42
S. Nicol et al.
viable. With increasingly stringent environmental regulations worldwide, there is the
need to determine alternative methods to reduce the lead contained in these slags.
Lead is lost to the slag through two mechanisms, entrainment and dissolution.
Entrained lead is present in the slag due to insufficient settling prior to the tapping
of the slag from the furnace or forehearth. The lead lost through dissolution is commonly classified as either sulfidic or oxidic, with the sulfidic losses incurred by the
incorporation of sulfur into the molten oxide solution. The entrained metal is able to
be recovered through further settling of the slag. To completely recover the remaining
dissolved material, chemical processes are required.
Selective reduction of lead is performed in the lead smelting process. As such, it
is reasonable to suggest that further selective reduction has the potential to recover
further quantities of lead from the slag. In this experimental work, methane (CH 4(g) )
has been used for this purpose. However, it is possible to use other reductants in
industrial processes.
The gaseous reduction of slags has been extensively researched. It has been
demonstrated that methane is able to reduce copper containing slags, resulting in
slags with about 0.3% Cu before iron begins to reduce to a significant percent [2].
The reduction of slags using methane focused more on copper, but treating lead
slags is also important. Fundamental research has been performed on the reduction
of PbO from a CaO–FeO x –MgO–PbO–SiO 2 slag with a CO/CO 2 gas mixture [3].
The reducing gas was blown over a slag, with variations in the gas composition, temperature, ‘FeO’ concentration, PbO concentration, slag agitation, and slag depth. It
was shown that, for the slag system and conditions investigated, the reduction of PbO
was dependent on the ‘FeO’ concentration, gas composition, and the slag temperature and composition. The rate-controlling step was suggested to be the formation
of the CO 2(g) at the slag/gas interface. Diffusion of ionic species within the slag was
rapid.
Based on the fundamental research on the kinetics of lead slag reduction, it is
proposed that the reduction of lead containing slag by methane injected into the melt
is possible. Injecting methane into the slag provides a reducing atmosphere, with
the bubbles providing a high surface area for the CO 2(g) formation at the slag/gas
interface. The aim of this paper is to examine the feasibility of the injection of
methane into a molten slag to reduce the lead contained in the slag.
Experimental Study
Characterization of the Slags
The slag used for this study was taken from the Blast Furnace at the Gopher Resource
Eagan Smelter. Slag was sampled from the slag pots, after settling of entrained bullion
and matte had occurred. The slag bulk composition is summarized in Table 1.
S. Nicol et al.
viable. With increasingly stringent environmental regulations worldwide, there is the
need to determine alternative methods to reduce the lead contained in these slags.
Lead is lost to the slag through two mechanisms, entrainment and dissolution.
Entrained lead is present in the slag due to insufficient settling prior to the tapping
of the slag from the furnace or forehearth. The lead lost through dissolution is commonly classified as either sulfidic or oxidic, with the sulfidic losses incurred by the
incorporation of sulfur into the molten oxide solution. The entrained metal is able to
be recovered through further settling of the slag. To completely recover the remaining
dissolved material, chemical processes are required.
Selective reduction of lead is performed in the lead smelting process. As such, it
is reasonable to suggest that further selective reduction has the potential to recover
further quantities of lead from the slag. In this experimental work, methane (CH 4(g) )
has been used for this purpose. However, it is possible to use other reductants in
industrial processes.
The gaseous reduction of slags has been extensively researched. It has been
demonstrated that methane is able to reduce copper containing slags, resulting in
slags with about 0.3% Cu before iron begins to reduce to a significant percent [2].
The reduction of slags using methane focused more on copper, but treating lead
slags is also important. Fundamental research has been performed on the reduction
of PbO from a CaO–FeO x –MgO–PbO–SiO 2 slag with a CO/CO 2 gas mixture [3].
The reducing gas was blown over a slag, with variations in the gas composition, temperature, ‘FeO’ concentration, PbO concentration, slag agitation, and slag depth. It
was shown that, for the slag system and conditions investigated, the reduction of PbO
was dependent on the ‘FeO’ concentration, gas composition, and the slag temperature and composition. The rate-controlling step was suggested to be the formation
of the CO 2(g) at the slag/gas interface. Diffusion of ionic species within the slag was
rapid.
Based on the fundamental research on the kinetics of lead slag reduction, it is
proposed that the reduction of lead containing slag by methane injected into the melt
is possible. Injecting methane into the slag provides a reducing atmosphere, with
the bubbles providing a high surface area for the CO 2(g) formation at the slag/gas
interface. The aim of this paper is to examine the feasibility of the injection of
methane into a molten slag to reduce the lead contained in the slag.
Experimental Study
Characterization of the Slags
The slag used for this study was taken from the Blast Furnace at the Gopher Resource
Eagan Smelter. Slag was sampled from the slag pots, after settling of entrained bullion
and matte had occurred. The slag bulk composition is summarized in Table 1.