Continuous synthesis of high purity KNO3 through electrodialysis metathesis

Abstract

The traditional metathesis (double replacement) method for preparing the chlorine-free fertilizers has its shortcomings, such as high energy consumption and limited conversion degree. Here, the environmental-friendly and economical electrodialysis metathesis (EDM) process was developed to synthesize the potassium nitrate of high purity continuously. The experiments were carried out by using an EDM membrane module of 200 cm2 effective membrane area with 5 repeating units. Effects of operating parameters, current density, initial KNO3 concentration and water flow rate of the KNO3 tank, on EDM performance (energy consumption and current efficiency) and KNO3 quality were investigated. Results showed that the lowest energy consumption (0.165 kWh/kg KNO3) can be attained, while the current efficiency and K2O content in the final product can be high to 94.10% and 44.61 wt%, respectively. After a preliminary and simple purification, the products can meet the requirements of the Chinese national standard GB/T20784-2006. What is more, results of the economic evaluation showed that the total process cost of the continuous EDM system is 0.119 $/kg KNO3, which is lower than that of batch mode (0.160 $/kg KNO3). In addition, the production cost of KNO3 is about 622.10 $/t KNO3, which is lower than the commercial product price (705 $/t KNO3). To sum up, the above results suggest that the continuous EDM process for generating KNO3 of high purity is economically feasible and has great potential to be industrialized.