quantity were large. Further, Patent Document 3 discloses a hexavalent chromium elution reducing agent for hydraulic substances, which contains both a fast-acting hexavalent chromium reducing substance and a slow-acting hexavalent chromium reducing substance. However, this hexavalent chromium elution reducing agent is expensive and impractical, and there is a problem that strength development may be reduced when the addition amount is increased.
Takahashi Shigeru, cement and concrete, No. 640, pp. 20-29 (Jun. 2000) JP 2000-308863 A JP 2003-246654 A JP 2000-86322 A

  An object of the present invention is to provide a cement composition having a good quality by reducing the amount of water-soluble Cr (VI) and a method for producing the same.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that, in the formation of water-soluble Cr (VI) in cement, only K ₂ O is selectively Cr among many alkali metal oxides. The present inventors have found that water-soluble Cr (VI) can be produced by binding to and that water-soluble Cr (VI) can be reduced by reducing the amount of K ₂ O, and the present invention has been completed.

That is, the present invention includes cement clinker and gypsum, and the amount of K ₂ O (% by mass) and the total amount of Cr (% by mass) in the cement clinker are the total amount of Cr × 10 ⁴ ≦ −222 × K ₂ O. It is a water-soluble Cr (VI) -reducing cement composition that satisfies the relationship +225. That is, in the present invention, as long as the above formula is satisfied, when the amount of K ₂ O is small, even if the total Cr amount is large, the water-soluble Cr (VI) is made a predetermined amount or less (for example, 20 × 10 ⁻⁴ mass%). be able to.

  According to the cement composition and the method for producing the same of the present invention, a cement composition capable of reducing the amount of water-soluble Cr (VI) present in the cement composition to an industry guideline value (20 mg / kg) or less. Can be provided.

  The cement composition of the present invention comprises a cement clinker and gypsum. As the cement clinker, ordinary Portland cement clinker, early strong cement clinker, intermediate heat cement clinker, low heat cement clinker and the like are used.

  Examples of the gypsum include natural gypsum, drainage gypsum, fluoric acid gypsum, and phosphoric acid gypsum, and the form thereof may be any form such as dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum.

The chemical composition of the cement composition obtained by adding gypsum to the cement clinker and pulverizing with a ball mill or the like is 20 to 80% by mass of C ₃ S, preferably 30 to 75% by mass, more preferably 50 to 70% by mass. It is. C ₂ S is 5 to 70 wt%, preferably from 7 to 50 wt%, more preferably 7 to 20 mass%. C ₃ A is 0 to 20 wt%, preferably 0-15 wt%, more preferably 0-12 wt%. C ₄ AF is 0 to 20% by weight, preferably 5 to 15% by weight, more preferably 7 to 12 mass%.

Here, the CaO, SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , Na ₂ O, and K ₂ O content (mass%) in the cement was determined according to JIS R 5202: 1999 “Chemical analysis method for Portland cement”. Measured accordingly. Further, the amount of C ₃ S, the amount of C ₂ S, the amount of C ₃ A, and the amount of C ₄ AF are values calculated by the following formulas (1), (2), (3), and (4).

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 (mass%) = 3.04 × Fe ₂ O ₃ (mass%) (4)

Fineness, JIS R 5201: 2500~5000cm with Blaine specific surface area defined by the 1997 "Physical testing methods for cement" ² / g, preferably 2800~4200cm ² / g, more preferably 3000~3900cm ² / g is there.

