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Agglomeration and column leaching behaviour of nickel laterite ores: effectof ore mineralogy and particle size distribution
Ataollah Nosrati, Keith Quast, Danfeng Xu, William Skinner, David J.Robinson, Jonas Addai-Mensah
PII: S0304-386X(14)00060-7DOI: doi: 10.1016/j.hydromet.2014.03.004Reference: HYDROM 3854
To appear in: Hydrometallurgy
Received date: 28 August 2013Revised date: 5 March 2014Accepted date: 6 March 2014
Please cite this article as: Nosrati, Ataollah, Quast, Keith, Xu, Danfeng, Skinner,William, Robinson, David J., Addai-Mensah, Jonas, Agglomeration and column leachingbehaviour of nickel laterite ores: eect of ore mineralogy and particle size distribution,Hydrometallurgy (2014), doi: 10.1016/j.hydromet.2014.03.004
This is a PDF le of an unedited manuscript that has been accepted for publication.As a service to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting, typesetting, and review of the resulting proofbefore it is published in its nal form. Please note that during the production processerrors may be discovered which could aect the content, and all legal disclaimers thatapply to the journal pertain.
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Agglomeration and column leaching behaviour of nickel laterite ores: effect
of ore mineralogy and particle size distribution
Ataollah Nosrati1*, Keith Quast
1, Danfeng Xu
1, William Skinner
1, David J. Robinson
2,
Jonas Addai-Mensah1
1Ian Wark Research Institute, University of South Australia
Mawson Lakes, SA 5095, Australia 2CSIRO Minerals Down Under National Research Flagship Australian Minerals Research
Centre, PO Box 7229, Karawara W.A. 6152, Australia
*Corresponding author: [email protected]
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Abstract
Nickel (Ni) laterites account for about 60-70% of the worlds nickel mineralization. The
processing of low grade (e.g., 1% Ni) laterite ores is favoured by the use of the more cost-
effective hydrometallurgical techniques (e.g., atmospheric agitated tank or heap leaching)
instead of smelting. Application of heap leaching which boasts of low capital and operating
expenditures, however, is very limited due to intractable challenges such as poor heap
porosity/permeability associated with most laterite feed ores. Feed particles agglomeration
into robust and porous agglomerates of right size range enables permeable and geotechnically
stable bed required for successful heap leaching to be constructed. In this paper, several basic
and applied studies of the agglomeration and column leaching behaviour of real Ni laterite
ores are reported. The work involved isothermal, batch agglomeration tests carried out to
produce 5 40 mm agglomerates which were characterized and subjected to >100 days of
laboratory column leaching. The effect of feed ore characteristics (e.g., mineralogy/
chemistry and particle size distribution) on agglomeration behaviour and agglomerates
column leaching behaviour was investigated through several characterization techniques
including agglomerate size, compressive strength, 3D micro-structure analyses and laboratory
column leaching tests. Links between feed mineralogy/chemistry and size, binder dosage,
agglomeration behaviour, agglomerate properties and leaching behaviour are established. The
significance of the findings to Ni laterite plant agglomeration for enhanced heap leaching is
discussed.
Keywords: Ni laterite; Agglomeration; Column leaching; Mineralogy; Particle size
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1. Introduction
Oxley et
al., 2007; Steemson and Smith, 2009;
Bouffard Dhawan et al., 2013 Steemson and Smith, 2009;
Readett and Fox, 2009/2010; Steemson
and Smith, 2009; Oxley et al., 2007
Readett and Fox, 2010
agglomerate
Long-term column leaching test is widely used to simulate the HL process and determine
value metal recovery, leaching rate, and reagent requirements (Agatzini-Leonardou and
Dimaki, 1994; Stamboliadis et al., 2004; Lewandowski and Kawatra, 2008,2009; Quast et al.,
2013). Despite some limitations and differences between column and real HL conditions
(e.g., more compactness and less solution-solid contact in real heap compared with column)
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the long history of industrial operation of this technique in nickel, copper, gold and uranium
mines has proved the column reactors to be reasonably good simulators of heaps of similar
height (Agatzini-Leonardou and Dimaki, 1994; Stamboliadis et al., 2004; Dhawan, et al.,
2013; Hernandez et al., 2003; Elliot et al., 2009; Kyle, 2010; Watling et al., 2010,2011).
Hence, undertaking laboratory column leaching studies in tandem with agglomeration studies
is essential (i) to determine the agglomerate performance over a period of time under real HL
conditions and (ii) characterise and evaluate their sulphuric acid leaching behaviour.
