Self-consumed strategy to reuse cathode residue for Zn stabilization in spent batteries: Structural properties and metal stabilization effect.

Due to ecotoxicity, zinc (Zn) as a heavy metal from electronic waste (e-waste) has been a source of pollution to soil and water for several decades. This study proposes a solution to this serious environmental problem via a self-consumed strategy to stabilize Zn in anode residues. This unique method uses cathode residues from spent zinc-manganese oxide (Zn-Mn) batteries as a stabilized matrix via thermal treatment. More specifically, the strategy incorporates zinc metal into a chemically durable matrix comprised of a lattice of AB2O4 compounds. Results demonstrate that 5-20 wt% of anode residue were fully incorporated into the cathode residue to form a Mn3-xZnxO4 solid solution after sintering at 1300 ℃ for 3 h. The lattice parameters of the Mn3-xZnxO4 solid solution reveal an approximately linear decreasing evolution with the addition of anode residue. To determine the occupancy of Zn in the crystal structure of the products, we used Raman and Rietveld refinement processes; the results reveal that Mn2+ in the 4a site was gradually replaced by Zn2+. We then used a prolonged toxicity leaching procedure to evaluate the Zn stabilization effect after phase transformation; this showed that the Zn leachability of sintered anode-doped cathode sample was over 40 folds lower than that of untreated anode residue. Therefore, this study presents an economical and effective strategy for mitigating the presence of heavy metal pollutants derived from e-waste.