Structure and Crystallization Behavior of Aqueous K₂SO₄-MgSO₄ Solutions

The foundation for the efficient utilization of potassium resources in Salt Lake brine is to reveal the structural characteristics of the solution, analyze the crystallization behavior process, and its correlation. This study investigated ionic hydration and binding structures in K₂SO₄-MgSO₄ mixed solutions using synchrotron X-ray scattering. Meanwhile, the crystallization behavior of mixed solution droplets was further studied using in situ Raman spectroscopy technology. Research has shown that as the mass fraction of MgSO₄ increases, the hydrogen bond network structure is disrupted in the solution. In the mixed solution, Mg²⁺ competes with K⁺ for SO₄^2-, promoting the transformation of the K⁺-SO₄^2- binding form from a bidentate contact ion pair to a monodentate contact ion pair, forming multi-ion clusters such as K⁺-SO₄^2--Mg²⁺. Under low humidity (RH < 40%), the droplets form a colloidal structure due to Mg²⁺-SO₄^2- chain MCIP, resulting in a 60-92% decrease in water loss rate (k = 0.0059-0.0179 s^-1) compared to pure K₂SO₄ (k = 0.0741 s^-1). In addition, the colloidal interfacial layer in the mixed droplets significantly delayed the nucleation and crystallization of K₂SO₄. This study provides a theoretical basis for extracting potassium sulfate from sulfate-type Salt Lake brine.