Stabilizing NaCl particles with Cd2+ in a saturated solution during ex situ PSD measurement

The measurement of a particle size distribution (PSD) of a soluble salt, NaCl, dispersed in a saturated solution using laser light scattering (LLS) is fraught with difficulty since this apparatus and others like it do not have strict temperature control in the sample chamber. A slight increase or decrease in temperature produces conditions where the crystals grow or dissolve spontaneously from or into background solution during PSD analysis. The difficulties introduced in particle size analysis can be overcome by adding 100ppm CdCl2 to the saturated solution used to disperse the crystals for analysis. The Cd2+ ion is known to adsorb on the surface of NaCl in solution, thus inhibiting the crystal growth/dissolution rate by pinning steps of NaCl crystals (Growth Crystal 8, (1969), 3). With this additive the PSD of NaCl produced during the crystallization from a NaCl contaminated 38 wt% CaCl2 solution cooled from 70degreesC to 30degreesC in a 1.4 liter jacketed-baffled-stirred tank is stabilized so that it call be reproducibly measured with the LLS. (C) 2004 Elsevier B.V. All rights reserved.