This paper presents results from our recent laboratory agglomeration and column leaching
studies undertaken on to characterise and evaluate
their sulphuric acid agglomeration and agglomerate leaching behaviour.
.
2. Experimental methods
2.1. Materials
The study involved three low grade Ni laterite ores (~1 wt. % Ni) described by their
dominant generic mineralogy and were designated as Goethitic (G), Siliceous Goethitic (SG)
and Saprolitic (SAP) ores. These are typical of deposits located in the arid region of Western
Australia and are characterized by the general mineralogy using QEMSCAN summarized in
Fig. 1. The ore complexity is also indicated in the QEMSCAN images in Fig. 2. Chemical
analyses of Run-of-Mine (ROM) ores are shown in Table 1 and the major mineral deportment
according to Quantitative X-ray diffraction analysis shown in Table 2. In Table 2, D stands for
dominant, SD for sub-dominant, M for minor and VM for very minor. Detailed mineralogical
analyses of these three samples of laterite have been reported by Swierczek et al. (2011, 2012).
In all three ores, the main Ni-bearing phase is asbolane, with magnetite, hematite and quartz
being virtually barren in Ni. Goethite is another main carrier for Ni.
2.2. Drum agglomeration: equipment and agglomeration procedure
Agglomeration tests were conducted in a batch, laboratory-scale drum (0.3 m diameter and
0.2 m in length) granulator operated at 60 rpm rotational speed (Fig. 3). The selection of
drum speed was based on preliminary agglomeration tests at 40, 60 and 80 rpm which
showed 60 rpm to be more efficient, taking into consideration the batch time and energy
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consumption required to get desired product size distribution. To investigate the effect of feed
particle size on agglomeration and column leaching behaviour of Ni laterites, four types of
feed ore material: (i) -15 mm ROM, (ii) -2 mm crushed from the -15 mm material, (iii) -38
m fraction obtained from stirred milling of -2 mm crushed material (Tong et al., 2013) and
(iv) -15 mm/-38 m blend (60/40 by weight) were used to produce agglomerates. The
justification for stirred milling of -2 mm ore and using the -38 m product for agglomeration
and column leaching was the noticeably higher Ni grade of the stirred mill product (Tong et
al., 2013; Quast et al., 2013). The concept of feed ore pre-concentration and upgrade before
acid leaching is often used in industrial practice, one example being its incorporation in the
design of the Ravensthorpe Ni laterite plant to treat a Western Australian Ni laterite deposit
(Adams et al., 2004; Miller, 2000; Miller et al., 2004).
For all agglomeration tests, the dry feed ore and 30% w/w H2SO4 used as liquid binder
were first pre-mixed in a tray by quickly (~2 min) hand spraying the latter and subsequently
transferring the mixture into the drum to commence agglomeration. During the agglomeration
process, where necessary, the drum was periodically stopped for 30 s to scrape the particles
and agglomerates that were adhering to the drum walls using a spatula. A maximum batch
time of 14 min for which agglomerates in the size range 540 mm were produced was used.
The relatively long batch time used in this study, compared with 1-2 min residence time often
used in plant agglomeration drums, is ascribed to large amounts of scats (e.g., 15-25 mm) and
moisture (e.g., 25 wt.%) in plant feed ores, both promoting fast agglomeration. With finer
particles and lower moisture contents (e.g., < 10 wt.%) of the feed ores used in this study,
they could be agglomerated to desired product size only after significantly longer time. The
full details of agglomeration procedure are reported elsewhere (Nosrati et al., 2012a). For
column leaching studies, all the agglomerates were air-dried for 48 h at room temperature
(~25 C and 30% relative humidity), prior to loading in the columns.
2.3. Agglomerate characterization
Evolution of agglomerate size distribution with time was characterized by fresh/moist
product sieving and cumulative mass fractions under size against mean agglomerates size
plots. The agglomeration tests were reasonably reproducible, with substantially similar
agglomerate products size distributions obtained from three replicate agglomeration tests. For
single agglomerate strength measurements on both wet and dry states, a bench top
compressive strength testing machine (Hounsfield, UK), which enables compressive force-
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distance measurements to be performed, was used. Compression consisted of applying a load
to an agglomerate held between two parallel flat surfaces, one of which was held stationary
while the other was attached to a constant velocity drive. The resultant force was measured
using a load cell (of known compliance) attached to the upper drive surface. Based on the
agglomerate diameter and the measured maximum applied uniaxial force (Pmax) at which
breakage or fracture occurred, the fracture stress was calculated from Eq. (1) (Hiramatsu,
1966):
2max8.2
d
Pf
(1)
where f is stress to failure and d is the diameter of the agglomerate.
