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Molecular weight effects in guar gum adsorption and depression of talc Garcia Vidal, Claudio Andres 2013

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MOLECULAR WEIGHT EFFECTS IN GUAR GUM ADSORPTION AND DEPRESSION OF TALC  by Claudio Andres Garcia Vidal  B.Sc., University of Concepcion, 2007  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF APPLIED SCIENCE  in  THE FACULTY OF GRADUATE STUDIES (Mining Engineering)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) March 2013 © Claudio Andres Garcia Vidal, 2013  Abstract The effect of the molecular weight of guar gum on adsorption, talc depression, and stability of talc suspensions was studied. Four guar gum samples of different molecular weights in the range from 0.162 MDa to 1.4 MDa were used. It was also found that the intrinsic viscosities of the guar gum samples were independent of the type of background solution (NaCl, KCl, distilled water). The adsorption density of the tested guar gum samples on talc was measured from the same background solutions at pH 9. The floatability of fine talc particles as well as their stability towards aggregation in the presence of guar gum were simultaneously determined so a direct relationship between talc depression and talc flocculation/dispersion by guar gum could be established. It was found that the effect of the molecular weight of guar gum on the adsorption density was negligible. No effect of the background electrolyte on guar gum adsorption was observed. All four guar gum samples were found to be equally strong depressants of talc flotation without any clear relationship with their molecular weights. It was determined that an adsorption density equal to about 20% of the complete surface coverage was sufficient to completely depress talc floatability. All guar gum samples also exhibited strong flocculating capabilities towards the talc particles at lower polymer dosages. As determined from turbidity data, higher molecular weight guar gum samples were more powerful flocculants than lower molecular samples. Most importantly, the strongest depression of talc flotation and the most pronounced flocculation of talc were found to occur at the same dosage. Higher doses of the polymers kept the talc particles completely depressed while simultaneously causing gradual steric redispersion of the mineral. The dispersing capabilities of the polymers were a function of the molecular weight, with the lower molecular weight samples bringing about stronger dispersion than higher molecular weight samples.  ii  It was concluded that a high molecular weight guar gum would be the best depressant, since such a polymer would strongly depress the flotation of talc while minimizing talc dispersion and subsequent mechanical entrainment in the flotation concentrate.  iii  Table of Contents Abstract..................................................................................................... ii Table of Contents ....................................................................................... iv List of Tables ............................................................................................. vi List of Figures ............................................................................................ vii Acknowledgements……………………………………………………….…………………………………………..viii 1  2  3  Introduction .......................................................................................... 1 1.1  Importance of this study .................................................................... 1  1.2  Specific research objectives................................................................ 2  Literature Review ................................................................................... 3 2.1  Talc ................................................................................................ 3  2.2  Floatability of talc ............................................................................. 5  2.3  Surface charge of talc ....................................................................... 5  2.4  Guar gum........................................................................................ 7  2.5  Solution properties of guar gum .......................................................... 9  2.5.1  Dilute solution viscometry ............................................................ 9  2.5.2  Molecular weight ....................................................................... 14  2.6  Adsorption mechanism of talc and guar gum ....................................... 15  2.7  Molecular weight effects in polysaccharide adsorption ........................... 17  2.8  Flocculation and dispersion effects during flotation ............................... 19  Experimental Program .......................................................................... 22 3.1  Materials ....................................................................................... 22  3.1.1  Talc ........................................................................................ 22  3.1.2  Guar gum ................................................................................ 27  3.1.3  Reagents ................................................................................. 27  3.2  Methodology .................................................................................. 28 iv  4  3.2.1  Preparation of guar gum solutions................................................ 28  3.2.2  Characterization of main functional groups of guar gum by FTIR ....... 30  3.2.3  Viscosity measurements ............................................................. 30  3.2.4  Adsorption tests ........................................................................ 34  3.2.5  Turbidity and volume of flocculated talc measurements ................... 35  3.2.6  Total organic carbon (TOC) analysis ............................................. 37  3.2.7  Flotation tests .......................................................................... 38  Results and Discussion.......................................................................... 40 4.1  Characterization of guar gum by FTIR spectroscopy ............................. 40  4.2  Intrinsic viscosity............................................................................ 43  4.3  Adsorption..................................................................................... 48  4.4  Turbidity ....................................................................................... 55  4.5  Flotation ....................................................................................... 60  4.5.1  Adsorption in flotation ................................................................ 60  4.5.2  Recovery of talc ........................................................................ 63  4.5.3  Turbidity in flotation .................................................................. 64  5  Conclusions......................................................................................... 70  6  Recommendations for Further Research ................................................... 72  References ............................................................................................... 74 Appendix I: Talc Sample Characterization...................................................... 80 Appendix II: Calibration TOC Curves ............................................................ 83 Appendix III. Viscosity Data ........................................................................ 85 Appendix IV: Adsorption Data ..................................................................... 89 Appendix V: Turbidity and Flocculation Data .................................................. 94 Appendix VI: Flotation................................................................................ 95 Appendix VII: Calculation of Surface Area ..................................................... 96 v  List of Tables Table 3.1. Talc samples characterization summary......................................... 244 Table 3.2. Summary correction factors for guar gum samples ........................... 29 Table 4.1. Description of guar gum samples .................................................. 44 Table 4.2. Intrinsic viscosities for guar gums dissolved in different background solutions .................................................................................................. 47 Table III-1. Viscosity data of HMW1, pH 9, 24 °C............................................ 85 Table III-2. Viscosity data of HMW2, pH 9, 24 °C............................................ 86 Table III-3. Viscosity data of HMW2, pH 9, 24 °C............................................ 87 Table III-4. Viscosity data of HMW2, pH 9, 24 °C............................................ 88 Table IV-1. Adsorption tests with HMW1 sample ............................................. 89 Table IV-2. Continuation of adsorption tests with HMW1 sample ....................... 90 Table IV-3. Adsorption tests with HMW2 sample ............................................. 91 Table IV-4. Adsorption tests with MMW3 sample ............................................. 92 Table IV-5. Adsorption tests with LMW4 sample ............................................. 93 Table V-1. Turbidity and volume of flocs data................................................. 94 Table VI-1. Flotation test results data ........................................................... 95  vi  List of Figures Figure 2.1. Schematic view of the crystal chemistry (edge view) of talc (Huang and Fuerstenau 2001) ........................................................................................ 4 Figure 2.2. The monomeric structure of guar gum (Wang et al. 2005) .................. 8 Figure 2.3. Adsorbed layer built up of several polymer molecules (Lyklema 1995) 15 Figure 2.4. Bridging flocculation by long polymer molecules ............................. 20 Figure 3.1. Talc pieces as received from Ward Natural Science Establishment. ..... 22 Figure 3.2. SEM pictures of the -38 µm size fraction........................................ 26 Figure 3.3. SEM pictures of the -105+75 µm size fraction ................................ 26 Figure 3.4. Schematic representation of the Cannon-Fenske capillary viscometer. 31 Figure 3.5. Viscometry equipment Lauda PVS1 ............................................... 33 Figure 3.6. Samples for turbidity measurements. Concentration increases from left to right: 0, 140, 280, 410, 630, 1,100 and 1,500 mg/L, HMW2. ........................ 36 Figure 3.7. Samples for flocculated volume measurement. Concentration increases from left to right: 0, 140, 280, 410, 630, 1,100 and 1,500 mg/L, HMW2. ........... 37 Figure 3.8. Flotation machine with the 500-mL cell (left), typical talc flotation concentrate (right). ................................................................................... 39 Figure 4.1. FTIR spectra of HMW2 guar films prepared at natural pH and pH 3. ... 41 Figure 4.2. FTIR spectra of MMW3 guar films prepared at natural pH and pH 3. ... 42 Figure 4.3. FTIR spectra of LMW4 guar films prepared at natural pH and pH 3. .... 42 Figure 4.4. Intrinsic viscosity of different guar gums in distilled water at pH 9. .... 43 Figure 4.5. Intrinsic viscosity of HMW1. ........................................................ 45 Figure 4.6. Intrinsic viscosity of HMW2. ........................................................ 45 Figure 4.7. Intrinsic viscosity of MMW3 ......................................................... 46 Figure 4.8. Intrinsic viscosity of LMW4 .......................................................... 46 Figure 4.9. Adsorption of HMW1 on talc ........................................................ 49 Figure 4.10. Adsorption of HMW2 in talc ........................................................ 49 Figure 4.11. Adsorption of MMW3 on talc ...................................................... 50 Figure 4.12. Adsorption of LMW4 on talc. ...................................................... 50 Figure 4.13. Adsorption of guar gum samples in distilled water background. ....... 51 Figure 4.14. Adsorption of guar gum samples in NaCl 0.01M background............ 52 vii  Figure 4.15. Adsorption of guar gum samples in KCl 0.01M background. ............ 52 Figure 4.16. Adsorption of HMW1 ................................................................. 53 Figure 4.17. Adsorption of HMW2 ................................................................. 54 Figure 4.18. Adsorption of MMW3................................................................. 54 Figure 4.19 Adsorption of LMW4 .................................................................. 55 Figure 4.20. Turbidity for HMW1 .................................................................. 56 Figure 4.21. Turbidity for HMW2 .................................................................. 57 Figure 4.22. Turbidity for MMW3 .................................................................. 57 Figure 4.23. Turbidity for LMW4 ................................................................... 58 Figure 4.24. Dispersion of talc for different MW guar gums. .............................. 59 Figure 4.25. Flocculated talc volume of adsorption tests .................................. 60 Figure 4.26. Adsorption density in function of equilibrium concentration ............. 61 Figure 4.27. Adsorption density versus guar gum initial concentration ................ 62 Figure 4.28. Adsorption densities for small and flotation scales, 0.01M KCl, pH 9. 62 Figure 4.29. Recovery of talc in flotation ....................................................... 64 Figure 4.30. Turbidity in the complete concentration range .............................. 65 Figure I-1. Particle size distribution of Talc A.................................................. 80 Figure I-2. Particle size distribution of Talc B.................................................. 80 Figure I-3. DFT of talc sample A................................................................... 81 Figure I-4. DFT of talc sample B .................................................................. 82 Figure II-1. Calibration TOC curve for HMW1 ................................................. 83 Figure II-2. Calibration TOC curve for HMW2 ................................................. 83 Figure II-3. Calibration TOC curve for MWM3 ................................................. 84 Figure II-4. Calibration TOC curve for LMW4 .................................................. 