Shunsaku Katoh

Recovery of Uranium from Seawater

Abstract Seawater contains various elements in solution. Deuterium, lithium, and uranium are the important ingredients for energy application at present and in the future. This paper deals with the recovery of uranium from seawater, with emphasis on the development of an adsorbent with high selectivity and rate of adsorption for uranium. Polyacrylamidoxime chelating resins were synthesized from various co-polymers of acrylonitrile and cross-linking agents. The resulting resins with the chelating amidoxime group showed selective adsorption for uranium in seawater. The amount of uranium adsorbed from seawater at room temperature reached 3.2 mg/g resin after 180 days. Polyacrylamidoxime fiber, which was prepared from polyacrylo-nitrile fiber and hydroxylamine, showed a high rate of adsorption for uranium. The polyacrylamidoxime fiber conditioned with 1 M HCl and 1 M NaOH adsorbed 4 mg U/g fiber from seawater in ten days.

Recovery of lithium from seawater by manganese oxide adsorbent

Abstract Ion-sieve (microporous) type manganese oxide (HMnO) was prepared by acid treatment of lithium-introduced manganese oxide which was obtained from γ-type manganese oxide and lithium hydroxide. The HMnO showed high selectivity for lithium ions in seawater. The maximum lithium uptake by the HMnO from seawater reached 7.8 mg/g which corresponded to a lithium content of 1.7% as Li2O. The adsorbed lithium could be easily eluted with 0.01 or 0.05 M hydrochloric acid solution. The adsorptive capacity for lithium ion scarcely changed during five repetitions of the adsorption-elution cycle. The column test was carried out by using granulated HMnO which was prepared with polyacrylic hydrazide as a binder.

Recovery of Lithium from Seawater Using a New Type of Ion-Sieve Adsorbent Based on MgMn2O4

Abstract A new type of ion-sieve manganese oxide, HMnO(Mg), was prepared by an acid treatment of MgMn2O4. The HMnO(Mg) showed a remarkably high selectivity for lithium ions among alkali metal and alkaline earth metal ions. The selectivity sequences were Na ≑ K ≪ Li for alkali metal ions and Mg ≤ Ca ≤ Sr ≤ Ba for alkaline earth metal ions at pH 8. The HMnO(Mg) showed a high selectivity for lithium ions in seawater. The lithium uptake increased with increasing solution pH and adsorption temperature. The maximum lithium uptake from native seawater reached 8.5 mg/g, corresponding to a lithium content of 1.8% in the form of Li2O. The adsorbed lithium could easily be eluted with a dilute acid solution. The adsorptive capacity for lithium ions gradually decreased through repeated adsorption/elution cycles. The HMnO(Mg) after 4 cycles showed a lithium adsorptivity which was about 60% of the initial value.

LITHIUM-ION SIEVE PROPERTY OF λ;-TYPE MANGANESE OXIDE

ABSTRACT The adsorptive properties of A-Mn02for mono and divalent metal ions were investigated by pH titration and by measurements of the distribution coefficients(Kds) of the metal ions. The pH titration curve showed an apparently monobasic acid type for a H+-Li+exchange. Those for H+-K+and H+-Cs+exchanges were nearly the same as that for blank titration. The lithium ion uptake increased with increasing solution pH and reached 5 meq/g at pH 11. X-ray diffraction analyses showed that the adsorption of lithium ions caused an increase in the lattice constant of a cubic unit cell. The potassium and cesium ion uptakes were nearly zero over a pH range between 4 and 11. A-Mn02showed a remarkably high Kd value for lithium ions, compared to a cation exchange resin. The selectivity sequences were Na+< K+< Rb+< Cs+<< Li+for alkali metal ions, Mg2+< Ca2+< Sr2+< Ba2+for alkaline earth metal ions, and Ni2+< Zn2+< Co2+< Cu2+for transition metal ions.

Electrochemical recovery of lithium ions in the aqueous phase

Abstract The electrochemical insertion of lithium ions into a Pt/λ-MnO2 electrode was investigated in various metal chloride solutions. The Li+ insertion occurred effectively in LiCl solutions with higher concentration than 10 mmol/dm3, but it could hardly occur in a 0.1 mmol/dm3 LiCl solution. Alkaline earth metal ions showed a stronger inhibition effect against the Li+ insertion into the Pt/λ-MnO2 electrode than alkali metal ions. However, since only Li+ ions were taken up from a mixed solution of lithium and alkaline earth metal chlorides, a high selectivity of the electrode for lithium ions was shown. It was possible to recover lithium ions from geothermal water by this electrochemical method using the Pt/λ-MnO2 electrode; the lithium uptake was 11 mg/g-MnO2.

