Categories
vol-11KINETICS OF DISSOLUTION OF THE ALKALINE
EARTH FLUORIDES
S.M. HAMZA, F.A. ALY and A.I. BELTAGY*
ChemlstrY,Department. Faculty of Science. Menofia University. Egypt.
Instltute of Oceanography and Fisheries. Alexandria. Egypt.
ABSTRACT
Constant composition technique have been used to study
the dissolution of the ·fluorides of magnesium calcium.
strontium and barium in aqueous solution at an ionic strength
of 0.15 M. as a function of concentration temperature and
fluid dynamics. The method enables kinetic data to be obtained
at very low undersatura~ion with a prelFision hitherto
unobtainable. With the exception of magnesium fluoride.
a striking change in the mechanism of dissolution is observed
as the driVing force is changed. At higher driving’ force
the first order dependance of the rate of dissolution on
the undersaturation suggests the diffusion controlled process
nonna.lly assumed for dissolution reactions. At low driVing
force. however, the effective order of reaction appears
to approach the value of 2. proposed for a surface controlled
reaction. The rate of dissolution mol. min-I. m- 2 increases
dramatically from Magnesium fluoride to Barium fluoride.
The results can be interpreted in the light of the stabil ity
constants. Iatti ce energy. thermodynami c parameters and
dehydration of cations.
