JPS62201604A - Method for removing cobalt ion - Google Patents

Abstract

PURPOSE:To simultaneously remove cobalt ion and colloidal substance in waste water by passing the radioactive waste water through a porous membrane obtained by grafting a carboxyl group-contg. side chain on a specified substrate membrane. CONSTITUTION:An electron beam is irradiated on the substrate membrane consisting of polyolefin such as polyethylene or the copolymer of an olefin and a halogenated olefin or polyvinylidene fluoride, the membrane is dipped in a carboxyl group-contg. monomer such as acrylic acid, and a porous membrane having a carboxyl group-contg. side chain is obtained by grafting. Radioactive waste water is passed through the porous membrane thus obtained to adsorb and remove cobalt ion in the radioactive waste water and simultaneously to remove a colloidal substance such as a clad.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention extracts multiple metal ions, such as iron and cobalt ions, which are simultaneously present in small amounts in the wastewater, from radioactive wastewater generated in nuclear power generation facilities and general industrial wastewater. At the same time, colloidal substances in wastewater are filtered and purified.

[Conventional technology]

Conventionally, various metal ions present in radioactive wastewater generated by nuclear power generation facilities have been removed using ion exchange resins, etc., and purified and processed through various semipermeable or porous membranes as necessary. Ta.

These treatment methods generally require a large amount of ion exchange resin, have a relatively short lifespan, and have problems such as disposal after use.

In particular, cobalt ions are removed relatively inefficiently, and therefore a large amount of resin is required for treatment, which poses problems both economically and in terms of pollution prevention. Various methods have been taken to overcome these problems, but it is difficult for any of these methods to have both the function of adsorbing ions and the function of removing particulates from wastewater, and it is difficult to completely overcome the above problems. Things were difficult.

[Problems to be solved by the present invention]

The present invention adsorbs and removes cobalt ions in radioactive wastewater, simultaneously removes colloidal substances such as crud through a porous membrane, efficiently purifies the wastewater, and at the same time performs a regeneration operation of the porous membrane so that it can be used repeatedly. The purpose is to make this possible and to minimize the amount of waste to be disposed of.

[Means for solving problems]

The inventors of the present invention have conducted intensive research on means for achieving the above object, and have found that the object can be achieved by the following means.

That is, radioactive Ji water is passed through a porous membrane in which side chains containing carboxyl groups are grafted onto a base membrane of polyolefin, a copolymer of olefin and halogenated olefin, or polyvinylidene fluoride, and cobalt ions and It has been found that the objective can be achieved extremely effectively by removing and purifying colloidal substances at the same time.

The present invention will be explained in more detail below.

The membrane to be grafted in the present invention must be a hydrophobic porous membrane made of polyolefin, olefin and halogenated olefin copolymer, polyvinylidene fluoride, etc., and must have the mechanical properties necessary as a base membrane. Helps with retention.

Specific examples of the above-mentioned polyolefins, olefin and halogenated olefin copolymers include polyolefin resins such as polyethylene, polypropylene, polybutylene or mixtures of two or more of the above, or ethylene,
A copolymer made of a mixture of two or more of propylene, butene, hexene, tetrafluoroethylene, chlorotrifluoroethylene, or a resin for polyvinylidene fluoride is used.

Next, acrylic acid and methacrylic acid are common examples of carboxyl group-containing monomers that are grafted onto these base films.

Further, the content of carboxyl groups to be grafted is preferably 0.1 to 5 milliequivalents per gram of the porous membrane.

Here, 1 gram of membrane is a value based on the macroscopic weight of the membrane, for example, 1 part of the membrane surface or 1 gram of the inside.
It's not just the weight taken out. In order to carry out the carboxylation treatment while maintaining the excellent mechanical properties of the base membrane, it is easier to achieve the objective by preferentially grafting the graft onto the surface of the pores as much as possible.

Therefore, the meaning of 1 gram of the base film mentioned here indicates the value measured evenly over the entire surface of the film, and does not mean the weight from a microscopic viewpoint.

The porous membrane grafted according to the present invention preferably has an average pore diameter in the range of 0.01 μm to 5 μm in terms of cobalt ion adsorption, colloidal substance removal performance, and permeation rate. The average pore size here refers to the value obtained by the method described in ASTM F316-70, which is usually called the air flow method, and measures the air permeation flux through dry membranes and wet membranes by changing the air pressure. It is calculated from that ratio.

