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| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
1 The Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University of Technology, GPO Box U 1987, Perth, Western Australia 6845, Australia
2 CSIRO Minerals (The Parker Centre), PO Box 7229, Karawara, Perth, Western Australia 6152, Australia
Correspondence: * E-mail: N.Timms{at}curtin.edu.au
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ABSTRACT |
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 Top Abstract IntroductionExperimental methodsResultsDiscussionAcknowledgmentsReferences cited |
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Key Words: Scale • microstructure • defects • mineral • growth • jarosite
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INTRODUCTION |
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TopAbstractIntroductionExperimental methodsResultsDiscussionAcknowledgmentsReferences cited |
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). The resultant supersaturated leachate brings about the build up of mineral scale inside autoclaves. The build up of scale on the autoclave walls and stirring rods (agitators) decreases the processing efficiency of the autoclaves, and removal of scale (descaling) is a laborious hydraulic process that involves temporary plant closure and loss of production, and as such is very costly. Scale represents a significant industrial problem for HiPAL plants (Whittington and Muir 2000). For example, a five- to seven-day monthly shutdown for descaling purposes was required at the Moa Bay operation, Cuba (Queneau et al. 1984). Previous investigations of HiPAL scale have focused on the effects of pressure, temperature, pH, and additives on the mineral chemistry, phase stability, and deposition rate of HiPAL scale (Johnson et al. 2005; Papangelakis et al. 1994; Scarlett et al. 2008; Whittington 2000; Whittington et al. 2003a, 2003b). These studies indicate that the scale consists of relatively resistant "growth" scale, formed predominantly by the precipitation of minerals on autoclave walls and agitator substrates, rather than "settling" scale, which is more porous and easier to remove. Consequently, it is important to understand processes of scale growth mechanisms to devise scale growth inhibitor solutions that prevent or reduce the growth of the scales, control autoclave conditions to alter the physical characteristics (e.g., hardness, toughness, or bonding) of the scales to make them easier to physically remove, and provide alternative descaling agents (similar to the use of ferric solutions for oxalate scales in the alumina industry).
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Crystal chemistry and structure of jarosite-alunite family minerals
The chemistry of the jarosite-alunite mineral supergroup is defined by the general formula AB3(TO4)2(OH, H2O)6, and is primarily subdivided based on the solid-solution series in which Fe3+ and Al3+ are substituted into the B site of alunite (Al3+ > Fe3+) and jarosite (Fe3+ > Al3+), TO4 is dominated (>75 mol %) by SO4, and A = K+ (Jambor 1999). Other common substitutions at A include Na+, Pb+, NH4+, and H3O+ and give rise to jarosite-alunite group minerals with the prefixes of natro-, plumbo-, ammonio-, and hydronium respectively. Other crystallochemical substitutions common in mine-waste environments at A can include Ca, Cr, Cd, Cu, Zn, As, and rare earth elements (REE) (Dutrizac and Jambor 2000; Smith et al. 2006). Members of the jarosite-alunite family are isomorphous and consist of corner-linked Al(Fe)O2(OH)4 octahedra and SO4 tetrahedra, and have R
m (trigonal) symmetry. Ionic substitutions that define the common end-member compositions lead to variations in the length of unit-cell parameters with a range in a and c of 7.288–7.356 and 16.55–17.69 Å, respectively (Dutrizac and Jambor 2000; Stoffregen et al. 2000). The crystal form of jarosite is usually dominated by the growth of pseudocubic, dipole-free {01
2} rhombohedral, and less commonly, {0001} basal pinacoid crystal faces (Becker and Gasharova 2001; Gasharova et al. 2005). Synthetic K-dominant jarosite has dominance of {012} rhombohedral faces, whereas {0001} basal pinacoids tend to dominate terminations of K-dominant jarosite from mine-waste dumps (Gasharova et al. 2005).
