Cupellation

cupellation

Separation of gold or silver from impurities by melting the impure metal in a cupel (a flat, porous dish made of a refractory material) and directing a blast of hot air on it in a special furnace. The impurities, including lead, copper, tin, and other unwanted metals, are oxidized and partly vaporized and partly absorbed into the pores of the cupel.

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cupellation [‚kyü·pə′lā·shən]

(metallurgy)

Method using a cupel for assaying precious metals.

Process for refining gold and silver by alloying them with lead and then oxidizing the molten lead to separate the base metal from the precious metal.

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Cupellation 

oxidation melting of an alloy of lead with noble metals (gold and silver) to separate them in pure form. Cupellation is based on the fact that lead and other base metals are easily oxidized at high temperatures by atmospheric oxygen, whereas the noble metals are unchanged.

Cupellation is used in assaying to establish the purity of a sample (the content of the noble metals in their alloys). The process takes place in cupels, which are small cups made from a porous refractory material (bone ash, magnesite, and others), at a temperature of 850°-900°C. During cupellation, lead and other base metals are converted into molten oxides, which are absorbed by the cupel, whereas the noble metals remain on its surface as “beads.”

In metallurgy, cupellation is the operation of separating noble metals from argentiferous lead; it is carried out in reverberatory furnaces at a temperature of about 1000°C. Lead and base metals are oxidized by the oxygen blast. The mixture of oxides, in which lead oxide (PbO) predominates, is in liquid form and flows continuously from the surface of the melt into a receptacle. A gold-silver alloy that sometimes contains platinum metals is produced on the hearth of the furnace.

REFERENCES

Loskutov, F. M. Metallurgiia svintsa. Moscow, 1965.
Priborootbiranie i analiz blagorodnykh metallov. Edited by I. F. Barysh-nikov. Moscow, 1968.

V. L. BELOVA and IU. F. VAIMAN