Structural and Mechanistic Investigation of Rubidium Ion Exchange in Potassium Zirconium Trisilicate Academic Article uri icon

abstract

  • Complete and intermediate incorporation of rubidium into the hydrothermally prepared mineral umbite has been accomplished by ion exchange. Potassium zirconium trisilicate, K2ZrSi3O9·H 2O, is an open framework ion exchanger composed of polymeric chains of trisilicate groups linked by zirconium atoms. This arrangement creates a three-dimensional tunnel network. The exchangeable cations are found in two unique tunnels along the c-axis inside the framework. Site 1 is marked by a 12-membered ring and contains two cations. Site 2, a 16-membered ring, contains two cations and two water molecules. The parent compound, K2ZrSi 3O9·H2O, was used to prepare compound 1, Rb2ZrSi3O9·H2O, in which the original space group, P212121, is conserved. Cell dimensions of a = 10.4821(6) Å, b = 13.3869(5) Å, and c -7.2974(3) Å were found for compound 1. Analysis of Rb-O coordination shows average contact distance approaching the sum of the O2- and Rb+ ionic radii. Compound 2, K0.29H0.1Rb 161ZrSi3O9·H2O, shows that Rb+ has completely substituted K+ in site 2 and only partially in site 1. Upon structural analysis of ∼50% incorporation of Rb+, K0.9H0.1RbZrSi3O 9·H2O (3), and ∼22.5% incorporation, K 1.45H0.1-Rb0.45ZrSi3O 9·H2O (4), it becomes apparent that the mechanism of exchange involves population of site 2 first. Further investigation of the mechanism of exchange through examination of the exchange kinetics has shown a plausible intermediate hydrolysis step occurs where K+ is replaced by H+ and subsequently H+ exchanges with Rb+. © 2007 American Chemical Society.

author list (cited authors)

  • Fewox, C. S., Kirumakki, S. R., & Clearfield, A.

citation count

  • 11

publication date

  • February 2007