Ion-Exchange Properties of Microporous Tungstates

Abstract

Hydrothermally prepared microporous, hexagonal tungsten bronze (HTB) phases display promising distribution coefficients (K d) for both Cs+ (2−100 ppm) and Sr2+ (0.5−60 ppm) cations in acidic (1.0 M HNO3) radioactive waste (radwaste) simulants. The selectivity for Cs+ and Sr2+ increases significantly on isomorphous substitution of molybdenum into the tungstate framework and is optimal for material of composition Na0.2Mo0.03W0.97O3·ZH2O. This composition results from attempts to prepare materials doped at a 10 atom % level viz. Na0.2Mo0.1W0.9O3·ZH2O (Mo0.1−HTB). Both the parent HTB and Mo0.1−HTB phases reach maximum uptake of Cs+ and Sr2+ after 30−60 min contact. The cation exchange capacity (CEC) of the parent HTB phase for Cs+ and Sr2+ is ca. 0.2 mmol·g-1 (26.6 g·kg-1) and 0.12 mmol·g-1 (10.5 g·kg-1), respectively, with a 100% increase displayed on 0.03 atom % molybdenum incorporation into the tungstate framework. The optimized Mo0.1−HTB sorbent displays good tolerance of the alkali metal cations, Na+, K+, and Ca2+, with respect to the sorption of Cs+ from acidic solutions. In contrast, the sorption of Sr2+ from similar solutions is reduced to a much greater extent by the presence of these cations.

A Simple Hydrothermal Method for the Large‐Scale Synthesis of Single‐Crystal Potassium Tungsten Bronze Nanowires

“…The layers are stacked along [001] axis, leading to one-dimensional hexagonal channels, which are occupied randomly by potassium ions (Figure 1 b). [22] The chemical nature (i.e. oxidation state) of the tungsten and the potassium/tungsten ratio in the samples were determined by X-ray photoelectron spectroscopy (XPS).…”

Tungsten bronze-based nuclear waste form ceramics. Part 1. Conversion of microporous tungstates to leach resistant ceramics

“…A detailed study of the ion-exchange properties of both the undoped (W-HTB) and Mo-doped materials (MoW-HTB) has been reported recently [6] and a preliminary investigation of the immobilization of the sorbed Cs has also been reported [21]. Because the most effective form of the tungstate adsorbent developed to date is that in which some Mo replaces W in the HTB framework [6] we first address the calcination of this phase in air.…”

“…Over the past two decades a significant effort has been under way to develop inorganic ion-exchange materials for isolating specific radioisotopes such as 137 Cs and 90 Sr from chemically corrosive fission product solutions or radioactive wastes (radwastes) [1][2][3][4][5][6][7][8][9][10] and other waste waters [11]. These two isotopes have a relatively short half life of about 30 years but are extremely problematic due to their high solubility and therefore mobility in the environment.…”

“…Recently we reported that microcrystalline hydrated hexagonal tungsten bronze (HTB) materials could be used for the simultaneous adsorption of Cs + and Sr 2+ from acidic solutions [6,19,20] and also provided preliminary results indicating that calcination of the Cs-and Sr-saturated HTB materials in air to modest temperatures in the range 600-1000°C could yield highly crystalline materials with very low solubility in the pH range from 0 to 12 [21]. In addition it was demonstrated that higher temperatures result in melting which also produces highly durable materials with little or no Cs volatilization.…”

Tungstate-based glass–ceramics for the immobilization of radio cesium

“…We have similarly shown recently that hexagonal tungsten bronze (HTB) based ion exchange materials can also be considered for the selective removal of both 137 solutions [35][36][37]. It has also been demonstrated for these materials that it is viable to prepare a durable tailored ceramic directly from Cs-and Sr-saturated hexagonal tungsten bronze (HTB) selective adsorbent compounds with general formula A x WO 3 or A x-M y W 1Ày O 3 where A cations can be Cs or Sr while M is an element that can substitute for W in the hexagonal tungsten bronze framework [38][39][40][41].…”