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

An anion adsorbent was developed based on a Cobalt(III)-loaded chelating resin containing 1, 4, 8, 11-tetraazacyclo-tetradecane-5, 7-dione. Batchwise adsorption study has revealed that the adsorbent exhibits an anti-Hofmeister anion selectivity sequence (OH->SCN->NO2-) and that it takes up thiocyanate preferentially in the presence of excess perchlorate as well. Column-mode study has also clarified that the adsorbent takes up thiocyanate preferentially even in the presence of tenfold excess perchlorate. The adsorbed thiocyanate is rapidly and quantitatively eluted with 0.2M sodium hydroxide, unlike to the case of a conventional anion exchange resin (Bio-Rad AG 1-X4) column. In addition, the adsorbent was able to be regenerated with hydrochloric acid solution for repeated use. During repeated use of the adsorbent for a half year, no loss of the loaded cobalt(III) was observed.

An Anion Adsorbent of the Anti-Hofmeister Type Based on Cobalt(III)-Loaded Chelating Resins Containing 1, 4, 8, 11-Tetraazacyclotetradecane-5, 7-dione

In order to choose the most practical macroreticular chelating resins for the removal and recovery of heavy metal ion from industrial waste solution, the influence of the porosity of macroreticular chelating resins on the adsorption for metal ion was studied. The four macroreticular chelating resins (RST) containing triethylenetetramine side chain with different porosity were used. It was found that the adsorption of zinc ion at its low concentration solution was affected by the porosity of the RST. Among the four resins with average pore radius of 21.0, 24.5, 28.0, and 66.5 nm, a resin with that of 66.5 nm gave the highest initial adsorption rate and the largest breakthrough capacity for zinc ion at a space velocity of 15 h−1.

Studies of selective adsorption resins. XVIII: The influence of porosity of macroreticular chelating resin on adsorption of heavy metal ions in an aqueous solution

Chloride salts of cobalt(III) complexes of 1, 4, 8, 11-tetraazacyclotetradecane-5, 7-dione (L1) and 6-(2-(2-pyridyl)ethyl)-1, 4, 8, 11-tetraazacyclotetradecane-5, 7-dione (L2), acting as a water-soluble anion carrier capable of a selective recognition of nitrite and thiocyanate, were isolated, and their solid state structures and properties in water were studied. IR spectroscopic and X-ray crystallographic approaches have clarified that the isolated complexes have iminol tautomeric structures, in which the amide oxygen atoms are protonated, but the amide nitrogen atoms bound to cobalt(III) are deprotonated. Conductivity and pH titration studies on aqueous solutions of the complexes have revealed that the iminol groups act as a strong acid in water; the acid-dissociation constants of the water molecule axially coordinated to the cobalt(III) are 10-6.65 and 10-7.01 for the L1 and L2 complexes, respectively.

Structures and Properties of Cobalt(III) Complexes of Ligands Having the 1,4,8,11-Tetraazacyclotetradecane-5,7-dione Moiety.

Photocrosslinking of polymers bearing episulfide groups in the solid phase

The polyampholytes were prepared by treating potassium polymethacrylate with (3-chloro-2-hydroxypropyl)trimethylammonium chloride. The solution viscosity behavior and the potentiometric titration of the polyampholytes were studied. The flocculating ability of the polyampholytes was also investigated by the use of kaolin suspensions. The amine/acid ratio could be varied as desired to some extent by means of changing the reaction temperature. However, the polyampholytes containing more amino groups than about 46% could not be obtained. The resulting polyampholytes showed characteristic viscosity behavior. The results of the flocculation of kaolin suspensions with the polyampholytes showed that the polyampholytes can be expected to become a new type of polymeric flocculants, in which the chain expansion and the charge sign can be varied by changing the pH values of the solutions.

Hiroaki Egawa

Papers

An Anion Adsorbent of the Anti-Hofmeister Type Based on Cobalt(III)-Loaded Chelating Resins Containing 1, 4, 8, 11-Tetraazacyclotetradecane-5, 7-dione

Studies of selective adsorption resins. XVIII: The influence of porosity of macroreticular chelating resin on adsorption of heavy metal ions in an aqueous solution

Structures and Properties of Cobalt(III) Complexes of Ligands Having the 1,4,8,11-Tetraazacyclotetradecane-5,7-dione Moiety.

Photocrosslinking of polymers bearing episulfide groups in the solid phase

Studies of Polymeric Flocculants. XI. The Preparation and Properties of Polyampholytes