1. 1
THE MONDO MINERALS NICKEL SULFIDE BIOLEACH PROJECT:
CONSTRUCTION, COMMISSIONING AND EARLY PLANT OPERATION
A presentation to the ALTA Nickel-Cobalt-Copper Conference on 25 May 2016
Authors: 1John Neale, 2Janne Seppälä, 2Arto Laukka, 3Pieter van Aswegen, and 4Stephen Barnett, and
1Mintek, South Africa | 2Mondo Minerals Nickel Oy, Finland | 3P Met. Consulting cc., South Africa | 4Consultant, United Kingdom
Presenting authors:
John Neale, Specialist Engineer, Biotechnology Division, Mintek; & Arto Laukka, Process Development Engineer, Mondo Minerals Nickel Oy
2. 2
• Follow-up on paper presented at ALTA 2015: “… From Test Work to Design”
• A bit about talc, nickel and Mondo Minerals
• The focus of this presentation is to describe the commissioning of the plant
• The build-up of the bioleach inoculum is a key element
• Production plant commissioning:
– Bioleaching
– Iron-arsenic precipitation
– Metal precipitation (MHP production)
• Remaining challenges
• Conclusions
Outline of presentation
3. 3
• Finland is a significant producer of talc, with large reserves and the
two largest producers in the world, one of which is Mondo Minerals
• Mondo has talc mining and processing operations at Sotkamo and
Vuonos in Finland, and a talc refinery in the Netherlands (where the
company is headquartered)
• Mondo operates advanced talc processing plants, having developed a
froth flotation process to upgrade their ores, and using
superconducting electromagnets to remove magnetic impurities
Finland, talc & Mondo Minerals
4. 4
• Nickel concentrate has been a by-product of Finnish talc production for almost 50
years
• A side stream from Mondo’s operations is a flotation concentrate that contains
pyrrhotite (FeS), pentlandite (Fe,Ni)₉S₈, pyrite (FeS₂), gersdorffite (NiAsS), magnesite
(MgCO₃) and some residual talc (Mg₃Si₄O₁₀(OH)₂)
• The main value is in the nickel, but there is also a small amount of cobalt
• The concentrate can no longer be sold to local smelters, because of the arsenic
content
• A hydrometallurgical solution was sought to recover the metal values and to
produce a stable arsenic-bearing waste, suitable for impoundment
• Bioleaching was selected because of its ability to satisfy both of these criteria
Mondo Minerals & nickel
5. 5
Hydrometallurgy … a new venture for Mondo
• Mondo’s talc processing operations include large-scale
continuous unit operations such as crushing, milling, flotation,
magnetic separation, thickening, filtration and drying
• These are mainly physical processes
• Large-scale, continuous hydrometallurgical processing involving
chemical transformation is a venture into uncharted territory for
Mondo
6. 6
A brief recap…
• The new nickel sulfide treatment plant is located at Vuonos in eastern Finland
• It is designed to treat a 50:50 blend of concentrates from Mondo’s two operations:
Sotkamo (pictured here) and Vuonos
• The mines are a couple of hundred kilometres apart, and concentrate from Sotkamo is
trucked to Vuonos
• The plant is designed to treat 35 t/d of concentrate
• The bioleach feed rate is 18 t/d, after upgrading
• Major circuits are concentrate preparation,
bioleaching, iron-arsenic precipitation, and metal
precipitation (MHP production)
• It is a small plant, producing 1,000 t/a of nickel
7. 7
Bioleach inoculum build-up
• Inoculum prepared at Mintek’s laboratory in Randburg, South Africa
• Air-freighted to site in filter cake form (several hundred grams)
• On-site inoculum build-up strategy planned as follows:
– Phase 1: operation of a continuous bioleach miniplant to produce 100 L of inoculum
pulp
– Phase 2: operation of a 1 m3 batch bioleach reactor, inoculated with pulp from the
miniplant
– Phase 3: operation of a 10 m3 batch bioleach reactor, inoculated with pulp from the
1 m3 reactor
– Phase 4: inoculation of one of the 112 m3 Primary Bioleach Reactors, using pulp from
the 10 m3 reactor
8. 8
Phase 1 – continuous miniplant
• Five-stage continuous
bioleach miniplant
• 21.2 L primary
bioleach reactor
• Four 5.8 L secondary
bioleach reactors
• Inoculum build-up
began in June 2015
9. 9
Miniplant start-up & operation
• Bacterial activity was
established within a few days
(as indicated by rise in redox
potential, pictured left)
• Twenty days later, the plant
was filled and production of
inoculum began
• A further 20 days later, the
first 100 L of inoculum had
been produced
10. 10
Phase 2 – 1 m3 batch reactor
• Existing tank modified for use as a temporary bioleach reactor
• Impeller not ideal, but proved adequate
11. 11
1 m3 batch reactor – failure!
