KR20020049815A - The method for manufacturing of alkali absorbent - Google Patents

Abstract

PURPOSE: Provided is an alkali absorbent which is used in treating cement for the construction works. The treated cement enhances the beautiful surface appearances of the structure, reduces the additional repair work, gives no getting-loose phenomena because the absorbing material is similar material as the substrate and has excellent absorbent effect due to the chemical bonding between alkali ion and the absorbent. CONSTITUTION: The preparation method includes the steps of blending calcium hydroxide 20 wt.%, furnace slag 30-50 wt.%, and fly ash 30-50 wt.% to prepare a slurry with a water/solid ratio of 10 to 15, wherein the mole ratio of CaO and SiO is 0.5 to 1.2; holding the temperature of the slurry at 60-80°C; stirring the obtained C-M¬3+-S-H with high speed mixer; rinsing the C-M¬3+-S-H two times with pure water; drying it at 60-80°C; and ball-milling agglomerated slurry. In the method, Al is substituted for C-S-H in an amount of 5 to 10 parts by weight.

Description

The method for manufacturing of alkali absorbent}

The present invention relates to a method for producing an alkali adsorbent, which will be described in detail, by effectively adsorbing alkali ions eluted from cement secondary products or concrete structures used as a building material, to prevent groundwater contamination due to a large amount of leakage as well as the appearance of the building surface. It relates to a method for producing an alkali adsorbent that prevents and improves durability.

The present invention relates to a technique for producing an alkali adsorbent for stably adsorbing and fixing alkali contained in various cement secondary products. More specifically, the present invention relates to a method for producing an alkaline adsorbent, which has a molar ratio such that a trivalent cation such as alumina is structurally substituted with a controlled calcium silicate hydrate (hereinafter, C-S-H).

In general, cement-based materials used as main materials for building finishing and cement secondary products contain high concentrations of alkalis. Most of them are water-soluble and precipitate water on the surface of the material through capillary pores and increase the surface aesthetics of products. It also acts as a factor that damages and further reduces the durability of the product and pollutes the surrounding environment.

Korean Patent Publication No. 1985-0000255 describes a technique for producing a CSH cured product using sodium silicate and blast furnace slag, but this method has a disadvantage in that it generates a high amount of CSH but contains a large amount of alkali in itself. Korean Laid-Open Patent Publication No. 95-18360 describes a technique related to an inorganic coating composition prepared by mixing weatherproof additives and the like with an inorganic binder, such as colloidal silica and colloidal alumina, treated with a silane compound. As a method of blocking the alkali elution passage by coating the surface using a material having a low or no content, it has a disadvantage of exfoliation phenomenon and expensive material due to the base material and other material composition, and has not obtained a great effect.

In order to solve the problems as described above, an object of the present invention is to provide a method for producing an inorganic-based absorbent material that significantly reduces the elution of alkali through effective adsorption.

²⁹ Si NMR analysis of the Fig. 1 CSH

Alkali adsorption mechanism of C- (A) -S-H

In order to achieve the above object, the present invention selects and adjusts the appropriate material so that the molar ratio of CaO and SiO ₂ , which are the main components of CSH, is 0.5 to 1.2, and the water / solid ratio is 10 to 15 to maintain a sufficient slurry state. Adjust to the state.

In preparing a CM ³⁺ -SH substituted with a trivalent cation, a suitable material is selected to add 5 to 20 parts by weight of Al ions to the CSH, and then the stirring is maintained. When the Al content is 5 parts by weight or less, the alkali ion adsorption effect is lowered. When the Al content is 20 parts by weight or more, a compound of CAHx is formed, thereby limiting the production of CASH.

Since CM ^{3 +} -SH by this method takes a long time to reach the chemical equilibrium, as a faster manufacturing method, 20 parts by weight of slaked lime is added uniformly in the composition of the preceding paragraph to produce CM ³⁺ -SH. It is necessary to raise the initial pH of to 12 or more. In addition, the slurry temperature is maintained at 60-80 ^° C. to facilitate the reaction. When the reaction temperature of the slurry is higher than 80 ^o C, there is a risk of decrease of specific surface area and lower alkali adsorption capacity due to CSH crystallization, and lower than 60 ^o C has a disadvantage of lowering reaction rate of CASH formation. The prepared CM ³⁺ -SH is forcibly stirred in a high speed rotary mixer to be washed twice in clean water to remove trace components that may be contained in industrial raw materials. The prepared CM ³⁺ -SH is filtered and dried to loosen the lightly coagulated particles by milling or the like. At this time, the drying temperature relates to a method for producing an inorganic absorbent material so as not to exceed 80 ^o C for the same reason.

