Abstract
The Oiola archeological site, located in the mining complex of La Arboleda (Biscay, North Spain) was an important iron smelting center from the Roman Period to the Middle Ages and even in more current times (19th–20th centuries). Tap-slags and some plano-convex slags were identified as smelting slags. Samples were analyzed by optical microscopy, X-ray powder diffraction, scanning electron microscopy coupled with electron-dispersive spectroscopy and Raman microspectroscopy to perform a mineralogical and textural characterization. Additionally, thermogravimetric and thermodiffraction analyses were carried out to determine furnace operating temperatures. The mineral assemblage reflects furnace temperatures and cooling rates and the addition of quartz as the main flux to decrease the melting temperature of the iron ore. The comparison of slags from the Roman Period and the Middle Age reveals changes in the pyrometallurgical process through time.
Highlights
IntroductionAges (10th century BC–20th century AD) iron was obtained by the direct solid-phase reduction method, called “bloomery” method
In ancient times, from the Iron Age to the appearance of cast iron and blast furnaces in the MiddleAges (10th century BC–20th century AD) iron was obtained by the direct solid-phase reduction method, called “bloomery” method
The iron oxides from the ore are processed in one step in a furnace with carbon-based fuel where charcoal acts as reducing agent reaching temperatures of about 1200 ◦ C. [1,2,3,4,5,6]
Summary
Ages (10th century BC–20th century AD) iron was obtained by the direct solid-phase reduction method, called “bloomery” method. The iron oxides from the ore are processed in one step in a furnace with carbon-based fuel where charcoal acts as reducing agent reaching temperatures of about 1200 ◦ C. Carbon monoxide (CO) gas emanating from the charcoal reacts with iron oxide (FeO) in the ore to form solid iron particles and carbon dioxide (CO2 ) gas [7]. To reach the high temperatures needed, bellows were used to blow air into the furnace through one or more blowing holes in the furnace sides. Fluxes can be added deliberately to promote greater iron efficiency and lower melting temperatures [6]. The flux materials usually consist of limestones, quartz rich sands and sandstones [2,7,8]
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