Isotopic fractionation and overall permeation of lithium by a thin-film composite polyamide reverse osmosis membrane

Thomas M. Whitworth, Benito J. Mariñas, Steven J. Fritz

Research output: Contribution to journalArticle

Abstract

A small, but significant fractionation of lithium isotopes was observed during reverse osmosis experiments performed with a thin-film composite polyamide membrane (FilmTec FT-30 membrane). Relative to the feed solution, the heavier lithium isotope 7Li was depleted in the permeate from 4.3 to 10.6 per mil (±3.3 per mil) during six experimental runs. The observed isotopic fractionation might be the result of the slightly different permeabilities of 6Li and 7Li across the FT-30 membrane. The heavier of two solute isotopes has a slightly lower mobility due to its slightly greater mass. Therefore, the heavy isotope permeates slightly more slowly inside the membrane than its isotopically lighter counterpart. As a result, more of the heavier isotope is retained on the high-pressure side of the membrane during each run. The magnitude of isotopic fractionation generally increased with increasing water permeation rates. Additionally, experimental evidence shows that the FT-30 membrane exhibits essentially identical solute rejection with NaCl and LiCl under the same operating conditions.

Original languageEnglish (US)
Pages (from-to)231-241
Number of pages11
JournalJournal of Membrane Science
Volume88
Issue number2-3
DOIs
StatePublished - Mar 16 1994
Externally publishedYes

Keywords

  • Flat-leaf cell
  • Isotopic fractionation
  • Lithium chloride
  • Reverse osmosis
  • Thin-film composite membrane

ASJC Scopus subject areas

  • Biochemistry
  • Materials Science(all)
  • Physical and Theoretical Chemistry
  • Filtration and Separation

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