Synthesis of magnetic adsorbents from titanium gypsum and biomass wastes for enhanced phosphate removal

A novel scheme was proposed to prepare magnetic adsorbents by co-pyrolysis of titanium gypsum (TiG) and agricultural biomass wastes for phosphate (P) recovery. Co-presence of biomass wastes could improve TiG decomposition in inert atmosphere to generate magnetic centers and active sites, and P adsorption correlated well with organic volatiles of biomass wastes. The adsorption process evolved from a biomass-controlled process to a TiG-controlled process when increasing the mass ratio of corncob above 10 %. The optimal adsorbent (i.e. GC10) exhibited higher P adsorption capacity (Qm 183 mg/g) than many previous adsorbents; moreover, it can be magnetically separated from water after P adsorption. Active sites including CaO, CaS and Fe3O4 were deemed as the main factors for P chemisorption and surface precipitation. Most of adsorbed P could be released continuously and slowly by dilute NaHCO3. These results highlight potential applications of TiG and biomass waste derived adsorbents in P purification and recovery.