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 of the alkaline-conditioned adsorbent, while the decrease in water uptake was observed with the unconditioned adsorbent. The IR spectra of the adsorbent showed a probability of reactions of amidoxime groups with acid and alkaline solutions, which can explain the change in uranium adsorption during the adsorption-desorption cycle.     

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 diameter or increasing the surface area was effective for increasing the adsorption of uranium.     

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.     

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.     

Kinetics of Uranium Adsorption from Seawater with Imidedioxime Adsorbent

Abstract

Complexation between glutar-imidedioxime and uranyl ion in artificial seawater containing 600 ppm uranium at pH 10.3 was investigated by a spectroscopic method. The complexation rate and the complex concentration at equilibrium increased with decreasing concentration of total carbonate ions. In the range of the total carbonate concentration of 4 x 10^?3 to 5 x 10^?2 mol·L^?1, the complexation proceeded by ligand exchange between a carbonate ion and a deprotonated imidedioxime. At lower total carbonate concentrations, the elimination of more than two carbonate ions from one uranyl ion was suggested.     

Status of Technology for the Recovery of Uranium from Seawater

Abstract

Experimental work involving recovery of uranium from seawater is currently under way in several countries. Hydrous titanium oxide has been repeatedly identified as the most promising candidate adsorbent. However, many of its properties such as distribution coefficient, selectivity, loading, and possibly long-term stability may be inadequate for a practical recovery system. Also, evaluations of the energy efficiency of pumped or tidal power methods of contacting the seawater with the hydrous titanium oxide are in major disagreement. Published estimates of the cost of recovering U₃O₈ vary by an order of magnitude. Needed future research and development activities are defined, based on a literature review of the available chemical information. The prime recommendation is for a fundamental laboratory chemical development program to achieve improved absorbent properties, either with hydrous titanium oxide or other materials. Some unresolved engineering aspects of uranium recovery from seawater are also identified.     

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 Uranium from Seawater by Immobilized Tannin

Abstract

Tannin compounds having multiple adjacent hydroxy groups have an extremely high affinity for uranium. To prevent the leaching of tannins into water and to improve the adsorbing characteristics of these compounds, we tried to immobilize tannins. The immobilized tannin has the most favorable features for uranium recovery; high selective adsorption ability to uranium, rapid adsorption rate, and applicability in both column and batch systems. The immobilized tannin can recover uranium from natural seawater with high efficiency. About 2530 μg uranium is adsorbed per gram of this adsorbent within 22 h. Depending on the concentration in seawater, an enrichment of up to 766,000-fold within the adsorbent is possible. Almost all uranium adsorbed is easily desorbed with a very dilute acid. Thus, the immobilized tannin can be used repeatedly in the adsorption-desorption process.     

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.     

Effect of Ultrasonic Irradiation on the Recovery of Uranium from Seawater with Adsorbents

Abstract

Ultrasonic irradiation is reported to promote chelate formation between metal ions and polymeric ligands in solution (1). It is expected that the recovery of uranium from seawater with adsorbents is affected by ultrasonic irradiation because this process is also based on chelation between the ligands of the adsorbent and uranyl ion in seawater. In the present note, adsorption of uranium from seawater was carried out under ultrasonic irradiation with an amidoxime-group-containing polymeric adsorbent.     

Rate of Adsorption of Uranium from Seawater with a Calix[6]arene Adsorbent

Abstract

The rate of complex formation between calix[6]arene-p-hexasulfonate and uranyl ion is studied over a wide range of carbonate ion concentrations. The presence of carbonate ion decreases the complexation rate. The distribution of various uranyl species is calculated from a set of mass balances of participating ions with their stability constants. UO₂(CO₃)₃ ^4? has the highest concentration, followed by UO₂(OH)₃ ^? and UO₂(CO₃)₂ ^2?. Other uranyl species are negligible. The complexation rate is proportional to the 0.27–1.0 power of the total concentration of uranyl species other than UO₂(CO₃)₃ ^4?. This implies that the rate-determining step of the complexation is the reaction between calix[6]arene-p-hexasulfonate and UO₂(OH)₃ ^? or UO₂(CO₃)₂ ^2?.     

