Akio Katakai

Aquaculture of Uranium in Seawater by a Fabric-Adsorbent Submerged System

Abstract The total amount of uranium dissolved in seawater at a uniform concentration of 3 mg U/m3 in the world’s oceans is 4.5 billion tons. An adsorption method using polymeric adsorbents capable of specifically recovering uranium from seawater is reported to be economically feasible. A uranium-specific nonwoven fabric was used as the adsorbent packed in an adsorption cage 16 m2 in cross-sectional area and 16 cm in height. We submerged three adsorption cages in the Pacific Ocean at a depth of 20 m at 7 km offshore of Japan. The three adsorption cages consisted of stacks of 52 000 sheets of the uranium-specific non-woven fabric with a total mass of 350 kg. The total amount of uranium recovered by the nonwoven fabric was >1 kg in terms of yellow cake during a total submersion time of 240 days in the ocean.

Preparation of hydrophilic amidoxime fibers by cografting acrylonitrile and methacrylic acid from an optimized monomer composition

Abstract To improve the adsorption rate of uranium from seawater, hydrophilic amidoxime (AO) fibers were prepared by cografting of methacrylic acid (MAA) with acrylonitrile (AN) onto polypropylene fibers and subsequent conversion of the produced cyano group to an amidoxime group by reaction with hydroxylamine. An optimum amidoximation time of 0.75 h was selected at a weight ratio of AN to MAA (x/y) of 80/20. By varying x/y in the monomer mixture, cografted polymers were prepared. The value of x/y governed the AO group density and water content of the resultant fibrous adsorbents. As x/y increased, the AO group density of the fiber increased and its water content decreased. The AO/MAA adsorbent, based on the PP fibers prepared by cografting at an x/y of 60/40 and subsequent amidoximation, exhibited the highest uranium adsorption rate in the flow-through mode.

A New Type of Amidoxime-Group-Containing Adsorbent for the Recovery of Uranium from Seawater

Abstract A new type of adsorbent containing amidoxime groups for the recovery of uranium from seawater was synthesized by the radiation-induced graft polymerization of acrylonitrile onto polymeric fiber followed by amidoximation with hydroxylamine. When amidoxime groups were introduced superficially on the fiber, the amount of uranium adsorbed by the amidoxime groups was higher than that with the amidoxime groups introduced homogeneously in the fiber. The introduction of the poly(acrylic acid) chain and the increase in temperature and flow rate in the adsorption process were effective in increasing the amount of adsorbed uranium. Although alkali metals and alkaline earth metals were found in the adsorbent, the concentration factors for these metals were less than 1/103 of that for uranium. The present adsorbent had a high stability to various treatments such as contact with alkali and seawater.

A New Type of Amidoxime-Group-Containing Adsorbent for the Recovery of Uranium from Seawater. III. Recycle Use of Adsorbent

Abstract An amidoxime-group-containing adsorbent for recovering uranium from seawater was made by radiation-induced graft polymerization of acrylonitrile onto polymeric fiber, followed by amidoximation. Uranium adsorption of the adsorbent contacted with seawater in a column increased with the increase in flow rate, then leveled off. The relationship between uranium adsorption in a batch process and the ratio of the amount of seawater to that of adsorbent was found to be effective in evaluating adsorbent contacted with any amount of seawater. The conditioning of the adsorbent with an alkaline solution at higher temperature (80°C) after the acid desorption recovered the adsorption ability to the original level. This made it possible to apply the adsorbent to recycle use. On the other hand, the adsorbent conditioned at room temperature or that without conditioning lost adsorption ability during recycle use. The increase in water uptake was observed as one of the physical changes produced during recycle use o...

Fine Fibrous Amidoxime Adsorbent Synthesized by Grafting and Uranium Adsorption–Elution Cyclic Test with Seawater

Abstract Fibrous amidoxime adsorbents were prepared by radiation‐induced co‐grafting of acrylonitrile (AN) and methacrylic acid (MAA) and subsequent amidoximation. Adsorption of uranium in seawater was evaluated by pumping seawater into the adsorbent column. The best monomer ratio of AN and MAA was 7:3 for continual usage of uranium adsorption. Though hydrochloric acid is an effective eluting agent for the metals adsorbed on the adsorbent, amidoxime groups were simultaneously damaged after five cycles of adsorption–desorption. This deterioration was reduced by an alkaline treatment of the adsorbents after each elution. Furthermore, various organic acids were examined as elution agents. It was found that the 80% of adsorption activity was still maintained after five cycles of adsorption–desorption when tartaric acid was used for eluting agent.