In producing the cement composition, the amount of K ₂ O (mass%) and the total amount of Cr (mass%) in the cement clinker satisfy the relationship of the total Cr amount × 10 ⁴ ≦ −222 × K ₂ O amount + 228. Thus, the amount of K ₂ O and the total amount of Cr are adjusted. Thus, when the total Cr amount is large, the amount of K ₂ O is reduced, or when the total amount of K ₂ O is large, the total Cr amount is decreased, whereby the water-soluble Cr (VI ) Amount can be reduced to 20 mg / kg or less. When the water-soluble Cr (VI) amount is 15 mg / kg or less as a safer control value, the total Cr amount x 10 ⁴ ≦ −222 × K ₂ O amount + 200, and the water-soluble Cr (VI) amount is 10 mg / kg or less. In this case, the K ₂ O amount and the total Cr amount are adjusted so as to satisfy the total Cr amount × 10 ⁴ ≦ −222 × K ₂ O amount + 172.

The total Cr amount and the water-soluble Cr (VI) amount are measured according to JCAS I-51: 1981 “Method for quantifying trace components in cement and cement raw material”. The amount of Na ₂ O and the amount of K ₂ O are measured according to JIS R 5202: 1999 “Chemical analysis method of Portland cement”, and the total alkali amount is calculated as total alkali amount = Na ₂ O + 0.658 K ₂ O. The

The reason why the amount of water-soluble Cr (VI) can be reduced by controlling the amount of K ₂ O in the cement composition is not clear, but the following is presumed.

It is said that Cr combines with Na ₂ O and K ₂ O to produce highly soluble sodium chromate or potassium chromate to become water-soluble Cr (VI) (Non-patent Document 1), which originally increases the total alkali amount. Was thought to lead to an increase in water-soluble Cr (VI). However, the present inventors have found that because of the high proportion of Na 2 _O is present in solid solution in the clinker minerals such alite or belite in cement clinker, sodium chromate by bonding and Na 2 _O and Cr We think that the possibility to generate is low. On the other hand, since K ₂ O has a small solid solution ratio in alite and belite in the clinker, it easily binds to Cr to form potassium chromate, and the K ₂ O content is more than a certain content. Then, it is thought that potassium chromate with high solubility is produced and the amount of water-soluble Cr (VI) increases.

The amount of K ₂ O in the cement clinker may be any value as long as it satisfies the above formula, but is preferably 0.20 to 0.65% by mass, and more preferably 0.25 to 0. 50% by mass. When the amount of K ₂ O is 0.20% by mass or more, the amount of potassium sulfate is extremely reduced and sufficient sulfate ions cannot be supplied to suppress hydration of C ₃ A, resulting in a decrease in fluidity. Can be avoided. On the other hand, when the amount of K ₂ O is 0.65% by mass or less, the aluminate in which K ₂ O is dissolved takes an orthorhombic polymorph having extremely high reactivity, and causes an initial decrease in fluidity. The problem can be avoided.

Further, the total Cr amount may be any value as long as it satisfies the above formula, but is preferably 200 mg / kg (200 × 10 ⁻⁴ mass%) or less, more preferably 160 mg / kg (160 × 10 ⁻⁴ mass). %) Or less, and particularly preferably 150 mg / kg (150 × 10 ⁻⁴ mass%) or less, the relational expression between the total Cr amount and the K ₂ O amount can be applied. However, if the total Cr amount increases, for example, exceeding 200 mg / kg, chromium becomes water-soluble Cr (VI) that takes a form other than potassium chromate, so there is a possibility that it cannot be dealt with only by reducing the K ₂ O amount. .

More preferably, the total Cr amount is 100 mg / kg or less, and the K ₂ O amount is 0.43 mass% or less.

In order for the K ₂ O amount (% by mass) and the total Cr amount of the cement composition to satisfy the above formula, the K ₂ O amount and the total Cr amount in the raw material for producing cement clinker are adjusted.

The amount of K ₂ O is adjusted by the method of using the clay material. Specifically, the clay material is divided into a high K clay material having a K ₂ O content of 1.6% by mass or more and a low K clay material having a K ₂ O content of less than 1.6% by mass. However, it is easy to operate by adjusting the usage ratio. Specifically, for example, when the K ₂ O content increases, the use ratio of the low K clayey raw material is increased to reduce the K ₂ O content. This includes the case of using only low K clay raw materials.