Recovery of Uranium from Seawater: A Review of Current Status and Future Research Needs

The recovery of uranium (U) from seawater has been investigated for over six decades in efforts to secure uranium sources for future energy production. The majority of the research activities have focused on inorganic materials, chelating polymers, and nanomaterials. Previous studies of uranium adsorption from aqueous solutions, mainly seawater, are reviewed here with a focus on various adsorbent materials, adsorption parameters, adsorption characterization, and marine studies. Continuous progress has been made over several decades, with adsorbent loadings approaching 3.2 mg U/g adsorbent in equilibrium with seawater. Further research is needed to improve first, the viability including improved capacity, selectivity, and kinetics, and second, the sorbent regeneration for multicycle use. An overview of the status of the uranium adsorption technology is provided and future research needs to make this technology commercially competitive are discussed.     

Desorption of Uranium from Amidoxime Fiber Adsorbent

Abstract

An amidoxime fibrous adsorbent is contacted with uranium-enriched seawater (10 ppm); about 10 mg uranium is loaded per 1 g dry fiber. Then the rate and yield of uranium desorption from the fiber are determined with various eluents. Acid solutions are superior to alkali carbonate solutions as eluents. With a 0.1 mol·L^?1 HCl solution, desorption is completed in 2 hours regardless of the presence of uranium in the leaching solution up to 15 ppm (? 6 × 10^?5 mol·L^?1). Serial operation of the adsorption-desorption cycle four times does not affect desorption efficiency, but the addition of heavy metal ions to the eluent at a level of 1.8 × 10^?3 mol·L^?1 significantly decreases desorption efficiency.     

Extraction of Uranium from Seawater Using Magnetic Adsorbents

Abstract

A new process for the extraction of uranium from seawater was developed. In the process, uranium adsorption is effected using powdered magnetic adsorbents; the adsorbents are then separated from seawater using magnetic separation technology. This process is superior to a column method using a granulated hydrous titanium oxide adsorber bed in the following ways: (1) a higher rate of adsorption is realized because smaller particles are used in the uranium adsorption; and (2) blocking, which is inevitable in an adsorber bed, is eliminated.

The composite hydrous titanium-iron oxide as a magnetic adsorbent having high uranium adsorption capacity and magnetization can be prepared by adding urea to a mixed solution of titanium sulfate and ferrous sulfate. Adsorption and desorption of uranium and the removal of the adsorbent using a small-scale uranium extraction plant (about 15 m³/d) is reported, and the feasibility of uranium extraction from seawater by this process is demonstrated.     

海水卤水提锂高效吸附剂的合成及应用研究

高效吸附剂的研究和开发是高镁锂比海水卤水中锂分离提取的关键,当前最具工业应用前景的吸附剂为锂锰氧化物离子筛。本研究探讨了各合成条件对锂锰氧化物离子筛吸附剂的结构及吸附性能的影响,合成出了适用于不同镁锂比及锂浓度海水卤水的高容量吸附剂,吸附容量最高可达41.02 mg/g,锰溶损率为3.06%;此外,还开展了锂吸附分离的动态模拟试验,为所合成吸附剂用于海水卤水提锂的应用研究奠定基础。     

Uranium Recovery from Seawates by Adsorption

Abstract

Results are presented of a 10 weeks field experiment producing uranium from seawater by the so-called “adsorber-loop-concept”. For the adsorption process polyamidoxin (PAO) granulate has been used with grain sizes between 0.3–1.2 mm diameter. The performance of the adsorber and the efficiency of the adsorption process—especially with regard to high volume flows of seawater—are presented.     

Design and Cost Studies on the Extraction of Uranium from Seawater

Abstract

For a country like Japan, which has very limited energy resources, nuclear power generation is an attractive energy option. However, since known domestic resources of uranium are limited, it is desirable to develop less-conventional uranium sources. To investigate the technical and economic feasibility of extracting uranium from seawater, a research program has been carried out since 1975 by the Metal Mining Agency of Japan, under sponsor-ship of the Ministry of International Trade and Industry. The program includes studies in the following research areas: chemical process selection, adsorbent development, continuous adsorption and elution performance, eluate recovery by steam stripping or electrodialysis, and secondary concentration of uranium in the eluate. Several site selections around the Japanese coast have been examined along with a comparison of various seawater contacting structures. Conceptual designs and tentative cost estimations have been conducted on two types of commercial plants: pumping and fixed bed, and direct sea current utilization. This paper summarizes the conceptual design and cost estimation results.     

