JPH0321390A - Removal of heavy metal ion in water - Google Patents

Abstract

PURPOSE:To efficiently remove heavy metal ions and colloidal substances in water simultaneously by adsorbing and collecting heavy metal ions such as Ni, Co or the like and colloidal substances dissolved in a very small amount in water treatment technique by using a specific porous membrane and holding pH to 3 or more. CONSTITUTION:In simultaneously removing heavy metal ions and colloidal substances contained in water or waste water in various fields of precise electronics, medical treatment, pharmacy or pressurized water atomic power generation, treatment is performed by employing a porous membrane having a chelate group bonding heavy metal ions in its side chain and holding pH of water to be treated to 3 or more. This removing method is especially pref. when the heavy metal ions of water to be treated are nickel and cobalt ions and the porous membrane is composed of a hollow yarn like porous membrane having an iminodiacetate group contained in its side chain in an amount of 3 miliequivalent per/1g of a base membrane or more, an average pore size of 0.01-5mum, a void ratio of 20-90% and a thickness of 10mum-5mm. This method can largely contribute to the purification and effective utilization of waste water related to atomic power.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is intended to reduce heavy metal ions and colloidal substances contained in industrial wastewater in various fields such as precision electronics, medicine, pharmaceuticals, and nuclear power generation such as pressurized water type. At the same time, this is an efficient method for removing.

(Conventional Technology) In conventional water treatment technology, colloidal particles, bacterial cells, and the like are removed in advance using a microfilter or cake filtration, and then dissolved metal ions are removed using an ion exchange resin or the like. These treatment methods are complicated to operate, require a large amount of ion exchange resin, have a relatively short lifespan, and have problems such as disposal of the used resin. Studies have been underway to introduce ion exchange groups into micro membranes, but it has been difficult to completely overcome the above-mentioned problems because the ion collection performance deteriorates in low concentration regions.

(Problems to be Solved by the Invention) The present invention aims to efficiently remove trace amounts of heavy metal ions such as nickel and cobalt and colloidal substances dissolved in water treatment technology by adsorption and collection.

(Means for Solving the Problems) In order to achieve the above object, the inventors of the present invention have made extensive studies and have arrived at the following invention.

In other words, when removing heavy metal ions from water,
Trace amounts of heavy metal ions and colloidal substances in the treated water are simultaneously removed by raising the pH of the treated water to 3 or higher, preferably 7 or higher, and using a porous membrane that has a chelate group in its side chain that binds to the heavy metal ions. This is the way to do it.

Furthermore, per 1 gram of the base membrane, the side chain contains 3 milliequivalents or more of iminodiacetic acid groups, and the average pore size is 0. Olμm～5μm
1 Porosity 20%~90%, film thickness 10μm~5Inff+
This method uses a hollow fiber porous membrane to remove nickel and cobalt from treated water.

Next, the present invention will be specifically explained.

Specifically, the heavy metal ions are iron, copper, cobalt, nickel, etc., and the colloidal substances are water-insoluble components such as metal component cladding, polymeric organic matter, and bacteria.

A porous base membrane is a base membrane that has not undergone any chemical modification.

Preferred examples of the chelate group that binds to heavy metals used in the present invention include iminodiacetic acid and the like.

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 hollow fiber porous membrane in which a functional group having a chelate group is chemically bonded to the inner and outer surfaces of the porous membrane and at least a portion of the surface of the pores. The bond may be direct or may be bonded 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 at least a portion or the entire surface of both the inside and outside surfaces of the membrane and the pores are covered with a functional material having a chelate group. It is preferable to carry out treatment and purification using a hollow fiber porous membrane to which a polymer having groups or functional groups is chemically bonded.

This functional group must contain 3 milliequivalents or more of chelate groups per gram of base film.

Below this range, the ion removal ability of the membrane decreases. Note that the milliequivalent here is a value per functional group, and for example, 1 mmol of iminodiacetic acid is 2 milliequivalent. The average pore size of the porous membrane is in the range of 0.01 μm to 5 μm, preferably
0. It is selected from the range of 1 μm to 1 μm. If it is smaller than this range, the water permeability will not be sufficient for practical performance, and if it is larger than this, problems will arise in terms of ion removal.

