KR101605544B1 - Prepartion method of cement admixture for reducing hexavalent chromium - Google Patents

Abstract

The present invention relates to a process for producing a rosaceous material, comprising the steps of: a) molding a rosaceous raw material; b) a first heating activation step for removing organic impurities present in the raw material; c) adding an additive to adjust the chemical composition; d) a second heating activation step for chemical stabilization; And e) a particle size adjusting step for compatibility with cement, and a rosin-inorganic cement admixture prepared by the method.
The rosin-inorganic cement admixture according to the present invention can reduce the concentration of water-soluble / acid-soluble hexavalent chromium present in cement and cement clinker. Accordingly, the rosin-inorganic cement admixture according to the present invention can significantly reduce leaching concentration of hexavalent chrome from the cement concrete to the aquatic environment.

Description

TECHNICAL FIELD [0001] The present invention relates to a cement admixture,

The present invention relates to a cement admixture and a method for producing the same, and more particularly, to a method for reducing the concentration of hexavalent chromium present in cement concrete and inhibiting leaching in a hydrosphere environment.

Cement refers to a substance that bonds a substance with a substance in a broad sense, but generally refers to a binding curing agent for minerals for civil engineering and construction purposes. Among these, Portland cement is often called cement today. The main components of Portland cement are lime (calcium oxide, CaO), silica (silicon dioxide, SiO ₂ ), alumina (aluminum oxide, Al ₂ O ₃ ), iron oxide (Fe ₂ O ₃ )

Cement concrete is a typical construction material that is widely used in civil engineering and construction, and many studies have been carried out with a focus on performance improvement and quality control. In recent years, development of multi-faceted methods for development as materials meeting social issues of environmental pollution abatement and green growth is underway.

Alkali ions and heavy metal harmful substances leached from cement concrete cause ecological destruction, skin diseases, asthma and cancer. In addition, it has been reported that ecological problems occur in the construction of the suseo environment of cement concrete structures in domestic and foreign cases. Domestic and foreign regulations are undergoing various standardization processes.

Among them, the perception of the risk of hexavalent chromium present in cement is greatly increasing. When the oxidation number of potassium dichromate (K ₂ Cr ₂ O ₇ ) or sodium dichromate (Na ₂ Cr ₂ O ₇ ) is calculated, the compound having a value of +6 is referred to as hexavalent chromium (Cr ^{6 +} ). All chromium compounds are toxic and when exposed for long periods, trivalent chromium and hexavalent chromium show almost the same toxicity, and hexavalent chromium is generally more harmful. Hexavalent chromium is highly irritant and causes severe irritation to the mucous membranes of the respiratory tract, and when contacted through the skin, it irritates the mucous membranes of the skin and causes dermatitis such as edema and ulcers. In addition, hexavalent chromium is classified as a carcinogen and accumulates in the liver, kidney, and bone marrow, and is excreted through the kidneys and feces. If long time inhaling, the nasal septum with circular perforation in the septum cartilage and inflammation in the mucous membrane of the throat, and if it is concentrated to a large extent, will cause seizures such as abdominal pain. Chronic damage includes chronic catarrhal rhinitis, emphysema, pulmonary edema, chronic bronchial carcinoma, acute lung injury, bronchitis, and lung cancer.

In the case of hexavalent chromium present in cement, there is autonomous regulation of less than 20 ppm in Korea, however, concrete and reliable method of leaching and abatement of hexavalent chromium in cement is not presented.

As a method to solve this problem, a method has been proposed in which a concrete surface is coated with an adjusting agent or a ferrous sulfate hydrate (FeSO ₄ .nH ₂ O) is mixed with cement to produce concrete. However, in the case of the method of applying the concrete surface, the applied surface falls off with time and the usability is deteriorated. In the case of the chemical additive, the effect of reducing the hexavalent chromium is drastically reduced when exposed to air. In addition, a method of adding strontium compounds to cement has been proposed, but it is highly effective in reducing hexavalent chromium but is very useless due to the risk of radioactive materials.

In this connection, Korean Patent Laid-Open Publication No. 10-2010-0111055 discloses a method of controlling the content of CaO (particularly basicity (molar ratio of CaO / SiO ₂ )) in the raw material or adjusting the chemical composition CaO, SiO _2, while the Al ₂ O _3, Fe ₂ O ₃ content of the poles (Na ₂ O + K ₂ O) that is not changed (in particular, the molar ratio of _{((Na 2 O + K 2} O) / SO 3)) control There is proposed a method for manufacturing hexavalent chrome cement clinker characterized in that a raw material combination of cement clinker is designed and a raw material of the designed cement clinker is fired to produce a cement clinker. There is, however, a need for more effective 6-chromate mitigation methods.

