JPS62246808A - Method for concentrating slurry - Google Patents

Abstract

PURPOSE:To easily and efficiently concentrate a slurry of fine inorg. oxide powder obtd. by wet grinding by applying ultrafiltration. CONSTITUTION:An inorg. oxide such as silica or alumina is wet ground to <=10mum average particles size. The resulting slurry of fine inorg. oxide powder is concentrated by ultrafiltration and sent to an evaporation drying stage provided with a spray dryer or the like. Thus, the slurry can be easily concentrated to >=60% concn. without damaging or clogging a filter membrane even when the fine powder has <=10mum average particle size, so the cost in the next drying stage can be reduced.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to a method for producing fine powder of inorganic oxides such as silica and alumina, which are raw materials for ceramics used in fields such as electronic materials. In particular, the present invention relates to a method for concentrating a fine powder slurry in a process of handling the fine powder slurry.

(Prior Art) (Problems to be Solved by the Invention) Generally, pulverization methods are broadly classified into wet methods and dry methods. In the dry method, agglomeration tends to occur along with pulverization, and a dispersant is usually added to prevent agglomeration, but even in that case, the average particle size after pulverization is generally larger than that in the wet method.

On the other hand, with the wet method, there is no need to take dust countermeasures and the powder has a good dispersion effect, so it is relatively suitable for fine pulverization. It has the disadvantage of requiring large equipment and high energy costs.

However, when producing fine powder of inorganic oxides such as silica and alumina, a wet method is generally adopted. Drying methods such as

In the case of a spray dryer, after wet grinding, it is first filtered,
Next, in order to charge the powder into a spray dryer, it is necessary to prepare a slurry of the fine powder by adding an appropriate amount of water to ensure smooth transportation between the spray dryers.

However, when the average particle size of the fine powder in the slurry is less than 10μ, it must be filtered under reduced pressure or increased pressure, and clogging occurs during the operation, so it is very difficult to implement it industrially. Furthermore, when the average particle size of the fine powder reaches the submicron order, it becomes virtually impossible to implement the filtration method industrially.

Therefore, in order to obtain fine powder from a slurry containing fine powder with an average particle size of 10μ or less, it is necessary to wet-pulverize it, then transport it as a wet slurry and charge it into a spray dryer. First, it has the drawback that the cost for evaporating the water is higher.

(Means for solving the problem) However, in advanced technology fields such as ceramics used as electronic materials, fine powder of inorganic oxides of not only about 10 microns but also micron to submicron orders are required as raw materials. Therefore, wet pulverization has become an indispensable means.

Therefore, in order to overcome the drawbacks associated with the above-mentioned wet method, the present inventors conducted intensive studies on a method for removing water from a fine powder slurry. It has been found that water can be effectively removed as filtered water at low cost.

In general, ultrafiltration methods filter and concentrate proteins, enzymes, nucleic acids, viruses, urine, serum, etc. at the molecular size level, and separate, purify, or concentrate substances with molecular weights from several hundred to several million. A filtration technique used to remove
It is mainly used in the field of biochemistry. However, when filtering fine particles of inorganic oxides, especially particles with high hardness and many sharp edges, such as silica and alumina, there is a concern that they may cause mechanical damage to the ultrafiltration membrane.
An example of application to concentration of a slurry of fine powder as in the present invention is not disclosed.

However, according to the results of studies conducted by the present inventors, there is no
．． When a gas pressure of 1 to 5 kg/cd is applied and ultrafiltration is performed in the usual manner, a fine powder slurry of inorganic oxide can be easily obtained without causing any damage or clogging to the filtration membrane. The present invention was achieved by discovering that it is possible to carry out concentration of .

The inorganic oxide fine powder to which the present invention can be applied may be anything that is normally used as a raw material for ceramics, but it is particularly effectively applied to fine powders of silica and alumina.

The concentration of the inorganic oxide slurry to be concentrated varies depending on the type of inorganic compound and its particle size, but is usually 50% or less, preferably 30% or less.

By applying the ultrafiltration method according to the method of the present invention to the slurry having the above concentration, the slurry concentration can be concentrated to 60% or more.

