Gypsum nucleation into sodium chloride solutions

The nucleation of gypsum into a NaCl solution was studied within a supersat uration range of 2-4 at 25-70 degreesC. The experiments were carried out us ing a lab-scale apparatus consisting of a batch crystallizer with the relat ed measurement devices. Signals of scattereded and transmitted light coming from a He - Ne laser source were analyzed to measure e the induction perio d that is, the time delay necessary for homogeneous nucleation to take plac e. Comparison of the experimental results with those previously obtained in the absence of added NaCl in solution showed that NaCl strongly affects gy psum precip itation. They were compared in terms of the activation energy a nd the interfacial tension between crystals and the surrounding aqueous sol ution.