84  viii  Acknowledgements I would like to express my complete gratitude to Dr. Pawlik for all his support, patience and giving me the opportunity to come to UBC. He was a fundamental pillar during my research and helped me to develop strong research skills. Without him, it would have been impossible to carry out successfully this thesis. The sweetness and unconditional love from my wife Cecilia and my daughters Matilde and Antonia have been with me during the whole process, making this period a beautiful part of my life. All the support, motivation and patience from Cecilia helped me to focus on my research and at the same time to fully enjoy this familiar experience. The materialization of a whole life of effort and constancy makes that obtaining the degree to be more than a personal achievement, an achievement from my parents: Maria and Jose. They have dedicated a great part of their lives to educate and give me all the tools to face successfully any challenge. I would express my thanks to all the professors and the staff of NBK, especially to Sally Finora, Maria Lui, Leslie Nichols and Pius Lo for all their help with all of my doubts and for the really nice environment that they generate in the department. I also want to thank my colleagues and friends Esau Arinaitwe, Jophat Engwayu and Avishan Atrafi for all their help and good disposition, and especially to Leopoldo Gutierrez, Fernando Parada and Mariela Zuñiga for all their advices and help when I was thinking to apply for the program, they motivated me and made me decide to come. Finally, I want to thank the governments of Chile and Canada because through their financial support provided by the scholarship “Becas Chile” and the NSERC Discovery Grant made this possible.  ix  1 Introduction 1.1 Importance of this study In the processing of platinum group minerals (PGM), polysaccharide-based depressants have been extensively used to inhibit the flotation of naturally hydrophobic gangue minerals. In the flotation process of potash ores, some of these polymers are also used, but in this case to prevent collector adsorption onto non-floatable gangue minerals. Talc is one of the most common and problematic gangue minerals in PGM and sulphide ores. Since talc is naturally hydrophobic, it causes difficulties in concentration  and  subsequently  in  smelting  processes.  In  order  to  avoid  contamination of the flotation concentrate with talc during flotation, two techniques are applied: 1) pre-flotation of talc as a first stage; and 2) depression of talc during the main separation stage. In talc depression, a dedicated depressant is used to render the talc particles hydrophilic and to prevent their flotation. Several types of polysaccharides are used by the industry, of which guar gum is the most common. Different studies have been carried out to understand the interactions between anisotropic silicate minerals and polysaccharides, but the complex behavior of these minerals in aqueous solutions plus the lack of understanding of polymer properties under different conditions makes this research area quite challenging. This thesis is focused on the talc-guar gum system, particularly on the impact of guar gums with different molecular weights on adsorption on talc, depression of talc floatability, and talc dispersion and/or flocculation. To the author's knowledge, this research is the first study in which carefully prepared, well-characterized non-ionic guar gum samples were systematically studied.  1  1.2 Specific research objectives  The overall objective of this study was to assess the effect of the molecular weight of guar gum on talc-guar gum interactions. The research program was divided into several sub-studies with the following specific objectives:   To characterize guar gum samples of various molecular weights through their intrinsic viscosity.    To determine the effect of the molecular weight of guar gum on guar gum adsorption onto talc.    To assess the extent of talc flocculation and dispersion phenomena in the presence of guar gums of different molecular weights.    To establish a relationship between guar gum adsorption, resulting depression of talc flotation, and flocculation/dispersion phenomena, all as a function of the molecular weight of the polysaccharide.  2  2 Literature Review  2.1 Talc Talc is an industrial mineral with several desirable characteristics such as extreme softness, luster, slip, oil and grease adsorption, chemical inertness, high dielectric strength, and low heat conductivity (Fuerstenau et al. 2003). On the other hand, it is an unwanted mineral that occurs as a gangue component in many base metal sulfide ore deposits around the world. These ores are normally beneficiated by froth flotation processes. Despite being a minor constituent in the gangue of base metal sulfide ores (less than 10%), talc normally has a disproportionately large effect on flotation efficiency (Steenberg and Harris 1984; Fuerstenau et al. 1988). Due to its natural hydrophobicity, talc readily reports to the froth in flotation processes, thereby reducing the concentrate grade and also producing difficulties downstream in smelting processes because of its high MgO content (Fuerstenau et al. 2003; Burdukova et al. 2007). Talc is a magnesium-rich phyllosilicate composed of three repeating sandwich-like layers: a brucite-like (Mg(OH)2) layer of octahedrally coordinated magnesiumhydroxyl ions between two silica-like layers of tetrahedrally coordinated siliconoxygen ions. This structure is illustrated in Figure 2.1. The brucite layer and two silica layers are held together by strong ionic bonds while the entire sandwich structures are linked by weak oxygen-oxygen Van der Walls forces (Fuerstenau et al. 1988). In some cases, small amounts of titanium or aluminum can substitute for silicon in the tetrahedral layer, while calcium may substitute for magnesium in the octahedral brucite layer. The level of substitution of aluminum for silicon varies depending on the source of the mineral between 0.01 and 3.04% (Deer et al. 1978; Deer et al. 1992). By breaking talc particles, two different types of surfaces can be formed: the basal plane (or face); and the edge. The basal plane results from the cleavage of the 3  weak bonding between silica layers. The basal plane is considered to be uncharged because the tetrahedral layers are fully charge-compensated. The weak bond exposed to the surrounding water also makes the basal planes quite hydrophobic. On the other hand, the edge forms from the rupture of strong ionic and covalent bonds of the silica and brucite layers. As such, the edges are electrostatically charged with high polarity, and are therefore strongly hydrophilic (Fuerstenau et al. 2003; Chander et al. 1975). The complexity of the surface properties of this mineral, with the hydrophobic faces and the hydrophilic edges, makes the surface chemistry of talc particles difficult to understand.  Figure 2.1. Schematic view of the crystal chemistry (edge view) of talc (Huang and Fuerstenau 2001)  4  2.2 Floatability of talc It is generally accepted (Fuerstenau et al. 2003; Huang and Fuerstenau 2001; Rath et al. 1997; Nalaskowski et al. 2007) that the basal plane (or the face) of talc particles is hydrophobic and the edge surface is hydrophilic. It is the hydrophobicity of the faces that allows talc to float without any additional reagents. However, the pronounced anisotropy of the mineral is often the source of disagreements in the literature data on the surface properties of talc. Different studies (Rath et al. 1997; Morris et al. 2002) showed that the floatability of talc was not affected by pH. By cleaving talc and exposing fresh surfaces, Fuerstenau et al. (2003) found that the contact angle of the face is on average 65° and of the edge 12.5°. This study also reported that these angles were almost independent of pH in the range from 2 to 12. However, Fuerstenau et al. (2003) also reported that the induction time and floatability of talc were well correlated and decreased with increasing pH.  2.3 Surface charge of talc Using electrophoretic zeta potential measurements, different studies (Fuerstenau et al. 1988; Morris et al. 2002; Ma and Pawlik 2007a) found that the isoelectric point (IEP) of talc particles is near pH≈2.5. According to Swartzen-Allen and Matijevic (1974), the Smoluchowski’s equation — used to relate the electrophoretic mobility to the electrokinectic (zeta) potential — cannot be applied for electrophoretic measurements on anisotropic particles such as talc because of their plate-like shape and charge heterogeneity. The difference in charging  characteristics  between  the  basal  plane  and  the  edge  makes  electrophoretic results difficult to interpret. In fact, it is still not exactly clear what the measured electrophoretic mobility of an anisotropic mineral represents (Gupta and Miller 2010). Due to the anisotropic behavior and plate-like shape of kaolinite 5  particles (similar to talc), electrophoretic zeta potential measurements on such systems should be treated as apparent and used for comparative purposes only (Lyklema 1995). Nalaskowski et al. (2007) studied the surface charge of the basal plane and the edge plane of talc separately by using a streaming potential analyzer. They obtained the IEP for both surfaces at pH~3. However, this technique has similar theoretical  restrictions  for  zeta  potential  measurements  as  the  micro-  electrophoresis of fine particles (Burdukova et al. 2007). Okuda et al. (1969) found that positively-charged AgI colloid adhered to the talc basal planes under acidic and alkaline conditions. They concluded that the basal planes of talc were negatively charged. Then, based on similar results obtained for kaolinite, they explained that the presence of the negative charge was due to the substitution of silicon ions in the tetrahedral layer for ions of a lower valency. Using microprobe analysis, Burdukova et al. (2007) found that New York talc presented negative charge on the basal plane. They concluded that this was due to random substitution of silicon ions for aluminum and titanium ions in the tetrahedral silica-like structure of talc, which caused a local proton deficiency. They also confirmed the discrepancy among the electrokinetic determination of i.e.p. at pH≈2.5 (Fuerstenau et al. 1988; Morris et al. 2002); potentiometric titration measurements of point of zero charge at pH 7.7; and Casson yield stress measurements of the maximum aggregation point at pH 5.5. This discrepancy indicates that — besides Van der Walls forces — another attractive force exists that makes talc particles coagulate when the surface charge is substantial. Such arguments also support the hypothesis of electrostatic attractive forces acting between the negative basal plane and the positive edge.  6  2.4 Guar gum Guar gum is a nearly odorless white to yellowish-white powder produced from the seeds of two annual leguminous plants, Cyamopsis tetragonalobus and C. psoraloide. It is one of the most important crops and export commodities of India (Mutalik et al. 2006; Vishwakarma et al. 2011). Guar gum and its derivatives are widely used in food, paper, cosmetic, pharmaceutical, textile, explosives, oil, gas and mining industries. Currently, India is the main producer of cluster bean, accounting for 80% of the world production, with the state of Rajasthan occupying the largest area (82.1%) of guar cultivation (Vishwakarma et al. 2011; Vishwakarma et al. 2009). Principal components of guar gum seeds are hull, endosperm, and germ. After separation from hull and germ, the remaining endosperm cotyledons better known as guar gum splits are pulverized to make guar gum powder. This endosperm powder contains about 78-82% of galactomannan gum (guar gum) (Vishwakarma et al. 2011). The guar gum macromolecule is a chain of (1→ 4)-linked β-D-mannopyranose units with α-D-galactopyranose units connected to the mannose backbone through (1→ 6) glycosidic linkages. The poly-mannose chain is randomly substituted with galactose units at a mannose–to–galactose ratio of 1.8–1.0 (Painter et al. 1979; Whistler and Hymowitz 1979).  7  Figure 2.2. The monomeric structure of guar gum (Wang et al. 2005)  Canadian potash ores typically contain over 90% halite (NaCl) and sylvite (KCl). The gangue is composed of water-insoluble ultrafine minerals represented mostly by clays and carbonates. In the froth flotation process, a primary amine collector is used to selectively render sylvite hydrophobic and separate it from the hydrophilic halite. Unfortunately, the gangue minerals also have a high affinity for this cationic collector. Guar gum is used to selectively coat the fines, preventing the adsorption of the collector onto these unwanted particles, and thus avoiding slime flotation. This action, commonly known in the flotation process as blinding, also helps to reduce collector consumption and to improve the quality of the sylvite (KCl) concentrate. Guar gum also plays an important role in base metal and platinum group metal (PGM) ore processing, where the occurrence of the naturally hydrophobic and problematic talc is common. In flotation processes, guar gum is used to adsorb selectively onto talc particles, rendering them hydrophilic and depressing their natural floatability. Many of polysaccharides, such as starch, dextrin, carboxymethyl cellulose and guar gum, are currently used as flotation depressants and/or dispersants. As opposed to many modifying agents currently used, polysaccharides are biodegradable, nontoxic products. These properties make them very popular for use as flotation  8  reagents and the increasingly rigorous environmental restrictions make research in this area essential (Laskowski et al. 2007).  2.5 Solution properties of guar gum 2.5.1 Dilute solution viscometry Viscometry is one of the basic analytical methods used to characterize polymer properties in dilute solutions. It allows for a fast and relatively simple determination of significant parameters such as solution structure, polymer concentration, polymer chain dimensions, molecular weight, and other thermodynamic properties of a polymer in solution (Kulicke and Clasen 2004). Viscosity  is defined as the resistance to flow when a shear force is applied,  reflecting the frictional forces of all molecules in solution including those of the dissolved polymer. It is calculated as the ratio of the shear stress rate  to the shear  (eq. 2.1), where the shear rate is the force F that is applied on the surface  element of area A (eq. 2.2) parallel to the flow direction. The shear rate represents the difference of velocity  of fluid layers separated by distance  (eq. 2.3)  (Kulicke and Clasen 2004).  a  Viscosity:  s  Shear stress:  m2  a  (2.1)  a  (2.2)  m s  Shear rate:  (2.3)  m  Capillary viscometers commonly measure the kinematic viscosity ( ), which is the ratio of viscosity  to the density  of the solution.  9  a  Kinematic viscosity:  k  mm2 s-  (2.4)  In the viscosity measurement with the use of a capillary viscometer, a certain amount of the polymer solution is placed in the capillary that has two marks at different levels. The flow time required by the solution to pass between these two marks is proportional to the kinematic viscosity of the solution (more details in the Section 3.2.3). (2.5) Then, the relative viscosity (  ) is also often defined as the ratio of solution  viscosity to solvent viscosity. In the case of a polymer solution, the solvent itself, and  is the viscosity of  is the viscosity of a polymer solution (Kulicke and Clasen  2004). Relative viscosity:  (2.6)  The viscosity of a solution is the sum of the viscosity of the dissolved polymer plus the viscosity of the solvent  (Kulicke and Clasen 2004). In order to describe  an incremental change in solvent viscosity upon dissolution of a polymer, the term specific viscosity (  ) is often used, which is defined as:  Specific viscosity:  The reduced viscosity  (2.7)  is defined as the specific viscosity divided by the  concentration of the polymer.  