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

Abstract

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.