JP3508185B2 - Method for producing stable aqueous nitrite solution - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a stable aqueous solution in which calcium nitrite and lithium nitrite are dissolved. This stable nitrite aqueous solution is used as an admixture for cement,
It is used as a coating agent and concrete repair agent. [0002] Conventionally, an aqueous solution of calcium nitrite has been used as a rust preventive for concrete steel containing a reinforcing steel.
It is used as a cement hardening accelerator, a concrete antifreeze, and the like, and an aqueous solution of lithium nitrite is also used as a rust preventive for concrete steel containing a reinforcing steel material, an alkali aggregate reaction preventive in concrete, and the like. [0003] Japanese Patent Application Laid-Open No. 50-96621 describes that a nitrite such as sodium, potassium, calcium, magnesium, zinc or the like, alone or in combination, is used as a rust preventive for concrete. Japanese Patent Publication No. 5-41595 discloses that an aqueous solution of a calcium salt, a sodium salt or a lithium salt of nitrite is used as a rust preventive for reinforced concrete. [0004] The sodium and potassium salts of nitrite act on a certain kind of aggregate contained in concrete to cause a chemical reaction called an alkali-aggregate reaction. May cause cracking of concrete due to expansion. Aqueous solutions of nitrites such as magnesium and zinc have low saturation solubility, and may cause formation and decomposition of double salts, so that 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, the purpose is sufficiently achieved when used in combination with other admixtures for concrete, for example, a fluidizing agent, an AE agent, etc., or when applied to the concrete surface to prevent rust of reinforcing steel in concrete. Such a concentration is not practically sufficient, for example, it is not performed or requires a large number of operations. In addition, calcium nitrite has poor ability to prevent alkali-aggregate reactions that occur in concrete. [0006] Lithium nitrite not only has a high ability to prevent alkali-aggregate reaction occurring in concrete, but also has a rust-preventing ability for reinforcing steel in concrete, and its aqueous solution is stable at a high concentration. It is often used as an aqueous solution of about 40% by weight. However, when added to concrete, it does not have the ability to promote concrete hardening. Although it is often preferable to add calcium nitrite and lithium nitrite together to concrete, it is often convenient to use the same in the above-mentioned manner, by using a high-concentration aqueous solution of calcium nitrite and lithium nitrite as described above. When mixed with a high-concentration aqueous solution for use, a precipitate is formed in the mixed solution, and it is particularly difficult to practically use it as an industrial product. The present invention provides a method for efficiently producing a stable aqueous solution of these nitrites such that even if calcium nitrite and lithium nitrite are dissolved at a high concentration in water, no precipitation occurs in the aqueous solution. It is assumed that. [0008] The method for producing a stable aqueous solution of calcium nitrite and lithium nitrite according to the present invention comprises an aqueous solution of lithium nitrite having a lithium hydroxide content adjusted to 0.1% by weight or less. And an aqueous solution of calcium nitrite. The aqueous solution of calcium nitrite used in the present invention preferably has a calcium nitrite concentration of 5% by weight or more, particularly preferably about 20 to 60% by weight. Such an aqueous solution of calcium nitrite is
It can be easily obtained as a commercial industrial product. The aqueous solution of lithium nitrite preferably has a concentration of 5% by weight or more, particularly preferably about 10 to 50% by weight. The aqueous solution of lithium nitrite, which is an ordinary commercial industrial product, contains:
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. A method for adjusting the amount of lithium hydroxide in an aqueous solution of lithium nitrite to 0.1% by weight or less includes:
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 preferred 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. The addition of these acids to the aqueous solution of lithium nitrite is preferably performed while avoiding the pH value of the aqueous solution of lithium nitrite from becoming locally acidic. As a preferable method, a method of introducing carbon dioxide gas into an aqueous solution of lithium nitrite under stirring is mentioned. The amount of the acid to be added may be such that the amount of lithium hydroxide in the aqueous solution of lithium nitrite is 0.1% by weight or less, and it is preferable to avoid excessive addition as long as the amount of lithium hydroxide is achieved. As described above, the amount of lithium hydroxide is 0.1% by weight.
