1900
Sulfide Oxidation and Gold Dissolution of a Refractory
Gold‑Molybdenum Concentrate Using Hypochlorite Solution
John Rossmon M. Resuello, Eden May B. Dela Peña, and Manolo G. Mena
Department of Mining, Metallurgical and Materials Engineering, University of the Philippines-Diliman, Philippines,
ABSTRACT: In this study, a two-stage leaching of a refractory gold-molybdenum concentrate involving sulfide
oxidation in the first stage and gold dissolution in the second stage using hypochlorite solution was investigated.
Gold and molybdenum extraction were determined using the optimized sulfide oxidation time, liquid-to-solid
(L:S) ratio, and hypochlorite (OCl–) concentration. At sulfide oxidation of 6 hours, L:S ratio of 13, and 1.89 M
OCl–, 93.51% gold and 88.54% molybdenum were extracted indicating that both gold and molybdenum can
simultaneously be extracted in this process. This shows that the use of hypochlorite solution can be a potential
eco-friendly and simplified process for treating refractory gold-molybdenum concentrates.
Keywords: Refractory gold-molybdenum concentrate, sulfide oxidation and gold dissolution, hypochlorite
INRODUCTION
The rapid depletion of high-grade and easily extracted gold
ores raised challenges and difficulties in using conventional
cyanidation for gold extraction. With the decreasing grade
of gold ore supply, gold cyanidation no longer becomes
economical. The use of more cyanide in the process also
increases risk in health and safety of the community and
damage to the environment (Senanayake, 2004 Zhang et
al., 2022 Li et al., 2023). Thus, processing of readily-avail-
able low-grade gold ores has become important.
Gold ores can be classified based on the difficulty of
processing. These are free-milling, complex, and refractory.
Free-milling ores attain gold recovery of 90% or more by
cyanidation. Complex ores achieve favorable gold recov-
eries under modified and more extreme conditions (e.g.,
high temperature and high pressure). Refractory gold ores
do not yield acceptable gold recoveries using conventional
methods because gold is physically locked as very fine parti-
cles in sulfides such as pyrite, arsenopyrite, and chlacopyrite
(Valenzuela et al., 2013 Youlton et al., 2021).
Processing refractory gold ores requires pretreatment
prior to leaching to increase gold recovery. Pretreatment
decomposes the sulfide matrix that encapsulates gold and
hinders its reaction with the lixiviant. The decomposition
of sulfide matrix unlocks and exposes the encapsulated gold
which enables contact of lixiviant and gold to proceed.
Pretreatment can be done through physical treatment
such as fine grinding which reduces particle size to liberate
fine gold, or through oxidative pretreatment such as roast-
ing which produces sulfur dioxide gas by employing oxida-
tive atmosphere and temperature, pressure oxidation which
involves high pressure and temperature conditions, biologi-
cal oxidation which uses bacteria in sulfide decomposition,
and chlorine oxidation (Hasab et al., 2013 Ahtiainen et al.,
2021 Azizitorghabeh et al., 2022).
Chlorine oxidation uses chlorine species to oxidize and
decompose sulfides. The oxidizing species in an aqueous
chlorine solution depends on the solution pH. Aqueous
chlorine (Cl2), hypochlorous acid (HOCl), and hypochlo-
rite (OCl–) are stable at pH 3.5, pH of 3.5–7.5, and pH
Sulfide Oxidation and Gold Dissolution of a Refractory
Gold‑Molybdenum Concentrate Using Hypochlorite Solution
John Rossmon M. Resuello, Eden May B. Dela Peña, and Manolo G. Mena
Department of Mining, Metallurgical and Materials Engineering, University of the Philippines-Diliman, Philippines,
ABSTRACT: In this study, a two-stage leaching of a refractory gold-molybdenum concentrate involving sulfide
oxidation in the first stage and gold dissolution in the second stage using hypochlorite solution was investigated.
Gold and molybdenum extraction were determined using the optimized sulfide oxidation time, liquid-to-solid
(L:S) ratio, and hypochlorite (OCl–) concentration. At sulfide oxidation of 6 hours, L:S ratio of 13, and 1.89 M
OCl–, 93.51% gold and 88.54% molybdenum were extracted indicating that both gold and molybdenum can
simultaneously be extracted in this process. This shows that the use of hypochlorite solution can be a potential
eco-friendly and simplified process for treating refractory gold-molybdenum concentrates.
Keywords: Refractory gold-molybdenum concentrate, sulfide oxidation and gold dissolution, hypochlorite
INRODUCTION
The rapid depletion of high-grade and easily extracted gold
ores raised challenges and difficulties in using conventional
cyanidation for gold extraction. With the decreasing grade
of gold ore supply, gold cyanidation no longer becomes
economical. The use of more cyanide in the process also
increases risk in health and safety of the community and
damage to the environment (Senanayake, 2004 Zhang et
al., 2022 Li et al., 2023). Thus, processing of readily-avail-
able low-grade gold ores has become important.
Gold ores can be classified based on the difficulty of
processing. These are free-milling, complex, and refractory.
Free-milling ores attain gold recovery of 90% or more by
cyanidation. Complex ores achieve favorable gold recov-
eries under modified and more extreme conditions (e.g.,
high temperature and high pressure). Refractory gold ores
do not yield acceptable gold recoveries using conventional
methods because gold is physically locked as very fine parti-
cles in sulfides such as pyrite, arsenopyrite, and chlacopyrite
(Valenzuela et al., 2013 Youlton et al., 2021).
Processing refractory gold ores requires pretreatment
prior to leaching to increase gold recovery. Pretreatment
decomposes the sulfide matrix that encapsulates gold and
hinders its reaction with the lixiviant. The decomposition
of sulfide matrix unlocks and exposes the encapsulated gold
which enables contact of lixiviant and gold to proceed.
Pretreatment can be done through physical treatment
such as fine grinding which reduces particle size to liberate
fine gold, or through oxidative pretreatment such as roast-
ing which produces sulfur dioxide gas by employing oxida-
tive atmosphere and temperature, pressure oxidation which
involves high pressure and temperature conditions, biologi-
cal oxidation which uses bacteria in sulfide decomposition,
and chlorine oxidation (Hasab et al., 2013 Ahtiainen et al.,
2021 Azizitorghabeh et al., 2022).
Chlorine oxidation uses chlorine species to oxidize and
decompose sulfides. The oxidizing species in an aqueous
chlorine solution depends on the solution pH. Aqueous
chlorine (Cl2), hypochlorous acid (HOCl), and hypochlo-
rite (OCl–) are stable at pH 3.5, pH of 3.5–7.5, and pH