Challenges with elemental sulfur removal during the leaching of copper and zinc sulfides, and from the residues; a review

Abstract

The hydrometallurgical recovery of metal values from sulfide concentrates, such as chalcopyrite, enargite, and sphalerite, typically generates elemental sulfur in the oxidative leaching processes. The main disadvantage of the generation of sulfur is that it retards or hampers the efficiency of the leaching process. The oxidative leaching of sulfide mineral concentrates at temperatures above 180°C and at high pressures, known as total pressure oxidation (TPOX), completely converts the sulfide minerals to sulfate ions and sulfuric acid. However, the TPOX process has several negative aspects that increase costs, including the capital cost of the TPOX operations, the high oxygen demand to convert sulfide to sulfate, and the lime that is required to neutralize the excess acid in the autoclave discharge. Alternative processes that can reduce the capital and operating costs associated with the treatment of sulfidic concentrates include the medium temperature pressure oxidation (MT-POX) processes that operate at or below 150°C, such as the Cominco Engineering Services Ltd. (CESL) process, and atmospheric leaching (ATL) processes, such as the Albion and Galvanox™ processes. In the MT-POX and ATL processes, a proportion of the sulfides from the sulfide concentrates are oxidized to elemental sulfur, reducing the generation of acid and the oxygen demand of the oxidative leaching processes. Despite the lower operating and capital costs of the MT-POX and ATL processes, elemental sulfur may cause environmental problems such as acid mine drainage, or downstream process operation problems such as low solid/liquid separation efficiency or leaching efficiency. Thus, it is important to remove the elemental sulfur effectively during the leach process or from the residues after the leach process. In this paper, we present a summary of the research that has been conducted to decrease the passivating effect of molten or solid sulfur during the leaching of copper sulfide and zinc sulfide, and the approaches to remove the elemental sulfur from the leach residues. Also, the paper reviews the most important approaches that have been developed to address the elemental sulfur issue, including the application of polytetrafluoroethylene (C2F4)n, carbon tetrachloride (CCl4), ozone, nanosilica, sulfur-oxidizing bacteria, thermophilic iron-oxidizing archaea, sulfur-reducing bacteria (SRB), calcium lignosulfonate, quebracho, tetrachloroethylene (C2Cl4), Na2S leaching–CO2 precipitating, and vacuum and atmospheric distillation.