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J. Wood et al.
(i) Neutral leach residues as part of the “classical” RLE plant scheme. Such
plants were typically implemented prior to the development of the hot acid
leach/jarosite processes to enable improved zinc recoveries.
(ii) Processing of zinc secondaries, most notably steel plant electric arc furnace
dusts (EAFD).
The Waelz kiln relies on gas–solid phase reactions under counter current conditions in a rotary kiln. Due to the counter current nature of the process and moderate
operating temperatures, the Waelz kiln is thermally efficient and considered reliable
and well proven based on its application in the cement industry. The primary disadvantage of leach residue processing in the Waelz kiln, however, is the nature of the
final iron-bearing product (clinker) generated, which is considered less stable than
fayalite slag produced in the other fuming processes operating with a molten slag
bath. This can present a major challenge in terms of long-term disposal of such material, effectively turning one form of metallurgical waste into another. Additionally,
the recovery of silver and other valuable minor metals (In, Ge and Ga) is significantly reduced compared with alternatives such as the Ausmelt fuming process.
Recovery of these metals is often critical to the economic viability of zinc leach
residue processing.
Comparison with Box Fuming Process
The box fuming process is another classical pyrometallurgical technology with many
decades of operating history. The process has been widely employed in lead smelters,
to recover lead and zinc from molten blast furnace slag. Typically, these furnaces are
operated in a batch mode although a continuous zinc fuming process was successfully
utilised by KCM at their lead smelter in Bulgaria until 2016 [9]. Primary limitations
of the box fuming process include the maximum quantity of solid charge able to
treated and level of process air oxygen enrichment able to be employed, making it
less well suited to the processing of stockpiled zinc leach residues and more amenable
to handling molten, zinc-bearing slags. The box fumer is also limited in its ability to
cope with certain impurities, particularly high levels of copper, which may give rise
to formation of a matte/metal phase in the furnace.
Comparison with Side-Blowing Process
The side-blowing process, a derivative of the Russian Vanyukov technology, attempts
to overcome some of the disadvantages of the box fuming process as a result of its
more robust furnace construction, ability to tolerate the presence of matte/metal and
capability to operate with oxygen enrichment levels as high as 80% [10]. The process
J. Wood et al.
(i) Neutral leach residues as part of the “classical” RLE plant scheme. Such
plants were typically implemented prior to the development of the hot acid
leach/jarosite processes to enable improved zinc recoveries.
(ii) Processing of zinc secondaries, most notably steel plant electric arc furnace
dusts (EAFD).
The Waelz kiln relies on gas–solid phase reactions under counter current conditions in a rotary kiln. Due to the counter current nature of the process and moderate
operating temperatures, the Waelz kiln is thermally efficient and considered reliable
and well proven based on its application in the cement industry. The primary disadvantage of leach residue processing in the Waelz kiln, however, is the nature of the
final iron-bearing product (clinker) generated, which is considered less stable than
fayalite slag produced in the other fuming processes operating with a molten slag
bath. This can present a major challenge in terms of long-term disposal of such material, effectively turning one form of metallurgical waste into another. Additionally,
the recovery of silver and other valuable minor metals (In, Ge and Ga) is significantly reduced compared with alternatives such as the Ausmelt fuming process.
Recovery of these metals is often critical to the economic viability of zinc leach
residue processing.
Comparison with Box Fuming Process
The box fuming process is another classical pyrometallurgical technology with many
decades of operating history. The process has been widely employed in lead smelters,
to recover lead and zinc from molten blast furnace slag. Typically, these furnaces are
operated in a batch mode although a continuous zinc fuming process was successfully
utilised by KCM at their lead smelter in Bulgaria until 2016 [9]. Primary limitations
of the box fuming process include the maximum quantity of solid charge able to
treated and level of process air oxygen enrichment able to be employed, making it
less well suited to the processing of stockpiled zinc leach residues and more amenable
to handling molten, zinc-bearing slags. The box fumer is also limited in its ability to
cope with certain impurities, particularly high levels of copper, which may give rise
to formation of a matte/metal phase in the furnace.
Comparison with Side-Blowing Process
The side-blowing process, a derivative of the Russian Vanyukov technology, attempts
to overcome some of the disadvantages of the box fuming process as a result of its
more robust furnace construction, ability to tolerate the presence of matte/metal and
capability to operate with oxygen enrichment levels as high as 80% [10]. The process