1773
Optimizing Gold Operation and Cyanide Consumption in
Carbon-in-Leach (CIL) Processes
Alireza Kheradmand, Bill Gough, Jingyi Wang, Daniel Borim
Andritz Ltd.
ABSTRACT: This paper presents an advanced process control (APC) solution designed to improve the carbon-
in-leach (CIL) process to reduce sodium cyanide consumption while maximizing gold recovery. The CIL APC
solution effectively manages the residual cyanide concentration and pH levels in CIL tanks, enhancing the
efficiency of gold leaching. Through real-time monitoring and precise control, substantial gains in gold recovery
rates are obtained while environmental impacts are minimized by optimizing sodium cyanide consumption.
This innovative solution offers significant economic and environmental benefits, making it a valuable asset for
sustainable and efficient gold processing operations.
INTRODUCTION
Mining and mineral processing unit operations face many
challenges in controlling the processes. Most of the concen-
trators and metallurgical plants have fewer control points
compared to unit operations in other industries. However,
these control points are very critical as they determine the
throughput, recovery, and efficiency of the plant. Therefore,
proper control and automation have become quite impor-
tant in mineral processing plants. The carbon-in-leach
(CIL) leaching tanks in gold mines are crucial units where
gold particles are adsorbed on carbon from a cyanide solu-
tion, which significantly impacts plant recovery. To assure
that gold is not lost to tails, cyanide is typically overdosed.
However, cyanide solutions are relatively expensive and
toxic, which imposes an extra cost to eliminate residual cya-
nide in a destruct circuit. In other words, an extra cyanide
dosage on top of what is needed to recover gold imposes
both environmental and operational costs. Therefore, auto-
mation and control in CIL are important for both gold
recovery performance, environmental protection, and cost
savings.
The most common type of automatic controllers in
distributed control systems (DCS) and programmable logi-
cal controllers (PLC) are proportional-integral-derivative
(PID) controllers. The PIDs are reactive controllers and
only take actions to the error between the set-point (SP)
and the process variable (PV). They are relatively easier
and faster to implement compared to other technologies.
However, their performance degrades when they control
processes with long deadtimes, slow dynamics, multivari-
ate control objectives, or interacting loop behaviors. Gold
leaching circuits are typically very slow processes with long
deadtime and time constants. The rule-based expert logic
system is an alternative to PIDs, and they have been devel-
oped to close the gap and better control the mining unit
operations where PIDs fall short, but they also have certain
limitations. To push the process under the control of an
expert system, the rules must drive the process to its limi-
tations, but it is difficult to manage the process response
dynamics. They often introduce high and low excursions,
increasing the variation of the process variables – which
is cyanide concentration in a leaching circuit. Essentially,
rule-based expert systems are not ideal to properly address
Optimizing Gold Operation and Cyanide Consumption in
Carbon-in-Leach (CIL) Processes
Alireza Kheradmand, Bill Gough, Jingyi Wang, Daniel Borim
Andritz Ltd.
ABSTRACT: This paper presents an advanced process control (APC) solution designed to improve the carbon-
in-leach (CIL) process to reduce sodium cyanide consumption while maximizing gold recovery. The CIL APC
solution effectively manages the residual cyanide concentration and pH levels in CIL tanks, enhancing the
efficiency of gold leaching. Through real-time monitoring and precise control, substantial gains in gold recovery
rates are obtained while environmental impacts are minimized by optimizing sodium cyanide consumption.
This innovative solution offers significant economic and environmental benefits, making it a valuable asset for
sustainable and efficient gold processing operations.
INTRODUCTION
Mining and mineral processing unit operations face many
challenges in controlling the processes. Most of the concen-
trators and metallurgical plants have fewer control points
compared to unit operations in other industries. However,
these control points are very critical as they determine the
throughput, recovery, and efficiency of the plant. Therefore,
proper control and automation have become quite impor-
tant in mineral processing plants. The carbon-in-leach
(CIL) leaching tanks in gold mines are crucial units where
gold particles are adsorbed on carbon from a cyanide solu-
tion, which significantly impacts plant recovery. To assure
that gold is not lost to tails, cyanide is typically overdosed.
However, cyanide solutions are relatively expensive and
toxic, which imposes an extra cost to eliminate residual cya-
nide in a destruct circuit. In other words, an extra cyanide
dosage on top of what is needed to recover gold imposes
both environmental and operational costs. Therefore, auto-
mation and control in CIL are important for both gold
recovery performance, environmental protection, and cost
savings.
The most common type of automatic controllers in
distributed control systems (DCS) and programmable logi-
cal controllers (PLC) are proportional-integral-derivative
(PID) controllers. The PIDs are reactive controllers and
only take actions to the error between the set-point (SP)
and the process variable (PV). They are relatively easier
and faster to implement compared to other technologies.
However, their performance degrades when they control
processes with long deadtimes, slow dynamics, multivari-
ate control objectives, or interacting loop behaviors. Gold
leaching circuits are typically very slow processes with long
deadtime and time constants. The rule-based expert logic
system is an alternative to PIDs, and they have been devel-
oped to close the gap and better control the mining unit
operations where PIDs fall short, but they also have certain
limitations. To push the process under the control of an
expert system, the rules must drive the process to its limi-
tations, but it is difficult to manage the process response
dynamics. They often introduce high and low excursions,
increasing the variation of the process variables – which
is cyanide concentration in a leaching circuit. Essentially,
rule-based expert systems are not ideal to properly address