Sulfide minerals are one of the most important sources of metal values. On the other hand, some sulfides such as pyrite are considered as one of the major impurities in solid fossil fuels such as coal. Oxidation of these sulfides has been one route to obtain base metals and to remove sulfur by leaching. This work summarizes the results obtained regarding the use of ozone in the oxidation of sulfide ores containing gold, silver, and copper. Results show that the extraction of gold and silver is increased by at least 15%, with lower cyanide consumption; the extraction of copper increased by 16% and in less time; and in the case of coal, sulfur is removed above 70%. These results indicate that oxidation treatment with ozone could be a promising clean technology to optimize ore processing, which is difficult to treat by current industrial methods.

The present work reports the direct leaching of zinc from a sphalerite concentrate in acid media. Lab-scale and pilot-scale experiments were conducted in atmospheric-pressure and low-pressure reactors, respectively. Leaching of zinc and precipitation of iron was achieved in the same stage using different reagents like Fe³⁺, O₂, O₃, and Fe²⁺ (which is continuously oxidized in the leaching solution by H₂O₂ and O₂). The highest percentage of zinc extraction (96%) was obtained in pilot-scale experiments using H₂SO₄, Fe²⁺, and O₂. Experimental results were compared with those of other researchers to provide a better understanding of the factors influencing the dissolution of zinc. In the first instance, it was determined from analysis of variance that leaching time and the use of an oxidant agent (O₂ or O₃) were the most influential factors during the direct leaching of zinc from the sphalerite concentrate. Kinetic models were also evaluated to determine the rate-limiting step of the sphalerite leaching; it was concluded that the type of the sulfur layer formed in the residue (porous or non-porous) depends on the type of the oxidant used in the leaching media, which determines the dissolution kinetics of zinc.

The use of ozone for the oxidation of cyanidation wastewater has been studied since the 1950's. In the last 2 decades, the use of ozone to oxidize sulfide ores has been studied. This report presents some of the results obtained concerning the use of ozone in the oxidation of raw ores containing gold and silver as well as the treatment of tails or residues of the cyanidation process. The results show that oxidation treatment with ozone prior to cyanidation may help to optimize this process, mainly through reduction of the consumption of cyanide.

This research focused on the evaluation of the Fe₂O₃/TiO₂ composite and two industrial wastes, a kaolin (Clay-K) and a blast furnace sludge (BFS), as adsorbents and/or photocatalytic materials to enhance the removal of cyanide from aqueous solutions. Cyanide adsorption tests were conducted in the absence of light. In contrast, cyanide photodegradation tests were conducted under three types of irradiations: visible light, ultraviolet (UV) light, and natural sunlight. For the latter case, two irradiance conditions were evaluated. Cyanide adsorption from aqueous phases was similar for Clay-K and TiO₂/Fe₂O₃ materials, which adsorbed almost twice as much cyanide compared to the BFS sample. The differences observed in cyanide removal were explained in terms of the material’s surface area and chemical composition, and a complexation of cyanide ions with surface metals was suggested as the most feasible adsorption mechanism. The set of cyanide photodegradation experiments promoted, in general, higher cyanide removal from the aqueous solution compared to the adsorption processes. Under the conditions used in this study and when using Clay-K and BFS as promoters, cyanide photodegradation progressively enhanced with the following radiations: visible light < UV light ~ UV+solar ≤ Visible+solar. In the case of the TiO₂/Fe₂O₃ composite, cyanide photodegradation increased in the following order: UV light < visible light < UV+solar ~ Visible+solar. Clearly, solar radiation had a significant effect on promoting cyanide removal. For experiments conducted with natural sunlight, the set with irradiance of 600–800 W/m² exhibited the highest cyanide removal percentage, and the BFS had the best performance among the three tested samples over a period of 2 h. Results showed the benefit of using industrial wastes to remove cyanide from aqueous solutions and illustrates remediation of industrial effluents is potentially feasible within the framework of a circular economy.