The EZINEX ® Process for Secondary Zinc Bearing Materials
787
that have led to the closing of most of the existing plants. But even with these longstanding treatment processes, one critical technical issue remains: this CZO cannot
be fed untreated in these processes. It contains elements that make it difficult to be
used both in the ISP and in the sulphate electrowinning. In fact, the CZO must be
treated to eliminate or reduce some of the contained impurities before being fed to
one of these two processes.
Chlorides and fluorides are the most harmful elements to these processes. And
EAFD is not the only zinc containing feed with this issue. Many potential CZO
sources, such as galvanizing ashes, brass foundry, and converters fumes, contain
recoverable zinc. But, as with EAFD, they also contain halides that will be transferred
to the CZO and must be removed. Chlorides fed into the zinc sulphate electrowinning (EW) system cause anodic chlorine evolution, which is a major personnel health
concern. It also increases the lead anode corrosion rate impacting costs and compromising zinc quality. Even a low concentration of a few hundred ppb of fluorides
seriously impacts the stripping of the Zn cathodes.
The presence of these halides also causes problems in the condenser unit of the ISP.
In recent years, processes to avoid these issues for CZO treatment have been studied
and installed. These systems are based on the use of a water wash solution, better if it
contains Na 2 CO 3 , but they are not without their own difficulties. In fact, some were
introduced [3] at the beginning of the twenty-first century but they were unsuccessful.
For these reasons, a chloride-based recovery system that directly produces metallic
Zn would be valuable [4–6]. The major drawback in zinc chloride EW is the Cl 2
anodic evolution and its management versus the typical O 2 evolution in the sulphate
EW system [7, 8].
At the beginning of the 1990s, Engitec developed the EZINEX
® Process [9]
capable of directly treating zinc bearing materials such as EAFD. In 1993, a 500 t/y
zinc cathode pilot plant treating EAFD was erected and operated. After one year
of operation, an industrial plant producing 2000 t/y of zinc cathode was designed,
erected, and operated. During the industrial plant operation, a thermal pilot plant
for the conversion of zinc bearing materials to CZO was also built and operated.
This thermal process, known as INDUTEC
® , is a modification of induction furnace
technology. EZINEX
® [10] is a hydrometallurgical process based on an NH 4 Cl
electrolyte and capable of producing metallic zinc directly from CZO without any
further pre-treatment. The first industrial scale EZINEX
® plant [11] was designed
to produce zinc directly from EAFD. During operation, several campaigns replacing
the EAFD feed with a CZO feed were conducted producing very good results.
Engitec recently received inquiries from steel producers that have a scrap preheater installed in front of their furnace. This furnace feed design produces an EAFD
that is quite different from that without the pre-heating. The zinc concentration in this
case reaches 40–45% and also has a strong reduction in iron concentration. Engitec
realized that this EAFD is suitable for direct treatment in the EZINEX
® Process.
787
that have led to the closing of most of the existing plants. But even with these longstanding treatment processes, one critical technical issue remains: this CZO cannot
be fed untreated in these processes. It contains elements that make it difficult to be
used both in the ISP and in the sulphate electrowinning. In fact, the CZO must be
treated to eliminate or reduce some of the contained impurities before being fed to
one of these two processes.
Chlorides and fluorides are the most harmful elements to these processes. And
EAFD is not the only zinc containing feed with this issue. Many potential CZO
sources, such as galvanizing ashes, brass foundry, and converters fumes, contain
recoverable zinc. But, as with EAFD, they also contain halides that will be transferred
to the CZO and must be removed. Chlorides fed into the zinc sulphate electrowinning (EW) system cause anodic chlorine evolution, which is a major personnel health
concern. It also increases the lead anode corrosion rate impacting costs and compromising zinc quality. Even a low concentration of a few hundred ppb of fluorides
seriously impacts the stripping of the Zn cathodes.
The presence of these halides also causes problems in the condenser unit of the ISP.
In recent years, processes to avoid these issues for CZO treatment have been studied
and installed. These systems are based on the use of a water wash solution, better if it
contains Na 2 CO 3 , but they are not without their own difficulties. In fact, some were
introduced [3] at the beginning of the twenty-first century but they were unsuccessful.
For these reasons, a chloride-based recovery system that directly produces metallic
Zn would be valuable [4–6]. The major drawback in zinc chloride EW is the Cl 2
anodic evolution and its management versus the typical O 2 evolution in the sulphate
EW system [7, 8].
At the beginning of the 1990s, Engitec developed the EZINEX
® Process [9]
capable of directly treating zinc bearing materials such as EAFD. In 1993, a 500 t/y
zinc cathode pilot plant treating EAFD was erected and operated. After one year
of operation, an industrial plant producing 2000 t/y of zinc cathode was designed,
erected, and operated. During the industrial plant operation, a thermal pilot plant
for the conversion of zinc bearing materials to CZO was also built and operated.
This thermal process, known as INDUTEC
® , is a modification of induction furnace
technology. EZINEX
® [10] is a hydrometallurgical process based on an NH 4 Cl
electrolyte and capable of producing metallic zinc directly from CZO without any
further pre-treatment. The first industrial scale EZINEX
® plant [11] was designed
to produce zinc directly from EAFD. During operation, several campaigns replacing
the EAFD feed with a CZO feed were conducted producing very good results.
Engitec recently received inquiries from steel producers that have a scrap preheater installed in front of their furnace. This furnace feed design produces an EAFD
that is quite different from that without the pre-heating. The zinc concentration in this
case reaches 40–45% and also has a strong reduction in iron concentration. Engitec
realized that this EAFD is suitable for direct treatment in the EZINEX
® Process.