Reduced Viscosity:  (2.8)  10  Since the reduced viscosity is a function of polymer concentration, the true viscosity enhancing properties of a polymer can be assessed by extrapolating the reduced viscosity data to zero polymer concentration in order to obtain the intrinsic viscosity of a polymer: (2.9) It should be noted that the units of the reduced viscosity and of the intrinsic viscosity are "volume/mass". The intrinsic viscosity can also be treated as a measure of the natural ability of a polymer to increase the viscosity of the solution (Huggins 1942). Therefore, the intrinsic viscosity depends on the size, shape, and the molecular weight of a polymer. The dilute solution of a polymer can be defined as such a solution in which the polymer macromolecules are sufficiently far apart from one another so that their mutual interactions are eliminated and only polymer-solvent interactions take place. The most general relationship between intrinsic viscosity and the viscosity of dilute polymer solutions is a power series of concentration and can be given as (Lovell 1989):  (2.10)  where  are dimensionless constants. Equation 2.10 is often reduced to a linear  approximation known as the Huggins equation (Huggins 1942): (2.11) The  intrinsic  versus  viscosity  can  be  determined  experimentally  by  plotting  . According to the Huggins equation, the intercept of a plot of  11  versus  represents the intrinsic viscosity  2.11), then  can be easily solved for  and the slope is equal to  (Eq.  , the Huggins constant.  Experimental findings on the Huggins constant may be summarized as follows: (a) a polymer displays a higher value of  in a poor solvent; (b) it has a value of about  0.5 in an ideal solvent; (c) the magnitude of  may be influenced by the branching  and/or the molecular weight distribution of the polymer; (d)  is very sensitive to  the formation of molecular aggregates; (e) an effect of the shear rate on  is also  observed; (f) some of the above features for flexible chain polymers differ from those for stiff-chain polymers (Sakai 1968). The most important requirement for reliable intrinsic viscosity measurements is that the tested solution must be sufficiently dilute to eliminate polymer-polymer interchain interactions, so only polymer-solvent interactions and perhaps some intrachain forces govern the size and conformation of individual polymer chains. This state is called ideal dilute solution. In this case, the polymer concentration tends to zero, and the single polymer molecule interacts only with the solvent. The dimension of this single coil in dilute solution is what defines the intrinsic viscosity of the polymer (Kulicke and Clasen 2004). As the concentration of a polymer is gradually increased, the individual molecules are brought into contact with one another, producing a change in flow behavior. In diluted solutions, polymer coils must be spatially separated to prevent the formation of mechanical entanglements between the polymer chains. The critical concentration ( ) at which this process starts occurring is inversely related to the volume occupied by isolated polymer coils, or inversely related to the intrinsic viscosity of the polymer. At concentrations above  , the flow behavior is governed  by intermolecular interactions of the polymer coils; while below  , it is dominated  mainly by the polymer-solvent interactions. Truly dilute polymer solutions are Newtonian while the presence of entanglements usually leads to non-Newtonian effects, such as time-dependent flow or visco-elasticity. This critical transition concentration is polymer-specific, and it was shown to be 12  for guar gum  (Robinson et al. 1982). Lovell (1989) argued that in the most general case the transition concentration is at  to ensure truly dilute solution conditions.  Guar gum — as well as other polysaccharides such as starch — do not completely hydrate and dissolve in water to form truly molecular solutions. Consequently, the “solutions” are dispersions of undissolved colloidal (at the molecular level) aggregates  in  a  solution  of  partly-  and  fully-dissolved  polysaccharide  macromolecules. The size of guar gum aggregates was found to be of the order of tens of microns (Gittings et al. 2000; Gittings et al. 2001). These aggregates have little influence on the intrinsic viscosity because they are usually compact spheres, but they have a large impact on light-scattering measurements to determine the molecular weight since they appear as apparently large molecular weight fractions leading to an overestimate of the true molecular weight (Picout et al. 2001). Picout et al. (2001) studied the effect of heating and high pressure on the dissolution of guar gum aggregates. The study was carried out by using a combination of absolute determination of molecular weight, and intrinsic viscosity. They found that a combination of high pressure (4-12 bar) and temperature (above 130 °C) resulted in the dissolution of guar aggregates, while high temperature treatment alone led to chain degradation. It was also observed that low temperature treatment (below 70 °C) reduced molecular weight without affecting the intrinsic viscosity. Ma and Pawlik (2007b) measured the intrinsic viscosity and Huggins constants of guar gum in alkali metal chloride solutions of different concentrations. They found that, below 4.1 M of chlorides concentration, the intrinsic viscosity remained nearly constant (compared with distilled water). However, the Huggins constants — which represent the solvent quality — showed marked differences over the same electrolyte concentration range. At concentrations lower than 0.1 M, all the electrolyte solutions promoted the formation of aggregates. While at concentrations higher than 0.1 mol/L, the decreasing Huggins constants showed that the electrolytes promoted the dissolution of guar gum aggregates. 13  2.5.2 Molecular weight The average molecular weight of a polymer can be calculated from the intrinsic viscosity of the polymer using the Mark-Houwink-Sakurada (MHS) equation, sometimes with the name Staudinger appended (Picout and Ross-Murphy 2007). The equation can be written as: (2.11)  The MHS parameters  and  are constants for a given solvent, polymer, and  temperature. This equation (2.11) yields the viscosity-average molecular weight (  ), which lies between the number-average molecular weight (  weight-average molecular weight (  ). The exponent  ) and the  is a measure of the solvent  quality and the structure of the dissolved polymer (branched, sphere, rod or coil). On the other hand  is related principally to the local chain flexibility, including the  orientation of the bonds to and from the constituent monosaccharides (Kulicke and Clasen 2004; Picout and Ross-Murphy 2007). According to the MHS equation, the intrinsic viscosity values can be plotted on a logarithmic scale as a function of the logarithm of the molecular weight to obtain a straight line with slope equal to Picout and Ross-Murphy (2007) critically reviewed the experimental values of the MHS parameters for guar gum polymers published over the previous 25 years and concluded that only certain sets of those values could be considered as reliable. Picout and Ross-Murphy suggested that an average of those most reliable MHS parameters could be used for calculating the molecular weight from the intrinsic viscosity. Based on the tabulated data the average values in distilled water are: and  .  A characteristic parameter of polymers related to the molecular weight is the radius of gyration. This parameter represents the effective radius of the polymer in 14  solution and can be obtained directly by size exclusion chromatography coupled with multiangle laser light scattering (SEC/MALLS). Picout et al. (2001) studied the presence of aggregates in guar gum solutions by SEC/MALLS. Aggregates affect the molecular weight of guar gum, but have little influence on the viscosity of the solution. In their work, Picout et al. (2001) also obtained the molecular weights and the radius of gyration of treated and untreated guar gums of different molecular weights. These results will be used in Section 4.2.  2.6 Adsorption mechanism of talc and guar gum It is generally accepted that adsorbed polymers assume various conformations known as tails, loops and trains (Scheutjens and Fleer 1979; Scheutjens and Fleer 1980). The trains are directly attached to the surface while loops and tails are oriented away from it, as shown in Figure 2.3.  Figure 2.3. Adsorbed layer built up of several polymer molecules (Lyklema 1995)  The mechanism of adsorption of polysaccharides onto various mineral surfaces was studied extensively, and the experimental results were reviewed and summarized by Liu et al. (2000) and Laskowski et al. (2007). Despite the large volume of experimental data on polysaccharide adsorption on mineral surfaces, there are still disagreements about polysaccharide-mineral interactions. Almost all possible adsorption mechanisms were postulated even for the same mineral-polysaccharide 15  system. For example, the adsorption of carboxymethyl cellulose (CMC) on talc was proposed to proceed through: chemical complexation with metal hydroxyl sites on the basal planes (Laskowski and Liu 2007); chemical interactions with the edges (Cuba-Chiem et al. 2008); hydrogen bonding (Wang and Somasundaran 2005); and hydrophobic interactions (Steenberg and Harris 1984). Combinations of mechanisms were also suggested (Cuba-Chiem et al. 2008). Similar discrepancies are very common in the adsorption data for dextrin, starch, and guar gum (Laskowski et al. 2007; Liu et al. 2000) . In a systematic study, Rath et al. (1997) carried out adsorption tests with guar gum and dextrin with molecular weights of 4.22 MDa and 3.98 kDa (1Da = 1g/mol) onto three different talc size fractions. They showed that higher adsorption took place on the hydrophobic face compared to the edge. They also showed the importance of brucite layers and magnesium sites in the interaction mechanisms and concluded that the main adsorption mechanisms were hydrogen bonding and chemical interaction. They suggested that, compared to dextrin, the higher adsorption densities of guar gum on talc were due to the more favorable cisconfiguration of hydroxyl groups in guar gum, in addition to its higher molecular weight. Somasundaran et al. (2005) determined that the effect of pH and ionic strength on the  adsorption  of  guar  gum  onto  talc  was  insignificant.  In  fluorescence  spectroscopic studies, no evidence of the formation of hydrophobic domains at the talc-solution interface was found. They also observed that urea, a hydrogen bond breaker, decreased guar gum adsorption onto talc. These findings suggested that the main interaction in guar gum adsorption onto talc was through hydrogen bonding. Ma and Pawlik (2005) studied the effect of alkali metal chlorides on guar gum adsorption onto quartz. They found that the quartz-guar system was strongly affected by the type of background electrolyte. Less hydrated cations or water structure breakers (Cs+ and K+), even at low concentrations (0.01N), enhanced 16  markedly the adsorption of guar gum, while more hydrated cations or water structure makers (Na+ and Li+) had a lower effect on adsorption. It was concluded that hydrogen bonding is the main driving force in the guar gum adsorption onto quartz. The role of water-structure breaking ions was to disturb the interfacial water layer around hydrophilic quartz particles allowing guar gum chains to more densely adsorb on the quartz surface.  2.7 Molecular weight effects in polysaccharide adsorption The basic model of polymer adsorption (Scheutjens and Fleer 1979; Scheutjens and Fleer 1980), with some additions and modifications (Fleer et al. 1993; Fleer 2010), also predicts that a polymer with a high molecular weight should give a higher adsorption density compared to a polymer with a low molecular weight. Considering the large volume of adsorption data, in general, very few studies systematically investigated the effect of molecular weight of a polymer on its adsorption on a given mineral, and the experimental results sometimes do not agree with the theoretical predictions. For example, Solari et al. (1986) tested the adsorption of two carboxymethyl cellulose (CMC) samples of different average molecular weights on graphite, and found that the lower molecular weight sample (~80kDa) actually produced a higher adsorption density than the higher MW sample (~700kDa) on the fresh graphite surface. After the graphite sample was leached to remove metal impurities, adsorption became independent of molecular weight. Nanthakumar et al. (2010) investigated lignosulfonate adsorption on hematite using three lignosulfonates of different molecular weights, from 5 kDa to 25 kDa, and did not observe any correlations with the molecular weight of the samples. Greenwood (2003) tested seven samples of polyacrylic acid with molecular weights ranging from 3.5 kDa to 225 kDa, and did not find any statistically significant  17  effects of the molecular weight of the polymers on their adsorption density on alumina. Ansari and Pawlik (2007) studied lignosulfonate adsorption on molybdenite and chalcopyrite using six types of the anionic polyelectrolytes with a weight-average MW in the range 5-25 kDa. Data analysis was based on measuring total adsorption densities  and  comparing  the  molecular  weight  distributions  of  the  tested  lignosulfonates before and after adsorption using size exclusion chromatography (SEC). It was concluded that the high adsorption density of lignosulfonates on both molybdenite and chalcopyrite was primarily due to the adsorption of high MW fractions. Very few authors have studied the effect of molecular weight of a polysaccharide on adsorption onto talc. Shortridge et al. (2000) studied the effect of CMC molecular weight on depression of talc using four samples with molecular weights ranging from 205 kDa to 552 kDa (estimated through Mark-Houwink-Sakurada equation using intrinsic viscosity measurements in 0.01 M KNO3). There was no effect of molecular  weight on depression  of talc.  In this  work,  too high polymer  concentrations were used to measure the intrinsic viscosities, therefore the estimated MW were not entirely reliable. However, the order of MW could still be inferred from the intrinsic viscosity estimations. Parolis et al. (2005) also found that there was no effect of the molecular weight of CMC on the adsorption density onto talc. They used New York talc and almost the same CMC samples (three of the four) used previously by Shortridge, with molecular weights ranging between 114 kDa and 277 KDa (determined by size exclusion chromatography and low-angle laser-light scattering). Using talc from a different source with the same CMC samples used by Parolis et al. (2005), Khraisheh et al. (2005) found that CMC adsorption onto talc increased with increasing CMC molecular weight. The molecular weight ranged from 108 kDa to 194 kDa determined by size exclusion chromatography and laser light scattering. 