328 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
A set of lessons from the earlier tests (at 5%) were
applied, and included:
• Copper concentrations in the leach solution were
increased from those that proved successful at 5%
slurry density.
• Carbon Monoxide flow rates were increased to
achieve target Oxidation/Reduction potential levels.
• Longer leach residence times were also tested.
RESULTS
Six of the leach tests at 10% solids densities resulted in
extractions greater than 90% for cobalt, with 86% extrac-
tion of nickel, 40–57% for manganese and 50% for copper.
The primary leaching reaction is the reduction of
Manganese in Oxy-hydroxide minerals, which is exother-
mic, heating the leach solution. At 10% solids, this effect
is much more noticeable than at lower slurry densities. At
10% solids the ratio of solids mass to leach solution mass
is 4 times that at 2.5% solids. Because of this the same
amount of liquid receives 4 times the amount of heat, so
temperature increases are greater.
In one unsuccessful test the temperature of the leach
slurry rose from 30°C to 42°C. This appeared to have an
adverse effect on the extraction of cobalt (30% extracted)
to the leach solution. An explanation of that result could
be that cobalt sulfate demonstrates an inverse solubil-
ity-temperature relationship. That means cobalt sulfate
becomes less soluble as solution temperature rises. At 42°C
the cobalt sulfate may have precipitated, thus reducing the
overall extraction.
Subsequent tests at 10% solids were carried out with
the temperature of the solution controlled at 30°C by sur-
rounding the leaching vessel with a cooling bath. These
tests achieved much higher extractions of cobalt.
The observation that copper concentration must rise
in proportion to solids concentration indicates that cop-
per is not behaving in a manner consistent with a catalyst
but rather as a regular reagent in these tests. Apparently the
cupric (Cu++) ions formed by reducing the manganese are
not reduced to cuprous (Cu+) ions by reacting with carbon
monoxide at a rate that keeps up with the reduction of man-
ganese. A recent paper (Dreisinger 2023) reported results of
2022 Cuprion process testing of CCZ nodules and suggests
that low reaction rates for the reduction of cupric copper to
cuprous copper could explain similar effects in their testing.
Monitoring and keeping ORP levels near or below
–400 mV is critical. Double washing of leached solids is
recommended to ensure accurate recovery results.
Throughout the entire testing program, analysis of
solution samples was difficult. Dilution of samples for ICP
analysis may cause precipitation of some of the dissolved
metals. After solution analysis issues with initial tests,
extraction values for later tests were calculated by ALS only
on solids assays. (BGRIMM had also used feed and residue
assays to calculate extractions.) ALS has since developed a
promising solution analysis approach which will be used
going forward.
Manganese Oxidation Tests
As part of the Cuprion Sulfate process flowsheet (Figure 4),
oxidation of the leachate solution is required to precipitate
the manganese prior to subsequent solvent extraction of the
other metals.
Preliminary oxidation tests were conducted by ALS
on Cuprion Sulfate leach solution samples and the manga-
nese was oxidized in those samples by bubbling air through
the solution. Subsequent analysis of the oxidized solutions
demonstrated that manganese concentrations were reduced
to low levels. Additional work on this procedure will be
part of the next stage of testing. It should be noted that
BGRIMM oxidation tests resulted in 99.8% of the leachate
manganese reporting to the precipitate.
Scoping Tests on Extraction of Rare Earth Elements
The rare earth elements (REEs) in the nodules do not leach
in the alkaline Cuprion Sulfate process and so concentrate
in the primary residue. Preliminary acid leach tests (scop-
ing tests) with sulphuric and hydrochloric acids demon-
strated that the REEs were extracted from the residue by
such leaching. Also, a large majority of remaining amounts
of cobalt, nickel, copper &manganese in the residue were
extracted by acid leaching.
However, acid leaching tests on residue after manga-
nese carbonate flotation from the C-S leaching have not
been conducted. Indications from previous BGRIMM
manganese flotation tests indicates that the REEs remain
in the flotation tailings. The removal of manganese could
result in lower acid consumption and improved econom-
ics of REE extraction after manganese carbonate flotation.
This will be investigated during the next stage of testing.
RECAPPING RESULTS
• Testing has shown that at 10% solids extractions
of over 90% for Cobalt, over 86% for Nickel and
over 40% for Manganese can be achieved using the
Cuprion Sulfate process.
• As solids concentrations are increased there is a need
to increase carbon monoxide addition rate.
