TY - JOUR
T1 - Diffusion of seawater ions. Part II. The role of activity coefficients and ion pairing
AU - Katz, Amitai
AU - Ben-Yaakov, Sam
PY - 1980/2
Y1 - 1980/2
N2 - A theoretical evaluation of basic thermodynamic relationships reveals that variation of activity coefficients, ion pairing and electrical interactions must be considered when modelling ionic diffusion in seawater. The contributions of ion-pair formation and change in activity coefficient along the diffusion path were studied experimentally by conducting diffusion experiments in which solutions of KCl, NaCl, MgCl2, Li2SO4, K2SO4, Na2SO4 and MgSO4, at an ionic strength of 0.7, were allowed to diffuse into distilled water. The study reveals that the thermodynamic factor, required to correct for changes in the activity coefficient along the diffusion path, is significant for all the salts studied. Agreement between a simple diffusion model, which does not include ion pairing, and observed data was good for completely dissociated salts, but poor for salts which are known to form ion pairs at the concentration levels studied. The diffusion of MgSO4, 0.425 of which is associated at I = 0.7, was successfully modelled by assuming that the diffusion coefficient of the MgSO40 ion pair is different from the diffusion coefficient of the dissociated salt. The diffusion coefficient of this ion pair is estimated to be 1.9 × 10-5 cm2 s-1 at 30°C, as compared to 0.49 × 10-5 cm2 s-1 for the dissociated salt. It is suggested that the high mobility of this ion pair could cause magnesium enrichment in pore water of sulfate depleted sediments.
AB - A theoretical evaluation of basic thermodynamic relationships reveals that variation of activity coefficients, ion pairing and electrical interactions must be considered when modelling ionic diffusion in seawater. The contributions of ion-pair formation and change in activity coefficient along the diffusion path were studied experimentally by conducting diffusion experiments in which solutions of KCl, NaCl, MgCl2, Li2SO4, K2SO4, Na2SO4 and MgSO4, at an ionic strength of 0.7, were allowed to diffuse into distilled water. The study reveals that the thermodynamic factor, required to correct for changes in the activity coefficient along the diffusion path, is significant for all the salts studied. Agreement between a simple diffusion model, which does not include ion pairing, and observed data was good for completely dissociated salts, but poor for salts which are known to form ion pairs at the concentration levels studied. The diffusion of MgSO4, 0.425 of which is associated at I = 0.7, was successfully modelled by assuming that the diffusion coefficient of the MgSO40 ion pair is different from the diffusion coefficient of the dissociated salt. The diffusion coefficient of this ion pair is estimated to be 1.9 × 10-5 cm2 s-1 at 30°C, as compared to 0.49 × 10-5 cm2 s-1 for the dissociated salt. It is suggested that the high mobility of this ion pair could cause magnesium enrichment in pore water of sulfate depleted sediments.
UR - http://www.scopus.com/inward/record.url?scp=0042530141&partnerID=8YFLogxK
U2 - 10.1016/0304-4203(80)90016-X
DO - 10.1016/0304-4203(80)90016-X
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AN - SCOPUS:0042530141
SN - 0304-4203
VL - 8
SP - 263
EP - 280
JO - Marine Chemistry
JF - Marine Chemistry
IS - 4
ER -