JPS6118494A - Method for removing heavy metal ion in waste water - Google Patents

Abstract

PURPOSE:To permit complete removal of ions by irradiating waste water contg. heavy metal ions with light in the presence of catalyst contg. a semiconductor as primary component and depositing the heavey metal ions in the waste water on the catalyst. CONSTITUTION:Powdery semiconductor comprising TiO2, strontium titanate, barium titanate, etc. is added to waste water contg. heavy metal ions, and the waste water is irradiated with light emitted from a superhigh pressure mercury lamp, halogen lamp, xenon lamp, etc. as light source. Thus, heavy metal ions are deposited on the surface of the semiconductor. Suitable wavelength of the irradiating light is 350-420nm.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing heavy metal ions from wastewater by oxidizing them using the oxidizing power of semiconductor powder when irradiated with light and allowing the ions to immerse as oxides.

Since the publication of groundbreaking research that uses titanium dioxide electrodes to decompose water and generate hydrogen, oxygen, and hydrogen through light irradiation, attempts have been made to utilize light energy using semiconductors.
I'm at t. Semiconductor catalysts are characterized by their strong oxidation and reduction powers; they generate hydrogen through reduction and oxygen through oxidation of water. The present invention utilizes the oxidizing power of such semiconductors when irradiated with light to convert heavy metal ions in wastewater into oxides and efficiently remove them.

Methods for removing heavy metal ions from wastewater include adsorbing them with a ion-exchange resin or making the wastewater alkaline to precipitate them as hydroxides. However, ion exchange resins are expensive and deteriorate with repeated use. In addition, if wastewater is made alkaline, it is necessary to further neutralize it by adding acid after removing heavy metal ions, and even if this method is used, it may not be possible to completely remove metal ions if the concentration of metal ions is small. . The present inventors have overcome these drawbacks and provided a method for removing heavy metal ions in wastewater, which can be carried out easily and is characterized by irradiating with light and submerging the heavy metal ions in wastewater onto the catalyst. Ru.

The catalyst used in the present invention has a semiconductor as its main component, and when wastewater containing heavy metal ions is irradiated with light in the presence of such a semiconductor catalyst, the heavy metals are oxidized and the oxidized heavy metal ions are deposited on the semiconductor surface. Submerge as a substance.

The catalyst used in the present invention is immersed on the surface of a semiconductor, and the oxide is easily removed with an acid solution, and there is almost no loss of semiconductor or platinum due to this treatment, and the catalyst can be used repeatedly. Conventionally, when using light for pollution removal,
In most cases, ultraviolet light from a low-pressure mercury lamp is used, but in the present invention, 35
It can be carried out using light in the visible light range of 0 mμ or more. Therefore, the container does not need to be made of quartz glass, but can be made of Pyrex glass.

The semiconductor used in the present invention has a size between the valence band and the conduction band that is large enough to absorb light from the light source, and the position of the valence band is more positive than the oxidation potential so that oxidation of the metal can occur. The conductor position is 02+e →0□ and 21-T →
−2e −+ enough to cause the reaction of H2, −
〇, 5 Vs NHE J: Must be negative.

Such conditions are necessary to oxidize heavy metal ions in the valence band and at the same time reduce dissolved oxygen or water with the reducing power of the conduction band, thereby efficiently separating the charges generated inside the semiconductor.

Semiconductors that can be used in the present invention include, for example, titanium dioxide, strontium titanate, barium titanium, etc., and are usually used in the form of powder, and the smaller the particle size, the more preferable it is. In the present invention, commercially available powdered semiconductors can be used as they are. Indeed, in the present invention, noble metals can be supported on the semiconductor as a promoter.

In this case, the noble metal can be supported on the semiconductor using a conventionally known method such as "Chemical Society (C-hem)".
Soc, ) J Vol. 100, p. 4317 (1978
It can be carried out by the method described in 2003 (see the description of Examples below). As a precious metal supported.

