John A Whiteman Edwin E Okafor

Abstract

Fifty-one bloomery iron smelting slags from four sites in the Nsukka Division of Nigeria have been characterized. Radiocarbon dating has shown that smelting in this area took place over about two millennia. The chemical compositions of typical phase mixtures and individual phases were determined using EDS analysis in an SEM, and phase proportions were obtained from the SEM back-scattered electron images and by point counting of optical microscopy images. All the slags were essentially contained within the Al2O3–SiO2–FeO ternary system, with the major phases being fayalite, hercynite and glass, with wüstite in some of the earlier slags. The liquidus temperature of the slags could be inferred from the ternary diagram. The earliest slags, which had high liquidus temperatures,
could have been made directly from ore currently found on site; these slags were tapped into slag pits. Later slags had lower liquidus temperatures and in general could not have been made from current ores; they were raked out of the furnace as agglomerates. Mass
balance calculations showed that the later slags were associated with a higher output of iron per unit of charged ore. The change in liquidus temperature is associated with a change in smelting technology from forced draught to natural draught furnaces, and a change in slag removal method. It is concluded that ore sizing was carried out at all the sites, and that sand or ore fines were added to the burden at the later sites.

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How to Cite
Characterization of Nigerian bloomery iron smelting slags. (2021). Historical Metallurgy, 37(2), 71-84. https://hmsjournal.org/index.php/home/article/view/254
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How to Cite

Characterization of Nigerian bloomery iron smelting slags. (2021). Historical Metallurgy, 37(2), 71-84. https://hmsjournal.org/index.php/home/article/view/254