Cupellation

CuO 2Co203 6H20 Cupel furnace Cupellation Cupferron... 

In 1986 Britannia Refined Metals (Northfleet, U.K.) introduced technology for the treatment of Parkes cmst, a triple alloy of Ag, Zn, Pb, which by 1992 had been adopted by seven lead refineries (22). The technology consists of a three-stage process in which the silver-rich cmst is first Hquated to reduce its lead content, then placed in a sealed furnace where the 2inc is removed by vacuum distillation and, finally, the silver—lead metal is treated in a bottom blown oxygen cupel (BBOC) to produce a Htharge slag and dorn metal. 

Fig. 15. Bottom blown oxygen cupel (BBOC) in positions for (a) blowing oxygen and (b) tapping slag.

Miscellaneous. Where a copper refinery is adjacent to a lead (qv) plant it is feasible to recover the selenium in slimes by smelting them in conjunction with lead-bearing materials. Utilizing the lower temperatures needed to melt lead, the selenium is volatilized from a lead bath or cupel blown with air. The selenium is recovered from flue dust and fume by scmbbing. This is the process used by Union Miniere at its Hoboken plant in Belgium. 

The fire assay, the antecedents of which date to ancient Egypt, remains the most rehable method for the accurate quantitative determination of precious metals ia any mixture for concentrations from 5 ppm to 100%. A sample is folded iato silver-free lead foil cones, which are placed ia bone-ash cupels (cups) and heated to between 1000 and 1200°C to oxidize the noimoble metals. The oxides are then absorbed iato a bone-ash cupel (ca 99%) and a shiny, uniformly metaUic-colored bead remains. The bead is bmshed clean, roUed fiat, and treated with CP grade nitric acid to dissolve the silver. The presence of trace metals ia that solution is then determined by iastmmental techniques and the purity of the silver determined by difference. 

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 monetary use of silver may well be as old as that of gold but the abundance of the native metal was probably far less, so that comparable supplies were not available until a method of winning the metal from its ores had been discovered. It appears, however, that by perhaps 3000 BC a form of cupellation was in operation in Asia Minor and its use gradually... 

Abartf /. variety, modification, variant. abarteUt v.i. vary deviate degenerate, abatmen, abatmen, v.t. glow (a cupel) cupel anneal. 

Abtreib(e) apparat, m. distilling apparatus, still, -herd, m. refining hearth. pelle, /. refining cupel, -kolonne, /. separating column, distilling column, -mittel, n. expulsive agent abortifacient,... 

Kapelle,/. cupel sand bath subliming dish ... 

Ldtrohr-flamme, /. blowpipe flame, -fluss, m. blowpipe flux. -gebl e, n. blast lamp, -kapelle, /. blowpipe cupel, -kohle, /. blowpipe charcoal, -lampe, /. blowpipe lamp, -probe,/, blowpipe teat, -priifgeratschaft,/. apparatiis for blowpipe testing, -reagens, n. blowpipe reagent, -versuch, m. blowpipe experiment or test. 

Scb cben, n. little dish or cup, capsule cupel. Scbale, /. dish, basin, bowl pan tray cup (dished) cover pan, scale (of a balance) shell husk, skin, peel, rind, bark cover (of a book) (Founding) chill, scbalen, v.t. shell, husk, peel, pare, bark. — v.r. peel off, scale off. 

Scherbe, /. potsherd, shard fragment, piece crock, pot (esp. fiowerpot) cupel scorifier (Ceram.) body. 

Test, m. test cupel test furnace cupella-tion furnace indicator graphite molybdenite. -asche, /. bone ash. -benzin, n. 

Treib-strahl, m, propulsive jet. -verfahren, n. Metal.) cupellation process. 

Precious metals such as silver and gold, which are seldom oxidized even at high temperatures, are often refined by cupellation, a process for removing from them base metal impurities such as lead and tin, with which they are associated in many ores. Hot lead and tin are easily oxidized. In the cupellation process, a crude, impure precious metal is placed in a shallow cup or crucible made of bone ash, known as a cupel, and is then heated by a blast of hot air. At high temperatures, the base metal impurities are oxidized by oxygen in the hot air, and the oxides thus formed are absorbed by the porous bone ash. The Chaldeans are said to have been the first to have utilized (ca. 2500 b.c.e.) cupellation to remove lead and purify silver from lead-silver ores. 

After extraction from its ores, crude silver is generally refined by the process of cupellation, mentioned earlier. Since ancient times the main use of silver has been for making articles of value such as ornaments, decorative objects, jewelry, and coins. In Mesopotamia, much silver was used between the twentieth and fifteenth centuries b.c.e. to make decorative and ornamental objects. It seems that in Egypt, during the same period of time, the metal was scarcer and perhaps even more costly than gold (Hess et al. 1998 Mischara and Myers 1974). 

Brittania A process for removing silver from lead, operated by Brittania Refined Metals in England, using ore from the Mount Isa mine in Australia. After initial concentration by the Parkes process, and removal of the zinc by vacuum distillation, the mixture, which contains silver (70 percent), lead, and some copper is treated in a bottom blown oxygen cupel in which lead and copper are removed by the injection of oxygen through a shielded lance. 

Cupellation An ancient metallurgical operation, still in use, for removing lead and other base metals from silver by blowing air over the surface of the molten metal. The lead oxidizes to lead monoxide (litharge), which floats on the molten silver and is separated off. The molten litharge dissolves the other base metal oxides present. A cupel is the shallow refractory dish in which the operation is conducted. 

Pattinson (1) A process for extracting silver from lead by selective crystallization. When molten lead is cooled, the first crystals of lead contain less silver than the residual melt. Repetition of this process a number of times yields a silver concentrate which is further purified by cupellation. Invented in 1833 by H. L. Pattinson. Largely superseded by the Parkes process, except for metals containing bismuth for which the Pattinson is the preferred process. See also Luce-Rozan. 

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