The present invention has been developed to meet the above-mentioned development needs, and develops a technology for preventing the hexavalent chromium from being dissolved in water and leaching from the concrete surface by chemically insolubilizing the water-soluble hexavalent chromium present in the cement concrete .

Problems to be solved by the present invention are as follows.

First, we intend to develop a cement substitute that can maintain the strength, durability and stiffness of cement concrete above the performance of existing concrete.

Second, the concentration of water soluble hexavalent chromium present in the cement is to be reduced.

Third, the concentration of acid-soluble hexavalent chromium present in the cement is to be reduced.

Fourth, to prevent the hexavalent chromium present in the cement concrete from being dissolved and leached in the water environment.

Accordingly, in order to achieve the above-mentioned object, the present invention has been carried out intensively and as a result, a method for reducing hexavalent chromium in cement concrete has been developed through the activation of inorganic compounds. Specifically, the present invention provides a process for producing a rosaceous material, comprising the steps of: a) molding a rosaceous raw material; b) a first heating activation step for removing organic impurities present in the raw material; c) adding an additive to adjust the chemical composition; d) a second heating activation step for chemical stabilization; And e) a particle size adjusting step for compatibility with cement, and a rosin-inorganic cement admixture prepared by the method.

The rosin-inorganic cement admixture according to the present invention can reduce the concentration of water-soluble / acid-soluble hexavalent chromium present in cement and cement clinker. Accordingly, the rosin-inorganic cement admixture according to the present invention can significantly reduce leaching concentration of hexavalent chrome from the cement concrete to the aquatic environment.

1 is a schematic view showing an example of a production line and a production belt for the production of the rosin-inorganic cement admixture of the present invention.
FIG. 2 shows the appearance of the loose ball after the first heating activation step in the embodiment of the present invention.
FIG. 3 is a graph illustrating changes in color intensity of hexavalent chromium according to an embodiment of the present invention.
4 is a graph showing the relationship between the concentration of hexavalent chromium and the absorbance according to an embodiment of the present invention.
5 is a graph showing the concentrations of hexavalent chromium in the Loess and the ordinary portland cement (OPC) of the present invention according to the concentration of acid.
Fig. 6 shows an example of an experimental apparatus for measuring the leaching amount of hexavalent chromium.
FIG. 7 is a graph showing leaching concentrations of hexavalent chrome in the initial chromium admixture of the cement hardened material to which the Loess of the present invention and the ordinary Portland cement (OPC) are added.

Hereinafter, the present invention will be described in detail. However, it should be understood that the present invention may be embodied in many other specific forms without departing from the spirit or essential characteristics thereof.

The present invention relates to a Loess-inorganic cement admixture for reducing the concentration of hexavalent chromium contained in cement and cement concrete and for suppressing the leaching of hexavalent chromium when the concrete structure is exposed to aqua environment, .

The present invention is based on the principle that ettringite existing in cement is adsorbed by chemical reaction with hexavalent chromium and development of cement admixture is not a conventional cement manufacturing method but a core technical feature.

The rosin-inorganic cement admixture of the present invention uses Loess, or loess, as a base material, and the rosin generally contains organic impurities. In order to remove these organic impurities, additional inorganic substances (such as fly ash and silica fume) are added in consideration of suitability (strength and durability) when used in concrete after calcination.

Therefore, in the present invention, the "Loose-inorganic cement admixture" is used in the same sense as a loose-inorganic compound, a loose-inorganic cement substitute, a loose-inorganic cement substitute, and uses organic loam as a main material. Which can be used as a substitute for cement.

In one embodiment, the present invention is directed to a process for producing a rosaceous material, comprising: a) molding a rosaceous raw material; b) a first heating activation step for removing organic impurities present in the raw material; c) an additive adding step (also referred to as chemical composition adjusting step or chemical adjusting step) for adjusting the chemical composition; d) a second heating activation step for chemical stabilization; And e) a particle size adjusting step for compatibility with cement, and a rosin-inorganic cement admixture prepared by the method.

The use of the thus-prepared rosin-inorganic cement admixture can reduce ecosystem destruction and reduce the risk of disease induction by reducing the concentration of hexavalent chromium contained in the cement concrete.

