Converter Blowing of Matte

the pyrometallurgical oxidation processing of molten copper, nickel, and lead mattes to produce a crude metal or a nonferrous metal sulfide. Converter blowing is performed in a converter by blasintg the molten matte with air or industrial oxygen. When the jet of air passes through the melt, mainly the sulfides of metals that have a greater affinity for oxygen than for sulfur are oxidized. In mattes from nonferrous metallurgy this metal is iron. The resulting molten ferric oxides are slagged with silica, which is added to the converter as a flux.

The slag contains 21–30 percent SiO₂; the balance is ferric oxides. The converter slag, which is less dense than the matte, floats to the surface and is periodically removed from the converter.

In the copper industry the converter blowing process is divided into two periods. The first period ends with the removal of all iron from the matte. In the second period, the remaining copper sulfide (white matte, or white copper) is oxidized by atmospheric oxygen according to the reaction Cu₂S + O₂ = 2Cu + SO₂. The final product of converter blowing of copper matte is blister copper.

In the lead industry converter blowing is used for copper-lead mattes containing up to 30 percent copper, 10–20 percent lead, 5–15 percent zinc, 20–40 percent iron, and 18–22 percent sulfur. In the first blast period the zinc and lead sulfides are partially oxidized together with the iron sulfide. Upon interaction with the silica, the oxides of these metals form a slag. Some of the zinc and lead passes into the vapor phase and is entrained in dust collectors in the form of converter dust. During processing of the copper-lead mattes, the blister copper produced in the second period is characterized by increased lead content (up to 4 percent).

In the nickel industry, the production of crude metal from nickel mattes is difficult, since after the removal of all ferrous sulfide in the first period, the reaction Ni₃S₂ + 2O₂ = 3Ni + 2SO₂ can take place only at temperatures above 1500°C. However, the temperature in conventional horizontal converters does not exceed 1400°C. Therefore, the converter blowing of nickel matte ends in the first period with the production of converter matte (77–79 percent nickel, 23–21 percent sulfur), which, when blasted with industrial oxygen, can produce nickel. Vertical converters for the production of crude nickel from converter matte are similar in design to converters used in ferrous metallurgy; the oxygen is supplied from above through a tuyere.

The converter process is autogenous. The heat given off during oxidation of the sulfides is sufficient not only to maintain the matte in a molten state in the converter but also to melt the cold additives containing nonferrous metals that are added to the melt. At some plants, the converters are loaded with ore concentrate that has undergone preliminary pelletizing and drying. The gases formed during conversion contain an average of 3–4 percent SO₂ and are partially used in the production of sulfuric acid. The converter slags, which contain up to 3 percent nonferrous metals, are a repetition material and are returned to the smelting units. The converter dust, containing 20–30 percent nonferrous metals, is usually returned to the converters.