The micro-CT analysis was conducted on ~15 mm air-dried agglomerates using an Xradia
microXCT-400 tomography machine (Xradia, USA). Agglomerates were scanned in the 010
interval rotation using a 0.225 scan rotation step producing 800 images. The collected
projections were reconstructed, using Xradia XMReconstructor software (Miller and Lin,
2009; Dhawan et al., 2012).
2.4. Column leaching tests
The column leaching tests were conducted using Perspex columns, 125 mm in diameter
and 2 m long (Fig. 4). A layer of ~20 mm size quartz chips approximately 140 mm deep was
placed in the bottom of each column to prevent the agglomerates from plugging the pregnant
solution outlet. A known mass of air-dried/cured agglomerates (produced from 5 kg dry feed
ore) was gently placed in the column to a depth of ~0.5 m. This was followed by another layer
of coarse silica chips which facilitated the even distribution of the lixiviant (200 g/L H2SO4)
over the bed of agglomerates. The leach solution was metered over ~100 days without recycle,
and checked periodically to allow calculation of the acid consumption. The irrigation rate for
each column was 96 mL/h corresponding to ~8.5 L/m2.h which is within typical irrigation rate
range (5-10 L/m2.h) for Ni laterites heap leaching (Dhawan et al., 2013; Hunter et al., 2013).
Pregnant leach solutions were sampled daily for the first 30 days, and then every four days for
the remainder of the test. The elemental concentrations measured were for Ni, Co, Al, Fe, Mg
and Mn by standard ICP. The extractions of elements other than Ni and Co have previously
been reported by Quast et al. (2013) and will not be reported here. The height and slumping of
the ore bed was recorded periodically by % slump=(change in height/initial column
height)100. In order to simulate the effect of hydrostatic load and hence increasing the bed
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height up to 3.5 m on the strength and slumping of the agglomerate beds during heap leaching,
weights up to 30 kg were added on top of the agglomerate beds after the columns had been
irrigated for approximately 100 days. Thereafter, irrigation was continued while the slump was
measured.
3. Results and discussion
3.1. Agglomeration behaviour: effect of feed ore mineralogy and particle size distribution
The agglomeration behaviour and binder dosage requirement of -2 mm SG, G and SAP
ores are shown in Fig 5. For all three ore types, 5 40 mm agglomerates were produced within
8 min. For initial feed powder wetting and nucleation, however, SAP ore required significantly
greater acidic solution (agglomeration medium) addition compared with SG and G ores
mainly due to its higher acid-consuming clay content as well as greater fines content. Taking
into account (i) the key role of binder dosage in controlling the hydro-texture of solid-liquid
mixtures and hence, their agglomeration behaviour, and (ii) the fact that agglomeration of
different feed ores (e.g., in terms of mineralogy, PSD) with similar binder dosage was not
practicable, considerable attempt was made via preliminary tests to wet all feed powders to the
similar extent before agglomeration. This ensured that the hydro-texture of all mineral-binder
mixtures were as close as possible and consistent, despite the differences in their binder
dosages. The data in Fig. 5 show that in the presence of adequate binder liquid, regardless of
the mineralogy of -2 mm feed ores, agglomerate growth occurred via coalescence and pseudo-
layering as major and minor growth mechanisms, respectively.
Fig. 6 shows that -15 mm ROM nickel laterite ores (which contain larger fraction of coarse
particles) display noticeably different binder dosage requirement and agglomeration behaviour
compared with -2 mm ores. The presence of competent coarse fraction in the former leads to
(i) less binder dosage requirement due to reduced particle specific surface area or wetted
perimeter, (ii) enhanced initial agglomerate growth rate (no need for nucleation to start
agglomeration due to presence of coarse particles), (iii) absence of massive coalescence
(layering of fines around coarse particles/agglomerates becomes major growth mechanism),
and (iv) narrower product size distribution. Fig. 6A specifically highlights the critical role of
binder dosage on feed powder wetting and promotion of agglomerate size growth. For -15 mm
SG ore, whilst addition of 12 wt.% binder appeared to completely wet the powder, it was not
enough to promote reasonable size growth. Increasing the binder dosage to 15 wt.%, however,
led to production of 5 30 mm agglomerates within 8 min.
