Pattinson process

Luce-Rozan A variation of the Pattinson process, in which steam is blown through the molten metal as cold water is sprayed on the surface. 

PATTINSON PROCESS. Process for the removal of silver from lead. The silver-lead mixture is melted in one of a series of pots and allowed to cool slowly. The lead, that is free from silver or poorer in silver separates out as crystals, which aie removed, leaving the silver-iich lead in the molten state. From a number of such operations in series, a lead rich in silver is obtained, collected, and the silver recovered. 

In some operations, particularly for those processing lump feed, the roast-reduction cycle was repeated a number of times, with the temperature raised for each cycle. In this situation silver tended to concentrate in the first ran lead bullion, and could be four times the silver content of the final lead ran. This was a useful approach to handling high silver ores, so as to reduce the effort required in silver recovery by the Pattinson Process or by cupellation. 

Separation of low levels of silver was not practised until the development of the Pattinson Process in 1829 as detailed in the next section. The Parkes Process for silver and gold removal by zinc addition was introduced in 1872. 

The separation of silver by the Pattinson process used fractional crystallisation, in which molten lead was cooled and partly solidified in a pan while being briskly stirred. The solid lead crystals were relatively pure, leaving silver in the remaining liquid. A row of about nine pans were used, each heated by a fire from below. Crude bullion from the smelter was fed to the middle pan, from which solid crystals were transferred to the first pan on one side and the remaining liquid to the first pan on the other side. This process was repeated from one pan to the next up and down the line to give a purified lead with low silver content at one end and a residual liquid of around 9 kg of silver per tonne at the other end. The silver rich lead was subjected to cupellation to recover a silver bullion. Today, precious metals are separated from lead bullion using the Parkes Process, following the removal of copper, arsenic and antimony. In this process, zinc is added and the lead bulUon is cooled to precipitate a zinc-silver alloy, which is removed and separately treated. 

The Pattinson process was replaced around 1880 by the Parkes process, which used zinc to extract silver, and is now obsolete. 

Lead ores, poor in silver, are first concentrated by flotation. Lead is then produced by roasting and reduction. The content of silver in the lead metal is low. A metallurgical concentration occurs by the so-called Pattinson process (pattinsonizing). The method relies on the fact that silver-lead alloys have a eutectic composition with a silver content of 2.7%, see Figure 6.4. A melt of an alloy with a silver content lower than 2.7% is allowed to solidify slowly. The solid lead formed is gradually removed mechanically and the silver content of the melt increases. In theory a residual alloy with 2.7% Ag can be obtained. In practice it is possible to obtain at least 2% silver. Lead and silver can be separated from this residual alloy by the cupeUation process. 

Pattinson process proceso Pattison patnlin patulina Pauli exclusion principle... 

Pattinson process A process formerly used for the extraction of silver from lead. Developed in 1833 in the UK by H. L. Pattinson, it involved a repeated melting and cooling... 

Pattinson (1) A process for extracting silver from lead by selective crystallization. When molten lead is cooled, the first crystals of lead contain less silver than the residual melt. Repetition of this process a number of times yields a silver concentrate which is further purified by cupellation. Invented in 1833 by H. L. Pattinson. Largely superseded by the Parkes process, except for metals containing bismuth for which the Pattinson is the preferred process. See also Luce-Rozan. 

The Pattinson s process is a rival of the Parke s process in desilverising crude lead. The lead is melted and allowed to solidify partially the solid portion consists of... 

Problem 8 Apply phase rule to lead-silver system. Mention the effect of cooling and also explain the Pattinson s process for desilverisation of lead ores. 

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