Cement hydrate accounts for about 60% of the total hydrate upon complete hydration of the cement to the extent that it can be represented by C-S-H. C-S-H is a nanometer-sized material with high specific surface area, long-term stability against moisture and other environments, and is an important factor in determining the properties of cement. In particular, the high specific surface area is the main cause for the basic characteristics as a solidifying material, such as adsorption of heavy metal ions and radioactive materials in cement-based materials, lattice replacement, and the like. However, the alkali adsorption capacity of CSH is not very good. Alkali, which occupies about 1% of cement, is about 90% water-soluble, and most of it is not adsorbed or bonded to the hydrate, so that it is not stabilized and dissolved in the pore solution. Precipitates on the surface.

The reason that CSH, a cement hydrate, does not exhibit alkali adsorption performance is due to the high CaO / SiO ₂ value of CSH. That is, the average molar ratio of CSH in the cured body completely hydrated from cement is 1.8, and according to ²⁹ Si NMR analysis (FIG. 1), monomer (Q ¹ ) occupies most of its configuration and very small amount of dimer (Q ² ) exists. The alkali adsorption mechanism will be described based on Q ¹ and Q ² as follows (Fig. 2-a).

Structure of the CSH is makin made to form a long chain structure of a SiO ₄ appears as a repeated form of tetrahedron unit structures usually two paired SiO ₄ (Q ¹⁾ and one bridging SiO ₄ (Q ²⁾ tetrahedra in particular Q of the ^two-digit Due to the lack of positive charge, the alkali metal is adsorbed in this position in electrical balance. Therefore, for the adsorption of alkali ions in the CSH, the amount of dimer (Q ² ) must be increased, which means that the molar ratio of CSH, that is, CaO / SiO ₂ , should be controlled to a very low level. Therefore, in order to enhance the alkali ion adsorption effect of CSH, the value of CaO / SiO ₂ should be lowered to 1.2 or less at the current level (∼1.8), which is not obtained in the existing cement material system.

In order to maximize the alkali adsorption effect, it is not enough to reduce the molar ratio of C-S-H. In general, trivalent cations in cement, ie, Al, may be substituted and employed at Si sites in C-S-H. When the trivalent cation is substituted, the C-S-H structure causes one cation deficiency in the bonding structure to adsorb more alkali ions for balance of charge. (Figure 2-b). However, the reaction time required for complete hydration of cement and lattice employment of Al ions in CSH is long for several decades under normal conditions, i.e., low molar ratio use, and sufficient formation of CSH is difficult, as well as trivalent ions such as Al. It is also difficult to be easily employed in the lattice of CSH. Thus, new means for the solid solution of trivalent cations within the C-S-H structure are needed.

The present invention relates to a method for producing improved CSH through controlling the molar ratio of CaO / SiO _2, the effective solution control of Al ions in CSH, which is the most important technical element necessary for improving the intrinsic alkali adsorption performance of CSH.

In the present invention, as the CaO source, it is preferable to use slag lime and blast furnace slag as a by-product of the steel industry, and as an Si source, fly ash and silica fume in an amorphous form. As the trivalent cation, Al contained in slag and fly ash is used. In order to improve the reactivity of the powder of each raw material, it is preferable to use it by grinding so that it may be 3000 cm <^2> / g or more.

Lightly crushed CASH has a specific surface area of nanometer scale and is very fine, and when mixed with cement, it has the function of adsorbing alkali and environmental harmful ions eluted from the sphere as well as alkali of surface finish layer of cement secondary products. Due to the pore filling effect to achieve a compact structure, the durability enhancement effect is also improved.

The present invention will be described in more detail with reference to the following Examples.

