3
decomposition was identified as a challenging unit opera-
tion requiring further development.
HIGH PRESSURE ACID LEACHING
High pressure acid leaching (HPAL) is applied for the
recovery of nickel and cobalt from high iron lateritic ores
(limonite), generally containing 1.0–1.2% nickel and
0.10.2% cobalt. Typical process conditions include an
operating temperature of 240260°C, residence time of 1
hour, and an acid dosage of 250 to 400 kg/t. HPAL leach-
ing was considered in past publications from the 1970s and
1980s for the treatment of nodules, but not pursued for
various reasons. Han [17] considered pressure acid leaching
of nodules at 200°C, 0.26 t/t acid addition, and 690 kPa
oxygen overpressure, reporting recoveries of 90% Ni, 91%
Cu, 44% Co and 6% Mn. Anand [18] investigated HPAL
processing at 150°C under an oxygen partial pressure of
550 kPa and reported metal recoveries of 90% for Ni and
Cu, 88% Co, and 28% Mn.
Seaborn [11] commented on HPAL testing conducted
on polymetallic nodules which led to high (94–99%) recov-
eries of nickel, copper, cobalt, and manganese. Haynes [1]
considered HPAL processing of nodules at 245°C, with a res-
idence time of 1.5 hours and acid addition of 0.4 t/t, report-
ing recoveries of 98% nickel, 95% copper, 92% cobalt, and
only 5% manganese. The variability in manganese behavior
across several studies is significant and may be due to differ-
ent feed samples used or process conditions applied.
Relevant literature on HPAL processing of manga-
nese nodules is sparse, relatively old, and yet it appears to
show promising performance. The literature also showed
significant variable behavior of manganese, encouraging
the authors to reconsider HPAL processing. Based on the
apparent potential of manganese rejection, high recover-
ies of nickel/copper/cobalt, and the mature state of HPAL
technology (and associated lower technical risks), SGS ini-
tiated a small internal R&D program consisting of a single
series of tests investigating HPAL processing of an avail-
able nodule sample. Preliminary results of this work have
been published elsewhere by Verbaan and Johnson [19] and
Verbaan [20]. This paper includes an update to the earlier
presented work.
HPAL LEACHING TESTWORK AT SGS
Feed Source
The nodules used in the study were sourced from the Pacific
Ocean, with the average nodules composition from such
deposits given in Table 1, though the range for impurity
elements such as iron can be large depending on the exact
location of nodule harvesting. Prior to using the nodules in
the testwork, they were crushed, dried at low temperature,
and then pulverized to 100% passing 75 µm.
Experimental
The testwork was conducted using 2 L Parr titanium auto-
clave vessels equipped with dual impellers and temperature
control (via external electrically powered heating mantles
and internal cooling coils). Reagents were of laboratory
grade, with 96% sulfuric acid provided by Fisher Scientific
and 99% oxygen supplied by Messer. In the majority of the
tests, the nodules were pulped in water to the target solids
density before adding the acid to the pulp and then heating
to the target temperature after pressure testing. One test was
performed where acid was not added until the nodules slurry
had reached temperature, injecting the acid at pressure.
HPAL Test Conditions and Key Results at SGS
The first HPAL test conditions were inspired by previ-
ous testwork [18] that utilized nodules collected from the
Indian Ocean and applied relatively low temperatures to
the leaching process (130–170°C), along with 380–550
kg/t acid addition in the presence of oxygen (550 kPa par-
tial/overpressure) for four hours at 5% solids. Additional
tests were conducted with varying acid addition, as detailed
in Table 2, increasing from 500 kg/t to 800 kg/t.
Figure 1 presents the calculated extractions from the
first three tests conducted at the same temperature, over-
pressure, and pulp density, only varying the acid addition.
While reduced iron and manganese leaching was accom-
plished, key metal extractions were incomplete, with ≤75%
Ni, ≤20% Co, and ≤80% Cu recovered to the leach solu-
tion. As more acid was added, extractions did increase, but
such high acid additions were uneconomical based on the
nodule grades.
The second set of tests aimed to investigate leaching
conditions without the use of oxygen, under the hypothesis
Table 2. Initial Nodule Pressure Leach Test Conditions (with
oxygen)
Test ID 1 2 3
Temperature (°C) 150 150 150
Overpressure (kPa) 690 690 690
Retention Time (h) 4 4 4
Initial Pulp Density (%)5% 5% 5%
Acid Addition Method Pretreat Pretreat Pretreat
Acid Addition (kg/t) 500 650 800
Final Acidity (g/L) 14 20 28
Acid Consumption (kg/t) 236 278 268
decomposition was identified as a challenging unit opera-
tion requiring further development.
