XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 31
The conditions for MHP Precipitation Stage 1 are pH
7.8–8.5, natural temperature (40–70 °C) and 1–4 hours of
contact time.
The MHP Precipitation Stage 1 slurry is thickened,
and the underflow is filtered and washed. The wash solu-
tion is returned to the thickener from the filter.
In the MHP Stage 2, lime is added to precipitate resid-
ual nickel and cobalt for recycle to a point that the auto-
clave acid can redissolve nickel and cobalt.
NiSO4 +CaO +3H2O =Ni(OH)2 +CaSO4·2H2O
CoSO4 +CaO +3H2O =Co(OH)2 +CaSO4·2H2O
MHP Precipitation Stage 2 slurry is thickened. The under-
flow solids are returned to react with acid and ensure that
no nickel and cobalt is lost. The solution, barren of any
nickel and cobalt, is directed to an evaporation to crystallize
magnesium sulfate crystals.
MgSO4 +6H2O =MgSO4·6H2O
The combined solids from the autoclave leach and the vari-
ous precipitation steps are filtered and washed.
Process Development Testing
The process development was conducted first at the bench
scale and then via a continuous pilot plant program. The
bench scale work showed that fine grinding of the concen-
trate and the presence of small amounts of chloride acceler-
ated the extraction of nickel, cobalt and copper (Dreisinger
et al., 2023).
Following completion of the bench scale testing, a pilot
plant test was conducted to demonstrate the overall pro-
cess flowsheet, produce MHP product for potential future
customer evaluation and to obtain engineering data for
completion of a feasibility study.
The heart of the pilot plant program was use of a 30 L,
4 compartment autoclave fed at a rate of about 3.5 kg/h
of West Musgrave nickel concentrate. A total of 470 kg of
concentrate was processed. The block flow diagram for the
pilot plant is shown in Figure 6. The mineralogy report on
the concentrate indicated the major phases were pentland-
ite, chalcopyrite, pyrrhotite and pyrite (Table 3).
The pilot plant operation was successfully completed.
The following sections describe key results in each part of
the flowsheet.
Autoclave Operation. The autoclave was fed a 60%
solids slurry of West Musgrave concentrate with 10 kg/t
ligninsulfonate addition (Borregard D-748). The auto-
clave temperature was controlled to 153 °C with an
operating pressure of 1630 kPag and an oxygen overpres-
sure of 1120 kPag. The cooling solution was overflow from
the autoclave leach discharge thickener added at a rate of
12.6 g/g concentrate. Chloride was added to the cooling
solution to a target of 2 g/L Cl.
Typical results during a stable period of operation
yielded extraction of 98.1% Ni, 97% Co and 85% Cu,
with residue assaying 0.25% Ni, 0.011% Co, 0.23% Cu,
42.6% Fe, 22.9% S(tot) and 15.3% S(elem). Solution anal-
ysis showed 31 g/L Ni, 3.41 g/L Cu, 0.94 g/L Co and 20.2
g/L H2SO4.
Autoclave Discharge Residue Processing. The
Secondary Hydroxide Precipitate (SHP) solids recycle was
added to the autoclave slurry before thickening. The acid in
the discharge redissolved the nickel and cobalt hydroxide
present in the SHP solids to ensure a high overall recovery.
Filtration and washing was applied to the mixed slurries to
produce a final process residue.
A typical solid assay of the combined filter cake solid
(autoclave residue and PN solids) analyzed 0.164% Ni,
0.185% Cu, 0.007% Co, 36.8% Fe, 5.4% Ca, 23.3%
S(tot) and 13.2% S(elem). There was no evidence of excess
precipitation of pay metals in the final combined solids,
supporting a high overall extraction value for Ni, Co and
Cu.
Primary Neutralization. The Primary Neutralization
process combined the autoclave discharge thickener over-
flow with Secondary Neutralization U/F slurry, followed
by addition of lime slurry or limestone slurry to neutralize
and precipitate iron. During a period of stable operation
with lime slurry addition, a precipitate was formed with
0.1% Ni, 0.005% Co, 0.04% Cu, 14.6% Fe and 17.1%
Ca at pH 2.5–3.0. During the same period the PN thick-
ener O/F solution (advancing to copper removal) analyzed
32.3 g/L Ni, 0.92 g/L Co, 1.3 g/L Fe and 0.9 g/L Al. The
remaining iron in solution was predominantly ferrous iron.
There was no evidence of co-precipitation losses of pay met-
als in this part of the circuit.
Copper Removal. During a typical period of stable
operation, the CuS solids analyzed 57% Cu, 3.23% Ni,
0.23% Co, 0.006% Zn and 0.063% Fe. The correspond-
ing solution analysis showed a residual level of 0.02 g/L Cu,
confirming almost complete copper recovery. The Ni con-
tent of the solids was somewhat elevated, but it is expected
with tighter control of NaSH addition and greater seed
recycle, the Ni content of the solids will be lower.
Secondary Neutralization. Typical levels of residual
metals in the secondary neutralization solution were up to
35 g/L Ni, 0.88 g/L Co, along with as low as 0.01 g/L Cu,
0.01 g/L Fe, 0.01 g/L Al and 0.044 g/L Zn.