18  Shortridge et al. (2000) also studied the effect of guar gum molecular weight on depression of talc. Poorly characterized anionic, cationic, and unmodified guar gum samples were used, and again a too high polymer concentration range was used for intrinsic viscosity measurements. The molecular weight of the samples was not reported but the order was inferred from the intrinsic viscosity estimations. They concluded that talc recovery from micro-flotation tests decreased with increasing molecular weight of guar gum, although the differences between the recoveries were very small and the overall trend was not very clear. Somasundaran et al. (2005) showed that unmodified guar gums with molecular weights of 1.45 MDa and 242 kDa did not show a marked difference in the depression of talc in micro-flotation tests. Maximum depression was achieved at low concentrations, and reached a plateau far below the conditions corresponding to maximum polymer adsorption. A related study by Wiese et al. (2008) concluded that low molecular weight starch (21 kDa) can be an effective depressant. The performance of starch was compared with the action of high molecular weight CMC and modified guar gum (MW of 325 kDa and 230 kDa, respectively). The results showed that guar gum was a superior depressant compared to starch and CMC, with the latter two producing similar results.  2.8 Flocculation and dispersion effects during flotation Sometimes the same polymers can function as dispersants or depressants. The most obvious feature of these polymers is their hydrophilicity. Their adsorption leads to the formation of a protective layer around the solid particles. Since polymers are hydrophilic, the adsorbed layer strongly interacts with water through hydrogen bonds preventing particles from aggregating (Laskowski et al. 2007).  19  Bridging is considered to be the most important flocculation mechanism. It is a consequence of the simultaneous adsorption of the segments of the same flocculant macromolecule onto the surfaces of several particles (Figure 2.4). While adsorption of the polymer is necessary for bridging flocculation to occur, it is important to realize that adsorption and flocculation are not separate, sequential processes, but occur simultaneously (Hogg 1999).  Figure 2.4. Bridging flocculation by long polymer molecules  Flocculants are most efficient at adsorption densities corresponding to only a fraction of the complete surface coverage (Kitchener 1972). Incomplete surface coverage ensures that there is sufficient surface available on each particle for adsorption during collisions of segments of the flocculant chains attached to the particles (Hogg et al. 1993). In a given dewatering application, an effective flocculant must be of the right molecular weight and charge density and contain functional groups that are predisposed to interact favorably with specific sites on the particle surfaces, for given dispersion conditions, including temperature (Hogg 2000). Moreover, the flocculant must also have an extended and flexible configuration in solution to achieve better particle bridging and to produce flocs capable of resisting moderate shearing forces without rupturing (Somasundaran and Moudgil 1988). 20  Mechanical and hydraulic entrainment of fine hydrophilic mineral particles is a severe problem that limits the effectiveness of the processing of low-grade finely disseminated ores by froth flotation. In flotation separations, fine mineral particles are usually kept highly dispersed. However, it was shown by Liu et al. (2006) that dispersion of fine hydrophilic particles increased their mechanical entrainment. They showed that moderately high MW polymer depressants such as corn starch and CMC (with a MW of 700 kDa) also flocculated these particles. This not only depressed the flotation of the particles but also reduced their mechanical and hydraulic entrainment. The low molecular weight polymeric depressants such as corn dextrin and CMC with a low MW of 80,000 could blind/depress the iron oxide and hydroxyapatite particles, but could not reduce their entrainment. Thus, when used as depressants in the separation of artificial mixtures of quartz and iron oxide or hydroxyapatite by a cationic collector, the high MW polymers performed better (Liu et al. 2006). By studying the effect of alkali metal cations (Cs+, K+, Na+ and Li+) on the adsorption of a high molecular weight guar gum onto quartz, Ma and Pawlik (2005) observed that guar gum acted as a weak flocculant. There was a common drop in turbidity at low concentrations of guar gum for all electrolyte solutions. When guar gum concentration was increased, the turbidity of quartz suspensions prepared in dilute NaCl and LiCl solutions increased rapidly due to redispersion of quartz until it reached values obtained in distilled water. On the other hand, the steric redispersion of fine quartz in dilute CsCl and KCl solutions was much weaker when guar gum concentration was increased over the same range of concentrations.  21  3 Experimental Program  3.1 Materials 3.1.1 Talc Talc samples were obtained from Ward Natural Science Establishment. The mineral was received as large pieces (approximately 5 cm by 5 cm as observed in Figure 3.1). Depending on the type of test, two talc samples were prepared. They were named Talc A and Talc B.  Figure 3.1. Talc pieces as received from Ward Natural Science Establishment.  22  Talc pieces were hammer-crushed to below 20 mm and separated into two subsamples. Talc A was dry-ground below 38 µm, which was used for adsorption and turbidity tests. Talc B was dry-ground below 106 µm, and this size fraction was used for flotation tests. Both samples were then characterized in terms of the particle size distribution, surface area, and porosity. The BET (Brunauer, Emmett, Teller) specific surface areas were determined by nitrogen adsorption after outgassing at 24 °C. The size distribution analysis was carried out in a Malvern Mastersizer 2000. The microporosity of the sample was obtained from the Autosorb-1MP BET analyzer (Quantachrome), using the DFT (density functional theory) method to obtain pore size distribution (more information on size analysis and porosity measurement is given in Appendix I). An x-ray diffraction analysis (Rietveld refinement) of this sample revealed the presence of 82% of talc, as well as roughly equal quantities of tremolite (Ca2Mg5Si8O22(OH)2), anthophyllite (Mg7Si8O22(OH)2), and lizardite (Mg3Si2O5(OH)4). The mineral was used as-received without any further purification. The flotation recovery of lizardite was reported to be due to mechanical and hydraulic entrainment (Peng and Bradshaw 2012), which suggests that lizardite is naturally hydrophilic. Tremolite is more hydrophilic than talc due, in part, to a more hydrated calcium ion. Anthophyllite is similar in structure to tremolite (Ciullo and Anderson 2002). The difference in the specific surface areas from nitrogen adsorption (BET) and from particle size analysis (Malvern) shows that the talc samples were quite porous. Since the relatively large guar gum macromolecules are unlikely to enter the pores it was necessary to estimate the real/external talc surface available for guar gum adsorption. For this, the average size of the guar gum coils was estimated and compared with the pore size distribution, thus the fraction of the BET surface area accessible for guar gum adsorption could be calculated (more details in Section 4.2). 23  The surface area given by Malvern Mastersizer was calculated assuming a spherical shape of the particles, which as observed in Figure 3.2. and Figure 3.3. is not an accurate representation of the morphology of the talc particles. The instrument is capable of calculating the particle size distribution from laser scattering data assuming a spherical shape of the particles as well as a generic non-spherical shape. However, the surface area calculation from the particle size distribution can only be done assuming a spherical shape of the particles. The “Malvern S. Area” given in Table 3.1 was obtained assuming spherical particles. Table 3.1. Talc samples characterization summary.  Talc  BET,  Malvern S. Area,  Calculated S. Area,  d90,  d50,  sample  m2/g  m2/g  m2/g  µm  µm  A  10.78  0.268  0.355  35.54  14.11  B  6.55  0.180  0.205  63.81  24.42  By adsorption of a dye (p-nitrophenol) onto New York talc (the same source as in the present thesis), Steenberg and Harris (1984) calculated the contribution of the basal planes to the total surface area as 71% and that of the edges as 29% for a talc sample with a BET specific surface area of 8.0 m2/g. Taking these proportions into account and assuming a plate-like disc shape of the particles, with the disc diameter equal to D and the thickness of the disc equal to W, the computed ratio of D to W is about 4.89. Using this ratio value and the d50 particle size given by Malvern Mastersizer — this time calculated assuming a non-spherical shape — as the diameter D of the talc plates, the value of W and the specific surface area of the particles can be obtained (Appendix VII). In this way, the specific surface areas of the two talc samples were calculated to be 0.355 m2/g and 0.205 m2/g for Talc A and Talc B, respectively. These values are given in Table 3.1 as “Calculated S. Area”, and these specific surface areas were used for calculating the adsorption densities. The choice of these values was based on the observation that the ratio of the two specific surface areas for Talc A and B was about 1.7 (0.355/0.205), which was very similar to the ratio of the specific surface areas obtained from BET (1.6) 24  and from the particle size distribution (1.5). This means that the relative adsorption densities measured for the two different talc samples were not significantly affected by the value of the specific surface area although the absolute adsorption densities were effectively corrected for the porosity of the samples as only the external surface areas were used in the calculation. Backscatter electron images (BSE) of each sample are shown in Figure 3.2. and Figure 3.3. Samples were examined using backscattered electron (BSE) imaging in a Philips XL30 scanning electron microscope (SEM) equipped with a Bruker Quantax 200 energy-dispersion X-ray microanalysis system and light element XFLASH 4010 Silicon Drift detector and Esprit software. The samples were previously coated with evaporated carbon in an Edwards Auto 306 coating system. The plate-like shape of the talc particles is evident in the SEM pictures (Figure 3.2. and Figure 3.3.). It can also be recognized that reducing the particle size also reduces the ratio of the surface areas of the basal planes to the edges. As the x-ray analysis of the samples revealed, the talc samples contained lizardite. The needle-like particles visible in Figure 3.2. and Figure 3.3. are referred to as "lizardite scrolls" (Wicks and Chatfield 2005) and the mineral is known to form such elongated anisotropic particles. Tremolite and anthophyllite are also known to form these needle-like shapes.  25  Figure 3.2. SEM pictures of the -38 µm size fraction  Figure 3.3. SEM pictures of the -105+75 µm size fraction  26  3.1.2 Guar gum Guar gum samples were supplied by Rantec Corporation (Ranchester, WY, USA) under the trade names of KP4000, RX5048, RX5051, and RX5055. The RX samples come from the same sample of guar gum. The difference is that RX5051 and RX5055 were produced by breaking the RX5048 to obtain polymers with shorter chains and consequently with lower molecular weights (MW). All four samples were non-ionic uncharged guar gums. They were renamed with more intuitive acronyms to facilitate analysis of the experimental results. Thus KP4000 is HMW1, RX5048=HMW2, RX5051=MMW3 and RX5055=LMW4. The molecular weight of the samples changes in the order: HMW1>HMW2>MMW3>LMW4. The meanings of the acronyms are: HMW: high molecular weight MMW: medium molecular weight LMW: low molecular weight The molecular weights of the samples were also estimated from intrinsic viscosity measurements parameters  using and  the  Mark-Houwink-Sakurada  equation.  The  empirical  , were obtained from the study of Picout and Ross-Murphy  (2007) (section 2.5.2). The results are summarized in Table 4.1. 3.1.3 Reagents 0.01 mol/L solutions of KCl and NaCl were used as background electrolytes. They were prepared using analytical grade potassium chloride and sodium chloride. Distilled water was utilized to prepare all solutions. All tests were performed at pH 9 unless otherwise specified. Concentrated solutions of hydrochloric acid and sodium hydroxide (analytical grade) were used as pH modifiers. For flotation tests, methyl iso-butyl carbinol (MIBC) was used a frother. The reagent was added as a stock 1% (wt) solution in distilled water.  27  3.2 Methodology 3.2.1 Preparation of guar gum solutions Fresh guar gum solutions were prepared daily because it decomposes very quickly. First, a “raw” guar gum stock solution of 4 g/L was prepared by mixing 0.8 g of guar gum powder with 200 ml of distilled water. Guar gum was slowly added over the vortex formed in water by a fast-spinning magnetic stirrer, and the solution was left mixing for four hours at room temperature. Natural guar gum contains water-insoluble residues. In order to purify the guar gums stock solutions, the following method was applied. The raw guar gum stock solutions were centrifuged in test tubes at 10,000g in a Heraeus Biofuge Primo centrifuge for 30 minutes. Then, the settled insoluble residues at the bottom of the tubes were separated by transferring the clean solution to another container. This changed the initial mass composition, therefore it was necessary to determine a correction factor (percentage of insoluble matter, Insoluble %) for calculating the actual guar gum concentration in the stock solution after centrifuging. The correction factor was calculated by measuring total organic carbon (TOC) before and after centrifuging (more details about TOC in Section 3.2.6). The waterinsoluble percentage of the raw guar gum solution was computed using the following formula:  (3.1)  The percentage of insoluble matter was calculated for all guar gum samples and is summarized in Table 3.2. The content of water-insoluble residues in the samples  ranged from 9.0% to 13.2 %, which agrees very well with the published data for natural guar gums from Chatterji and Borchardt (1981).  