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The data in Fig. 6B also indicate that after initially faster and more efficient agglomeration
observed for -15 mm ROM ores within 8 min (compared with -2 mm ores), prolonged
agglomeration time of 14 min had no effect on further agglomerate size growth. This is
opposite to the agglomeration behaviour of -2 mm feed ores where longer agglomeration time
leads to formation of very large agglomerates due to massive coalescence (Fig. 7A). The effect
of feed ores PSD on predominant agglomerate growth mechanism is also further clarified in
Fig. 7 (A & B). For agglomeration of -38 m feed ores; greater binder dosage values were
required due to increased particle surface area while they displayed growth behaviour very
similar to that of -2 mm feed ores. During agglomeration of -15 mm/-38 m blends, on the
other hand, the mixtures displayed growth behaviour similar to that of -15 mm ores.
3.2. Single agglomerate structure and strength: effect of ore mineralogy and PSD
Fig. 8 shows the typical internal structure of agglomerates produced from -15 mm feed
ores, where they generally exhibit a distinct coarse particle core/fine particle shell structure.
As expected, this structural feature is not seen in agglomerates of finer feed ores (e.g., -2 mm).
The presence of coarse (e.g., 5 15 mm), competent particles (e.g., goethite, hematite and
quartz) in feed is also expected to facilitate the formation of more robust agglomerates which
lead to enhanced agglomerate bed strength/stability and hence, good acid percolation
behaviour.
Fig. 9A shows the effect of ore mineralogy and agglomerate drying state (residual moisture
content) on compressive strength of 10-15 mm agglomerates produced from -2 mm feed ores.
The results indicate that (i) all freshly made (wet) agglomerates display statistically similar
compressive strength, (ii) their strength noticeably increases upon air-drying or curing at high
temperature (e.g., 50 C), and (iii) dry G agglomerates exhibit dramatically higher
compressive strength than dry SG and SAP agglomerates. It is worth mentioning that the
results from single agglomerate compression testing alone cannot be used as basis for
evaluation or prediction of agglomerate bed strength and stability during column/heap
leaching process. This is due to the limitations of this test as it does not take into account the
effect of other parameters such as dynamic loading and re-wetting which agglomerates
experience under heap/column leaching conditions.
Enhanced agglomerate strength upon drying is attributed to moisture evaporation and
solidification/recrystallization of acid-leached species within agglomerates also leading to
slight agglomerate shrinkage. Greater dry strength of G agglomerates compared with SG and
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SAP ones is also linked to larger fraction of ultrafine particles in the former. Upon
agglomerate drying, these very fine particles can act as intra-agglomerate cementing/bonding
media further enhancing the compressive strength. The dry agglomerate strength enhancement
with increasing feeds fine content can also be linked to increased density and lower porosity.
This hypothesis is supported by Fig. 9B where increasing the feed ores fine content markedly
enhances agglomerate compressive strength.
3.3 Column leaching: effect of agglomerates feed ore mineralogy and particle size
A summary of the column leaching results on agglomerates produced from different feed
ores is given in Table 3. The symbols in Table 3 are: SM means stirred mill material, B means
blocked; NM means Ni recovery not measured and NL means no load i.e., no additional load
(30 kg) was applied. It is worth mentioning that columns loaded with un-agglomerated -15
mm ores blocked overnight indicating the need for and importance of agglomerating the nickel
laterite ores prior to leaching. Some Ni leaching kinetic and acid consumption data are also
given in Figs. 10 to 13.
The data for SG in Table 3 clearly show the advantage of further crushing the
agglomeration feed finer (from -15 to -2 mm) prior to agglomeration and leaching. This leads
to a higher Ni release rate at lower acid consumption. Thus, by reducing the size of feed ore
particles, more Ni-bearing material is liberated and available to the acid, and less acid is being
consumed by the acid-resistant and coarser Ni-poor phases. This is evidenced by the -15 mm
SG feed consuming more than 100 kg/t of acid, accompanied by 10% less Ni recovery
compared with -2 mm SG feed. Agglomeration and column leaching tests were also conducted
on -38 m material from stirred milling because this technique has shown to be effective in
selectively grinding the softer higher Ni-bearing material, resulting in an increase in Ni grade
by rejecting the coarse material (Tong et al., 2013). It is worth mentioning that the -38 m SG
stirred-mill product contained 80% of the original sample mass at ~1.3% Ni grade. The
rejected +38 m components comprised 25% of the quartz, 14% of the clays, 12% of the
goethite and ~30% of the amorphous material in the original mill feed. The data in Table 3
shows that for both SGs stirred milled fines (-38 m) and its blend with -15 mm SG (40/60
mass ratio) the Ni recovery is higher than that of -2 mm SG whilst the acid consumption is
lower.
The data for G agglomerates in Table 3 show that column leaching was successful only for
agglomerates produced from -15 mm feed ore whilst columns with agglomerates made of -2
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mm, -38 m and -38 m/-15 mm G feed ores blocked after 1, 20 and 24 days, respectively.