There are many methods for measuring the average pore diameter, but in the present invention, we use the air permeation method between dry and wet membranes when changing the air pressure, which is usually called the air flow method, which is described in ASTM F-316-70. Conforms to the method of measuring from flux.

The porosity of the porous membrane is 20% to 90%, preferably 50%
~80% is used.

Here, the porosity is measured by immersing the membrane in a liquid such as water in advance, then drying it, and measuring the weight change before and after that. Porosity values outside the above range are unfavorable in terms of permeation rate and mechanical properties.

The shape of the porous membrane may be a flat membrane (including pleats or spirals), a tube, or a hollow fiber, with hollow fibers being particularly preferred.

The pore structure of the porous membrane serving as the base material can be formed in various ways using shaping methods. 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 made using a solvent, etc., and then it is discharged from a nozzle in the form of a hollow fiber and shaped with a coagulant, etc. can do. In the case of polyolefin, it is possible to make a porous membrane by a stretching method or a so-called etching method, which is made by chemical treatment after electron beam irradiation. For example, rather than a hole-through type hole structure,
The practical performance of those having a three-dimensional network structure formed by the micro phase separation method, mixed extraction method, etc. shown in Japanese Patent Publication No. 9 2, Japanese Patent Publication No. 40-95-7, and Japanese Patent Publication No. 47-17460 It is preferable.

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 can be used to introduce a functional group having a chelate group into the side chain of the polymer constituting the porous membrane. For example, a method for introducing iminodiacetic acid into the side chain of polyethylene is to irradiate a polyethylene film with an electron beam or the like, perform a graft reaction with glycidyl methacrylate in the gas phase, and then add iminodiacetic acid using a known method. Be taken.

In order to introduce the functional group into the side chain of the polymer constituting the porous membrane, it can be introduced before forming it into a membrane.
A preferred method is to form the membrane into a membrane and then chemically attach it to at least a portion of the inner and outer surfaces of the membrane and the surface of the pores. Although it is desirable that the functional groups are bonded to each surface of the membrane as uniformly as possible, it may be preferentially bonded to the pore surfaces of the membrane in some cases.

In the present invention, the amount of functional groups refers to milliequivalents per gram of porous base membrane, and 1 gram of membrane here refers to a value based on the rather macroscopic weight of the membrane, for example:
It does not refer to the weight of only a part of the membrane surface or the inside. In order to bond functional groups while maintaining the membrane's excellent mechanical properties, it is preferable to make the functional groups exist as uniformly and preferentially as possible on the surface of the pores of the membrane. Homogeneity is acceptable. 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 an extremely microscopic viewpoint.

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

That is, when using the above-mentioned porous membrane having a chelate group in its side chain, not only can colloidal substances be removed, but also far superior ion removal properties can be obtained compared to when using an ion exchange resin.

Furthermore, the amount of membrane used can be reduced, and above all, the amount of regenerating liquid can be dramatically reduced, and the regeneration process can be completed completely. This is a huge advantage in reducing the amount of eluted components.

Furthermore, the aforementioned membranes with chelate groups have incomparably smaller pore diameters than ion exchange resins (resin's pore size is from several tens of microns to 100 microns, whereas membranes are less than 5 microns), so eluted components There is less leakage.

To adjust the pH to 3 or more, add an alkali metal hydroxide such as lithium.

(Example) Example and Comparative Example 1 22.1 parts by weight of Tansei black fine powder silicic acid (Nipsil VN3LP) containing a chelate group suitable for the present invention, 55.0 parts by weight of dibutyl phthalate (DBP), polyethylene After premixing a composition of 123.0 parts by weight of resin powder [manufactured by Asahi Kasei ■, SH-800 grade], it was extruded into a hollow fiber shape with an inner diameter of 7 mm and a thickness of 0.25 mm using a 30 mm twin screw extruder. DBP
was extracted. Further, it was immersed in a 40% aqueous solution of caustic soda at a temperature of 60° C. for about 20 minutes to extract fine powder silicic acid, followed by washing with water and drying.

