Marek Pawlik


Relevant Thesis-Based Degree Programs


Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Composition and structure in flocculated mineral systems (2023)

An investigation of model quartz floc structure and composition was made using X-ray computed tomography to understand how floc breakage could contribute to consolidation in the dewatering process.It was concluded that floc macro-structure, defined by the connectivity and arrangement of sub-units in medium- and large-sized flocs plays an important role in the formation and breakage of flocs. Sub-units in flocs were found to be connected by lower solids concentration regions and the shared surface area between sub-units was found to decrease as a function of distance from the floc centroid. These observations indicated a tendency for flocs to break in a large-scale deformation mode (i.e., rupture along sub-unit boundaries), rather than smaller-scale fragmentation or attrition.From compression tests evaluated with CT scans and correlated with the gravimetric method, it was found that negligible changes in the solids concentration of flocs occurred at low applied pressures (
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Stabilization of zirconium oxide suspensions by cellulose nanocrystal (CNC) (2023)

Colloidal gels of cellulose nanocrystals (CNCs) were prepared by increasing ionic strength. The ultimate objective was to investigate stabilization of zirconia suspensions by using a small amount of CNC by changing electrolyte concentration or pH. First, the rheological behavior of CNC hydrogels in the presence of a monovalent electrolyte (NaCl) as a function of CNC and salt concentration was explored using a variety of linear and nonlinear rheological tests. Two step-yielding behavior was observed for CNCs in the presence of high electrolyte concentration from amplitude sweep experiment. The first yielding corresponds to the maximum in the loss modulus at the crossover point between storage and loss modulus due to disconnection of link between CNC clusters. The second yield stress is due to the deformation of clusters to smaller flocs and individual nanorods (corresponding to the change in the slope of loss modulus at higher shear strains). Small angle light scattering measurements, confocal laser scanning microscopy and polarized microscopy images confirmed the gradual breakup of clusters to smaller ones and eventually to nearly individual fibers with an increase in the applied shear strain and rate.CNCs were used as a dispersant to stabilize water-based zirconia suspensions. The zirconia suspensions as functions of solid content, pH and CNC concentration were studied to produce stable highly concentrated suspensions. The achieved stability was found to be due to the adsorption of CNC nanofibers around the zirconia particles revealed by Scanning Electron Microscopy (SEM) images. Suspensions with the lowest viscosity and highest stability over 24 h achieved at pH 4 i.e., 30 wt.% zirconia particles stabilized with the addition of 1 wt.% CNC.Finally, the effect of CNC and NaCl concentration was studied on the stability, adsorption, zeta potential, size, and rheology of slurries. The results confirm that the adsorption capacity of CNC on the surface of zirconia particles increases as salt concentration increases, associated with rise in the viscoelastic properties and denser structure on the surface of adsorbent. It has been concluded that zirconium oxide suspensions of high concentration (>30 wt.%) can be effectively stabilized by using a small amount of CNC (
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Surface-chemical interactions between apatite and hematite in aqueous suspensions (2020)

In relation to separation between apatite and hematite by froth flotation, surface-chemical interactions between apatite and hematite were studied as a function of pH and constituent ion concentrations. The surface charge characteristics of the minerals and their mixtures were determined using zeta potential measurements. Aggregation and dispersion phenomena were followed using laser light scattering techniques. Measurements of the amount of fine hematite attached to a large apatite crystal were conducted to assess the extent of slime coatings in the system. The results were supplemented by apatite solubility studies, and by measurements of calcium and phosphate adsorption on hematite under selected conditions.Calcium and phosphate released by apatite into supernatant strongly affected the zeta potential and aggregation-dispersion of hematite. The various phosphate species were attracted towards the positively charged hematite surface below the iso-electric point of the mineral (pH 6.8) while calcium cation showed high affinity towards the hematite surfaces above the iep value.Extensive coating of apatite by fine hematite occurred in the pH range from 7 to 9, and no coatings formed at pH 10-11 in the absence of calcium and phosphate ions. As the constituent ion concentrations increased in background solution, the amount of fine hematite on the crystal surface became independent of pH. These results were explained by a dispersing effect of phosphate at lower pH and by a coagulating effect of calcium at high pH.Co-adsorption of phosphate and calcium ions on the hematite surface was also observed, and it was proposed that calcium cations at pH 10-11 adsorbed in the inner Helmholtz plane while phosphate co-adsorption proceeded into the outer Helmholtz plane. Calcium adsorption caused hematite aggregation, while co-adsorption of phosphate led to partial dispersion. In apatite-hematite mixtures, addition of apatite resulted in hematite dispersion, while removal of apatite caused hematite aggregation. It was recognized that the tested minerals systems were under non-equilibrium conditions in terms of apatite dissolution. The aggregation-dispersion phenomena were interpreted in terms of variations in calcium and phosphate ion concentrations in solution in the presence and absence of apatite, and the resulting changes in the adsorption of those ions on hematite.

