JPH0316691A - Method for simultaneously removing plural kinds of heavy metal ions - Google Patents

Abstract

PURPOSE:To reduce the concn. of heavy metal ions having the highest adsorption equilibrium with chelate groups to <=1/10 of the initial concn. by carrying out filtration with a porous membrane of a polymer having the chelate groups bonding to heavy metal ions in the side chain. CONSTITUTION:When part of plural kinds of heavy metal ions in water are Ni and Co ions, the water is filtered with a porous membrane of a polymer having chelate groups bonding to the heavy metal ions in the side chain until the concn. of the heavy metal ions having the highest adsorption equilibrium with the chelate groups is reduced to <=1/10 of the initial concn. The polymer of the porous membrane has imidodiacetic acid groups in the side chain by >=3 milliequiv. per 1g of the membrane and the membrane is composed of hollow fibers and has 0.01-5mu average pore diameter, 20-90% porosity and 10mu-5 mm thickness. By this method, plural kinds of heavy metal ions contained in waste water from a nuclear power plant are simultaneously removed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is a method for simultaneously and efficiently removing various heavy metal ions contained in wastewater particularly from nuclear power generation.

[Conventional technology]

Conventionally, multiple types of heavy metal ions contained in wastewater from nuclear power generation have been mainly removed using ion exchange resins.

However, with these ion-exchange resins, water is deionized by passing between relatively large spherical gels with particle sizes of several tens of microns or more, and due to diffusion (equilibrium) between these water flows and the inside of the gel. Ion adsorption takes place. Therefore, adsorption of a plurality of types of ions having different reactivities to the exchange resin requires a large amount of ion exchange resin because complex reactions of desorption and adsorption occur.

Furthermore, ion leakage has become a problem, and the process has been extremely disadvantageous due to its structure.

[Problem to be solved by the invention]

The object of the present invention is to simultaneously and efficiently remove and adsorb a plurality of types of heavy metal ions contained in the nuclear power generation wastewater.

[Means to solve the problem]

As a result of intensive studies to solve the above-mentioned extremely inefficient problem, the inventor has arrived at the following invention. That is, the present invention provides a porous membrane having a chelate group in its side chain that binds multiple types of heavy metal ions in water. This is a method for simultaneously removing a plurality of heavy metal ions, which is characterized by carrying out furnace overtreatment until the concentration of heavy metal ions reaches /10 or less.

Furthermore, in the above method, some of the plurality of types of heavy metal ions in the water are nickel and cobalt, and the porous membrane has an average pore diameter of 0.5 mm, having 3ξ equivalents or more of igonodiacetic acid groups in the side chains per gram of the membrane. 01~5μ, porosity 20~90%,
It has been found that the present invention is highly effective when the membrane is a hollow fiber-like porous membrane with a membrane thickness of 10 μm to 5 mm. Next, the present invention will be specifically explained. Specifically, the multiple types of polymerized metal ions to which the present invention can be applied include iron, copper, cobalt, nickel, etc. For example, in the case of cobalt and nickel, in the case of an acidic liquid, nickel is preferable. It has overwhelmingly high reactivity (adsorption) to iminodiacetic acid groups.

Here, the meaning of "ion with the highest adsorption equilibrium" is:
Refers to the ion with the highest adsorption amount when the membrane is immersed in a solution containing multiple types of heavy metal ions at the same molar concentration. Even though multiple types of ions differ greatly in their reactivity with the chelate group to which they bind, the overall adsorption effect of each ion is determined only by the most reactive ion (in the above case, 21 ions). It turns out that

This shows that the adsorption behavior of ions to the ion-adsorbent membrane is significantly different from that of ion-exchange resins, and adsorption to the membrane occurs in a layered manner from the raw water side over time. This fact shows the superiority of the membrane method in removing and purifying multiple heavy metal ions. The rate-limiting effect due to the balance of ions and hydrogen in the membrane is considerably smaller than in the case of ion exchange resins.

Of course, the furnace filtration may be stopped before the breakthrough point of the most highly adsorbed ions is reached.

As an example of the chelate group that binds to heavy metals used in the present invention, iminodiacetic acid is preferred.

The porous membrane having a chelate group in its side chain used in the present invention is preferably made of a polyolefin, a copolymer of an olefin and a halogenated olefin, polyvinylidene fluoride, or polysulfone. It is preferable to use a porous membrane in which a functional group having a chelate bond is chemically bonded to the inner and outer surfaces of the porous membrane and at least a portion of the surface of the pores inside the membrane, and the pores of the functional group! The membrane may be bound directly or may be bound to a polymer containing a functional group.

More preferably, the membrane material of the porous membrane is polyolefin, the membrane structure has a three-dimensional network structure, and the chelate bonding group is present on both the inner and outer surfaces of the membrane and at least a portion or the entire surface of the pores inside the membrane. a functional group having
Alternatively, treatment and purification may be carried out using a porous membrane to which polymers having these functional groups are chemically bonded.

