International Journal of Mineral Processing 125 (2013) 149–156
Contents lists available at ScienceDirect
International Journal of Mineral Processing
j ourna l homepage: www.e lsev ie r .com/ locate / i jm inpro
The effect of phyllosilicate minerals on mineral processing industry
Bulelwa Ndlovu, Saeed Farrokhpay ⁎, Dee BradshawJulius Kruttschnitt Mineral Research Centre, The University of Queensland, 40 Isles Road, Indooroopilly, QLD 4068, Australia
The increased exposure to low grade ores has highlighted the importance of understanding phyllosilicate ganguemineralogy. Theseminerals exist as commongangueminerals andhavebeen shown to present challenges duringore beneficiation, with issues arising throughout the processing circuit. Nonetheless, the industry's understand-ing of the issues and solutions related to these minerals remains poor; a likely result of the gap betweenmineralprocessing and mineralogy. This paper gives a comprehensive description of the phyllosilicate group; classifyingthe minerals according to variations in structure. The typical problems encountered with these minerals arediscussed, with specific reference to industrial operations. The current practices being used tomitigate the effectsof phyllosilicate minerals are also reviewed. This paper provides a better understanding of the effect ofphyllosilicate minerals on mineral processing.
The increased exposure to finely disseminated, low grade ores hashighlighted the importance of understanding gangue mineralogy as ameans to diagnose problems and improve processing in mineral indus-try. The presence of multiple phases of unwanted ganguematerial oftenhinders the liberation of valuable minerals, and ultrafine grinding isthen required to achieve sufficientmineral recovery. Often broadly clas-sified as ‘clays’, phyllosilicate group minerals exist as common ganguecomponents in many low grade ores (e.g. serpentine in Mt. Keith nickelsulphide ore, Western Australia (Senior and Thomas, 2005) and talc inthe Bushvelt Complex, South Africa (Schouwstra et al., 2000)). In thepast, the processing of some of these ores has been problematic; withdifficulties such as reduced production performance, complex tailingstreatment, and pumping challenges arising. However, the industry's
61 7 33655999.y).
ghts reserved.
understanding of the specific effects and potential solutions tophyllosilicate related processing problems remains poor. Research intothe fundamental analysis of the flow behaviour of phyllosilicatemineralsuspensions is an area of growing interest, particularly in the context oflow grade ore beneficiation. Such knowledge would be beneficial to-wards finding long term solutions to the processing problems currentlybeing encountered.
As the most likely products of chemical weathering, hydrothermalalteration and sedimentary deposition, phyllosilicate minerals are com-mon accessory minerals in several mineral deposits including copperporphyrys, nickel laterites, volcanic volatile-rich igneous rocks andcoal deposits. As a result, phyllosilicate minerals are associated withseveral valuable minerals including (but not limited to) copper, nickel,iron, gold and uranium. Therefore, the adverse effects arising from thepresence of phyllosilicate gangue minerals are prevalent throughoutmining and mineral processing industries. This makes the significanceof phyllosilicate gangue mineralogy on the overall processing oflow grade ores seem obvious. Most studies linking mineralogy and
150 B. Ndlovu et al. / International Journal of Mineral Processing 125 (2013) 149–156
metallurgical performance have been limited to ores often creatingan environment that is both difficult to control and quantify. (e.g.Burdukova et al., 2008; Shabalala et al., 2011; Wiese et al., 2007;Jorjani et al., 2011). However, there has been little research aimed atidentifying the specific behaviour of the different phyllosilicatemineralswithin the context of specific unit operations. In fact, this area, is rela-tively new in its application to the mineral processing industry.
Indeed there has been some valuable fundamental research con-ducted on some minerals belonging to the phyllosilicate group; withmost studies limited to kaolinite and montmorillonite (e.g. Cruz et al.,2013). However, most of these studies have been angled towardsother industries such as nanocomposite science, ceramicmanufacturing,cosmetics, paper making and soil decontamination (e.g. Miano andRabaioli, 1994; Dai and Huang, 1999; Gier and Johns, 2000; Plotzeet al., 2003; Banfill et al., 2009; Viseras et al., 2010; Duman et al.,2012). In those applications, the key issues are not necessarily thesame points of interest as pertained to the mineral processing context.However, research in these fields has been foundational in identifyingthe asymmetric particle shape, colloidal particle size and anisotropicsurface charge properties as the key factors proven to be useful to the re-spective industries (Rand andMelton, 1977; James andWilliams, 1982;Vali and Bachmann, 1988; Scales et al., 1990; Permien and Lagaly, 1994;Johnson et al., 1998; Benna et al., 1999; Luckhamand Rossi, 1999; Lagalyand Zeismer, 2003; Tombácz and Szekeres, 2006; Burdukova et al.,2007).
Some contemporary definitions have categorised ‘clay’ minerals asparticles with sizes less than 20 μm (e.g. Deer et al., 1992; Boggs,2006; Środoń, 2006). At these colloidal particle sizes, surface specificarea is larger and the influence of surface charge is greater. The likeli-hood of entrainment of fine gangue to the concentrate, the formationof slime coatings' poor settling rates and increased residence time arealso enhanced (Arnold and Aplan, 1986). When present in an ore theywill enter the processing circuit because their fine size makes them vir-tually unavoidable.
Phyllosilicate minerals are also characterised by their distinctivenon-spherical particle shapes. Fundamental rheological studies usingsynthetic materials have been beneficial in demonstrating that suspen-sion rheological behaviour becomes increasingly complex with a largerdeviation from spherical morphology (Barnes et al., 1989). Rheologicalcomplexity, in this case, describes the non-Newtonian behaviour expe-rienced by suspensions associated with nonlinear increases in yieldstress and viscosity with increasing solid content. The relevance ofnon-spherical morphology in mineral systems was verified in densemedium separation studies, with suspensions of spherical ferrosiliconparticles, of equivalent slurry density and particle size, exhibitinglower viscosities than irregular shaped magnetite particles (Collinset al., 1974). This difference was attributed to variations in length to di-ameter (L/D) ratios, where non-Newtonian behaviour is more pro-nounced with particles of larger L/D ratios (Horie and Pinder, 1979).
