KR20090054859A - Activation of blast furnace slag, cement and concrete using wasted na2so4 from desulfurization process - Google Patents

Abstract

Blast furnace slag using waste soda sulphate and an activating method for cement and concrete are provided to recycle the waste soda sulphate as an activating agent in order to supplement the properties of the cement. A method for activating blast furnace slag cement and concrete comprises the following steps of: preparing waste soda sulphate; and adding the waste soda sulphate to the blast furnace slag cement and concrete so as to show excellent intensity. The waste soda sulphate consists of 54-67% of sodium sulfate(Na2SO4), 8-14% of sulfur(S), 3-5% of sodium carbonate(Na2CO3), 3-10% of iron oxide(T.Fe) and 1.5-4% of metallic iron(M.Fe). The waste soda sulphate functions as an activating agent for concrete and cement.

Description

Activation of blast furnace slag, cement and concrete using wasted Na2SO4 from desulfurization process}

<Table 1> Chemical Composition of Abandoned Forage

<Table 2> Physical Characteristics of Reclaimed Slag

<Table 3> Chemical Composition of Blast Furnace Slag

<Table 4> Chemical Composition of Manganese Used in Examples

<Table 5> Mixing Ratios and Conditions

<Table 6> Hydration Rate of Slag

<Figure 1> Process of using the forget-me-not according to the present invention

<Figure 2> Carbide X-ray Diffraction Patterns According to Various Conditions in Adding Meshes

<Figure 3> Differential Thermal Analysis of Hydrates Having Activators

<Figure 4> Electron microscopy (SEM) photograph of the hydrate when using forget-me-not as an activator (addition of activator 7%)

<Figure 5> Amount of non-hydrated slag according to the amount of activator (activator added amount 3 · 5 · 7%)

<Figure 6> Amount of Unhydrated Slag According to the Type of Activator

<Figure 7> Cumulative heat depending on the amount of activator

<Figure 8> Heat release rate by type and amount of activator

<Figure 9> Compressive strength of AAS mortar with different amounts of forget-me-not

<Figure 10> Compressive strength of AAS mortar according to the replacement rate of OPC (activator: Na ₂ SO4)

The present invention is added to the production of blast furnace slag powder using cement by using the by-product waste (Na ₂ SO ₄ ) by-product waste containing a large amount of impurities from the desulfurization process to prevent air pollution when added to the slag or concrete manufacturing It is a method of activating cement to improve mechanical properties such as initial strength, and by using two low-cost by-products of the steelmaking process and using them as a raw material for activating agents such as cement.

In general, the steady development of cement and concrete materials aims to have higher strength and better durability, but the potential to significantly improve the properties of ordinary Portland cement in a universal manner is at its limit. On the other hand, with the rise of energy crisis and environmental problems, interest in the utilization of waste resources emitted as a series of process by-products such as smelting and steelmaking has increased, and research on the utilization of these waste resources as cement substitute materials has been actively conducted mainly for special purposes. have. Among them, slag is a by-product from the steel industry and is a useful resource that has been used in the construction and civil engineering sectors as slag cement, aggregate, roadbed, and other cement additives. In addition, blast furnace slag is a very useful resource to improve the concrete long-term strength, heat of low hydration and chemical durability. Used as a cement mixture, it reduces the generation of CO ₂ gas due to cement production and is a resource that can save finite resources.

Therefore, in the steel industry that produces slag, it is desirable to produce recycled slag with higher recyclability, and recycling should be actively promoted by improving utilization of the slag.

Since blast furnace slag is a latent hydraulic material, it is the most effective way to improve its hydration properties. Since slag shows low heat of hydration in the early stage of reaction, it is essential for the construction of large structures, improving the long-term strength of concrete and improving chemical durability. However, low initial heat of hydration means low initial strength on the one hand, which is the biggest problem in the utilization of slag. Mechanical activation using mechanochemistry and one of the solutions to this problem is the activation using alkali stimulants such as sodium hydroxide (NaOH), sodium carbonate (Na ₂ CO 3), sodium silicate (Na ₂ SiO 3).

In general, hydrolyzed slag proceeds very slowly with water, but exhibits hydration activity in alkaline atmosphere. In particular, when coexisting with strong alkalis, such as sodium hydroxide, sodium carbonate, sodium silicate, etc., the slag exhibits a rapid hydration reaction and can be utilized as a fast-hard binder. However, these are activators capable of activating, but have the disadvantage of being excessively expensive for practical application in the field.