In the present invention, a rosaceous raw material means a cement raw material containing a rosin as a main component.

In one embodiment, in step a), the raw material may be mixed with water and molded into a sphere (loose ball) having a size of 5 mm to 50 mm.

In one embodiment, the first heating activation of step b) may be carried out at a temperature of from 120 ° C to 1,200 ° C. It is preferred that the heat activation of step b) is carried out at a temperature of 300 ° C to 1,000 ° C. If the temperature is in the range of less than 120 캜, the organic substance may actually remain. If the temperature exceeds 1,200 캜, additional heat may be applied in the inorganic state, which may deform the surface due to unnecessary combustion. The temperature can be applied through a method of setting the heating plate (heating pad) to the above temperature range.

Conditions other than the temperature at this stage may include heating (activation) time, mixing conditions, and the like. The heating time depends on the removal condition of the organic impurities, and the time can be adjusted according to the heating temperature. For example, at 1000 ° C, it is heated to about 1 hour, while at 300 ° C it is most suitable for heating for about 5 hours. The heating time is also changed depending on the grain size of the rocess can do.

In a preferred embodiment, after the maximum heating temperature of the first heating activation step, the mineralization state of the reactor can be determined by setting a thermal (cooling) time. For example, a heat-up time of 5 hours after the maximum heating temperature of the first heating activation step can be set. Here, the direct heat (cooling) means until the room temperature is reached. This is to check the mineralization state of the reactor. If the mineralization state is sufficiently reached, the second heating activation step is a kind of confirmation work, and if the organic impurities remain, the second heating activation is performed.

In one embodiment, the additive of step c) is selected from the group consisting of fly ash, blast furnace slag fine powder, silica hume and aluminum oxide (Al ₂ O ₃ ) powder. Or more.

The addition amount of these additives is determined according to the characteristics of each of the additives within a range not deviating from the properties of the present invention. For example, in consideration of harmony with concrete properties, fly ash is preferably within 30% of the total weight of the total rosin-inorganic cement admixture, and silica fume is preferably within 5%. If the fly ash content exceeds 30%, the degree of hydration may be decreased to lower the concrete strength. In case of silica fume, when SiO ₂ , the main component of silica fume, exists in the cement at 5% or more, There is a risk for this and it is necessary to limit the amount.

In one embodiment, the additive of step c) may be a powder of one or more alkaline compounds selected from the group consisting of potassium hydroxide (KOH), sodium hydroxide (NaOH) and calcium hydroxide (Ca (OH) ₂ ).

In one embodiment, the powder of the alkaline compound may be added in an amount of 0.1% to 1.0% based on the weight of the rosin-inorganic cement admixture.

In one embodiment, the heating time of the second heating activation step of step d) may be 1/3 to 1/2 of the heating time of the first heating activation step of step b).

As described above, the second heating activation step is a kind of verification step, which is performed at the same temperature as the first heating activation step, and the period may be limited to 1/3 to 1/2. It is also possible to set a different temperature range from the first heating activation step, in which case the heating time may also vary. For example, if the substrate is heated at 500 ° C for 3 hours in the first heating activation step and then heated to 800 ° C in the second heating activation step, the heating time is preferably within 1 hour.

In one embodiment, in step e), the particle size (degree of powder) can be adjusted in the range of from 2,000 cm ² / g to 5,000 cm ² / g.

In one embodiment, the ros-inorganic cement admixture comprises from 35% to 45% silicon dioxide (SiO ₂ ), from 25% to 40% aluminum oxide (Al ₂ O ₃ ) based on the weight of the rosin- , 3% to 8% iron oxide (Fe ₂ O ₃ ), and 1% or less calcium oxide (CaO). Furthermore, loess-inorganic cement admixture from 40% to 43% of silicon dioxide (SiO _2), 35% to 39% of aluminum oxide _{(Al 2 O 3), 3} % to 8% of iron oxide (Fe ₂ O _3), and It is preferable to contain 1% or less of calcium oxide (CaO).

The content of such an oxide sets the optimum range for limiting the amount of ettringite produced. The adsorption of hexavalent chromium in the flux-based inorganic matter is carried out through the use of ettringite. When the quantity is not produced, that is, when the ettringite is excessively generated, the intumescent ettringite is hydrated Internal cracks may occur due to internal stress in the hydrated body itself. On the other hand, if the amount of ettringite is too small, the adsorption amount of hexavalent chromium may decrease.