Development of Sorbers for the Recovery of Uranium from Seawater. 1. Assessment of Key Parameters and Screening Studies of Sorber Materials

Abstract

At an average uranium content of 3.3 ppb the oceans can be considered as a very low-grade but practically unlimited source of uranium. Some essential chemical aspects of a large-scale sorptive recovery of uranium from seawater are discussed with special emphasis on required sorber properties such as high physical and chemical stability in seawater, fast and selective uptake of uranium, as well as a sufficient loading capacity. Systematic screening tests, including about 200 sorber materials on the basis of organic ion-exchange resins, identified cross-linked poly(acrylamidoximes) as the most promising candidate sorbers. Their uranium uptake closely approaches the uranium content of actually explored uranium ores.     

Development of New Cationic Exchangers for the Recovery of Uranium (VI) from Concentrated Phosphoric Acid

The extraction of uranium (VI) from 5.3 mol.L^?1 phosphoric acid with a series of phosphoric, phosphinic, dithiophosphoric, or dithiophosphinic acid derivatives (0.5 mol.L^?1) in mixture with 0.125 mol.L^?1 TOPO in Isane IP 185 has been investigated. In the frame of the present work, eight acidic phosphorus and thiophosphorus compounds have been synthesized: bis(1,3-diisobutoxypropan-2-yl) phosphoric acid, bis(1,3-bis-(butylthio)propan-2-yl) phosphoric acid, bis(5,8,12,15-tetraoxanonadecan-10-yl) phosphoric acid, bis(1-butoxyheptan-2-yl) phosphoric acid, bis(undecan-6-yl) phosphoric acid, bis(2-(1,3-dibutoxypropan-2-yloxy)ethyl) phosphoric acid, bis(3-butoxy-2-(butoxymethyl)-2-methylpropyl) phosphinic acid, bis(1,3-dibutoxypropan-2-yl) dithiophosphoric acid. The properties of these molecules in mixtures with TOPO have been compared with those of other extractants such as bis(2-ethylhexyl) phosphoric acid, bis(2-ethylhexyl) dithiophosphoric acid, bis(2-ethylhexyl) phosphinic acid, Cyanex® 272, and Cyanex® 301. The replacement of phosphoric acid-type extractant by their phosphinic homologues dramatically decreases the affinity for uranium (VI) whereas the replacement of the phosphoric and phosphinic acid-type extractants by their dithio homologues affects positively the distribution coefficient of uranium (VI). It also appears that the steric hindrance effect is responsible for a significant decrease of the distribution coefficient of uranium (VI). Supplemental materials are available for this article. Go to the publisher's online edition of Separation Science and Technology to view the free supplemental file.     

Kinetics of Adsorption of Uranium on Amidoxime Polymers from Seawater

Abstract

Distributions of uranium adsorbed on amidoxime polymers crosslinked with tetraethyleneglycol dimethacrylate (4EGDM) and/or divinylbenzene (DVB) from seawater were examined by x-ray microanalysis in order to elucidate the diffusion behavior of uranium into the polymer matrix. The uniform distribution of the ligands on the polymers was confirmed by the distribution of Cu(II) adsorbed from copper(II) dichloride solutions. It was found that the distribution of uranium adsorbed is changed significantly by the composition of 4EGDM and DVB. Thus, the polymer crosslinked with 4EGDM exhibits a uniform distribution of uranium; however, as the ratio of DVB to 4EGDM increases, a more predominant distribution of uranium near the periphery of the polymer particle appears and the intensity decreases. This suggests that the adsorption rate of uranium is governed by the diffusion of uranium into the polymer matrix, explaining well the dependence of the adsorption rate on the hydrophilicity of the polymer. On the basis of these results, the diffusion constant of uranium into the polymer matrix was estimated to be 3.3 × 10^?-7 cm²/s.