Reusable self-floating carriers recover heavy metals from industrial wastewater through heterogeneous nucleation for resource reuse

Coagulation-flocculation in industrial wastewater treatment drives environmental pollution from landfilling heavy metal-laden sludge. Efficient separation of the sludge is crucial for cost-effective metal recovery. This study explored a new separation method of Cu2+, Ni2+, Zn2+ and Cr3+ via self-floating metal hydroxides assisted by hollow glass microsphere (HGM) carriers. The amount of OH- was stoichiometric to the positive charges of metal ions, mixed with 1 mg mL-1 HGM, causing metal hydroxides to attach to HGM surface via heterogeneous nucleation. The self-floating system removed 37.5% and 14.0% more metals than sedimentation at 50 and 200 mg L-1 metal concentrations. HGM additions increased the particle size of metal hydroxides by up to 12.5 times to that of HGM at 18.8 +/- 1.1 mu m, benefiting their solid-liquid separation. By pumping the wastewater downward in column reactor at velocities equal to or less than the self-floating sludge, 96.4% metals were removed in continuous flow. The recovery rates of HGM and metals reached 92.0 +/- 2.2% and 92.7 +/- 3.2%, and the concentration of the recovered metal reached 19,339 +/- 394 mg L-1 for potential reutilization in industrial electroplating. This research investigated a new separation strategy based on solid self-flotation for sustainable treatment of metal-laden wastewater.