The agglomeration behaviour of phyllosilicate minerals is furthercomplicated by their anisotropic surface charge properties; which re-sults in edges and faces of different charges. The derivation of chargeon these surfaces has been investigated considerably, and is still anarea of much debate. Traditionally, the face surfaces are believed tocarry a permanent structural negative charge due to isomorphous sub-stitution of higher valence ions (e.g. Si4+) with lower valence ions (e.g.Al3+) (Okuda et al., 1969; Zhou and Gunter, 1992; Johnson et al., 2000).However, advances in electrokinetic, streaming potential and directforce measurements have revealed that the basal faces also showionisation trends, not inconsistent with the pH dependent hydrolysisof silicon in the surface plane. This is particularly the case in the pH re-gime 4–8, suggesting the presence of a small amount of pH dependentnegative charge (Scales et al., 1990). The exact contribution to the facecharge of layered silicates due to either isomorphous substitution orionisation is not clearly understood and more detailed research is war-ranted. However, it can generally be assumed that the charging on the
basal plane of phyllosilicateminerals is largely due to isomorphous sub-stitution resulting in a negative charge, whose change with pH may beattributed to the pH dependent ionisation of exposed silanol groupson the surface. The charge derivation on the edges has not been conclu-sively established either, but is thought to be due to the ionisation of ex-posed hydroxyl groups, dependent on solution pH. Therefore, in acidicsolution the edge is expected to carry a positive charge, while in alkalinesolution the edge is negatively charged. It should be noted that the ef-fective surface charge also depends on the ions adsorbed from the solu-tion, which is influenced by the surface charge density and the ionsavailable from the compounds used to adjust the pH.
While there is still much debate over the derivation of charges on thedifferent surfaces, there is common agreement that there is a charge sep-aration between the edges and faces, with the faces carrying a predomi-nantly negative charge while the charge on the edges changes frompositive to negative. This charge heterogeneity results in irregular stack-ing. Although there exist differing schools of thought regarding the prev-alent modes of particle interaction, three main modes have beenidentified, namely; edge–face (EF), edge–edge (EE) and face–face (FF);each with different implications on the suspension flow behaviour(Van Olpen, 1977; Rand and Melton, 1977; James and Williams, 1982;Permien and Lagaly, 1994; Benna et al., 1999; Johnson et al., 2000;Lagaly and Zeismer, 2003; Burdukova et al., 2007; Ndlovu et al., 2011a,b). FF association leads to the formation of lamellar structured aggregates(tactoids) with low yield stress requirements; whilst EF and EE associa-tions lead to three dimensional voluminous ‘house of cards’ structures,which exacerbate the suspension colloidal behaviour and give rise tomore complex colloidal behaviour and processing difficulties (Tombáczand Szekeres, 2006; Gupta et al., 2011). It is likely that these structuresoccur simultaneously in suspension, resulting in ‘heterocoagulated’aggregates.
The prediction of the metallurgical behaviour of phyllosilicate bear-ing ores is often complicated by difficulties in phyllosilicate mineralidentification and characterisation. The mineralogical characterisationof these minerals has been a longstanding challenge. This makes theuse of techniques such as X-ray Diffraction (XRD), which is primarilyconcerned with structural aspects, most suited to the recognition ofstructural groups. However, the differentiation between the componentspecies is often difficult. This is exacerbated by the multiplicity of spec-trawhenmany components are present, aswell as the poor crystallinityand/or small size of crystals. Moreover, extraneous organic carbonatesor iron compounds (cementing agents) often occur and obscurepeaks; resulting in increased peak intensity which is undesirablefor XRD analysis (Brindley and Brown, 1980). The application of aux-iliary techniques such as thermal and acid treatment can be used toresolve some of these problems (Brewster, 1980; Hassellov et al.,2001; Środoń, 2006; Deng et al., 2009). The identification ofphyllosilicate minerals may be best achieved by using a combinationof mineralogical (e.g. XRD, Mossbauer spectroscopy, Mineral Libera-tion Analysis (MLA), Differential Thermal Analysis spectroscopy(DTA)), colloidal (e.g. atomic force microscopy, zeta potential, set-tling tests and rheology) and macroscopic (e.g. gamma ray logging,triaxial shear strength) analytical techniques. However, such a com-prehensive analysis may prove costly.
Kaminsky et al. (2006, 2009) have extensively characterisedclays. While their work was related to oil sands, but their methodcan be also applied for general characterisation and understandingclay minerals. They used X-ray diffraction of oriented clay slidesand random powder samples to quantify the clay minerals in theoil sands ore. They also used transmission electron microscopy lat-tice fringe imaging, and electron diffraction to evaluate the funda-mental particle size of the clay minerals. Kaminsky et al. (2006,2009) have shown that the mean fundamental particle thicknessesof kaolinite and illite in the minus 2 μm fraction are less than10 nm, which would explain the large surface areas reported forthese clays in the literature.
151B. Ndlovu et al. / International Journal of Mineral Processing 125 (2013) 149–156
This paper seeks to provide a better understanding of the differentminerals belonging to the phyllosilicate group. A classification of thephyllosilicate group is given, based on differences in mineralogicalstructure. This will provide clarity on the minerals beyond the scopeof kaolinites and swelling clays, which have been studied extensively.Current practices employed in dealing with these issues are alsooutlined, demonstrating the need for a better fundamental understand-ing of the specific effects of these minerals.
2. Phyllosilicate mineralogy
Phyllosilicate minerals comprise tetrahedral ‘T’ and octahedral ‘O’layers which are the basic building blocks of this group. A tetrahedrallayer consists of silica (SiO4) tetrahedral units.Within eachunit, four ox-ygen atoms are arranged symmetrically around a silicon atom. Succes-sive tetrahedra are held together by shared apical oxygen atoms toform rings of tetrahedral ‘T’ layers. An octahedral unit consists of a cen-tral cation in a six fold co-ordination bonded to six hydroxyl groups,resulting in an octahedral symmetry. These hydroxyl groups are inturn linked to other surrounding metallic atoms. Charge balance ismaintained, dependent on the cation valence in the octahedral unit.When the cations are divalent, brucite (Mg(OH)2)makes up the octahe-dral layer, resulting in the formation of a trioctahedral phyllosilicate. Inthe case of trivalent cations, however, gibbsite (Al(OH)3) forms the ‘O’layer, resulting in dioctahedral phyllosilicate minerals, as shown inFig. 1.
