JPS58176124A - Preparation of calcium hydroxide plate crystal - Google Patents

Abstract

PURPOSE:To prepare calcium hydroxide plate crystals having uniform particle size, by neutralizing calcium oxide in an aqueous solution containing a weak acid or its calcium salt. CONSTITUTION:Calcium oxide is neutralized in an aqueous solution containing a weak acid such as acetic acid, acrylic acid, formic acid, lactic acid, butyric acid, etc. or its calcium salt. The concentration of the weak acid or its calcium salt is about 0.1-10wt%, and the amount of calcium oxide is preferably about 1-30pts.wt. per 100pts.wt. of the aqueous solution. When the solution is allowed to stand at room temperature, a large plate crystal of calcium hydroxide can be obtained.

Description

[Detailed Description of the Invention] The invention relates to a method for producing plate-like hydroxide crystals with uniform particle size, and more specifically, a method for hydrating calcium oxide in an aqueous solution containing a weak acid or its calcium salt. This invention relates to a method for producing plate-shaped calcium hydroxide crystals.

Calcium hydroxide is known by the name of slaked lime, and in Japan it is a rich resource and is inexpensive.It is used for many purposes, such as as a farmland improvement agent, as a white wall material in buildings, and in flue gas as a pollution control measure. It is widely used as a sulfur dioxide gas recovery agent, an alkali source for collecting magnesium resources from seawater, and for chemical industry applications such as bleach, soda, and paper valves.

By the way, when calcium hydroxide is used for these uses, it is usually preferable to use calcium hydroxide having a particle size and shape depending on the use. For example, for agricultural fertilizers, thick particles with a slow reaction are desired, and for sulfur dioxide gas recovery agents, the reaction with dilute sulfur dioxide in the flue is instantaneous and complete. Therefore, colloidal calcium hydroxide in extremely fine particles is used.1
Plasticity, stability, water retention, and whiteness are required for plastering, and it is said that in order to obtain these properties, it is necessary to have a plate shape.

However, although it is necessary to control the shape and particle size of calcium hydroxide, it cannot be said that sufficient consideration has been given to this in the past.

This calcium hydroxide (Oak) is obtained by calcining limestone and hydrating it using a dry or wet method.The reaction process is as follows. .

Calcination 0aCO3-1→C! aO+002--- (1) Oa
O+H2O-→C! a(OH)2 ---(11) As can be seen from the micrograph in Figure 1, the calcium hydroxide powder produced in this way has particles in a consolidated state, and the particle size is extremely irregular. It is.

In view of these circumstances, the inventors did not simply crush and classify the particles of calcium hydroxide in the solidified state to make the particle size uniform, but instead developed a method to improve the shape and size of individual calcium hydroxide crystals. Development of a method to actively control scales Based on this knowledge, he was able to complete his invention.

That is, the present invention provides a plate characterized in that, in producing calcium hydroxide through a hydration reaction of calcium oxide, calcium oxide is hydrated in an aqueous solution containing a weak acid or its calcium salt. The present invention provides a method for producing calcium hydroxide crystals.

Oxidizing runium used as a raw material in the uninvented method can be obtained by thermally decomposing limestone or shells containing calcium carbonate as a main component, or by dehydrating calcium hydroxide. The temperature of this thermal decomposition and dehydration is 6
The range of 00 to 1400°C is preferable, especially 1000°C
The front and rear are preferred.

In addition, regarding the acid group of the weak acid or its calcium salt contained in the aqueous solution used for the hydration reaction in the method of the present invention,
There are no particular limitations as long as it is a weak acid, but organic acids such as acetic acid, acrylic acid, formic acid, lactic acid, and butyric acid are preferred.

The concentration of these weak acids and their calcium salts in an aqueous solution is preferably in the range of 0.1 to 1O f#4, particularly 0.1 to 1O f#4.
A weight range of 5 to 5 is preferred.

