XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 765
converted, or NaCN produced, and maintaining concen-
tration in solution. This placement of EO within SART
offers the following advantages:
• Reduces cyanide losses to cyanate (OCN)
By taking advantage of the acidic pH contained in
the SART copper stage overflow, cyanide oxidation
to cyanate is minimized. At higher pH, OCN devel-
opment becomes a significant parasitic anodic reac-
tion due to the presence of CN–., as opposed to the
HCN(aq) present at acidic conditions.
• Avoids copper plating
By removing copper upstream of the Electro-
Oxidation circuit, this prevents the accumulation
of copper on the EO cathode. Otherwise, this could
impact the current efficiency of the electro-oxidation
process, increasing the maintenance required by the
circuit.
The thiocyanate EO process starts with the copper cir-
cuit clarifier overflow from the SART plant flowing into
the EO feed tank, where it would be pumped via an EO
feed pump to sets of electrocells. In the current design, the
electrocells are configured/grouped into banks with cath-
odes and anodes arranged as parallel plates. Both cathodes
and anodes are made of titanium coated with a layer of
Mixed Metal Oxide (MMO). As the process solution passes
through the cells, thiocyanate is oxidized to cyanide on the
anodes and hydrogen is evolved on the cathodes. The elec-
trocell effluent containing recovered cyanide flows into the
effluent tank and is then pumped to the existing SART
neutralization circuit reactors.
The electrocell off-gas, containing hydrogen and hydro-
gen cyanide, will be pulled through the packed column
scrubber using a blower, with the resulting scrubbed air
being discharged to the atmosphere. The spent scrubbing
solution, containing high concentrations of NaCN, is then
sent to the SART facility, or otherwise used directly as a
concentrated cyanide solution in the cyanide leach circuit.
Testwork Results and Discussion
Samples of SART feed solution were shipped from site to
BQE Water’s laboratory in Vancouver, BC, Canada, where
the overall objective was to verify the feasibility of integrat-
ing the EO process for NaCN recovery from SCN into the
overall metallurgical circuit.
Table 1 shows the dissolved concentrations of the main
constituents in the solution received from site for both the
as-received CN recovery thickener overflow (SART feed)
sample and after SART processing in the BQE lab (acidifi-
cation and sulphidization). Further, a synthetic solution was
created to determine the effect of co-occurring anions on
the EO process performance and gain insight into the EO
process efficiency. As expected, the SART process removed
copper, while generating free cyanide. The increase in Na
and SO4 concentrations matched the respective increases
caused by the additions of NaHS and H2SO4. However,
SART is not expected to affect thiocyanate concentrations,
so from this perspective, the results of SCN and total dis-
solved sulfur assays shown in Table 1 provide an indication
of the magnitude of analytical error for these constituents.
The solutions being tested, the leach solution shipped
from the site and a synthetic solution including, underwent
testing to trial two known configurations of electrocells:
1. low current density with low linear velocity of
solution between electrodes, approximately typical
parallel plate configurations and,
2. high current density with high linear velocity of
solution between electrodes, mimicking condi-
tions for the emew type cylindrical cells.
Figure 2. Electro-oxidation circuit incorporation into existing SART process
converted, or NaCN produced, and maintaining concen-
tration in solution. This placement of EO within SART
offers the following advantages:
• Reduces cyanide losses to cyanate (OCN)
By taking advantage of the acidic pH contained in
the SART copper stage overflow, cyanide oxidation
to cyanate is minimized. At higher pH, OCN devel-
opment becomes a significant parasitic anodic reac-
tion due to the presence of CN–., as opposed to the
HCN(aq) present at acidic conditions.
• Avoids copper plating
By removing copper upstream of the Electro-
Oxidation circuit, this prevents the accumulation
of copper on the EO cathode. Otherwise, this could
impact the current efficiency of the electro-oxidation
process, increasing the maintenance required by the
circuit.
The thiocyanate EO process starts with the copper cir-
cuit clarifier overflow from the SART plant flowing into
the EO feed tank, where it would be pumped via an EO
feed pump to sets of electrocells. In the current design, the
electrocells are configured/grouped into banks with cath-
odes and anodes arranged as parallel plates. Both cathodes
and anodes are made of titanium coated with a layer of
Mixed Metal Oxide (MMO). As the process solution passes
through the cells, thiocyanate is oxidized to cyanide on the
anodes and hydrogen is evolved on the cathodes. The elec-
trocell effluent containing recovered cyanide flows into the
effluent tank and is then pumped to the existing SART
neutralization circuit reactors.
The electrocell off-gas, containing hydrogen and hydro-
gen cyanide, will be pulled through the packed column
scrubber using a blower, with the resulting scrubbed air
being discharged to the atmosphere. The spent scrubbing
solution, containing high concentrations of NaCN, is then
sent to the SART facility, or otherwise used directly as a
concentrated cyanide solution in the cyanide leach circuit.
Testwork Results and Discussion
Samples of SART feed solution were shipped from site to
BQE Water’s laboratory in Vancouver, BC, Canada, where
the overall objective was to verify the feasibility of integrat-
ing the EO process for NaCN recovery from SCN into the
overall metallurgical circuit.
Table 1 shows the dissolved concentrations of the main
constituents in the solution received from site for both the
as-received CN recovery thickener overflow (SART feed)
sample and after SART processing in the BQE lab (acidifi-
cation and sulphidization). Further, a synthetic solution was
created to determine the effect of co-occurring anions on
the EO process performance and gain insight into the EO
process efficiency. As expected, the SART process removed
copper, while generating free cyanide. The increase in Na
and SO4 concentrations matched the respective increases
caused by the additions of NaHS and H2SO4. However,
SART is not expected to affect thiocyanate concentrations,
so from this perspective, the results of SCN and total dis-
solved sulfur assays shown in Table 1 provide an indication
of the magnitude of analytical error for these constituents.
The solutions being tested, the leach solution shipped
from the site and a synthetic solution including, underwent
testing to trial two known configurations of electrocells:
1. low current density with low linear velocity of
solution between electrodes, approximately typical
parallel plate configurations and,
2. high current density with high linear velocity of
solution between electrodes, mimicking condi-
tions for the emew type cylindrical cells.
Figure 2. Electro-oxidation circuit incorporation into existing SART process