Variations in ‘T’ and ‘O’ layer configurations result in minerals of rel-atively similar structure, but with different physical and chemical prop-erties. Consequently, there have been many different classifications ofphyllosilicate minerals reported in literature (e.g. Brindley and Brown,1980; Dixon and Weed, 1989; Klein and Hurlbut, 1993; Hurlbut andSharp, 1998). The classification used here is in accordance with thephyllosilicate classifications made by Deer et al. (1992) and is shownin Fig. 2. In this case, the phyllosilicate minerals are grouped accordingto the proportion of the tetrahedral and octahedral layers, as wellas the interlayer connections that may occur between successive struc-tural units. This categorises the minerals into serpentinites, talc/pyrophillite, micas, chlorites and clay minerals. The clay minerals canbe further classified into non-swelling (kaolinites and illites), and swell-ing (smectites and vermiculites) clays. Alternative classifications mayincorporate the chlorites into the clay mineral group (e.g. Dixon andWeed, 1989). It is worth noting that there is a distinct difference be-tween clays and clay minerals. Clays are sediments which compriseclay minerals and accessory ‘non-clay’ minerals (Deer et al., 1992;
Fig. 1. (a) SiO4 tetrahedral units and silica ‘T’ layers (b) octahedral (XOAdapted from Klein and Dutrow (2008).
Boggs, 2006) while clay minerals are pure sheet silicates that are re-sponsible for the classic properties of clay, such as plasticity when wetand hardness when dry or heated (Guggenheim and Martin, 1995). Bythis definition, bentonite, for example, is a type of clay which is com-posed mostly of montmorillonite (clay mineral) and will mimic theproperties of montmorillonite, but can include other non-clay mineralsor phyllosilicate minerals (e.g. quartz). The difficulty with clay mineralsstems from their ability to change from one form to another (interstrat-ification), such that they typically comprise alternate layers of otherclays in either ordered and regular or highly unordered and irregular se-quences. In such cases, mineral identification is difficult, as they tend tomask each other.
A summary of the main differences in mineral structure and para-genesis of the different phyllosilicate groups is given in Table 1. Thepolymorphs belonging to each group are given, with examples ofphyllosilicate bearing ores also provided.
The variations in structure result in minerals with different mor-phologies. Indeed most phyllosilicate minerals have a platy morphol-ogy, although the variations in mineral structure affect the degree oflayering, irregularities in stacking behaviour, crystallinity and cleavageof theminerals (Deer et al., 1992). Fig. 3 shows SEM images of differentphyllosilicate minerals. Here, the fibrous morphology of chrysotile (ser-pentine group) is evident (Fig. 3a); a result of convolution of T-O unitsdue to a mismatch in the constituent layers. The platy morphology oftalc (talc/pyrophillite group) and kaolinite (Fig. 3b and e respectively)can also be seen, while the brittle and flaky habit of muscovite (micagroup) and chlorite (chlorites) (Fig. 3c and d) is also presented. Fig. 3fshows the characteristic formation of pores on the surface of montmo-rillonite (smectites group). Montmorillonite particles have a higher in-terlayer swelling potential than vermiculite, primarily due to a lowerlayer charge (0.2–0.5 mol per unit cell) relative to vermiculites (0.6–0.9mol per unit cell) (Brindley and Brown, 1980; Laird, 2006). More-over, isomorphous substitutions in vermiculites occur in the interlayerregion between successive T-O-T layers, where the swelling potentialis limited by the interaction between charge balancing cations and theT sheets. Substitution in smectites such as montmorillonite, on theother hand, occurs in the octahedral sheets, away from the interlayerspacing where balancing cations are present, resulting in relativelylarge interlayer expansion (Abollino et al., 2008). The swelling behav-iour ofmontmorillonite occurs by the formation of pores on themineralsurface; enhancing the absorption of water and resulting in the forma-tion of gels/sols (McBride and Baveye, 2003; Laird, 2006). The limitedswelling potential of vermiculite is evident at temperatures above400 °C. At these conditions, the heat causes the release of structural
6) units and the difference between brucite and gibbsite ‘O’ layers.
Fig. 2. Classification of phyllosilicate group minerals.
152 B. Ndlovu et al. / International Journal of Mineral Processing 125 (2013) 149–156
and absorbed interlayer water as steam. This causes vermiculite parti-cles to exfoliate in aworm-like (vermiculare) or concertina-likemanner(Fig. 3g). The spacing between adjacent plates typically accounts for onewater molecule (Deer et al., 1992), while expansion in montmorillonitecan result in up to three water molecules in the interlayer region (Deeret al., 1992;McFarlane et al., 2005; Pils et al., 2007). Fig. 3h shows a SEMimage of interstratified illite–smectite, associated with kaolinite. This isthe form in which most phyllosilicate minerals exist, resulting in morecomplex mineral systems.
3. Typical processing problems encountered with phyllosilicatebearing ores
In general, the problems associated with phyllosilicate bearing oresare physicochemical, impacting all facets of the mineral processing cir-cuit, with inefficiencies arising during slurry transportation and benefi-ciation through to dewatering and disposal. For example, the ‘sticky’nature of phyllosilicate minerals renders the use of conveyors, idlersand screens difficult; resulting in a significant reduction in pump capac-ity during material handling. Due to their characteristic small particlesizes and high viscosities, phyllosilicate minerals may also result inpreg robbing and restrict percolation during leaching. Tanks are subjectto overflowing because of the insufficient fall on the tanks (Tremoladaet al., 2010; Farrokhpay and Bradshaw, 2012). In comminution, thegrinding efficiency is lowered, making it necessary to operate the millat significantly lower densities (Tangsathitkulchai, 2003). Moreover,an increase in the quantities of fine clay particles in the crushing and
grinding circuits often results in a retardation of the overall grindingprocess, particularlywithin the ultrafine grinding regime, due to viscos-ity effects (Shi and Napier-Munn, 2002). The risk of wall collapse andleakage is also enhanced during the treatment of high phyllosilicatetailings; resulting from their poor dewaterability (de Kretser andBoger, 1992). Table 2 gives a summary of some of the problems typicallyencounteredwhen treating phyllosilicate bearing ores; highlighting theubiquitous effects of these minerals throughout the processing circuit.
