National University of Science and Technology “MISiS ”, Moscow, Russia

A. N. Fedorov, Professor, e-mail: fedorov_a_n@mail.ru

Satbayev University, Almaty, Kazakhstan
N. K. Dosmukhamedov, Associated Professor
E. E. Zholdasbay, Research Fellow

MMC Norilsk Nickel PJSC, Moscow, Russia
S. L. Lukavyy, Chief Manager

This paper describes the liquidus temperature of molten high-copper slags determined through differential thermal analysis and identifies optimum compositions of Cu₂O – FeO – CaO – SiO₂ slags that ensure the presence of one stable liquid phase saturated with copper oxide. A liquidus curve was built in the Cu₂O – FeO – SiO₂ – CaO system as a projection on the Cu₂O – FeO/SiO₂ – CaO plane. The authors established the effect produced by how the liquid slags saturated with copper oxide (I) are arranged on the two-phase region (liquid slag and solid oxides herein referred to as ‘spinel’) of the Cu₂O – FeO – SiO₂ – CaO system. It is shown that when the concentration ratio of iron oxide to silica is higher than 1, the ‘spinel’ inclusions tend to become coarser as the solubility of copper oxide in the slags drops. It was found that a higher concentration of calcium oxide leads to a finer structure of the ‘spinel’ inclusions when the slag is saturated with copper oxide. The liquidus temperature curve tends to have an insignificant maximum, which can obviously be explained by both silica and calcium oxide influencing the size of the ‘spinel’ inclusions as the slags become less saturated with copper oxide (I). With a further increase in the concentration of calcium oxide and silica in the slags, one should expect the copper oxides dissolved in the slag to substitute the iron oxides, which will eventually lead to a slight decrease in the liquidus temperature of the molten slags in view. The paper shows the solubility of Cu₂O in a completely liquid region of the slag, and how the solubility of copper oxide in the slag is influenced by the CaO/SiO₂ and SiO₂/Fe ratios. A minimum concentration of copper oxide in the slag is observed on the ‘spinel’ isotherm for all the temperatures considered, with the temperatures of 1,200 and 1,250 ^оC being most indicative. This supports the conclusion that the lowest concentration of copper oxide (I) in the slags being in the liquid region is observed when the CaO/SiO₂ ratio is varying within 0.75 and 1.2. The minimum concentration of copper oxide is observed within the change range of 0.7 to 0.85 for the CaO/SiO₂ ratio, which is quite consistent with the findings from other studies. It was found that an increase in the SiO₂/Fe ratio to ~0.46 leads to a decreased concentration of copper oxide in the slag, whereas when the ratio is >0.46, a rise in the concentration of copper oxide in the slag is observed. It is shown that at 1,200 and 1,250 ^оC the effect of rising copper oxide solubility is most pronounced. At the temperatures of 1,300 and 1,350 ^оC and with the SiO₂/Fe ratio being >0.46, the concentration of copper oxide in the slag rises due to saturation. The maximum solubility of copper oxide in the slag (33.89%) is achieved when the SiO₂/Fe ratio is ~0.52. The results obtained suggest that the addition of lime (CaO/SiO₂) to the Cu₂O – FeO – SiO₂ – CaO system leads to a decreased concentration of copper oxide in the slag. A higher concentration of silica in the system under study, within the change range of the SiO₂/Fe ratio from 0.42 to 0.46, decreases the solubility of copper oxide in the slag, and its minimum concentration is reached when the SiO₂/Fe ratio is ~0.44.

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