DOI Artikel:
Brockner, Wolfgang; Hegerhorst, Karin: Early copper, lead and silver production processes
DOI Seite / Zitierlink:https://doi.org/10.11588/diglit.56859#0082
58
Normally, impure (black) copper with sulphidic inclusions (Schwarzkupfer)
was produced, which might have been refined in a second step (Tylecote 1976).
Lead / silver line
a. Roast reaction process
Lead ores are often associated with silver minerals. In order to extract silver,
lead, as precious-metal collector has first to be produced. Mainly galena, origi-
nating from Upper Harz vein ores, was used in the one-step (ancient) roast
reaction process using „primitive“ smelting furnaces (AGRICOLA 1977. Tylecote
1976). The time window for this process stretches from the 9th to the 12th
centuries AD. The skill lies in running the following two reactions synchronously:
Roasting
Reaction
Balance
2 PbS + 3 O2
PbS + 2 PbO
3 PbS + 3 O2
2 PbO + 2 SO2
3Pb/(Ag) + SO2
3 Pb/(Ag) + 3 SO2
PbS is galena, O2 oxygen (air), PbO lead oxide (lithargite), Pb/(Ag) argentiferous lead
(Werkblei), and SO2 gaseous sulphur dioxide.
A greatly enhanced understanding was gained from the excavation of the
smelting site Johanneser Kurhaus near Clausthal-Zellerfeld with its respective
find complexes, consisting mostly of heterogeneous „slag“ material arising from
local, Upper Harz vein ores (Heimbruch, Koerfer, Brockner 1989.
Heimbruch 1990. Klappauf, Linke, Brockner 1990. Koerfer 1990.
Klappauf, Linke 1996). The corresponding heterogeneous waste (slag) consists
mostly of the heat-treated gangue material, which is only sintered. The chemical
analyses and phase composition are not indicative of the process because these
„slags“ are related more strongly to the different ore/gangue materials used in the
charges. The lowest process temperature2, determined by dilatometric methods,
was found around 700 °C, or even lower.
b. Roast reduction process
Another process for lead/silver winning was the (younger) two-stage roast
reduction process, which required additional charcoal and fluxes, but allowed
larger amounts of ore to be smelted. The first, separate step consists of the
roasting, that is the removal of the sulphur content. This is followed by the
2 Vid. footnote above
Normally, impure (black) copper with sulphidic inclusions (Schwarzkupfer)
was produced, which might have been refined in a second step (Tylecote 1976).
Lead / silver line
a. Roast reaction process
Lead ores are often associated with silver minerals. In order to extract silver,
lead, as precious-metal collector has first to be produced. Mainly galena, origi-
nating from Upper Harz vein ores, was used in the one-step (ancient) roast
reaction process using „primitive“ smelting furnaces (AGRICOLA 1977. Tylecote
1976). The time window for this process stretches from the 9th to the 12th
centuries AD. The skill lies in running the following two reactions synchronously:
Roasting
Reaction
Balance
2 PbS + 3 O2
PbS + 2 PbO
3 PbS + 3 O2
2 PbO + 2 SO2
3Pb/(Ag) + SO2
3 Pb/(Ag) + 3 SO2
PbS is galena, O2 oxygen (air), PbO lead oxide (lithargite), Pb/(Ag) argentiferous lead
(Werkblei), and SO2 gaseous sulphur dioxide.
A greatly enhanced understanding was gained from the excavation of the
smelting site Johanneser Kurhaus near Clausthal-Zellerfeld with its respective
find complexes, consisting mostly of heterogeneous „slag“ material arising from
local, Upper Harz vein ores (Heimbruch, Koerfer, Brockner 1989.
Heimbruch 1990. Klappauf, Linke, Brockner 1990. Koerfer 1990.
Klappauf, Linke 1996). The corresponding heterogeneous waste (slag) consists
mostly of the heat-treated gangue material, which is only sintered. The chemical
analyses and phase composition are not indicative of the process because these
„slags“ are related more strongly to the different ore/gangue materials used in the
charges. The lowest process temperature2, determined by dilatometric methods,
was found around 700 °C, or even lower.
b. Roast reduction process
Another process for lead/silver winning was the (younger) two-stage roast
reduction process, which required additional charcoal and fluxes, but allowed
larger amounts of ore to be smelted. The first, separate step consists of the
roasting, that is the removal of the sulphur content. This is followed by the
2 Vid. footnote above