28  Table 3.2. Summary correction factors for guar gum samples  Insoluble,  Slope of calibration curve s,  (%)  (ppm TOC/ppm of guar gum)  HMW1  13.23  0.4426  HMW2  11.28  0.4389  MMW3  11.34  0.4513  LMW4  9.03  0.4920  In order to adjust the ionic strength of the guar gum stock solution (~3.5 g/L), an adequate amount of salt crystals was added and mixed for 30 minutes with a magnetic stirrer at room temperature. All guar gum solutions were prepared the same day or used within 24 hours of their preparation. A calibration curve relating the guar gum concentration to the total organic carbon content in the solutions was created with the aim of measuring the concentration after adsorption (equilibrium concentration). Thus, different solutions with known and corrected (after centrifuging) concentrations of guar gum were prepared by diluting guar gum stock solution (~3.5 g/L) in distilled water, and the total organic carbon was measured for each solution. The calibration curves are straight lines as shown in Appendix II: Calibration TOC Curves. They were obtained for all four guar gum samples, and the slopes  of the straight lines are summarized in Table 3.2.  Finally, the actual guar gum concentration in equilibrium after adsorption was calculated as follows:  (3.2)  All guar gum solutions were acidified to pH 2.5-3.0 to convert any dissolved carbonates into carbon dioxide. The solutions were slightly heated to expel carbon dioxide and so to eliminate its contribution to the TOC reading. 29  3.2.2 Characterization of main functional groups of guar gum by FTIR All Fourier transform infrared spectroscopy (FTIR) measurements were performed on guar gum films prepared from solutions in distilled water following the procedure described by Rogers and Poling (1978) for polyacrylamides. A droplet of 1 g/L guar gum solution was first frozen on an AgCl infrared window, then evaporated under vacuum (freeze-dried). The resulting film of guar gum on the AgCl window was used for infrared analysis. A Perkin-Elmer 2000 FTIR spectrophotometer was used for these measurements. Films of each guar gum sample were prepared at two pH values: pH 3 (adjusted with HCl); and natural pH ~5.5 for all the samples. The main purpose of this analysis was to detect the presence (or absence) of any anionic functional groups in the polymer samples.  3.2.3 Viscosity measurements Kinematic viscosity measurements of guar gum solutions in distilled water, KCl and NaCl were carried out. The measurements were made using two Cannon-Fenske capillary viscometers (Schott Gerate GmbH, Germany) (Figure 3.4) of different calibration constants in a PVS1 Lauda photo-timing and processing system. Before the first use, the viscometers were cleaned with a mixture of 15% hydrogen peroxide (H2O2) and 15% HCl as recommended by the manufacturer. The capillaries were carefully calibrated using distilled water at 25°C to obtain viscosity values equal to the accepted literature value of 0.89304 mm2/s (Weast 1970).  30  Figure 3.4. Schematic representation of the Cannon-Fenske capillary viscometer.  Figure 3.4 shows the type of capillary used in the study, with its parts labeled as follows: the left arm (A); the upper solution bulb (B); the upper timing mark (C); the measuring bulb (D); the lower timing mark (E); the capillary (F); the connecting tube (G); the sample reservoir (H); and the venting tube (I). In order to establish pH conditions for viscosity measurements, a blank adsorption test was made. The experiment showed that a 10% (wt) suspension of talc in water in the absence of guar gum gave a natural pH value of 9.0. Therefore, all viscosity measurements were also performed at pH 9 using NaOH for pH adjustment. The stock guar gum solution (~3.5 g/L) was diluted to 50 ml in a beaker to the desired guar gum concentration, and pH was adjusted to 9 and the diluted solution was stirred for a total of 30 minutes. Then, using a syringe, 7 ml of the diluted solution was transferred to the viscometer reservoir (H in Figure 3.4). The viscometer was then placed in the water bath of the viscometer system, and the temperature was kept constant at 24 ± 0.1°C for an equilibration time of 30 minutes. The kinematic viscosity was then determined automatically by the Lauda Viscometer. 31  The pump connected to the venting tube (I) applies a pressure until the tested solution flows into the upper bulb (B). Then the pressure is released and the guar gum solution flows down through the capillary by gravity. The PVS1 Lauda phototiming and processing system measures the time that the meniscus of the tested solution takes to pass from marker C to E (Figure 3.4). The Lauda viscometer was set up to perform triplicate measurements with one premeasurement test under the same conditions to pre-wet the capillary walls. Then, the Lauda software collected three flow times, the average of which was used to calculate the kinematic viscosity, v (in mm2/s) according to Equation 3.3: v K(t-ʋ)  (3.3)  Where K is the capillary calibration constant, t is the average flow time (s), and ʋ (s) is the Hagenbach kinetic energy correction. The correction was taken automatically by the instrument depending on the flow time of the tested solution. The kinematic viscosity was obtained for all four guar gum samples using distilled water, 0.01M NaCl and 0.01M KCl as background solutions, all of them at the natural pH of the blank test (pH 9). Once the kinematic viscosity was determined, the relative viscosity, the specific viscosity, the reduced viscosity and the intrinsic viscosity for each test were calculated using the formulas from section (2.5.1):  Relative viscosity:  (2.6)  Specific viscosity:  (2.7)  Reduced Viscosity:  (2.8)  32  Figure 3.5. Viscometry equipment Lauda PVS1  Then, the reduced viscosity was plotted as a function of polymer concentration. The resulting plot should be a straight line according to the Huggins equation: (2.11) Finally, the intrinsic viscosity was obtained from the intercept of the line with the reduced viscosity axis by extrapolation to zero polymer concentration. In order to avoid polymer-polymer interactions in solution, all guar concentrations for kinematic viscosity measurements were below  33  .  The experimental error of the viscosity measurements was about 2%. Considering differences in the intrinsic viscosities of guar gum obtained in the different background electrolytes as a measure of reproducibility and experimental errors, the standard deviation of  is on average 0.06 dl/g.  3.2.4 Adsorption tests The adsorption density can be defined as the total mass of guar gum adsorbed (in milligrams) per unit surface area of the mineral (m2).  and  are the initial  (known) concentration and the final equilibrium (measured) concentration of guar gum solutions, respectively.  is the volume of the solution and  is the specific  surface area available for guar gum adsorption (m2/g).  Adsorption density:  3.4  When complete adsorption is achieved, the guar gum equilibrium concentration in solution is equal to zero. Thus, adsorption density is only a function of the initial concentration, as shown in Equation 3.6.  3.5  Complete adsorption  3.6  Adsorption measurements were done under two sets of conditions: a) as a small scale measurement in a 50 mL container; and b) as a large scale measurement performed simultaneously with the flotation test in a flotation cell. For small scale tests, 5 g of the fine talc sample (Talc A, -38 micron size fraction) were placed in a 50 mL bottle with 25 g of a background solution. The bottle was placed in an IKA ks 4000 incubating shaker at 200 rpm at room temperature for 30 minutes to ensure thorough wetting of the talc particles with the background 34  solution. Then 25 g of a guar gum solution of known concentration was added to achieve the desired concentration. The bottle was placed again in the shaker for another 30 minutes to ensure adsorption equilibrium (minimum of 15 minutes according to Rath et al. (1997)). The agitated solution was taken out of the shaker and left settling for eight hours. Due to the high turbidities observed, a long time of settling was necessary to obtain turbidity values within the measuring limit of the turbidimeter. Then a pipette was submerged 1 cm into the container to extract 30 ml of the solution for further analysis of turbidity and TOC. The adsorption of the guar gum onto talc was also studied under flotation conditions. The flotation procedure is given in Section 3.2.7. After the flotation test, the tailings slurry was transferred to a 600 ml container and left settling for 30 minutes. Then a pipette was submerged 1 cm from the surface and 30 ml of the solution were extracted for further turbidity and TOC analysis. The standard deviation of adsorption tests increased with increasing guar gum concentration  and  with  increasing  adsorption  density.  At  an  equilibrium  concentration of 200 mg/L of guar gum, the adsorption density was 12.9 mg/m2 with a standard deviation of 0.3 mg/m2 (2%). At an equilibrium concentration of 900 mg/L the adsorption density was 16.2 mg/m2 with a standard deviation of 2 mg/m2 (12%).  3.2.5 Turbidity and volume of flocculated talc measurements The turbidity of talc suspensions after adsorption tests was studied in order to find a relationship between guar gum adsorption and the dispersion of talc particles left in solution. The 30 ml solution extracted with the pipette in the adsorption test was transferred to a clean standard vial, which was placed in a Hach-2100AN turbidimeter. The measured turbidity values were expressed in nephelometric turbidity units (NTU), representing the level of light scattering as it passes through 35  the suspension. The measuring range of the equipment is from 0 to 10,000 NTU, 0 being the clearest and 10,000 the most turbid solution. Therefore, highly turbid suspensions required extra settling time to bring their turbidity down to the measuring range of the instrument.  Figure 3.6. Samples for turbidity measurements. Concentration of guar gum increases from left to right: 0, 140, 280, 410, 630, 1,100 and 1,500 mg/L, HMW2.  The percent standard deviation of these tests ranged from 12 to 30% depending on the polymer type and concentration. Values of typical experimental errors are given in Appendix V. The turbidity results were supplemented by the flocculated volume measurement on the same samples. The samples were left settling for 8 hours after adsorption. The reading was taken directly from the graduated scale in the 50 ml containers.  36  Figure 3.7. Samples for flocculated volume measurement. Concentration of guar gum increases from left to right: 0, 140, 280, 410, 630, 1,100 and 1,500 mg/L, HMW2.  The standard deviation of these tests was 14±0.25 ml at a guar gum concentration of 900 mg/L, and 12.5±0.5 ml at a guar gum concentration of 1,500 mg/L. 3.2.6 Total organic carbon (TOC) analysis The concentration of guar gum left in the solution after adsorption was determined based on the total organic carbon (TOC) content in the solution. The TOC measurements were performed using a Shimadzu TOC-VCHP/CPN Total Organic Carbon Analyzer. The instrument is capable of measuring TOC levels on the order of 5 ppb. The determination of the TOC content in solution is based on the complete combustion of the sample in the presence of a catalyst, and the amount of carbon dioxide released is recalculated to the total organic carbon content. In order to avoid the interference from dissolved carbonates the solution samples were acidified to pH 3 with HCl (1%wt) prior to TOC analysis to expel carbon dioxide from inorganic sources (e.g., dissolved carbonates). The guar gum concentration was read from calibration curves (section 3.2.1). For automatic measurements, up to 68 sample containers of 40 ml can be placed in the TOC analyzer, but to prevent excessive aging of guar gum solution, no more than ten samples were tested at one time. The Shimadzu control software was configured to calculate the average of three measurements, repeating up to two of them in case the standard deviation (0.1) and the coefficient of variation (2%) were exceeded. 37  3.2.7 Flotation tests The floatability of talc was studied in the guar gum concentration range from 0 to 500 mg/L (0 to 5000 g/ton). A 0.01 mol/L KCl solution was used as the background electrolyte. An Agitair LA-500 flotation machine with adjustable air flow rate and a 500 ml flotation cell was used in these experiments (Figure 3.8). The water and talc masses used in the small-scale adsorption tests were increased proportionally to keep the same solids-to-liquid ratio in the flotation test. The pH was adjusted using NaOH. The following conditions were kept constant: Flotation conditions: Solids percent  : 9 % wt  Talc  : 50 g  Background solution  : KCl 0.01M  Cell Agitation  : 700 rpm  Frother (MIBC)  : 40 g/ton  Talc conditioning time  : 6 min.  Guar gum cond. time  : 6 min  MIBC conditioning time  : 2 min.  pH conditioning time  : 2 min.  pH  : 9.0 ± 0.1  Air flow rate  : 4 L/min.  Scraping  : every 5 s  Flotation time  : 5 min.  It should also be noted that adsorption measurements performed at the end of each flotation test allow the effect of aeration on guar gum adsorption to be directly assessed. The standard deviation of talc recovery was less than 5%.  38  Figure 3.8. Flotation machine with the 500-mL cell (left), typical talc flotation concentrate (right).  39  4 Results and Discussion 4.1 Characterization of guar gum by FTIR spectroscopy The modification process to reduce molecular weight of natural guar gum may introduce anionic groups onto the main polymer chain. Hence, FTIR spectroscopy was used to characterize the potential anionicity of the tested guar gum samples. Figure 4.1 to Figure 4.3 show FTIR spectra of guar gum films prepared at pH 3 and natural  pH.  The  spectra  exhibit  all  bands  and  peaks  characteristic  of  polysaccharides. The 2800–3000 cm-1 wavenumber range is associated with the stretching modes of the C–H bonds of methyl groups (–CH3), the broad band at 3400 cm-1 results from the presence of –OH groups, and the 900–1200 cm-1 range represents various vibrations of C–O–C glycosidic and C–O–H bonds. Of special interest to this research is the range between 1500 and 1800 cm -1, typically used to detect the presence of carboxylic groups. It can be seen that there is a small peak on both guar gum spectra at 1640 cm -1 which is often assigned to the dissociated carboxylate group (–COO-). When the pH is lowered to 3, a shift of the peak at 1640 cm-1 towards the 1730–1760 cm-1 range would be expected if carboxylic groups were present. However, the peak does not change its relative position or intensity, and no new peak appears near a wavenumber of 1740 cm -1 where  the  protonated  COOH  group  should  produce  a  strong  band.  This  characteristic shift can readily be detected for other anionic polymers such as carboxymethyl cellulose (Ma and Pawlik 2007b) or hydrolyzed polyacrylamide (Arinaitwe and Pawlik 2009). It appears that the guar gum samples are free from any residual carboxylic derivatives and can thus be treated as totally non-ionic. Natural gums are known to contain a fraction of uronic derivatives, which would impart a weak anionic character to the guar gum macromolecule (Wang et al. 2003). It is also worth pointing out that a peak near 1640 cm-1 may originate from in-plane deformations 40  of water molecules hydrogen-bonded to polysaccharide molecules (Synytsya et al. 2003). Since guar gum samples appear to be non-ionic, any changes in the viscosity of their solutions in the presence of electrolytes cannot originate from changes in the conformation of the macromolecules (coiled vs. extended) resulting from the screening of anionic functional groups by dissolved ions.  0.50 0.45  HMW2 pH nat HMW2 pH3  0.40  Absorbance  0.35 0.30 0.25 0.20 0.15 0.10 4000  3600  3200  2800 2400 2000 1600 Wavenumber [cm-1]  1200  800  400  Figure 4.1. FTIR spectra of HMW2 guar films prepared at natural pH and pH 3.  