Novel forward osmosis process to effectively remove heavy metal ions

Abstract

In this study, a novel forward osmosis (FO) process for the removal of heavy metal ions from wastewater was demonstrated for the first time. The proposed FO process consists of a thin-film composite (TFC) FO membrane made from interfacial polymerization on a macrovoid-free polyimide support and a novel bulky hydroacid complex Na4[Co(C6H4O7)2]·2H2O (Na–Co–CA) as the draw solute to minimize the reverse solute flux. The removal of six heavy metal solutions, i.e., Na2Cr2O7, Na2HAsO4, Pb(NO3)2, CdCl2, CuSO4, Hg(NO3)2, were successfully demonstrated. Water fluxes around 11L/m2/h (LMH) were harvested with heavy metals rejections of more than 99.5% when employing 1M Na–Co–CA as the draw solution to process 2000ppm(1 ppm=1 mg/L) heavy metal solutions at room temperature. This FO performance outperforms most nanofiltration (NF) processes. In addition, the high rejections were maintained at 99.5% when a more concentrated draw solution (1.5M) or feed solution (5000ppm) was utilized. Furthermore, rejections greater than 99.7% were still achieved with an enhanced water flux of 16.5LMH by operating the FO process at 60°C. The impressive heavy metal rejections and satisfactory water flux under various conditions suggest great potential of the newly developed FO system for the treatment of heavy metal wastewater.