This not only indicates the key role of coarse particles (e.g., scats) but also highlights the
negative impact of too much fines in the feed ores. The results also show that the column
leaching of agglomerates produced from -38 m SAP ore failed after 2 days due to blockage.
The column leaching performance of agglomerates produced from -38 m G and SAP feeds
was opposite to that of -38 m SG agglomerate. For the latter, not only the column did not
block, but also it showed an enhanced Ni release compared with agglomerates produced from
its -15 mm and -2 mm feeds. Furthermore, despite displaying highest dry strength (Fig. 9A), G
agglomerates were generally less stable/robust than SG and SAP ones under wet leaching.
This is mainly due to the G feed ores low silicate/aluminosilicate clay content which can
enhance agglomerate robustness/stability via acid cementation and formation of intra-
agglomerate solid bridges (Nosrati et al., 2012c). Hence, it explains why the -38 m G/-15
mm SG blend agglomerates showed good stability under column leaching conditions. SG ore
provided more silicate component to the blend which facilitated intra-agglomerate
cementation and also enhanced structural support.
Column slumping during leaching was relatively low for SG agglomerate beds, but higher
for the G and SAP agglomerates (Table 3). Values of slump are typical of high slumping
laterites reported by Eliot et al. (2009), with columns containing coarser feeds (-15 mm)
generally giving lower slumps than for agglomerates made from finer material. This is
probably due to the presence of competent coarse particles in the agglomerates (Fig. 8)
causing a network structure to be developed where the competent particles support the
agglomerate material made from the finer particles. This would simulate the effect of the
addition of scats to the Murrin Murrin heap leach to reinforce its geotechnical strength or
stability (Readett and Fox, 2009). Taking into account the small scale of columns and initial
agglomerate bed heights (0.5 m), the overall loaded slump values recorded for different SG
agglomerates were reasonably close (9-16%). In other words, despite differences in the SG
feed ores particle size distribution, all agglomerates were reasonably robust leading to stable
agglomerate beds during >100 days of irrigation.
The recovery of Ni and Co from -15 mm SG, G and SAP feed ores as a function of
leaching time and their acid consumption as a function of Ni recovery are shown in Fig. 10.
The agglomerated ores released Ni in the order of SAP>SG>G in line with their mineralogy,
i.e. relative abundance of oxide and layer aluminosilicate mineral content (Fig. 1). For Co
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release, however, the order changes to SAP>G SG. At 60 days, Ni recovery for these feeds
was G (35%), SG (60%) and SAP (85%). For Co, on the other hand, the recovery at 60 days
was SG (35%), G (43%) and SAP (66%). Acid consumption over the equivalent period for G,
SG and SAP was approximately 280, 450 and 420 kg/t, respectively (Fig. 10 C). Completed
100 day column leaching tests for -15 mm SG, G and SAP agglomerates showed maximum Ni
extractions and acid consumptions of 72%/680 kg/t, 55%/450 kg/t and 97%/500 kg/t,
respectively. According to Robertson and van Staden (2009), low grade Ni laterite processing
is normally associated with very high sulphuric acid consumption (typically 500 kg/t), so the
acid consumptions shown in Fig. 10C are in line with operating practice. Robertson and van
Staden (2009) also reported an almost linear increase in acid consumption with increasing Ni
recovery, with acid consumptions of ~400 kg/t for Ni recoveries of 70%. Eliot et al. (2009)
reported acid consumption rates of 200-800 kg/t for similar Ni recovery values. From the data
in Figs. 10 and 11 it can also be seen that -15 mm SAP ore which is dominated by
silicate/aluminosilicate mineralogy, exhibited superior Ni and Co leaching performance,
yielding a lower acid consumption for a given Ni recovery.
It is worth noting that both SG and SAP columns show two-stage Ni release behaviour with
an initial fast early release (up to 50-60% Ni recovery) followed by a slower, final release
period. We attribute this behaviour to the quick extraction of Ni from fine, clay-type minerals,
followed by the slow acid attack of the goethite component of the ores. In terms of acid
consumption per kg Ni recovered, all three ores fell within the range of 30-95 kg acid/kg Ni,
depending on the leaching time, i.e. fast or slow release regimes (Fig. 11). Post-leach loading
of all the three columns to 3.5 m equivalent heap height indicated good column stability, even
though irrigation was continued throughout the time of additional loading. This would indicate
that constructing and operating agglomerated Ni laterite heap heights of ~3.5 m should be
possible with these materials, even in the absence of scats which would increase the bulk
density of the bed of agglomerates in many commercial operations.