Of particular interest is the effect of phyllosilicate minerals on theflotation performance of mineral suspensions. The characteristic highsurface area of phyllosilicate minerals makes them highly reactive andresponsive to changes. It has been observed that the presence of alumi-nosilicate andmagnesium silicateminerals in froth flotation affects per-formance through (i) slime coating on themineral surfaces aswell as airbubbles (Tao et al., 2010), (ii) higher reagant consumption, poorer se-lectivity and impeded flotation kinetics (Connelly, 2011a) (iii) entrain-ment of large quantities to the concentrate during both roughing andscavenging stages (Patra et al., 2010; Vasudevan et al., 2010; Jorjaniet al., 2011) (iv) increasing pulp viscosity (Arnold and Aplan, 1986;Genc et al., 2010) and (v) increasing or decreasing the froth stability(Dippenaar, 1988; Bulatovic, 2007; Farrokhpay, 2011). The exact mech-anisms of clay interactions with other minerals during flotation havenot been clearly identified, but are thought to be largely due to their an-isotropic surface charge properties, high surface area, complex suspen-sion rheology and hydrophobicity effects.
The formation of slime coatings has been attributed to the electro-static attractive forces between minerals and the clay particles of
153B. Ndlovu et al. / International Journal of Mineral Processing 125 (2013) 149–156
opposite surface charges at specific pH conditions (Guidice, 1934;Fuerstenau, 1958; Ralston and Fornasiero, 2006; Tao et al., 2010;Jorjani et al., 2011). It has been postulated that the formation of a coat-ing on air bubbles by the silicates with colloidal particle sizes preventsthe attachment of larger mineral particles (Wen and Sun, 1977). Therole of the fibrousmorphology ofmagnesium silicates such as chrysotilein silicate transportation to the froth phase has also been demonstrated.It is hypothesised that the entrapment of particles by entanglement inthe fibres renders the gangue flotable (Vasudevan et al., 2010; Patraet al., 2010). It has also been previously demonstrated that phyllosilicatemineral suspensions exhibit more complex rheological behaviour thannon-phyllosilicate minerals (Ndlovu et al., 2011a,b; 2013). High pulpviscosities often result in poor gas dispersion, cavern formation, in-creased turbulence damping and bubble coalescence. In the case ofpoor gas dispersion, the small bubbles generated within the vicinity ofthe impellor are not efficiently dispersed throughout the cell by bulkfluid flow, due to the high (apparent) viscosity of the slurry. This is ex-acerbated by the formation of a regionwith yielded fluid (cavern), with-in the vicinity of the impellor, while the rest of the slurry remainsstagnant (Bakker et al., 2009; Shabalala et al., 2011) Flotation kineticsare impeded and may influence the froth stability and mobility(Schubert and Bischofberger, 1978; Bakker et al., 2009; Genc et al.,2010; Farrokhpay, 2012). This is often manifested in the occurrence ofthe ‘flocculation phenomenon’ in the froth zone (Dippenaar, 1988;Bulatovic et al., 1999).
It is worth noting that even with such a broad understanding of theeffects of this class of minerals on process performance, phyllosilicateminerals behave differently and in some cases their behaviour mayvary from ore type to ore type. For example, studies by Hussain et al.,1996 indicated that illite and chlorite reduce coal recovery (28% and20% reduction respectively), while studies in the oil sands industryhave demonstrated that the addition of illite does not have a significanteffect on the bitumen recovery (Kasongo et al., 2000). However, it isthrough its characteristic degradation to smectites and its occurrenceas interstratified illite–smectite that it reduces bitumen recovery(Wallace et al., 2004). Therefore, the effects of these minerals may beore specific. In general, chrysotile has been found to pose a major chal-lenge in the overall processing of many nickel sulphide ores (e.g.Norseman-Wiluna, Western Australia and Jinchuan, Northwest China)by reducing the nickel grade in the concentrate; either by entrainmentas fine liberated particles or by true flotation, as composite hydrophiliccoatings on the negatively charged sulphide particles (Patra et al.,2010; Laskowski et al., 2010). Due to its natural hydrophobicity, talcreadily reports to the flotation concentrate, effectively increasing theviscosity in the froth phase, resulting in a reduction in both grade andrecovery (Becker et al., 2009; Wiese et al., 2010). Large quantities oftalc in the concentrate can cause problems during smelting; oftenresulting in smelting penalties for mineral processing companies(Beattie et al., 2006). It has been found that the flotation of copper por-phyry ores is limited by the presence of aluminosilicates, such as kaolin-ite, vermiculite and muscovite, and can produce concentrates with lowlevels of copper grade and recovery and high levels of alumina and silica(Jorjani et al., 2011). The high alumina content in hematite ores inAustralia has been attributed to the presence of kaolinite, and hasoften been detrimental to the blast furnace and sinter plant operations,due to the prevalence of highly viscous slags and high coke rates (Maet al., 2009).
4. Current mitigation strategies for dealing with phyllosilicatebearing ores
Despite the abundance and adverse effects associated withphyllosilicateminerals, the industry understanding of the processing is-sues, and potential solutions to treating phyllosilicate bearing ores, re-mains poor. In many cases, these problems are simply avoided byeither not processing the ores at all, while some operations opt to run
Fig. 3. (a) Fibrous morphology of chrysotile; (b) Platy morphology of talc (c) flaky, layered structure of mica (muscovite);(d) platy habit of chlorites and (e) kaolinite (Du et al., 2010);(f) gel/sol structure of montmorillonite (g) exfoliated vermiculite and (h) platy morphology of illite.Unpublished data, University of Cape Town, 2008-1011, 2: Glasmann, J. R., Williamette Analytical Geological Services.
