Preparation of chloride-free potash fertilizers by electrodialysis metathesis

Traditional preparation processes of chloride-free potash fertilizers (KNO3, K2CO3 and K2SO4) have certain limitations, such as complicated operation and existing potential pollution. In this work, electrodialysis metathesis (EDM) was used to prepare these fertilizers using KCl and acid radical salt (nitrate, carbonate and sulfate) as raw materials. Firstly, as current density increases from 10 to 25 mA/cm2, energy consumption grows from 0.41 to 0.64 kW h/kg KNO3, while KNO3 product purity improves from 92.36 to 95.91 wt%. Secondly, different sulfate sources, such as MgSO4, Na2SO4 and (NH4)2SO4, were used to investigate the effects of cation species, showing that the orders of energy consumption and impurity cations in product are EMgSO4>ENa2SO4>E(NH4)2SO4 and WNH4>WNa>WMg, and (NH4)2SO4 is regarded as the suitable sulfate source. Thirdly, NaNO3, Na2CO3 and Na2SO4 were selected to investigate the effects of anion species. The order of average energy consumption is E‾K2CO3>E‾K2SO4≈E‾KNO3, while that of average current efficiency is η‾K2SO4>η‾K2CO3>η‾KNO3. Besides, compared with other two fertilizers, generated KNO3 product purity is comparatively higher. Finally, economic evaluation results showed that EDM has great potential applications in preparing chloride-free potash fertilizers, especially for KNO3 and K2CO3.