Fig. 12 clearly shows the enhanced Ni/Co release and leach kinetics for SG ore upon (i)
decreasing the agglomeration feed particle size (from -15 to -2 mm) and/or (ii) upgrading/size
reduction of agglomeration feed via stirred milling (-38 m). The effect of further grinding is
understandable and anticipated since the higher surface area of the initial feed particles will
give a greater area of contact with the lixiviant. These agglomerates have been shown to be
porous (Nosrati et al., 2012b), providing good contacts between acid and soluble species in the
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agglomerate. The data in Fig. 13 indicate that both size reduction and upgrading has no effect
on overall SAP leaching behaviour and Ni/Co recovery. Furthermore, the blends of coarse and
fine sizes for SG and SAP ores follow very similar trends in Ni extraction, consistent with
faster release from the finer component in the initial stages, followed by a slower release rate.
The agglomerated -38 m G/-15 mm SG blend, produced to mitigate failure of the fine G
column collapse, ran for 74 days without blockage, which coincided with the end of the
project (Fig. 13). This trial highlights the role of clay content for agglomerate integrity and the
presence of coarse supporting material. Overall, the incorporation of the -38 m material in
the agglomerates gives similar leaching rates to the pure -38 m material.
3.4 Overall discussion of column leaching results
The un-agglomerated -15 mm ores column blocked within a day, indicating the key role of
agglomeration and superiority of agglomerates for leaching Ni laterites. A balance between
silicate/aluminosilicate and goethite composition is essential for sustained Ni release and long-
term agglomerate integrity/stability (good percolation) under heap leaching conditions. The
good performance of SG ore, compared with SAP and G ores, is due to an optimum balance
between the compositions mentioned above. Size reduction in upgraded agglomerate feed
generally benefits the Ni/Co release rates and enhances the final recovery due to more
exposure of Ni-bearing phase and increased available surface area. Feed size deduction,
however, may not be considered a favorable option due to generating further fines which can
pose a real challenge to successful heap leaching. Sized blend (e.g., -38 m/-15 mm) also
gives a fast initial Ni release rate from fine components followed by a slower release;
however, total Ni benefit may or may not be significant in the long term (100 days) depending
on the ore type. Ore blending needs to be considered if the main feed ore lacks the mineral
components which are essential in generating strong and robust agglomerates. Slumps
observed during >100 days of column leaching varied between 5 and 15% for SG and SAP
ores and >20% for G ore. These together with post-leach loading of the columns to 3.5 m
equivalent heap height indicated good stability of agglomerate beds under leaching conditions.
4. Conclusion
Agglomeration and column leaching behaviour of 3 different Ni laterite ores with varying
sizes are reported in this paper. The results suggest that:
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Agglomeration is shown to be crucial pretreatment step for successful heap leaching of
run-of-mine and/or comminuted Ni laterite ores. The columns filled with un-
agglomerated ores blocked within 24 h indicating the key role of agglomeration.
Feed ores mineralogy and average particle size exert significant impact on (i) binder
dosage requirement during agglomeration, (ii) agglomeration behaviour, (iii) single
agglomerate structure/strength, and more importantly (iv) agglomerate beds structural
strength and column leaching performance.
For agglomerated ores during column leaching, Ni release rate follows the order of
SAP>SG>G, which is in line with their mineralogy. The Co release rate also follows the
order of SAP>G SG indicating that Ni and Co are not disseminated similarly in different
mineral phases of the feed ores.
A balance between acid reactive clay (for acid cementation and Ni/Co release) and
goethite (higher acid resistance and longer term structural support) content in the feed ore
is essential to produce robust agglomerates with acceptable column leaching performance.
Size reduction in agglomerate feed enhance the Ni/Co release rates and final recovery,
however, it generally leads to less stable columns due to increased fine fraction.
Up to 90% Ni and 70% Co recovery was achieved within 100 days of column leaching of
agglomerated Ni laterite ores. The observed acid consumption and Ni recoveries are in
good agreement with the data reported in literature.
Acknowledgments
The authors wish to thank CSIRO through their Minerals Down Under National Research
Flagship for their in-kind and generous financial support for the Nickel Laterite Cluster
project. Micro-CT analysis of agglomerates was performed at the South Australian node of the
Australian National Fabrication Facility (ANFF-SA) under the National Collaborative
Research Infrastructure Strategy. The authors also thank Ms Zofia Swierczek for
QEMSCAN data.