  The clay material includes a high K clay material selected from the group consisting of clay and construction generated soil, and a low K clay material selected from the group consisting of coal ash and blast furnace slag.

  Further, the total Cr amount is adjusted by the use ratio of the high Cr iron raw material and the low Cr iron raw material in the iron raw material. Specifically, when the total Cr amount increases, the total Cr amount is reduced by increasing the usage ratio of the low Cr iron raw material and decreasing the usage ratio of the high Cr iron raw material. Examples of the Cr iron raw material include high Cr iron raw materials such as iron concentrate, converter slag, and iron-containing sludge, and low Cr iron raw materials such as copper tangles.

When manufacturing cement clinker, limestone as CaO source, silica as SiO _{2 source,} clay material as Al ₂ O 3 · SiO ₂ source, a source of iron and other raw materials as _Fe 2 _{O 3} source It mix | blends according to the target composition of a clinker.

  The basic unit of each raw material is 900-1500 kg / t-clinker for limestone, preferably 1000-1400 kg / t-clinker, 0-120 kg / t-clinker for silica, preferably 5-100 kg / t-clinker, clayey raw material 100-500 kg / t-clinker, preferably 100-400 kg / t-clinker, iron raw material 5-80 kg / t-clinker, preferably 30-70 kg / t-clinker, other raw materials 0-300 kg / t-clinker 10 to 200 kg / t-clinker is preferable.

  Other raw materials include sewage sludge having a high moisture content of 50% by mass or more.

  Regarding the above clay material, the high K clay material is 0-80 kg / t-clinker, preferably 5-60 kg / t-clinker, and the low K clay material is 20-500 kg / t-clinker, preferably 120-300 kg. More preferably, it is a / t-clinker.

  The iron raw material is a high Cr iron raw material of 0 to 40 kg / t-clinker, preferably 5 to 25 kg / t-clinker, and a low Cr iron raw material of 0 to 80 kg / t-clinker, preferably 30 to 70 kg / t. -More preferred is a clinker.

  EXAMPLES The present invention will be described in detail below using examples, but the present invention is not limited to these examples.

(1) Raw material of cement composition (i) Raw fuel used for manufacturing cement clinker Table 1 shows the types and chemical compositions of main clinker raw fuels used. In addition to those shown in Table 1, a small amount of raw material was partially used.

(Ii) Gypsum Exhaust dihydrate gypsum was used as the gypsum used in the cement composition. Further, when the cement composition was pulverized, the dihydrate gypsum was dehydrated, and 30 to 95% by mass of the added drained dihydrate gypsum was present as hemihydrate gypsum.

(2) Manufacture of a cement composition The raw material of the cement clinker of Table 1 was mixed by the specific mixture ratio, and it baked with the cement kiln. An example of the blending ratio is shown in Table 2.

  In addition, gypsum was added to the obtained cement clinker and pulverized with a ball mill to produce a cement composition.

(3) Evaluation test Next, the water-soluble Cr (VI) content and the K ₂ O content of various cement compositions were quantified. An example of the measurement results is shown in Table 3, but the data related to the present invention is not limited to these. The present invention is a finding based on all experimental data shown in FIGS. In addition, the number (No.) of the cement composition in Table 3 corresponds to the number (No.) of the cement clinker in Table 2. Specifically, the evaluation test result of the cement composition manufactured using the cement clinker manufactured under the condition of No. 1 in Table 2 corresponds to No. 1 in Table 3.

FIG. 1 shows the relationship between the total alkali amount and the water-soluble Cr (VI) amount for all experimental data including the data in Table 3. If Cr in the cement composition is combined with an alkali metal and present as sodium chromate and potassium chromate, a significant relationship should be observed between them. However, in the cement clinker and the cement composition actually manufactured by test, the correlation coefficient between them is not so high as R ² = 0.5235 (R = 0.7235), and the prediction line (solid line in FIG. 1) There is a maximum difference of 17 mg / kg from the line (dotted line in FIG. 1) obtained by extrapolating the maximum value of the actually measured values. Therefore, it is shown that not all alkali metals necessarily affect the production of water-soluble Cr (VI).

