A green sulfidation roasting–flotation process using desulfurized gypsum for sustainable copper recovery and waste valorization

Abstract

Desulfurized gypsum (DG), a large-volume industrial by-product, was repurposed as a green sulfidation reagent for the recovery of cuprite through a sustainable sulfidation roasting–flotation process. Thermodynamic analysis confirmed that DG can effectively react with cuprite under a clean hydrogen (H₂) atmosphere, producing CuS and Cu₂S without generating SO₂. Sulfidation relies on solid-state reactions between CaSO₄ and Cu₂O, where CaSO₄ is reduced to CaS and CaO, thereby replacing conventional sulfur-based reagents that release toxic gases. The effects of roasting temperature, time, DG dosage, and H₂ concentration on flotation performance were systematically examined. Under optimal conditions (350 °C, 30 min, DG dosage 1.0, and 40% H₂), a maximum copper recovery of 89.19% was achieved with zero secondary emissions. The sulfidation reaction initiated at the mineral surface and progressed inward, forming a mesoporous (∼4.2 nm) layer. Contact angle measurements indicated a continuous increase in hydrophobicity with temperature, reaching 87.13° after collector adsorption at 350 °C. A two-stage particle growth kinetic model was developed to quantitatively describe the sulfidation behavior. This study demonstrates a clean, waste-to-resource approach for copper recovery from oxide ores, providing a feasible route toward emission-free metallurgical processing.