Presentation on theme: "Measurement of concentrated chloride brines by water liquid- vapour equilibration Geoff Koehler Environment Canada, University of Saskatchewan Saskatoon,"— Presentation transcript:
Measurement of concentrated chloride brines by water liquid- vapour equilibration Geoff Koehler Environment Canada, University of Saskatchewan Saskatoon, SK
Brines Analytical difficulties with composition methods Must somehow remove dissolved salts Distillation – can result in back- reaction to form HCl NaOH Autosamplers Increased memory effects Slow equilibration times for CO 2
Stable isotopic measurment of liquid water Composition methods TCEA(H,O) Zn reduction (H) U reduction (H) Mn reduction (H) Cr reduction(H) Laser liquid injectors(H,O) AquaSIRA(H,O) BrF 5 (O) Guadadine hydrochloride(O) LiAl(OH) 4 (H) Activity Methods H 2 equilibration CO 2 equilibration =? Only for pure water
5 Henry Taube born Neudorf (pop 281), Saskatchewan B.Sc. 1935, M.Sc. 1937 - UofS. Berkeley, DOD, Chicago, Stanford Nobel prize for Chemistry, 1983 for his work on the mechanisms of electron transfer reactions, especially in metal complexes
6 Taube was studying coordination chemistry of hydration spheres Discovered the isotope salt effect by equilibrating CO 2 with various ionic solutions Found that the 18O/16O of CO2 equilibrated with solutions is different than that of pure water, and that the difference varies linearly with concentration. Varies with cation, but not anion Structure makers, breakers Frank and Wen, 1957
7 = R (soln) /R (H2O) 1000ln ~ (soln) – (H2O) Few data for hydrogen salt effect Involved in studies that require measuring porewater in drill cores – is there a salt effect?
8 Can measure D, 18 O activity in solutions using H 2 0 (l) – H 2 O (v) equilibration OA-ICOS or WS-CRDS technology
Problems decreased vapour pressure from decreased water activity with Brines Reference waters are pure water General method Similar to measurement of liquid waters 24-48 hour equilibration times – w(l) – w(v) exchange is rapid Normalization by determination of known reference waters 4-5 minute integration times Precisions of about 2 per mil H, 0.3 per mil O a w = λ w x w = p/p 0 Water activity is the effective mole fraction of Water activity is defined as: Laser spectrometers measure directly water activity
Often have a significant isotope ratio dependence on vapour pressure in the laser cavity Must be corrected for With very concentrated solutions (ie 5m MgCl2), can be 10 per mil more enriched Can measure non-linearity with a variable reference source (WVISS) or with NaCl solutions
15 Conclusions Isotopic measurement of brines probematic at best Equilibration methods yeild activity ratios Reduction or distillation yeild concentration ratios For years, D and 18 O measuments done by H20- CO2 for oxygen and hot reduction for hydrogen Plausible there might be differences between water- vapour equilibration and CO2-water equilibration or H2- water equilibration.