Synthesis of Chloride-Free Potash Fertilized by Ionic Metathesis Using Four-Compartment Electrodialysis Salt Engineering

A sustainable approach for the production of high-purity potash fertilizers devoid of chloride is highly needed. Conventional preparation processes for chloride-free potash fertilizers have certain limitations, such as complicated synthesis procedure, including high-temperature requirement, causing environmental pollution. In this work, a novel approach has been proposed for the production of high-purity potash fertilizer (KNO 3 , K 2 SO 4 , and KH 2 PO 4 ) from KCl by metathesis electrodialysis (MED). Sulfonated poly(ether sulfone)-based cation-exchange membrane and quaternized brominated poly(2,6-dimethyl-1,4-phenylene oxide)-based anion-exchange membranes are used for the MED experiments. The membranes show adequate water uptake, ionic conductivity, and ion-exchange capacity with good mechanical and thermal stabilities. The yields of KNO 3 , K 2 SO 4 , and KH 2 PO 4 are found to be 90, 86, and 90%, respectively. The power consumptions during MED experiment for KNO 3 , K 2 SO 4 , and KH 2 PO 4 are calculated to 0.94, 0.89, and 1.04 kWh/kg, respectively. The purity of products is confirmed by inductively coupled plasma and X-ray diffraction analysis and by measuring ionic contents. The process provides an energy-intensive way for high-purity synthesis of KNO 3 , K 2 SO 4 , and KH 2 PO 4 .