Arsenic removal from water/wastewater using adsorbents—A critical review

More than 1000× uranium exists in the oceans than exists in terrestrial ores. With nuclear power generation expected to increase over the coming decades, access to this unconventional reserve is a matter of energy security. With origins in the mid-1950s, materials have been developed for the selective recovery of seawater uranium for more than six decades, with a renewed interest in particular since 2010. This review comprehensively surveys materials developed from 2000–2016 for recovery of seawater uranium, in particular including recent developments in inorganic materials; polymer adsorbents and related research pertaining to amidoxime; and nanostructured materials such as metal–organic frameworks, porous-organic polymers, and mesoporous carbons. Challenges of performing reliable and reproducible uranium adsorption studies are also discussed, as well as the standardization of parameters necessary to ensure valid comparisons between different adsorbents.

Materials for the Recovery of Uranium from Seawater

Preparation and applications of ion exchange membranes by radiation-induced graft copolymerization of polar monomers onto non-polar films

Chelating polymers and related supports for separation and preconcentration of trace metals.

Uranium is the main source for nuclear energy but also one of the most toxic heavy metals. The current methods for uranium removal from water present limitations, such as narrow pH operating range, limited tolerance to high salt concentrations, or/and high cost. We show here that a layered sulfide ion exchanger K2MnSn2S6 (KMS-1) overcomes these limitations and is exceptionally capable in selectively and rapidly sequestering high (ppm) as well as trace (ppb) quantities of UO22+ under a variety of conditions, including seawater. KMS-1 can efficiently absorb the naturally occurring U traces in seawater samples. The results presented here reveal the exceptional potential of sulfide-based ion-exchangers for remediating of uranium-containing wastes and groundwater and for extracting uranium from the sea.

Layered Metal Sulfides Capture Uranium from Seawater

Macroreticular chelating resins (RNH) containing amidoxime groups with various degrees of crosslinking were synthesized by using various amounts of ethyleneglycol dimethacrylate (1G), dimethyleneglycol dimethacrylate (2G), triethyleneglycol dimethacrylate (3G), tetraethyleneglycol dimethacrylate (4G), and nanoethyleneglycol dimethacrylate (9G) as crosslinking reagent. The effect of crosslinking reagents on the pore structure, ion exchange capacity, swelling ratio, and adsorption ability for uranium of RNH was investigated. RNH (RNH–1G) prepared by using 1G were showed to have macroreticular structures by the measure of specific surface area. RNH–1G had the high adsorption ability and physical stability. Though RNH (RNH–4G) obtained by using 4G have little macroreticular structure (macropore), these resins showed the high adsorption ability for uranium by the treatment with 0.1 mol dm−3 NaOH at 30°C for 15 h (alkali treatment). These results suggest that the formation of not only the favorable macropore but also the micropore is important for the effective recovery of uranium in sea water, whereas RNH–4G was defined to be low physical and chemical stability. For the preparation of RNH which have effective pore structure for the recovery of uranium, chemical, and physical stability, the simultaneous use of divinylbenzene (DVB) and 1G or 4G as crosslinking reagent was examined (abbreviated as RNH–DVB–1G and RNH–DVB–4G). The specific surface area of RNH–DVB–1G increased with an increase of 1G used. These RNH–DVB–1G have been shown the high adsorption ability for uranium. On the other hand, the specific surface area and adsorption ability for uranium of RNH–DVB–4G decreased with an increase of 4G used. Repeated use did not cause the deterioration of both RNH–DVB–1G and RNH–DVB–4G. This result suggests that the simultaneous use of DVB and 1G or 4G contributed the improvement of chemical and physical stability. In particular, RNH–DVB–1G has the effective macropore and micropore for the recovery of uranium.

