Electro-kinetically upgraded sustainable approach and process optimization for synthesis of dual nutrient potassium fertilizer from ammoniacal filtrate wastewater model

Abstract

Traditional methods for wastewater repurposing and value-added product recovery are associated with operational shortcomings viz. high energy requirements, poor conversion efficiency, purity and sustainability, thus it is highly desirable to upgrade the same via. zero-emission sustainable processes. Herein, electro-kinetically upgraded sustainable approach “metathesis electrodialysis” (mED) is developed and meticulously optimized for synthesis of high value potassium nitrate (KNO3) using low cost KCl and ammoniacal filtrate NH4NO3 electrolyte model as reactants. mED experiments have been carried out using indigenously designed interpolymer based cation and anion exchange membranes with high counter-ion transport selectivity. In order to optimize suitable potential for mED process, the influence of varied applied potential from 1.5 V/cell pair to 2.5 V/cell pair and its effect on KCl to KNO3 conversion, KNO3 purity, and mED process efficiency have been investigated. In particular, 2.0 V/cell pair applied potential has been found optimum with 97.67% KNO3 purity and 61.87% energy efficiency of mED process. Further, effect of initial feed concentration of KCl and NH4NO3 have been investigated in greater details. Up to 94% KCl to KNO3 conversion and 96.71% product purity has been achieved at optimized applied potential of 2.0 V/cell pair using 0.8 M initial feed concentrations of KCl and NH4NO3. Under these operating parameters, mED showed moderate energy consumption of 1.25 kWhkg-1 with 91.73% energy efficiency. The product purity was evaluated in comparison to commercial grade KNO3 using FT-IR and XRD analysis. Moreover, KNO3 purity exceeded 98% when mED operated using 0.2 M initial feed concentration. It is interesting to note that electro-osmotic water transport and solute back diffusion have not been realized during mED process. Finally, based on above results we anticipate that mED has great potential application in chloride free potassium fertilizer synthesis, especially KNO3.