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Removal of Thiocyanate from Gold Mining Process Water
Yasemin Ozturk
Hacettepe University, Mining Engineering Department
ABSTRACT: Thiocyanate is a common contaminant in gold mining effluent. The high level of cyanide used
in gold and silver extraction leads to the formation of thiocyanate (SCN–) in the presence of sulfide minerals.
It is a hydrophilic species and reacts with metal sulfides to suppress their flotation. Gold mine wastewater can
contain up to 1,000 mg/L of SCN– ions, which increase with water reuse and can adversely affect the flotation
of gold-bearing sulfide minerals. Managing cyanide effluents in mineral processing is extremely important given
their negative impact on process efficiency and environmental concerns.
In this work, environmentally friendly electrochemical advanced oxidation process (EAOPs) was applied to
remove thiocyanate from gold mining process water. An electrochemical cell was fabricated using a pair of car-
bon electrodes as the anode and cathode. Electrodes were prepared by casting an aqueous carbon/PVDF binder
slurry onto graphite sheets.
Batch recirculation experiments showed that SCN– was oxidized to sulfate (SO42–) at an applied voltage of 5 V
and a constant flow rate of 1.5 mL/min. The concentration of SCN– was reduced from 160 mg/L to 3 mg/L,
while 120 mg/L of SO42– was produced after 180 minutes of operation. Continuous flow tests revealed that at
3 V, 85% of the SCN– was removed with a total thiocyanate removal of 2301 mg/m2 at a flow rate of 1.5 mL/
min for 5 mg/L SCN– solution during 180 minutes of operation. The removal efficiency decreased from 85% to
22% as the influent concentration increased from 5 mg/L to 20 mg/L at 3 V and 1.5 mL/min. In the treatment
of gold mining process water, 47% of the SCN– was removed in 5 minutes of operation, but then decreased to
about 25% in 120 minutes of treatment at 5 V with a flow rate of 1.5 mL/min.
INTRODUCTION
Cyanidation is an easy, selective and cost effective method
to extract gold. Cyanide is lost through evaporation, precip-
itation, complex formation, and oxidation during the pro-
cess (Adams 2001). Cyanide loss negatively impacts process
economics and efficiency. During the processing of gold-
bearing sulfide minerals, cyanide reacts with elemental sul-
fur and polysulfides to produce thiocyanate (Adams 1990).
S0 +CN– ↔ SCN–
2S2– +2CN– +O2 +2H2O ↔ 2SCN– +4OH–
S2O32– +CN– ↔ SCN– +SO32–
Although seven times less toxic than cyanide, thiocyanate
can harm the environment and humans at high concentra-
tions (Kuyucak and Akcil 2013). Therefore, the amount of
thiocyanate in the wastewater should be decreased to an
acceptable level for the environment (4 mg/L) prior to dis-
charge (Raper et al., 2019).
Thiocyanate is a strong complexing agent, forming
compounds with the first group transition metals via nitro-
gen and with the second and third group transition metals
Removal of Thiocyanate from Gold Mining Process Water
Yasemin Ozturk
Hacettepe University, Mining Engineering Department
ABSTRACT: Thiocyanate is a common contaminant in gold mining effluent. The high level of cyanide used
in gold and silver extraction leads to the formation of thiocyanate (SCN–) in the presence of sulfide minerals.
It is a hydrophilic species and reacts with metal sulfides to suppress their flotation. Gold mine wastewater can
contain up to 1,000 mg/L of SCN– ions, which increase with water reuse and can adversely affect the flotation
of gold-bearing sulfide minerals. Managing cyanide effluents in mineral processing is extremely important given
their negative impact on process efficiency and environmental concerns.
In this work, environmentally friendly electrochemical advanced oxidation process (EAOPs) was applied to
remove thiocyanate from gold mining process water. An electrochemical cell was fabricated using a pair of car-
bon electrodes as the anode and cathode. Electrodes were prepared by casting an aqueous carbon/PVDF binder
slurry onto graphite sheets.
Batch recirculation experiments showed that SCN– was oxidized to sulfate (SO42–) at an applied voltage of 5 V
and a constant flow rate of 1.5 mL/min. The concentration of SCN– was reduced from 160 mg/L to 3 mg/L,
while 120 mg/L of SO42– was produced after 180 minutes of operation. Continuous flow tests revealed that at
3 V, 85% of the SCN– was removed with a total thiocyanate removal of 2301 mg/m2 at a flow rate of 1.5 mL/
min for 5 mg/L SCN– solution during 180 minutes of operation. The removal efficiency decreased from 85% to
22% as the influent concentration increased from 5 mg/L to 20 mg/L at 3 V and 1.5 mL/min. In the treatment
of gold mining process water, 47% of the SCN– was removed in 5 minutes of operation, but then decreased to
about 25% in 120 minutes of treatment at 5 V with a flow rate of 1.5 mL/min.
INTRODUCTION
Cyanidation is an easy, selective and cost effective method
to extract gold. Cyanide is lost through evaporation, precip-
itation, complex formation, and oxidation during the pro-
cess (Adams 2001). Cyanide loss negatively impacts process
economics and efficiency. During the processing of gold-
bearing sulfide minerals, cyanide reacts with elemental sul-
fur and polysulfides to produce thiocyanate (Adams 1990).
S0 +CN– ↔ SCN–
2S2– +2CN– +O2 +2H2O ↔ 2SCN– +4OH–
S2O32– +CN– ↔ SCN– +SO32–
Although seven times less toxic than cyanide, thiocyanate
can harm the environment and humans at high concentra-
tions (Kuyucak and Akcil 2013). Therefore, the amount of
thiocyanate in the wastewater should be decreased to an
acceptable level for the environment (4 mg/L) prior to dis-
charge (Raper et al., 2019).
Thiocyanate is a strong complexing agent, forming
compounds with the first group transition metals via nitro-
gen and with the second and third group transition metals