Examples (1-4)

CASH was prepared according to the preparation method shown in Table 1 with respect to 100 parts by weight of the composition consisting of 20 parts by weight of lime, 30 to 50 parts by weight of blast furnace slag, and 30 to 50 parts by weight of fly ash having a small amount of unburned carbon. In addition, 10 parts by weight of Al (OH) ₃ with respect to 100 parts by weight of the composition consisting of 50 parts by weight of quicklime and 50 parts by weight of amorphous silica to prepare a CASH as shown in Table 1 by the preparation method shown above.

Comparative Example (1 to 3)

10 parts by weight of Al (OH) ₃ was added to 100 parts by weight of the composition consisting of 50 to 70 parts by weight of quicklime and 30 to 50 parts by weight of amorphous silica to prepare C- (A) -SH as shown in Table 1 by the preparation method shown above. Prepared.

Test Methods

1 g of C- (A) -SH prepared in Examples and Comparative Examples was dispersed in 20 ml of Na (K) OH solution having an initial concentration of 300 mM / l, left to stir for 3 days, filtered, and the alkali of the filtrate. The concentration of (Na, K) was measured and the degree of adsorption by C- (A) -SH was evaluated by the following equation. The results are shown in Tables 2 and 3.

Alkali concentration adsorbed in C- (A) -S-H (mM / g)

Rd (Distribution ratio) = -------------------------------------------- -

Alkali concentration remaining in solution (mM / l)

The higher the R _d coefficient, the higher the alkali adsorption effect of the prepared CASH, which means that the alkali in the solution is adsorbed and moved into the solid, ie, the structure inside the CASH.

Table 1.

division Slaked lime (% by weight) Blast furnace slag (% by weight) Amorphous silica Fly ash Al (OH) ₃ Example 1 20 30 - 50 - Example 2 20 50 - 30 - Example 3 50 - 50 - 10 Example 4 50 - 50 - 10 Comparative Example 1 50 - 50 - - Comparative Example 2 70 - 30 - - Comparative Example 3 70 30 10

Table 2.

division Na in C- (A) -S-H (mM / g) Na in solution (mM / l) R _d (ml / g) Example 1 3.46 0.13 27.2 Example 2 2.32 0.18 12.9 Example 3 3.08 0.15 20.5 Example 4 2.08 0.20 10.4 Comparative Example 1 1.18 0.24 4.91 Comparative Example 2 0.20 0.29 0.69 Comparative Example 3 0.98 0.25 3.92

Table 3.

division K in C- (A) -S-H (mM / g) K in solution (mM / l) R _d (ml / g) Example 1 3.26 0.14 23.3 Example 2 2.96 0.15 19.7 Example 3 3.52 0.12 29.3 Example 4 2.34 0.18 13.0 Comparative Example 1 1.04 0.25 4.16 Comparative Example 2 0.08 0.30 0.03 Comparative Example 3 0.80 0.26 3.08

The present invention as described above has the advantage of low cost and easy production. Cement secondary products treated with alkali adsorbent have the following advantages.

First, it improves the surface aesthetics of building structures or concrete structures. Second, the chemical bonding between the adsorbent and alkali ions is excellent in the adsorption effect. Third, additional repair processes such as building structures can be omitted. Fourth, the material configuration of the adsorbent itself is similar to that of the substrate used, thereby achieving integration without lifting phenomenon.

Claims (2)

In the method for producing an alkali adsorbent, water / solid by mixing 20 parts by weight of lime, 30 to 50 parts by weight of blast furnace slag, and 30 to 50 parts by weight of fly ash so that the molar ratio of CaO and SiO ₂ , which are the main components of CSH, is 0.5 to 1.2. After preparing the slurry in a ratio of 10 to 15, and maintaining the slurry temperature at 60-80 ^o C to prepare an alkali adsorbent, the prepared CM ³⁺ -SH was stirred in a high speed rotary mixer and washed twice in clean water. And after the drying process at 60-80 ^° C to remove the coagulated particles by using a ball milling method for producing an alkali adsorbent, characterized in that to prepare a powder form. The method of claim 1, wherein the Al ions are substituted by 5 to 10 parts by weight in C-S-H to maximize alkali adsorption effect.