Therefore, the present inventors have investigated to clarify the influence on the amount of water-soluble Cr (VI) for each type of alkali metal in order to identify the factors resulting from the formation of water-soluble Cr (VI). . FIG. 2 shows the relationship between Na ₂ O and water-soluble Cr (VI), and FIG. 3 shows the relationship between K ₂ O and water-soluble Cr (VI).

From FIG. 2, it was found that there was no correlation between the amount of Na ₂ O and the amount of water-soluble Cr (VI), and Na ₂ O was not present as chromate.

On the other hand, FIG. 3 shows that there is a significant correlation between the amount of K ₂ O and the amount of water-soluble Cr (VI), and it is found that only the amount of K ₂ O among alkali metals exists as chromate. did it. Therefore, it is possible to control the water-soluble Cr (VI) content by _{K 2} O content, namely when the _{K 2} O content below 0.43 wt%, water-soluble Cr (VI) content to 20 mg / kg It turns out that it can reduce to (20 * 10 < ^-4 > mass%) or less.

Further, as shown in FIG. 4, the total Cr amount is also related to the water-soluble Cr (VI) amount. Therefore, in order to examine a more preferable method for reducing water-soluble Cr (VI), as shown in FIG. 5, a prediction formula of water-soluble Cr (VI): water-soluble Cr (VI) = 39 × K ₂ O + 0.18 * All Cr-20.5 was created and the prediction precision was confirmed.

As a result, when the water-soluble Cr (VI) amount is controlled only by the K ₂ O amount shown in FIG. 3, the difference between the water-soluble Cr (VI) amount prediction line (solid line in FIG. 3) and the actual measurement value is Although the amount of K ₂ O is about 0.3% by mass and about 5 mg / kg, the amount of K ₂ O becomes about 10 mg / kg when the amount of K ₂ O is about 0.5% by mass and the prediction accuracy decreases. However, as can be seen from the comparison of the calculated value and the actual value of Cr (VI) shown in FIG. 5, the prediction formula using the K ₂ O amount and the total Cr amount is the difference between the predicted value and the actual value of all the data. Since the difference can be within 5 mg / kg or less, the prediction accuracy is high. This makes it possible to reduce the amount of water-soluble Cr (VI) with higher accuracy.

FIG. 6 shows the relationship between the K ₂ O amount and the total Cr amount. A circle in FIG. 2 is a sample in which the amount of water-soluble Cr (VI) was 10 mg / kg or less, a triangle is a sample in excess of 10 mg / kg and 15 mg / kg or less, and a square is in excess of 15 mg / kg. Samples that were 20 mg / kg or less, x marks indicate samples that exceeded 20 mg / kg. From this figure, in order to reduce the amount of water-soluble Cr (VI) to 20 mg / kg (20 × 10 ⁻⁴ mass%) or less, the amount of K ₂ O (mass%) and the total Cr content (mass%) It can be seen that the cement may be manufactured so as to satisfy the relationship of the amount x10 ⁴ ≦ −222 × K ₂ O amount + 228. That is, as long as this equation is satisfied, the amount of water-soluble Cr (VI) is reduced by reducing the amount of K ₂ O when the amount of total Cr is large, or by reducing the amount of total Cr when the amount of K ₂ O is large. Can be reduced to a predetermined amount of 20 × 10 ⁻⁴ mass% or less. Further, when the amount of water-soluble Cr (VI) is set to 15 mg / kg or less as a safe control value, the total amount of Cr × 10 ⁴ ≦ −222 × K ₂ O amount + 200 may be satisfied, and the amount of water-soluble Cr (VI) is In the case of 10 mg / kg or less, it is understood that the total Cr amount × 10 ⁴ ≦ −222 × K ₂ O amount + 172 may be satisfied.

