Influence of Trivalent Metal Ions on the Metastable Zone Width of Ammonium Sulfate

Abstract

The metastable zone width (MZW) is a vital parameter for the design of industrial crystallization processes of inorganic salts and could be affected by the addition of impurities. Here, the effect of the trivalent ions Fe 3+ , Cr 3+ , and Al 3+ on the MZW of ammonium sulfate was observed. All the experiments were performed with the help of ultrasonic speed measurements. Impurity concentrations up to 100 ppm at a solution pH of 4 increase the MZW depending on the metal ion. The pH value also showed a major influence on the effect of trivalent metal impurities. The results were compared to the distribution of metal-aquo-complexes existing in aqueous solutions contaminated by trivalent metal ions. The distribution was determined by using the computer-based simulation software Hyss. The first hydrolysis product was identified to be active in widening the MZW.

Prediction of metastable zone widths of ammonium sulphate: modification of the nucleation potential model in an electrolyte system

“…38 Trivalent ions Fe 3+ , Cr 3+ , and Al 3+ were reported to widen the MSZWs of ammonium sulphate, where the pH also played an important role in the effect of impurity ions. 34 The crystal size can be optimized with the content level of impurity in the solution. 31 In addition, study have shown that ultrasound can narrow the crystal size distribution and reduce agglomeration.…”

“…[26][27][28] The nucleation process of ammonium sulphate crystallization has been reported. 4,5,[29][30][31][32][33][34][35] The influences of the existence of different impurity ions, 30,31,33,34,36 pH value, 5,32,35,37 and stirring speed 4,5 on the crystal habit and particle size distribution of ammonium sulphate have been investigated, which will also influence the morphology and size distribution of the final crystalline product. 38 Trivalent ions Fe 3+ , Cr 3+ , and Al 3+ were reported to widen the MSZWs of ammonium sulphate, where the pH also played an important role in the effect of impurity ions.…”