TRANSFER OF COPPER CATIONS IN IRON VACANCIES OF NON-STOICHIOMETRIC WUSTITE IN THE MAGNETITE PHASE

ABSTRACT

The main reasons for the disappearance of copper with waste slag, one of the actual problems of copper production, are considered in the article. The results of the research showed that the main factor influencing the chemical loss of copper during the converting process is the settling of copper oxides in the iron vacancies in magnetite.

АННОТАЦИЯ

В статье рассмотрены основные причины потери меди с отвальными шлаками, одной из актуальных проблем медного производства. Результаты исследований показали, что основным фактором, влияющим на химические потери меди в процессе конвертирования, является осаждение оксидов меди в вакансиях железа в магнетите.

Keywords: magnetite, copper, wustite, iron, vacancy, non-stoichiometric structure, metal-loss, slag phase.

Ключевые слова: магнетит, медь, вюстит, железо, вакансия, нестехиометрическая структура, потеря металла, шлаковая фаза.

As a result of the diffusion of oxygen in the three-component Fe-Cu-S system during the conversion of copper steins, the oxidation process begins to take place at a high temperature. In this case, due to the higher tendency of iron to oxygen among the three components, initially the iron in the system and the sulfur attached to it are oxidized. When iron is oxidized, divalent iron oxide is formed in the 1st stage of the reaction mechanism [1-5]. However, its chemical formula is Fe_0.84O to Fe_0.95O due to its non-stoichiometric crystal lattice structure. In it, there is a deficiency of iron atoms in the amount of 0.16 mol to 0.05 mol. When the partial pressure of oxygen increases, magnetite is formed in step 2 according to the reaction mechanism [6]. At the same time, copper sulfides are oxidized and monovalent copper oxide is formed in the system. Its chemical formula is non-stoichiometric and corresponds to Cu_1.56O composition [7]. A deficiency of 0.44 mol of copper atoms was also observed in this compound. It has been found in practice that when the amount of magnetite in the converter slag increases, the chemical wastage of copper also increases. The main reason for this is that oxidized copper cations occupy iron vacancies in wustite (Fe_1-xO) crystals in magnetite [8]. The chemical reaction between such non-stoichiometric compounds can be conventionally written as follows:   

Fe_0,84O + 0,08 Cu₂O = Cu_0,16Fe_0,84O_1,08                             (1)

Cu_1,56O + 0,44 FeO = Cu_1,56Fe_0,44O_1,44                              (2)

The indices of the substances involved in the reaction equation (1) were written in accordance with the law of multiple ratios and were made to look like this:

Fe₂₁O₂₅ + 2Cu₂O = Cu₄Fe₂₁O₂₇                                  (3)

According to the reaction equation (3), every 25 molecules of non-stoichiometric free wustite absorbed 2 molecules of cuprite. In this process, the loss of copper chemically to the slag composition was 16.24% compared to the initial non-stoichiometric mass of free wustite [9-11]. 

Cu₃₅O₂₃ + 10 FeO = Cu₃₅Fe₁₀O₃₃                                (4)

According to reaction equation (4), every 23 molecules of non-stoichiometric free cuprite absorbed 10 wustite molecules. In this process, the oxidized copper compound dissolves 27.6% of wustite.

Table 1.

Effect of different amounts of magnetite on other components of slag

It follows that the chemical loss of copper with slag increases with the increase in the amount of non-stoichiometric free wustite in the slag phase. Since non-stoichiometric free wustite molecules are mainly found in magnetite, increasing the amount of magnetite in the slag phase increases the solubility of copper in the converter slag. This can also be seen from the values presented in Table 1. Table 1 presents the statistical values obtained from the influence of the decrease in the amount of magnetite in the converter slag on the concentration of other copper and iron compounds in the slag. In this case, the decrease in the amount of magnetite in the slag also led to a decrease in the chemical wastage of copper.

According to the data in Table 1 and the diagram in Figure 1, the amount of copper (I)-oxide also decreased with the decrease in the amount of magnetite in the slag phase.  

The reduction of oxidized copper compounds also leads to a reduction of the amount of copper that has been forced (chemically) in the slag phase. As the amount of oxidized copper compounds in the system increases, the amount of lower copper sulfide increases proportionally.

As a result of reduction of magnetite in the slag phase by recovery, the concentration of non-stoichiometric free wustite (that is, FeO in magnetite) decreases in the system, binds with quartz in the slag and forms a fayalite compound:

2FeO + SiO₂ = Fe₂SiO₄                                           (5)

Figure 1. Changes in the concentration of other components with the increase in the amount of magnetite in the converter slag

The addition of divalent metal oxides (FeO, MgO, CaO, etc.) to the slag phase causes the breaking of the chemical bonds connecting silicon and oxygen, which increases the viscosity of the slag. As a result, the overall viscosity of the slag decreases.

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