A potential industrial waste–waste co-treatment process of utilizing waste SO2 gas and residue heat to recover Co, Ni, and Cu from copper smelting slag

Highlights: • An industrial waste-waste co-treatment process was proposed to recover Co, Ni, and Cu from copper smelting slag. • Reaction mechanism of the proposed sulfation roasting by water leaching process was experimentally defined and verified. • The extraction yields of Ni, Co, and Cu can reach 95.8% and 91.8%, 81.6%, respectively under the optimized condition. • A potential environmentally friendly industrial process referred to the energy flow and material flow was presented. A potential industrial waste-waste co-treatment process was proposed and verified for the recovery of the valuable metals Co, Ni, and Cu from copper smelting slag by utilizing high temperature SO₂ off-gas. Sulfation roasting followed by water leaching under designed thermodynamic conditions was conducted to facilitate the selective formation of Co, Ni, and Cu sulfates while separating iron as oxide. Several parameters were studied such as roasting temperature, roasting time, the addition of Na₂SO₄, and leaching agent. Under the optimized sulfation roasting conditions (Gas flow: 500 mL/min, 5% SO₂ + 20% O₂ + 75% Ar; Roasting temperature: 650 °C; Roasting time: 4 h; Addition of Na₂SO₄: 30%) followed by water leaching (Leaching temperature: 80 °C; Leaching time: 5 h; solid to liquid ratio: 0.05 g/mL), the extraction yields of Ni, Co, and Cu were shown to reach 95.8% and 91.8%, 81.6%, respectively. Furthermore, the sulfation roasting – water leaching process was confirmed on lab-scale as a feasible and efficient way to recover valuable metals and the mechanism was determined and verified from the microstructural evolution. Finally, a potential environmentally friendly industrial process in terms of the energy flow and material flow was presented based on preliminary assessments for environmental benefits, economic benefits, and heat recovery.