A New Type of Amidoxime-Group-Containing Adsorbent for the Recovery of Uranium from Seawater. II. Effect of Grafting of Hydrophilic Monomers

Abstract A fibrous adsorbent containing amidoxime groups (AOF) for recovering uranium from seawater was synthesized by the radiation-induced grafting of acrylonitrile (AN) to a fiber followed by the amidoximation of cyano groups of poly(AN) graft chains. When such hydrophilic monomers as N, N-dimethyl-acrylamide (DMAAm) and acrylic acid (AAc) were preliminarily grafted, both the water uptake and the mobility of the sorbed water in AOF were improved in the order: AOF-containing poly-(DMAAm) graft chains (AOF-DMAAm) > AOF-containing poly(AAc) graft chains (AOF-AAc) > AOF without hydrophilic graft chains. The uranium uptake with these adsorbents was, on the other hand, in the order: AOF-AAc > AOF-DMAAm > AOF. The adsorption of alkaline earths was related to the distribution pattern of poly(AAc) graft chains inside the fiber. The adsorbed alkaline earths were eliminated from the adsorbent fiber by introducing a solution of heavy metal ions such as Cu2+.

Effect of Shape and Size of Amidoxime-Group-Containing Adsorbent on the Recovery of Uranium from Seawater

Abstract An amidoxime-group-containing adsorbent for the recovery of uranium from seawater was synthesized by radiation-induced graft polymerization of acrylonitrile onto polypropylene fiber of round and cross-shaped sections. The tensile strength and elongation of the synthesized adsorbent, both of which were one-half those of the raw material, were not affected by the shape of the fiber. The deterioration of the adsorption ability induced by immersing the adsorbent in HC1 was negligible because of the short immersion time required for the desorption with HC1. The concentration factors for uranium and transition metals in 28 days were in the order of 105, while those for alkali metals and alkaline earth metals were in the order 10−1-101. The recovery of uranium with the cross-shaped adsorbent was superior to that of the round-shaped one. XMA line profiles show that the distribution of uranium is much restricted to the surface layer when compared with that of alkaline earth metals. Diminishing the diamete...

Preparation of amidoxime-fiber adsorbents by radiation-induced grafting

The fibrous adsorbents containing amidoxime groups were synthesized by radiation-induced graft polymerization of acrylonitrile onto polypropylene fibers, followed by functionalization of cyano groups to amidoxime groups with hydroxylamine. The polypropylene-based fibrous adsorbents exhibited a high grafting rate. The adsorption tests proved the performance of these fibrous adsorbents as a promising material for uranium recovery from seawater.

Complex-forming polymer prepared by electron beam radiation-induced graft polymerization

Abstract In order to prepare a complex-forming polymer useful as a selective adsorbent, radiation-induced graft polymerization of acrylonitrile onto a fibrous tetrafluoroethylene ethylene copolymer has been studied by using preirradiation method. The resulting grafted fibers were treated with 3% hydroxylamine alcohol-water solution, followed by controlling in alkali solution. The adsorbents containing amidoxime are able to take up transition metal ions from neutral and weakly acidic solutions while not sorbing the ions of alkaline and alkaline earth metals to any significant extent. It was shown that by introducing a small amount of hydrophilic groups to the fiber, it was possible to increase the exchange rate between the external water and the internal water interacted with functional groups in polymer matrix and to induce the diffusion of hydrated metal ions. The efficiency for adsorption of transition metal ions was successfully improved either by adding small amount of hydrophilic part composed of poly(acrylic acid) or by restricting the distribution of amidoxime groups at the fiber surface. A high stability of this adsorbents to various treatments ( alkali treatment at 80° C, contact with seawater for 24 h at 30° C, etc.) was confirmed. Its applicability to the recovery of uranium from seawater is demonstrated by laboratory scale experiments.

Use of Amidoxime-Group-Containing Adsorbent for the Recovery of Uranium and Other Elements from Phosphoric Acid Solution

Abstract An amidoxime-group-containing fibrous adsorbent which was made by the radiation-induced grafting of acrylonitrile onto a synthetic fiber was applied to the recovery of uranium and other elements (V, Ti, Fe, etc.) from phosphoric acid solution of a fertilizer plant. The adsorption amount of these elements increased in proportion to the concentration of amidoxime groups introduced in the adsorbent. The distribution of the metals adsorbed in 24 h was homogeneous in the adsorbent containing more than 4.9 meq/g amidoxime groups while it was limited to the surface region of the adsorbent containing 1.5 meq/g amidoxime groups. The rise in the pH of the solution brought about by adding sodium hydroxide produced a maximum amount of adsorption at pH = 3. The concentration factors for U, V, Ti, and Fe were 2.8 × 102, 8.6 × 103, 4.2 × 103, and 6.1 × 102, respectively.