JPH04325414A - Production of zinc oxide-zinc hydroxide mixture - Google Patents

Abstract

PURPOSE:To obtain a high-quality zinc oxide-zinc hydroxide mixture having high separability from water. CONSTITUTION:Acidic waste water contg. zinc salts is added to an aq. soln. of sodium hydroxide or potassium hydroxide to produce a zinc oxide-zinc hydroxide mixture by a batch system. At the end of reaction, pH is about 9.5-12.5.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a batch process for producing a zinc oxide and zinc hydroxide mixture by adding acidic wastewater containing zinc salts to an aqueous solution of caustic soda or potassium hydroxide.

0002

[Prior Art] JP-A-57-149827 discloses a simultaneous addition reaction in which an inorganic zinc aqueous solution and an alkaline aqueous solution are simultaneously and continuously added to a stirring reaction tank and reacted with stirring.
Lower limit pH value of the reaction slurry = 8-0.033
While keeping within the range from 4t to upper limit pH value = 12.7-0.0578t (where t indicates the reaction temperature [°C]),
In addition, the total Zn concentration in the resulting slurry produced by the simultaneous addition reaction is 20 g/L or more, and in some cases, an alkali or inorganic zinc salt is additionally added to the slurry produced after the simultaneous addition reaction, and all inorganic zinc is The ratio of the total amount of alkali used to the amount of salt used is 0.95 equivalent or more (i.e. the ratio of 1.9 or more OH groups of the total amount of alkali used to one Zn atom of the total amount of inorganic zinc salt used) A method for producing zinc oxide is described, which is characterized in that a precipitate is obtained as follows. Further, Japanese Patent Application Laid-Open No. 53-61593 describes a method for producing zinc hydroxide free of basic salts, in which an acidic solution containing zinc is added to an alkaline solution such as caustic soda. Furthermore, JP-A-60-
No. 171222 discloses that pH 12.5 containing zincate
Add acid to the above alkaline solution to pH 12.5~p
A method for producing zinc oxide by a wet method is described, which is characterized in that zinc oxide is directly produced by neutralizing to H8.

0003

[Problem to be Solved by the Invention] When a zinc oxide and zinc hydroxide mixture is produced by treating acidic wastewater containing zinc salts with an alkali, it is necessary to separate the zinc oxide and zinc hydroxide mixture from water in the reaction mixture. For example, the filterability is poor, and therefore, it takes a long time to dry a cake with a high water content after separation, which significantly impairs productivity. The present inventors have completed the present invention as a result of intensive studies on a method for producing a zinc oxide and zinc hydroxide mixture with good separability and therefore good productivity.

0004

[Means for Solving the Problems] The present invention is a batch method for producing a zinc oxide and zinc hydroxide mixture by adding acidic wastewater containing zinc salts to a caustic soda or caustic potassium aqueous solution, and pH of about 9.5 to about 12.
This method is characterized by a range of 5. Examples of acidic wastewater containing zinc salts include factory wastewater containing zinc salts such as zinc chloride, zinc acetate, zinc sulfate, and zinc nitrate, or mixtures thereof. Preferably, zinc chloride and/or zinc acetate as zinc salts are added in acidic wastewater at a concentration of about 10 to
Examples include those containing about 30% by weight. As for the addition time of acidic wastewater, if the addition time is long, the particle size of the zinc oxide and zinc hydroxide mixture that is produced becomes large, and the separability, for example, the filterability is also good. However, from the viewpoint of productivity, the time is usually about 30 minutes to about 20 hours, preferably about 1 hour to about 10 hours. Regarding the reaction temperature, a high temperature, for example 60°C or higher, is not preferable because it increases the amount of fine particles in the produced zinc oxide and zinc hydroxide mixture.
The temperature is preferably 0 to 40°C. Particularly preferably 10
~30°C. The concentration of zinc salt in the reaction mixture is usually about 30 to about 120 g/L as Zn, preferably about 6
0 to about 110 g/L. After the reaction is completed, from the suspension of the reaction mixture of zinc oxide and zinc hydroxide,
After separating the mixture from water by a suitable separation means such as sedimentation separation, pressure filtration, vacuum filtration, centrifugal filtration, decanter, etc., the resulting wet cake is dried by a known method to obtain zinc oxide and zinc hydroxide. A mixture is obtained.

[0005]

[Effects of the Invention] According to the present invention, the separation between the zinc oxide and zinc hydroxide mixture and water, for example, the filtration performance is good (that is, the specific resistance α value during filtration is small), so the time required for separation is reduced. Can be shortened. Furthermore, since the separability is good, the moisture content of the wet cake obtained after water separation is low, and the time required for drying can be shortened. That is, a mixture of zinc oxide and zinc hydroxide can be produced with high productivity. Furthermore, since the mixture does not contain basic salts and is of high quality, it can be directly isolated as zinc oxide by calcination, and then refined to obtain metallic zinc.