Each of these functional groups must contain at least 3 milliequivalents of chelate groups per gram of porous membrane. Below this range, the ion removal ability of the membrane decreases.

The average pore diameter of the porous membrane is 0.01 to 5μ, preferably 0.01μ.
It is selected from the range of 01μ to lμ. If it is smaller than this range, the water permeability is not sufficient for practical performance, and if it is larger than this range, ion removal becomes a problem.

Although there are many methods for measuring average pore size, the method used in the present invention is described in ASTM F-316-70. It is based on a method called the air flow method, which measures the air permeation flux through the dry membrane and wet membrane when changing the air pressure.

The porosity of the porous membrane is 20% to 90%, preferably 50%
Those within the range of ~80% are used. The porosity here is measured by immersing the membrane in a liquid such as water, then drying it, and measuring the weight change before and after.
When the porosity is outside the above range, the permeation rate and
Unfavorable in terms of mechanical properties. The shape of the porous membrane may be a flat membrane (including pleats or spirals), a tube, or a hollow fiber. Hollow fibers are particularly preferred, but spiral flat membranes can also be used.

The pore structure of the porous 1t film serving as the base material can be shaped in various ways depending on a certain processing method. For example, if the base polymer is polysulfone, a three-dimensional network structure film can be created by using a so-called wet method, in which a mixed solution is prepared using a solvent, etc., and then it is discharged from a nozzle in the form of a hollow fiber, and then shaped with a coagulant, etc. It can be done. In the case of polyolefin, it is made by a stretching method or a chemical treatment after electron beam irradiation, and it is also possible to make a porous membrane by a so-called etching method. For example, Japanese Patent Publication No. 59-37292, Japanese Patent Publication No. 40-957, and Japanese Patent Publication No. 47-174, rather than a through-hole type hole structure.
Those having a three-dimensional network structure formed by the microphase separation method or mixed extraction method shown in Publication No. 60 are preferred from the viewpoint of practical performance. In particular, it is preferable to use a film having the structure shown in Japanese Patent Application Laid-Open No. 55-131028.

A known method is used to introduce a functional group having a chelate group into the side chain of the polymer that makes up the porous membrane. For example, a method for introducing iminodiacetic acid groups into the side chains of polyethylene is to irradiate a polyethylene film with an electron beam or the like, graft styrene in a gas phase, and then graft iminodiacetic acid using a known method. It will be done.

In addition, after irradiating the polyethylene film with an electron beam, etc.,
The method used is to graft glycidyl methacrylate in the gas phase and then add iminodiacetic acid. In order to introduce the functional group into the side chain of the polymer constituting the porous membrane, it can be introduced before forming the membrane, but
A preferred method is to form a membrane and then chemically bond it to at least a portion of the inner and outer surfaces of the membrane and the surfaces of the pores. Although it is desirable that the functional groups are bonded to each surface of the membrane as uniformly as possible, there are cases where it is better to bond them preferentially to the pore surfaces of the membrane.

The amount of functional groups in the present invention is porosity 1! It refers to the milliequivalent per Ig, and here 1 g of membrane is a value based on the fairly macroscopic weight of the membrane, for example, when only a part of the membrane surface or a part of the inside is taken out. It's not about weight. In order to bond functional groups while maintaining the membrane's excellent mechanical properties, it is necessary to bind the functional groups as uniformly as possible to the surface of the membrane's pores.
Since it is preferable to have functional groups present more preferentially, partial heterogeneity is naturally allowed. Therefore, the meaning of 1 g of membrane here indicates the value measured evenly over the entire surface of the membrane, and does not mean the weight from a microscopic viewpoint.

The role of the porous membrane having chelate groups in the present invention is very important.

In other words, when using a porous membrane having chelate-bonded side chains, it is possible to obtain ion removal properties that are much better than when using an ion exchange resin, and the amount of membrane used can be reduced, which makes it possible to reduce the amount of regenerated liquid. The amount required is dramatically smaller, and it can be completely recycled. This is a huge advantage in reducing the amount of eluted components.

Furthermore, the membrane having the chelate binding group has an incomparably small pore diameter compared to ion exchange resins (resins have a diameter of several tens of microns to 100 microns, while membranes have a diameter of 5 microns or less).
There will be less leakage of precepts.

Next, the present invention will be explained below with reference to Examples, but these are not intended to limit the present invention.

