The influence of sodium chloride on the crystallization rate of gypsum

The growth kinetics of gypsum was studied in supersaturated solutions both in pure water and in the presence of NaCl, using a seeded growth technique. Radioactive tracer techniques were employed to follow the growth process.The mean linear growth rate R was plotted against the relative supersaturation σ. For low σ values the relation between R and σ is given by a linear law, for higher σ values by a parabolic law and for the highest σ values by a growth “order” higher than two.It was shown that the addition of sodium chloride increased the crystallization rate remarkably. The higher the NaCl concentration the higher the growth rate.