[0006]

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way. Reference Example 1 The following reaction was carried out using a reaction pot (diameter 1.5 m), a rotating shaft installed in the vertical direction of the reaction pot, and a four-bladed inclined paddle blade (θ = 45°) installed at the bottom of the rotating shaft. and post-treatment was carried out [however, the rotation speed was 150 rpm, and the ratio of the diameter of the paddle blade to the diameter of the reaction pot was 0.6]. 5-methyl furfural 22.8 kg, toluene 68.7 kg and water 86.
5.4 kg of 50% acetic acid, 23.1 kg of zinc powder, and 32.4 kg of 2,3-dichloro-1-propene were added simultaneously over 30 minutes to this mixture at 45°C. After the addition was completed, the mixture was stirred at the same temperature for 6 hours until the reaction was completed. After the reaction was completed, the pH was adjusted with 19 kg of concentrated hydrochloric acid. Next, the reaction mixture was taken out from the discharge hole at the bottom of the reaction vessel, and insoluble matter was removed by filtration. The obtained filtrate was separated, and the aqueous layer was acidic wastewater containing zinc salts (pH
= approx. 4) 143 kg was obtained. The analysis results of acidic wastewater were as follows. Moisture 70.1% by weight, zinc chloride 26%
．． 2% by weight, zinc acetate 2.3% by weight.

Example 1 20 kg of the acidic wastewater containing the zinc salt obtained in Reference Example 1 was added to 12 kg of a 27% caustic soda aqueous solution at 24 to 26°C over a period of 6 hours, and after the addition was completed, the mixture was heated at the same temperature for 30 minutes. Stirred (
The pH at the end of the reaction was 11.5). The zinc oxide and zinc hydroxide mixture was separated from water by pressure filtration (specific resistance α during filtration = 1.1 x 108 m/kg) from the reaction mixture to obtain 5.2 kg of wet cake (in the filtrate). Zinc ion concentration is 6 mg/L). This wet cake was dried to obtain a 4.2 kg dry cake (solid content in the wet cake was 80.6% by weight). In addition, the average particle diameter (D50) of the dry cake is 53 μm, and the particle size distribution is expressed by the following formula as determined by Microtrack.
It was found that it follows the sin-Rammler distribution formula (
n = 2.3, D* = 58 μm). R = 100e - (D/D*) n [In the formula, R is the cumulative weight % of the cake, D is the diameter of each particle of the cake, n is the uniformity, and D* is the D when r = e-1. represents the representative particle diameter that can be determined regardless of n. ] The experiment was repeated in the same manner as in Example 1 except that the addition time θ (minutes) of the acidic wastewater containing zinc salt obtained in Reference Example 1 was varied, and the following relationship was found between the average particle diameter and addition time. The formula was obtained. D50 (μm) = -39.1376 +15.687
logθ

Comparative Example 1 The reaction, filtration and drying were carried out in the same manner as in Example 1 except that the reaction temperature was changed from 24 to 26°C to 59 to 61°C to obtain the following results. Specific resistance α during filtration = 1.1 x 1011 m/kg Dry cake 6.9 kg (Solid content in wet cake is 60.8
In addition, the particle size distribution of the dry cake is bimodal with two peaks, and the average particle size on the fine particle side (D5
0) is 3.4 μm, and the average particle diameter on the coarse particle side (D5
0) was 14 μm (the weighted average D50 of the entire dry cake was 9 μm).

Comparative Example 2 The pH at the end of the reaction was increased by increasing the amount of acidic wastewater containing zinc salt.
The reaction and filtration were carried out in the same manner as in Example 1, except that the value was changed to 8.0, and the following results were obtained. Zinc ion concentration in filtrate = 47mg/L

Comparative Example 3 The pH at the end of the reaction was adjusted by reducing the amount of acidic wastewater containing zinc salts.
The reaction and filtration were carried out in the same manner as in Example 1 except that the value was changed to 13.0, and the following results were obtained. Zinc ion concentration in filtrate = 250mg/L

[0011]
Example 2 Reaction, filtration and drying were carried out in the same manner as in Example 1 except that acidic wastewater having the following composition was used. [Moisture 73% by weight, zinc chloride 2
6.2% by weight] Similar to Example 1, the specific resistance value during filtration (
A suspension of a mixture of zinc oxide and zinc hydroxide with a small α) and therefore good filterability was obtained, and the concentration of zinc ions in the filtrate was also 6 mg/L or less.

Comparative Example 4 The reaction and filtration were carried out in the same manner as in Example 1, except that a 27% aqueous solution of caustic soda was added to acidic wastewater containing zinc salts, and the following results were obtained.

Claims (5)

[Claims] 1. A batch process for producing a mixture of zinc oxide and zinc hydroxide by adding acidic wastewater containing zinc salts to a caustic soda or caustic potash aqueous solution, and the pH at the end of the reaction is about 9.5. to about 12.5. 2. A process according to claim 1, comprising from about 10 to about 30% by weight of zinc chloride and/or zinc acetate as the zinc salt in the acidic wastewater. Claim 3: The concentration of zinc salt in the reaction mixture is about 6 as Zn.
3. The method of claim 1 or 2, wherein the amount is from 0 g/L to about 110 g/L. 4. The method according to claim 1, wherein the reaction temperature is 0°C to 40°C. 5. The method of claim 1, wherein the acidic wastewater addition time is about 1 to about 10 hours.