Refining of Lead
The production lead after melting process has a grade of 99 – 99.9%Pb.and the rest is numerous dissolved impurities. These maximum impurities [in %] can be as follow:
| Cu | Sb | As | Sn | Zn | Fe | Ni | Bi | Au + Ag | S |
| 3 | 6 | 1.5 | 4 | 0.5 | 0.2 | 0.2 | 7 | 2 | 0.3 |
The purpose of refining is:
- Remove or recovery these impurities, which can have negative influence of the mechanical and chemical effects of lead.
- Remove and recovery of Novel metals.
There are two methods for the refining of lead
- Pyrometallurgy; this method is useful and will be used in industries
- Electrolytic refining; this method is complicated and will be used in some cases in the industries
Pyrometallurgy
De-coppering
There is a two stage operation process:
- Stage 1: Copper is soluble in lead at room temperature to only 0.06 % Cu. When the lead cools copper more than this amount will be precipitated in form such as Cu2As, Cu2Sb, Cu2S base on the Segregation mechanism.
- Stage 2: In this stage elemental sulphur is mixed into the molten lead at the lowest possible temperature (320 0C) base the following reaction:
[Cu]pb + S = (CuS)
[Cu]Pb + CuS = (Cu2S)
Pb + S = PbS
The removal of copper will be occurred in the industry in a batch manner system, but a continuous drossing furnace was developed by Broken Hill Associated Smelter (BHAS) at Port Pirie Australia.