Abstract: A method of adsorbing and separating a heavy metal element by using a tannin adsorbent comprising:(a) adjusting the pH of a solution containing a plurality of heavy metal elements to a predetermined pH;(b) contacting the adsorbent with the solution in which the pH thereof is adjusted;(c) adjusting the pH of the solution contacted with the adsorbent to a pH different from the predetermined pH; and(d) contacting the solution in which the pH thereof is adjusted at the step (d) with the adsorbent prepared at the step (a).According to the inventive method, all of the heavy metal elements can be efficiently separated and adsorbed by using a tannin adsorbent from a solution containing a number of heavy metal elements. A method of regenerating a tannin adsorbent are also disclosed.

Abstract: A method of adsorbing and separating a heavy metal element by using a tannin adsorbent comprising:(a) adjusting the pH of a solution containing a plurality of heavy metal elements to a predetermined pH;(b) contacting the adsorbent with the solution in which the pH thereof is adjusted;(c) adjusting the pH of the solution contacted with the adsorbent to a pH different from the predetermined pH; and(d) contacting the solution in which the pH thereof is adjusted at the step (d) with the adsorbent prepared at the step (a).According to the inventive method, all of the heavy metal elements can be efficiently separated and adsorbed by using a tannin adsorbent from a solution containing a number of heavy metal elements. A method of regenerating a tannin adsorbent are also disclosed.

Abstract: A method of estimating the crystal grain size of a nuclear fuel pellet. A plurality types of UO.sub.2 powders are heated at a predetermined temperature raising speed in dry air so as to measure weight change ratios occurring due to the oxidation of each of the UO.sub.2 powders. From a value at which the weight change ratio changes, a temperature at which the composition of the powder from the UO.sub.2+x phase to the U.sub.3 O.sub.7 phase is determined for each type of the powders. Sintered pellets are produced from the plurality types of UO.sub.2 powders in which the arrival temperatures are known. Crystal grain sizes of the plurality types of the sintered pellets produced are measured. According to the U.sub.3 O.sub.7 phase arrival temperature determined and the crystal grain size of the sintered pellet measured, a correlation between the both is recognized. A U.sub.3 O.sub.7 phase arrival temperature of a UO.sub.2 powder of a test sample is determined under the same conditions as described above.

Abstract: A metal element adsorbent in the form of a hydrogel prepared by treating a condensed tannin with a base, in the presence or absence of an aldehyde so as to avoid precipitation of cross-linked tannin and produce a hydrogel. The inventive adsorbent exhibits high adsorption properties for metal elements and a low flow resistivity when used in a packed column. Methods for use of the inventive adsorbent are disclosed.

Abstract: An insoluble hydrolysable tannin is prepared by dissolving a hydrolysable tannin powder in aqueous ammonia; mixing the resulting solution with an aldehyde aqueous solution to form a precipitate; heating the precipitate; mixing the heated precipitate with a mineral acid; and filtering the resulting mixture to leave a residue on a filter. The inventive insoluble tannin exhibits high adsorption properties for heavy metal elements and is insoluble in either water, acid, or alkali. Methods for treating waste liquids and recovering heavy metal elements therefrom using the inventive insoluble tannin are disclosed.

Abstract: An insoluble hydrolysable tannin is prepared by dissolving a hydrolysable tannin powder in aqueous ammonia; mixing the resulting solution with an aldehyde aqueous solution to form a precipitate; heating the precipitate; mixing the heated precipitate with a mineral acid; and filtering the resulting mixture to leave a residue on a filter. The inventive insoluble tannin exhibits high adsorption properties for heavy metal elements and is insoluble in either water, acid, or alkali. Methods for treating waste liquids and recovering heavy metal elements therefrom using the inventive insoluble tannin are disclosed.

Abstract: An insoluble hydrolysable tannin is prepared by dissolving a hydrolysable tannin powder in aqueous ammonia; mixing the resulting solution with an aldehyde aqueous solution to form a precipitate; heating the precipitate; mixing the heated precipitate with a mineral acid; and filtering the resulting mixture to leave a residue on a filter. The inventive insoluble tannin exhibits high adsorption properties for heavy metal elements and is insoluble in either water, acid, or alkali. Methods for treating waste liquids and recovering heavy metal elements therefrom using the inventive insoluble tannin are disclosed.

Abstract: Separation of hafnium tetrachloride from zirconium tetrachloride by introducing zirconium tetrachloride containing about 2-4 wt percent of hafnium tetrachloride into an electrolytic cell filled with a molten salt and dissolving it to make an electrolytic bath. Running first phase electrolysis which produces zirconium trichloride containing a lower hafnium content than the dissolved zirconium tetrachloride at the cathode. Running second phase electrolysis using the first cathode, but switching the first cathode to become an anode and using a second cathode. Producing zirconium trichloride of a lower hafnium content than the dissolved zirconium tetrachloride at the second cathode. Evolving a gaseous zirconium trichloride at the anode by electrolytic oxidation of the zirconium trichloride produced in the first phase electrolysis. Recovering this evolved zirconium tetrachloride which has a lower hafnium content than the dissolved zirconium tetrachloride and the zirconium trichloride produced at the cathodes.

Abstract: A process for separation of hafnium tetrachloride from zirconium tetrachloride and electrode is disclosed. Zirconium tetrachloride containing hafnium tetrachloride in natural ratio dissolved in a molten salt is reduced in the first phase electrolysis using an anode composed of a substance formed by firing a mixture of more than one kind of compound selected from the group consisting of silica, silicate containing zirconium or zirconium oxide and carbon with a binder under maintenance of an initial concentration of the zirconium tetrachloride in order to produce zirconium trichloride containing a hafnium content lower than that of the zirconium tetrachloride at a cathode.

Abstract: A process of separation of hafnium from zirconium by molten salt electrolysis in which zirconium tetrachloride with ordinary hafnium tetrachloride content is dissolved in a molten salt and the zirconium tetrachloride is electrolytically reduced to zirconium trichloride with lower hafnium content at a cathode in the molten salt and hafnium tetrachloride is remained. Next, the cathode on which the zirconium trichloride is formed by the cathode reaction is used as an anode. The electrolytic reduction of zirconium tetrachloride at another cathode in the molten salt is carried out and at the same time the zirconium trichloride formed on the anode is oxidized to zirconium tetrachloride with a low hafnium content and the zirconium tetrachloride is evaporated for separation. The obtained zirconium tetrachloride containing a low hafnium content is suitable for production of reactor grade zirconium containing about 100 ppm of hafnium.