Floatable magnetic aerogel based on alkaline residue used for the convenient removal of heavy metals from wastewater

The present work introduces a novel strategy for preparation of a recyclable aerogel absorbent for heavy metal purification of industrial wastewater. The absorbent (Fe3O4/SA-AR) is based on a combination Fe3O4, alginate (SA) and industrial alkaline residue (AR) waste, forming a cost-efficient and easily recyclable spherical aerogel. The magnetic aerogel spheres of the Fe3O4/SA-AR are light-weight with a loose porous structure and a mechanical strength 10 times that of conventional SA aerogels, thus sustaining up to 20 cycles of compression relaxation. This excellent structure stability guarantees long-term integrity and floatability of the aerogel spheres in water. Adsorption experiments on the heavy metal Cd(II) suggested that equilibrium was approached within 2 h. The maximum adsorption capacity was 38.83 mg/g, higher than reported for conventional SA aerogel absorbents. After 5 cycles of adsorption-desorption, the aerogel spheres still maintained an adsorption efficiency of 90%, and had good stability and reusability. Studies on kinetic and adsorption isotherm models showed that the adsorption of Cd(II) to Fe3O4/SA-AR correlated well with the pseudo-second-order kinetic model and the Langmuir isotherm model. FTIR, SEM-EDS and XPS analyses indicated that the adsorption of Cd(II) to the Fe3O4/ SA-AR aerogel was mainly driven by formation of OH complexation, electrostatic adsorption and ion exchange. In summary, this work suggests a new route for synergetic resource utilization of value-less and pollutive alkaline residual for the removal of heavy metals in wastewater.