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R. Vanparys et al.
Introduction
The lead blast furnace has historically been a staple in the lead smelting process. Its
main purpose is the reduction of a PbO-rich feed with metallurgical coke, in order to
produce metallic lead. Despite the rise of new technologies over the past decades, it
remains highly relevant, as many lead production sites still use a blast furnace in their
flow sheets [1, 2]. A schematic illustration of the lead blast furnace is provided in
Fig. 1. Different reaction mechanisms for the reduction of lead-rich slags are known,
and all of them can occur in parallel in the blast furnace. The main reactions are
the indirect reduction reaction and the direct reduction reaction. The former implies
that the reductant is a gaseous CO environment (Eq. 1), whereas the latter involves a
solid carbon reductant, such as coke, to interact locally with the slag, regardless of the
atmosphere present (Eq. 2). The exact mechanism of these reactions is still subject
to some debate, but most hypotheses include either a hopping mechanism of O
2−
species in the slag phase with counter-current electron transport, or the development
of a localised bubble of gas containing CO and CO 2 , where the CO is regenerated
by the Boudouard reaction with coke.
PbO(slag, l) + CO(g) → Pb(l) + CO 2 (g)
(1)
PbO(slag, l) + C(s) → Pb(l) + CO(g)
(2)
Several studies on lead blast furnaces, using sinter as feed, indicate that the majority of reduction reactions occur in the region where the temperature exceeds 800 °C,
labelled “melting zone” in Fig. 1, since feed material starts to melt there [3–9]. This
illustrates the importance of reactions between liquid slags, rich in PbO, and metallurgical coke. However, because the conditions of this zone are hard to replicate
in a laboratory experiment and because coke is a very complex material, previous
kinetic studies have been limited to simplified reaction geometries. Some examples
include sessile drop testing and the submersion of carbonaceous materials, with an
accurately specified shape, in liquid slags.
The need for a different test method has been raised in the previous work [10].
In the current work, the first steps towards this new approach are taken. An initial experimental study is performed in a laboratory-scale set-up that more closely
resembles the conditions of the dripping zone of the lead blast furnace. In the study,
synthetic lead-rich slag is molten on a small-scale bed of metallurgical coke, inside
a vertical tube furnace. The mechanism of reduction as well as the flow behaviour of
the dripping slag is investigated. Studied parameters include temperature, reaction
time, and coke particle size.
R. Vanparys et al.
Introduction
The lead blast furnace has historically been a staple in the lead smelting process. Its
main purpose is the reduction of a PbO-rich feed with metallurgical coke, in order to
produce metallic lead. Despite the rise of new technologies over the past decades, it
remains highly relevant, as many lead production sites still use a blast furnace in their
flow sheets [1, 2]. A schematic illustration of the lead blast furnace is provided in
Fig. 1. Different reaction mechanisms for the reduction of lead-rich slags are known,
and all of them can occur in parallel in the blast furnace. The main reactions are
the indirect reduction reaction and the direct reduction reaction. The former implies
that the reductant is a gaseous CO environment (Eq. 1), whereas the latter involves a
solid carbon reductant, such as coke, to interact locally with the slag, regardless of the
atmosphere present (Eq. 2). The exact mechanism of these reactions is still subject
to some debate, but most hypotheses include either a hopping mechanism of O
2−
species in the slag phase with counter-current electron transport, or the development
of a localised bubble of gas containing CO and CO 2 , where the CO is regenerated
by the Boudouard reaction with coke.
PbO(slag, l) + CO(g) → Pb(l) + CO 2 (g)
(1)
PbO(slag, l) + C(s) → Pb(l) + CO(g)
(2)
Several studies on lead blast furnaces, using sinter as feed, indicate that the majority of reduction reactions occur in the region where the temperature exceeds 800 °C,
labelled “melting zone” in Fig. 1, since feed material starts to melt there [3–9]. This
illustrates the importance of reactions between liquid slags, rich in PbO, and metallurgical coke. However, because the conditions of this zone are hard to replicate
in a laboratory experiment and because coke is a very complex material, previous
kinetic studies have been limited to simplified reaction geometries. Some examples
include sessile drop testing and the submersion of carbonaceous materials, with an
accurately specified shape, in liquid slags.
The need for a different test method has been raised in the previous work [10].
In the current work, the first steps towards this new approach are taken. An initial experimental study is performed in a laboratory-scale set-up that more closely
resembles the conditions of the dripping zone of the lead blast furnace. In the study,
synthetic lead-rich slag is molten on a small-scale bed of metallurgical coke, inside
a vertical tube furnace. The mechanism of reduction as well as the flow behaviour of
the dripping slag is investigated. Studied parameters include temperature, reaction
time, and coke particle size.