(Example) Example and Comparative Example Cation Star League Fine Powder Nipsil Silicate V N 3 LP ) 22.1
After premixing the composition of 55.0 parts by weight, 55.0 parts by weight of dibutyl phthalate (DBP), and 23.0 parts by weight of polyethylene resin powder (SH-800 grade manufactured by Asahi Kaei),
0mm twin screw extruder with inner diameter of 0.7am and thickness of 0.25mm
After extruding into a hollow fiber shape, 1.1. 1-}Immersed in dichloroethane [Chlorocene VG (trade name)] for 60 minutes to extract DBP.Furthermore, immersed in a 40% aqueous solution of caustic soda at a temperature of 60°C for about 20 minutes to extract a small amount of silicic acid. After that, it was washed with water and dried.The obtained porous film was subjected to an electron accelerator (pressure voltage 1.5
100κ under nitrogen atmosphere using electron beam current 1 mA)
After electron beam irradiation with cy, glycidyl methacrylate (glycidyl methacrylate) was almost completely grafted in the gas phase and washed and dried.

The amount of glycidyl methacrylate added was 1 g per gram of il (7.0 ξ equivalents). (By gravimetric method) Next, this graft membrane was immersed in a 0.4 mol/l aqueous solution of sodium iminodiacetate in which p}I was adjusted to 12 with sodium carbonate, and reacted at 80°C for 24 hours. A multifunctional membrane was obtained in which the ξ-nodiacetic acid groups contained 1.7 -ii lmol (11 lmol per 3.4 mmol) of chelate-form groups per gram of membrane.

The quantitative determination of ξinodiacetic acid groups was calculated using two methods: gravimetric method and cobalt adsorption equilibrium method. Next, 2000 ppm of boric acid as the raw water to be tested,
LiO. 2 ppm, NiO. 5ppa
When the membrane was immersed in a large amount of water containing 0.5 ppm of Co, and the adsorption equilibrium of Ni and Co adsorbed on the membrane was measured, the adsorption amount of Ni was 0.4 mol/kg of the membrane and Co.
The amount of adsorption is 0.05 woI! ．． /kg membrane, and the ratio was approximately 8:1. Next, 3000 ppm of boric acid
, The following raw water was prepared without changing Li 0.2 ppm.

Ni concentration (ppm) 0.5 0.9 Co concentration (ppm) 0.5 0.1 (The ion concentration was measured by Walley-Hares atomic absorption spectrometry. The same applies hereinafter).

When the water was applied to the membrane at a differential pressure of 1 kg, the following removal performance was obtained.

Ni removal level near Ni breakthrough point 1 ppb or less Furnace overcapacity 4.7 ffi/1 m graph}Ni adsorption to membrane near Ni breakthrough point 12.3-ii gram/1
m-graft membrane CO? ! Co removal level near the limit 1 ppb or less Overcapacity 3.6 1/1+s Graft film
Amount of Co adsorbed to the membrane: 1.8 mg/lm Graft membrane Co removal level at Ni breakthrough point: 0.2 (concentration in reactor water/concentration in raw water) Ni concentration in water/concentration in raw water reached 0.25 C of time
o Removal level 0.9 The above result shows that even though the reactivity ratio of Ni and Co is 8:1, the adsorption amount ratio of Ni and Co is 2.3:1 at the time when the breakthrough point of Ni is reached. 7, which is an extremely small difference.

On the other hand, beyond the breakthrough point of Ni, the adsorption efficiency of Co drops extremely, and after a 30% increase, Co is no longer removed.

Equilibrium adsorption ratio of Ni and Co 29/l Ni removal level near the Ni breakthrough point 1 ppb or less Finished excess capacity 5.2 1/l m Graft membrane //
Ni adsorption M4.0 mg/lm Graft membrane Co removal level near CO breakthrough point lρpb or less
Furnace overcapacity 4,9 Il/l m Graft membrane CO adsorption amount 0.4 mg/lm Graft membrane CO removal level near Ni breakthrough point 0.3 (concentration in finished water/concentration in raw water) Concentration of Ni in water / Co removal level when the raw water concentration reaches 0.15 1.05 (Concentration in reactor water / Concentration in raw water) The above data is based on Ni / C, o O. 5/0.
The result is almost the same as in case 5.

〔Effect of the invention〕

The present invention is capable of efficiently removing ions with relatively low reactivity among multiple types of heavy metals, and is particularly suitable for the treatment of radioactive waste liquid using Go ions during nuclear power generation.

Claims (2)

[Claims] (1) A porous membrane that has a chelate group in its side chain that binds multiple types of heavy metal ions in water, and the ion concentration of the heavy metal that has the highest adsorption equilibrium with the chelate group is 1/10 or less of the initial concentration. A method for simultaneously removing multiple heavy metal ions characterized by filtering until (2) Some of the multiple types of heavy metal ions in water are nickel and cobalt, and the porous membrane has an average pore size of 0.0 with iminodiacetic acid groups in the side chain of 3 milliequivalents or more per gram of membrane.
The method for simultaneously removing a plurality of heavy metal ions according to claim (1), wherein the hollow fiber porous membrane has a porosity of 1 to 5 μm, a porosity of 20 to 90%, and a thickness of 10 μ to 5 mm.