An electron accelerator (pressure voltage 1.5 Mev) was applied to the obtained porous membrane.
, 100KG under nitrogen atmosphere using electron beam current 1mA)
After irradiation with an electron beam at y, glycidyl methacrylate was almost completely grafted in the gas phase, followed by washing and drying.

The amount of glycidyl methacrylate added was Ig (one amount per 20 mm) per tg of the base film. (Based on the gravimetric method.) Next, this graft membrane was immersed in a 0.4 mol 1/1 aqueous solution of sodium iminodiacetate whose pH was adjusted to 12 with sodium carbonate, and reacted at 80°C for 24 hours. group is 1.7 mmol (3.4
A multifunctional membrane with chelate-forming groups (milliequivalents) was obtained.

The quantitative determination of iminodiacetic acid groups was calculated using two methods: a gravimetric method and a cobalt adsorption equilibrium method.

For comparison, extrusion, DBP, and
The untreated membrane after extracting the fine silicic acid was used as a comparative example membrane.
It was used in the following experiments.

When the Example membrane and Comparative Example membrane obtained here were actually subjected to an overtest using the following model liquid, the results shown in Table 1 below were obtained. The properties of the stock solution are shown below.

[Standard liquid properties]

・Fine particle concentration in stock solution ++ 2×104 co/1・Cobalt ion concentration 2 1 1 p pm●pH
7 1) Value measured by direct microscopy using a 0.2 μm polycarbonate flat membrane 2) Value measured by atomic absorption method or less Margin Table-1 As shown in Table-1, the method for removing heavy metal ions in water of the present invention is as follows: In addition to its excellent particle removal properties, it also has excellent ion removal properties.

Example 2 Using a hollow fiber membrane having iminodiacetic acid groups obtained in the same manner as in Example 1, using the following model liquid,
When we actually conducted an overtest by changing the pH, we obtained the results shown in Table 2 below. The properties of the stock solution are shown below.

[Standard liquid properties]

・Fine particle concentration in the stock solution ++ 2Xl04 co/1 ・Cobalt ion concentration 2 1 1 p p m1) 0.2
Measured values by direct microscopy using a μm polycarbonate flat membrane 2) Measured values by atomic absorption method Table-2 As shown in Table-2, the method for removing heavy metal ions in water of the present invention has excellent fine particle removal properties. In addition, it has excellent ion removal properties when the pH of the treatment liquid is 3 or more, especially at pH 7 or more.

Example 3 Using a polypropylene microporous membrane (film thickness 100 μm, average pore diameter 0.1 μm) as a base material, in the same manner as in Example 1,
Perform a graft polymerization reaction of gucidyl methacrylate,
After that, as a result of immobilization reaction of iminodiacetic acid group,
The iminodiacetic acid group is 1.7 mmol (3
．． A composite functional membrane having a chelate group of 4 equivalents was obtained.

Using this flat membrane, at pH 7, a fine particle concentration of 2 x 10' co/
When an overtest was conducted using a model solution with a nickel ion concentration of 1 nl and a nickel ion concentration of 1 ppm, the nickel ion concentration of the overflow solution was 0. It was 0.02 ppm or less. Also,
The particle removal rate was 99.5%. As a result, the method for removing heavy metal ions in water of the present invention has excellent nickel ion removal properties in addition to its excellent ability to remove fine particles.

(Effects of the invention) The present invention makes it possible to simultaneously and efficiently remove heavy metal ions and colloidal substances from water, which has been considered difficult in the past, and can greatly contribute to the purification and effective use of nuclear wastewater. Became.

Claims (2)

[Claims] (1) When removing heavy metal ions from water, a porous membrane having a chelate group in its side chain that binds to the heavy metal ions is used to raise the pH of the treated water to 3 or more, and remove one or more heavy metals from the treated water. A novel heavy metal ion removal method characterized by simultaneous removal of ions and colloidal substances. (2) The heavy metal ions in the treated water are nickel and/or cobalt, the porous membrane contains iminodiacetic acid groups in the side chain of 3 milliequivalents or more per gram of the base membrane, has an average pore diameter of 0.01 μm to 5 μm, and has a void. Porosity 20% to 90%, film thickness 1
Claim (1) The membrane is a hollow fiber porous membrane having a diameter of 0 μm to 5 mm.
) Heavy metal ion removal method described.