Phase diagrams of the quinary system K+, NH4+, Mg2+// SO42−, Cl−- H2O at 273.15 K and 298.15 K and their application

Abstract Based on the requirement of the new technology for producing chloride-free potassium fertilizers by the reaction of KCl·MgCl 2 ·6H 2 O and (NH 4 ) 2 SO 4 , the phase equilibrium of the mutual quinary system K + , NH 4 + , Mg 2+ //SO 4 2− , Cl − - H 2 O at 273.15 K and 298.15 K were studied using the isothermal dissolution equilibrium method under atmospheric pressure, and the corresponding phase diagrams were plotted. According to the diagrams, there are seven saturation points and eight solid phase crystalline fields. Fields of K 2 SO 4 ·MgSO 4 ·6H 2 O and (NH 4u ,K 1-u ) 2 SO 4 ·MgSO 4 ·6H 2 O are larger than other crystalline fields, which indicates that these two salts can crystallize out from solution easily. By analyzing and calculating the phase diagrams at 273.15 K and 298.15 K, chloride-free compound fertilizers can be produced via KCl·MgCl 2 ·6H 2 O and (NH 4 ) 2 SO 4 as raw materials, and the by-product NH 4 Cl can crystallize out.