Novel Multicharge Hydroacid Complexes That Effectively Remove Heavy Metal Ions from Water in Forward Osmosis Processes.

Suitable draw solutes are crucial to maximize the potential of forward osmosis (FO) in water treatment. In this study, a novel three-dimensional, multicharge draw solute of oxalic acid (OA) chromium complex in a tetramethylammonium salt of [N(CH3)4]3[Cr(C2O4)3] (NMe4-Cr-OA) was developed for electroplating wastewater treatment using FO processes. The newly designed NMe4-Cr-OA has a Cr-centered octahedral structure and can ionize a multicharge anion [Cr(C2O4)3]3- and three cations [N(CH3)4]- in its aqueous solution. Such characteristics are conducive to not only generating a high osmotic pressure but also minimizing reverse solute flux in an FO process, thus resulting in good FO performance. A high water recovery with a negligible reverse solute flux was achieved for NMe4-Cr-OA in electroplating wastewater treatment via the FO process. Furthermore, a significant increase of 77% in FO efficiency was obtained when NMe4-Cr-OA replaced the conventional draw solute of NH4HCO3 for FO electroplating wastewater treatment with a copper rejection higher than 99.9%, which surpasses the best performance of other technologies reported for copper ion removal.