Production of SHG Zinc From 100% Recycled Materials
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• SX depletion—bleed treatment (gypsum precipitation, cadmium cementation,
Zn(OH) 2 precipitation).
The process loops are separated by the aqueous/organic interface, which offer the
following distinct advantages:
• The organic offers a very effective barrier against the classical Zn circuit impurities,
such as Cu, Cd, Ni, Co. Moreover, the process provides a barrier against Cl and
F, which conventional Zn processing technologies do not, offering the distinct
advantage to treat secondary materials, such as WOX, galvanizing ashes, and
dross.
• The process yields consistent and predictable electrolyte quality, even at fluctuating
impurity levels in feed materials, which further enhances the ability to treat a
variety of complex feed materials.
• The SX step allows for the significant upgrading of low concentration Zn solutions, which facilitates the treatment of low Zn grade feed materials, without the
requirement to blend with higher grade feed materials.
• The Mooresboro process is designed to yield >90% Zn recovery, and AZR treats
leach residue from the Mooresboro facility in its Waelz kilns, which yields an
overall Zn recovery of >99% from the AZR business, with no leach residue disposal
requirements.
The Mooresboro Restart Project
The Mooresboro Restart Project, recently completed by AZR and its technical
partners addressed the following detail design issues, which led to the difficulties
experienced during the initial start-up in 2014:
• Bleed treatment capacity. Capacity increased by 40% to meet nominal production
requirements.
• Reagent cost reduction. Limestone will be used instead of lime for neutralization.
• Gypsum byproduct quality improvements. Initial operating experience at Mooresboro yielded gypsum which did not meet the specifications for agricultural use,
in respect of Zn, Cd and moisture content. Bench scale and piloting work, performed in collaboration with Pocock, confirmed that a 4:1 gypsum seed recycle rate
increased thickener underflow solids concentration from 15 to 35% and reduced
the required thickener unit area from 40 to 2 m
2 /t/day. A hydro cyclone cluster
was therefore incorporated into the gypsum flowsheet, to produce the required
seed recycle.
• Electrolyte quality improvements. The MZP produces excellent quality electrolyte
in respect of all the classical Zn impurities, with current efficiency values in the
range of 90–92% achievable on a consistent basis. Contamination from external
sources and organic entrainment in the electrolyte fed from SX to EW yielded low
current efficiencies in the initial operation. Several components were replaced with
super duplex stainless steel to minimize electrolyte contamination and improve
carbon filter reliability to reduce organic entrainment to specified values.
85
• SX depletion—bleed treatment (gypsum precipitation, cadmium cementation,
Zn(OH) 2 precipitation).
The process loops are separated by the aqueous/organic interface, which offer the
following distinct advantages:
• The organic offers a very effective barrier against the classical Zn circuit impurities,
such as Cu, Cd, Ni, Co. Moreover, the process provides a barrier against Cl and
F, which conventional Zn processing technologies do not, offering the distinct
advantage to treat secondary materials, such as WOX, galvanizing ashes, and
dross.
• The process yields consistent and predictable electrolyte quality, even at fluctuating
impurity levels in feed materials, which further enhances the ability to treat a
variety of complex feed materials.
• The SX step allows for the significant upgrading of low concentration Zn solutions, which facilitates the treatment of low Zn grade feed materials, without the
requirement to blend with higher grade feed materials.
• The Mooresboro process is designed to yield >90% Zn recovery, and AZR treats
leach residue from the Mooresboro facility in its Waelz kilns, which yields an
overall Zn recovery of >99% from the AZR business, with no leach residue disposal
requirements.
The Mooresboro Restart Project
The Mooresboro Restart Project, recently completed by AZR and its technical
partners addressed the following detail design issues, which led to the difficulties
experienced during the initial start-up in 2014:
• Bleed treatment capacity. Capacity increased by 40% to meet nominal production
requirements.
• Reagent cost reduction. Limestone will be used instead of lime for neutralization.
• Gypsum byproduct quality improvements. Initial operating experience at Mooresboro yielded gypsum which did not meet the specifications for agricultural use,
in respect of Zn, Cd and moisture content. Bench scale and piloting work, performed in collaboration with Pocock, confirmed that a 4:1 gypsum seed recycle rate
increased thickener underflow solids concentration from 15 to 35% and reduced
the required thickener unit area from 40 to 2 m
2 /t/day. A hydro cyclone cluster
was therefore incorporated into the gypsum flowsheet, to produce the required
seed recycle.
• Electrolyte quality improvements. The MZP produces excellent quality electrolyte
in respect of all the classical Zn impurities, with current efficiency values in the
range of 90–92% achievable on a consistent basis. Contamination from external
sources and organic entrainment in the electrolyte fed from SX to EW yielded low
current efficiencies in the initial operation. Several components were replaced with
super duplex stainless steel to minimize electrolyte contamination and improve
carbon filter reliability to reduce organic entrainment to specified values.