Scale development at the Bulong processing plant, Western Australia
In this study, a scale sample from an autoclave agitator from the Bulong nickel processing plant, 20 km east of Kalgoorlie, Western Australia, was examined. An example of a typical Bulong nickel laterite ore consists of ~49% nontronite [Na0.3Fe23+Si3AlO10 (OH)2·4(H2O)], ~23% goethite [Fe3+O(OH)], ~15% serpentine group minerals [(Mg, Fe, Ni, Al, Zn, Mn)2–3(Si, Al, Fe)2O5(OH)4], ~9% iron oxides (maghemite, Fe23+O3), and ~2% quartz (SiO2) (Czerny and Whittington 2000; Whittington et al. 2003a). The walls of HiPAL autoclaves at Bulong are fabricated from steel with an internal cladding of 8 mm thick ASTM Grade 17 titanium alloy (240 MPa minimum tensile strength titanium + 0.05% Pd) (Banker 1999), and stirring rods (agitators) are manufactured from ASTM Grade 7 titanium alloy (345 MPa minimum tensile strength titanium + 0.115% Pd).
The scale sample formed at ~250 °C using hypersaline process water over a period of 122 h, which translates to a growth rate of ~72–170 mm/year (Whittington and Muir 2000). Mineralogically similar scale developed on the walls and agitators throughout the autoclave at the Bulong plant, but varies in thickness and with jarosite composition throughout the different compartments of the autoclave. The scale from the Bulong autoclave predominantly consists of large (~200 µm diameter) jarosite-alunite grains (~99%) with minor hematite (Fe23+O3) and amorphous silica (SiO2) (Whittington 2000). Previous analyses of the scale from the Bulong autoclave by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) show fluctuations in the Fe and Al composition of jarosite with Al/(Al + Fe) ranging from 0.6 to 0.8 throughout the thickness of the scale, with an average composition of Na0.91K0.04H3O0.05(Al1.15Fe1.85)(SO4)2(OH)6, (i.e., natrojarosite) with minor Cr and Si (Whittington 2000; Whittington and Muir 2000). There is no particular trend in Fe/Al compositional changes over time, and variations are manifest as fine-scale oscillatory compositional zoning that can be resolved by atomic number contrast (ANC) imaging (also known as backscatter electron, or BSE imaging) in the scanning electron microscope (Whittington and Muir 2000). Fluctuations in natrojarosite chemistry have been attributed to small variations in liquor acidity and relative supersaturation of Al and Fe at the scale-liquor interface that forms over timescales of 20 to 40 min (Whittington 2000).
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EXPERIMENTAL METHODS |
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TopAbstractIntroductionExperimental methodsResultsDiscussionAcknowledgmentsReferences cited |
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Instrumentation
ANC imaging, orientation contrast imaging (Lloyd 1987), and EBSD mapping (Prior et al. 1999) were carried out using a Philips XL30 SEM fitted with a Nordlys I detector and HKL Technologies EBSD system at the Electron Microscopy Facility, Curtin University, a node of the state-funded Nanoscale-Characterization Centre, Western Australia. ANC images were acquired with a pole piece detector using a 30 kV beam, spot 5 (<1 µm), and a working distance of 5 mm. Orientation contrast images were collected with 20 kV beam, spot size 5, a working distance of 20 mm, and sample tilt of 70°.
Electron backscatter diffraction analysis of jarosite
Several EBSD maps were collected from different positions within the scale. Acquisition settings for EBSD analyses are given in Table 1. All EBSD data were acquired and processed using Oxford Instruments Channel 5 (SP9) software. EBSD is a technique that relies on a comparison of an empirically obtained electron diffraction pattern (EBSP) with theoretical reflector files, or "match unit," to constrain the orientation of a crystalline material at the point at which the diffraction pattern is generated (for details see Reddy et al. 2008). In this study, reflector files of 50–80 kikuchi bands for hexagonal (Laue group = 7) jarosite were created using kinematical structure factor calculations undertaken with Oxford Instruments Channel 5 Twist software. Structure parameters needed for these calculations were obtained from the crystallographic data of Menchetti and Sabelli (1976) (unit-cell parameters of a = 7.3150 Å; c = 17.2240 Å). Electron backscatter patterns were indexed using the strongest 5–7 reflectors, and the quality of fit of indexing solutions have an average "mean angular deviation" (MAD) of <0.75°, indicating a good fit (Table 1; Fig. 2). The variations in the Al/Fe ratio did not influence the EBSD pattern quality (band contrast, band slope), or lead to variations in EBSD indexing properties, indicating that a single match unit was suitable for the range in natrojarosite compositions present.
