JPH07149506A - Production of stabilized aqueous nitrite solution - Google Patents

Abstract

PURPOSE:To efficiently obtain a stabilized aqueous solution of nitrites causing no precipitation in the solution even when calcium nitrite and lithium nitrite are dissolved therein in high concentrations. CONSTITUTION:The stabilized aqueous solution of calcium nitrite and lithium nitrite is prepared by mixing an aqueous solution of lithium nitrite whose lithium hydroxide content is adjusted to less than 0.1wt.% with an aqueous solution of calcium nitrite.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a stable aqueous solution in which calcium nitrite and lithium nitrite are dissolved. This stable aqueous nitrite solution is a cement admixture,
It is used as a coating agent and concrete repair agent.

[0002]

2. Description of the Related Art Conventionally, an aqueous solution of calcium nitrite has been used as an anticorrosive agent for concrete steel containing a reinforcing steel.
It is used as a cement hardening accelerator, antifreeze for concrete, etc., and an aqueous solution of lithium nitrite is also used as an anticorrosion agent for steel materials in concrete containing a reinforcing steel material and an anti-alkali agent reaction agent in concrete.

Japanese Unexamined Patent Publication (Kokai) No. 50-96621 describes the use of nitrites such as sodium, potassium, calcium, magnesium and zinc alone or as a mixture as a rust preventive agent for concrete. Japanese Examined Patent Publication No. 5-41595 also describes the use of an aqueous solution of nitrous acid calcium salt, sodium salt, lithium salt or the like as a rust preventive agent for reinforced concrete.

[0004]

[Problems to be Solved by the Invention] Sodium salts, potassium salts, etc. of nitrous acid act on a certain kind of aggregate contained in concrete to cause a chemical reaction called alkali-aggregate reaction, and expand to concrete. May cause cracking due to. Aqueous solutions of nitrites such as magnesium and zinc have low saturation solubility, and the formation and decomposition of double salts may occur. Therefore, they cannot be generally used as high-concentration aqueous solutions.

On the other hand, an aqueous solution of calcium nitrite does not have such a problem and is generally used as an aqueous solution having a concentration of about 30% by weight or less. However, when used in combination with other admixtures for concrete, such as superplasticizers and AE agents, or when applied to the surface of concrete to prevent corrosion of reinforcing bars in concrete, the objective is sufficiently achieved. Such a concentration is not sufficient for practical use because it is not performed or requires a lot of work. In addition, calcium nitrite also has a poor ability to prevent alkaline aggregate reactions that occur in concrete.

[0006] Lithium nitrite not only has a high ability to prevent alkali-aggregate reaction that occurs in concrete, but also has a rust-preventing ability for reinforcing bars in concrete, and its aqueous solution is stable at high concentrations. It is often used as an aqueous solution of about 40% by weight. However, it does not have the ability to accelerate the hardening of concrete when added to it.

Although it is often preferable to add both calcium nitrite and lithium nitrite to concrete in combination, it is convenient to use them to prepare a highly concentrated aqueous solution of calcium nitrite and lithium nitrite as described above. When used by mixing with a high-concentration aqueous solution, precipitation occurs in the mixed solution, which is particularly difficult to put to practical use as an industrial product. The present invention provides a method for efficiently producing a stable aqueous solution of these nitrites, which does not cause precipitation in the aqueous solution even when calcium nitrite and lithium nitrite are dissolved in high concentration in water. It is what

[0008]

Means for Solving the Problems A method for producing a stable aqueous solution of calcium nitrite and lithium nitrite of the present invention comprises: an aqueous lithium nitrite solution having a lithium hydroxide content adjusted to 0.1% by weight or less; It is characterized by mixing with an aqueous calcium solution. The aqueous solution of calcium nitrite used in the present invention preferably has a calcium nitrite concentration of 5% by weight or more, and more preferably about 20 to 60% by weight. Such an aqueous solution of calcium nitrite,
It can be easily obtained as a commercial product. The aqueous solution of lithium nitrite preferably has a concentration of 5% by weight or more, and more preferably about 10 to 50% by weight. Normal commercial industrial product lithium nitrite aqueous solution,
Since lithium hydroxide is contained in an amount of about 0.1 to 0.3% by weight, when such an aqueous solution of lithium nitrite is used, the concentration of the contained lithium hydroxide is adjusted to 0.1% by weight or less to provide the present invention. be able to.

As a method for adjusting the amount of lithium hydroxide in the aqueous solution of lithium nitrite to 0.1% by weight or less,
It can be easily carried out by introducing an inorganic acid, an organic acid or the like into an aqueous solution of lithium nitrite with stirring. Examples of preferable acids include inorganic acids such as nitric acid, carbonic acid and sulfamic acid, and organic acids such as acetic acid, citric acid, gluconic acid and maleic acid.

Addition of these acids to the lithium nitrite aqueous solution is preferably carried out while avoiding local pH value of the lithium nitrite aqueous solution. A preferable method therefor is a method of introducing carbon dioxide gas into an aqueous solution of lithium nitrite under stirring. The acid may be added in an amount such that the amount of lithium hydroxide in the aqueous lithium nitrite solution is 0.1% by weight or less, and it is preferable to avoid adding it in excess as long as this amount of lithium hydroxide is achieved.