41  0.50 MMW3 pH nat  0.45  MMW3 pH3  Absorbance  0.40 0.35 0.30  0.25 0.20 0.15  0.10 4000  3600  3200  2800 2400 2000 1600 Wavenumber [cm-1]  1200  800  400  Figure 4.2. FTIR spectra of MMW3 guar films prepared at natural pH and pH 3.  0.50 LMW4 pH nat 0.45 LMW4 pH3  Absorbance  0.40 0.35 0.30 0.25 0.20 0.15 0.10 4000  3600  3200 2800  2400  2000  1600  1200  800  400  Wavenumber [cm-1] Figure 4.3. FTIR spectra of LMW4 guar films prepared at natural pH and pH 3.  42  4.2 Intrinsic viscosity The reduced viscosities of the different samples of guar gum as a function of their concentration are shown in Figure 4.4. All the concentrations for viscosity measurements were below  to prevent the formation of intermolecular  entanglements (Lovell 1989). The lines are the Huggins fits (Equation 2.9) to the individual sets of data where the intercept point of each line with the reduced viscosity scale represents the intrinsic viscosity. The MW order of the samples can be visually determined from their intrinsic viscosities. HMW1 and HMW2 are highMW samples and their intrinsic viscosities are relatively high; sample MMW3 is a medium MW; and LMW4 is a low MW guar gum sample. The results are summarized in Table 4.1. 25  HMW1  Reduced Viscosity [dl/g]  20  HMW2 MMW3 LMW4  15  10  5  0 0  200  400  600  800  1000  1200  1400  1600  Guar Gum Concentration mg/L Figure 4.4. Intrinsic viscosity of different guar gums in distilled water at pH 9.  From the intrinsic viscosity measurements, the molecular weights of the guar gum samples were calculated (Table 4.1) according to the Mark-Houwink-Sakurada 43  equation explained in Section 2.5.2, using the average values of  and  reported  in the study of Picout and Ross-Murphy (2007).  Table 4.1. Description of guar gum samples  Intrinsic viscosity[n],  Molecular weight,  Diameter of gyration,  dl/g  MDa  nm  HMW1  12.47  1.400  268  HMW2  12.06  1.337  262  MMW3  6.51  0.572  166  LMW4  2.60  0.162  85  Table 4.1 also presents the diameters of gyration. These values were calculated from the tabulated radius of gyration in Picout et al. (2001) obtained by size exclusion chromatography and multi-angle laser light scattering (SEC/MALLS) for guar gum samples of similar molecular weights and intrinsic viscosities to those tested in this thesis. Picout et al. (2001) measured the weight-average molecular weight (Mw) and the radius of gyration (Rga) of various types of guar gum. They presented the results in a Log(Mw) vs. Log(Rga) plot with a very good linear fit. This trend line was used for interpolating the data in Table 4.1. The diameter of gyration (taken as the radius of gyration times 2) can be interpreted as an approximate diameter of the polymer chain in solution. The intrinsic viscosity was experimentally obtained in KCl, NaCl and distilled water background solutions for all guar gum samples. The results are plotted in Figure 4.5 to Figure 4.8., and Table 4.2 shows a summary of the obtained intrinsic viscosities and Huggins constants. All the data were obtained at pH 9.0.  44  35  HMW1  Reduced Viscosity [dl/g]  30 H2O KCl 25  NaCl  20  15  10 0  200  400 600 Guar Gum Concentration [mg/L]  800  Figure 4.5. Intrinsic viscosity of HMW1.  35  HMW2  Reduced Viscosity [dl/g]  30 H2O KCl NaCl  25  20  15  10 0  200  400 600 Guar Gum Concentration [mg/L]  Figure 4.6. Intrinsic viscosity of HMW2.  45  800  25  MMW3  Reduced Viscosity [dl/g]  20  H2O KCl NaCl  15  10  5  0 0  200 400 600 Guar Gum Concentration [mg/L]  800  1000  Figure 4.7. Intrinsic viscosity of MMW3  25  Reduced Viscosity [dl/g]  LMW4 20 H2O KCl NaCl  15  10  5  0 0  200  400 600 800 1000 Guar Gum Concentration [mg/L]  1200  Figure 4.8. Intrinsic viscosity of LMW4  46  1400  Table 4.2. Intrinsic viscosities for guar gums dissolved in different background solutions  Sample HMW1  HMW2  MMW3  LMW4  Background solution H2O NaCl KCl H2O NaCl KCl H2O NaCl KCl H2O NaCl KCl  Intrinsic Viscosity, [n] 12.47 12.49 12.41 12.06 12.03 11.95 6.51 6.59 6.48 2.60 2.60 2.48  Huggins constant, (k) 0.89 0.87 0.84 0.93 0.89 0.89 0.61 0.60 0.63 0.56 0.53 0.77  It is observed that the intrinsic viscosity is essentially independent of the type of the background electrolytes. In other words, these electrolyte solutions do not affect the solvent-polymer and polymer-polymer interactions in the different guar gum solutions. The results agree with Ma and Pawlik (2007b) who showed that dilute sodium and potassium chloride solutions had no effect on the intrinsic viscosity of a high-molecular weight guar gum. Since in this thesis, several samples of  much  lower  molecular  weight  were  investigated,  it  was  important  to  assess/verify the effect of the background salts on the solution behavior of the tested guar gum samples. Huggins constants higher than 0.5 indicate that a substantial amount of guar gum occurs in solution in the form of undissolved colloidal aggregates (Sakai, 1968). It seems that aggregation is more pronounced for the higher MW polymers, but the different salts do not have a significant effect on the aggregation state of a given guar gum sample.  47  4.3 Adsorption In order to estimate a surface area of talc available for guar gum adsorption, the pore size distribution and the size of guar gum coils (diameter of gyration) were considered in the analysis. By contrasting the diameter of gyration from Table 4.1 with pore size distribution (Figure I-3. and Figure I-4. in Appendix I), it is possible to observe that the size of pores on talc samples are much smaller than the estimated sizes of the coils of guar gum. Hence, the total specific surface area calculated by BET, which includes the surface area contained inside the pores, is not useful in calculating the adsorption density because it would be physically impossible for the large coils of guar gum to adsorb inside the pores. Therefore, the surface area from pores can be generally neglected with the exception of the lowest molecular weight sample that is discussed later. It should be noted that the porosity results indicate that at least 90% of the total BET specific surface areas of Talc A and Talc B are in fact contained within the pores leaving less than 0.9 m 2/g as the external surface area available for guar gum adsorption. As discussed in earlier sections (Section 3.1.1), calculations based on the observed plate-like particle shapes indicated that the specific surface area is about 0.20-0.35 m2/g which qualitatively agrees with the porosity data. Figure 4.9. to Figure 4.12 present the adsorption results from small scale tests for the different samples of guar gum onto talc surface in the presence of different background electrolytes (NaCl, KCl and H 2O). It should be noted that the finer talc (Talc A) was used in these tests.  48  22  HMW1  20 18  Amount Adsorbed [mg/m2]  16 14 12 10 8  NaCl H2O KCl  6 4 2 0 0  200  400 600 800 1000 Equilibrium Guar Gum Concentration [mg/L]  1200  Figure 4.9. Adsorption of HMW1 on talc  22  HMW2  20 18 Amount Adsorbed [mg/m2]  16 14 12 10  8  NaCl H2O KCl  6 4 2  0 0  200  400 600 800 1000 Equilibrium Guar Gum Concentration [mg/L]  Figure 4.10. Adsorption of HMW2 in talc  49  1200  22  MMW3  20 18 Amount Adsorbed [mg/m2]  16 14 12 10 8  6  NaCl H2O KCl  4 2 0 0  200  400  600  800  1000  Equilibrium Guar Gum Concentration [mg/L] Figure 4.11. Adsorption of MMW3 on talc  22  LMW4  20 18 Amount Adsorbed [mg/m2]  16 14 12  10 8 6  NaCl H2O KCl  4 2 0 0  200  400 600 800 1000 Equilibrium Guar Gum Concentration [mg/L]  Figure 4.12. Adsorption of LMW4 on talc.  50  1200  It is possible to observe that guar gum adsorption onto talc is not affected by the background electrolyte solutions. The three adsorption curves of NaCl, KCl and H 2O (distilled water) overlap, and this is observed for all four guar gum samples. All the adsorption isotherms fall in the L2 Langmuir type — according to Giles et al. (1960) classification — which agrees with Rath et al. (1997) results. All curves reach a plateau at equilibrium concentrations of over 200 mg/L, and only a small increase in guar gum adsorption is observed at higher concentrations. In order to show the effect of molecular weight, adsorption results are presented in groups by background solution type (Figure 4.12, Figure 4.13 and Figure 4.14). The results show that the three highest molecular weight samples have a similar adsorption behavior while LMW4 consistently gives a slightly higher adsorption density for the three background electrolytes. 22  H2O  20  Amount Adsorbed [mg/m2]  18 16 14 12 10 8  HMW1 HMW2 MMW3 LMW4  6 4 2 0 0  200 400 600 800 Equilibrium Guar Gum Concentration [mg/L]  1000  1200  Figure 4.13. Adsorption of guar gum samples in distilled water background.  51  22  NaCl  20  Amount adsorbed [mg/m2]  18 16 14 12 10 8 HMW1 HMW2 MMW3 LMW4  6 4 2 0  0  200 400 600 800 1000 Equilibrium Guar Gum Concentration [mg/L]  1200  Figure 4.14. Adsorption of guar gum samples in NaCl 0.01M background.  22  KCl  20  Amount adsorbed [mg/m2]  18 16 14 12 10 HMW1  8  HMW2  6  MMW3  4  LMW4  2 0 0  200  400 600 800 1000 Equilibrium Guar Gum Concentration [mg/L]  1200  Figure 4.15. Adsorption of guar gum samples in KCl 0.01M background.  52  Figure 4.16. to Figure 4.19 show the adsorption density from small scale tests as a function of the initial guar gum concentration for every background solution, grouped by guar gum sample. The dotted line represents complete adsorption, i.e., when all guar gum is adsorbed by talc and there is no polymer left in solution. This set of graphs shows that complete adsorption takes place up to an initial concentration of approximately 400 mg/L for the three highest MW samples, and up to ~500 mg/L for LMW4. Above that point, there is still some adsorption taking place, but to a much lower degree, and the excess of guar gum is left in solution. HMW1, HMW2 and MMW3 reach a plateau at ~16 mg/m2, while LMW4 gives a slightly higher plateau value of ~19 mg/m2.  22 HMW1  20  Amount Adsorbed [mg/m2]  18 16  14 12 10 8 NaCl  6  H2O  4  KCl  2 0 0  200  400  600  800  1000  1200  Initial Guar Gum Concentration [mg/L] Figure 4.16. Adsorption of HMW1  53  1400  1600  22  HMW2  20  Amount Adsorbed [mg/m2]  18 16 14 12 10 8 NaCl H2O KCl  6 4  2 0 0  200  400 600 800 1000 1200 1400 Initial Guar Gum Concentration [mg/L]  1600  1800  Figure 4.17. Adsorption of HMW2  22 MMW3  20  Amount Adsorbed [mg/m2]  18 16 14  12 10 8 6  NaCl H2O KCl  4 2 0 0  200  400  600  800  1000  1200  1400  Initial Guar Gum Concentration [mg/L] Figure 4.18. Adsorption of MMW3  54  1600  1800  22 LMW4  20  Amount Adsorbed [mg/m2]  18 16 14  12 10  8 NaCl  6  H2O  4  KCl  2  0 0  200  400 600 800 1000 1200 1400 Initial Guar Gum Concentration [mg/L]  1600  1800  Figure 4.19 Adsorption of LMW4  4.4 Turbidity Since no significant effect of the background salts was observed on both the intrinsic viscosity and adsorption density of guar gum, turbidity measurements were performed only in 0.01 M KCl as the background electrolyte. In order to study the effect of molecular weight of guar gum on the stability of talc suspensions, turbidity measurements on the adsorption test supernatants were carried out. Figure 4.20. to Figure 4.23. show the turbidity results together with the adsorption data as a function of the initial guar gum concentration. The logarithmic turbidity scale should be noted. The dashed lines drawn in the figures indicate complete adsorption values at a given initial guar gum concentration, i.e., the entire amount of guar gum adsorbs on talc leaving no residual polymer in solution.  55  As the turbidity results show, low amounts of guar gum decrease the turbidity of talc suspensions used in the adsorption tests. At some guar gum dosage, the turbidity of the supernatants reaches a minimum and then steadily increases as the guar gum concentration increases. The initial decrease in turbidity with guar gum dosage is consistent with the flocculation of fine talc particles by guar gum until an optimum flocculation dosage is reached. Above that critical dosage, the turbidity of talc suspensions increases indicating that the fine talc particles gradually became redispersed due to steric stabilization. This overall trend is typical for industrial flocculants and the increase in turbidity results from the steric dispersion of talc.  22  1000  20 18 100  14  Turbidity [NTU]  Amount Adsorbed [mg/m2]  16  12 10 8  10  6  Adsorption  4  Turbidity  2 0 0  200  400  600 800 1000 1200 1400 1600 Initial Guar Gum Concentration [mg/L]  Figure 4.20. Turbidity for HMW1  56  1 1800  22  1000  18 16 100  14 12 10 8  10  6  Adsorption  4  Turbidity  Turbidity, NTU  Amount Adsorbed [mg/m2]  20  2 0 0  200  1 400 600 800 1000 1200 1400 1600 1800 Initial Guar Gum Concentration [mg/L] Figure 4.21. Turbidity for HMW2  22  10000  20 18 Amount Adsorbed [mg/m2]  14 12  100  10 8 6  Adsorption  4  10  Turbidity  2 0 0  200  400  600  800  1000  1200  1400  Initial Guar Gum Concentration [mg/L] Figure 4.22. Turbidity for MMW3  57  1600  1 1800  Turbidity [NTU]  1000  16  22  10000  20 1000  16 14 12  100  10 8 6  Adsorption  4  turbidity  Turbidity [NTU]  Amount Adsorbed [mg/m2]  18  10  2 0 0  200  400  600  800  1000  1200  1400  1600  1 1800  Initial Guar Gum Concentration [mg/L] Figure 4.23. Turbidity for LMW4  Below an initial guar gum cocentration of 200 mg/L, all the guar gum samples act as flocculants by decreasing the turbidity from an average of 79 NTU without guar gum to minimun values of 3.0, 1.8, 10.8 and 7.0 NTU for HMW1, HMW2, MMW3 and LMW4 respectively. High molecular weight samples are stornger flocculants than lower molecular weight samples as judged from the minimum turbidity values. This trend can also be seen from Figure 4.25. where the total volume of flocculated talc after adsorption reaches a maximum at the same guar gum concentration as the minimum turbidity value. The lowest flocculated volume was obtained for LWM4 while the highest volume was seen in the case of HMW1 and HMW2. It is observed that all guar gum samples act as flocculant because they increase the volume of the settled talc. However, higher molecular weight samples act as more powerful flocculants than lower molecular weight guar gum samples. After reaching a maximum volume of the flocculated/settled talc, all samples started decreasing the flocculated volume due to gradual redispersion of talc: more talc was now suspended as judged by the increasing turbdity of the samples.  58  Above the concentration corresponding to the minimum turbidity and maximum flocculated volume, all guar gum samples begin acting as dispersants, but to quite different degrees and with a marked trend. In Figure 4.24 all stability curves are plotted together. It is interesting to observe that in this guar gum concentration range turbidity correlates very well with the molecular weight of guar gum. Lower MW samples act as more powerful dispersants compared to the higher molecular weight samples. This dispersant effect is larger above the highest concentration at which the adsoprtion of guar gum was still complete for all guar gum samples.  