2
considered). Should all four metals be dissolved in a simple
sulphuric acid leach, it can also be calculated that man-
ganese contributes to 92% of the sulphuric acid demand.
Downstream treatment of the resulting leach liquors to
separate manganese from copper/nickel/cobalt will fur-
ther contribute to overall processing costs. Clearly, a key
challenge in processing polymetallic nodules relates to the
behavior of manganese, and that processes with an inherent
selectivity of nickel/copper/cobalt against manganese are of
economic interest.
ON SHORE PROCESSING OF
POLYMETALLIC NODULES
Much attention has been paid to the mining aspects of the
nodules and potential environmental impacts. However, little
attention has been paid to the on-shore processing of nodules.
Similar questions exist as in traditional “terrestrial” mining
projects, such as:
• What is the Capex and Opex of the processing plant?
• What is the metallurgical performance (recovery,
product grade, and reagent consumption)?
• What is the “operability” of the selected flowsheet
and how robust is the flowsheet for circuit upsets and
changing feed compositions?
• What are the environmental impacts of the process-
ing plants and produced residues?
An overview of various processing techniques has been
previously provided and detailed by Dames and Moore [1],
Dreisinger [4], and Verbaan [5] and can be briefly summa-
rized as follows:
• Ammoniacal systems – such as:
– Cuprion process
– Gas reduction and ammoniacal leaching
• Sulphate systems – such as:
– Smelting and hydrometallurgical processing of
matte
– High pressure acid leaching (HPAL)
– Reducing acid (H2SO4/SO2) leaching
• Other hydrometallurgical routes based on chloride
and nitrate chemistries.
The Cuprion process as described by various authors
[6–8] and recently piloted at SGS Canada [9] offers selec-
tivity against manganese dissolution but suffers from
depressed cobalt extraction at elevated leach liquor concen-
trations. In this flowsheet, manganese does not report to
the primary leach solution and instead remains in the leach
residue as MnCO3. Some, all, or none of this residue may
be further processed into EMM (Electrolytic Manganese
Metal) or HPMSM which will obviously contribute to
reagent requirements. Metal recoveries using the Cuprion
process were measured during the SGS pilot plant at
approximately 90–95% copper and 97–100% nickel, with
decreasing cobalt recoveries with time. Cobalt extractions
never stabilized and continuously decreased from ~95% at
the outset of the campaign (when cobalt levels in the PLS
were very low), to around 85% after five days as cobalt ten-
ors in the PLS increased due to PLS recycling. Seaborn [11]
reported cobalt extractions as low as 30% at 2 g/L Co in the
PLS, and Haynes [10] reported Cuprion recoveries of 90%
for copper and nickel and 50% for cobalt.
TMC [2] intends to use a combined pyro/hydro-
metallurgical flowsheet. Nodules are mixed with reductant
(coal), flux (silica) and residues from the hydrometallurgical
refinery before feeding to a rotary kiln (~900°C). The cal-
cine discharge is smelted (1450°C) in electric arc furnaces
to produce a metal alloy and a Mn silicate stream (sold into
the manganese industry, predominately the steel making
industry). The molten alloy is further processed in Peirce-
Smith convertors (1300°C) where it is mixed with sulphur
to produce a NiCuCo matte. Expected recoveries into the
matte are 94.6% nickel, 86.5% copper, and 77.4% cobalt.
The matte is further treated using a two-stage atmospheric/
pressure oxidation leach process and sequential purification
to ultimately produce copper cathode, cobalt sulphate, and
nickel sulphate. The overall process has been described by
Von Schroeter [12], Boulby [13], and Verbaan [5] and has
been tested at SGS Canada.
Global Sea Mineral Resources (GSR, a subsidiary of
Belgian dredging company DEME) patented a reductive
acid leach process [15]. GSR contracted SGS in 2021
to confirm and optimize that flowsheet. The process is
described by Alvarenga [16] and a high-level overview
was presented at the DeepSea Mining Summit in 2022
[5]. The process is based on single step reductive leaching
using H2SO4 and SO2 which effectively recovers all of the
nickel, copper, cobalt, and manganese into a leach solu-
tion. Copper is precipitated from the leach solution as cop-
per sulphide, nickel and cobalt are recovered as a mixed
sulphide precipitate (MSP), and crude manganese sulphate
is crystallized at elevated temperature and subsequently
pyrolyzed to produce an iron-manganese oxide. SO2 con-
tained in the off-gas is recovered and processed into sulph-
uric acid for recycle. Reported leach extractions were high
at 99% NiCoMn, 98% Cu. Metal precipitation efficien-
cies were also high (99% Cu and 99% NiCo into MSP).
