Sustainable process for the preparation of potassium sulfate by electrodialysis and its concentration and purification by a nanofiltration process

摘要

A sustainable approach for the production of high purity potassium fertilizer (K2SO4) is highly needed to cope with the food crisis. High value K2SO4 produced by the conventional process as well as by metathesis electrodialysis (mED) contains precursor salts as impurities. With the increase of produced K2SO4 concentration, the amount of impurity in the product also increases. Hence, a suitable strategy is required for the rapid and effective production of high concentration and relatively pure K2SO4. Herein, we report a combination of electrodialysis and nanofiltration (NF) processes for the scalable production, purification and concentration of K2SO4. Several parameters such as applied voltage, ratio of the reactants (Na2SO4 and KCl) and their concentrations were optimized to obtain K2SO4 with relatively high concentration along with good purity via the mED process. The K2SO4 obtained by mED was further subjected to NF using a poly(piperazineamide) thin film composite NF membrane to concentrate and to eliminate the chloride (Cl-) and associated monovalent cations from the product stream. The NF parameters such as feed pH and applied pressure were adjusted to obtain a high concentration of aqueous K2SO4 with purity as high as ca. 99%. This process thus provides a suitable way for the production and recovery of solid K2SO4.