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01}, and 90° ± 5° around (0
21) and (101). Grains were defined based on a minimum grain boundary misorientation angle of 15°, which corresponds to the maximum value of non-random correlated misorientations between neighboring pixels (i.e., subgrain boundaries). The minimum grain diameter cutoff for crystallographic preferred orientation analysis was 6 µm (i.e., three times step size) to avoid representation of misindexed points. Grain sizes were calculated using an ellipse fitting routine within Tango. Cumulative misorientation maps of individual grains were produced using the Channel 5 "texture" component in which each pixel is colored for minimum misorientation relative to a user-defined reference orientation. Low-angle boundaries were represented as solid lines between pixels on the cumulative misorientation map using the Tango module of the Channel 5 software.
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RESULTS |
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TopAbstractIntroductionExperimental methodsResultsDiscussionAcknowledgmentsReferences cited |
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). Hematite also occurs as cuboid grains of approximately 10 µm in diameter (Fig. 3e). The thickness of individual layers varies from 10–200 µm (Fig. 3). Trails of micro-pores occur along compositional interfaces seen in ANC imaging, and are regularly spaced approximately 500 µm throughout the thickness of the scale.
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2} crystal terminations defined by compositional zoning bands is observed throughout the scale (Fig. 3
). Compositional zoning defines elongate grains ~100 µm wide (Fig. 3). EBSD analysis confirms that large elongate grains defined by high-angle (>15°) orientation boundaries contain continuous crystal forms. The long axes of the grains are aligned at high angles to the agitator substrate, and have irregular margins (Fig. 4ii). The long axes of the large grains are locally oblique to the substrate, but they do not have a consistent asymmetry at the scale of the whole sample. Some of the grain boundaries are ornamented by trails of micro-pores and secondary phases (Fig. 3b).
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). Data from each individual map define local point maxima in {0001}, but the combined data set shows that, over a broad region of scale, the {0001} poles are distributed along a great circle that is parallel to the agitator surface. None of the areas show a CPO in {010} or {100}.
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). The grains are polygonized into orientation domains (subgrains) that are typically 10 µm in diameter. The subgrain structure is illustrated by an EBSD band contrast map, where localized bands of low band contrast correspond to orientation boundaries (Fig. 4i). The scale also contains heterogeneously distributed patches of small (<10 µm) subgrains with significantly lower band contrast that could not be indexed. All of the mapped areas preserve similar subgrain microstructure, with no significant differences between them.
Misorientation analysis shows that the relative frequency of low-angle (<15°) correlated misorientations greatly exceeds that of a random distribution, consistent with the observed substructure within large natrojarosite grains (Fig. 6). This translates to boundary line lengths per unit area of 1.36 x 10–1 µm and 6.95 x 10–2 µm for 1–5° and 5–15° boundaries, respectively, which compares to 5.18 x 10–2 µm for higher-angle (15–90°) grain boundaries. This illustrates that subgrain boundaries constitute a significant proportion of the scale microstructure. Individual grains cumulatively accommodate up to 40° misorientation via low-angle boundaries (Fig. 7). This is shown by complex dispersion patterns of crystallographic poles that have many dispersion axes (Fig. 7ii), and supported by analysis of low-angle misorientation axes, which show complex distributions within single grains (Fig. 7iii).
