JPS60171222A - Manufacture of zinc oxide by wet process - Google Patents

Abstract

PURPOSE:To manufacture high purity zinc oxide by simple operation at a low cost by neutralizing an alkaline soln. of a specified pH contg. a zinc salt with an acid so that the soln. is adjusted to a specified pH. CONSTITUTION:Sodium hydroxide is added to an aqueous soln. of a zinc salt such as zinc sulfate to prepare an alkaline soln. of >=12.5pH, e.g., 13-14pH. This alkaline soln. is neutralized with sulfuric acid so that the soln. is adjusted to 12.5-8pH, e.g., 10-8pH. By the neutralization, a finely divided precipitate of zinc oxide is directly formed. Thus, zinc oxide is obtd. in >=about 99.9% yield.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing zinc oxide, in which zinc oxide is directly produced by adding an acid to an alkaline solution containing zincate.

The conventional methods for producing zinc oxide are dry method and wet method. There are two earth classes. A typical dry method is the fume method, in which gold and zinc are turned into scum at high temperatures, and then oxidized with air. This method uses metallic zinc as the raw material,
It is more expensive than metal zinc because it requires a large amount of heat engineering due to high-temperature heating. As a wet method, Ii1
i An aqueous solution containing a lead salt is neutralized and recovered as basic zinc carbonate, which is thermally decomposed at high temperature to produce zinc oxide.

Another method is to neutralize an aqueous solution containing zinc salts, accurately control temperature and pH, and hold it for a long time to produce zinc oxide, but these methods require high temperature heating or reaction temperature. However, it has drawbacks such as requiring control of pH value and long reaction time.

The present invention eliminates the drawbacks of these conventional production methods and provides an economically inexpensive method of supplying zinc oxide with simple operations.

That is, the present invention provides a pH/. This is a method for producing zinc oxide by a wet method, which is characterized in that zinc oxide is directly produced by adding an acid to an alkaline solution of 2 J or more and neutralizing it to pH t 2.3-pH g.

Next, the method for producing zinc oxide of the present invention will be described in the case where zinc sulfate is used.

When caustic soda is added to an aqueous solution of zinc sulfate, translucent zinc hydroxide precipitates, but when an excess of caustic soda is added, the zinc hydroxide completely redissolves and forms sodium zincate. The pH at this time is 13-/4'. When sulfuric acid is added to this solution, a fine white precipitate is formed, and the reaction is completed at a pH of 0 to pH t O, yielding a white precipitate with excellent sedimentation properties and good flowability. X-ray diffraction analysis of this white precipitate confirmed that it was zinc oxide. Subsequently, when zinc oxide was recovered in the same manner using solutions with varying zinc concentrations, zinc oxide was obtained with a yield of 99.9% or more.

When neutralizing a solution with a high auxiliary complex concentration, if handling such as stirring is difficult due to the zinc hydroxide produced, the zinc-11-containing solution may be dropped into the alkaline solution.

According to the method of the present invention, zinc oxide can be easily recovered from high to low zinc concentrations with high yield, and zinc oxide can be easily produced simply by adding acid to an alkaline solution containing curvedate. It can be applied to zinc dissolved in an alkaline solution regardless of the type of alkali. What should be particularly regulated in the method of the present invention is the pH at the end of the zinc oxide production reaction.If the pH value is high (pH 72, S or higher), the reaction will not be completed completely, and the produced zinc oxide will have a tendency to settle. The upper limit should be set to pH/2. ! ; Toshi, p
If the H value is low, the generated zinc oxide will be redissolved, so the lower limit is set to pHg, 0.

Although there is no particular restriction on temperature, it is preferable that the reaction for producing zinc oxide be performed at room temperature or higher, and it is also possible to heat the zinc oxide as the higher the temperature, the better the reactivity.

When carrying out the method of the present invention using a solution containing a zinc salt,
It is desirable to carry out the neutralization reaction promptly. If neutralization is carried out gradually, the excess alkali will produce insoluble substances, which is inconvenient and may consume more alkali than necessary. In order to prevent these disadvantages, especially when the elongation lead concentration is high, it is preferable to drop the salivary lead salt-containing solution into the alkaline solution.

The details of the zinc oxide production reaction are unknown, but it is thought to be a hydrolysis reaction of zincate dissolved in excess alkali. However, this reaction is not observed in other metals that dissolve in excess alkali, and is a unique reaction limited to zinc.

The present invention will be explained below based on Examples and Comparative Examples.

Example 1 Zinc sulfate containing 0, 9/l of zinc was neutralized with caustic soda, a bath solution dissolved in sulfuric acid, to pH/J, s~147.
If the value is 0, the lead hydroxide produced during neutralization will be completely redissolved. When sulfuric acid is added to this solution, a white precipitate will form from around pH 73, and the reaction will almost complete at pH 9.3. Zinc oxide with good oxidation yield was 1 p, lead yield was qq, 9% or more.

Example - 5g/e! A bath solution in which zinc chloride salt containing 1+r-lead was dissolved in hydrochloric acid was neutralized with caustic soda to give pI-I / , ? J
When the concentration is ~/Da, O, lead hydroxide produced during neutralization is completely dissolved. When hydrochloric acid was added to this solution, a white precipitate was formed at around pH/J, and the reaction was almost completed at pH 9J, producing zinc oxide with good sedimentation separation properties.

The yield of zinc oxide was 99.9% or more.

Example 3 / o o A solution of zinc chloride dissolved in sulfuric acid containing 13 g/g of zinc was dropped into a caustic soda solution, and the dropping was stopped when a white precipitate began to form.

When hydrochloric acid was added to this solution to adjust the pH to 9.3-/0.0, zinc oxide with good sedimentation and separation properties was obtained. The yield of zinc oxide was qq, 9% or more.

Example q! When a solution of lead dissolved in hydrochloric acid in a caustic soda solution is added to + containing 0 &/l of zinc, and after the hydroxide formed is completely dissolved, it is treated with sulfuric acid, the pH becomes 8,
0-9. Zinc oxide with good sedimentation separation property was obtained at θ. The yield of zinc oxide was 9% or more.

Comparative Example/Example - When sulfuric acid is added to the redissolved sodium zincate solution according to the Tokyo case, the pH becomes 9! ; the reaction is almost complete, but after adding sulfuric acid to adjust the pH to 7.3, the yield of zinc oxide is 8.
It was 7%.

When hydrochloric acid was added to the sodium zincate solution redissolved under the conditions of Comparative Example and Example C and the reaction was interrupted at pH 13, the yield of zinc oxide was less than 1.

As described above, the method for producing zinc oxide of the present invention is easy to operate, does not require particularly precise pH control, and the zinc oxide produced has good sedimentation and separation properties and can be easily carried out by a simple one-pass operation. It is a method of producing zinc oxide that is energy-saving and inexpensive compared to conventional methods, as the amount of energy required is only that of dry zinc oxide.

According to the method of the present invention, it is possible to directly produce high-purity zinc oxide from the electrolyte in wet smelting of zinc, and by applying the present invention, it is possible to provide inexpensive zinc oxide, which increases the demand for zinc oxide. Contribute to this industry.

Claims (1)

[Claims] pH i with zincate 2. ! ; Add an acid to the above alkaline solution to adjust the pH/Y. ．． A method for producing zinc oxide by a wet method, characterized in that zinc oxide is directly produced by neutralizing to t-pH g.