• The batch was started by adding
an acidified nutrient solution
and Sotkamo concentrate,
heating to 45 °C, and
introducing the inoculum
• The first batch operation in the
1 m3 reactor failed to start up
• The batch was characterised by
the production of a strong
sulfurous smell…
12. 12
1 m3 batch reactor – success!
• The second batch was started
by adding an acidified nutrient
solution but no Sotkamo
concentrate, heating to 45 °C,
and introducing an inoculum
• Bacterial activity was achieved
within three days
• Concentrate was added over the
following nine days, to achieve
an effective solids concentration
of 5 %
13. 13
Phase 3 – 3 & 6 m3 batch reactors
• Once again, existing tanks
were adapted for
temporary use
• Rather than a single 10 m3
vessel, this phase utilised
3 and 6 m3 vessels
• Heating was via a hot
water tank (in the middle)
and heating coils in the
tanks
14. 14
3 & 6 m3 batch reactors – failure!
• The batches were started by
adding acidified nutrient
solutions, heating to 45 °C, and
introducing the inocula
• The first batch operations in the
3 and 6 m3 reactors (and the re-
started 1 m3 reactor) failed to
start up
• In this case, the reason for the
failure was never determined
– Water quality?
– Oil from instrument air
compressor?
15. 15
3 & 6 m3 batch reactors – success!
• Fortunately, 100 L of inoculum
from the previous 1 m3 batch had
been preserved
• This was used to restart the 1 m3
reactor – successfully
• The 3 and 6 m3 reactors were
then restarted, and bacterial
activity was achieved within two
days
• As before, concentrate was added
over the following 12 days, to
achieve an effective solids
concentration of 5 %
16. 16
Phase 4 – production plant (112 m3 reactor)
• Inoculation started in September 2015
• Manual operation, utilising a crane to hoist materials
• Small hot water tank was used to provide heating via internal
coils
17. 17
Primary Bioleach Reactor 1 – failure!
• Pre-heated water (36 m3) introduced to the vessel
• 1 % Sotkamo concentrate, nutrients and H2SO4 added
• 9 m3 of inoculum introduced
• Crucially, acid was added before aeration was started
• This attempt to inoculate P1 failed to start up
• At that stage, the reason was not apparent
• Hot water tank heating was not adequate, so a steam
generator was hired to raise the water temperature
18. 18
• A second attempt to inoculate the plant was initiated
• By that stage, the 1 m3 reactor had produced sufficient inoculum for this purpose
• A similar procedure was employed, but less concentrate (0.25 %) was added initially
• Pre-heating of the charge was achieved by direct steam injection
• Again, aeration was started after the acid addition to adjust the pH level to 1.8
• On this occasion, as soon as the air was introduced, the atmosphere around the tank
was filled with the unmistakeable sulfurous smell of H2S
• Pyrrhotite reaction with H2SO4 in absence of air lead to H2S formation
• Inoculum was not added
• This probably also happened in previous failed start-ups: first 1 m3 batch reactor and
Primary Reactor 1
Primary Bioleach Reactor 3 – failure!
19. 19
Primary Bioleach Reactor 2 – success!
