Fire refining

Impurities can be removed by formation of a gaseous compound, as in the fire-refining of copper (qv). Sulfur is removed from the molten metal by oxidation with air and evolution of sulfur dioxide. Oxygen is then removed by reduction with C, CO, in the form of natural gas, reformed... 

Other Meta.Is, Although most cobalt is refined by chemical methods, some is electrorefined. Lead and tin are fire refined, but a better removal of impurities is achieved by electrorefining. Very high purity lead is produced by an electrochemical process using a fluosiUcate electrolyte. A sulfate bath is used for purifying tin. Silver is produced mainly by electrorefining in a nitrate electrolyte, and gold is refined by chemical methods or by electrolysis in a chloride bath. 

No. 1 copper wire and heavy 99+ Cu Copper scrap 420 melted and fire refined, cast in shapes for... 

Copper. Domestic mine production of copper metal in 1994 was over 1,800,000 t. Whereas U.S. copper production increased in the 1980s and 1990s, world supply declined in 1994. There are eight primary and five secondary smelters, nine electrolytic and six fire refiners, and fifteen solvent extraction—electro winning (SX—EW) plants. Almost 540,000 t/yr of old scrap copper and alloy are recycled in the United States accounting for - 24% of total U.S. consumption (11). New scrap accounted for 825,000 t of contained copper. Almost 80% of the new scrap was consumed by brass mills. The ratio of new-to-old scrap is about 60 40% representing 38% of U.S. supply. 

Fire refining, the final smelting operation, removes further impurities and adjusts the oxygen level ia the copper by air oxidation followed by reduction with hydrocarbons, ammonia, or reformed gas (CO + H2). 

Fire Refining. The impurities in bhster copper obtained from converters must be reduced before the bUster can be fabricated or cast into anodes to be electrolyticaHy refined. High sulfur and oxygen levels result in excessive gas evolution during casting and uneven anode surfaces. Such anodes result in low current efficiencies and uneven cathode deposits with excessive impurities. Fite refining is essential whether the copper is to be marketed directly or electrorefined. 

Fite refining adjusts the sulfur and oxygen levels in the bhster copper and removes impurities as slag or volatile products. The fire-refined copper is sold for fabrication into end products, provided that the chemistry permits product specifications to be met. Some impurities, such as selenium and nickel, are not sufficiently removed by fire refining. If these impurities are detrimental to fabrication or end use, the copper must be electrorefined. Other impurities, such as gold, silver, selenium, and tellurium, are only recovered via electrorefining. Virtually all copper is electrorefined. 

The end product is either cast as anodes for electrolytic refining or, rarely, as ingots for sale as fire-refined copper. A horizontal casting wheel with 12—32 horizontal molds is normally used for anode casing. Using continuous casting machines, the copper is cast as a continuous strip to be cut to the required anode shape (28). 

Chemistry. Fire refining of bhster copper is achieved by oxidation, fluxing, and reduction. The copper is partially oxidized by blowing air into the fire-refining furnace, where the copper oxide and the impurities that oxidize preferentially react. 

Impurities ate elirninated in fire refining in the foUowing sequence slag, that is, oxides of iron, magnesium, aluminum, and sihcon fluxing, that is, arsenic and antimony and vapors, that is, sulfur (as SO2), cadmium, and zinc. 

If the fire-refined copper is to be cast into anodes for electrorefining, the oxygen content of the copper is lowered to 0.05—0.2%. If the copper is to be sold directly for fabrication, the oxygen level is adjusted to 0.03—0.05%, which is the range for tough-pitch copper. The principal reactions of fire refining are... 

In the electrorefinery, anodes produced from fire-refined copper as described above are dissolved electrolytically in acidic copper sulfate and the copper is deposited on starting sheets to produce cathodes. These operations are carried out in tanks, and refineries are often known as tank houses. The cathodes are sold direcdy or melted and cast into a number of forms. 

The roaster product is then charged to the Dorn furnace where it is melted and the resulting metal is fire-refined to eliminate the arsenates, selenates, antimonates, teUurates, and residual copper. 

When the copper content in the Dorn metal has been reduced to less than 1% by fire refining, the metal is cast into anodes for electrolytic separation of silver. A typical analysis of Dorn metal is... 

Blister copper, produced from sulfide ores by matte smelting and converting, is refined to the grade known as tough pitch copper by a multistage operation known as fire refining. 

In contrast to the fire refining of copper, where the oxidation stage needs to be followed by a deoxidation step, no deoxidation step is necessary in the fire refining of lead. This is because the solubility of oxygen in liquid lead at typical refining temperatures is quite low (2 10 2 to ltT1 at-% at 600 to 700 °C). 

In the copper electrorefining process, fire refined copper or blister copper is cast to form the anodes and the cathode is either a reusable stainless steel sheet or a thin sheet of electro deposited copper which finally becomes a part of the refined cathode. The electrolyte is an acidified solution of copper sulfate. 

After pretreatment, the scrap is ready for smelting. Although the type and quality of the feed material determines the processes the smelter will use, the general fire-refining process is essentially the same as for the primary copper smelting industry. 

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