Novel strategy for preparing a magnetic drawing solute for use in forward osmosis to reclaim water from the wastewater of diamond wire sawing of silicon ingots

The speedy growth of the semiconductor industries and global water scarcity issues have caused great demand for energy-saving water reclamation technologies such as forward osmosis (FO). Magnetic nanoparticles functionalized with osmotic polymer were believed to be one of the emerging materials used as the drawing solute in FO because they can be simply recovered with magnet. This study employed a novel strategy to prepare an FO drawing solute that balances the tradeoff between the amount of surface-immobilized ionic polymer for generating osmotic pressure and particle size with strong magnetization for ensuring steady recovery. The drawing solute was designed to be applied to the FO reclamation of water from the wastewater generated during the diamond wire sawing of Si ingots. Coprecipitation and polyol reduction were employed to synthesize poly(sodium acrylate)-functionalized magnetic nanoparticles (PSA-MNPs) as the drawing solute. The polyol route produced particles (PSA-MNPpolyol) sized 150–220 nm and composed of spherical subunits sized 3–5 nm. By contrast, coprecipitation resulted in irregular aggregated clusters and discrete 3–8-nm particles (PSA-MNPcp). Adding the electrostatic stabilizer sodium acetate to the precursor in the coprecipitation route (creating PSA-MNPcp+AC) significantly improved the particles’ dispersion and slightly increased their osmolality. When the optimal concentration of iron precursor was employed, the saturation magnetization and the osmolality of the PSA-MNPpolyolreached 45.89 emu/g and 258 mOsmol/kg, respectively. The average water flux generated when PSA-MNPpolyolwas employed as the drawing solute was approximately 3.8 times higher than that generated when PSA-MNPcp+ACwas used over a 3-h FO process on waste produced by ingot sawing. The homogeneous particle sizes of PSA-MNPpolyolare conductive to post-FO recovery through magnetic separation.