The nucleation kinetic aspects of gypsum nanofiltration membrane scaling

Gypsum NF-200 (Filmtec) membrane scaling was examined with respect to the nucleation theory. First the gypsum nucleation kinetic parameters - nucleation rate constant k(N) and heterogeneous nucleation factor f(theta) - were calculated, with the model based on classical nucleation theory using the nonlinear (quasi-Newtonian) estimation method. Subsequently, the method of the maximum permissible water recovery bound (here expressed as maximum NF retentate supersaturation, S-max) prediction was proposed. When comparing the predicted and experimental data, it was found that predicted S-max values were lower than the measured ones; however, most of the results were within about a 10% confidence interval. The difference in the measured and predicted S,,. values was identified to be the result of mass gypsum nucleation and the nuclei growth mechanism. Furthermore, when considering that the presence of the solid phase inside the NF module retentate channel is not recommended, we concluded that the proposed S m prediction procedure better describes maximum permissible gypsum retentate supersaturation than the experimental one. Powder X-ray diffraction data show that the only solid phase present under our measurements conditions is gypsum.