HIGH PRESSURE ACID LEACHING
High pressure acid leaching (HPAL) is applied for the
recovery of nickel and cobalt from high iron lateritic ores
(limonite), generally containing 1.0–1.2% nickel and
0.10.2% cobalt. Typical process conditions include an
operating temperature of 240260°C, residence time of 1
hour, and an acid dosage of 250 to 400 kg/t. HPAL leach-
ing was considered in past publications from the 1970s and
1980s for the treatment of nodules, but not pursued for
various reasons. Han [17] considered pressure acid leaching
of nodules at 200°C, 0.26 t/t acid addition, and 690 kPa
oxygen overpressure, reporting recoveries of 90% Ni, 91%
Cu, 44% Co and 6% Mn. Anand [18] investigated HPAL
processing at 150°C under an oxygen partial pressure of
550 kPa and reported metal recoveries of 90% for Ni and
Cu, 88% Co, and 28% Mn.
Seaborn [11] commented on HPAL testing conducted
on polymetallic nodules which led to high (94–99%) recov-
eries of nickel, copper, cobalt, and manganese. Haynes [1]
considered HPAL processing of nodules at 245°C, with a res-
idence time of 1.5 hours and acid addition of 0.4 t/t, report-
ing recoveries of 98% nickel, 95% copper, 92% cobalt, and
only 5% manganese. The variability in manganese behavior
across several studies is significant and may be due to differ-
ent feed samples used or process conditions applied.
Relevant literature on HPAL processing of manga-
nese nodules is sparse, relatively old, and yet it appears to
show promising performance. The literature also showed
significant variable behavior of manganese, encouraging
the authors to reconsider HPAL processing. Based on the
apparent potential of manganese rejection, high recover-
ies of nickel/copper/cobalt, and the mature state of HPAL
technology (and associated lower technical risks), SGS ini-
tiated a small internal R&D program consisting of a single
series of tests investigating HPAL processing of an avail-
able nodule sample. Preliminary results of this work have
been published elsewhere by Verbaan and Johnson [19] and
Verbaan [20]. This paper includes an update to the earlier
presented work.
HPAL LEACHING TESTWORK AT SGS
Feed Source
The nodules used in the study were sourced from the Pacific
Ocean, with the average nodules composition from such
deposits given in Table 1, though the range for impurity
elements such as iron can be large depending on the exact
location of nodule harvesting. Prior to using the nodules in
the testwork, they were crushed, dried at low temperature,
and then pulverized to 100% passing 75 µm.
Experimental
The testwork was conducted using 2 L Parr titanium auto-
clave vessels equipped with dual impellers and temperature
control (via external electrically powered heating mantles
and internal cooling coils). Reagents were of laboratory
grade, with 96% sulfuric acid provided by Fisher Scientific
and 99% oxygen supplied by Messer. In the majority of the
tests, the nodules were pulped in water to the target solids
density before adding the acid to the pulp and then heating
to the target temperature after pressure testing. One test was
performed where acid was not added until the nodules slurry
had reached temperature, injecting the acid at pressure.
HPAL Test Conditions and Key Results at SGS
The first HPAL test conditions were inspired by previ-
ous testwork [18] that utilized nodules collected from the
Indian Ocean and applied relatively low temperatures to
the leaching process (130–170°C), along with 380–550
kg/t acid addition in the presence of oxygen (550 kPa par-
tial/overpressure) for four hours at 5% solids. Additional
tests were conducted with varying acid addition, as detailed
in Table 2, increasing from 500 kg/t to 800 kg/t.
Figure 1 presents the calculated extractions from the
first three tests conducted at the same temperature, over-
pressure, and pulp density, only varying the acid addition.
While reduced iron and manganese leaching was accom-
plished, key metal extractions were incomplete, with ≤75%
Ni, ≤20% Co, and ≤80% Cu recovered to the leach solu-
tion. As more acid was added, extractions did increase, but
such high acid additions were uneconomical based on the
nodule grades.
The second set of tests aimed to investigate leaching
conditions without the use of oxygen, under the hypothesis
Table 2. Initial Nodule Pressure Leach Test Conditions (with
oxygen)
Test ID 1 2 3
Temperature (°C) 150 150 150
Overpressure (kPa) 690 690 690
Retention Time (h) 4 4 4
Initial Pulp Density (%)5% 5% 5%
Acid Addition Method Pretreat Pretreat Pretreat
Acid Addition (kg/t) 500 650 800
Final Acidity (g/L) 14 20 28
Acid Consumption (kg/t) 236 278 268