The mixing of the aqueous solution of lithium nitrite and the aqueous solution of calcium nitrite adjusted as described below can be easily performed 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 with a content of as high as about 50% by weight, and a precipitate-free aqueous solution is obtained. A small amount of precipitate formed when an approximately 30% by weight aqueous solution of calcium nitrite of a commercial industrial product is mixed with an approximately 40% by weight aqueous solution of lithium nitrite of a commercially available industrial product is formed by lithium hydroxide and lithium hydroxide. It was found to be a double salt of calcium nitrite. Further studies have shown that, when producing an aqueous solution of lithium nitrite, if the amount of lithium hydroxide in the produced aqueous solution of lithium nitrite is suppressed to 0.1% by weight or less, the by-product lithium nitrate content increases in the solution, The aqueous solution was poor in long-term stability, but it was found that the lithium hydroxide component present at a content of 0.1% by weight or more stabilized the aqueous solution of lithium nitrite. It is surprising that when an aqueous solution of lithium nitrite whose lithium hydroxide content is adjusted to 0.1% by weight or less and an aqueous solution of calcium nitrite are mixed, a stable aqueous solution can be obtained without precipitation. . Possibly, in this solution, lithium nitrite was stabilized by calcium nitrite. As the acid added to reduce the lithium hydroxide content in the aqueous solution of lithium nitrite, it is preferable to use a preferable acid.For example, when hydrochloric acid is used, an aqueous solution of nitrite containing the same is used for concrete. When added, the hydrochloric acid is entrained in the concrete and causes corrosion of reinforcing steel in the concrete. Addition of sulfuric acid causes precipitation of calcium sulfate in the solution when the aqueous solution containing lithium nitrite and the aqueous solution of calcium nitrite are mixed. The organic acid added to reduce the content of lithium hydroxide in the aqueous solution of lithium nitrite to 0.1% by weight or less has almost no effect on the setting of the cement even if it is accompanied by the cement. [0014] nitrite acid added to reduce the lithium hydroxide content of lithium nitrate in the aqueous solution is preferably added as a uniform addition in liquid occurs, is otherwise the occurrence of brown of the NO _X gas Easy to happen. EXAMPLE A carbon dioxide gas was blown 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 to adjust the pH of the solution to 8.5. did. The amount of lithium hydroxide in the adjusted aqueous solution was 0.02% by weight. Next, this adjusted aqueous solution was evaporated and concentrated at 50 ° C. to obtain a 60% by weight aqueous solution of lithium nitrite. Separately, a 30% by weight aqueous solution of calcium nitrite is similarly concentrated by evaporation to obtain a calcium nitrite solution.
A 40% by weight aqueous solution was obtained. Then, the lithium nitrite
A 60% by weight aqueous solution and a 40% by weight aqueous solution of calcium nitrite were mixed at a ratio of 1: 3 to obtain a mixed aqueous solution containing 15% by weight of lithium nitrite and 30% by weight of calcium nitrite. This mixed aqueous solution maintained a clear solution state without precipitation even after storage 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 the above adjustment and 73 parts by weight of a 30% by weight aqueous solution of a commercially available calcium nitrite before the above adjustment were mixed. A precipitate formed in the liquid. For reference, the commercially available lithium nitrite aqueous solution concentrated to 45% by weight and the commercially available calcium nitrite aqueous solution concentrated to 45% by weight were stored at 0 ° C for reference. As a result of the tests, it was confirmed that the precipitation of the crystal occurred in each case. According to the present invention, a stable aqueous solution of high-concentration nitrite containing calcium nitrite and lithium nitrite can be easily and efficiently produced. Since this aqueous solution has a high concentration of nitrite and a low concentration of each of the calcium and lithium components, the influence on the cement setting of the cement is higher than when the aqueous solution of calcium nitrite alone or the aqueous solution of lithium nitrite alone is used. Less is. This aqueous solution may be used after adding various additives and auxiliaries according to the purpose and use. For example, it can be used as a concrete admixture in combination with a concrete fluidizer, an AE agent, and the like. Further, it is also useful as a rust preventive agent for internal rebar applied to the surface of reinforced concrete or the like. Especially when using this highly concentrated aqueous solution, it not only improves the working efficiency, but also
Improved concrete, reinforced concrete, etc. can be obtained.

──────────────────────────────────────────────────の Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C01B 21/50 CA (STN)

Claims (1)

(57) [Claim 1] Lithium nitrite characterized by mixing an aqueous solution of lithium nitrite adjusted to a content of lithium hydroxide of 0.1% by weight or less with an aqueous solution of calcium nitrite. For producing a stable aqueous solution of calcium nitrite and calcium nitrite.