On the other hand, as a by-product in the desulfurization process of removing sulfur dioxide (SO ₂ ) in the steel industry, the generation of manganese (Na ₂ SO ₄ ) containing a large amount of impurities is generated, reaching over 20,000 tons a year. Industrially, by-products are produced in large quantities, which are used in builders, which are additives added to increase the washing power of synthetic detergents, and in medicines such as pulp, glass, metal, dye, and diarrhea. At present, it is possible to refine the forget-me-not to obtain high-purity manure which is used industrially, but it is expensive. On the other hand, in the case of waste forget-me-not generated in the steelmaking process, there is a lot of impurities, and thus, it is impossible to find a suitable use place. In the present invention, as part of increasing the strength of the wood slag and cement or concrete using the alkaline agent, it is to select and use the discarded forage.

<Table 1> Chemical Composition of Waste Forage

Since the blast-furnace slag and its secondary products are cement materials with latent hydraulic properties, it is the most effective way to improve their hydration properties. Since slag shows low heat of hydration at the beginning of the reaction, it is essential for the construction of large structures, improving the long-term strength of concrete and improving chemical durability. However, low initial heat of hydration, on the one hand, means low initial strength, which is the biggest problem in the utilization of slag. As one of the solutions to this problem, the present invention intends to use an alkali stimulant for impurity forget-me-not generated in the desulfurization process coming out of the steelmaking process.

In general, hydrolyzed slag proceeds very slowly with water, but exhibits hydration activity in alkaline atmosphere. In particular, when coexisting with strong alkalis, such as sodium hydroxide, sodium silicate, and the like, the slag exhibits a rapid hydration reaction, so that the use as a fast-hard binder is high, but the price is high, and thus a lower-cost alkali activator is required. The present inventors have attempted to use a forget-me-not that is discarded by containing a large amount of impurities as a substitute. Therefore, the alkali activation method of the present invention is to improve the quality of the blast furnace slag to promote the amount of blast furnace slag having stable properties and to be used for concrete secondary products and other high value-added applications.

<Example 1>

As a sample, blast furnace slag was used as a by-product from the steel mill, and the chemical composition was shown in Table 2 and the chemical composition in Table 3 in comparison with the specifications shown in KS.

<Table 2> Physical Properties of Reclaimed Slag

<Table 3> Chemical Composition of Blast Furnace Reclaimed Slag

As shown in <Table 2>, it can be seen that it meets the type 1 slag specified in the KS standard. It was shown to meet the conditions having a basicity of 1.4 or higher specified in KS.

Exemplary stimulants of the examples are also the exact chemical composition of the used forage (Na ₂ SO ₄ ) is shown in Table 4.

<Table 3> Chemical Composition of Forages Used in Examples

Hydration and physical experiments were carried out by adding 1, 3, 5, and 7 wt.% Of each to the slag with Na ₂ O base as the mixing condition for Na ₂ SO ₄ , and the water / solid ratio (w / c) Was fixed at 0.5 to perform the experiment. Table 4 shows the mixing conditions of the alkali stimulant and the slag.

<Table 5> Mixing Ratios and Conditions

Paste hydration experiment water / solid (w / s) = 0.5 in the moisture into the respective stimulator 1, 3, 5, 7wt. % (Na 2 O base) was added to the slag after stirring for 3 minutes, and the plastic container 98 %, And stored in a humidity of 23 ± 2 ℃ temperature. The hydration time was 12 hours, 1, 3, 5, 7, 28 days, hydrated with acetone, dried for one day in a dryer (45 ℃) and stored in a vacuum desiccator.

X-ray diffraction analysis (XRD) was used to analyze CuKα, 30 mA, scanning speed of 4 degrees / min, and 20: 5 to 65 degrees.

Differential thermal analysis (DSC) was measured at 700 ° C. at a rate of 5 ° C./min. Al2O3 powder was used as a standard material, and the sample amount was 20 mg.

In the case of electron micrograph (SEM), the formation of hydrate was analyzed at a magnification of x5,000 using the hydrated stopped specimen.

