Concentration-dependent structure of mixed (NH4)2SO4 and K2SO4 aqueous solutions using the X-ray diffraction, Raman spectroscopy and molecular dynamics simulations

Abstract

In the production of potassium sulfate by ammonium sulfate, the purity of potassium sulfate product is relatively low due to the presence of potassium sulfate and ammonium sulfate solid solution. The microstructure of mixed aqueous solution of potassium sulfate and ammonium sulfate have been studied by X-ray diffraction, Raman spectroscopy and molecular dynamics simulation. And the molality of SO42− in the solution remained unchanged, and the molality of K+ and NH4+ were changed respectively. Reduced structure function [F(Q)], reduced pair distribution function [G(r)], excess Raman spectroscopy, radial distribution function (RDF), and structure of hydrogen bond network were obtained. With the decrease of K+ concentration and the increase of NH4+ concentration, a variety of new ion contact pairs were formed in the solution. The original hydrogen bond network is disrupted, and the cations would rebuild the hydrogen bond in the solution. When the NH4+ replaces the K+, the destruction to the hydrogen bond network is reduced. The addition of NH4+ might weaken the interaction between water molecules and anions, and exceed a certain critical concentration of 0.8 mol·L-1, NH4+ could promote the interaction between water molecules and anions. Moreover, the experimental results are in good agreement with the simulation results. This article provides certain theoretical guidance for its separation by studying the microstructure of its mixed solution.