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

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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: Ataollah.nosrati@unisa.edu.au

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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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References

Adams, M., van der Meulen, D., Czerny, C., Adamini, P., Turner, J., Jayasekera, S.,

Amaranti, J., Mosher, J., Miller, M., White, D., Miller, G., 2004. Piloting of the

beneficiation and EPAL circuits for Ravensthorpe Nickel Operations. In: Imrie, W.P., et

al. (Ed.), Proceedings, International Laterite Nickel Symposium. The Minerals, Metals

and Materials Society, pp. 193202.

Agatzini-Leonardou, S., Dimaki, D., 1994. Heap leaching of poor nickel laterites by

sulphuric acid at ambient temperature. Hydrometallurgy 94, 193-208.

Bouffard, S.C., 2008. Agglomeration for heap leaching: Equipment design, agglomerate

quality control, and impact on the heap leach process. Minerals Engineering 21 (15),

1115-1125.

Chamberlin, P.D., 1986. Agglomeration: Cheap insurance for good recovery when heap

leaching gold and silver ores. Mining Engineering, 38, 1105-1109.

Dalvi, A.D., Bacon, W.G., Osborne, R.C., 2004. The past and the future of nickel laterites. in

PDAC 2004 International Conference Trade Show and Investors Exchange, Toronto,

Canada.

Dhawan, N., Safarzadeh, M.S., Miller, J.D., Moats, M.S., Rajamani, R.K., 2013. Crushed ore

agglomeration and its control for heap leach operations. Minerals Engineering, 41, 5370.

Dhawan, N., Safarzadeh, M.S., Miller, J.D., Moats, M.S., Rajamani, R.K., Lin, C.L., 2012.

Recent advances in the application of X-ray computed tomography in the analysis of heap

leaching systems. Minerals Engineering, 35, 7586.

Elias, M., 2002. Nickel laterite deposits Geological overview, resources and exploitation.

in: David, R.C., June, P. (Eds.), Giant ore Deposits: Characteristics, Genesis and

Exploration. Codes Special Publication, vol. 4, pp. 205220.

Eliot,A., Fletcher, H., Li, J., Watling, H., Robinson, D.J., 2009. Heap leaching of nickel

laterites-a challenge and an opportunity. in Proceedings of Hydrometallurgy of Nickel

and Cobalt 2009, edited by J.J. Budac, R. Frazer, R. Mihaylov, L. Papangelakis and D.J.

Robinson, CIM, Montreal, Canada, (2009) pp. 537-552.

Gleeson, S.A., Butt, C.R.M., and Elias, M., 2003. Nickel laterites, a review. SEG Newsletter,

54, 1118.

Hernandez, R., Schlitt, W.J., Lopez, M.E., 2003. The El Abra run of mine leach testwork

program. In: Proceedings of Copper 2003, 5th International Conference. Leaching and

Process Development, vol. VI, November 30December 03, Santiago, pp. 1329.

ACCE

PTED

MAN

USCR

IPT

ACCEPTED MANUSCRIPT

15

Hiramatsu, Y.O., 1966. Determination of the tensile strength of rock by a compression test of

an irregular test piece. International Journal of Rock Mechanics and Mining Society, 3,

89-99.

Hunter, H.M.A., Herrington, R.J., Oxley E.A., 2013. Examining Ni-laterite leach mineralogy

& chemistry a holistic multi-scale approach. Minerals Engineering, 54, 100109.

Kyle, J., 2010. Nickel laterite processing technologieswhere to next? ALTA Nickel/Cobalt/

Copper Conference, 2427 May, Perth, Western Australia (pp. 36).

Lewandowski, K.A., Kawatra, S.K., 2008. Development of experimental procedures to

analyze copper agglomerate stability. Minerals & Metallurgical Processing, 28 (2), 110-

116.

Lewandowski, K.A., Kawatra, S.K., 2009. Effect of agglomeration binders on the copper

solvent extraction process. Minerals and Metallurgical Processing 26 (3), 121126.

McDonald, R.G., Whittington, B.I., 2008. Atmospheric acid leaching of nickel laterites

review Part I. Sulphuric acid technologies. Hydrometallurgy, 91, 35-55.

Miller, G., 2000. Pilot plant testwork and design of the Ravensthorpe beneficiation plant.

Proceedings, Ni/Co ALTA conference (17 pp.).

Miller, G.W., Sampson, D., Fleay, J., Conway-Mortimer, J., Roche, E., 2004. Ravensthorpe

Nickel Project beneficiation prediction MLR and interpretation of results. In: Imrie, W.P.

