The "better method" for separating lead and silver, mentioned below by
Malcolm Henry, is called the Parkes Process, after Alexander Parkes (about
1850). He correctly states that lead and zinc are immiscible, but inasmuch
as metallic zinc is not produced in the smelting of lead (even when zinc may
be present in the raw material), metallic zinc is actually added to molten
lead so as to enable recovery of the silver which occurs in the lead. This
recovery is, as is stated below, achieved by skimming the silver-containing
zinc which has separated from the molten lead below because of their
differences in density.
Turn to descriptions of the Pattison and Parkes process.
Noel Kirshenbaum
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On Sun, Aug 14, 2011 at 7:30 AM, Robert M Henry <[log in to unmask]>wrote:
> Adrian,
> Once you've sorted out the ore dressing you need to get your head round the
> chemistry. Its complicated by the fact that lead usually comes with a little
> silver. The accounts for the silver rich ores from Shildon and Jeffry's
> (near Blanchland) around 1736 showed they were extracting about 1 lb of
> silver for every ton of lead refined. It may not sound like much but the
> income from lead was much the same as the income from silver!
> Around 1836 Pattison recognised that when molten lead cools one gets
> crystals of pure lead in a molten matrix of lead/silver. The process allowed
> about 90% of the lead to be removed before the remaining mixture needed to
> be first oxidised, the silver removed and the lead oxide reduced back to
> lead.
> Much later a better method was found. Zinc does not mix with lead - and all
> the silver will go with the zinc. So skim off the molten zinc that you've
> added and distill off the zinc leaving silver.
> Obviously oxidising lead sulphide produced sulphur dioxide but there
> weren't too many rules about that sort of thing in the early days - just a
> lot of unhappy neighbours! Most of the rest was about furnace design/fuel
> efficiency/control of oxidising vs reducing conditions.
>
> Malcolm Henry
>
>
> [log in to unmask]
>
>
>
>
> ________________________________
> From: Adrian Pearce <[log in to unmask]>
> To: [log in to unmask]
> Sent: Sunday, 14 August 2011, 0:39
> Subject: Lead Smelting
>
> I have been exploring and researching mines for 44 years and, to be honest,
> the subject of lead smelting always left me cold.
> I just couldn't get myself interested in the subject.
>
> ...... but that has all changed ......
>
> I was recently asked by English Heritage to take on the management
> agreement on behalf of the owner to clear the flues and repair the buildings
> of Snailbeach Mine New Smeltmill. I now find myself trying to figure out
> how it all worked. Also, as part of creating mine trails for Wrexham and
> Deeside in North Wales, I have been visiting lead smelting sites and GASP
> found that they can be quite interesting after all. I was asked by the
> houseowner at Llannerch-y-Mor smelter chimney for a simple explanation of
> how smelting worked and I failed dismally.
>
> So I now want to understand exactly how the process worked with different
> systems, including the use of condensing flues, etc. Boles were quite
> simple and I can understand them but when we get to things like
> reverberatory furnaces I am lost. I am hinting very broadly now to Mike
> Gill and others who are experts in this field. I know it is cheeky but
> rather than read a book, I would prefer to collect online descriptions so
> that I can collate them into a definitive working description of a lead
> smelter and then summarise it into a simple description for the general
> public.
>
> I know Mike and Hazel have translated several foreign visitor
> descriptions. So..... would anyone here be prepared to help me out by
> pointing me in the direction of online descriptions of the lead smelting
> process or sending me unlocked pdf files, etc?
>
> many thanks in advance
>
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