Efficient removal of Congo red from wastewater by gas-assisted low-gradient magnetic separation

Gas-assisted low-gradient magnetic separation (GAMS) was proposed for removing Congo red (CR) from wastewater. GAMS included the adsorption removal process of nanoparticles for CR and GAMS recovery process for CR-loaded nanoparticles from wastewater. Polyethylene glycol (PEG) modified Fe3O4 (Fe3O4/PEG) nanoparticles showed maximum saturated adsorption capacity of 133.3 mg/g. The results indicated that the adsorption process conditions changed the loading amounts of CR on Fe3O4/PEG nanoparticles, showing indirect effect on the separation efficiency of GAMS. And the separation performance of GAMS could be significantly improved by changing gas flow rate, ionic strength, pH, and dyes loading amounts on nanoparticles. The comparison results of MS and GAMS suggested that the limitation of magnetic force on the capture distance could be overcome and the separation efficiency of MS could be significantly improved by the bubbles. These made it feasible to rapidly recover dyes-loaded nanoparticles from large volume wastewater. GAMS combined the efficient removal of dyes by magnetic nanoparticles with rapid recovery of dyes-loaded nanoparticles from large volume wastewater, showing great potential for wastewater treatment.