10,000  Turbidity [NTU]  1,000  100 LMW4 MMW3 HMW2 HMW1  10  1 0  200  400 600 800 1000 1200 Initial Guar Gum Concentration [mg/L]  1400  1600  Figure 4.24. Dispersion of talc for different MW guar gums.  59  24 HMW1 HMW2 MMW3 LMW4  Flocculated talc Volume [mL]  22 20 18 16 14 12 10 0  200  400 600 800 1000 1200 Initial Guar Gum Concentration [mg/L]  1400  1600  Figure 4.25. Flocculated talc volume of adsorption tests  4.5 Flotation The first step was to study guar gum adsorption on a small and easy-to-control scale. The next step was to study guar gum adsorption under more realistic hydrodynamic conditions in a small laboratory flotation cell. 4.5.1 Adsorption in flotation As observed in Figure 4.26. and Figure 4.27., the adsorption of guar gum onto talc during flotation is in general independent of the molecular weight of guar gum. All the guar gum samples fall on the same adsorption curve; however LMW4, as observed in small scale results, seems to give a slightly higher adsorption than the other guar gum samples.  60  From Figure 4.27., it is possible to observe that maximum complete adsorption (MCA) is ~8.0 mg/m2 and is reached at ~200 mg/L of initial guar gum concentration, while complete surface coverage (CMC) is ~10.7 mg/m2 and is reached above 350 mg/L. These curves also follow the L2 Langmuir type of adsorption isotherm according to Giles et al. (1960).  14 13 12 11  Amount Adsorbed [mg/m2]  10 9 8 7 6 5  LMW4  4  MMW3  3  HMW2  2  HMW1  1 0  0  50  100 150 200 250 Equilibrium Guar Gum Concentration [mg/L]  300  Figure 4.26. Adsorption density as a function of equilibrium concentration  61  14  13 12  CSC  11 Amount Adsorbed [mg/m2]  10 MCA  9 8  7 6 5  LMW4 MMW3 HMW2 HMW1  4 3 2  1 0 0  100  200 300 400 500 600 700 Initial Guar Gum Concentration [mg/L]  800  900  Figure 4.27. Adsorption density versus guar gum initial concentration  18  KCl  16 14  Amount adsorbed [mg/m2]  12 10 8 Small scale  6  HMW1 HMW2 MMW3 LMW4  4 2  Flotation scale HMW1 HMW2 MMW3 LMW4  0 0  50  100 150 200 250 300 Equilibrium Guar Gum Concentration [mg/L]  350  400  Figure 4.28. Adsorption densities for small and flotation scales, 0.01M KCl, pH 9.  62  In Figure 4.28 are shown the adsorption densities for all guar gum samples in KCl background solution and for both experimental scales. As observed, both sets of curves behave qualitatively in a very similar manner although there is a decrease in the adsorption densities in the flotation scale tests. Small scale data reach a plateau in the adsorption density at ~16 mg/m2, while in the larger scale flotation data the plateau appears at ~10.7 mg/m2.  4.5.2 Recovery of talc The effect of guar gum molecular weight on the recovery of talc in flotation is represented in Figure 4.29. It can be seen that all guar gum samples behave similarly. There are two guar gum concentration ranges. A big drop of talc flotation is observed in the initial guar gum concentration range up to 20 mg/L. The total depression of talc flotation occurs between 20 and 55 mg/L. Although the tests were performed up to an initial guar gum concentration of 500 mg/L, no talc flotation was observed at guar gum concentrations above 55 mg/L, and only barren bubbles were bursting at the pulp surface. In order to highlight the differences between the two concentration ranges, the results over 60 mg/L are not shown (zero talc recovery). It may be interesting to note that at a guar gum concentration of 20 mg/L the recovery of talc is only about 10% for the two lowest MW guar gums, and around 20% for higher MW guar gum samples. It is also noteworthy that a zero recovery of talc means that the mechanical entrainment of depressed hydrophilic talc particles was basically eliminated and the data reflect the true flotation of fine talc.  63  75 70 65 60 Recovery [%]  55 50  45 40  35 30 25 20 15 10 5 0 0  10  20 30 40 Initial Guar Gum Concentration [mg/L]  50  60  Figure 4.29. Recovery of talc in flotation  4.5.3 Turbidity in flotation Figure 4.30. shows turbidity measurements taken from the tailings slurry 30 minutes after flotation tests. The results are qualitatively very similar to the data obtained from small-scale tests. A direct relationship between turbidity and molecular weight is observed. All guar gum samples behave similarly, flocculating talc and decreasing turbidity at concentrations below ~55 mg/L, starting from an average of 430 NTU without guar gum and decreasing to the minimum values of 31.55, 34.8, 56.5 and 120 NTU for HMW1, HMW2, MMW3, and LMW4, respectively. There is a marked difference in the flocculation capacity of the guar gum samples, the highest MW samples being the strongest flocculant and the lowest MW sample the weakest. Above ~55 mg/L, all guar gums act as dispersants. There is also a marked trend in their dispersion capabilities; the lower the guar gum molecular weight, the better the dispersing power of the polymer. 64  10,000  Turbidity [NTU]  1,000  100  HMW2 - no flotation 10 0  50  100  150  200  250  300  350  Initial Guar Gum Concentration [mg/L]  400  450  500  Figure 4.30. Turbidity in the complete concentration range  As mentioned earlier all the samples for turbidity measurements were taken after flotation. Since under good flotation conditions the solids content in the tailings (the amount of depressed talc) is low, the turbidity of tailings should be low as well. As talc depression progresses at higher doses of guar gum, the solids content in the tailings should gradually increase and the turbidity of tailings under strong depression of talc should also increase. Since complete talc depression was achieved at a guar gum concentration of 55 mg/L, the turbidity data in Figure 4.30 above 55 mg/L are affected only by the dispersion/flocculation of talc and not by changes in the solids content since all talc was left in tailings. However, the turbidity results below 55 mg/L reflect a combined contribution of partial flotation/depression and talc dispersion/flocculation. In order to delineate the effect of dispersion/flocculation only, two tests were repeated without carrying out any flotation: one in the absence of a polymer and one in the presence of 25 mg/L of HMW2. A talc suspension was conditioned in a flotation cell, and the slurry was left  65  to settle. Samples of the supernatant were then taken for turbidity tests. The results of those two tests are shown as solid rectangles. These points confirm that the general shape of the curve follows the same trend, and that turbidity indeed decreases as the guar gum concentration increases from 0 to 55 mg/L. According to the theory of polymer adsorption, high molecular weight guar gum samples should produce a higher adsorption density, and consequently a better depression of talc could be expected. As shown in Chapter 2, even in the limited amount of information available in the literature about the impact of molecular weight  on  adsorption  and  depression of  guar  gum  onto  talc,  there  are  discrepancies. The present study aims to contribute through systematic studies, to the understanding of the surface chemistry science of the talc-guar gum system. In contrast to the theory, the laboratory test results presented in this thesis revealed that the molecular weight of guar gum does not have a marked impact either on adsorption onto talc or on the depression of talc. These findings agree with the published results by Somasundaran et al. (2005) and Shortridge et al. (2000). The insignificant effect of MW in systems involving talc and other polysaccharides (carboxymethyl celluloses, other samples of guar gum) was also reported (Shortridge et al. 2000; Parolis et al. 2005) which may suggest that the lack of the effect of MW is characteristic of the surface properties of talc rather than of the interfacial behavior of guar gum. Complete depression of talc was achieved at an initial guar gum concentration of 55 mg/L (Figure 4.29.), which is the same point where maximum flocculation was obtained, above which guar gum started acting as a dispersant (Figure 4.30.). At this critical point, the adsorption density of all the samples reached a value of about 2.1 mg/m2 (Figure 4.27.). Since the maximum adsorption density of guar gum at the plateau was about 10.7 mg/m2, it can be concluded that less than 20% of complete surface coverage by the polymer is sufficient to completely depress the flotation of talc.  66  Kitchener (1972) and Hogg et al. (1993) indicated that flocculants are most efficient at adsorption densities corresponding to only a fraction of the complete surface coverage. The behavior of guar gum is basically the same as that of flocculants. All the guar gum samples tested were effective flocculants. The depression of talc flotation by polysaccharides is usually explained by increased hydrophilicity of talc particles as a result of polymer adsorption. The present study strongly suggests that the depression of talc is also associated with the simultaneous flocculation of the talc particles by guar gum. In this case, flocculation leads to increased effective particle sizes of the flocs, and the flotation of such large aggregates is inhibited. At higher guar adsorption densities, steric stabilization takes place and brings about redispersion of the talc particles. All the polymers sterically redisperse talc although above the maximum concentration for flocculation, there is a clear relation between guar gum molecular weight and dispersion of talc. The guar gum samples of lower molecular weights produce the stronger dispersion of talc in the supernatant. As the adsorption density of guar gum increases, less and less of the surface area becomes available for adsorption on several particles at the same time. The bridging flocculation of fine talc no longer takes place and the particles become redispersed. This flocculating and depressing behavior was also observed by Ma and Pawlik  (2005)  in  a  guar  gum-quartz  system,  which  suggests  that  this  flocculation/dispersion behavior of guar gum is typical of the polymer and independent of the hydrophobicity or hydrophilicity of the mineral surface. The role of steric redispersion of fine talc particles by excessive doses of guar gum in talc flotation cannot be overlooked. Although talc depression can be expected to remain very strong at high guar gum doses, the sterically dispersed talc particles will be more likely to be mechanically and/or hydraulically entrained in the froth compared to the large fast-settling flocs. As showed by Liu et al. (2006), the dispersion of fine hydrophilic particles increased their mechanical entrainment. The present work showed that, at high dosages of guar gum, talc behaves like a finely dispersed hydrophilic solid. Therefore, the results strongly indicate that the 67  optimum conditions for talc depression are achieved when talc particles are rendered hydrophilic, and also when talc flocculation is most pronounced. From this point of view, a guar gum sample of high molecular weight would be a preferred depressant because the depressing power of such a polymer is basically the same as that of a low molecular weight reagent, however the flocculating capability of the higher molecular weight sample is stronger than that of a low molecular guar gum. The beneficial roles of high molecular weight polymer depressants in reducing mechanical entrainment of hydrophilic gangue minerals should be exploited. Flotation depressants should be evaluated in terms of not only their ability to make the target minerals hydrophilic but also by their ability to reduce the mechanical entrainment of the target gangue minerals (Liu et al. 2006). High molecular weight guar gum appears to offer such dual functions towards fine talc. It was observed that the lowest molecular weight (LMW4) has a slightly larger adsorption density than the other samples of guar gum, but there is no clear trend in the adsorption densities as a function of the molecular weight. This can be explained as follows: the surface area used for the adsorption density calculation was the same for all guar samples. However, the LMW4 due to its smaller size seems to be capable of penetrating some of the largest pores in the talc particles. In this way, the low MW polymers adsorb on the surfaces that are not accessible to the higher MW guar gums. Indeed, the diameter of gyration of LMW4 is 85 nm, and by extrapolating the pore size distribution (Figure I-3. and Figure I-4. in Appendix I), it is observed that at ~850 Å = 85 nm, the surface area is ~10.0 m2/g for Talc A and ~5.8 m2/g for Talc B. The total surface areas from BET are 10.78 and 6.55 m2/g for Talc A and Talc B, respectively, resulting in an extra ~0.8 m2/g of the specific surface area available in both talc samples for this low MW guar gum sample. The coil sizes of the three highest MW samples are larger than all the pores in both talc samples.  68  Despite the differences in hydrodynamic conditions of the two sets of tests (50 ml container and 500 ml flotation cell), and in the particle size distributions of Talc A and Talc B, the adsorption results were qualitatively very similar. NaCl and KCl background solutions do not diminish or enhance guar gum adsorption onto talc, which is in contrast to the results reported by Ma and Pawlik (2005) for the hydrophilic quartz-guar gum system. These authors suggested that small poorly-hydrated potassium cations were able to disturb the interfacial water layer around quartz particles thus allowing guar gum to adsorb by hydrogen bonding with the surface silanol groups. As a result, a significant increase in guar gum adsorption was observed in the presence of 0.01 M KCl compared to guar gum adsorption from distilled water or from 0.01 M NaCl. The very different adsorption response of talc suggests that interfacial water around the hydrophobic talc particles is inherently unstable and guar gum can easily adsorb on the talc surface regardless of the presence of water-structure making (Na) or breaking (K) ions. Since it is the basal plane of talc that is naturally hydrophobic, this comparison of the quartz and talc data also suggests that the basal planes of talc are the adsorption sites for guar gum.  69  5 Conclusions The intrinsic viscosity for all guar gum samples was independent of the type of the background electrolytes (NaCl and KCl). In other words, these electrolytes did not affect the solvent-polymer and polymer-polymer interactions in the different guar gum sample solutions. Dilute NaCl and KCl electrolyte solutions did not interfere with or enhance guar gum adsorption onto talc compared to adsorption from distilled water. This result suggested that the interfacial water layer around talc particles was quite unstable and the adsorption of guar gum onto talc did not depend on whether the background electrolyte was a water structure maker (Na) or breaker (K). The adsorption density of guar gum onto talc and the resulting depression of talc floatability were found to be independent of the molecular weight of the polymer. All the guar gum samples tested in this thesis were very effective depressants. Complete depression was achieved by all guar samples at a similar polymer dosage, when the coverage of talc by guar gum was less than 20% of the total talc surface area. In the same low concentration range, all guar gum samples also acted as flocculants of fine talc particles. In this case, the flocculating power of guar gum increased with the molecular weight. However, above the maximum flocculation concentration, all samples started acting as steric dispersants, increasing turbidity of talc suspensions as the guar gum concentration increased. The steric redispersion of fine talc particles was also a function of the molecular weight of guar gum, with the strongest dispersion observed for the lowest molecular weight sample. The combined flotation, flocculation, and adsorption results strongly indicated that the depression of talc flotation was accompanied by strong flocculation of the talc 70  particles as the strongest depression and most pronounced flocculation occurred at the same guar gum dosage. This observation also suggested that under optimum depression conditions large talc flocs would not be easily carried/lifted to the froth phase. However, higher dosages of guar gum led to steric redispersion of talc particles and such individual fine particles are more likely to be mechanically and hydraulically entrained in the froth. Therefore, excessive dosages of guar gum for talc depression should be avoided.  