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DISCUSSION |
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TopAbstractIntroductionExperimental methodsResultsDiscussionAcknowledgmentsReferences cited |
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). The preservation of euhedral grain termination indicates that precipitation of natrojarosite occurred by progressive accumulation on well-defined crystal faces of grains seeded with a spacing on the order of 50 µm. The cause of compositional variations during growth could include localized temporal fluctuations in pressure, temperature, or the composition of the slurry within the autoclave (Whittington 2000). The irregular lateral morphology of the "large" natrojarosite grains defined by high-angle grain boundaries resembles textures predicted from simulations of competitive unitaxial grain growth and impingement into fluid-filled veins (Bons 2001; Nollet et al. 2005; Urai et al. 1991), and the precipitation of evaporites (Spencer 2000; Warren 1982).
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). This is a natural consequence of self-organization of the free-growth of prismatic minerals, and does not necessarily require epitaxial seeding of aligned grains on a substrate or reflect the substrate roughness. The role and potential importance of the agitator interface on scale seeding requires microstructural characterization of a contiguous section of substrate and scale, which is currently unavailable.
The distribution of secondary phases and micro-porosity
Secondary phases such as iron oxide preferentially occur as small grains that are localized along the natrojarosite grain boundaries. These grains typically occur as isolated, randomly orientated cubic forms in topographic lows between protruding natrojarosite crystal terminations on the scale surface. They are interpreted to have accumulated on the scale surface from suspension in the slurry and subsequently passively overgrown by further precipitation of natrojarosite, rather than nucleated and grown on the scale. It is unclear why micro-pores also tend to be concentrated along natrojarosite grain boundaries. Layers of micro-pores that formed parallel to compositional zoning formed during growth could be due to changes in the local physico-chemical environment (i.e., temperature, pressure, and/or local chemical environment) at the scale-slurry interface.
Interpretation of the intragrain low-angle boundary microstructure
The low-angle boundaries in the natrojarosite grains are interpreted to be extended defect structures related to dislocations rather than fragmentation via brittle processes. The orientation relationships between the subgrains are complex and cannot have resulted from simple twin relationships or dislocation slip by a few low-index slip systems. They most probably resulted from mixed populations of different dislocation slip systems, or high index systems that cannot be resolved with the data. The formation of such microstructures is not predicted by simple "conventional" models of mineral precipitation from a fluid, such as in veins (Bons 2001; Nollet et al. 2005; Urai et al. 1991) or evaporate deposits (Spencer 2000; Warren 1982), and can be explained by two alternative models: post-growth deformation-related strain via dislocation creep, or coeval grain growth and subgrain formation.
This progressive crystallographic distortion of grains with subgrain microstructure is consistent with materials that contain low-angle boundaries as a result of dislocation creep (e.g., Bestmann et al. 2008; Brenker et al. 2002; Reddy et al. 2007; Trépied et al. 1980; Toy et al. 2008). However, deformation by dislocation creep requires shear stress. If the scale was subject to shear stress due to friction and viscosity of the leachate slurry, then the large grains would be re-oriented with consistent obliqueness to the agitator substrate, and possibly with a consistent preferred shape orientation of the subgrains. However, these relationships are not observed across the sample. Furthermore, strain partitioning during post-growth shear deformation would most likely result in strain gradients throughout the thickness of the scale, possibly with high strain zones located at the agitator-scale and scale-slurry interfaces. These relationships are not observed, and intragrain "strain" appears to be homogeneous throughout the scale.
The fact that subgrain boundaries transect the compositional layering cannot necessarily be used as relative timing criteria to distinguish between syn-growth and post-growth formation. It is possible that defects such as stacking faults, impurities, and screw dislocations could nucleate at the crystal interface, which could then seed extended defects that would propagate during subsequent grain growth. It has been shown elsewhere that even normal grain growth during static annealing can be accompanied by propagation of pre-existing low-angle boundaries (Bestmann et al. 2005; Haddad et al. 2006). If the scale has grown in this way, then the similarity of the scale microstructure throughout the thickness of the scale suggests that no particular changes in growth style occurred as the layers accumulated.
