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A phase diagram of the Na2O–PbO–H2O system at 130 °C was studied using Schreinemakers's method, to provide fundamental data for producing PbO via hydrometallurgical process. In the phase diagram, saturated solubility of PbO has two maximum values vs the sodium hydroxide concentration in the solution. The equilibrium solid phases of lead oxide (PbO), sodium plumbite hydroxide (Na2O·PbO·H2O) and sodium hydroxide (NaOH) were identified in the different alkali concentration regions, which is different from that at low temperature presented in literature. Copyright © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.

Various types of polyoxometalates (POMs) have been synthesized since the 19th century, but their assortment has been mostly limited to Groups 5 and 6 metals. Herein, a new family of POMs composed of a carbon group element as the addenda atoms with two distinct phases, LnPbOClO4‐1 (Ln = Sm to Ho, Y) and LnPbOClO4‐2 (Ln = Er and Tm) is reported. Both structures are built from [Ln6O8] rare‐earth metal hexamers being incorporated in [Pb18O32]/[Pb12O24] polyplumbites, and unbound perchlorates as charge‐balancing anions. Impressively, YPbOClO4‐1 and ErPbOClO4‐2 exhibit exceptional uptake capacities (434.7 and 427.7 mg g−1) toward ReO4−, a chemical surrogate for the key radioactive fission product in the nuclear fuel cycle 99TcO4−, which are the highest values among all inorganic anion‐exchange materials reported until now. The sorption mechanism is clearly elucidated and visualized by single‐crystal‐to‐single‐crystal structural transformation from ErPbOClO4‐2 to a perrhenate‐containing complex ErPbOReO4, revealing a unique ReO4− uptake selectivity driven by specific interaction within Pb···O‐ReO3− bonds.