For unreacted slag analysis, test reagents are salicylic acid, acetone, methanol, and samples hydrated and stopped under the respective conditions. First, 35 ml of acetone and 15 ml of methanol are mixed to prepare a mixed solution, and 2.5 g of salicylic acid and 0.5 g of sample are weighed into a beaker. The weighted mixture is stirred for 1 hour using a magnetic stirrer. At this time, the stirring temperature is at room temperature. The sample remaining after the filtration is heat-treated for 10 minutes to 850 ℃ in an electric furnace. The weight of the heat-treated sample is weighed. The% undissolved when tested using the various samples by the above method is% undissolved = undissolved part / sample-combustion loss x 100 (weight.%) .

Microhydration heat analysis was performed using a microhydration calorimeter (TTC type) to determine the rate of hydration of each sample. Water / solid (W / C = 0.5, the sample amount was 3g, measured up to 72 hours.

In the physical property test, the mortar physical property test was performed based on KSL 5105 for compressive strength. The water ratio was 55% by weight as a result of flow 110 ± 5 based on OPC, and was molded in 5 × 5 × 5 cm 3 square mold for 1 day curing and demolding for 3, 7, 28 days in moisture. The compressive strength according to age was measured. In the case of flows, it was carried out in the manner specified in KSL 5105.

In the case of addition of forget-me-not, needle-like ethrinzide hydrate is shown as the main hydrate, and it can be seen that as the hydration time increases, it grows even more. In the case of using (c) forage, the degree of hydration was almost similar when 3 and 5 wt% was added, and slightly higher reactivity was added when 7 wt.% was added. The hydration rates at 28 days were 36, 37 and 40% slag hydration, which was less than other stimulants. This is quantified by dissolving hydration products CSH, C ₄ AH ₁₃ and the like in the unreacted slag quantitative analysis. However, in the case of the sample using the forget-me-not, even if the AFt phase is present in the quantitative analysis using salicylic acid, only about 35% of the solubility seems to have not been accurate.

In the case of cumulative hydration analysis, (c) shows a very low cumulative hydration heat as a whole using forget-me-not as a stimulant. Usually substantially forget-me-not is used as a material used as a heat absorber. As shown in the figure, as the amount of addition increases, the hydration heat decreases significantly as the hydration time increases.

In Fig. 2, the hydration calorific curve of slag stimulated with Na ₂ SO ₄ is shown. As shown in the figure, the hydration curve is lower than that of other stimulants except for the first 10 hours. This is the material Na ₂ SO ₄ is used as an endothermic agent, as shown in the cumulative hydration heat graph in the previous section. Initially, a fast gel-like ethrinzite product begins to form an ethrinzite layer. Hydration is delayed temporarily by this layer, which in turn destroys the layer by the ethrinzite acicular crystal and surrounding Na ⁺ ions, resulting in continuous hydration products. In the figure, the first peak was confirmed, but the second peak was not seen.

As a result of hydration analysis of blast furnace slag using alkali stimulant, the main hydration product was produced by CSH phase by the forget-me-not. It was found that AFt (ettringite) and Al (OH) ₃ exist as hydration products when the forget-me-not is added (Fig. 1).

As a result of hydration fever characterization, the relatively low hydration fever was the case of using forget-me-not as a stimulant. However, there was some difficulty in explaining the influence on the strength as a result of the heat of hydration data <Fig. 2>, <Fig. 7>, and <Fig. 8>.

In order to determine the hydration rate of slag according to the degree of formation of hydration products, unreacted slag quantitative analysis was performed. As a result, the hydration rate of manganese slag was lower than that of sodium carbonate (Na ₂ CO ₃ ) <Fig. 4> and <Fig. 6>.

As a result of the compressive strength test, when the forget-me-not was used as a stimulant, the highest compressive strength was obtained when 7wt.% Was added. In the case of using a forget-me-not, the compressive strength was the highest. FIG. 9 The compressive strength was found to decrease as the slag substitution rate increased. The compressive strength of Na ₂ SO ₄ increased as the amount of stimulant added increased.

The present invention complements each other with only by-products used as an activator of slag for cement, which is another by-product, from the degassing process in the steelmaking process. It is a useful invention that can be used as a system.

Claims (2)

Blast furnace slag fine powder, cement production using it or concrete ready-mixed concrete, waste slag is added to activate the slag, cement, concrete to express strength The chemical composition of the waste Glauber's salt of claim 1 sodium sulfate _{(Na 2 SO 4) 54~67%} , sulfur (S) 8~14%, sodium carbonate _{(Na 2 CO 3) 3~5%} , train minutes (T.Fe) 3 A method of using a spent forage of ˜10% and metal iron (M.Fe) 1.5 to 4% as an activator.

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