154 B. Ndlovu et al. / International Journal of Mineral Processing 125 (2013) 149–156
at significantly lower solid concentrations. Slurry dilution with water isalso frequently used to reduce medium viscosity throughout the circuit(Connelly, 2011b). However, this puts a strain on an increasingly scarceresource, especially since many mines are located in arid or desert re-gions. Indeed some operations have approached the processing prob-lems by finding short term chemical and engineering solutions. Theseinclude the use of viscosity modifiers such as sodium pyrophosphateand caustic soda in stabilising colloidal systems during milling and clas-sification, gold carbon in pulp leaching (CIP) and flotation (Mpofu et al.,2004; McFarlane et al., 2005; Xiao et al., 1999). The application of thesecompounds is suggested to bemainly due to their ability to adsorb ontoclay surfaces, altering the surface chemistry properties of the particlesand inducing electrostatic repulsive forces and disperse systems (Kleinand Pawlik, 2005). However, these phosphate dispersants may not bestable in severe conditions such as low pH or high temperatures. More-over, the physical aspects (morphology), which also contribute towardsclay behaviour, may not necessarily be controlled by the modifiers(Vasudevan et al., 2010).
Engineering solutions include feeding directly to semi-autogeneousmilling (SAG), bypassing crushing and screening to avoid problems of‘sticky’ clays during secondary crushing in the comminution circuit. Inmineral sands operations, the incorporation of hydrosizers upfrontaids the separation of clays from the feed. Similarly, the inclusion ofscrubbers early on is beneficial in clay removal to the tailings dam indense media separation. It is worth noting, however, that the inclusionof such modifications may not necessarily improve recovery andthroughput. This was observed at the Mt. McLure and Mt. Muro plants,
Table 2Typical mineral processing problems experienced during the processing of phyllosilicate beariAdapted from Connelly (2011a).
which were specially designed for heavy clays but still proved inopera-ble (Connelly, 2011a). Other methods for mitigating clay effects includedilution and blending of high clay oreswith less complex ores. However,these are limited to mixture concentrations below which the clay con-tent starts to cause problems. Such information has not been clearlydefined and a better fundamental understanding, particularly of therheological properties of the different phyllosilicate minerals, is re-quired for long-term solutions to these processing problems.
5. Conclusions
Themineral processing industry's approach to the processing of highphyllosilicate bearing ores has, in most cases, been rather simplistic;typically leading to an adverse outcome. If not identified at an earlystage, phyllosilicate minerals have the potential to significantly affectthe planning, operation and economics of a project. Understanding thegeology and mineralogy of an ore is critical in optimising ore beneficia-tion, as the presence of phyllosilicate minerals influences the selectionof equipment and the flow sheet design. The deleterious effects ofphyllosilicate minerals throughout the processing circuit have beenbroadly described. Engineering and chemical solutions have been de-vised to mitigate the problems associated with phyllosilicate bearingores, but these are often unsustainable and do not fully vitiate the diffi-culties encountered. There is a need to build a fundamental understand-ing of the behaviour of phyllosilicate minerals in order to be able tobetter deal with the processing issues.
155B. Ndlovu et al. / International Journal of Mineral Processing 125 (2013) 149–156
This paper has provided a simplified classification of the group,highlighting the main differences between the different minerals. Thekey issues associated with this group have been discussed within thecontext of specific mineral processing operations. This is foundationalin establishing a better understanding of phyllosilicate mineralogy,and is beneficial towards on-going efforts to bridge the gap betweenfundamental research on clay minerals and the complex mineral sys-tems typically encountered in the mineral processing industry. Thereremains a need to establish the effects of different phyllosilicate min-erals on the operability of specific unit operations. More research inthe area of phyllosilicate minerals, within the context of mineral pro-cessing, is required. Such an understanding could be used in collabora-tion with geometallurgical early detection techniques (e.g. hy-logging)for future mineralogical based predictions of clay containing oreperformance.
Acknowledgments
This work has been facilitated by the Mineral Chemistry ResearchAlliance (MiCRA) at the Julius Kruttschnitt Minerals Research Centre(JKMRC), The University of Queensland. Special thanks toMs. CatherineCurtis for her contribution in the early stages of the research. Dr. MeganBecker and Dr. Elizaveta Forbes are also acknowledged for some of theSEM images.
References
Abollino, O., Giacomino, A., Malandrino, M., Mentasti, E., 2008. Interaction of metal ionswith montmorillonite and vermiculite. Appl. Clay Sci. 38, 227–236.
Arnold, B.J., Aplan, F.F., 1986. The effect of clay slimes on coal flotation, part 2: the role ofwater quality. Int. J. Miner. Process. 17, 243–260.
Bakker, C.W., Meyer, C.J., Deglon, D.A., 2009. Numerical modelling of non-Newtonianslurry in a mechanical flotation cell. Miner. Eng. 22, 944–950.
Banfill, P.F.G., Rodriguez, O., Sanchez de Rojas, M.I., Frias, M., 2009. Effect of activation con-ditions of a kaolinite based waste on rheology of blended cement pastes. Cem. Concr.Res. 39, 843–848.
Barnes, H.A., Hutton, J.F., Walters, K., 1989. An Introduction to Rheology. Elsevier SciencePublishers, Amsterdam.
Beattie, D.A., Huynh, L., Kaggwa, G.N., Ralston, J., 2006. The effect of polysaccharides andpolyacrylamides on the depression of talc and the flotation of sulphide minerals.Miner. Eng. 19, 598–608.
Becker, M., Harris, P.J., Wiese, J.G., Bradshaw, D.J., 2009. Mineralogical characterisation ofnaturally floatable gangue in Merensky Reef ore flotation. Int. J. Miner. Process. 93,246–255.
Benna, M., Kbir-Ariguib, N., Magnin, A. And, Bergaya, F., 1999. Effect of pH on rheologicalproperties of purified sodium bentonite suspensions. J. Colloid Interface Sci. 218,442–455.