The amount of calcium oxide used in the uninvented method is suitably 1 to 30 parts by weight, more preferably 10 to 20 parts by weight, based on 100 parts by weight of the aqueous solution.

In the uninvented method, the crystal growth rate of calcium hydroxide produced by the hydration reaction of calcium oxide is fast, and plate-like crystals are produced shortly after the reaction starts, but if left standing for about one day, the second crystal will grow. As shown in the micrograph in the figure, a large number of crystal grains with a uniform plate shape are produced, with a particle size of about 311 nm in diameter per plate with a thickness of 0.3 μm. , this calcium hydroxide crystal becomes larger.The temperature while standing is 0~
A temperature in the range of 90°C is desirable, and standing at room temperature is particularly preferred. Calcium hydroxide thus obtained has large, plate-shaped particles, making it easy to filter and dehydrate, and since the particles themselves are single crystals, they are highly pure and do not contain impurities. The roller solution can be used repeatedly and is economical.

Calcium hydroxide obtained by the uninvented method not only satisfies the properties required as a material for plastering, but also
Its shape characteristics can also be used as a filler for composite materials.

Next, the non-invention will be explained in more detail with reference to examples.0 Example 1 1 Electric storage 16 Calcium oxide (quicklime) obtained by heating calcium carbonate at 1000°C for 1 hour in a calcium acetate aqueous solution Zoo cc 10 After stirring, it was sealed tightly and allowed to stand at room temperature for one day. When the calcium hydroxide powder obtained by filtering and drying was observed with a scanning electron microscope, it was found to be plate-shaped crystals. , thickness 0.3μm
The crystals had a uniform particle size with a diameter of 2.5 to 3 μm per plate.

Example 2 10 I of calcium oxide (quicklime) obtained by dehydrating calcium hydroxide at 1000° C. was added to 100 cc of a 5 weight aqueous solution of calcium acetate, stirred, and then allowed to stand at 90° C. for 1 day. Calcium hydroxide powder has a thickness of 0.
It was a thin plate-like crystal with a diameter of about 1.5 μm and one plate of 1 μm.

Example 3 1400°C in 100cc of acetic acid aqueous solution of 0.5 weight range
The calcium hydroxide powder obtained by stirring and adding calcium oxide 17.9% obtained by calcining, allowing it to stand at 0°C for 1 day, filtering and drying the powder, has a thickness of 0.3 μm per plate. The crystals had a uniform particle size of 3 to 3.5 μm in diameter.

Example 4 10 g of calcium oxide obtained by treating calcium hydroxide at 1000° C. was added to 100 cc of a 2-weight width calcium acrylate aqueous solution, stirred, and then allowed to stand at room temperature for 1 day. The calcium hydroxide powder obtained by filtration and drying was plate-shaped crystals with a diameter of about 2.5 μm and one plate with a thickness of 0.3 μm.

Example 5 Calcium hydroxide obtained by putting 10 I of calcium oxide into 100 cc of calcium formate aqueous solution of 1 weight range, stirring, and leaving it at room temperature for 2 days was plate-shaped with a thickness of 0.3
The powder was relatively uniform in particle size with a diameter of 2 μm per μm plate.

[Brief explanation of the drawing]

Figure 1 is a photograph of commercially available calcium hydroxide observed with a scanning electron microscope, and Figure 2 is a plate obtained by hydrating calcium oxide using a 1-weight width calcium acetate aqueous solution by an uninvented method. This is a photograph of calcium hydroxide. Note that the magnification is 10,000 times. Patent applicant: Makoto Ishizaka, Director of the Agency of Industrial Science and Technology - Designated agent: Naito, Director of the Osaka Institute of Industrial Science and Technology, Agency of Industrial Science and Technology

Claims (1)

[Claims] 1. Production of plate-shaped calcium hydroxide crystals characterized in that calcium oxide is hydrated in an aqueous solution containing a weak acid or its calcium salt when producing calcium hydroxide by a hydration reaction of calcium oxide. Method.