The most important operation of processing copper ore is smelting on matte. Matte is a sulphide alloy formed during the smelting of copper ore, mainly copper and iron (usually 80-90%), the rest being sulphides of zinc, lead, nickel, as well as oxides of iron, silicon, aluminum and calcium, concentrating mainly in slag, But partially soluble in matte. Liquid mattes dissolve gold and silver well, and if these precious metals are in the ore, they almost completely concentrate in matte.
The purpose of smelting on matte is the separation of sulfur compounds of copper and iron from the impurities present in the ore, which are present in it in the form of oxidized compounds. The resulting matte should not contain too little copper, since this makes the subsequent redistribution unproductive, but also very copper-rich mattes can not be obtained, since a significant amount of copper is lost in the slags.
Depending on the chemical composition of the ore and its physical state, matte is produced either in shaft furnaces, if raw materials are lumps of copper ore containing a lot of sulfur, or in reflective or arc-furnace electric furnaces, if powdered flotation concentrates are the starting material.
The reflecting furnace is built in length 35-40, width 7-10 and height 3.5-4.5 m. The walls and the vault are made of dinas or magnesite bricks. Refractories are chosen depending on the prevalence of basic or acid oxides in the charge, since the composition of the charge and refractory materials is longer than their service life. Under the stove is made in several layers, and the surface is covered with quartz sand, which before melting the furnace is melted, turning into a dense mass.
Reflective furnaces are heated with fuel oil, coal dust or gas, injecting fuel with injectors (4-10 pcs.) Through the windows available at the end of the furnace. The maximum temperature at the head of the furnace is 1550 ° C and, gradually decreasing, to the tail part is usually 1250-1300 ° C. The charge in these furnaces is fed through the vaults located along the furnace at the side walls. When charging, the burden falls along the walls along slopes, preventing the clutch from direct exposure to slags and gases. As the charge is heated, partial reduction reactions of higher oxides of iron and copper, sulfur oxidation and slag formation begin.
Smelting of copper concentrates in electric furnaces due to power shortage and the possibility of using low-grade sulfur fuels in this operation has not yet found wide application. But for the smelting of lumps of copper ore, mine-based water-jet furnaces are still widely used. There are often cases when even sulfur-rich concentrates are pre-agglomerated in order to subject them to smelting in shaft furnaces. This furnace has in the plan a rectangular section with a width of about 1 m and several meters in length.
The main working walls of the furnace are made of hollow steel boxes, cooled from the inside by water, called caissons, since known technical refractories are not sufficiently stable under these conditions. During melting on the cold walls, the melted charge stiffens, protecting the caisson from destruction. The charge is loaded from a platform located at the level of the upper edge of the caisson, the combustion air is fed through tuyeres along the longitudinal walls in the lower part of the caissons.
The release of matte and slag from the furnace is performed jointly and continuously through a drain chute having a hydraulic shutter. The liquid viscous mixture flows into a large oval sump, called the front rock, lined with chromium-magnesite brick. It is a slow stratification of matte and slag. Excess slag is drained along the gutter in the opposite end of the front bugle, and the matte is discharged as needed through the tapholes located at the berm of the hearth. Over the stove, a so-called tent for collecting and discharging off-gases and lining them for dust collection and gas cleaning are made with fireproof materials lined.
Copper matte processing
The most common are now cylindrical barrel-shaped converters. The outer diameter of the converter is usually 2.3-4 m, the length is 4.3-10 m. The largest converters produce up to 100 tons of copper per process cycle. Air to the converter is fed through a series of tuyeres located along the generatrix of the cylinder. The cylinder is supported by two strong bandages for four pairs of rollers. Turn the converter on the rollers to the required angle for pouring the matte into the neck and casting out the smelting products by a gear transmission and a toothed rim fixed to the steel casing. Inside the converter is lined with magnesite and chromium-magnesite brick.
Matte processing in the converter takes place in two periods. The converter is loaded with lump quartz, poured the molten matte and blows it with air,).
The resulting slag is periodically drained and fresh portions of copper matte and lump quartz are added to the converter. The temperature of the matte to be filled is usually about 1200 ° C, but during the purging time, due to a greater heat release during the oxidation of sulphides, the temperature rises to 1350 ° C. The duration of the first period depends on the amount of copper in matte and is 6-20 hours.
The introduction of an oxygen blast in the air blast increases the temperature in the converter and allows the cold concentrate to be loaded into it, replacing some of the molten matte.
The first period ends when sulphurous iron is oxidized in the blown matte. After that, the slag is carefully removed and blowing continues without the addition of matte and quartz. The second period begins when only the Cu2S, called the white matte, remains in the converter, and in some factories “white matte”.
The second period ends when in the converter the entire white matte turns into copper, which usually takes 2-3 hours. In the converter and in the second period, a small amount of copper-rich slag is formed, which remains in it after the casting of the blister copper and is processed in the next cycle. Convertor slags of the first period are sent for processing to reflective furnaces.
When the process is finished, the blister copper is tilted into a bucket and poured into molds. The copper obtained in the converter is called rough, that is, not yet finished copper, since it contains 1.0-2.0% of iron, zinc, nickel, arsenic, antimony, oxygen, sulfur and other impurities, and precious metals are dissolved, Previously in matte.