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A. Abadías Llamas et al.
Introduction
The metallurgical infrastructure is a key for the circular economy (CE) since it provides solutions for the metal production, processing, and recycling. However, this
infrastructure has material losses and generates residues [1]. One of the base metals
within the metallurgical infrastructure composing the CE is zinc. This zinc production process generates iron-rich precipitates, e.g. jarosite, goethite or hematite. For
instance, 88.33 kt of jarosite are generated in a plant with an annual zinc production
of 200 kt of zinc [2]. Therefore, zinc smelters have been researching possibilities of
dealing with these residues, since they require a large ponding area for their disposal.
One of these alternatives is the Direct Zinc Smelting (DZS) technology, which is a
process preventing the iron precipitate from being produced [3].
DZS is composed by two stages. In the first one, concentrate is smelted to eliminate
the sulfur as sulfur dioxides through the off-gases, at the same time that elements
such as Zn, Pb, Ag, In or Ge volatilize partially and are collected as oxide dust. In the
second stage, the slag produced in the first smelting stage (25 wt% of Zn) is reduced
to fume zinc, along with Cd, Pb, Sb or Ge to produce a clean iron-rich slag (2–3%
of Zn) [3]. This slag can be safely disposed or used as construction material if it
is cleaned enough to comply with the specifications for metals in these materials.
Additionally, as the zinc content of the smelting slag must be below 25% due to
viscosity issues, part of the clean slag can be circulated to the smelting stage to
mitigate these situations.
However, if DZS is integrated with a Roast-Leach-Electrowinning (RLE) plant,
the iron residue produced during the RLE can be fed to the DZS smelting stage to
control its slag chemistry, while the zinc oxide rich dust can be leached in the neutral
and weak acid leach stages of the RLE. This would free the land occupied by residue
dumps and recover co-precipitated elements during jarosite process such as indium
and germanium. Additionally, this option would extend the life of the current RLE
plants [3] as jarosite dumping is minimized. Recent industrial trails [4] have shown
that >90% of zinc is already recovered during the smelting stage.
Another alternative is to use a reactive approach, i.e. the treatment of these iron
residues once they are produced through the RLE process [2, 5]. One of these reactive alternatives can be, for instance, the pyrometallurgical treatment of the jarosite
produced [6]. This alternative would transform the jarosite into a slag, which requires
less landfill volume since it is a dry and high density by-product.
These pyrometallurgical alternatives and their integration into the current RLE
plants are quite promising from the point of view of decreasing the hydrometallurgical iron-rich precipitates. However, they require high temperatures and the use
of reducing agents to be conducted. Therefore, the resource consumption, material
recovery and losses, environmental impact, and residue production of these circular
actions must be carefully evaluated so that the resource efficiency of the integrated
system can be assessed objectively [7, 8]. For this reason, ten scenarios integrating
A. Abadías Llamas et al.
Introduction
The metallurgical infrastructure is a key for the circular economy (CE) since it provides solutions for the metal production, processing, and recycling. However, this
infrastructure has material losses and generates residues [1]. One of the base metals
within the metallurgical infrastructure composing the CE is zinc. This zinc production process generates iron-rich precipitates, e.g. jarosite, goethite or hematite. For
instance, 88.33 kt of jarosite are generated in a plant with an annual zinc production
of 200 kt of zinc [2]. Therefore, zinc smelters have been researching possibilities of
dealing with these residues, since they require a large ponding area for their disposal.
One of these alternatives is the Direct Zinc Smelting (DZS) technology, which is a
process preventing the iron precipitate from being produced [3].
DZS is composed by two stages. In the first one, concentrate is smelted to eliminate
the sulfur as sulfur dioxides through the off-gases, at the same time that elements
such as Zn, Pb, Ag, In or Ge volatilize partially and are collected as oxide dust. In the
second stage, the slag produced in the first smelting stage (25 wt% of Zn) is reduced
to fume zinc, along with Cd, Pb, Sb or Ge to produce a clean iron-rich slag (2–3%
of Zn) [3]. This slag can be safely disposed or used as construction material if it
is cleaned enough to comply with the specifications for metals in these materials.
Additionally, as the zinc content of the smelting slag must be below 25% due to
viscosity issues, part of the clean slag can be circulated to the smelting stage to
mitigate these situations.
However, if DZS is integrated with a Roast-Leach-Electrowinning (RLE) plant,
the iron residue produced during the RLE can be fed to the DZS smelting stage to
control its slag chemistry, while the zinc oxide rich dust can be leached in the neutral
and weak acid leach stages of the RLE. This would free the land occupied by residue
dumps and recover co-precipitated elements during jarosite process such as indium
and germanium. Additionally, this option would extend the life of the current RLE
plants [3] as jarosite dumping is minimized. Recent industrial trails [4] have shown
that >90% of zinc is already recovered during the smelting stage.
Another alternative is to use a reactive approach, i.e. the treatment of these iron
residues once they are produced through the RLE process [2, 5]. One of these reactive alternatives can be, for instance, the pyrometallurgical treatment of the jarosite
produced [6]. This alternative would transform the jarosite into a slag, which requires
less landfill volume since it is a dry and high density by-product.
These pyrometallurgical alternatives and their integration into the current RLE
plants are quite promising from the point of view of decreasing the hydrometallurgical iron-rich precipitates. However, they require high temperatures and the use
of reducing agents to be conducted. Therefore, the resource consumption, material
recovery and losses, environmental impact, and residue production of these circular
actions must be carefully evaluated so that the resource efficiency of the integrated
system can be assessed objectively [7, 8]. For this reason, ten scenarios integrating