Physical-chemical transformations during reduction treatment of copper concentrate smelting slags

Highly efficient autogenous methods introduced for smelting copper sulfide concentrates led to large volumes of copper-rich slags produced. Existing methods for their processing (such as flotation, various methods of reduction smelting) in separate units are ineffective and require significant costs. The use of Vanyukov furnaces for copper concentrate processing allows for slag reduction treatment in the furnace itself by creating a separate recovery zone. Due to the need for depleting copper-containing slags, the possibility of their reduction treatment was investigated. For these purposes, the feed including copper concentrates and quartz flux was subjected to oxidizing smelting at t = 1280÷ ÷1300 °C several times. The resulting slags were subjected to reduction treatment and analyzed using thermal, X-ray phase, mineralogical, electron probe and chemical analysis. The complete melting temperatures of oxidizing smelting slag samples are noted in the range of t = 1225÷ ÷1280 °С. According to mineralogical studies, the main phases of these slags are magnetite (Fe₃O₄) and fayalite (2FeO·SiO₂) represented by large grains. In addition, the samples contain sulfide compounds: chalcosine and bornite solid solutions (Cu₂S–Cu₅FeS₄), sphalerite (ZnS), galena (PbS). Slag reduction treatment was carried out at t = 1300 °С in the presence of activated carbon following by a decrease in the copper content in slags by an average of 0.45–0.65 % with the magnetite content reduced by 3.6–3.8 times. Slag samples featured strongly pronounced large fayalite crystals where the faylaite content increased sharply due to magnetite reduction with metallized phases reach in lead and zinc concentrated on grain boundaries. Reduction treatment intensifies the following transformations: the transition of iron from one oxidation state to another (Fe³⁺→Fe²⁺) to form fayalite, coalescence of sulfide inclusions, and formation of a matte phase containing copper and iron. During the reduction treatment of slags, lead and zinc can be sublimed with their further extraction.

copper concentrates, smelting, slags, reduction treatment, chemical composition, physical-chemical transformations, magnetite, fayalite

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