764 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
1. impact on the metallurgical circuit performance,
resulting in financial losses for the project.
2. increased toxicity potential.
To control the TDS increase, a bleed is usually incorpo-
rated into the circuit, which is typically sent to the cyanide
destruction to neutralize residual cyanide. While this miti-
gates the potential toxicity from cyanide, it does not reduce
the TDS of the solution, nor does it reduce the impact of
thiocyanate on the receiving environment.
To mitigate the toxicity, a method to control thiocya-
nate is necessary. Typical methods of removing SCN utilize
biological means, or chemical precipitation. With the high
TDS and large array of other contaminants, the biological
system would likely require pretreatment to reduce toxic
effects to the biological population, while the chemical oxi-
dation would likely require an increased dosage due to the
other constituents contained within the process solution.
Further, both potential solutions would completely oxidize
the SCN into its base constituents of SO42–, HCO3–, and
NO3–, increasing solution TDS.
As previously described, the EO process does not
increase the solution TDS, but instead, can lower the TDS
through partial oxidation of SCN in a controlled manner
which allows for the production and reuse of NaCN. In
this manner, the EO process can act as a kidney to clean up
recirculating process solutions from metallurgical circuits
which have closed water balances, ensuring TDS gain is
kept to a minimum. Further, the NaCN production offsets
purchasing new cyanide thereby reducing the total project
liabilities and risks.
Description of EO Process Integration into Existing
Metallurgical Flowsheet
The mine’s metallurgical process is a typical CIP process,
with the slurry output from grinding going to a pre-leach
thickener, where the overflow goes through a small carbon
in columns (CIC) circuit, whilst the bulk of the slurry flow
goes to the cyanide leaching circuit, which is followed by a
carbon-in-pulp (CIP) circuit. The loaded carbon is stripped
with a concentrated cyanide solution, with the stripped
solution going through electrowinning to produce the
projects doré. The tailings go to a CN recovery thickener,
where the solution is recycled back to leach, and the solids
are treated in the CN detoxification process. A slight altera-
tion to this process is the inclusion of the SART process,
which is due to the high CN-soluble copper in the ore. As
with SCN, if left untreated, the copper would consume a
significant amount of cyanide, adversely affecting the proj-
ect economics. With the SART process incorporated, the
cyanide is recycled, and the copper is recovered in the form
of a high-grade copper concentrate. The process is depicted
below in Figure 1.
The inclusion of the SART process is significant for the
inclusion of EO, as this allows for the optimal placement
of thiocyanate recovery within the overall metallurgical
flowsheet. Specifically, as shown in Figure 2, the EO stage
would treat a slip stream of SART copper clarifier overflow
and discharge leach solution with a lower SCN concentra-
tion into the SART neutralization stage. This allows for
a variable flow to the EO circuit, where the flow can be
increased or decreased to maintain the mass load of SCN
Figure 1. Simplified block flow diagram of Mexican mine, showing inclusion of SART plant
1. impact on the metallurgical circuit performance,
resulting in financial losses for the project.
2. increased toxicity potential.
To control the TDS increase, a bleed is usually incorpo-
rated into the circuit, which is typically sent to the cyanide
destruction to neutralize residual cyanide. While this miti-
gates the potential toxicity from cyanide, it does not reduce
the TDS of the solution, nor does it reduce the impact of
thiocyanate on the receiving environment.
To mitigate the toxicity, a method to control thiocya-
nate is necessary. Typical methods of removing SCN utilize
biological means, or chemical precipitation. With the high
TDS and large array of other contaminants, the biological
system would likely require pretreatment to reduce toxic
effects to the biological population, while the chemical oxi-
dation would likely require an increased dosage due to the
other constituents contained within the process solution.
Further, both potential solutions would completely oxidize
the SCN into its base constituents of SO42–, HCO3–, and
NO3–, increasing solution TDS.
As previously described, the EO process does not
increase the solution TDS, but instead, can lower the TDS
through partial oxidation of SCN in a controlled manner
which allows for the production and reuse of NaCN. In
this manner, the EO process can act as a kidney to clean up
recirculating process solutions from metallurgical circuits
which have closed water balances, ensuring TDS gain is
kept to a minimum. Further, the NaCN production offsets
purchasing new cyanide thereby reducing the total project
liabilities and risks.
Description of EO Process Integration into Existing
Metallurgical Flowsheet
The mine’s metallurgical process is a typical CIP process,
with the slurry output from grinding going to a pre-leach
thickener, where the overflow goes through a small carbon
in columns (CIC) circuit, whilst the bulk of the slurry flow
goes to the cyanide leaching circuit, which is followed by a
carbon-in-pulp (CIP) circuit. The loaded carbon is stripped
with a concentrated cyanide solution, with the stripped
solution going through electrowinning to produce the
projects doré. The tailings go to a CN recovery thickener,
where the solution is recycled back to leach, and the solids
are treated in the CN detoxification process. A slight altera-
tion to this process is the inclusion of the SART process,
which is due to the high CN-soluble copper in the ore. As
with SCN, if left untreated, the copper would consume a
significant amount of cyanide, adversely affecting the proj-
ect economics. With the SART process incorporated, the
cyanide is recycled, and the copper is recovered in the form
of a high-grade copper concentrate. The process is depicted
below in Figure 1.
The inclusion of the SART process is significant for the
inclusion of EO, as this allows for the optimal placement
of thiocyanate recovery within the overall metallurgical
flowsheet. Specifically, as shown in Figure 2, the EO stage
would treat a slip stream of SART copper clarifier overflow
and discharge leach solution with a lower SCN concentra-
tion into the SART neutralization stage. This allows for
a variable flow to the EO circuit, where the flow can be
increased or decreased to maintain the mass load of SCN
Figure 1. Simplified block flow diagram of Mexican mine, showing inclusion of SART plant