Leaching of critical elements from decopperizing sludge: A comparative study of atmospheric and pressure leaching

Decopperizing sludge (DS) generated during purification of the electrolyte by copper electrowinning contains high concentrations of copper and arsenic, along with antimony, lead and bismuth, primarily in the mineral phases of metadomeykite (Cu₃As), koutekite (Cu 5 As 2 ), arsenolite (As₂O₃), galenobismutite (PbBi₂S₄), and cuprosbitite (Cu 2 Sb). This makes it a valuable secondary resource for critical raw materials extraction. This study explores the extraction of Cu, As, Sb, and Bi from DS via atmospheric and pressure leaching using various oxidants while assessing the influence of leaching parameters. Atmospheric leaching with 1.88 M H₂SO₄ and 2 M H₂O₂ can extract 86.3% of Cu, 83.3% of As, 49.5% of Sb, and 29.7% of Bi within ≤ 3 mins. Pressure leaching at 160°C with Cu²⁺ and oxygen demonstrated a strong selectivity for Cu and As with recoveries up to 93.3% and 85.8% and only 5.35% and 21.1% extraction of Sb and Bi, respectively. While Fe 3+ oxidant at 180°C resulted in Sb and Bi dissolution of 88.7% and 80.0% respectively. The results align well with XRD and SEM-EDS analyses and confirm that oxidant selection is a key to developing a selective extraction method. The use of Cu²⁺ as oxidant under pressure leaching strongly favors Cu and As dissolution, while Fe³⁺ favors oxidative dissolution of Sb and Bi. However, atmospheric leaching with H₂O₂ results in high leaching efficiency of Cu and As together with Sb and Bi. • Decopperizing sludge (DS) is identified as valuable secondary source rich (Cu, As, Sb, Bi). • Oxidant selection in acidic leaching controls selective extraction of critical elements • Atmospheric leaching with H₂SO₄–H₂O₂ achieved a rapid and high extraction efficiency of Cu and As with moderate leaching of Sb and Bi in ≤3 minutes. • Pressure leaching with Cu²⁺ oxidant at 160 °C provided selective dissolution of Cu and As. • Fe³⁺ oxidant at 180 °C markedly enhanced Sb and Bi extraction. • Mineralogical (XRD, SEM–EDS) analyses confirmed phase stability (Cu₃As, PbSO₄) and selectivity mechanisms. • Findings support circular, low-impact metal recovery technologies