Novel forward osmosis process to effectively remove heavy metal ions

• FO process has great potential to remove heavy metal ions from wastewater.
• Higher concentration of draw solution enhances the removal of heavy metal ions.
• FO process maintains high rejections under high concentration of heavy metal ions.
• The rejections to heavy metal ions ameliorate with increasing temperature.

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 11 L/m2/h (LMH) were harvested with heavy metals rejections of more than 99.5% when employing 1 M Na–Co–CA as the draw solution to process 2000 ppm(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 (1.5 M) or feed solution (5000 ppm) was utilized. Furthermore, rejections greater than 99.7% were still achieved with an enhanced water flux of 16.5 LMH 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.

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