Parkes process

The Parkes - process is a separation process metallurgy.

According to the inventor Alexander Parkes ( 1842) the silver from argentiferous lead can be pulled by zinc. If you melt silver-bearing lead along with zinc, the latter shall withdraw the lead the silver. If one uses the zinc several times to de-silvering, we obtain a very rich silver- zinc, from which the zinc is separated by distillation, while the remaining silver still contains lead and is driven off. This is done by the method of Parkesierens. The method is based on the different solubility of silver and lead in zinc. At temperatures up to 400 ° C, then the liquid lead and the solid zinc is virtually immiscible.

In a first process the silver from the largest part of the lead has to be separated. First, at temperatures C is added to the molten zinc lead higher than 400 °. Thereafter, the mixture is cooled. Since silver in the molten zinc is readily soluble, it goes over into the zinc phase. Then the zinc melt solidifies as a so -called Zinc foam ( Zn-Ag mixed crystals ). This allows the silver to be separated from the major part of the lead. This is also referred to as a zinc foam Armblei. It is subsequently ( 327 ° C) heated to the melting point of the lead, so that a part of the lead melt and can be removed. Thereafter, the remaining zinc -lead-silver - melt is heated to the boiling point of zinc (908 ° C) and the zinc removed by distillation. The product thus obtained is called rich lead and contains about 8-12% silver.