In addition, the particle size of the inorganic oxide fine powder in the slurry is 10μ
Although the method of the present invention can be applied to the above cases,
Since ordinary reduced pressure or pressure filtration methods can be used, there is no need to rely on ultrafiltration methods.The particle size is 10μ or less, especially in the submicron order, which is virtually impossible to concentrate with reduced pressure or pressure filtration methods. The method of the present invention can be advantageously carried out on fine powders.

The method of the present invention is usually carried out after performing wet pulverization, optionally performing further operations such as acid washing, and before starting an evaporative drying step using a spray dryer or the like. There are no particular restrictions on the method of wet pulverization, and it can be applied to fine powder obtained by any method, but it is applicable to fine powder slurry obtained by commonly used wet ball mills, wet medium stirring mills, etc. Can be applied to advantage.

When the present invention is carried out industrially, a batch method is used in which one or more ultrafiltration membrane modules are installed in series or in parallel and water is extracted from the system while the slurry is circulated, or the slurry is concentrated in one direction. Depending on the amount of slurry to be treated, the treatment method can be selected as appropriate, such as a continuous method that concentrates the slurry by continuously supplying it from the tank, or a method that simply attaches an ultrafiltration membrane to the bottom of the tank and filters and concentrates it while stirring with a pump. You can choose.

The ultrafiltration membrane used in the present invention is not particularly limited, and may be one that is widely used in the food industry, pharmaceutical industry, and other general industries, such as polyolefin with wood-philic properties or heat-resistant polymers such as polysulfone. Commercially available ultrafiltration membranes can be used, and the method of the present invention can be advantageously carried out using any ultrafiltration membrane.

(Example) The present invention will be explained in more detail with reference to Examples below.

Example 1 In a conventional ball mill made of alumina, 0.0% was used as a dispersant.
Wet milling of silica was carried out at a slurry concentration of 20% by mixing 3% sodium hexametaphosphate, and the average particle size was 2.
A slurry of 4 μm fine silica powder was obtained.

A 75φ polysulfone membrane (TOYO
(manufactured by IJK200), charged with 500 g of the above slurry, and heated at room temperature, pressure 1, 6 kg/c while stirring.
Ultrafiltration was performed under rA conditions. After 20 minutes, the slurry was concentrated to 62%, and clear colorless water was obtained from the bottom. During this period, no scratches on the filtration membrane were observed, and the operation was extremely smooth.

Comparative Example 1 Pressure filtration was carried out using the same method and apparatus as in Example 1, except that the bottom was equipped with two ordinary qualitative filter papers for chemical experiments, but clogging occurred a few minutes after the start of the operation, and filtration was almost impossible. It was possible.

Example 2 Two pieces manufactured by Nitto Electric.

Ultrafiltration membrane (x+ '
Three J-Olefin NTU-2000) tubular modules are connected in series, and the slurry liquid in the tank is pumped through the series modules to allow self-circulation. I made it possible to keep it at .

On the other hand, 2 with an average particle size of 1.1μ obtained by wet ball milling
5% alumina fine powder slurry 10 +r was charged into the above tank, and the system pressure was increased to 2 with a flow rate of 6001/Hr using a pump.
A 60 minute ultrafiltration operation was carried out at kg/c++1. The concentration of the obtained alumina fine powder slurry was 50%.

During this period, operations were extremely smooth.

(Effects of the Invention) The present invention provides a novel method for concentrating inorganic oxide fine powder slurry with an average particle size of 10 μm or less, particularly on the order of microns to submicrons, using a commercially available ultrafiltration membrane. It has a similar effect.

(1) Slurry containing submicron-order silica or alumina particles, which cannot be concentrated using normal reduced pressure or pressure filtration methods due to clogging, can be easily concentrated.

(2) Water generated by concentrating the slurry can be easily removed from the system as permeated water.

(3) It can be easily implemented industrially by appropriately installing ultrafiltration membrane modules and selecting a treatment method.

Claims (4)

[Claims] (1) When concentrating the slurry of inorganic oxide fine powder,
A method for concentrating a slurry, characterized by using an ultrafiltration method. (2) Claim (1) in which the inorganic oxide is silica
Method described. (3) Claims (1) in which the inorganic oxide is alumina
) method described. (4) The method according to claim (1), wherein the inorganic oxide fine powder has an average particle size of 10 μm or less.