Solder and method for producing high purity lead

A process for the separation by distillation of a metal mixture containing lead (Pb) and tin (Sn), the process comprising the step of pre-treating a liquid molten metal feed composition,

• a) the feed composition containing substantial portions of tin and lead and comprising at least 0.16% wt of the total of chromium (Cr), manganese (Mn), vanadium (V), titanium (Ti), tungsten (W), copper (Cu), nickel (Ni), iron (Fe), aluminium (Al) and/or zinc (Zn),
• the feed composition having a temperature of at least 500° C.,
• the pre-treatment step comprising the steps of:
• b) cooling the feed composition down to a temperature of at most 825° C., to produce a bath containing a first supernatant dross which by gravity becomes floating upon a first liquid molten metal phase,
• c) adding a compound selected from the group consisting of an alkali metal, an earth alkali metal, a chemical compound comprising an alkali metal, a chemical compound comprising an earth alkali metal, and combinations thereof, to the first liquid molten metal phase to form a bath containing a second supernatant dross which by gravity comes floating on top of a second liquid molten metal phase, and
• d) removing the second dross from the second liquid molten metal phase,
• whereby the liquid molten metal phase which is obtained as product from the pre-treatment forms the metal mixture containing lead (Pb) and tin (Sn) and further comprising, on a weight basis
• at least 10% tin,
• at least 45% lead,
• at least 90% of tin and lead together,
• more lead than tin,
• at least 1 ppm and at most 5000 ppm of copper,
• at least 0.42% of antimony (Sb),
• at least 0.0001% wt of sulphur (S), and
• at most 0.1% of the total of chromium (Cr), manganese (Mn), vanadium (V), titanium (Ti) and tungsten (W),
• at most 0.1% of aluminium (Al),
• at most 0.1% of nickel (Ni),
• at most 0.1% of iron (Fe), and
• at most 0.1% of zinc (Zn),
• the process further comprising the step of subjecting the metal mixture to a distillation step wherein lead (Pb) is removed from the metal mixture by evaporation and a bottom product is obtained which comprises at least 0.6% wt of lead.