Transforming waste into resources: Pyrometallurgical recovery of copper and zinc from spent CuO-ZnO-Al2O3 catalysts.

CuO-ZnO-Al2O3 catalysts are designed to produce methanol through low-temperature synthesis gas conversion. Coke deposition and spinel structure formation resulting from interactions between metal oxides and alumina lead to catalyst deactivation. This study investigated the thermal treatment of spent CuO-ZnO-Al2O3 catalysts, with emphasis on metal recovery and by-product characterization. The proposed method enables effective recovery and separation of metallic copper and zinc, while the residual solid, zinc aluminate (ZnAl2O4), could be reused for various applications (optical coatings, photocatalysis and gas sensors, among others) facilitating complete recycling of the spent material. Pre-treatment by grinding and calcination at 800 °C to 1000 °C showed no significant effect on spinel formation. Heat treatment effectively removed carbon from the catalyst, with an average mass loss of 7.1 ± 0.5 wt%. Cu and Zn chlorides were extracted selectively by dry chlorination at 600 °C. Multiple polymorphic forms of ZnCl2 and CuCl2 were the condensate products. Cu and Zn extraction from the catalyst were 99.2 % and 83.6 % in mass, respectively. Furthermore, ZnCl2 volatilization and CuCl2 reduction to metallic Cu were achieved at 400 °C after 8 h under a hydrogen atmosphere. The overall process yielded total recoveries of 30 wt% for Cu and 40 wt% for Zn, which are significantly below the extraction recovery ratio observed in the chlorination stage, indicating inefficiencies in the capture of the volatile products.