(Ed.), Proceedings, International Laterite Nickel Symposium. The Minerals, Metals and

Materials Society, pp. 121136.

Miller, J.D., Lin, C.L., 1990. High resolution X-ray micro CT (HRXMT) - advances in 3D

particle characterization for mineral processing operations, International Seminar on

Mineral Processing Technology (MPT-2009), Bhubaneswar, India, 2009.

Mudd, G.M., 2010. Global trends and environmental issues in nickel mining: Sulfides versus

laterites. Ore Geology Reviews, 38, 9-26.

Nosrati, A., Addai-Mensah, J., Robinson, D.J., 2012a. Drum agglomeration behaviour of

nickel laterite ore: effect of process variables. Hydrometallurgy, 125-126, 90-99.

Nosrati, A., Skinner, W., Robinson, D.J., Addai-Mensah, J., 2012b. Microstructure analysis

of Ni laterite agglomerates for enhanced heap leaching. Powder Technology, 232, 106-

112.

Nosrati, A., Robinson, D.J., Addai-Mensah, J., 2012c. Establishing nickel laterite

agglomerate structure and properties for enhanced heap leaching. Hydrometallurgy 134-

135, 6673.

ACCE

PTED

MAN

USCR

IPT

ACCEPTED MANUSCRIPT

16

Oxley, A., Sirvanci, N. and Purkiss, S., 2007. Caldag nickel laterite atmospheric heap leach

project. Metalurgija Journal of Metallurgy, 13 (1), 5-10.

Quast, K., Xu, D., Skinner, W., Nosrati, A., Hilder, T., Robinson, D.J., Addai-Mensah, J.,

2013. Column leaching of nickel laterite agglomerates: Effect of feed size.

Hydrometallurgy, 134-135, 144-149.

Readett, D.J., Fox, J., 2009. Development of heap leaching at its integration into the Murrin

Murrin operations. in Proceedings ALTA Nickel Cobalt Conference 2009, Perth.

Readett, D.J., Fox, J., 2010. Commercialisation of heap leaching at Murrin Murrin

operations. XXV International Mineral Processing Congress 2010 Proceedings, Brisbane,

QLD, Australia.

Robertson, S.W., van Staden, P.J., 2009. The progression of metallurgical testwork during

heap leach design. Hydrometallurgical Conference 2009, Southern African Institute of

Mining and Metallurgy, pp. 31-42.

Stamboliadis, E., Alevizos, G., Zafiratos, J., 2004. Leaching residue of nickeliferous laterites

as a source of iron concentrate. Miner. Eng. 17, 245252.

Steemson, M.L., Smith, M.E., 2009. The development of nickel laterite heap leaching

projects. Proceedings of ALTA 2009 Nickel/Cobalt Conference, ALTA Metallurgical

Services, Perth, Australia, May 2009.

Sudol, S., 2005. The thunder from down under: everything you wanted to know about

laterites but were afraid to ask. Canadian Mining Journal. 126 (5), 8-12.

Swierczek, Z., Quast, K., Addai-Mensah, J., Connor, J., Li, J., Robinson, D.J., 2011.

Mineralogical characterisation of a sample of an Australian nickel laterite. in Proceedings

of CHEMECA 2011, (Engineering a Better World), Sydney, 18-21 September, 2011.

Swierczek, Z., Quast, K., Addai-Mensah, J., Connor, J., Li, J., Robinson, D.J., 2012.

Challenges in the mineralogical characterisation of low-grade nickel laterites. in

Proceedings of XXVI International Mineral Processing Congress, New Delhi, India, pp.

5352-5364, September 2012

Tong, T., Klein, B., Zanin, M., Quast, K., Skinner, W., Addai-Mensah, J., Robinson, D.J.,

2013. Stirred milling kinetics of siliceous goethitic laterite for selective comminution.

Minerals Engineering, 49, 109-115.

Watling, H.R., Elliot, A.D., Fletcher, H.M., Robinson, D.J., Sully, D.M., 2011. Ore

mineralogy of nickel laterites: controls on processing characteristics under simulated

heap-leach conditions. Australian Journal of Earth Sciences, 58 (7), 725-744.

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Watling, H., Das, G., Elliot, A., Li, J., McDonald, R., Robinson, D., 2010. Process options

for difficult arid-region nickel laterites. Proceedings, XXV International Mineral

Processing Congress, Brisbane, Australia, September, pp. 417427.

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.