Recovery of uranium from sea water. IV. Influence of crosslinking reagent of the uranium adsorption of macroreticular chelating resin containing amidoxime groups

A number of lightly cross-linked poly(acrylonitrile-co-divinylbenzene) beads (RN-5) have been synthesized by suspension polymerization. The use of solvating diluents such as chloroform, dichloroethane, and tetrachloroethane resulted in copolymer beads having highly porous structures. The chelating resins containing amidoxime as a functional group (RNH-5) have been prepared by the reaction of copolymer beads with 3% hydroxylamine in methanol. A detailed analysis is made of the pore structure of lightly cross-linked copolymers of acrylonitrile–divinylbenzene and their amidoxime derivatives in the anhydrous state including pore-size distribution, specific surface area, and pore structure in the aqueous media by means of gel permeation chromatography (GPC). A set of experiments have been performed to ascertain the potential of the resins for the adsorption of uranium from seawater. Because of their modified pore structures, the chelating resins exhibited a marked adsorption rate for uranium in seawater as high as 23 μg of U/cm3 of resin/day without alkaline treatment.

Recovery of uranium from seawater. XII. Preparation and characterization of lightly crosslinked highly porous chelating resins containing amidoxime groups

Despite the low concentration of uranium in seawater (3.3 ppb), a special emphasis has been placed on its recovery. Although the concentration is low, it has been estimated that the world's oceans contain about 4 × 109 tons of uranium—theoretically an unlimited supply of nuclear fuel. Adsorption has been considered to be a technically feasible procedure for a uranium recovery process with regard to economic and environmental impacts. The present paper restricts its coverage to those applications using chelating polymeric resins containing amidoxime groups as the most promising adsorbent. ∗Dedicated to Prof. Iwao Tabushi for his endeavors in the field of “recovery of uranium from seawater.”

Chelating Polymers for Recovery of Uranium from Seawater

Recent Advances in Development of Chelating Polymers for Recovery of Uranium from Seawater

Polypropylene fibers and polyethylene hollow fibers were used as trunk polymers and were irradiated by electron beams with a dose of 200 kGy under N{sub 2} atmosphere. Grafting of acrylonitrile to those irradiated fibers was carried out at 40{degree} C for different periods of time. The degree of grafting was determined as a function of time. The fibrous adsorbents containing amidoxime groups were prepared by the reaction of acrylonitrile-grafted polymers with 3% hydroxylamine in a methanol-water mixture (1:1). Distribution of copper ions complexed with amidoxime groups at various adsorption times was obtained by electron-probe X-ray microanalysis. The amidoxime groups are homogeneously distributed in the cross section of fibrous adsorbents. The fibrous adsorbents based upon polypropylene fiber of 40 {mu}m showed a remarkable kinetic behavior for Cu{sup 2+}. Even after 15 min, the adsorption capacity was 2.32 mmol Cu{sup 2+} per gram of fiber. Also, the functionalization with hydroxylamine was carried out at different conditions to compare the adsorption characteristics of the resultant adsorbents. Despite having superficially different properties (elemental microanalysis, ion-exchange capacities, adsorption capacity for UO{sup 2+}{sub 2}), the polypropylene-based fibrous adsorbents showed similar adsorption properties for uranium from sea water. The adsorption tests proved the performance of the polypropylene-basedmore » fibrous adsorbents as a promising material for uranium recovery from sea water. In addition, uranium uptake of fibrous adsorbents increased in proportion to the volume of sea water.« less

Hiroaki Egawa

Papers

Recovery of uranium from sea water. IV. Influence of crosslinking reagent of the uranium adsorption of macroreticular chelating resin containing amidoxime groups

Recovery of uranium from seawater. XII. Preparation and characterization of lightly crosslinked highly porous chelating resins containing amidoxime groups

Chelating Polymers for Recovery of Uranium from Seawater

Recent Advances in Development of Chelating Polymers for Recovery of Uranium from Seawater

Preparation of fibrous adsorbents containing amidoxime groups by radiation‐induced grafting and application to uranium recovery from sea water