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Publication Detail
The direct precipitation of rhabdophane (REEPO4 · H 2O) nano-rods from acidic aqueous solutions at 5-100 °c
  • Publication Type:
    Journal article
  • Publication Sub Type:
    Journal Article
  • Authors:
    Roncal-Herrero T, Rodríguez-Blanco JD, Oelkers EH, Benning LG
  • Publication date:
    01/09/2011
  • Pagination:
    4049, 4062
  • Journal:
    Journal of Nanoparticle Research
  • Volume:
    13
  • Issue:
    9
  • Status:
    Published
  • Print ISSN:
    1388-0764
Abstract
The precipitation of lanthanum and neodymium phosphate phases from supersaturated aqueous solutions at pH ~1.9 was studied at 5, 25, 50, and 100 °C in batch reactors for up to 168 h. Crystalline La and Nd-rhabdophane phases precipitated immediately upon mixing of the initial aqueous La or Nd and PO4 solutions. Changes in aqueous PO4 and Rare Earth Element (REE) concentrations during the experiments were determined by ICP-MS and UV- Vis spectrophotometry, while the resulting solids were characterized via powder XRD, SEM, TEM, and FTIR. All precipitated crystals exhibited a nano-rod morphology and their initial size depended on temperature and REE identity. At 5 °C and immediately after mixing the La and Nd-rhabdophane crystals averaged ~44 and 40 nm in length, respectively, while at 100 °C lengths were ~105 and 94 nm. After 168 h of reaction, the average length of the La and Nd rhabdophanes increased by 23 and 53% at 5 °C and 11 and 59% at 100 °C, respectively. The initial reactive solutions in all experiments had activity quotients for rhabdophane precipitation: REE3++ PO3-4 + nH2O = REEPO4 · H2O of ~10-20.5. This activity quotient decreased with time, consistent with rhabdophane precipitation. The rapid equilibration of rhabdophane supersaturated solutions and the progressive rhabdophane crystal growth observed suggests that the REE concentrations of many natural waters may be buffered by rhabdophane precipitation. In addition, this data can be used to guide crystallization reactions in industrial processes where monodisperse and crystalline La or Nd rhabdophane materials are the target. © Springer Science+Business Media B.V. 2011.
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