Refining antimony from lead involves several steps, as antimony is often present as an impurity in lead ores or lead bullion. The process typically includes the following stages:
1. Initial Separation
– Liquation: Lead bullion containing antimony is heated to a temperature just above the melting point of lead (327°C). Antimony has a higher melting point (630°C), so it remains solid while the molten lead is drained off. This process reduces the antimony content in the lead.
– Drossing: During the melting of lead, antimony forms a dross (a layer of impurities) on the surface. This dross can be skimmed off and further processed to recover antimony.
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2. Oxidation and Refining
– Harris Process: This is a common method for refining lead to remove impurities like antimony. Air or oxygen is blown through molten lead, oxidizing impurities such as antimony, arsenic, and tin. These oxides form a slag that can be removed.
– Pyrometallurgical Refining: The oxidized impurities (including antimony oxide) are separated from the molten lead and collected for further processing.
3. Recovery of Antimony
– Reduction of Antimony Oxide: The collected antimony oxide (Sb₂O₃) can be reduced to metallic antimony using carbon (as charcoal or coke) in a furnace at high temperatures (around 1000°C). The reaction is:
\[
\text{Sb}_2\text{O}_3 + 3\text{C} \rightarrow 2\text{Sb} + 3\text{CO}
\]
– Electrolytic Refining: In some cases, electrolytic methods are used to further purify the recovered antimony.
4. Final Purification
– Zone Refining: For high-purity antimony, zone refining can be employed. This involves passing a molten zone through a solid antimony ingot, concentrating impurities at one end.
– Vacuum Distillation: Antimony can also be purified by vacuum distillation, where it is heated under reduced pressure to separate it from remaining impurities.
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Summary
The process of refining antimony from lead involves initial separation techniques like liquation and drossing, followed by oxidation and reduction processes to recover metallic antimony. Final purification steps ensure high-purity antimony is obtained.
This process is essential