71  6 Recommendations for Further Research The surface chemistry of anisotropic mineral particles, such as talc is a complex subject. Guar gum adsorption on talc proceeds most likely on both the faces and edges of the particles, but the contributions of those two crystal surfaces to the total adsorption density are not known. It is also not known whether guar gum shows stronger affinity towards the faces or towards the edges. Therefore, of particular significance would be an investigation of polysaccharide adsorption at low polymer concentrations to assess any preferential adsorption onto faces or edges. This work could be supported by recent advances in fluorescence spectroscopy to detect organic molecules on mineral surfaces. Along these lines, a technique is needed, perhaps a combination of SEM with EDX and image analysis software, to directly measure the contributions of the basal planes (faces) and of the edges to the total surface area of talc particles. Since polysaccharides, and guar gum in particular, do not form truly molecular solutions, it is recommended that a study be performed to determine the role of undissolved colloidal aggregates in the guar gum adsorption process. This is a neglected topic and many adsorption models assume adsorption of single chains while ignoring the presence of aggregates. The resulting depression of talc and perhaps flocculation/dispersion phenomena are probably also affected by the presence of such aggregates. Although the presented results were discussed in terms of the average molecular weight of guar gum, it would be interesting to determine the effect of the molecular weight distribution of the polymers, or which molecular weight fractions are most active in the adsorption process and in subsequent talc depression and dispersion. The molecular weight distribution could be determined before and after adsorption and the data could be compared to identify the active molecular weight fraction(s). It would also be important to study the flotation behavior of talc in a model mixture with another mineral not readily depressed by guar gum, for example a sulphide 72  mineral rendered hydrophobic by the addition of xanthates. The main objective would be to evaluate the extent of talc entrainment in the sulfide concentrate as a function of polysaccharide dosage.  73  References Ansari, A., and Pawlik, M. (2007). "Floatability of chalcopyrite and molybdenite in the presence of lignosulfonates. 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"Scrolling of thin crystals of lizardite: An expression of internal stress." Mineralogical Association of Canada, 1993-2004. Wiese, J. G., Harris, P. J., and Bradshaw, D. J. (2008). "The use of very low molecular weight polysaccharides as depressants in PGM flotation." Minerals Eng, 21(6), 471-482.  79  Appendix I: Talc Sample Characterization Size distribution of talc samples  Figure I-1. Particle size distribution of Talc A  Figure I-2. Particle size distribution of Talc B  80  Microporosity of talc samples (A)  Figure I-3. DFT of talc sample A  81  Figure I-4. DFT of talc sample B  82  Appendix II: Calibration TOC Curves  500 Total Organic Carbon [ppm]  450 400 350 300  250  y = 0.4426x R² = 0.9974  200 150 100 50 0 0  200  400  600  800  1000  1200  Guar Gum Concentration [ppm] Figure II-1. Calibration TOC curve for HMW1  500  Total Organic Carbon [ppm]  450 400 350 300 250  y = 0.439x R² = 0.9975  200 150 100 50 0 0  200  400  600  800  1000  1200  Guar Gum Concentration [ppm] Figure II-2. Calibration TOC curve for HMW2  83  500  Total Organic Carbon [ppm]  450 400 350 300 250 200  y = 0.4514x R² = 0.9964  150 100 50 0 0  200  400  600  800  1000  1200  Guar Gum Concentration [ppm] Figure II-3. Calibration TOC curve for MWM3  500  Total Organic Carbon [ppm]  450 400 350 300 250 200  y = 0.4921x R² = 0.9945  150 100 50 0 0  200  400  600  800  1000  1200  Guar Gum Concentration [ppm] Figure II-4. Calibration TOC curve for LMW4  84  Appendix III. Viscosity Data Table III-1. Viscosity data of HMW1, pH 9, 24 °C  H2O Concentration [mg/L] 176 349 380 522 699 728  Kinematic viscosity 2  [mm /s] 1.1309 1.4333 1.4815 1.7999 2.2817 2.3676  Relative viscosity 1.27 1.60 1.66 2.02 2.55 2.65  Specific viscosity 0.27 0.60 0.66 1.02 1.55 1.65  Reduced viscosity  Relative viscosity 1.26 1.60 1.99 2.52  Specific viscosity 0.26 0.60 0.99 1.52  Reduced viscosity  Relative viscosity 1.29 1.62 2.04 2.55  Specific viscosity 0.29 0.62 1.04 1.55  Reduced viscosity  [dl/mg] 15.16 17.33 17.35 19.47 22.23 22.67  0.01 mol/L NaCl Concentration [mg/L] 173 355 512 690  Kinematic viscosity 2  [mm /s] 1.1253 1.4329 1.7767 2.2531  [dl/mg] 15.08 17.02 19.33 22.08  0.01 mol/L KCl Concentration [mg/L] 193 363 540 712  Kinematic viscosity 2  [mm /s] 1.1535 1.4455 1.8253 2.2815  85  [dl/mg] 15.05 17.00 19.29 21.80  Table III-2. Viscosity data of HMW2, pH 9, 24 °C  H2O Concentration  Kinematic viscosity  [mg/L] 177 237 480 744  [mm2/s] 1.1227 1.2186 1.6756 2.3722  Relative viscosity 1.26 1.36 1.88 2.66  Specific viscosity 0.26 0.36 0.88 1.66  Reduced viscosity  Relative viscosity 1.35 1.65 2.20 2.58  Specific viscosity 0.35 0.65 1.20 1.58  Reduced viscosity  Relative viscosity 1.34 1.63 2.18 2.73  Specific viscosity 0.34 0.63 1.18 1.73  Reduced viscosity  [dl/mg] 14.50 15.38 18.24 22.27  0.01 mol/L NaCl Concentration  Kinematic viscosity  [mg/L] 231 382 614 725  [mm2/s] 1.2049 1.4701 1.9640 2.3003  [dl/mg] 15.14 16.92 19.54 21.75  0.01 mol/L KCl Concentration  Kinematic viscosity  [mg/L] 231 377 604 788  [mm2/s] 1.2015 1.4552 1.9466 2.4426  86  [dl/mg] 14.95 16.65 19.52 22.00  Table III-3. Viscosity data of HMW2, pH 9, 24 °C  H2O Concentration  Kinematic viscosity  [mg/L] 177 264 373 530 709 921  [mm2/s] 1.0038 1.0625 1.1413 1.2636 1.4194 1.6275  Relative viscosity 1.12 1.19 1.28 1.41 1.59 1.82  Specific viscosity 0.12 0.19 0.28 0.41 0.59 0.82  Reduced viscosity  Relative viscosity 1.15 1.29 1.43 1.65 1.89  Specific viscosity 0.15 0.29 0.43 0.65 0.89  Reduced viscosity  Relative viscosity 1.15 1.28 1.42 1.65 1.89  Specific viscosity 0.15 0.28 0.42 0.65 0.89  Reduced viscosity  [dl/mg] 7.01 7.20 7.44 7.83 8.31 8.93  0.01 mol/L NaCl Concentration [mg/L] 211 375 544 754 970  Kinematic viscosity 2  [mm /s] 1.0280 1.1490 1.2766 1.4746 1.6847  [dl/mg] 7.15 7.64 7.90 8.64 9.14  0.01 mol/L KCl Concentration [mg/L] 213 373 531 759 982  Kinematic viscosity 2  [mm /s] 1.0272 1.1451 1.2656 1.4707 1.6926  87  [dl/mg] 7.03 7.54 7.84 8.51 9.11  Table III-4. Viscosity data of HMW2, pH 9, 24 °C  H2O Concentration  Kinematic viscosity  [mg/L] 220 342 815 1285 1543  [mm2/s] 0.9452 0.9772 1.1051 1.2484 1.3310  Relative viscosity 1.06 1.09 1.24 1.40 1.49  Specific viscosity 0.06 0.09 0.24 0.40 0.49  Reduced viscosity  Relative viscosity 1.06 1.10 1.15 1.22 1.30  Specific viscosity 0.06 0.10 0.15 0.22 0.30  Reduced viscosity  Relative viscosity 1.06 1.10 1.15 1.22 1.30  Specific viscosity 0.06 0.10 0.15 0.22 0.30  Reduced viscosity  [dl/mg] 2.66 2.76 2.91 3.10 3.18  0.01 mol/L NaCl Concentration  Kinematic viscosity  [mg/L] 229 373 549 762 1000  [mm2/s] 0.9477 0.9839 1.0297 1.0871 1.1576  [dl/mg] 2.68 2.73 2.79 2.86 2.96  0.01 mol/L KCl Concentration [mg/L] 227 370 558 767 1012  Kinematic viscosity 2  [mm /s] 0.9458 0.9816 1.0321 1.0880 1.1614  88  [dl/mg] 2.57 2.66 2.78 2.84 2.96  Appendix IV: Adsorption Data Table IV-1. Adsorption tests with HMW1 sample  Guar gum sample  Background solution  H2O  HMW1  NaCl 0.01 mol/L  Initial concentration  Equilibrium concentration  Adsorbed amount  [mg/L] 49 98 197 286 392  [mg/L] 6 7 11 24 24  [mg/m2] 0.89 1.86 3.79 5.36 7.55  474  64  8.39  602 637 690 789 888  161 186 222 317 377  9.12 9.18 9.54 9.66 10.41  974 1,125 1,254 1,283 1,467  451 608 677 730 908  10.80 10.57 11.55 11.29 11.50  1,536 140 397 617 633 814  954 12 30 171 178 326  11.87 2.63 7.50 9.12 9.34 9.96  1,095  629  10.72  1,100 1,273 1,529 1,532  552 774 942 953  11.18 10.26 12.06 11.89  1,562  1,043  10.54  89  Table IV-2. Continuation of adsorption tests with HMW1 sample  Guar gum sample  HMW1  Background solution  KCl 0.01 mol/L  Initial concentration  Equilibrium concentration  Adsorbed amount  [mg/L]  [mg/L]  [mg/m2]  142 279 404 408 629 630 640 650 818 1,096 1,097 1,097 1,098 1,240 1,278 1,285 1,517 1,546 1,548 1,555 1,556  6 14 34 35 181 168 188 198 329 563 607 527 552 692 769 777 887 1,027 922 1,023 927  2.77 5.44 7.53 7.78 9.17 9.43 9.25 9.19 9.99 10.88 9.97 11.68 11.13 11.18 10.39 10.38 12.91 10.57 12.89 10.87 12.82  1,567  914  13.29  90  Table IV-3. Adsorption tests with HMW2 sample  Guar gum sample  Background solution  H2O  NaCl 0.01 mol/L HMW2  KCl 0.01 mol/L  Initial concentration  Equilibrium concentration  Adsorbed amount  [mg/L] 397 622 856 1,114 1,249  [mg/L] 22 150 364 543 687  [mg/m2] 7.68 9.68 10.04 11.74 11.54  1,698  1,062  13.33  405 628 855 1,128 1,267  23 161 344 536 696  7.80 9.56 10.41 12.07 11.68  1,771  1,104  13.65  145 294 428 625 651 840 934 1,057 1,282 1,497 1,518  5 13 25 159 159 346 386 487 666 840 972  2.86 5.75 8.22 9.68 10.03 10.22 11.13 11.71 12.58 13.38 11.17  91  Table IV-4. Adsorption tests with MMW3 sample  Guar gum sample  Background solution  H2O  NaCl 0.01 mol/L  MMW3  KCl 0.01 mol/L  Initial concentration  Equilibrium concentration  Adsorbed amount  [mg/L] 413 628 847 1,130 1,310 1,501  [mg/L] 39 144 330 580 750 905  [mg/m2] 7.65 9.90 10.55 11.27 11.43 13.31  401 601 817 1,118 1,322  24 135 311 568 794  7.68 9.55 10.35 11.25 10.88  1,498  934  11.56  170 354 371 596  6 14 33 120  3.36 6.90 6.91 9.71  602 786 867 1,089 1,098 1,282  139 287 337 546 559 731  9.45 10.21 10.82 11.12 10.91 11.31  1,404  847  11.37  1,476  898  11.80  92  Table IV-5. Adsorption tests with LMW4 sample  Guar gum sample  Background solution  H2O  NaCl 0.01 mol/L  LMW4  KCl 0.01 mol/L  Initial concentration  Equilibrium concentration  Adsorbed amount  [mg/L] 347 637 876 877 1,126  [mg/L] 14 117 289 286 515  [mg/m2] 7.16 10.68 12.12 12.08 12.69  1,276  628  13.25  1,555 418 586 869 1,140  862 20 90 268 476  14.15 8.11 11.05 12.27 13.59  1,296  623  13.73  1,547 188 366 509 586 719 875 900 1,102 1,168 1,320  827 7 13 29 69 169 298 299 482 535 691  14.76 3.70 7.20 9.76 10.59 11.25 11.83 12.24 12.73 12.91 12.80  1,442 1,515 1,516 1,570  759 851 880 924  14.08 13.54 12.96 13.26  1,756  1,075  14.06  93  Appendix V: Turbidity and Flocculation Data Table V-1. Turbidity and volume of flocs data  Guar gum sample  HMW1  HMW2  MMW3  LMW4  Initial concentration  Turbidity  Volume of flocs  [mg/L] 142 279 408 629 1,096 1,098 1,548  NTU 14 3 29 193 480 384 484  mL 18.3 -  1,567 145 294 428 625 934  896 2 2 31 154 335  18.0 22.0 20.0 19.0 18.0 17.5  1,518 170 354 596 867 1,098 1,404 188 366 586 875 900 1,168 1,515  762 11 18 309 898 1,830 3,120 7 17 540 3,810 1,966 4,127 7,000  17.5 17.5 17.0 16.5 16.0 15.5 15.3 14.8 14.5 14.0 14.9 13.0 12.5  1,516  4,696  13.5  Examples of experimental errors: at a concentration of 1,500 mg/L it is 690±200 NTU (29%) for HMW1 and 5,800±1,100 (19%) NTU for LMW4, at 900 mg/L is 2,900±900 NTU (30%) for LMW4, at 1,100 mg/L is 430±50 NTU (12%) for HMW1, and at 0 mg/L is 79±12 NTU (15%).  94  Appendix VI: Flotation Table VI-1. Flotation test results data Guar gum sample No guar gum  HMW1  HMW2  MMW3  LMW4  Initial concentration [mg/L] 0.0 0.0 0.0 0.0 4.9 5.1 14.5 20.2 49.8 150.1 300.3 430.3 800.2 1,549.8 5.2 10.3 20.4 30.0 50.2 206.0 448.0 29.9 5.0 9.9 17.0 25.0 50.0 153.2 253.0 360.8 499.7 5.1 10.2 14.8 20.7 50.4 201.7 335.0 497.9  Equilibrium concentration [mg/L] 0.0 0.0 0.0 0.0 0.7 2.0 2.1 5.1 3.1 7.7 109.2 223.9 615.6 1,297.2 1.0 0.8 2.3 3.8 5.4 32.7 229.5 0.6 0.3 0.0 1.9 2.9 4.2 9.4 61.2 149.1 293.7 1.0 0.3 1.5 2.0 3.2 11.8 98.6 267.7  95  Adsorbed amount [mg/m2] 0.00 0.00 0.00 0.00 0.15 0.11 0.44 0.53 1.64 5.02 6.73 7.27 6.50 8.89 0.15 0.33 0.64 0.92 1.58 6.10 7.69 1.03 0.17 0.35 0.53 0.78 1.61 5.06 6.75 7.45 7.26 0.14 0.35 0.47 0.66 1.66 6.69 8.32 8.11  Flotation recovery [%] No flotation 64.2 66.3 67.1 71.6 69.9 24.9 15.4 0.0 0.0 0.0 0.0 0.0 0.0 60.5 46.3 14.8 10.1 0.0 0.0 0.0 No flotation 51.2 41.9 9.6 4.6 0.0 0.0 0.0 0.0 0.0 60.1 47.3 19.7 7.3 0.0 0.0 0.0 0.0  Turbidity [NTU] 280.0 412.0 448.0 400.5 258.0 263.0 142.0 101.0 31.6 108.0 1,869.0 3,775.5 5,532.5 9,632.5 242.0 179.5 112.0 62.2 34.8 356.5 3,481.5 37.8 293.5 151.0 125.5 84.5 56.5 394.0 2,685.5 6,357.0 0.0 246.0 168.0 159.5 172.0 120.0 1,636.5 6,222.5 0.0  Appendix VII: Calculation of Surface Area The calculated surface area (S.A.) of talc was computed assuming a plate-like particle shape, with a diameter D is equal to the average particle size d50 from the size distribution.  If the percentage contributions of the basal plane and of the edges to the total surface are known (Steenberg and Harris 1984), the ratio of the diameter D to the thickness w can be calculated as follows:  96  Then, the surface area and volume of a single plate-like particle can be calculated in function its diameter (d50).  The specific surface area is defined as the surface area contained in one gram of the material (in this case talc). As the density of talc is known (2.75 g/cm3), the volume of one gram of talc is:  By knowing the total volume of one gram of talc and the volume of a single particle, the number of talc particles in one gram of talc can also be calculated.  Finally, the number of talc particles was multiplied by the surface area of a single plate-like talc particle to obtain the total surface area of one gram of talc. If d50=24.42 (Talc B), the specific surface area of talc is:  97  

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