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Tables
Table 1: Run-of-mine ores chemical analyses
Element Ore type
Goethitic Siliceous Goethitic Saprolitic
Ni (%) 0.96 1.0 0.92
Co (%) 0.065 0.068 0.039
Mg (%) 0.42 2.9 5.90
Fe (%) 42.2 20.0 21.8
Mn (ppm) 4600 2800 2200
Zn (ppm) 380 265 380
Cu (ppm) 130 20 25
Al (%) 5.06 1.85 3.55
Cr (%) 1.34 1.19 1.70
Ca (%) 0.02 0.03 0.03
Si (%) 5.10 23.0 17.0
Cl (%) 1.57 1.23 1.70
Table 2: Major mineral deportment
Mineral Ore type
Goethitic Siliceous Goethitic Saprolitic
Goethite D in all size fractions D in all size fractions SD
Hematite D in coarser sizes M in fine sizes SD
Quartz M D in coarser sizes D in coarser sizes
Kaolinite SD VM M
Serpentine M M D in coarser sizes
Smectite VM D in intermediate size fractions D in fine fractions
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Table 3: Summary of column leaching data
Feed
(mm) Days
Ni Recovery
(%)
Cum. Acid
Cons. (kg/t)
Final loaded
slump (%)
SG
-15 mm 102 71 684 12
-2 mm 104 81 569 16
SM -38 m 101 89 541 9
SM -38 m/-15 mm 101 89 510 13
G
-15 mm 106 55 453 28
-2 mm 1 (B) - - -
SM -38 m 20 (B) NM NM 22 (NL)
SM -38 m/-15 mm 24 (B) NM NM 25 (NL)
SAP
-15 mm 101 97 502 7
SM -38 m 2 (B) 21 (NL)
SM-38 m/-15 mm 98 92 614 3
BLEND
-38 m G/-15 mmSG 74 53 312 20 (NL)
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Figure Captions
Figure 1: Typical laterite deposit structure comprising the three ore types and their
mineralogical summary.
Figure 2: QEMSCAN images from -300 + 150 m goethitic sample showing asbolane in
blue, magnetite in dark brown, hematite in grey and goethite in light brown (from Swierczek
et al.(2012)).
Figure 3: The laboratory scale batch drum agglomerator.
Figure 4: Photograph of a section and packed columns of Ni laterite agglomerates used in the
column leach tests.
Figure 5: The agglomerate size distribution for the -2 mm siliceous goethitic (A), goethitic
(B) and saprolitic (C) ores with 22.5, 22.5 and 32.5 wt.% binder dosage (30% w/w H2SO4),
respectively, as a function of agglomeration time.
Figure 6: The agglomerate size distribution for the -15 mm siliceous goethitic (A), goethitic
(B) and saprolitic (C) ores with 22.5, 22.5 and 32.5 wt.% binder dosage (30% w/w H2SO4),
respectively, as a function of agglomeration time.
Figure 7: Agglomeration behaviour of (A) -2 mm and (B) -15 mm goethitic ores as functions
of agglomeration time.
Figure 8: 2D micro-XCT images of the internal cross sectional area of agglomerates made of
(A) -15 mm and (B) -2 mm SG feed ores, respectively.
Figure 9: (A) Effect of ore mineralogy and moisture mass content on strength of 10 mm size
agglomerates made of -2 mm feed ores. (B) Effect of fine (-150 m) particles mass content in -2 mm feed ore on dry SG agglomerate compressive strength.
Figure 10: Comparison of Ni/Co extraction (A/B) and acid consumption (C) data from
column leaching of agglomerates made of different -15 mm Ni laterite ores.
Figure 11: Cumulative Ni mass recovery as a function of cumulative acid consumption.
Figure 12: Effect of SG agglomerates feed PSD on Ni/Co recovery (A/B) and acid consumption (C) during column leaching tests.
Figure 13: Comparison of Ni/Co leaching data for some laterite ores.
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Fig. 1
Goethitic (or Limonitic): 66% goethite, 9% magnetite/
hematite, 5% kaolinite, 2% quartz, 1% nontronite and
0.5% Mg-bearing silicates.
Siliceous Goethitic: 25% goethite, 3% hematite/
magnetite, 19% nontronite, 9% Mg-bearing silicates
and 36% quartz.
Saprolitic: 14% goethite, 6% hematite/ magnetite, 16%
nontronite, 12% quartz and 38% Mg-bearing silicates.
