Patent Number: 056132395
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method and apparatus for decomposing an organic solution composed of a chelating solution and/or an organic acid containing radioactive metal ions, and further to a method and apparatus for collecting radioactive metals using the same, which are used for removing, or decontaminating, the radioactivity of radioactive metals coming out of atomic power plants and the like. 2. Description of the Related Art In decomposing waste solutions disposed out of atomic power plants and the like, there have hitherto been raised problems of collecting radioactive metals by way of dissolution. For instance, machinery and equipment installed at an atomic power plant are exposed to and laden with radioactivity and hence are required to be decontaminated by removal of their surface layers. and this poses a problem of collecting the resultant radioactive metals by way of dissolution. The above problem can generally be coped with by removing the surface layers of the machinery and equipment by sand blasting or the like and by dissolving the resultant metals in an acid or the like to collect them. Here, the term "collect" can be taken as meaning "remove", and in the present invention is used including such meaning. The dissolution and collection steps can be conducted with an inorganic acid, an organic acid or a chelating solution. However, since an inorganic acid is rather dangerous to handle, a chelating solution or an organic acid is, or both are, usually used. However, a chelating solution or an organic acid to be used for dissolution and collection of radioactive metals has a problem of its post-treatment in view of its mass volume needed for such treatment. Because metals to be treated are laden with radiactivity, a chelating solution and/or an organic acid having such metals dissolved therein must be stored in safety and will reach a vast amount in quantity. This invites a social problem as to selection of locations at which to store such solution and acid, expansion of the existing locations, etc. A chelating solution or an organic acid containing radioactive metal ions needs to be cemented at the final stage, but all or most of such solution contains carboxyl group (COOH--) which would adversely affect the structural strength of mortar, rendering cement fixation unfeasible. In order to solve this problem, it is necessary to decompose a chelating solution and/or an organic acid in which radioactive metals have been contained, but any suitable method which would allow the decomposition step to be conducted in an efficient manner has not been found. Moreover, because of low ionizing degree, such chelating solution and/or organic acid is difficult to be electrolyzed or made by any similar treatment, leaving such kind of treatment beyond consideration. SUMMARY OF THE INVENTION With the foregoing problems of the prior art in view, the present invention provides a method and apparatus for decomposing an organic solution composed of a chelating solution and/or an organic acid containing radioactive metal ions, which make it available to quite remarkably decrease the mass volume of radioactive metals which are required to be stored after collection thereof by way of dissolution, and a method and apparatus for collecting radioactive metals using the same. The invention also provides a method and apparatus for collecting radioactive metals in efficient and effective manner using the same. More specifically, the invention provides a method for decomposing an organic solution containing radioactive metal ions, which comprises: forming a solution containing radioactive metal ions by applying a chelating solution and/or an organic acid to radioactive metals laden with radioactivity; adding an alkaline agent to the resultant solution to elevate electrical conductivity thereof; and electrolyzing the solution elevated in electrical conductivity with an electrolytic device. There is also provided a method for collecting radioactive metals by way of dissolution, which comprises: forming a solution containing radioactive metal ions by applying a solution composed of a chelating solution and/or an organic acid to radioactive metals laden with radioactivity; adding an alkaline agent to the resultant solution to elevate electrical conductivity thereof; electrolyzing the solution elevated in electrical conductivity to generate therein metal hydroxides which are little soluble in water; and filtering the electrolyzed solution to separate metal hydroxides from the filtrate. There is also provided a method for collecting radioactive metals by way of dissolution, which comprises: forming a solution containing radioactive metal ions by applying a solution composed of a chelating solution and/or an organic acid to radioactive metals laden with radioactivity; adding an alkaline agent to the resultant solution to elevate electrical conductivity thereof and to generate therein metal hydroxides which are little soluble in water; filtering the solution to separate the metal hydroxides as a filter cake from the filtrate; electrolyzing the filtrate to further generate therein metal hydroxides which are little soluble in water; and filtering the filtrate to further separate metal hydroxides as a filter cake from the filtrate. There is also provided a method for collecting radioactive metals by way of dissolution, wherein organic matter contained in the filtrate which is separated by filtration after electrolysis is further decomposed by an ultraviolet irradiator. There is also provided a method for collecting radioactive metals by way of dissolution, wherein the matter decomposed by ultraviolet irradiation is separated from the filtrate by reverse osmosis. There is also provided a method for collecting radioactive metals by way of dissolution, wherein the matter decomposed by ultraviolet irradiation is separated from the filtrate by use of ion-exchange resin. Further, there is also provided apparatus for decomposing an organic solution containing radioactive metals, which comprises: an electrical conduction tank in which an alkaline agent is fed to a solution composed of a chelating solution and/or an organic acid having dissolved therein radioactive metals laden with radioreactivity, to elevate electrical conductivity of the solution; and an elecrolytic device located at a later stage than the electrical conduction tank to electrolyze the solution elevated in electrical conductivity. There is also provided apparatus for collecting radioactive metals, which comprises: an electrical conduction tank in which an alkaline agent is fed to a solution composed of a chelating solution and/or an organic acid containing radioactive metals laden with radioactivity, to elevate electrical conductivity of the solution; an electrolytic device located at a later stage than the electrical conduction tank to electrolyze the metal solution elevated in electrical conductivity; and a filtration device positioned at a stage next to and communicating with the electrolytic device. There is also provided apparatus for collecting radioactive metals, wherein the filtration device is provided between the electrical conduction tank and the electrolytic device. There is also provided apparatus for collecting radioactive metals, wherein the filtration device is provided with an ultraviolet irradiation device having a separation device, at a later stage than the filtration device. There is also provided apparatus for collecting radioactive metals, wherein the separation device is of a reverse osmosis type. There is also provided apparatus for collecting radioactive metals, wherein the separation device is of an ion-exchange resin type.