JPH0117737B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for extracting heavy metals from aqueous solutions such as seawater or industrial wastewater, particularly uranium from seawater, using porous glass as an adsorbent.

Traditionally, trace amounts of uranium (approx.
Various methods have been proposed to separate 3ppb), but the adsorption method is considered promising because its concentration is dilute. Adsorptive properties tests have been conducted on various adsorbents, but a satisfactory one has not yet been obtained because a large amount of adsorption is required in an extremely low concentration range. Basic adsorption properties such as equilibrium adsorption amount, adsorption rate, and desorption rate are important as the characteristics required for adsorbents for uranium in seawater, but in addition, the sustainability of adsorption performance against repeated adsorption and desorption, and the Chemical durability, strength to withstand the flow of seawater, formability into shapes that are advantageous for contact with seawater, and cost of the adsorbent cannot be ignored. Even from this point of view, the adsorbents that have been published so far have not been satisfactory in terms of practical performance.

The present inventors have conducted studies on adsorbents that satisfy the above characteristics, and found that porous glass made from borosilicate glass is effective against heavy metals in aqueous solutions such as seawater or industrial wastewater, and in particular against uranium in seawater. The present invention was developed based on the discovery that it has a large adsorption capacity and also has excellent properties from the viewpoint of industrially and economically separating heavy metals.

That is, the present invention includes a granular, rod-shaped, fibrous, or tubular porous glass produced by heat-treating borosilicate glass to separate the phases, and then eluting the sodium borate-rich phase using an acid, and a heavy metal. This can be achieved by adsorbing and separating heavy metals by contacting them with an aqueous solution.

The porous glass used in the present invention is manufactured by utilizing the phase separation phenomenon of borosilicate glass in a specific composition range. That is, the composition
_SiO2 22-75% by weight _{, B2O3} 18-67% by weight, _Na2O2-16 % by weight _{, Al2O30}
- When 5 weight percent borosilicate glass is melted and shaped and heat treated at temperatures of 500-600°C, phase separation occurs, forming a phase rich in acid-soluble sodium borate and a phase rich in nearly insoluble silicon dioxide. The phase splits into A subsequent treatment with acid to elute the sodium borate-rich phase yields a porous glass consisting primarily of silicon dioxide.

The porous glass thus obtained can be used as an adsorbent as it is, but it can also be used as an adsorbent after further heat treatment or surface treatment. For example, the surface or inside of the pores of the porous glass can be modified by immersing the porous glass obtained by the above method in a solution of a metal compound (for example, titanic acid) and then performing a heat treatment.

The porous glass in the present invention can be easily formed into a shape that is advantageous for contact with an aqueous solution such as seawater, and can be formed into, for example, a rod shape, a tube shape, a particle shape, a fiber shape, a hollow fiber shape, a honeycomb shape, etc. Adsorbents of various shapes can also be manufactured as aggregates or combinations of porous glasses of these shapes.

The porous glass of the present invention has a large pore volume and a sharp pore size distribution in relation to its composition, and by appropriately devising phase separation conditions and acid treatment conditions, the pore size peak suitable for separating heavy metals can be obtained. Values can be adjusted in the range 10-1000 Å. Furthermore, as shown in the Examples below, the porous glass of the present invention exhibits a particularly high adsorption rate for uranium in seawater. It also has the advantage of being highly resistant to chemicals and heat, and highly durable against repeated adsorption and desorption. In addition, many of the adsorbents that have been published so far are in the form of fine powder, but the porous glass of the present invention can be freely formed into granules, fibers, rods, etc., so it is particularly advantageous in industrial production where large quantities of uranium are extracted from the sea. be. Needless to say, the present invention is also effective for heavy metal ions other than uranium, such as Cr ions and Fe ions. Furthermore, porous glass has enough strength to withstand the flow of seawater if its shape and dimensions are selected, and because it is chemically stable, it can maintain high adsorption performance in seawater for a long time.

As described above, the present invention can be widely applied to wastewater treatment processes in which heavy metals are selectively adsorbed and separated from aqueous solutions containing heavy metals. For example, the purpose is to purify wastewater by bringing the porous glass into contact with wastewater containing heavy metal ions such as the Cr ions (industrial wastewater, laboratory wastewater, hospital wastewater, etc.) and adsorbing the heavy metal components onto the porous glass. It can be used for It goes without saying that radioactive wastewater containing radioactive heavy metals such as uranium can be brought into contact with the porous glass and the heavy metal components adsorbed onto the porous glass, which can be used to purify radioactive wastewater. As a different effect of the present invention, the porous glass after adsorbing radioactive heavy metal components such as uranium is sintered and homogenized to form a small volume solid material with no risk of the heavy metal components flowing out or being lost. It also has the added benefit of industrial safety in that it is formed into waste, making it an extremely important contribution to the treatment of radioactive wastewater.

Example 1 SiO ₂ 60.6%, Na ₂ O 9.7%, B ₂ O ₃ 26.7%,
Borosilicate glass having a composition of 3.0% Al ₂ O ₃ was heated and melted, drawn into a tube shape, and formed into a thin tube with an outer diameter of 2 mm and an inner diameter of 1 mm. This capillary was heat-treated at 560°C for 40 hours to separate the phases, then immersed in 3N sulfuric acid and kept at about 100°C for 24 hours to elute the phase consisting mainly of sodium borate, forming a porous glass capillary. Manufactured. The thus obtained thin tubes were cut into lengths of 15 mm to obtain a number of short tubes, which were used as adsorbent samples. On the other hand, a 10 ppm uranium solution was prepared and the pH was adjusted to 8.1 using ammonia water. Add 200 mg of adsorbent sample to 100 ml of this solution and stir at room temperature for 64 hours.
Holds time. At this time, the pH of the solution was 7.7.
Next, the adsorbent sample was taken out, washed with water, uranium was extracted with nitric acid, then extracted with oxine chloroform, and then back-extracted with perchloric acid containing arsenazo, and the amount of uranium adsorbed was determined by color development of arsenazo. Amount is 3.3mg per gram of adsorbent
It was hot.

Example 2 The outer diameter is 2 mm and the inner diameter is 1 mm by the same operation as in Example 1.
A thin tube was produced, which was cut into 15 mm lengths to form a number of short tubes, which were used as adsorbent samples. Then Cr ⁶⁺ ion
100 ml of an aqueous solution containing 10 ppm was prepared, and 1 gram of the above adsorbent sample was added thereto, treated at room temperature for 10 hours, and separated using a filter. The Cr ⁶⁺ ion concentration of the liquid was measured by atomic absorption spectrometry and was 7.8 ppm, and the amount of Cr ⁶⁺ ions adsorbed per gram of adsorbent was 0.2 milligrams.

Claims (1)

[Claims] 1 After heat-treating borosilicate glass to separate the phases,
A method for separating heavy metals, which comprises bringing a granular, rod-like, fibrous, or tubular porous glass produced by eluting a phase rich in sodium borate with an acid into contact with an aqueous solution containing heavy metals to adsorb and separate the heavy metals. .