Measuring the ratio of aqueous diffusion coefficients between [sup 6]Li[sup +]Cl[sup [minus]] and [sup 7]Li[sup +]Cl[sup [minus]] by osmometry

Journal Article · Thu Oct 01 00:00:00 EDT 1992 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(92)90170-N· OSTI ID:6893549

Fritz, S J ^[1]

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1. Purdue Univ., West Lafayette, IN (United States)

Osmotic equilibrium is a singular occurrence in the evolution of an osmotic cell because at this event the net solution flux is zero such that [minus]J[sub w] [center dot] [bar V][sub w] = J[sub s] [center dot] [bar V][sub s]. At this juncture, the diffusion coefficient of the solute through the membrane ([omega]) equals the solute flux (J[sub s]) divided by the osmotic pressure ([delta]II). Because the solute permeability coefficient ([omega]) is related to the Fickian diffusion coefficient (D) through the gas constant, temperature, and the membrane's thickness and tortuosity, the ratio of [omega] values for individual isotopic species equals the ratio of D values for the same isotopic components. A 0.9450 molal LiCl solution was placed within sealed dialysis tubing and osmoted against a kilogram of deionized water at 22C. Osmotic equilibrium occurred at 164 [plus minus] 10 min. The ratio of [omega][sub [sup 6]Li[sup +]Cl[sup [minus]]]/[omega][sub [sup 7]Li[sup +]Cl[sup [minus]]] was measured to be 1.011 [plus minus] 0.003 - a value close to the square root of the mass ratio between [sup 7]LiCl and [sup 6]LiCl (=1.012) as calculated by Graham's Law. The measured diffusion coefficient ratio was used to predict the degree of hyperfiltration-induced fractionation of Li isotopes as a function of membrane ideality. When a membrane's [sigma] exceed 0.95 (as is likely for low-porosity shales) the [sup 6]Li/[sup 7]Li ratio on the high-pressure side of the membrane can theoretically vary by more than 0.0017.

• DOE Contract Number: FG02-90ER14113
• OSTI ID: 6893549
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 56:10; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
LITHIUM CHLORIDES
MEMBRANE TRANSPORT
OSMOSIS
LITHIUM ISOTOPES
FRACTIONATION
ELECTROLYTES
EQUILIBRIUM
FICK LAWS
GEOCHEMISTRY
ISOTOPE RATIO
MOLECULAR WEIGHT
PERMEABILITY
ALKALI METAL COMPOUNDS
ALKALI METAL ISOTOPES
CHEMISTRY
CHLORIDES
CHLORINE COMPOUNDS
DIFFUSION
HALIDES
HALOGEN COMPOUNDS
ISOTOPES
LITHIUM COMPOUNDS
LITHIUM HALIDES
SEPARATION PROCESSES
580000* - Geosciences