However, the novel manganese sulphate crystallization step
(including the hot filtration step) and associated thermal
considered). Should all four metals be dissolved in a simple
sulphuric acid leach, it can also be calculated that man-
ganese contributes to 92% of the sulphuric acid demand.
Downstream treatment of the resulting leach liquors to
separate manganese from copper/nickel/cobalt will fur-
ther contribute to overall processing costs. Clearly, a key
challenge in processing polymetallic nodules relates to the
behavior of manganese, and that processes with an inherent
selectivity of nickel/copper/cobalt against manganese are of
economic interest.
ON SHORE PROCESSING OF
POLYMETALLIC NODULES
Much attention has been paid to the mining aspects of the
nodules and potential environmental impacts. However, little
attention has been paid to the on-shore processing of nodules.
Similar questions exist as in traditional “terrestrial” mining
projects, such as:
• What is the Capex and Opex of the processing plant?
• What is the metallurgical performance (recovery,
product grade, and reagent consumption)?
• What is the “operability” of the selected flowsheet
and how robust is the flowsheet for circuit upsets and
changing feed compositions?
• What are the environmental impacts of the process-
ing plants and produced residues?
An overview of various processing techniques has been
previously provided and detailed by Dames and Moore [1],
Dreisinger [4], and Verbaan [5] and can be briefly summa-
rized as follows:
• Ammoniacal systems – such as:
– Cuprion process
– Gas reduction and ammoniacal leaching
• Sulphate systems – such as:
– Smelting and hydrometallurgical processing of
matte
– High pressure acid leaching (HPAL)
– Reducing acid (H2SO4/SO2) leaching
• Other hydrometallurgical routes based on chloride
and nitrate chemistries.
The Cuprion process as described by various authors
[6–8] and recently piloted at SGS Canada [9] offers selec-
tivity against manganese dissolution but suffers from
depressed cobalt extraction at elevated leach liquor concen-
trations. In this flowsheet, manganese does not report to
the primary leach solution and instead remains in the leach
residue as MnCO3. Some, all, or none of this residue may
be further processed into EMM (Electrolytic Manganese
Metal) or HPMSM which will obviously contribute to
reagent requirements. Metal recoveries using the Cuprion
process were measured during the SGS pilot plant at
approximately 90–95% copper and 97–100% nickel, with
decreasing cobalt recoveries with time. Cobalt extractions
never stabilized and continuously decreased from ~95% at
the outset of the campaign (when cobalt levels in the PLS
were very low), to around 85% after five days as cobalt ten-
ors in the PLS increased due to PLS recycling. Seaborn [11]
reported cobalt extractions as low as 30% at 2 g/L Co in the
PLS, and Haynes [10] reported Cuprion recoveries of 90%
for copper and nickel and 50% for cobalt.
TMC [2] intends to use a combined pyro/hydro-
metallurgical flowsheet. Nodules are mixed with reductant
(coal), flux (silica) and residues from the hydrometallurgical
refinery before feeding to a rotary kiln (~900°C). The cal-
cine discharge is smelted (1450°C) in electric arc furnaces
to produce a metal alloy and a Mn silicate stream (sold into
the manganese industry, predominately the steel making
industry). The molten alloy is further processed in Peirce-
Smith convertors (1300°C) where it is mixed with sulphur
to produce a NiCuCo matte. Expected recoveries into the
matte are 94.6% nickel, 86.5% copper, and 77.4% cobalt.
The matte is further treated using a two-stage atmospheric/
pressure oxidation leach process and sequential purification
to ultimately produce copper cathode, cobalt sulphate, and
nickel sulphate. The overall process has been described by
Von Schroeter [12], Boulby [13], and Verbaan [5] and has
been tested at SGS Canada.
Global Sea Mineral Resources (GSR, a subsidiary of
Belgian dredging company DEME) patented a reductive
acid leach process [15]. GSR contracted SGS in 2021
to confirm and optimize that flowsheet. The process is
described by Alvarenga [16] and a high-level overview
was presented at the DeepSea Mining Summit in 2022
[5]. The process is based on single step reductive leaching
using H2SO4 and SO2 which effectively recovers all of the
nickel, copper, cobalt, and manganese into a leach solu-
tion. Copper is precipitated from the leach solution as cop-
per sulphide, nickel and cobalt are recovered as a mixed
sulphide precipitate (MSP), and crude manganese sulphate
is crystallized at elevated temperature and subsequently
pyrolyzed to produce an iron-manganese oxide. SO2 con-
tained in the off-gas is recovered and processed into sulph-
uric acid for recycle. Reported leach extractions were high
at 99% NiCoMn, 98% Cu. Metal precipitation efficien-
cies were also high (99% Cu and 99% NiCo into MSP).
However, the novel manganese sulphate crystallization step
(including the hot filtration step) and associated thermal