JPH0453561B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for settling various fine particles in wastewater discharged from various industries. Currently, various inorganic or organic flocculants are used alone or in combination to treat suspended water containing fine particles discharged in various industries, but their effects are extremely insufficient. We have no choice but to dry it in the sun. The present inventors conducted various studies to solve the above-mentioned problems, and as a result, they discovered that gypsum can be easily treated by coprecipitation, and have completed the present invention. That is, the present invention is characterized in that after adding 0.1 to 1.0% of coal or milk of lime as a lime content to the fine particle suspension water, the pH is adjusted to 6.0 to 8.0 using sulfuric acid, and the fine particles are precipitated. This is a method for treating fine particle suspension water. The particulate suspension water referred to in the present invention includes bentonite suspension water, clay suspension water, ferric hydroxide suspension water, pulp waste liquid, starch waste liquid, cement waste liquid, etc. Bentonite suspension water, which is difficult to separate and settle, is an example. Firstly, the method of the present invention will be explained. As is well known, bentonite-containing water forms extremely stable suspended water, and is used in large quantities in civil engineering and construction projects due to this property. It is extremely difficult to separate the bentonite from the bentonite, and it is not possible to obtain a clear supernatant even after leaving it for several days or using a centrifuge. In the method of the present invention, a small amount of lime powder or lime milk is added to this bentonite liquid, mixed uniformly, and then diluted sulfuric acid is used.
Although it is a simple process that only adjusts the pH to 6.0 to 8.0, centrifugation actually reduces the total liquid volume by 80%.
It is possible to separate as much as % of clear water. Although the mechanism of action of the addition of lime or milk of lime of the present invention is not clear, bentonite particles or other particles that are difficult to separate do not absorb centrifugal force because the particles are added with water and have a specific gravity close to that of water. It is difficult to settle even if the particles are multiplied, and it is presumed that by making these particles eutectoid with gypsum and increasing the specific gravity of the particles themselves, sedimentation becomes easier. The amount of lime or milk of lime to be added is 0.1 to 1.0% as lime content to the fine particle suspension water; if it is less than 0.1%, the fine particles cannot be sufficiently settled, and even if it is more than 1.0%, Since the effect of settling fine particles remains the same, there is no need to increase the amount more than 1.0%. The comparative test results between the present invention and the conventional method are as follows. (1) Bentonite liquid used in the test (a) Bentonite used: 250 manufactured by Nishige Kaihatsu Co., Ltd.
Mesh bentonite (b) Preparation of bentonite liquid: Add the above bentonite to pure water at a ratio of 5% w/v and stir and suspend thoroughly. (2) Test method: After adding various flocculants to 100 c.c. of each of the above bentonite liquids, the ratio of the transparent water layer to the total liquid volume that is generated when the mixture is placed in a centrifuge (3000 revolutions per minute) for 30 minutes, And the water content of the separated bentonite layer was measured. The results are shown in the table below.

【table】

[Table] The present invention will be described below with reference to Examples. Example 1 Add 1 part of 7.5% milk of lime to 10 parts of bentonite liquid (moisture 94%), stir, add 1.0 parts of 10% sulfuric acid to adjust the pH to 8.0, and centrifuge (3000 revolutions per minute) for 30 parts.
After 6.9 minutes of separation, clear water of 6.9% was separated, and the moisture content of the bentonite layer was 76%. Note that even if the bentonite liquid was directly applied to a centrifuge, clear water could not be obtained. Example 2 75 g of lime powder in clay suspension water (moisture 97.5%) 10
After adding and mixing uniformly, add 740 ml of 10% dilute sulfuric acid to adjust the pH to 6.9, and centrifuge (3000 revolutions per minute).
After 30 minutes, 8.8 ml of clear water was separated, and the moisture content of the separated clay layer was 68.3%. Note that even if the clay solution was directly applied to a centrifuge, clear water could not be obtained. Example 3 When a 2.5% ferric hydroxide suspension water 10 was subjected to the same operation as in Example 1, 8.4% transparent water was obtained, and the water content of the ferric hydroxide layer was 76%.
When the ferric hydroxide solution was centrifuged as it was, clear water of 7.0% was obtained, and the water content of the ferric hydroxide layer was 91.7%.

Claims (1)

[Claims] 1. Add 0.1 to 1.0% of lime or milk of lime to the fine particle suspension water, then PH it with sulfuric acid.
A method for treating fine particle suspended water, the method comprising adjusting the water to 6.0 to 8.0 and allowing the fine particles to settle.