Implications
Extended crystal defects, such as low angle boundaries, have higher stored strain energies than perfect crystal volumes. This may lead to enhanced surface reactivity, as indicated by enhanced dissolution and interface reaction kinetics (Lasaga and Luttge 2001; Morse and Arvidson 2002). It has been shown that the solubility of jarosite is preferentially increased at extended defects such as screw dislocations at crystal interfaces (Gasharova et al. 2005). A potential avenue for the development of scale-removal technologies or scale growth inhibitors is via solutions that exploit the enhanced reactivity of the defect-rich scale.
The development of extended defects during the growth of jarosite has previously been considered to be of much lower volumetric importance than our data suggests (Whittington 2000). The possibility that the development of low-angle boundaries could be a consequence of primary crystallization properties without the need for post-growth deformation has potential implications for the interpretation of sulfate mineral precipitation textures from other environments, such as acid mine drainage, or evaporite deposits. It has been shown in other materials that orientation boundaries are sites of preferential segregation of impurity ions that modify the local bonding environment (Buban et al. 2006). If this applies to jarosite, then growth-related low-angle boundaries could be a sink for impurities in sulfate precipitates that has previously been unrecognized or overlooked, with implications for the development of precipitates as a waste repository for toxic elements. However, if the jarosite subgrain structure detailed in this study is typical of the precipitation of jarosite in other environments, then our results have potential implications for the chemical and physical stability of sulfate waste produced by the metallurgical extractive industry (Dutrizac and Jambor 2000; Ribet et al. 1995), and for the reactivity of precipitates formed by acid mine drainage (Rose and Elliott 2000).
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ACKNOWLEDGMENTS |
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TopAbstractIntroductionExperimental methodsResultsDiscussionAcknowledgmentsReferences cited |
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Footnotes |
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MANUSCRIPT RECEIVED October 5, 2008; MANUSCRIPT ACCEPTED March 30, 2009
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REFERENCES CITED |
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TopAbstractIntroductionExperimental methodsResultsDiscussionAcknowledgmentsReferences cited |
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Banker, J.G. (1999) Titanium/steel explosion bonded clad for autoclaves and vessels. ALTA 1999 Nickel/Cobalt Pressure Leaching and Hydrometallurgy Forum, ALTA Metalurgical Services, Melbourne.
Becker, U. and Gasharova, B. (2001) AFM observations and simulations of jarosite growth at the molecular scale; probing the basis for the incorporation of foreign ions into jarosite as a storage mineral. Physics and Chemistry of Minerals, 28, 545–556.[CrossRef][Web of Science][GeoRef]
Bestmann, M., Piazolo, S., Spiers, C.J., and Prior, D.J. (2005) Microstructural evolution during initial stages of static recovery and recrystallization; new insights from in-situ heating experiments combined with electron backscatter diffraction analysis. Journal of Structural Geology, 27, 447–457.[CrossRef][Web of Science][GeoRef]
Bestmann, M., Habler, G., Heidelbach, F., and Thöni, M. (2008) Dynamic recrystallization of garnet and related diffusion processes. Journal of Structural Geology, 30, 777–790.[CrossRef][Web of Science][GeoRef]
Bons, A.-J. and Bons, P.D. (2003) The development of oblique preferred orientations in zeolite films and membranes. Microporous and Mesoporous Materials, 62, 9–16.
Bons, P.D. (2001) Development of crystal morphology during unitaxial growth in a progressively widening vein; I. The numerical model. Journal of Structural Geology, 23, 865–872.[CrossRef][Web of Science][GeoRef]
Brenker, F.E., Prior, D.J., and Müller, W.F. (2002) Cation ordering in omphacite and effect on deformation mechanism and lattice preferred orientation (LPO). Journal of Structural Geology, 24, 1991–2005.[CrossRef][Web of Science][GeoRef]
Buban, J.P., Matsunaga, K., Chen, J., Shibata, N., Ching, W.Y., Yamamoto, T., and Ikuhara, Y. (2006) Grain boundary strengthening in alumina by rare earth impurities. Science, 311, 212–215.
Czerny, C. and Whittington, B.I. (2000) Scale formation in the pressure acid leach process. ALTA 1999 Nickel/Cobalt Pressure Leaching and Hydrometalurgy Forum, ALTA Metallurgical Services, Melbourne.