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...

Binding Properties of a Polymer Having Amidoxime Groups with Proton and Metal Ions

Abstract The proton-binding behavior of a polymer having amidoxime groups was examined by the potentiometric titration method. Adsorptive properties of the polymer for UO2(VI), Mg(II), Fe(II), Ni(III), Co(II), Ni(II), Cu(II), and Zn(II) were also examined at very low concentrations in the 1–9 pH range. The amidoxime polymer possesses adsorptive affinities of the following order: (Mg(II), Ca(II)) < Zn(II) < Co(II) < Ni(II) < Cu(II) < UO2(VI). These adsorptive affinities are reasonably explained by the proton-binding and the metal ion-complexing abilities of the ligand, and are discussed from the standpoint of uranium recovery from seawater.

Ion-Exchange Properties of lon-Sieve-Type Manganese Oxides Prepared by Using Different Kinds of Introducing Ions

Abstract Three ion-sieve-type manganese oxides, HMnO(Li), HMnO(Na), and HMnO(K), were prepared by acid treatments of Li+-, Na+-, and K+-introduced manganese oxides, respectively. Three oxides were obtained from γ-MnO2 and the corresponding alkali metal hydroxides by heating at 600°C. The ion-exchange properties of the adsorbents were investigated by pH titration, Kd measurements, and the adsorption of metal ions from seawater. The selectivity sequences of alkali metal ions were Na+ < Cs+ < Rb+ < K+ < Li+ for HMnO(Li) and Li+ Na+ < Cs+ < K+ < Rb+ for HMnO(Na) and HMnO(K). The high selectivity of Li+ on HMnO(Li) can be ascribed to an ion-sieve effect of spinel-type manganese oxide which was produced from LiMn2O4 Since HMnO(Na) and HMnO(K) had [2 × 2] tunnels of edge-shared [MnO6] octahedra, the high selectivities of K+ and Rb+ on these samples were used to explain that the sizes of the [2 × 2] tunnels were suitable for filling ions of about 1.4 A in radius in a stable configuration. The order of metal-ion u...

Selective Elution of Uranium from Amidoxime Polymer. II

Abstract The separative elution of uranium from an amidoxime polymer was examined by the column method with hydrochloric acid solutions. The amidoxime polymer was immersed in seawater for 40 d for preparation of an uranium-loaded polymer sample for the elution experiments; the metal ions adsorbed were Mg(II), Ca(II), Fe(III), Ni(II), Cu(II), and Zn(II) as well as UO2(VI). It was found from the pH dependence of elution extent by a batch method that the order of elution pH values is Fe(III) < UO2(VI) < Cu(II) < Ni(II) < Zn(II) < Ca(II) < Mg(II). In the elution by a column method, Mg(II), Ca(II), Zn(II), and Ni(II) were eluted completely by 0.1 M HC1 and the eluate of enriched uranium was obtained by a succeeding elution with 0.5 or 1 M HC1. This eluate contained Cu(II). and Fe(III), which could be removed in the succeeding step. The elution treatment with hydrochloric acid solutions hardly affected the adsorptivity for uranium in seawater. It was suggested that the elution of uranium with hydrochloric acid ...

Preparation and ion-exchange properties of ion-sieve manganese oxide based on Mg2MnO4

A new type of ion-sieve manganese oxide (HMnO(2Mg)) was prepared by extracting magnesium from Mg2MnO4 with aqueous acid. The preparation conditions of HMnO(2Mg) and its ion-exchange properties were examined. The extraction of magnesium from Mg2MnO4 caused a decrease in the lattice constant of a spinel structure. The HMnO(2Mg) showed a selective adsorption of lithium from seawater when the Mg/Mn ratio of the sample was less than 1. The pH titration curve showed an affinity order of Cs ≒ K < Li above pH 3.5. The lithium-ion uptake increased with increasing solution pH and reached 3 meq/g at pH 12. The selectivity sequence was Na < Li < K < Rb < Cs for alkali metal ions at pH 3.1, while it changed to Na < Rb ≒ Cs < K < Li at pH 8. The selectivity sequences were Mg < Ca < Sr < Ba for alkaline earth metal ions and Ni < Zn < Cu < Co for transition metal ions at pH 3.1. The Li+-selective property is discussed based on the ion-sieve effect of the protonated octahedral sites at the cubic closed-packed oxygen framework of HMnO(2Mg).