Estimation of the Growth and Dissolution Kinetics of Ammonium Bicarbonate in Aqueous Ammonia Solutions from Batch Crystallization Experiments. 2. The Effect of Sulfate Impurity

In this study, we estimated the growth kinetics of ammonium bicarbonate crystallized from aqueous ammonia solutions containing an impurity in the form of ammonium sulfate. The evolution of the ammonium bicarbonate concentration of seeded desupersaturation experiments, estimated by attenuated total reflection-Fourier transform infrared measurements, has therefore been fitted to a population balance model that accounts for the real speciation of the system in the computation of the solution supersaturation. Furthermore, nonidealities of the liquid phase have been considered through the extended-UNIQUAC model. In this work, it has been found that the presence of sulfate ions in solution leads to a progressive decrease in the ammonium bicarbonate crystal growth rates as the concentration of the sulfate ions increases. A competitive adsorption model based on a Langmuir-type isotherm in which the sulfate ions represent the impurity in the system has been found to describe the experimental data rather well. Moreover, the analysis of the ammonium bicarbonate crystal purity revealed that sulfate ions have been sparingly included in the crystals at the experimental conditions reported, thus indicating that the foreign species is only temporary adsorbed on the crystal surface.