Boggs, S., 2006. Principles of Sedimentology and Stratigraphy, 4th edition. PearsonPrentice Hall, Upper Saddle River, NJ.
Brewster, G.R., 1980. Effect of chemical pre-treatment on X-ray powder diffraction char-acteristics of clay minerals derived from volcanic ash. Clay Clay Miner. 28, 303–310.
Brindley, G.W., Brown, G., 1980. Crystal structures of clay minerals and their X-ray Iden-tification. (London) In: Brindley, G.W., Brown, G. (Eds.), Mineralogical Society,pp. 98–104 (pp. 210–212).
Bulatovic, S.M., 2007. Handbook of Flotation Reagents: Chemistry, Theory and Practice:Flotation of Sulphide Ores Boston. Elsevier, Oxford.
Bulatovic, S.M., Wyslouzil, D.M., Kant, C., 1999. Effect of clay slimes on copper, molybde-num flotation from porphyry ores. Proceedings of the Copper′99–Cober′99 Interna-tional Conference, Phoenix, pp. 95–111.
Burdukova, E., Becker, M., Bradshaw, D.J., Laskowski, J.S., 2007. Presence of negativecharge on the basal planes of New York talc. J. Colloid Interface Sci. 315, 337–342.
Burdukova, E., Becker, M., Ndlovu, B., Mokgethi, B., Deglon, D.A., 2008. Relationship be-tween slurry rheology and its mineralogical content. In: Wang, D.D., Xao, S.C., Wang,F.L., Cheng, Z.U., Long, H. (Eds.), Proceedings of the 24th International Minerals Pro-cessing Congress. China Scientific Book Service Co.Ltd, Beijing, China, pp. 2169–2178.
Collins, B., Napier-Munn, T.J., Sciaronne, M., 1974. The production, properties and selec-tion of ferrosilicon powders for heavy-medium separation. J. South. Afr. Inst. Min.Metall. 75, 103–119.
Connelly, D., 2011a. High clay ores — a mineral processing nightmare. Australian Journalof Mining, July/August Edition: Mineral Processing—Flotation and Separation,pp. 28–29.
Connelly, D., 2011b. High clay ores — a mineral processing nightmare part 2. AustralianBulk Handling Review: September/October edition, pp. 78–81.
Cruz, N., Peng, Y., Farrokhpay, S., Bradshaw, D., 2013. Interactions of clay minerals in cop-per-gold flotation: Part 1 - rheological properties of clay mineral suspensions in thepresence of flotation reagents. Miner Eng 50-51, 30–37.
Dai, J.C., Huang, J.T., 1999. Surface modification of clays and clay–rubber composite. Appl.Clay Sci. 15, 51–65.
de Kretser, R.G., Boger, D.V., 1992. The compression, dewatering and rheology of slurriedcoal mine tailings. Proceedings 5th Australian Coal Science Conference, Newcastle,Australia, pp. 422–429.
Deer, W.A., Howie, R.A., Zussman, J., 1992. An Introduction to Rock Forming Minerals. Ad-dison Wesley Longman Limited, England.
Deng, Y., White, G.N., Dixon, J.B., 2009. Soil Mineralogy Laboratory Manual 11. Depart-ment of Soil and Crop Sciences, Texas A&M 26–37 (University, College Station,Texas, 77843–2474).
Dippenaar, A., 1988. The Effect of Particles on the Stability of Flotation Froth. (ReportNo. 81) IMM, South Africa.
Dixon, J.B., Weed, S.B., 1989. Minerals in Soil Environments, In: Dixon, J.B., Weed, S.B.(Eds.), 2nd edition. Soil Science Society of America, Madison, Wisconsin.
Du, J., Morris, G., Pushkarova, R.A., Smart, R.S.C., 2010. Effect of surface structure of kaolin-ite on aggregation, settling rate and bed density. Langmuir 26, 13227–13235.
Duman, O., Tunc, S., Çetinkaya, A., 2012. Electrokinetic and rheological properties of kao-linite in poly (diallyldimethylammonium chloride), poly(sodium 4-styrene sulfonate)and poly(vinyl alcohol) solutions. Colloids Surf. A Physicochem. Eng. Asp. 394, 23–32.
Fanning, D.S., Keramidas, V.Z., El-Desoky, M.A., 1977. “Chapter 12-Micas” in minerals insoil environments. In: Dixon, J.B., Weed, S.B. (Eds.), Soil Science Society of America,Madison, Wisconsin, USA, pp. 551–634.
Farrokhpay, S., 2011. The significance of froth stability in mineral flotation- a review Adv.Colloid Interface Sci. 166, 1–7.
Farrokhpay, S., 2012. The importance of rheology in mineral flotation: a review. Miner.Eng. 36–38, 272–278.
Farrokhpay, S., Bradshaw, D., 2012. The effect of clay minerals on froth stability in mineralflotation. Proceedings of the 26th InternationalMineral Processing Congress, NewDelhi.
Fuerstenau, D.W., 1958. Iron oxide slime coatings in flotation. Trans. Metall. Soc. AIME211, 792–793.
Genc, A.M., Kilickaplan, I., Laskowski, J.S., 2010. Pulp rheology in the flotation ofserpentinised ultramafic nickel sulfide ore and its effect on flotation. In: Pawlik, M.(Ed.), Proceedings 8th UBC-McGill-UA International Symposium on the Fundamentalsof Mineral Processing: Rheology and Processing of Fine Particles. The Canadian Insti-tute of Mining, Metallurgy and Petroleum, Vancouver, British Columbia, Canada,pp. 13–20.
Gier, S., Johns, W.D., 2000. Heavy metal adsorption on micas and clay minerals by X-rayphotoelectron spectroscopy. Appl. Clay Sci. 16, 289–299.
Guggenheim, S., Martin, R.T., 1995. Definition of clay and clay minerals Journal report ofthe AIPEA nomenclature and CMS nomenclature committees. Clay Clay Miner. 43,255–256.
Guidice, G.R.M.D., 1934. A study of slime coatings in flotation. Trans. Metall. Soc. AIME112, 398–409.