As described above, the amount of lithium hydroxide is 0.1% by weight.
Mixing of the lithium nitrite aqueous solution prepared below and the calcium nitrite aqueous solution can be easily carried out by ordinary stirring, and the mixing ratio of lithium nitrite and calcium nitrite may be arbitrary as desired. With this mixing,
Lithium nitrite and calcium nitrite are dissolved at a concentration of about 50% by weight, and a precipitation-free aqueous solution is obtained.

[0012]

[Function] A small amount of precipitate produced when an aqueous solution of calcium nitrite of about 30% by weight of a commercial industrial product and an aqueous solution of lithium nitrite of about 40% by weight of a commercial industrial product are mixed together is lithium hydroxide and calcium nitrite. It was found to be a double salt of. Further research showed that when the amount of lithium hydroxide in the produced lithium nitrite aqueous solution was suppressed to 0.1% by weight or less during the production of the lithium nitrite aqueous solution, the by-product lithium nitrate content increased, and Although the aqueous solution was poor in long-term stability, it was found that the lithium hydroxide content present at a content of 0.1% by weight or more made the lithium nitrite aqueous solution stable.

It is surprising that a stable aqueous solution can be obtained without precipitation by mixing the lithium nitrite aqueous solution in which the lithium hydroxide content is adjusted to 0.1% by weight or less with the calcium nitrite aqueous solution. . Presumably, in this solution, lithium nitrite is stabilized by calcium nitrite. As the acid added to reduce the lithium hydroxide content in the lithium nitrite aqueous solution, it is preferable to use a preferable one as much as possible. When added, this hydrochloric acid will be entrained in the concrete and cause corrosion of the reinforcing bars in the concrete. The addition of sulfuric acid causes precipitation of calcium sulfate in the liquid when the lithium nitrite aqueous solution containing this and the calcium nitrite aqueous solution are mixed. The organic acid added to reduce the lithium hydroxide content in the aqueous lithium nitrite solution to 0.1% by weight or less has little effect on the setting of the cement when it is entrained in the cement.

The acid added to reduce the lithium hydroxide content in the aqueous lithium nitrite solution is preferably added so as to cause a uniform addition in the liquid, otherwise brown NO _x gas is generated. It is easy to happen.

[0015]

Example The pH of the solution was adjusted to 8.5 by blowing carbon dioxide gas into a commercially available 40% by weight aqueous solution of lithium nitrite containing 0.3% by weight of lithium hydroxide while measuring the pH with a glass electrode. The amount of lithium hydroxide in this adjusted aqueous solution was 0.02% by weight. Next, this adjusted aqueous solution was evaporated and concentrated at 50 ° C. to obtain a 60 wt% aqueous solution of lithium nitrite.

Separately, a 30% by weight aqueous solution of calcium nitrite was similarly evaporated and concentrated to obtain calcium nitrite.
A 40% by weight aqueous solution was obtained. Then, of this lithium nitrite
A 60 wt% aqueous solution and a 40 wt% calcium nitrite aqueous solution were mixed in a ratio of 1: 3 to obtain a mixed aqueous solution containing 15 wt% lithium nitrite and 30 wt% calcium nitrite.

This mixed aqueous solution maintained a transparent solution state without precipitation even when stored at 0 ° C. On the other hand, for comparison, 27 parts by weight of a 40% by weight aqueous solution of commercially available lithium nitrite before adjustment and 73 parts by weight of a 30% by weight aqueous solution of commercially available calcium nitrite before adjustment were mixed. Precipitation occurred in the liquid. Further, for reference, each of the commercially available lithium nitrite aqueous solution concentrated to a concentration of 45% by weight and the commercially available calcium nitrite aqueous solution concentrated to a concentration of 45% by weight were stored at 0 ° C. When the test was conducted, it was confirmed that crystal precipitation occurred in all cases.

[0018]

EFFECTS OF THE INVENTION According to the present invention, a stable aqueous solution of high-concentration nitrite containing calcium nitrite and lithium nitrite can be simply and efficiently produced. Since this aqueous solution has a high concentration of nitrite but low concentrations of calcium and lithium, it has an effect on the setting of cement more than when calcium nitrite aqueous solution or lithium nitrite aqueous solution is used alone. Less is.

The aqueous solution may be used by adding various additives and auxiliaries depending on the purpose and use. For example, it can be used as a concrete admixture in combination with a fluidizing agent for concrete, an AE agent and the like. It is also useful as a rust preventive agent for internal reinforcing bars applied to the surface of reinforced concrete or the like. When using this highly concentrated aqueous solution, not only does it improve working efficiency,
Improved concrete, reinforced concrete, etc. can be obtained.

Claims (1)

[Claims] 1. A stable aqueous solution of lithium nitrite and calcium nitrite, which comprises mixing an aqueous solution of lithium nitrite adjusted to have a lithium hydroxide content of 0.1% by weight or less with an aqueous solution of calcium nitrite. Production method.