Leaching mechanisms of oxyanionic metalloid and metal species in alkaline solid wastes: A review

While the d0 transition-metal POMs of Group V (V5+, Nb5+, Ta5+) and Group VI (Mo6+, W6+) have been known for more than a century, the actinyl peroxide POMs, specifically those built of uranyl triperoxide or uranyl dihydroxidediperoxide polyhedra, were only realized within the last decade. While virtually every metal on the Periodic Table can form discrete clusters of some type, the actinyls are the only—in addition to the transition-metal POMs– whose chemistry is dictated by the prevalence of the ‘yl’ oxygen ligand. Thus this emerging structural, solution, and computational chemistry of actinide POMs warrants comparison to the mature chemistry of transition-metal POMs. This assessment between the transition-metal POMs and actinyl POMs (uranyl peroxide POMs, specifically) has provided much insight to the similarities and differences between these two chemistries. We further break down the comparison between the alkaline POMs of Nb and Ta; and the acidic POMs of V, Mo and W. This more indepth literature review and discussion reveals that while an initial evaluation suggests the actinyl POMs are more akin to the alkaline transition-metal POMs, they actually share characteristics unique to the acidic POMs as well. This tutorial review is meant to provide fodder for deriving new POM chemistries of both the familiar transition-metals and the emerging actinides, as well as fostering communication and collaboration between the two scientific communities.

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A comprehensive comparison of transition-metal and actinyl polyoxometalates

http://kth.diva-portal.org/smash/get/diva2:341411/FULLTEXT01

Modelling molybdate and tungstate adsorption to ferrihydrite

The molybdenum blue reaction for the determination of orthophosphate revisited: Opening the black box.

Calculating the partitioning of the isotopes of Mo between oxidic and sulfidic species in aqueous solution

Publisher Summary This chapter discusses protonation, oligomerization, and condensation reactions of vanadate(V), molybdate(VI), and tungstate(VI). The elements vanadium, molybdenum, and tungsten in their high oxidation states form the stable oxyanions [VO4]3-, [MoO4]2-, and [WO4]2-. In aqueous solution, these ions are easily protonated and show a strong tendency to form polyoxoanions by oxygen bridging, and the release of water molecules. Depending on pH and concentration, a great variety of ions can form in each case, giving rise to complex systems of simultaneous equilibria, which have proved difficult to characterize with certainty. The molybdate(VI) system, in particular, needs further clarification regarding the existence of some polyions. More kinetic and thermodynamic data would also help to improve the understanding of these systems and lead to a general inclusive explanation of the mechanism of polyoxoanion formation. In this respect, new information about some structural preferences of the different metals in mixed polyoxoanions is a useful addition to known facts regarding polyoxometalate structures.

J. J. Cruywagen

Papers

Protonation, Oligomerization, and Condensation Reactions of Vanadate(V), Molybdate(vi), and Tungstate(vi)

Protonation, Oligomerization, and Condensation Reactions of Vanadate(V), Molybdate(VI), and Tungstate(VI)