Continuous and simultaneous conversion of phosphogypsum waste to sodium sulfate and potassium sulfate using quaternary phase diagram.

Abstract

In this present work, the transformation of the Moroccan phosphogypsum (PG) waste, considered a potential source of sulfate, into potassium sulfate compound could help reduce environmental impact and create a new value chain for the phosphate industry. Generally, solid-liquid equilibria are frequently applied in chemical industries. They are a valuable aid in visualizing the precipitation, separation, and purification of a solid phase and the pathways by which crystallization can occur. This process aims to produce potassium sulfate (K2SO4), a high-value fertilizer, from sulfate solutions obtained after dissolving PG in a NaOH medium. The quaternary phase diagram Na+, K+//Cl-, SO42--H2O at 25°C was especially used to determine the operating conditions and the design of a crystallization process during the PG conversion into K2SO4. The Jänecke representation of this system enables the determination of the optimal trajectory in the phase diagram for the double decomposition reaction. X-ray fluorescent (XRF) and X-ray diffraction (XRD) techniques were conducted to identify the crystalline phases formed during our process. In summary, the results of this study could contribute to the development of a sustainable valorization PG. Furthermore, K2SO4 represents a good alternative to potassium chloride for chloride-sensitive crops.