Hassellov, M., Layven, B., Bengtsson, H., Jansen, R., Turner, D.R., Beckett, R., 2001. Particlesize distribution of clay-rich sediments and pure clay minerals: a comparison of grainanalysis with sedimentation field-flow fractionation. Aquat. Geochem. 7, 155–171.
Horie, M., Pinder, K.L., 1979. Time-dependent shear flow of artificial slurries in coaxial cyl-inder viscometer with a wide gap. Can. J. Chem. Eng. 57, 125–134.
Hurlbut, C.S., Sharp, W.E., 1998. Dana's Minerals and How To Study Them (After EdwardSalisbury Dana), 4th edition. John Wiley & Sons, New York 248–257.
Hussain, S.A., Dermirci, Ş., Özbayoglu, G., 1996. Zeta potential measurements on threeclays from Turkey and effects of clays on coal flotation. J. Colloid Interface Sci. 184,535–541.
James, A.E., Williams, D.J.A., 1982. Flocculation and rheology of kaolinite/quartz mixtures.Rheol. Acta 21, 176–183.
Johnson, S.B., Russell, A.S., Scales, P.J., 1998. Volume fraction effects in shear rheology andelectroacoustic studies of concentrated alumina and kaolin suspensions. Colloids Surf.A Physicochem. Eng. Asp. 141, 119–130.
Johnson, S.B., Franks, G.V., Scales, P.J., Boger, D.V., Healy, T.W., 2000. Surface chemistry–rheology relationships in concentrated mineral suspensions. Int. J. Miner. Process.58 (1–4), 267–304.
Jorjani, E., Barkhordar, H.R., Tayebi Khormani, M., Fazeli, A., 2011. Effects of aluminosili-cate minerals on copper–molybdenum flotation from Sarcheshmeh porphyry ores.Miner. Eng. 24, 754–759.
Kaminsky, H.A.W., Etsell, T.H., Ivey, D.G., Omotoso, O., 2009. Distribution of clay mineralsin the process streams produced by the extraction of bitumen from Athabasca oilsands. Can. J. Chem. Eng. 87, 85093.
Kasongo, T., Zhou, Z., Xu, Z., Masliyah, J., 2000. Effect of clays and calcium ions on bitumenextraction from Athabasca oil sands using flotation. Can. J. Chem. Eng. 78, 678–680.
Kirjavainen, V., Heiskanen, K., 2007. Some factors that affect beneficiation of sulphidenickel–copper ores. Miner. Eng. 20, 629–633.
Klein, C., Dutrow, B., 2008. Manual of Mineral Science, 23rd edition. John Wiley & Sons,New York 456–467 (519–534).
Klein, C., Hurlbut, C.S., 1993. Manual of Mineralogy (after J.D. Dana), 21st edition. JohnWiley & Sons, New York.
Klein, B., Pawlik, M., 2005. Rheology modifiers for mineral suspensions. Miner. Metall.Process. 22, 83–88.
Lagaly, G. And, Zeismer, S., 2003. Colloid chemistry of clay minerals: the coagulation ofmontmorillonite dispersions. Adv. Colloid Interf. Sci. 100–102, 105–128.
Laird, D.A., 2006. Influence of layer charge on swelling of smectites. Appl. Clay Sci. 34,74–87.
156 B. Ndlovu et al. / International Journal of Mineral Processing 125 (2013) 149–156
Laskowski, J.S., Ndlovu, B., Kilickaplan, I., 2010. Rheology of aqueous suspensions of needle-like mineral particles. In: Pawlik, M. (Ed.), Proceedings of the 8th UBC-McGill-UAInternational Symposium on the Fundamentals of Mineral Processing: Rheology andProcessing of Fine Particles. The Canadian Institute of Mining, Metallurgy and Petro-leum, Vancouver, Canada, pp. 193–203.
Luckham, P.F., Rossi, S., 1999. The colloidal and rheological properties of bentonite sus-pensions. Adv. Colloid Interf. Sci. 82, 43–92.
Ma, X., Bruckard, W.J., Holmes, R., 2009. Effect of collector, pH and ionic strength on thecationic flotation of kaolinite. Int. J. Miner. Process. 93, 54–58.
McBride, M.B., Baveye, P., 2003. Response to comments on diffuse double-layer models,long-range forces, and ordering of clay colloids. Soil Sci. Soc. Am. 67, 1961–1964.
McFarlane, A., Bremmell, K., Addai-Mensah, J., 2005. Microstructure, rheology anddewatering behaviour of smectite dispersions during orthokinetic flocculation.Miner. Eng. 18, 1173–1182.
Miano, F. And, Rabaioli, M.R., 1994. Rheological scaling of montmorillonite suspensions:the effect of electrolytes and polyelectrolytes. Colloids Surf. A Physicochem. Eng.Asp. 84, 229–237.
Ndlovu, B., Forbes, E., Becker, M., Deglon, D., Franzidis, J.P., Laskowski, J.S., 2011a. The ef-fects of chrysotile mineralogical properties on the rheology of chrysotile suspensions.Miner. Eng. 24, 1004–1009.
Ndlovu, B., Becker, M., Forbes, E., Deglon, D., Franzidis, J.P., 2011b. The influence ofphyllosilicate mineralogy on the rheology of mineral suspensions. Miner. Eng. 24,1314–1322.
Ndlovu, B., Forbes, E., Farrokhpay, S., Becker, M., Bradshaw, D., Deglon, D., 2013. A prelim-inary rheological classification of phyllosilicate group minerals. Miner. Eng. http://dx.doi.org/10.1016/j.mineng.2013.06.004.
Okuda, S., Inoue, K., Williamson, W.O., 1969. Negative surface charges of pyrophillite andtalc. In: Heller, L. (Ed.), International Clay Conference. Israel University Press, Tokyo,pp. 31–41.
