Summary: | 碩士 === 國立臺灣大學 === 化學工程研究所 === 81 === For sparingly solube crystals the solution method was usually
employed to study the kinetics of primary nucleation and
crystal growth. However, the gas bubbling method was mainly
used in the industrial production of Calcium Carbonate and in
the treatment of softening water. Few reports have been found
in the literature to study the kinetics of primary nucleation
and growth by the gas-injection method. Control of crystal
morphology was investigated in this study. It is found that
the pH value and the initial Calciumion concentr -ation,but
not the supersaturation, are the factors which dete -rmine
whether calcite, aragonite, or vaterite would be nucleated from
a supersatration Calcium Carbonate solution. The Calcium ion
concentration for themaximum yield of calcite is found to
be 0.015 M. Aragonite isonly found when the pH value is less
than 8.0. Low yield ofcalcite of can be obtained by the gas-
injection method. Additionally, the growth of small calcite
(20-163 micro meter) and large calcite crystal (163-327.5
micro meter) were conducted in the supersaturation range of
0.1-1.49 nad 0.51- 2.03, respectively. The results show
that surface integration was the rate- determining step
for the growth of small and large calcite crystals. The
growth rate of large calcite crystal was size independent,
but that of small calcite was size dependent.
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