Scheelite, CaWO4, has a dense three-dimensional structure and is therefore not expected to act as an ion-exchanger but we have discovered that in nanocrystalline form it selectively adsorbs aqueous heavy metals to produce the corresponding metal tungstates and release calcium ions into solution. The reaction causes little change in the morphology of the original CaWO4 particles suggesting a true ion-exchange process. Uranyl ions are also selectively sorbed but the tungstate particles are completely reconstructed by a surface nucleation/growth mechanism. Presumably the difference arises from the polyatomic nature of the UO22+ ion. The utilization of nanocrystalline CaWO4 for water purification and ocean mining for uranium will be discussed. These applications are facilitated by supporting CaWO4 on high surface area support pellets using a water-soluble single-source precursor.

Sorption of heavy metals and uranium by nanocrystalline scheelite

254th National Meeting (2017)

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