1
24-010
Analysis and Repair of Failed Copper SX Plant Mix Boxes:
An Application of First Principles
Ron Derrick
Derrick Mechanical, LLC, Gilbert, AZ
ABSTRACT
SX operators have conducted extensive shut-downs and
repairs over the years to mitigate solution leaks from failed
stainless steel false floors and walls in rectangular mixer-
settler mix boxes. Hydrodynamic modeling using first
principles and constitutive equations of fluid mechanics
can inform an efficient structural redesign sufficient to
eliminate the plate failures. Updated mix boxes have been
performing without failure for over a decade. Given the
extensive construction of the original Holmes and Narver
mixer-settler design throughout the world that includes
stainless steel lined rectangular primary and auxiliary mix
boxes, SX operators may benefit from the approach, elimi-
nating costly shutdowns, leaks to containment, and hazard-
ous repairs.
INTRODUCTION
The mixer-settler is in integral element of SXEW technol-
ogy used in many copper mining operations. It is essentially
a combination liquid-liquid contacting and phase separa-
tion piece of equipment which consists of a series of mixing
stages (mixers) where an Aqueous phase and Organic phase
are dispersed into each other through agitation and then
followed by a separation stage (settler) where the phases sep-
arate by gravity. Depending on the process function of the
settler, the ions of interest or process buildup, are selectively
retained or discarded via extraction, washing, or stripping.
The Aqueous phase comes to the primary mixer as Pregnant
Leach Solution (PLS) or Electrolyte. The PLS comes
directly from leached stockpiles. Electrolyte circulates from
the plant Tank Farm where it resides as feed for electro-
winning processes. The Organic phase loads or unloads the
ions of interest and circulates between the stripping, wash,
or extraction stages, or the plant Tank Farm. The mixing
stages disperse the phases into each other to provide ion
exchanges or washing, depending on the process function.
The mixing of the immiscible Organic and Aqueous phases
forms a dispersion into each phase. The volume fraction of
each phase (O:A ratio), viscosity, mix tank size, and mixer
impeller speed and size, can affect the breakup and coales-
cence of phase droplets and whether the Aqueous phase
is dispersed as droplets in a continuous Organic phase or
the Organic phase is dispersed as droplets in a continuous
Aqueous phase. Typically, settlers are operated as Organic-
continuous at stripping and Aqueouscontinuous at extrac-
tion. The settler allows for a quiescent phase disengagement
by gravity. The Aqueous and Organic phases are ultimately
removed from the settler at the settler weirs. Settlers are
operated to minimize entrained phases.1
The current study is from the Metcalf SX Plant at
the Freeport McMoRan Morenci Operation located in
Morenci, Arizona and was performed in 2012. The Metcalf
SX Plant was originally designed by Brown and Root
U.S.A. Incorporated for Phelps Dodge Mining Company
around 1986 as part of the original project that brought
heap leaching and SXEW technology to the Morenci cop-
per mining operation. The Metcalf SX Plant has two sep-
arate trains fed from an elevated pregnant leach solution
(PLS) plant feed pond. At the time of this particular study,
each train processed approximately 7,800 gpm of PLS for a
total of 15,600 gpm nominal plant capacity.
The Metcalf SX E1B mix box is the focus of the study
and is part of the “B” Train and first Extractor circuit, thus
E1B. This particular mix box is the first location that PLS
enters the SX process from the plant feed pond. The origi-
nal flow sheet values for PLS flow (commonly referred to
as “Aqueous”) into the E1B was 6,000 gpm along with
Organic flows of 6,000 gpm. See Table 1 for representative
24-010
Analysis and Repair of Failed Copper SX Plant Mix Boxes:
An Application of First Principles
Ron Derrick
Derrick Mechanical, LLC, Gilbert, AZ
ABSTRACT
SX operators have conducted extensive shut-downs and
repairs over the years to mitigate solution leaks from failed
stainless steel false floors and walls in rectangular mixer-
settler mix boxes. Hydrodynamic modeling using first
principles and constitutive equations of fluid mechanics
can inform an efficient structural redesign sufficient to
eliminate the plate failures. Updated mix boxes have been
performing without failure for over a decade. Given the
extensive construction of the original Holmes and Narver
mixer-settler design throughout the world that includes
stainless steel lined rectangular primary and auxiliary mix
boxes, SX operators may benefit from the approach, elimi-
nating costly shutdowns, leaks to containment, and hazard-
ous repairs.
INTRODUCTION
The mixer-settler is in integral element of SXEW technol-
ogy used in many copper mining operations. It is essentially
a combination liquid-liquid contacting and phase separa-
tion piece of equipment which consists of a series of mixing
stages (mixers) where an Aqueous phase and Organic phase
are dispersed into each other through agitation and then
followed by a separation stage (settler) where the phases sep-
arate by gravity. Depending on the process function of the
settler, the ions of interest or process buildup, are selectively
retained or discarded via extraction, washing, or stripping.
The Aqueous phase comes to the primary mixer as Pregnant
Leach Solution (PLS) or Electrolyte. The PLS comes
directly from leached stockpiles. Electrolyte circulates from
the plant Tank Farm where it resides as feed for electro-
winning processes. The Organic phase loads or unloads the
ions of interest and circulates between the stripping, wash,
or extraction stages, or the plant Tank Farm. The mixing
stages disperse the phases into each other to provide ion
exchanges or washing, depending on the process function.
The mixing of the immiscible Organic and Aqueous phases
forms a dispersion into each phase. The volume fraction of
each phase (O:A ratio), viscosity, mix tank size, and mixer
impeller speed and size, can affect the breakup and coales-
cence of phase droplets and whether the Aqueous phase
is dispersed as droplets in a continuous Organic phase or
the Organic phase is dispersed as droplets in a continuous
Aqueous phase. Typically, settlers are operated as Organic-
continuous at stripping and Aqueouscontinuous at extrac-
tion. The settler allows for a quiescent phase disengagement
by gravity. The Aqueous and Organic phases are ultimately
removed from the settler at the settler weirs. Settlers are
operated to minimize entrained phases.1
The current study is from the Metcalf SX Plant at
the Freeport McMoRan Morenci Operation located in
Morenci, Arizona and was performed in 2012. The Metcalf
SX Plant was originally designed by Brown and Root
U.S.A. Incorporated for Phelps Dodge Mining Company
around 1986 as part of the original project that brought
heap leaching and SXEW technology to the Morenci cop-
per mining operation. The Metcalf SX Plant has two sep-
arate trains fed from an elevated pregnant leach solution
(PLS) plant feed pond. At the time of this particular study,
each train processed approximately 7,800 gpm of PLS for a
total of 15,600 gpm nominal plant capacity.
The Metcalf SX E1B mix box is the focus of the study
and is part of the “B” Train and first Extractor circuit, thus
E1B. This particular mix box is the first location that PLS
enters the SX process from the plant feed pond. The origi-
nal flow sheet values for PLS flow (commonly referred to
as “Aqueous”) into the E1B was 6,000 gpm along with
Organic flows of 6,000 gpm. See Table 1 for representative