Effects of organic pollutants on the fractional crystallization of NaNO3 from high-saline wastewater

Abstract

In this study, the effect of organic pollutants on the fractional crystallization of NaNO3 from high-saline wastewater was investigated by experiments and theoretical methods. Prior to the investigation, the optimal condition of cooling rate, 10 K/h, stirring intensity, 200 rpm, and aging time, 10 min, were acquired for pursuing a high purity, large crystal particle and uniform size distribution. Based on the optimized process operation, different contents of organic contaminants represented by phenol and quinoline were added for NaNO3 crystallization. It is clear that both phenol and quinoline have no effect on the product morphology, while their negative effects on the crystal size are significant. The averaged crystal size decrease from 717 μm to 162 μm, when the phenol content reaches 2.0%. Similarly, the addition of 0.2% quinoline cause an obvious decline of the mean size to 197 μm. The results of XRD characterization, carbon content analysis and infraredspectrum show that phase transformation, incorporation into crystal lattice and selective adsorption are not the main modification mechanisms for the influence of organic matters on the crystal size. Hence, the reduced crystal size is mainly attributed to the inhibition of solute diffusion caused by the presence of organic pollutants. This was further verified by the molecular dynamics simulation. The calculated results indicate that when the system contains 40 Na+ ions, 40 NO3− ions, 20 phenol or quinoline molecules, the diffusion coefficient of Na+ reduce by 8.67% and 30.86%, while the diffusion coefficient of NO3− decrease by 29.33% and 39.51%, respectively. Related results provide an important reference for the industrial process control of high-saline wastewater fractional crystallization.