Enhanced Leaching of Zinc Ferrite by the Formation of a Solid Solution With Magnetite in Hydrochloric Acid Solution

The high zinc and iron contents of electric arc furnace (EAF) dust in the forms of zinc ferrite (ZnFe2O4) and magnetite (Fe3O4) make it a valuable secondary source of these metals. ZnFe2O4 and Fe3O4 are known to form a solid solution at all compositions, and while ZnFe2O4 is almost insoluble in aqueous solutions, Fe3O4 easily dissolves in acid. The present work investigated the enhanced leaching behavior of ZnFe2O4-Fe3O4 solid solutions by synthesizing a series of (1 - x)ZnFe2O4-xFe(3)O(4) solid solutions, where x = mol pct Fe3O4, via solid-state reaction and leaching using HCl acid solution. Lattice parameter variation of the synthesized solid solutions indicated a positive deviation from Vegard's law with a maximum deviation at x = 20 pct Fe3O4. Leaching results showed that almost complete dissolution was achieved using x = 30 pct Fe3O4 solid solution at 85 degrees C for 2 hours. The enhanced dissolution behavior at this composition was attributed to the displacement of Zn2+ ions (rZn(tetra)(2+) = 0.58 angstrom) by the larger Fe2+ ions (rFe(tetra)(2+) = 0.615 angstrom) in the tetrahedral site of the crystal lattice, which created local distortions and strains rendering the structure vulnerable to acid attack. Therefore, with proper modification of EAF dust, the dissolution of zinc and iron can be significantly improved, which is critical towards sustainable resource recycling.