Dutrizac, J.E. and Jambor, J.L. (2000) Jarosites and their application in hydrometallurgy. In C.N. Alpers, J.L. Jambor, and D.K. Nordstrom, Eds., Sulfate minerals—Crystallography, Geochemistry, and Environmental Significance, 40, p. 405–452. Reviews in Mineralogy and Geochemistry, Minerological Society of America, Chantilly, Virginia.
Elias, M. (2002) Nickel laterite deposits—geological overview, resources and exploration. CODES Special Publication, 4, 205–220.
Gasharova, B., Goettlicher, J., and Becker, U. (2005) Dissolution at the surface of jarosite; an in situ AFM study. Chemical Geology, 215, 499–516.[CrossRef][Web of Science][GeoRef]
Haddad, S.C., Worden, R.H., Prior, D.J., and Smalley, P.C. (2006) Quartz cement in the Fontainebleau Sandstone, Paris Basin, France: Crystallography and implications for mechanisms of cement growth. Journal of Sedimentary Research, 76, 244–256.
Jambor, J.L. (1999) Nomenclature of the alunite supergroup. Canadian Mineralogist, 37, 1323–1341.[Web of Science]
Johnson, J.A., McDonald, R.G., Muir, D.M., and Tranne, J.P. (2005) Pressure acid leaching of arid-region nickel laterite ore: Part IV: Effect of acid loading and additives with nontronite ores. Hydrometallurgy, 78, 264–270.[CrossRef][Web of Science]
Lasaga, A.C. and Luttge, A. (2001) Variation of crystal dissolution rate based on a dissolution stepwave model. Science, 291, 2400–2404.
Lloyd, G.E. (1987) Atomic number and crystallographic contrast images with the SEM: A review of backscattered electron techniques. Mineralogical Magazine, 51, 3–19.[CrossRef][Web of Science]
Menchetti, S. and Sabelli, C. (1976) Crystal chemistry of the alunite series; crystal structure refinement of alunite and synthetic jarosite. Neues Jahrbuch für Mineralogie, Monatshefte, 406–417.
Morse, J.W. and Arvidson, R.S. (2002) The dissolution kinetics of major sedimentary carbonate minerals. Earth Science Reviews, 58, 51–84.[CrossRef][Web of Science]
Nollet, S., Urai, J.L., Bons, P.D., and Hilgers, C. (2005) Numerical simulations of polycrystal growth in veins. Journal of Structural Geology, 27, 217–230.[CrossRef][Web of Science][GeoRef]
Papangelakis, V.G., Blakey, B.C., and Kambossos, J. (1994) Behaviour of aluminium during direct acid leaching of limonitic laterites. In B. Harris and E. Krause, Eds., Impurity Control and Disposal in Hydrometallurgical Processes, p. 315–325. Proceedings of the 24th Annual Hydrometallurgical Meeting, CIM, Toronto.
Prior, D.J., Boyle, A.P., Brenker, F., Cheadle, M.C., Day, A., Lopez, G., Peruzzo, L., Potts, G.J., Reddy, S., Spiess, R., Timms, N.E., Trimby, P., Wheeler, J., and Zetterström, L. (1999) The application of electron backscatter diffraction and orientation contrast imaging in the SEM to textural problems in rocks. American Mineralogist, 84, 1741–1759.[Abstract][Web of Science][GeoRef]
Queneau, P., Doane, R., Cooperrider, M., Berggren, M., and Rey, P. (1984) Control of autoclave scaling during acid pressure leaching of nickeliferous laterite ore. Metallurgical and Materials Transactions B, 15, 433–440.
Reddy, S.M., Timms, N.E., Pantleon, W., and Trimby, T. (2007) Quantitative characterization of plastic deformation of zircon and geological implications. Contributions to Mineralogy and Petrology, 153, 625–645.[CrossRef][Web of Science]
Reddy, S.M., Timms, N.E., and Eglington, B.M. (2008) Electron backscatter diffraction analysis of zircon: A systematic assessment of match unit characteristics and pattern indexing optimization. American Mineralogist, 93, 187–197.
