4
that the oxidation, while helpful in preventing Fe/Mn leach-
ing, was negatively impacting cobalt leaching (and Ni/Cu
as well, potentially). As outlined in Table 3, these tests were
conducted under natural steam pressure, and increased
both the temperature and the pulp density. The acid addi-
tion in Test 6 was reduced from 800 kg/t to 650 kg/t in
order to remain near the final leach solution acidity of Test
5, accounting for the change in pulp density.
Including Test 3 for comparison, Figure 2 shows the
calculated extractions for the tests that did not use oxygen.
Test 4 resulted in 93% Ni, 69% Co, and 94% Cu extrac-
tion, a significant improvement over Test 3, while manga-
nese extraction remained limited (5%). Iron extraction rose
(27% versus 10% previously), as was expected based on the
lack of additional oxidation to promote its reprecipitation.
Further improvement was seen in Test 5 after increasing the
temperature from 150°C to 225°C, yielding extractions of
99% Ni, 97% Co, 99% Cu, 19% Fe, and 10% Mn, with
the higher temperature promoting increased hydrolysis of
iron. Increasing the pulp density further and adjusting the
acid addition in Test 6 resulted in a decrease in extractions,
with 88% Ni, 84% Co, 84% Cu, 16% Fe, and 8% Mn.
The final two tests, Test 7 and Test 8, made further
reductions in the acid addition as well as comparing acid
addition methods, investigating whether pretreating the
pulp with acid before/during heat-up of the autoclave was
falsely improving the extractions (as a pseudo two-stage
leach in principle). The test conditions are summarized in
Table 4, and show similar levels of acidity in solution and
overall acid consumption.
0
10
20
30
40
50
60
70
80
90
100
Ni Co Cu Fe Mg Al Mn
Test 1: 5% solids, 690 kPa overpressure, 500 kg/t acid, 150°C
Test 2: 5% solids, 690 kPa overpressure, 650 kg/t acid, 150°C
Test 3: 5% solids, 690 kPa overpressure, 800 kg/t acid, 150°C
Figure 1. Metal Extractions from Test 1 through Test 3
Table 3. Follow-up nodule pressure leach test conditions (no
oxygen)
Test ID 4 5 6
Temperature (°C) 150 225 225
Overpressure (kPa) 0 0 0
Retention Time (h) 4 4 4
Initial Pulp Density (%)20% 20% 30%
Acid Addition Method Pretreat Pretreat Pretreat
Acid Addition (kg/t) 800 800 650
Final Acidity (g/L) 94 90 105
Acid Consumption (kg/t) 365 397 400
Table 4. Test Conditions Comparing Acid Addition Methods
Test ID 7 8
Temperature (°C) 225 225
Overpressure (kPa) 0 0
Retention Time (h) 4 4
Initial Pulp Density (%)30% 30%
Acid Addition Method Pretreat Inject
Acid Addition (kg/t) 500 500
Final Acidity (g/L) 78 77
Acid Consumption (kg/t) 293 308
Calculated
Extracti
(%)
that the oxidation, while helpful in preventing Fe/Mn leach-
ing, was negatively impacting cobalt leaching (and Ni/Cu
as well, potentially). As outlined in Table 3, these tests were
conducted under natural steam pressure, and increased
both the temperature and the pulp density. The acid addi-
tion in Test 6 was reduced from 800 kg/t to 650 kg/t in
order to remain near the final leach solution acidity of Test
5, accounting for the change in pulp density.
Including Test 3 for comparison, Figure 2 shows the
calculated extractions for the tests that did not use oxygen.
Test 4 resulted in 93% Ni, 69% Co, and 94% Cu extrac-
tion, a significant improvement over Test 3, while manga-
nese extraction remained limited (5%). Iron extraction rose
(27% versus 10% previously), as was expected based on the
lack of additional oxidation to promote its reprecipitation.
Further improvement was seen in Test 5 after increasing the
temperature from 150°C to 225°C, yielding extractions of
99% Ni, 97% Co, 99% Cu, 19% Fe, and 10% Mn, with
the higher temperature promoting increased hydrolysis of
iron. Increasing the pulp density further and adjusting the
acid addition in Test 6 resulted in a decrease in extractions,
with 88% Ni, 84% Co, 84% Cu, 16% Fe, and 8% Mn.
The final two tests, Test 7 and Test 8, made further
reductions in the acid addition as well as comparing acid
addition methods, investigating whether pretreating the
pulp with acid before/during heat-up of the autoclave was
falsely improving the extractions (as a pseudo two-stage
leach in principle). The test conditions are summarized in
Table 4, and show similar levels of acidity in solution and
overall acid consumption.
0
10
20
30
40
50
60
70
80
90
100
Ni Co Cu Fe Mg Al Mn
Test 1: 5% solids, 690 kPa overpressure, 500 kg/t acid, 150°C
Test 2: 5% solids, 690 kPa overpressure, 650 kg/t acid, 150°C
Test 3: 5% solids, 690 kPa overpressure, 800 kg/t acid, 150°C
Figure 1. Metal Extractions from Test 1 through Test 3
Table 3. Follow-up nodule pressure leach test conditions (no
oxygen)
Test ID 4 5 6
Temperature (°C) 150 225 225
Overpressure (kPa) 0 0 0
Retention Time (h) 4 4 4
Initial Pulp Density (%)20% 20% 30%
Acid Addition Method Pretreat Pretreat Pretreat
Acid Addition (kg/t) 800 800 650
Final Acidity (g/L) 94 90 105
Acid Consumption (kg/t) 365 397 400
Table 4. Test Conditions Comparing Acid Addition Methods
Test ID 7 8
Temperature (°C) 225 225
Overpressure (kPa) 0 0
Retention Time (h) 4 4
Initial Pulp Density (%)30% 30%
Acid Addition Method Pretreat Inject
Acid Addition (kg/t) 500 500
Final Acidity (g/L) 78 77
Acid Consumption (kg/t) 293 308
Calculated
Extracti
(%)