Cleaner zinc extraction from high silica-calcium oxygen-sulfur mixed lead-zinc concentrates with calcium and sulfur conservation

High-silica-calcium oxygen-sulfur mixed lead-zinc (HSC-PbZnOS) ore is a complex and refractory resource. This study proposed a novel and cleaner process to extract zinc and conserve sulfur and calcium in CaS form from HSC-PbZnOS concentrate. After mineral composition characterization of HSC-PbZnOS concentrate, thermodynamic and experimental investigations reveal that zinc oxides can be directly reduced by carbon, ZnS first reacted with CaO above 770 ℃ to form a stable intermediate CaZnSO (CaO + ZnS → CaZnSO), which is subsequently reduced above 1126 ℃ to Zn(g) and CaS (CaZnSO + C → Zn(g) + CO + CaS). Thus sulfur was fixed as CaS and SO₂ emission was avoided. SiO₂ tended to react with CaO to form silicates, partially inhibiting sulfur-fixation. However, under reducing conditions around 1300 ℃, silicate decomposed to release CaO, allowing it to regain reactivity with ZnS. In addition, pilot tests show that adding 10   wt% limestone increased the Zn reduction rate to 98.9% and the sulfur fixation rate to 98.1%. The gaseous product was ZnO, and the residue mainly consisted of individual SiO₂ and CaS. This work provides a clean, short-process route for efficient utilization of complex HSC-PbZnOS resources with industrial potential.