The conditions for MHP Precipitation Stage 1 are pH
7.8–8.5, natural temperature (40–70 °C) and 1–4 hours of
contact time.
The MHP Precipitation Stage 1 slurry is thickened,
and the underflow is filtered and washed. The wash solu-
tion is returned to the thickener from the filter.
In the MHP Stage 2, lime is added to precipitate resid-
ual nickel and cobalt for recycle to a point that the auto-
clave acid can redissolve nickel and cobalt.
NiSO4 +CaO +3H2O =Ni(OH)2 +CaSO4·2H2O
CoSO4 +CaO +3H2O =Co(OH)2 +CaSO4·2H2O
MHP Precipitation Stage 2 slurry is thickened. The under-
flow solids are returned to react with acid and ensure that
no nickel and cobalt is lost. The solution, barren of any
nickel and cobalt, is directed to an evaporation to crystallize
magnesium sulfate crystals.
MgSO4 +6H2O =MgSO4·6H2O
The combined solids from the autoclave leach and the vari-
ous precipitation steps are filtered and washed.
Process Development Testing
The process development was conducted first at the bench
scale and then via a continuous pilot plant program. The
bench scale work showed that fine grinding of the concen-
trate and the presence of small amounts of chloride acceler-
ated the extraction of nickel, cobalt and copper (Dreisinger
et al., 2023).
Following completion of the bench scale testing, a pilot
plant test was conducted to demonstrate the overall pro-
cess flowsheet, produce MHP product for potential future
customer evaluation and to obtain engineering data for
completion of a feasibility study.
The heart of the pilot plant program was use of a 30 L,
4 compartment autoclave fed at a rate of about 3.5 kg/h
of West Musgrave nickel concentrate. A total of 470 kg of
concentrate was processed. The block flow diagram for the
pilot plant is shown in Figure 6. The mineralogy report on
the concentrate indicated the major phases were pentland-
ite, chalcopyrite, pyrrhotite and pyrite (Table 3).
The pilot plant operation was successfully completed.
The following sections describe key results in each part of
the flowsheet.
Autoclave Operation. The autoclave was fed a 60%
solids slurry of West Musgrave concentrate with 10 kg/t
ligninsulfonate addition (Borregard D-748). The auto-
clave temperature was controlled to 153 °C with an
operating pressure of 1630 kPag and an oxygen overpres-
sure of 1120 kPag. The cooling solution was overflow from
the autoclave leach discharge thickener added at a rate of
12.6 g/g concentrate. Chloride was added to the cooling
solution to a target of 2 g/L Cl.
Typical results during a stable period of operation
yielded extraction of 98.1% Ni, 97% Co and 85% Cu,
with residue assaying 0.25% Ni, 0.011% Co, 0.23% Cu,
42.6% Fe, 22.9% S(tot) and 15.3% S(elem). Solution anal-
ysis showed 31 g/L Ni, 3.41 g/L Cu, 0.94 g/L Co and 20.2
g/L H2SO4.
Autoclave Discharge Residue Processing. The
Secondary Hydroxide Precipitate (SHP) solids recycle was
added to the autoclave slurry before thickening. The acid in
the discharge redissolved the nickel and cobalt hydroxide
present in the SHP solids to ensure a high overall recovery.
Filtration and washing was applied to the mixed slurries to
produce a final process residue.
A typical solid assay of the combined filter cake solid
(autoclave residue and PN solids) analyzed 0.164% Ni,
0.185% Cu, 0.007% Co, 36.8% Fe, 5.4% Ca, 23.3%
S(tot) and 13.2% S(elem). There was no evidence of excess
precipitation of pay metals in the final combined solids,
supporting a high overall extraction value for Ni, Co and
Cu.
Primary Neutralization. The Primary Neutralization
process combined the autoclave discharge thickener over-
flow with Secondary Neutralization U/F slurry, followed
by addition of lime slurry or limestone slurry to neutralize
and precipitate iron. During a period of stable operation
with lime slurry addition, a precipitate was formed with
0.1% Ni, 0.005% Co, 0.04% Cu, 14.6% Fe and 17.1%
Ca at pH 2.5–3.0. During the same period the PN thick-
ener O/F solution (advancing to copper removal) analyzed
32.3 g/L Ni, 0.92 g/L Co, 1.3 g/L Fe and 0.9 g/L Al. The
remaining iron in solution was predominantly ferrous iron.
There was no evidence of co-precipitation losses of pay met-
als in this part of the circuit.
Copper Removal. During a typical period of stable
operation, the CuS solids analyzed 57% Cu, 3.23% Ni,
0.23% Co, 0.006% Zn and 0.063% Fe. The correspond-
ing solution analysis showed a residual level of 0.02 g/L Cu,
confirming almost complete copper recovery. The Ni con-
tent of the solids was somewhat elevated, but it is expected
with tighter control of NaSH addition and greater seed
recycle, the Ni content of the solids will be lower.
Secondary Neutralization. Typical levels of residual
metals in the secondary neutralization solution were up to
35 g/L Ni, 0.88 g/L Co, along with as low as 0.01 g/L Cu,
0.01 g/L Fe, 0.01 g/L Al and 0.044 g/L Zn.