Basic principle of copper-sulfur smelting

Copper sulfide concentrate generally contains copper 10% ~ 30%, and besides gangue, it is often accompanied by a large amount of iron sulfide, which exceeds the main metal copper. Therefore, it is still difficult to smelt crude metal directly from concentrate by pyrometallurgy, and it is not easy to meet the requirements in metal recovery rate and metal product quality. Therefore, matte smelting-copper matte blowing process is widely used to treat copper sulfide concentrate in the world. The principle of this process is that the affinity of copper for sulfur is greater than that of iron and some impurity metals, and the affinity of iron for oxygen is greater than the physical properties of copper. Under the condition of high temperature and controlled oxidation atmosphere, impurity metals such as iron are gradually oxidized and removed by entering slag or smoke, while metal copper is enriched in various intermediate products, and purification is gradually mentioned.

In the process of copper smelting and enrichment, matte smelting is an important unit process, that is, copper sulfide concentrate, partial oxide calcine, returned materials and appropriate flux are smelted at the high temperature of 1423 ~ 1523 K, resulting in two immiscible liquid phases (matte and slag). The so-called matte refers to the sulfide melt formed by mutual melting of ferrous sulfide and heavy metal sulfide; Slag refers to the melt of metal silicate, ferrite and aluminate mixture formed by gangue in ore, flux in charge and other slagging components during smelting. Matte smelting mainly includes two processes of slagging and matte making, and the main reactions are as follows:

2 FeS(l)+3 O2(g)= 2 FeO(l)+2so 2(g)( 1)

2FeO(l)+SiO2(s)=2FeO。 Silica (1)(2)

xFeS(l)+yCu2S(l)= yCu2S . xFeS(l)(3)

The oxidation reaction of FeS (1) can achieve the purpose of partial desulfurization of burden; The slagging reaction (2) is mainly to remove part of the iron in the burden, and to remove the components and impurities in the burden such as SiO2 _ 2, Al _ 2O _ 3 and CaO by slagging. The matte-making reaction (3) is to make cuprous sulfide and unoxidized ferrous sulfide in the burden melt with each other to generate liquid matte (also known as matte) with high copper content. The total amount of copper, iron and sulfur in matte often accounts for 85% ~ 95%, and almost all the precious metals in charge enter matte. Slag is an ionic silicate melt containing 2FeO. SiO2 _ 2 (fayalite) is the main component, while matte is a valence sulfide melt with Cu2S and FeS as the main components. The two are immiscible with each other, and the density of copper matte is greater than that of slag, so copper matte and slag can be separated from each other. Traditional matte smelting methods include reverberatory furnace smelting, electric furnace smelting and closed blast furnace smelting; Modern intensified smelting methods include flash smelting, Noranda method, Mitsubishi method, Vanyukov method, Silver method, Issa method or Osmet method.

The purpose of matte smelting is to concentrate all the copper in the burden in the copper matte phase, collect gangue, oxide and impurity components in the slag phase, and then completely separate the copper matte from the slag phase. In order to achieve these two goals, matte making and smelting must follow two principles. One is that there must be a considerable amount of sulfur in the charge to form copper matte, and the other is that the slag contains nearly saturated silicon dioxide, which makes copper matte and slag immiscible.

When there is enough sulfur in the charge, at high temperature, because the affinity of copper for sulfur is greater than that of iron, and the affinity of iron for oxygen is greater than that of copper, FeS can sulfide copper according to the following reaction:

FeS(l)+Cu2O(l)=FeO(l)+Cu2S(l)

At the melting temperature of 1473K, Cu2O is almost completely sulfurized by FeS. Practice has proved that the above reaction can be carried out regardless of the form of copper oxide. This reaction is also used to recover copper from converter slag, which is an important reaction in pyrometallurgical copper smelting.

The study of slag properties shows that liquid oxides and sulfides are highly miscible when there is no silica. Experiments show that when the system does not contain SiO _ 2, such as copper matte containing 30% ~ 60% Cu, at 1427K K, FeO up to 50% of its own mass can be dissolved. Therefore, the sulfide-oxide system without SiO _ 2 is basically single-phase, that is, the slag cannot be separated from matte. However, with the increase of SiO _ 2 content in the system, the immiscibility of slag and matte gradually increased, until the SiO _ 2 content was higher than 5%, matte and slag began to separate. When the slag is saturated with SiO2 _ 2, the mutual solubility between slag and matte is the smallest, and the separation degree between matte and slag is the largest. Table 2-4 lists the equilibrium groups of two immiscible liquid phases in a set of Cu2S-FeS-FeO-SiO _ 2 systems saturated with SiO _ 2.

As for the mechanism of silica, it is generally believed that without silica, oxides and sulfides combine with valence bonds to form semiconductor (Cu-Fe-S-O) phase. When there is silica, it will combine with oxides to form strongly bonded silica anions, which will be collected into ionic slag phase. Sulfide shows no tendency to form this silica anion, but remains as copper matte phase with obvious valence bond. In this way, two immiscible layers are formed.

Other experiments show that both CaO and Al2O3 can form complexes with SiO2 _ 2, and can reduce the solubility of sulfides such as FeS in slag, thus improving the separation effect of slag and ice. Therefore, it is also beneficial to contain a small amount of calcium oxide and aluminum oxide in the slag.

Continue to ask: what is the next smelting method of copper matte with 30% ~ 60% Cu? Supplementary answer:

Copper matte is generally blown by P-S converter (1909 Peirce and Smith successfully blown copper matte by converter lined with alkaline or neutral refractories for the first time in Baltimore, so the horizontal converter is also commonly known as P-S converter), and the copper matte is blown to 98. The essence of converter blowing is to send air into liquid copper matte under a certain pressure, so that FeS in copper matte is oxidized into FeO and reacts with the added timely flux slag, and Cu2S reacts with oxidized Cu2O to become crude copper. The heat required in the blowing process depends entirely on the heat released by the oxidation and slagging reaction of sulfur and iron in matte, which is a self-heating process. The temperature of the blowing process is about 65438 0250 degrees Celsius.

Continue to ask: 98.5% ~ 99.5% of crude copper, what to do next? Supplementary answer:

Pyrometallurgical refining is still used to treat crude copper, and impurities such as iron, lead, zinc, bismuth, nickel, arsenic, antimony and sulfur should be removed from crude copper. The affinity of impurities for oxygen is greater than that of copper, and the solubility of impurity oxides in copper is low. Firstly, air is blown into the copper liquid to remove impurities, and then reducing agent is added into the copper liquid to remove oxygen. Finally, the anode copper whose chemical composition and physical specifications meet the requirements of electrolytic refining is obtained.

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