• Inoculum activated within two days
• Steam heating of hot water tank was sufficient to maintain
temperature
• Build-up of solids content and filling of reactor commenced
• Third attempt initiated a few days later in Primary
Reactor 2
• Similar start-up procedure followed, but no concentrate
added and aeration initiated from the start
20. 20
Primary Bioleach Reactor 2 – metal tenors
• Dissolved metal tenors rose as solids
concentration was increased and the
reactor was filled
• On day 21, filling of the reactor was
complete, and overflow to the rest of
the plant commenced
• The continuous feed system was not
yet fully commissioned, so a labour-
intensive manual feeding system was
temporarily instituted
• The rest of the plant was filled via
overflow pipes
• Manual feeding slowed progress
somewhat, but plant was filled eight
weeks after the inoculation of P2
21. 21
Troubleshooting – bioleach feed splitter box
• Bioleach feed splitter box was poorly designed
• No agitation; asymmetric design
• Unlikely to work with fast-settling high-grade sulfide
concentrate …
• … and so it proved, with significant settling of solids
occurring
• Operators have managed flow distribution by careful
manipulation of weirs
• Equipment will be replaced with a complete redesign
22. 22
Troubleshooting – foaming
• Excessive foaming has occurred
in the bioleach circuit
• The foam is caused by residual
talc in the concentrate
• The upgrading circuit,
comprising magnetic
separation and flotation, has
not yet been commissioned
• Once it is, almost all of the talc
will be removed from the
circuit via the flotation tails
• This should alleviate (hopefully,
eliminate) this foam
• The foam has been controlled
to some extent by the use of
an antifoam agent
23. 23
Troubleshooting – ambient temperature
• It gets cold in eastern Finland in winter!
• This year (2016), the cold period lasted longer
than usual
• There was a sustained period with
temperatures below -25 °C, and for a week, as
low as -30 °C
• Pipework and instrumentation were enveloped
in ice
• These extreme weather conditions coincided with a pump failure in the feed
preparation circuit, and so the feed to the plant stopped, and several lines froze
• This caused the temperatures in the reactors to fall, but they recovered quickly
24. 24
Bioleach plant performance
• Maximum throughput of about 11.4 t/d achieved thus far (which is
63 % of the design capacity of 18 t/d)
• Intensive sampling campaign recently conducted over bioleach plant
• Plant throughput then at about 36 % of capacity
• Feed concentrate grind size of 80 % passing 50 µm – considerably
coarser than target of 80 % passing 20 µm
• Average nickel extraction of 97.4 % and average cobalt extraction of
98.4 %
• Unexpectedly low sulfide oxidation level of 76.6 % (could be related
to coarse grind, or an analytical error)
Date: 25-Apr 26-Apr 27-Apr 28-Apr 29-Apr 30-Apr 01-May 02-May 03-May 04-May Average
Ni extraction (%) 97.6 97.1 97.0 97.3 96.7 97.5 97.7 97.6 98.1 97.7 97.4
Co extraction (%) 98.5 98.6 98.3 98.4 98.3 98.3 98.7 98.4 98.5 98.1 98.4
S2-
oxidation (%) 78.3 77.9 76.8 76.8 75.8 76.0 78.0 76.1 78.6 71.5 76.6
25. 25
Iron-arsenic precipitation circuit - commissioning
• Commissioned immediately after filling of bioleach circuit
• Five precipitation tanks were filled, and feeding of CaCO3 slurry was
started
• Thickener bed was built up, and recirculation of underflow to iron-
arsenic precipitation was initiated
• Overflow was directed to the metal precipitation circuit – it passes
through cartridge filters to remove remaining residual particulates
• Filtration of the thickener underflow has proven challenging – this is
ongoing as the correct operational parameters are sought
26. 26
Iron-arsenic precipitation circuit – key parameters
• The pH levels in the conditioning tank and the five precipitation
tanks
– CaCO3 addition
– Online pH level measurements
• Thickener overflow quality
– Metal tenors
– Solution clarity
• Quantity of slurry recirculated from thickener underflow to
precipitation tanks
27. 27
Iron-arsenic precipitation circuit – troubleshooting
• The first limestone valves wore out quickly – replaced with ceramic
ones
• Commissioning of the iron-arsenic filter has been challenging
– Material is very fine (P80 ±20 µm in the thickener feed)
• Several cloth types have been tested to find the correct permeability –
needs to produce a clear filtrate with no cloth blinding!