The present invention will be described in more detail with reference to the following examples. However, the following examples are for the purpose of illustrating the present invention and are not intended to limit the scope of the present invention.

[ Example ]

loess - Inorganic  cement Mixed  Produce

Fig. 1 is a schematic view of a unified production belt for the production of the rosin-inorganic cement admixture of the present invention. As shown in Fig. 1, an appropriate amount of water was supplied from an intake valve according to the absorption rate of the initial rosaceous raw material and mixed. Then, when the production belt is put into the production belt, it is heated by a loose ball of a certain size by using a cutting machine (molding frame) installed at the entrance of the belt. The primary heating and activation periods lasted until the moisture present in the rosaceous material had evaporated to dryness.

After reaching a sufficient drying state, the cross-section of the loose ball was cut off as shown in Fig. 2 to confirm the dry state and conduct a primary chemical composition investigation. The chemical composition included 35 to 45% of SiO ₂ , 25 to 40% of Al ₂ O ₃ , 3 to 8% of Fe ₂ O ₃ and 1% of CaO. Other chemical compositions included 40% to 43% SiO ₂ , 35% to 39% Al ₂ O ₃ , 3% to 8% Fe ₂ O _3, and 1% or less CaO.

The chemical composition was adjusted by using fly ash, blast furnace slag, silica fume and aluminum oxide powder. In addition, in the chemical composition adjustment step, the compatibility with cement concrete was improved by adding 0.1% to 1.0% of alkali-based cement admixture to be produced with alkaline additives such as KOH, NaOH and Ca (OH) ₂ .

After the chemical composition adjustment step, additional heating activation steps are carried out to stabilize the cement-inorganic cement admixture, and then grinding is carried out in the range of 2000 cm ² / g to 5000 cm ² / g for compatibility with cement, Cement admixture.

Concentration measurement of hexavalent chromium

Experiments were conducted to demonstrate that the concentration of hexavalent chromium in the cement and cement concrete was reduced by the above-prepared rosin-inorganic cement admixture.

Experimental Example  One  (Water soluble / Acid availability  Measurement of hexavalent chromium concentration)

The concentration of water - soluble, acid - soluble hexavalent chromium present in the mineral - cement admixture and the ordinary Portland cement (OPC) was measured by spectrophotometric method.

The hexavalent chromium measurement range of the spectrophotometer was determined using a standard solution. Specifically, 1.414 g of potassium dichromate (K ₂ Cr ₂ O ₇ ) was weighed and dissolved in 1,000 ml of distilled water to prepare a 50 mg / ml chromium solution. Then, 10 ml of a chromium solution of 50 mg / Ml to prepare a 5 CCr / ml standard solution. 0 to 40 ml of a chromium standard solution of 5 CCr / ml was gradually taken in a 50 ml volumetric flask, and 0.6 ml of sulfuric acid (1: 1) was added thereto, followed by shaking, followed by cooling. Here di phenylcarbamoyl azide solution _{(C 6 H 5 NHNH) 2} CO) into a 1 ㎖ shaken immediately filled with water to volume, and mix.

As shown in FIG. 3, the prepared standard solution has a pink color depending on the concentration of hexavalent chromium and a darker color with a higher concentration.

Using the relationship between the concentration of hexavalent chromium and the absorbance at 540 nm, which is the intrinsic wavelength of hexavalent chromium, the concentration of hexavalent chromium was defined as shown in Fig.

The rosin-inorganic cement admixture of the present invention and the ordinary portland cement were dried in a drying furnace at 101 ± 2 ° C. for 24 hours before measurement of hexavalent chromium to remove unnecessary moisture. Samples were weighed in 5 g portions and mixed with 100 ml of acid solution in which stepwise mixing of distilled water and 0 ml to 1 ml of hydrochloric acid was carried out and the mixture was stirred for 10 minutes. Immediately after the completion of the stirring, the mixture was filtered through a filter paper, and 25 ml of the filtrate was taken in a 50 ml measuring flask. 0.6 ml of sulfuric acid (1: 1) was added thereto, followed by cooling at room temperature. 1 ml of diphenylcarbazide solution was added and shaken. Water was added to the top line, and the absorbance at 540 nm was measured using a spectrophotometer to calculate the concentration of hexavalent chromium.

As a result, as shown in FIG. 5, it was confirmed that the concentration of hexavalent chromium in the ordinary portland cement (OPC) increased by 200 ppm or more depending on the acid concentration, but the loess-inorganic cement admixture (Loess) Respectively. That is, it was confirmed that the content of hexavalent chromium was extremely low in the rosin-inorganic cement admixture of the present invention.

