86
J. F. Pusateri et al.
• Improved process control. Although SX presents an effective barrier against most
of the classical Zn impurities, Fe is co-extracted with Zn. pH and ORP control in
leaching are therefore important to control Fe in the PLS. Unstable pH control,
mainly due to blockages in the WOX addition system, yielded highly dissolved Fe
values in the PLS, and Fe extracted onto the organic resulted in reduced SX capacity
and poor phase separation. The entire WOX addition system was redesigned to
eliminate WOX slurry blockages, a standby slurry system was installed, and control
valve and take-offs were replaced.
• Equipment reliability. As Fe extraction onto the organic is not totally avoidable,
HCl is used to strip Fe from the organic, which requires a significant volume
of HCl and produces spent FeCl 3 /HCl solution. Large scale facilities therefore
incorporate an HCl recovery process. The corrosive processing conditions of the
HCl recovery process necessitates the use of glass-lined process equipment and
PTFE-lined piping and mechanical equipment. Piping stress-related leaks yielded
low availability of the original Mooresboro HCl recovery circuit. The system was
redesigned, based on a detailed piping stress analysis.
• Leach solid/liquid separation capacity. Designing an MZP circuit requires great
attention to solid/liquid separation equipment design, particularly the leach clarifiers, due to the low tolerance of SX for suspended solids. At Skorpion, CRUD
accumulation was caused by total suspended solids (TSS) values in the pregnant
leach solution (PLS) averaging 45 mg/l, versus the specified value of 10 mg/l. A
CRUD run through SX ultimately led to a hydrogen fire in the EW cell house
[7]. A single 41 ft diameter leach clarifier presented one of the most significant
capacity constraints in the original Mooresboro leach circuit. The high rise rate of
0.35 ft/min led to significant and varying solids carryover, even at reduced throughput. The Asturiana de Zinc Reverse Leach® process, implemented in the restart
project, featured two new and one repurposed clarifier, each of 59 ft diameter,
yielding a rise rate to 0.06ft/min, or a capacity increase of 5.8 times.
• Improved environmental controls. The Mooresboro Restart Project included the
construction of covered product and reagent storage facilities, as well as the construction of sumps and installation of sump pumps to collect process spills and
contact stormwater. Process buffer capacity was increased, which minimizes the
risk of process spills and improves overall availability. New acid brick and membrane coating of process containments minimize environmental contamination
risk.
Project Execution
The project scope included the procurement, fabrication, and installation of 366
pieces of mechanical equipment (mainly pumps, tanks and agitators), the fabrication
and installation of 3477 piping spools and 538 tons of structural steel. Foundation and
containment construction included 6835 cubic yards of concrete and 612 tons of rebar.
Electrical and instrumentation installation included a new E-house, 3640 ft of cable
tray, 204,882 ft of cable, the installation of 248 new instruments, and refurbishment
of 586 existing instruments.
J. F. Pusateri et al.
• Improved process control. Although SX presents an effective barrier against most
of the classical Zn impurities, Fe is co-extracted with Zn. pH and ORP control in
leaching are therefore important to control Fe in the PLS. Unstable pH control,
mainly due to blockages in the WOX addition system, yielded highly dissolved Fe
values in the PLS, and Fe extracted onto the organic resulted in reduced SX capacity
and poor phase separation. The entire WOX addition system was redesigned to
eliminate WOX slurry blockages, a standby slurry system was installed, and control
valve and take-offs were replaced.
• Equipment reliability. As Fe extraction onto the organic is not totally avoidable,
HCl is used to strip Fe from the organic, which requires a significant volume
of HCl and produces spent FeCl 3 /HCl solution. Large scale facilities therefore
incorporate an HCl recovery process. The corrosive processing conditions of the
HCl recovery process necessitates the use of glass-lined process equipment and
PTFE-lined piping and mechanical equipment. Piping stress-related leaks yielded
low availability of the original Mooresboro HCl recovery circuit. The system was
redesigned, based on a detailed piping stress analysis.
• Leach solid/liquid separation capacity. Designing an MZP circuit requires great
attention to solid/liquid separation equipment design, particularly the leach clarifiers, due to the low tolerance of SX for suspended solids. At Skorpion, CRUD
accumulation was caused by total suspended solids (TSS) values in the pregnant
leach solution (PLS) averaging 45 mg/l, versus the specified value of 10 mg/l. A
CRUD run through SX ultimately led to a hydrogen fire in the EW cell house
[7]. A single 41 ft diameter leach clarifier presented one of the most significant
capacity constraints in the original Mooresboro leach circuit. The high rise rate of
0.35 ft/min led to significant and varying solids carryover, even at reduced throughput. The Asturiana de Zinc Reverse Leach® process, implemented in the restart
project, featured two new and one repurposed clarifier, each of 59 ft diameter,
yielding a rise rate to 0.06ft/min, or a capacity increase of 5.8 times.
• Improved environmental controls. The Mooresboro Restart Project included the
construction of covered product and reagent storage facilities, as well as the construction of sumps and installation of sump pumps to collect process spills and
contact stormwater. Process buffer capacity was increased, which minimizes the
risk of process spills and improves overall availability. New acid brick and membrane coating of process containments minimize environmental contamination
risk.
Project Execution
The project scope included the procurement, fabrication, and installation of 366
pieces of mechanical equipment (mainly pumps, tanks and agitators), the fabrication
and installation of 3477 piping spools and 538 tons of structural steel. Foundation and
containment construction included 6835 cubic yards of concrete and 612 tons of rebar.
Electrical and instrumentation installation included a new E-house, 3640 ft of cable
tray, 204,882 ft of cable, the installation of 248 new instruments, and refurbishment
of 586 existing instruments.