• Total process optimisation for the thickener and filter will be done
• Fines from the thickener overflow cartridge filters are now being
directed back to the thickener, rather than being sent to the filter feed
tank
28. 28
Iron-arsenic precipitation circuit – performance
• Performance has been good
• Average metal tenors in thickener overflow (January-April
2016):
• Metal tenors are diluted by introduction of CaCO3 slurry in
this circuit
Element Ni Fe Co As Ca Mg
Tenor (g/L) 8.183 0.021 0.367 0.001 0.519 1.155
Std. dev. (g/L) 0.683 0.015 0.030 0.001 0.036 0.241
29. 29
Metal precipitation circuit - commissioning
• Five precipitation tanks, with magnesia (MgO) addition to produce a
mixed hydroxide precipitate (MHP) containing nickel and cobalt
• Residence time in MgO hydration tank has varied between 5 and 15
minutes
• QMAG magnesia produced by Sibelco in Queensland, Australia has
been used
• MHP thickener
• Three refurbished MHP filters (two main filters, one recovery filter)
• A bagging station
30. 30
Metal precipitation circuit – key parameters
• MgO addition rate – stoichiometric ratio
of 0.6 to 0.7 seems to be close to the
correct one
– Nickel grade is controlled by quantity of MgO
added
– Higher MgO addition leads to lower nickel
grade in MHP due to magnesium
contamination, but higher recoveries
• pH level in the 5th precipitation tank (7.1)
• MHP thickener overflow quality
• Product quality
31. 31
Metal precipitation circuit - troubleshooting
• MgO dosing system was unreliable,
requiring changes to be made to the dosing
pump
– Screw pumps were replaced with hose pumps
• Refurbished MHP filters required adaption
to fit with the positive displacement pumps
and avoid development of an overpressure
33. 33
Metal precipitation circuit - performance
• Main impurities are iron and
carbon
• Spikes coincide with
breakthrough of particulates
from the cartridge filter during
commissioning
34. 34
Metal precipitation circuit - performance
Compound
Value
(%)
Element
Value
(%)
Element
Value
(%)
Element/
compound
Value
(%)
SiO2 0.76 Fe 0.16 As <0.005 C 0.38
Na2O 0.02 Co 1.30 Cd <0.002 S 3.86
MgO 15.42 Ni 30.20 Sn <0.002 SO4
2- 13.1
Al2O3 0.06 Cu 0.02 Sb <0.002 LOI* 42.6
K2O <0.01 Zn 0.03 Te <0.002
CaO 0.20 Ba <0.002
Cr2O3 <0.002 Pb <0.01
MnO 0.17 Bi <0.005
Ag <0.002
• Full analysis of MHP product during commissioning phase (with high MgO addition):
• Average grades of 243 bulk bags:
| 45.5 % Ni | 2.46 % Co | 3.64 % Mg | 0.42 % Fe | 0.017 % As | 0.90 % C |
35. 35
Remaining challenges
• Commissioning of the magnetic separation and flotation plants – talc
removal will overcome the foaming issue
• Introduction of Vuonos feed to the process (currently only Sotkamo)
• Commissioning of fourth Primary Bioleach Reactor
• Equipment-related challenges:
• Installation of screen in regrind mill
• Bioleach feed splitter box
• Iron-arsenic filter – highest priority item
• Carbon contamination of MHP
• Separate tailings storage facility is being considered to minimise impact of
water quality on talc refining operations
36. 36
Conclusions
• Design, construction, commissioning and operation of the nickel bioleach process has been
demonstrated
• All major circuits have been successfully commissioned
• High quality nickel-cobalt product has been produced
• Bioleach inoculum build-up was achieved within set time frame
• Equipment sizing and selection is critical to success
• A high level of resource deployment is needed in first twelve months to achieve success
• Bioleach process is robust, and performs consistently
• Severe winter conditions were withstood reasonably well
• Commissioning and production ramp-up of the world’s first nickel sulfide concentrate
bioleach treatment plant is expected to be completed within the next few months
