Conversion of Potassium Chloride into Potassium Sulfate by Four-Compartment Electrodialysis: Batch Operation Process

K2SO4 is a kind of potassic fertilizer, which is mainly prepared through converting KCl with dissolved sulfate or H2SO4. In this study, four-compartment electrodialysis was used to convert KCl with (NH4)2SO4 into K2SO4 to overcome the shortcomings of traditional methods. The phase of product crystals was identified by XRD and the crystal composition was determined by the ion content. Economic evaluation was conducted, and the effects of operation variables on conversion performance were investigated. Results showed that as current density increases from 10 to 25 mA/cm2, operation time decreases from 135 to 55 min while energy consumption increases from 0.26 to 0.50 kw·h/kg K2SO4. A slightly higher than theoretical molar ratio of (NH4)2SO4 to KCl can ensure the complete conversion of KCl into K2SO4. In addition, final K2SO4 concentrations could be increased by reducing the initial K2SO4 tank volume. Finally, higher temperature is beneficial for conversion performance and subsequent evaporation crystallization.