Examples include platinum, palladium, ruthenium, gold, and the like, with platinum being particularly preferred. In addition, the mutual amount of precious metals is 1
0005 to 0.3 parts by weight, preferably 0.0005 to 0.3 parts by weight.
02 to 01 parts by weight. The light used for light irradiation is
Although it varies depending on the semiconductor used, generally 350m
Light with a wavelength of μ ~ 600 mμ is used, for example, in the case of titanium dioxide or strontium titanate, light with a wavelength of 350 mμ ~
Light having a wavelength of 420 mμ is preferred.Next, the present invention will be explained in more detail based on examples.

Example 1 Platinum-supported catalysts o, oi, and p, in which platinum was supported on commercially available titanium dioxide (rutile), were placed in a 1010 x 10 x 45 Pyrex glass cell, and the concentration was 0.002 mol/l.
3 CC of lead solution was added. While stirring this suspension, the infrared light of a 500W high-pressure mercury lamp was cut off with a water filter, and ultraviolet light of 350 mμ or less was cut off with a Pyrex glass window of the water filter. A certain amount of the supernatant liquid of the suspension after irradiation was taken out, pyridylazoresorcinol was added to develop a color, and the concentration of remaining lead was analyzed by color analysis. After 30 minutes of irradiation, 94% of the lead was removed.

The platinum-supported semiconductor catalyst can be prepared by following the method described in "Chemical Society" Vol. 100, p. 4371.
It was manufactured as follows.

2g of semiconductor (rutile) powder was suspended in a 0.1M chloroplatinic acid aqueous solution, nitrogen gas was introduced into this to remove dissolved oxygen, and the semiconductor surface was irradiated with light from a high-pressure water fountain and lamp. Deposit platinum on. Thereafter, the semiconductors on which platinum has been deposited are separated and thoroughly washed with water.

Example 2 After blowing air into a suspension containing 3 cc of 0.002 mol/l thallium solution and 0.01 g of platinum-supported titanium dioxide for 20 minutes, the suspension was heated in the same manner as in Example 1 for 1 hour. Irradiated. 15% of the thallium was removed.

Example 3 Strontium titanate 001g and 10"mol/
Air was passed through the suspension containing 3 cc of the lead solution of d for 1 hour. Afterwards, irradiation was performed for 2 hours in the same manner as in Example 1.

Ta. 55 parts of lead were removed.

Example 4 10−3 m O in which the semiconductor catalyst obtained in “Example” was suspended
], /l of manganese was irradiated with light in the same manner as in Example 1. Almost all the manganese was removed after 1 hour.

Reference Example: 5% of lead oxide was immersed on the surface of the catalyst obtained by the operation of Example 1.
of hydrochloric acid for 1 hour. By this operation, 8 of lead oxide
9% was removed from the catalyst surface.

Procedural amendment (voluntary) No. 60 Kagiken No. 298 March 27, 1980 1, Case description 1982 Patent Application No. 140106 2, Title of invention Fuji removal method for heavy metal ions in wastewater 3,
Patent applicant address related to the person making the amendment: 1-3-1 Tomi, Kasumigaseki, Chiyoda-ku, Tokyo (u4) Tatsu Todoroki, Director of the Agency of Industrial Science and Technology (U4)
Date of dispatch (Showa year, month, day) 6. Number of inventions increased by amendment 08. Contents of amendment The following amendments are made in the specification of the present application.

Add Example 5 next to page 7, line 10.

Example 5 A suspension containing 0.015 L of titanium dioxide and 3 cc of 10-'' mol of mercury ions was irradiated for 60 minutes in the same manner as in Example 1, and then 82f6 of mercury was removed. ”
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Claims (1)

[Claims] (1) In the presence of a catalyst whose main component is a semiconductor or a semiconductor supporting a noble metal, wastewater containing heavy metal ions is irradiated with light so that the heavy metal ions in the wastewater are submerged onto the catalyst. Method for removing heavy metal ions in wastewater.