INTEGRATED CHARACTERIZATION AND RECOVERY STRATEGIES FOR HOT-DIP GALVANIZING WASTES: GRANULOMETRIC, CHEMICAL, AND PHASE ANALYSIS FOR SUSTAINABLE ZINC AND IRON VALORIZATION
Abstract
Hot-dip galvanizing (HDG) generates several zinc-and iron-bearing solid wastes—most notably top ash (zinc ash), bottom dross, galvanizing flue dust (GFD), and iron-rich sludges—whose hazardous classification is largely driven by high leachable Zn, chlorides, and associated impurities. GFD is typically an ultrafine material (particle size below 90 μm) and may contain ~27–30% Zn and significant chloride/ammonium phases, making targeted hydrometallurgical recycling attractive at small scale. This paper synthesizes an “integrated characterization-to-flowsheet” strategy for HDG wastes, combining granulometric and morphological diagnosis, bulk chemical/impurity constraints, phase assemblage (chlorides/oxides/hydroxychlorides/intermetallics), and (iv) recovery route selection (selective leaching–purification–electrowinning; oxide/pigment valorization; immobilization where recycling is not feasible). From the analyzed literature set, robust recovery is demonstrated for GFD via two-step leaching and zinc production, GFD residue via concentrated acid leaching achieving very high Zn concentration and efficiency (e.g., 136.532 g/L and 96.24% Zn leached at 4 M H₂SO₄, L/S = 3, 10 min), (c) top ash via sulfuric leaching and electrowinning under controlled pH/current density, and (d) iron sludge valorization to hematite pigments after calcination/washing with major Zn/Cl removal.