Ferricrete Cap
G
SG
SAP
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Fig. 2
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Fig. 3
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Fig. 4
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Fig. 5
A
B
SG
Binder dosage:
22.5 wt.%
G
Binder dosage:
22.5 wt.%
SAP
Binder dosage:
32.5 wt.%
C
20 mm
8 min
8 min
8 min
20 mm
20 mm
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Fig. 6
Size (mm)
0 10 20 30 40
Cu
mu
lati
ve
ma
ss f
racti
on
un
der
0.0
0.2
0.4
0.6
0.8
1.0
Feed
8 min
8 min
Size (mm)
0 10 20 30 40
Cu
mu
lati
ve
ma
ss f
racti
on
un
der
0.0
0.2
0.4
0.6
0.8
1.0
Feed
8 min
14 min
Size (mm)
0 10 20 30 40
Cu
mu
lati
ve
ma
ss f
ract
ion
un
der
0.0
0.2
0.4
0.6
0.8
1.0
Feed
8 min
A
B
SG
Binder dosage:
12 wt.%
15 wt.%
C
G
Binder dosage:
18 wt.%
SAP
Binder dosage:
18 wt.%
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Fig. 7
Size (mm)
0 10 20 30 40 50
Cu
mu
lati
ve
mass
fra
ctio
n u
nd
er
0.0
0.2
0.4
0.6
0.8
1.0
Feed
0 min
2 min
8 min
14 min
Size (mm)
0 10 20 30 40 50
Cu
mu
lati
ve
mass
fra
ctio
n u
nd
er
0.0
0.2
0.4
0.6
0.8
1.0
Feed
0 min
2 min
8 min
14 min
-2 mm G: 22.5 wt.%
binder dosage
Massive coalescence
-15 mm G: 18 wt.%
binder dosage
Pseudo-layering
A
B
C
u
m
ul
ati
ve
wt
.
fr
ac
tio
n
pa
ssi
ng
C
u
m
ul
ati
ve
wt
.
fr
ac
tio
n
pa
ssi
ng
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Fig. 8
A B
5 mm 5 mm
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Fig. 9
Agglomerate moisture content (wt.%)
0 10 20 30 40Ag
glo
mera
te c
om
pre
ssiv
e s
tren
gth
(P
a)
0
1x106
2x106
3x106
4x106
G agglomerates
SG agglomerates
SAP agglomerates
Fine (-150 m) particles mass ratio in -2 mm SG feed ore
0.0 0.2 0.4 0.6 0.8 1.0
Dry
ag
glo
me
rate
co
mp
ress
ive s
tren
gth
(P
a)
0
400x103
800x103
1x106
2x106
A
B
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Fig. 10
Leaching time (day)
0 20 40 60 80 100 120
Ni
Extr
act
ion
(%
)
0
20
40
60
80
100
SG
G
SAP
Leaching time (day)
0 20 40 60 80 100 120
Co E
xtr
act
ion
(%
)
0
20
40
60
80
100
SG
G
SAP
Ni Recovery (%)
0 20 40 60 80 100
Aci
d C
on
sum
pti
on
(k
g/t
)
0
200
400
600
800
SG
G
SAP
A
B
C
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Fig. 11
Cumulative acid consumption (kg)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Cu
mu
lati
ve
Ni
mass
rec
over
y (
kg)
0.00
0.01
0.02
0.03
SG
G
SAP
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Fig. 12
Leaching time (day)
0 20 40 60 80 100 120
Ni
Ex
tra
ctio
n (
%)
0
20
40
60
80
100
-15 mm
-2 mm
-38 m
Leaching time (day)
0 20 40 60 80 100 120
Co
Ex
tra
ctio
n (
%)
0
20
40
60
80
100
-15 mm
-2 mm
-38 m
Cumulative acid consumption (kg)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Cu
mu
lati
ve N
i m
ass
reco
very
(k
g)
0.00
0.01
0.02
0.03
0.04
0.05
0.06
-15 mm
-2 mm
-38 m
A
B
C
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Fig. 13
Leaching time (day)
0 20 40 60 80 100 120
Ni
Ex
tra
ctio
n (
%)
0
20
40
60
80
100
-15 mm SAP
-38 mm/-15 mm SAP
-15 mm SG
-38 mm/-15 mm SG
-38 mm SG
-15 mm G
-38 mm G/-15 mm SG
Leaching time (day)
0 20 40 60 80 100 120
Co
Ex
tra
cti
on
(%
)
0
20
40
60
80
-15 mm SAP
-38 mm/-15 mm SAP
-15 mm SG
-38 mm/-15 mm SG
-38 mm SG
-15 mm G
-38 mm G/-15 mm SG
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Research highlights
Ni laterite acid agglomeration is an essential pre-treatment for heap leaching.
Ore mineralogy and particle size impacts on agglomeration and leaching behaviour.
Ore blending is an option to enhance heap leaching performance of agglomerates.
Up to 90% Ni and 70% Co recovery was achieved within 100 days of column
leaching.