Incidentally, as a control method of the K _{2 O} content and the total Cr content, as can be seen in Table 2 and Table 3, K 2 _O amounts to adjust the amount of high K clayey material and low K clayey material Thus, the total Cr amount can be controlled by adjusting the amount of the high Cr iron raw material and the low Cr iron raw material.

Specifically, if the amount of K ₂ O is to be reduced, high-K clayy materials such as clay and construction generated soil are reduced, and low-K clayy materials such as coal ash and blast furnace slag are used. Moreover, if it is going to reduce the total Cr amount, high Cr iron raw materials, such as deiron slag and iron concentrate, will be reduced, and low Cr iron raw materials such as copper entanglements will be used.

Furthermore, when it is necessary to use a high Cr iron raw material due to the raw material circumstances, the high K clay source may be reduced so as to satisfy the total Cr amount × 10 ⁴ ≦ −222 × K ₂ O amount + 225.

It is the figure which showed the relationship between the total alkali amount and water-soluble Cr (VI) amount. It is a diagram illustrating a relationship between the Na ₂ O content and the water-soluble Cr (VI) content. It is a diagram showing the relationship between K ₂ O content and the water-soluble Cr (VI) content. It is the figure which showed the relationship between the total Cr amount and water-soluble Cr (VI) amount. It is the figure which showed the comparison with the water-soluble Cr (VI) amount calculation value by a prediction formula, and an actual value. It is a diagram showing the relationship between K 2 _O content and the total amount of Cr.

Claims (7)

The cement clinker and gypsum are included, and the K ₂ O amount (% by mass) and the total Cr amount (% by mass) in the cement clinker satisfy the relationship of the total Cr amount x 10 ⁴ ≦ −222 × K ₂ O amount + 225. A water-soluble hexavalent chromium-reducing cement composition. Total Cr content 100 × 10 ^-4 mass%, _{K 2} O content is not more than 0.43 wt%, claim 1 soluble hexavalent chromium reducing cement composition. A method for producing a water-soluble hexavalent chromium-reducing cement composition in which a cement clinker is fired using raw materials including limestone, silica, clayey raw material, and iron raw material, and gypsum is added and pulverized.
Clay raw material in the raw material so that the K ₂ O amount (% by mass) and the total Cr amount (% by mass) in the cement clinker satisfy the relationship of the total Cr amount × 10 ⁴ ≦ −222 × K ₂ O amount + 225. And a method for producing a water-soluble hexavalent chromium-reducing cement composition, comprising a step of adjusting a blending ratio of the iron raw material. The water-soluble solution according to claim 3, further comprising a step of adjusting the blending ratio of the clayey raw material and the iron raw material so that the total Cr amount is 100 × 10 ⁻⁴ mass% or less and the K ₂ O content is 0.43 mass% or less. Of producing a functional hexavalent chromium-reducing cement composition. The high K clayy raw material having a K ₂ O amount of 1.6% by mass or more and / or the low K clayy raw material having a K ₂ O amount of less than 1.6% by mass is used as the clay raw material. 4. A method for producing a water-soluble hexavalent chromium-reducing cement composition according to 4.   The high K clayey raw material is one or more selected from the group consisting of clay and construction generated soil, and the low K clayey raw material is one or more selected from the group consisting of coal ash and blast furnace slag. The manufacturing method of the water-soluble hexavalent chromium reduction cement composition of any one of 3-5. The raw material unit of the cement clinker is limestone 900-1500 kg / t-clinker, meteorite 0-120 kg / t-clinker, clayey raw material 100-500 kg / t-clinker, iron raw material 0-80 kg / t-clinker, high K clay material of basic unit including _{2 O} 1.6 wt% or less 80 kg / t-clinker, a water-soluble hexavalent chromium reducing cement composition according to any one of claims 3-6 Production method.

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