Ribet, I., Ptacek, C.J., Blowes, D.W., and Jambor, J.L. (1995) The potential for metal release by reductive dissolution of weathered mine tailings. Journal of Contaminant Hydrology, 17, 239–273.[CrossRef][Web of Science][GeoRef]
Rose, S. and Elliott, W.C. (2000) The effects of pH regulation upon the release of sulfate from ferric precipitates formed in acid mine drainage. Applied Geochemistry, 15, 27–34.[CrossRef][Web of Science][GeoRef]
Scarlett, N.V.Y., Madsen, I.C., and Whittington, B.I. (2008) Time-resolved diffraction studies into the pressure acid leaching of nickel laterite ores: A comparison of laboratory and synchrotron X-ray experiments. Journal of Applied Crystallography, 41, 572–583.[CrossRef][Web of Science]
Smith, A.M.L., Hudson-Edwards, K.A., Dubbin, W.E., and Wright, K. (2006) Dissolution of jarosite [KFe3(SO4)2(OH)6] at pH 2 and 8; Insights from batch experiments and computational modelling. Geochimica et Cosmochimica Acta, 70, 608–621.[CrossRef][Web of Science][GeoRef]
Spencer, R.J. (2000) Sulfate minerals in evaporite deposits. In C.N. Alpers, J.L. Jambor, and D.K. Nordstrom, Eds., Sulfate Minerals—Crystallography, Geochemistry, and Environmental Significance, 40, p. 173–192. Reviews in Mineralogy and Geochemistry, Minerological Society of America, Chantilly, Virginia.
Stoffregen, R.E., Alpers, C.N., and Jambor, J.L. (2000) Alunite-jarosite crystallography, thermodynamics, and geochronology. In C.N. Alpers, J.L. Jambor, and D.K. Nordstrom, Eds., Sulfate Minerals—Crystallography, Geochemistry, and Environmental Significance, 40, p. 453–479. Reviews in Mineralogy and Geochemistry, Minerological Society of America, Chantilly, Virginia.
Trépied, L., Doukan, J.C., and Paquet, J. (1980) Subgrain boundaries in quartz theoretical analysis and microscopic observations. Physics and Chemistry of Minerals, 5, 201–218.[Web of Science][GeoRef]
Toy, V.G., Prior, D.J., and Norris, R.J. (2008) Quartz fabrics in the Alpine Fault mylonites: Influence of pre-existing preferred orientations on fabric development during progressive uplift. Journal of Structural Geology, 30, 602–621.[GeoRef]
Urai, J.L., Williams, P.F., and van Roermund, H.L.M. (1991) Kinematics of crystal growth in syntectonic fibrous veins. Journal of Structural Geology, 13, 823–836.[CrossRef][Web of Science][GeoRef]
Warren, J.K. (1982) The hydrological setting, occurrence and significance of gypsum in late Quaternary salt lakes in South Australia. Sedimentology, 29, 609–637.[CrossRef][Web of Science][GeoRef]
Whittington, B.I. (2000) Characterization of scales obtained during continuous nickel laterite pilot-plant leaching. Metallurgical and Materials Transactions B, 31, 1175–1186.[CrossRef]
Whittington, B.I. and Muir, D. (2000) Pressure acid leaching of nickel laterites: A review. Mineral Processing and Extractive Metallurgy Review, 21, 527–599.[CrossRef]
Whittington, B.I., Johnson, J.A., Quan, L.P., McDonald, R.G., and Muir, D.M. (2003a) Pressure acid leaching of arid-region nickel laterite ore: Part II. Effect of ore type. Hydrometallurgy, 70, 47–62.[Web of Science][GeoRef]
Whittington, B.I., McDonald, R.G., Johnson, J.A., and Muir, D.M. (2003b) Pressure acid leaching of arid-region nickel laterite ore: Part I. effect of water quality. Hydrometallurgy, 70, 31–46.[Web of Science][GeoRef]
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