The range of the average pore diameter in the present invention is determined from the viewpoint of practical performance, and any other range is inappropriate in terms of permeation rate, mold removal effect, etc.

Next, the porosity of the porous membrane obtained by the present invention is preferably in the range of 20 to 80%. 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.

When the porosity is outside the range of the present invention, the permeation rate and
Unfavorable in terms of mechanical properties, etc.

The pore structure of the base membrane, which is the base of the porous membrane obtained in the present invention, can be obtained by various molding processes.

Specifically, the so-called stretching method and the etching method created by chemical treatment after electron beam irradiation are also applicable, but the pore structure is straight through-holes obtained by the stretching method or etching method. Rather than the pore structure, for example, Japanese Patent Publication No. 59-37292
Publication No. 40-957 and Special Publication No. 47-
Those having a three-dimensional network structure formed by the microphase separation method, mixed extraction method, etc. disclosed in Japanese Patent No. 17460 are preferred. In particular, with the establishment of the manufacturing technology for structures disclosed in JP-A No. 55-131028, the significance of the present invention has become clearer, and the manufacturing of materials with excellent performance that cannot be obtained with conventional techniques has become clear. method was able to be achieved.

The shape of the porous membrane can be flat membrane, tube, or hollow fiber membrane, but for the purpose of the present invention, an inner diameter of 0.
A hollow fiber type having a shape of 1 to 10 mm and a thickness of 0.05 to 5 mm is preferable.

The method of grafting the carboxyl group-containing side chain of the present invention onto the base film includes methods such as photochemical treatment, as known from Japanese Patent Publication No. 52-47538 and Japanese Unexamined Patent Publication No. 55-21833. However, the most effective method is to irradiate the base film with ionizing radiation.

In this method, the base film is less likely to be chemically degraded and free polymer is less likely to be produced. In addition, the porous membrane produced in this way has excellent mechanical and chemical properties.
Good filterability as well. The ionizing radiation used is alpha rays,
Examples include β-rays, γ-rays, accelerated electron beams, and X-rays, but electron beams or γ-rays are practically preferred. There are two methods for graft polymerization: a simultaneous irradiation method in which radiation is irradiated while the porous substrate and the monomer coexist, and graft polymerization occurs, and a simultaneous irradiation method in which only the porous substrate is irradiated with radiation in advance, and then the monomer is applied to the porous substrate. There is a pre-irradiation method in which graft polymerization is carried out by catalytic reaction, but in the simultaneous irradiation method, the graft polymerization of the monomer to the porous substrate progresses, and at the same time, only the monomers that do not participate in the graft polymerization are homopolymerized, and the porous substrate The pre-irradiation method is preferred because of the problem of blocking the pores.

In the pre-irradiation method, the base material is irradiated with radiation before contacting the monomer with the porous base material, and the temperature is kept below -1θ°C until it comes into contact with the monomer, and below 50°C, preferably between 15°C and 50°C. Graft polymerization is carried out by contacting with monomers at a low temperature of ℃.

If the porous substrate is not stored at a low temperature after irradiation with radiation, the generated radicals will rapidly decay, and the number will be halved after 30 minutes at room temperature (25° C.). Furthermore, at the same time, the generated radicals react with a trace amount of adsorbed oxygen, resulting in a defect that impairs the heat and chemical resistance of the target substance. Furthermore, if the graft polymerization temperature exceeds 60°C, a homopolymer of monomers that do not participate in the graft polymerization will be generated, which may block the pores of the porous base material, or a homopolymer of monomers that will not be extracted in the post-treatment process after the reaction. The polymer flows out after becoming hydrophilic.2
Problems arise, such as causing secondary pollution.

Hereinafter, the structure and effects of the present invention will be specifically described with reference to Examples, but these are not intended to limit the present invention.

