JPS6291288A - Method for treating waste water having fine particles suspended therein - Google Patents

Abstract

PURPOSE:To enhance a removing ratio, by adding an iron powder to a raw liquid of which the pH is made weakly acidic and subsequently adding an alkali agent and a polymer flocculant thereto in succession to perform solid-liquid separation. CONSTITUTION:After the pH of a raw liquid containing fine particles such as SiO2 is made weakly acidic to be adjust to 2-4, an iron powdery is added thereto to perform stirring for a definite time. Subsequently, an alkali agent is added to the raw liquid to adjust said raw liquid to an alkaline side with pH 8-10 and oxidizing treatment such as aeration is performed. Thereafter, a polymer flocculant is added to perform solid-liquid separation. By this method, SiO2 can be perfectly treated at low cost.

Description

Detailed Description of the Invention (a) Technical field The present invention relates to a method for treating wastewater in which fine particles are suspended, and in particular, it relates to a method for treating wastewater in which fine particles are suspended. It is characterized by its processing.

(b) Prior art In recent years, with the development of the semiconductor industry, opportunities to use silane gas such as monosilane in this manufacturing process have increased.
As a result, processing of the gas becomes a problem, and it is common practice to fix it as SiO2 by combustion or the like, and to treat it as a waste liquid by washing with water.

In this case, the SiO The current situation is that this has not yet been achieved.

(C) Structure of the Invention The present invention provides a novel method for treating wastewater containing fine particles, which solves the problems of the conventional methods as described above.

That is, in the present invention, when treating fine particles g and turbid water,
First, the pH of the stock solution is adjusted to slightly acidic, then # powder is added and stirred, then an alkaline agent is added to adjust the pH, and a polymer flocculant is added to perform solid-liquid separation. It is something to do.

For a better form, for example, after adjusting the pH of the wastewater to 1e* acidic (pH 4 or less, preferably 2 to 4) in which fine particles such as SiO After adjusting the pH to an alkaline side, preferably 8 to 10, using an agent and performing oxidation treatment such as aeration and stirring, a polymer flocculant is added to perform solid-liquid separation, which eliminates almost all Sing in the liquid. removed.

In the present invention, although the behavior of iron powder toward 5iC)2 has not been fully elucidated, the iron powder itself is dissolved by acid,
It is thought that SiO2 is adsorbed by active iron hydroxide and reacts with a polymer flocculant on the alkali side, resulting in sufficient co-precipitation.

The method of the present invention will be explained in detail below using examples.

(d) Example Example 1000 mg of SiO2 discharged from the semiconductor manufacturing process
Mineral acid was added to the wastewater lfL containing /i to adjust the pH to 3.0, 10g of iron powder was added to this wastewater, the mixture was stirred for 3 minutes, NaOH was added to adjust the pH to 8.2, and after aeration, polymer 7 g of polyacrylamide (nonionic) was added as a flocculant and stirred for 30 seconds. Thereafter, the mixture was allowed to stand for 3 minutes to perform solid-liquid separation.

The result of analyzing SiO2 in the five-door solution was 2 mg/liter.

Comparative Example 1 Same wastewater as in the above example 19. The pH was adjusted to about 8 by adding NaOH without adding iron powder, and after stirring for 3 minutes, 1 liter of polymer flocculant (polyacrylamide) was added.
After adding 0 mg/u and stirring again for 30 seconds, the mixture was allowed to stand for 3 minutes to perform solid-liquid separation, and the SiO2 in the liquid was analyzed.

As a result, SiO2 was 98C)og/JL and was hardly removed.

Comparative Example 2 To 1M of the same wastewater as in the above example, without adding iron powder, NaOH was added to adjust the pH to about 8, and after stirring for 3 minutes, 1% of sulfuric acid was added as a polymer flocculant. The mixture was added at the same ratio, stirred again for 30 seconds, left to stand for 3 minutes, solid-liquid separation was performed, and SiO2 in the liquid was analyzed.

As a result, the SiO2 content was 450 mg/ml, and it was further confirmed that suspended particles remained in the solution.

(e) Effects of the Invention As described above, the method of the present invention has the advantage of being able to completely treat fine particle suspended wastewater at low cost, which was inappropriate for various conventional treatment methods.

Patent applicant: Dowa Mining Co., Ltd. 1

Claims (2)

[Claims] (1) When treating fine particle suspended wastewater, after adjusting the pH to slightly acidic, iron powder is added and stirred, then after adjusting the pH with an alkaline agent, a polymer flocculant is added to solidify the liquid. A method for treating fine particle suspended wastewater, characterized by separating it. (2) The method for treating fine particle suspended wastewater according to claim 1, wherein the fine particles are SiO_2 discharged from a semiconductor manufacturing process or the like.