Pete,

Most of the old books like Collins, Percy, Hofman etc have drawings of shaft 
furnaces and Noel has explained the key features.  You say that it does n't 
seem to be a very widespread process but probably more lead has been smelted 
in shaft furnaces than in any other way.  They developed from single tuyere 
units, such as those described in Agricola, to the  large rectangular 
furnaces used in the States which had 60-80 tuyeres and more.

Galena was oxidised in various ways from roasting stalls used mainly in 
Germany, Austria and Eastern Europe, where hundreds of tons of ore would be 
slowly oxidised over several weeks, to multideck roasters working on 
powdered ore and later to sinter plants.  Late C19 and early C20 practice in 
the Missouri lead belt was to use multiple mechanised ore hearths which 
produced relatively little lead metal (unlike traditional British ore 
hearths) and which were effectively oxidation furnaces.  Their product was 
then reduced to lead in huge shaft furnaces.

One of the main difficulties in oxidising lead ores has been their low 
softening point and also that of the product litharge.  The oxidation 
process is exothermic and once the ore has softened the surface area 
diminishes and oxidation is retarded.

The huge shaft furnaces used  in lead smelting should be run with charges 
containing very low amounts of coke.  This is to keep the temperature low to 
minimise fuming of lead but mainly to minimise volatilisation of zinc which 
leads to accretion build-up in the furnace column.  After a few months this 
usually kills the furnace and the furnace has to be cut-out.  The tuyeres 
have to be poked after tapping which is normally every hour or so and should 
be very dull red in appearance.  Most of the large furnaces would normally 
operate with several tuyeres covered in frozen slag and not working.  There 
are various ways to get these back to life.

The presence of pyrite should not be too much of a problem as the sulphur 
would be oxidised in the pretreatment and iron would be slagged off in the 
furnace.  The Freiberg ores mentioned below are rather exceptional.

I wonder if the limekiln type of furnace you describe was used for slow 
roasting rather than smelting?  Apart from a little coal or peat to get it 
going , it would need almost no fuel and would almost certainly glaze the 
brickwork.

Regards

Richard Smith


----- Original Message ----- 
From: "Curator" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, May 09, 2009 2:26 PM
Subject: Re: Lead smelting


> Noel,
>
> Thanks for your reply. I would be very interested in seeing pictures of 
> any existing shaft smelters though it doesn't seem to have been a very 
> widespread process; this is not a type of feature that I have come across 
> before. I have recorded what may be a shaft furnace (it looks very much 
> like a lime kiln but the vitrification on the bricks contains a high lead 
> content) on a lead mine; it is is not of the blast furnace type. I presume 
> that it dealt with run-of-mine concentrate which I believe was low in 
> pyrite content.
>
>
> Pete
>
>
> ----- Original Message ----- 
> From: <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Saturday, May 09, 2009 1:23 AM
> Subject: Re: Lead smelting
>
>
>> You are apparently interested in historical literature dealing with
>> direct-charged lead ores rather than blast (or shaft) furnace smelting of
>> sintered
>> galena concentrates.
>> Leaving aside reverberatory and hearth smelting, a short reference to
>> shaft
>> furnaces is on p. 105, The Metallurgy of Lead, by Henry F. Collins,
>> London,
>> 1910, Charles Griffin & Co.
>> wherein it is stated, "The only furnace of this kind which has been
>> successfully used on pyritous lead ores is the well-known Gerstenhofer
>> [reference
>> is given], which at Freiberg puts through in twenty-four hours about 60
>> tons
>> of a pyritous ore containing 18 percent. galena, 60 per cent. pyrites, 
>> and
>> 22 per cent. gangue, and roasts it down to about 7 per cent. sulphur.
>> Ordinary lead ores, properly so called, could not, of course, be roasted
>> in such a
>> furnace at all."
>>
>> Another old reference I checked, The Metallurgy of Lead, by H. O. Hofman,
>> 2nd ed., 1893, New York, Scientific Publishing Co., states on p. 132, 
>> "...
>> in
>> the Hartz Mountains, in Prussia, concentrated galena ores have been for
>> years, and still are, smelted raw in the blast-furnace. In other 
>> districts
>> of
>> Germany as well as in France the sulphide ores are always roasted before
>> they
>> come to the blast-furnace, and oxidized ores are of such rare occurrence
>> that they are hardly treated separately."
>>
>> Noel Kirshenbaum
>>
>> In a message dated 5/8/09 4:41:07 PM, [log in to unmask]
>> writes:
>>
>>> Dear list
>>>
>>> Does anyone have any information on the use of shaft smelters for lead
>>> ore?
>>> I am particularly intersted in the 19th century process, which I believe
>>> was
>>> carried out in France, Belgium and Germany. Thanks in advance.
>>>
>>> Pete Joseph
>>
>>
>> **************
>> A Good Credit Score is 700 or Above. See yours in
>> just 2 easy steps!
>> (http://pr.atwola.com/promoclk/100126575x1221322931x1201367171/aol?redir=http://www.freecreditreport.com/pm/default.aspx?sc=668072&amp;
>> hmpgID=115&amp;bcd=May5509AvgfooterNO115)