Experimental Example  2  (Measurement of water soluble hexavalent chromium leached from concrete)

Experiments on hexavalent chromium leaching in Suseo environment were carried out. The concentration of water soluble hexavalent chromium leached from the concrete prepared from the above-prepared rosin-inorganic cement admixture was measured by spectrophotometric method.

(50 × 50 × 50 mm) with a water - cement ratio of 0.4 was used to evaluate the leaching ability of heavy metal leaching agent. The loess of the present invention, which is a heavy metal leaching reducing agent, was substituted with 20% of cement, and chromium (0, 250, 500, 750, 1000 mg / kg) per binder unit weight was prepared by using potassium dichromate And further mixed. After 24 hours of production, the film was demolded, sealed with a polystyrene film, and cured for 28 days. As shown in FIG. 6, a cell was fabricated and the specimen was immersed in 800 ml of distilled water. 25 ml of the leaching solution was placed in a 50 ml volumetric flask, and 0.6 ml of sulfuric acid (1: 1) was added thereto, followed by cooling at room temperature. 1.0 ml of diphenylcarbazide solution was added, and the mixture was shaken. Water was added to the line, and the absorbance at 540 nm was measured using a spectrophotometer to measure the concentration of the water-soluble hexavalent chromium.

As a result, as shown in FIG. 7, the amount of hexavalent chromium leached from the cement mortar was about 1.14 × 10 ^-3 ppm to 1.72 × 10 ^-3 ppm, which was about 11.57 mg / m ^{3 of the} cement concrete volume . On the contrary, the concentration of hexavalent chromium in the case of the cement hardener prepared by mixing the cement admixture of the present invention with the cement of the present invention was lower than that of the cement admixture of the present invention, It can be confirmed that the leaching concentration of chromium is remarkably decreased. Accordingly, it was confirmed that the rosin-inorganic cement admixture of the present invention reduces the concentration of hexavalent chromium present in the cement, and significantly reduces the amount of leaching in aquaculture environment.

Claims (12)

a) molding a rosaceous raw material;
b) a first heating activation step for removing organic impurities present in the raw material;
c) adding an additive to adjust the chemical composition;
d) a second heating activation step for chemical stabilization; And
e) a method for producing a Loess-inorganic cement admixture comprising a particle size adjustment step for compatibility with cement,
Wherein the additive of step c) is at least one inorganic admixture selected from the group consisting of fly ash, blast furnace slag fine powder, silica hume and aluminum oxide (Al2O3) powder; And a powder of at least one alkaline compound selected from the group consisting of potassium hydroxide (KOH), sodium hydroxide (NaOH) and calcium hydroxide (Ca (OH) ₂ ). The method according to claim 1,
A method for producing a rosin-inorganic cement admixture, characterized in that in step (a), the raw material is mixed with water to form a sphere having a size of 5 mm to 50 mm. The method according to claim 1,
characterized in that the heat activation of step b) is carried out at a temperature of from 120 ° C to 1,200 ° C. The method of claim 3,
characterized in that the heat activation of step b) is carried out at a temperature of 300 ° C to 1,000 ° C. delete delete The method according to claim 1,
Inorganic cement admixture characterized in that the powder of the alkaline compound is added in an amount of 0.1% to 1.0% based on the weight of the rosin-inorganic cement admixture. The method according to claim 1,
wherein the heating time of the second heating activation step of step d) is 1/3 to 1/2 of the heating time of the first heating activation step of step b). The method according to claim 1,
in step (e), the particle size is adjusted in the range of 2,000 cm ² / g to 5,000 cm ² / g. The method according to claim 1,
Loess-inorganic cement, 35% to 45%, by weight of the admixture of silicon dioxide (SiO _2), 25% to 40% of aluminum oxide (Al ₂ O _3), a 3% to 8% Iron oxide (Fe ₂ O ₃ ) And 1% or less of calcium oxide (CaO), based on the total weight of the cement admixture. 11. The method of claim 10,
(SiO ₂ ), 35 to 39% of aluminum oxide (Al ₂ O ₃ ), 3 to 8% of iron oxide (Fe ₂ O ₃ ), based on the weight of the cement- ) And 1% or less of calcium oxide (CaO), based on the total weight of the cement admixture. A rosin-inorganic cement admixture produced according to any one of claims 1 to 4 and 7 to 11.

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