Slags, copper

Enhancing -> passivation of iron and steel and dissolving refractory substances such as titanium slag, copper-yttrium oxide, and metal fluorides. 

The decomposition of the lower sulfides of the heavy metals and the recovery of the metal as soluble salts and of sulfur in the elemental form have been demonstrated for pyrite, pyrrhotite, chalcopyrite, sphalerite, galena, molybdenite, and associated metals such as nickel and cobalt. Pyrite and chalcopyrite are higher sulfides and to be amenable to this treatment have to be thermally decomposed at 600-650 C prior to leaching. The reactions with nitric acid are exothermic, and are carried out below 1 atm and at around 100°C. In addition to the sulfides, this technique has been applied successfully to the extraction of nonferrous metals from partly oxidized sulfide ores, fayalite slags, copper scrap, and other intermediate products, such as residue from electrolytic zinc plats. 

Boiler slag Copper slag Nickel slag... 

Open-Arc Furnaces. Most of the open-arc furnaces are used in melting and refining operations for steel and iron (Fig. 1). Although most furnaces have three electrodes and operate utilizing three-phase a-c power to be compatible with power transmission systems, d-c furnaces are becoming more common. Open-arc furnaces are also used in melting operations for nonferrous metals (particularly copper), slag, refractories, and other less volatile materials. 

The abundance of indium in the earth s cmst is probably about 0.1 ppm, similat to that of silver. It is found in trace amounts in many minerals, particulady in the sulfide ores of zinc and to a lesser extent in association with sulfides of copper, tin, and lead. Indium follows zinc through flotation concentration, and commercial recovery of the metal is achieved by treating residues, flue dusts, slags, and metallic intermediates in zinc smelting and associated lead (qv) and copper (qv) smelting (see Metallurgy, EXTRACTIVE Zinc and zinc alloys). 

The dross from this operation contains considerable quantities of copper and lead as well as other valuable metals. Separation and recovery is economically imperative. The dross is treated to produce readily separated stratified layers of slag, speiss, matte, and lead. Two processes are primarily used. 

The success of the process results from the fact that nowhere inside the furnace is heat extracted from the copper-saturated blast furnace buUion through a soUd surface. The problem of accretion formation (metal buUd-up), which has plagued many other attempts to estabUsh a copper dtossing operation of this type, does not arise. In the cooling launder, lead-rich matte and slag accumulate on the water-cooled plates, but these ate designed so that when they ate lifted from the buUion stream, the dross cracks off and is swept into the furnace via the cooled lead pot. 

The interelectrode insulators, an integral part of the electrode wall stmcture, are required to stand off interelectrode voltages and resist attack by slag. Well cooled, by contact with neighboring copper electrodes, thin insulators have proven to be very effective, particularly those made of alumina or boron nitride. Alumina is cheaper and also provides good anchoring points for the slag layer. Boron nitride has superior thermal conductivity and thermal shock resistance. 

Fig. 16. Insulator wall designs (a) peg wall (b) conducting bar wall and (c) segmented bar wall. The gas-side materials are tungsten and tungsten—copper composite, the base material, copper, and the insulators, boron nitride. Slagging grooves are shown.

The reacting particles melt rapidly, and the droplets fall to the slag layer. The sulfide drops settle through it to form the matte phase. Any oxidi2ed copper is reduced to the matte by the following reaction ... 

The equihbrium constants for these reactions are such that copper is not appreciably oxidi2ed by oxygen until most sulfur has been removed. This makes possible the production of bHster copper, 98.6—99.5% Cu that is low in both sulfur (0.02—0.1%) and oxygen (0.5—0.8%). The converter slag, however, contains a significant amount of copper and must be recycled to the smelting stage. 

In addition, molybdenum has high resistance to a number of alloys of these metals and also to copper, gold, and silver. Among the molten metals that severely attack molybdenum are tin (at 1000°C), aluminum, nickel, iron, and cobalt. Molybdenum has moderately good resistance to molten zinc, but a molybdenum—30% tungsten alloy is practically completely resistant to molten zinc at temperatures up to 800°C. Molybdenum metal is substantially resistant to many types of molten glass and to most nonferrous slags. It is also resistant to hquid sulfur up to 440°C. 

Blast furnaces are charged through the top with coke, flux (usually iron metal and siUca), and scrap while air is iajected through tuyeres continuously at the bottom just above the black copper. The coke (100 kg/1 slag) bums to maintain furnace temperatures of 1200°C, provides the reductant, and maintains an open border. A charge of 10 t/h is typical. The furnace produces a molten black copper that contains about 80% copper. The 2iac, lead, and... 

Tellurium is stUl recovered in some copper refineries by the smelting of slimes and the subsequent leaching of soda slags which contain both selenium and tellurium. The caustic slags are leached in water and, using the controlled neutralization process, tellurium is recovered as tellurium dioxide. 

The washed slime is dried and melted to produce slag and metal. The slag is usually purified by selective reduction and smelted to produce antimonial lead. The metal is treated ia the molten state by selective oxidation for the removal of arsenic, antimony, and some of the lead. It is then transferred to a cupel furnace, where the oxidation is continued until only the silver—gold alloy (dorn) remains. The bismuth-rich cupel slags are cmshed, mixed with a small amount of sulfur, and reduced with carbon to a copper matte and impure bismuth metal the latter is transferred to the bismuth refining plant. 

The copper and copper oxide ia equations 12 and 13 are from copper production via leaching or from recycled converter slag. 

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