A set of lessons from the earlier tests (at 5%) were
applied, and included:
• Copper concentrations in the leach solution were
increased from those that proved successful at 5%
slurry density.
• Carbon Monoxide flow rates were increased to
achieve target Oxidation/Reduction potential levels.
• Longer leach residence times were also tested.
RESULTS
Six of the leach tests at 10% solids densities resulted in
extractions greater than 90% for cobalt, with 86% extrac-
tion of nickel, 40–57% for manganese and 50% for copper.
The primary leaching reaction is the reduction of
Manganese in Oxy-hydroxide minerals, which is exother-
mic, heating the leach solution. At 10% solids, this effect
is much more noticeable than at lower slurry densities. At
10% solids the ratio of solids mass to leach solution mass
is 4 times that at 2.5% solids. Because of this the same
amount of liquid receives 4 times the amount of heat, so
temperature increases are greater.
In one unsuccessful test the temperature of the leach
slurry rose from 30°C to 42°C. This appeared to have an
adverse effect on the extraction of cobalt (30% extracted)
to the leach solution. An explanation of that result could
be that cobalt sulfate demonstrates an inverse solubil-
ity-temperature relationship. That means cobalt sulfate
becomes less soluble as solution temperature rises. At 42°C
the cobalt sulfate may have precipitated, thus reducing the
overall extraction.
Subsequent tests at 10% solids were carried out with
the temperature of the solution controlled at 30°C by sur-
rounding the leaching vessel with a cooling bath. These
tests achieved much higher extractions of cobalt.
The observation that copper concentration must rise
in proportion to solids concentration indicates that cop-
per is not behaving in a manner consistent with a catalyst
but rather as a regular reagent in these tests. Apparently the
cupric (Cu++) ions formed by reducing the manganese are
not reduced to cuprous (Cu+) ions by reacting with carbon
monoxide at a rate that keeps up with the reduction of man-
ganese. A recent paper (Dreisinger 2023) reported results of
2022 Cuprion process testing of CCZ nodules and suggests
that low reaction rates for the reduction of cupric copper to
cuprous copper could explain similar effects in their testing.
Monitoring and keeping ORP levels near or below
–400 mV is critical. Double washing of leached solids is
recommended to ensure accurate recovery results.
Throughout the entire testing program, analysis of
solution samples was difficult. Dilution of samples for ICP
analysis may cause precipitation of some of the dissolved
metals. After solution analysis issues with initial tests,
extraction values for later tests were calculated by ALS only
on solids assays. (BGRIMM had also used feed and residue
assays to calculate extractions.) ALS has since developed a
promising solution analysis approach which will be used
going forward.
Manganese Oxidation Tests
As part of the Cuprion Sulfate process flowsheet (Figure 4),
oxidation of the leachate solution is required to precipitate
the manganese prior to subsequent solvent extraction of the
other metals.
Preliminary oxidation tests were conducted by ALS
on Cuprion Sulfate leach solution samples and the manga-
nese was oxidized in those samples by bubbling air through
the solution. Subsequent analysis of the oxidized solutions
demonstrated that manganese concentrations were reduced
to low levels. Additional work on this procedure will be
part of the next stage of testing. It should be noted that
BGRIMM oxidation tests resulted in 99.8% of the leachate
manganese reporting to the precipitate.
Scoping Tests on Extraction of Rare Earth Elements
The rare earth elements (REEs) in the nodules do not leach
in the alkaline Cuprion Sulfate process and so concentrate
in the primary residue. Preliminary acid leach tests (scop-
ing tests) with sulphuric and hydrochloric acids demon-
strated that the REEs were extracted from the residue by
such leaching. Also, a large majority of remaining amounts
of cobalt, nickel, copper &manganese in the residue were
extracted by acid leaching.
However, acid leaching tests on residue after manga-
nese carbonate flotation from the C-S leaching have not
been conducted. Indications from previous BGRIMM
manganese flotation tests indicates that the REEs remain
in the flotation tailings. The removal of manganese could
result in lower acid consumption and improved econom-
ics of REE extraction after manganese carbonate flotation.
This will be investigated during the next stage of testing.
RECAPPING RESULTS
• Testing has shown that at 10% solids extractions
of over 90% for Cobalt, over 86% for Nickel and
over 40% for Manganese can be achieved using the
Cuprion Sulfate process.
• As solids concentrations are increased there is a need
to increase carbon monoxide addition rate.