Patra, P., Bhambhani, T., Nagaraj, D.R., Somasundaran, P., 2010. Effect of morphology ofaltered silicate minerals on metallurgical performance: transport of Mg silicates tothe froth phase. In: Pawlik, M. (Ed.), Proceedings 8th UBC-McGill-UA InternationalSymposium on the Fundamentals of Mineral Processing: Rheology and Processingof fine Particles. The Canadian Institute of Mining, Metallurgy and Petroleum,Vancouver, British Columbia, Canada, pp. 31–42.
Permien, T., Lagaly, G., 1994. The rheological and colloidal properties of bentonite disper-sions in the presence of organic compounds IV sodium montmorillonite and acids.Appl. Clay Sci. 251–263.
Pils, J.R.V., Laird, D.A., Evangelou, V.P., 2007. Role of cation demixing and quasicrystal for-mation and breakup on the stability of smectitic colloids. Appl. Clay Sci. 35, 201–211.
Plotze, M., Kahr, G. And, Stengele, H., 2003. Alteration of clayminerals—gamma irradiationeffects on physicochemical properties. Appl. Clay Sci. 23, 195–202.
Ralston, J., Fornasiero, D., 2006. Effect of MgO minerals on pentlandite flotation. In: Onal,G., Acarkan, N., Celik, M.S., Arslan, F., Atesok, G., Guney, A., Sirkeci, A.A., Yuce, A.E.,Perek, K.T. (Eds.), Proceedings of the 23rd International Minerals ProcessingCongress. Promed Advertising Ltd, Istanbul, Turkey, pp. 750–755.
Rand, B., Melton, I.E., 1977. Particle interactions in aqueous kaolinite suspensions: I. Effectof pH and electrolyte upon the mode of particle interaction in homoionic sodium ka-olinite suspensions. J. Colloid Interface Sci. 60, 308–320.
Scales, P.J., Greiser, F. And, Healy, T.W., 1990. Electrokinetics of the muscovite mica —
aqueous solution interface. Langmuir 6, 582–589.Schouwstra, R.P., Kinloch, E.D., Lee, C.A., 2000. A short geological review of the Bushvelt
Complex. Platin. Met. Rev. 44, 33–39.Schubert, H., Bischofberger, C., 1978. On the hydrodynamics of flotation machines. Int.
J. Miner. Process. 5, 132–142.Senior, G.D., Thomas, S.A., 2005. Development and implementation of a new flow sheet
for the flotation of a low grade nickel ore. Int. J. Miner. Process. 78, 49–61.Shabalala, N.Z.P., Harris, M., Leal Filho, L.S., Deglon, D.A., 2011. Effect of slurry rheology on
gas dispersion in a pilot scale mechanical flotation cell. Miner. Eng. 24, 1448–1453.Shi, F.N., Napier-Munn, T.J., 2002. Effects of slurry rheology on industrial grinding perfor-
mance. Int. J. Miner. Process. 65, 125–140.Środoń, J., 2006. Quantitative analysis of clay minerals in Handbook of Clay Science. In:
Bergaya, F., Theng, B.K.G., Lagaly, G. (Eds.), Developments in Clay Science, 1. ElsevierLtd, pp. 765–786.
Tangsathitkulchai, C., 2003. The effect of slurry rheology on fine grinding in a laboratoryball mill. Int. J. Miner. Process. 69, 29–47.
Tao, D., Dopico, P.G., Hines, J., Kennedy, D., 2010. An experimental study of clay binders infine coal froth flotation. Proceedings of the International Coal Preparation Congress,Lexington, USA, pp. 478–487.
Tombácz, E., Szekeres, M., 2006. Surface charge heterogeneity of kaolinite in aqueous sus-pension in comparison with montmorillonite. Appl. Clay Sci. 34, 105–124.
Tremolada, J., Dzioba, R., Bernardo-Sanchez, A., Menendez-Aguado, J.M., 2010. The preg-robbing of gold and silver by clays during cyanidation under agitation and heapleaching conditions. Int. J. Miner. Process. 94, 67–71.
Vali, H., Bachmann, L., 1988. Ultrastructure and flow behaviour of colloidal smectite dis-persions. J. Colloid Interface Sci. 126, 278–291.
Van Olpen, H., 1977. Clay Colloid Chemistry, 2nd edition. John Wiley & Sons, New York.Vasudevan, M., Nagaraj, D.R., Patra, P., Somasundaran, P., 2010. Effect of altered silicates
in flotation performance: role of changes in pulp rheology. In: Pawlik, M. (Ed.),Proceedings 8th UBC-McGill-UA International Symposium on the Fundamentalsof Mineral Processing: Rheology and Processing of Fine Particles. The Canadian Insti-tute of Mining, Metallurgy and Petroleum, Vancouver, British Columbia, Canada,pp. 21–30.
Viseras, C., Cerezo, P., Sanchez, A., Sacedo, I. And, Aguzzi, C., 2010. Current challenges inclay minerals for drug delivery. Appl. Clay Sci. 48, 291–295.
Wallace, D., Tipman, R., Komishke, B., Wallwork, V., Perkins, E., 2004. Fines/water interac-tions and consequences of the presence of degraded illite on oil sands extractability.Can. J. Chem. Eng. 82, 678–680.
Wen, W.W., Sun, S.C., 1977. An electrokinetic study of an amine flotation of oxidised coal.Trans. Metall. Soc. AIME 262, 174–180.
Wiese, J.G., Harris, P., Bradshaw, D.J., 2007. The response of sulphide and gangue mineralsin selected Merensky ores to increased depressant dosages. Miner. Eng. 20, 886–995.
Wiese, J.G., Harris, P., Bradshaw, D.J., 2010. The effect of increased frother dosage on frothstability at high depressant dosages. Miner. Eng. 23, 1010–1017.
Xiao, H., Liu, Z. And,Wiseman, N., 1999. Synergetic effect of cationic polymermicroparticlesand anionic polymers on fine clay flocculation. J. Colloid Interface Sci. 216, 409–417.
Yada, K., 1971. Study of the microstructure of chrysotile asbestos by high resolution elec-tron microscopy. Acta Crystalogr. A27, 659–664.
Zhou, Z., Gunter, W.D., 1992. The nature of the surface charge of kaolinite clays. ClayMineral. 20, 365–368.
