ABSTRACT
Silver present in lead ores is recovered as a by-product during the refining of lead by a desilverization step. The raw silver contains an appreciable amount of lead which is eliminated by process known as the “cupellation process” from Latin cupel = cup. The process is based on the principle of selective oxidation. When molten lead containing silver is subjected to a blast of air, the lead oxidizes selectively to PbO while silver is not affected. Lead oxide formed is easily fusible and acts as a solvent for other base metal oxides which may be present. The fluid mass of PbO is continuously run off leaving behind silver and any gold. When gold is present, the product is known a doré bullion. Separation of gold is achieved either by acid leaching or electrolytically. At present, the process is carried out in a small reverberatory furnace in two stages; each stage in a separate furnace. In the first stage, a product containing 50% Ag is obtained. The product is then processed further in the second furnace to yield 99% Ag.