Examples and Comparative Examples A composition of 23.1 parts by weight of Psil vN3LP), 55.4 parts by weight of dioctyl phthalate (DOP), and 21.5 parts by weight of polyethylene resin powder (Asahi Kasei 5H-800 grade) was premixed with finely powdered silicic acid. After that, it was extruded using a 30 mm twin-screw extruder into hollow fibers with an inner diameter of 0.7 fins and a thickness of 0.25 fins.
(trade name)] for 60 minutes to extract DOP. The sample was further immersed in a 40% aqueous solution of caustic soda at a temperature of 60° C. for about 20 minutes to extract the fine powder of silicic acid, followed by washing with water and drying.

The obtained porous membrane was subjected to an electron accelerator (pressure voltage 1.5 MeV,
100KG under nitrogen atmosphere using electron beam current 1mA)
After irradiating with an electron beam at y, the dissolved oxygen was reduced to 0,
It was immersed in acrylic acid adjusted to 1 ppn+ or less and grafted to obtain a membrane (example membrane) with an average pore diameter of 0.15 μ, a porosity of 62%, and a membrane of 2.5 milliequivalents of carboxyl groups/1 gram of membrane.

For comparison, an untreated polyethylene hollow fiber membrane extruded and extracted under the same conditions as in the example was sulfonated in the same manner as in Example 6 of JP-A No. 56-57836 to remove sulfone groups. .5 meq/g membrane (average pore size 0.5 meq/g membrane)
A comparative example membrane (A) having a diameter of 16 μm and a porosity of 65% was obtained.

Furthermore, after extracting DOP and silicic anhydride from the example membrane, the untreated membrane was used as a comparative example membrane (B) in the following experiment.

Note that the carboxyl groups in the Example membrane and the sulfone groups in the Comparative Example membrane were determined as follows.

[Quantification of carboxyl group]

After washing the graft-irradiated porous membrane with alkaline water,
After repeating water washing many times and confirming that there was no weight loss due to water washing after drying, the carboxyl group content was calculated backward from the weight difference between the dried film and the base film. In addition, before use, it was made into H type with hydrochloric acid.

[Quantification of sulfone group]

The sulfonated porous membrane was immersed in IN HCffi ag to form H type, washed with water, and then immersed in IN CaCj!
, ag, and immerse the liberated HCl in 0. IN
Titration was carried out using NaOHag and phenolphthalein as an indicator.

Before conducting the filtration test, the maximum adsorption amounts of the three types of membranes were measured and the results shown below were obtained. The cobalt ion concentration in the liquid used for adsorption was 2 mmol/l, and the pH of the liquid was adjusted to 5.5. The amount of cobalt adsorption was measured by atomic absorption spectrometry.

Margin Table 1 below: The above table clearly shows that carboxyl groups adsorb cobalt ions with maximum efficiency.

Next, an actual filtration test was conducted using the model liquid used in the test in Table 1, and the results shown in Table 2 below were obtained. The properties of the stock solution are shown below.

[Standard liquid properties]

Concentration of fine particles in stock solution 1) 2 x 104 ke/c, c Bacterial concentration t) 10'' ke/c, c Cobalt ion concentration = a> 1.B mmol/11) 0.2
2) Values directly measured using a microscope after staining with a μ polycarbonate flat membrane 3) Measured values using atomic absorption method Table 2 Particulate removal rate 99.5 99,4 99. 0
(%) As shown in Table 2, the cobalt ion removal method of the present invention has excellent properties in addition to its excellent ability to remove fine particles.

In addition, after conducting a filtration test for the example shown in Table 2 for about 5 hours, after regenerating it by immersing it in a strong hydrochloric acid solution, we measured the cobalt ion removal rate again. The retention rate was approximately 95%.

[Effects of the present invention]

The present invention has made it possible to efficiently remove cobalt ions and particulates at the same time, which has been considered difficult in the past, and has made a significant contribution to the purification and effective use of nuclear power-related wastewater.

Claims (2)

[Claims] (1) When removing and purifying cobalt ions in radioactive wastewater, a porous membrane in which side chains containing carboxyl groups are grafted onto a base film made of polyolefin, olefin and halogenated olefin copolymer, or polyvinylidene fluoride A method of passing the wastewater through a membrane to adsorb and remove cobalt ions and simultaneously removing colloidal substances in the wastewater. (2) The pore structure of the porous membrane is substantially a three-dimensional network structure, with an average pore diameter of 0.01μ to 5μ and a porosity of 20 to 80%. the method of.