Nucleation and crystal growth of
CaSO4·2H2O (gypsum) was studied under simulated
conditions of scale formation
using a reverse osmosis desalination technique. Calcium chloride and
sodium sulfate were mixed with concentrated sodium chloride solution
(40 g/L), and the reaction mixture turbidity was measured at different
time intervals to determine the induction time of precipitated gypsum.
Induction time was measured under different high supersaturation ratios
ranging from 3.92 to 6.71. The induction time decreases exponentially
with increasing the supersaturation. Using crystallization equations
that relate induction times with supersaturation ratios, the free
energy barrier and critical nuclei radius were calculated with and
without addition of a scale inhibitor (trisodium phosphate, TSP).
Rates of nucleation at a 4.47 supersaturation ratio are 0.4 ×
1028 and 0.5 × 1028 nuclei/cm3·s with and without TSP addition, respectively.
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