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Process engineering of functional metakaolin based geopolymers (2018)

Geopolymers (GPs) are a class of inorganic materials which can be used as construction and refractory cements and as functional materials for environmental applications. GPs are low CO₂ emissions binders with high durability that can replace traditional cementitious materials. However the effects and interactions of processing parameters on the different stages of GP setting (“geopolymerization”) are still under scrutiny and the molecular mechanisms and rate limiting steps controlling the setting kinetics are unknown. The crystallization in GPs, which ultimately controls their performance in advanced applications such as water purification and toxic waste encapsulation, is a poorly investigated topic.This dissertation provides new experimental evidences on the role of chemical composition and curing process on metakaolin-based GPs. Steady state and dynamic rheological studies, contact angle tests, microstructural (SEM), structural (XRD and FTIR) and mechanical analyses lead to better understanding of the fundamental transformations occurring during geopolymerization. GPs were seeded with different oxides and zeolites to determine the rate limiting step, increase the reaction rate and control the crystallization. This work contributes to clarification the complex effects of soluble silica on the geopolymerization process. It is shown that soluble and colloidal silicates (such as Na₄SiO₄ and Na₂SiO₃) can act as seeding agents, changing the geopolymerization rate limiting step at temperatures T≥35°C. However, they also slow down the reaction rate, possibly by forming passivation layers on the metakaolin particles, thus producing a more chemically stable and mechanically stronger amorphous gel. Silicates also decrease the water requirement in GPs and thus the porosity. Under certain conditions silicates can increase the percentage of crystalline Faujasite in GPs, but the crystallization process requires higher curing temperatures and times (T>40°C and t>4 days, depending on the amount of silicates). The alkali metals have also a structure-directing role in crystallization of GPs in the form of zeolite, favoring faujasite structure. Water has a templating effect in GPs, favoring the structure of zeolite LTA-type over hydrosodalite. This work also illustrates the compromises that need to be made when selecting appropriate processing parameters to tailor the rheology, structure and properties of geopolymers for specific applications.

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Aggregation and dispersion phenomena in the quartz-hematite system in the presence of polymers (2015)

Aggregation and dispersion phenomena in the quartz-hematite system in the presence of polymers were analyzed through the measurement of adsorption density of polymers, turbidity of mineral suspensions, and zeta potential distributions. All the tests were performed on single minerals as well as on their 1:1 mixtures (by volume). A procedure was developed to determine the composition of the tested supernatants using scanning electron microscopy in order to enhance interpretation of zeta potential distributions obtained for mineral mixtures. Two carboxymethyl celluloses and a sodium lignosulfonate were chosen as polymeric additives.It was found that carboxymethyl celluloses selectively adsorbed on hematite in mixtures with quartz and that the selectivity of adsorption was a result of a high affinity of the polysaccharides towards the hematite surface. Lignosulfonate exhibited low affinity type of adsorption on both minerals although preferential adsorption on hematite at pH 5.5 was also observed. At pH 5.5, carboxymethyl celluloses acted as flocculants towards hematite, while lignosulfonate functioned as a coagulant. The polymers strongly dispersed hematite at high pH. The polymers also showed dispersing capabilities towards quartz regardless of pH. Selective flocculation of residual hematite from mixtures with quartz was observed at low pH despite extensive heterocoagulation between the minerals. Lignosulfonate behaved as a selective dispersant of hematite at high pH despite similar adsorption densities of the polymer on the tested minerals.It was generally determined that conditions (pH, polymer concentration) leading to strong dispersion were associated with very narrow zeta potential distributions (10-20 mV), indicative of uniform surface charging characteristics of the tested particle population. In contrast, polymer-induced aggregation of mineral particles (flocculation or coagulation) was accompanied by broad zeta potential distributions (up to 70 mV) resulting from non-uniform adsorption of the polymers on mineral particles and surface charge heterogeneities. Such broad zeta potential distributions were also characteristic of heterocoagulated mixtures in the absence of polymers.Several recommendations were made regarding measurements of zeta potential distributions in mineral mixtures. In order to characterize the entire population of a mineral mixture, such measurements should be performed on very dilute samples of constant turbidity to limit the differential settling of aggregated components.

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Frothing Properties of Fatty Acid Collectors (2015)

The gas dispersion and foaming properties of aqueous solutions of fatty acids of different hydrocarbon chain lengths were assessed through measurements of bubble size distributions, gas hold-up, foam volume and growth rate. The adsorption behavior of the tested fatty acids at the gas-solution interface was assessed and the results were supplemented by measurements of the partition of each surfactant between the bulk solution and foam phase as a result of continuous aeration.Two mechanisms of gas dispersion were identified depending on the pH and speciation of the tested solutions. Solutions of long chain fatty acids containing colloidal precipitates at low pH exhibited low surface tensions, and only a small decrease in bubble sizes was observed for such solutions compared to bubble sizes measured in water. This relatively small change in bubble sizes could theoretically be predicted based only on the corresponding change in the surface tension of the solutions. In contrast, true solutions of long chain fatty acids affected bubble sizes to a much greater extent even though their surface tension values were higher and in some cases comparable to the surface tension of water. A combination of the surface tension and surface tension gradient effects was found to be operative in this case. Experimental results strongly suggested that the associated acid species were more surface-active and more capable of reducing bubble sizes than the dissociated carboxylate anion. The ability of the surfactants to quickly generate a large foam volume was found to be a strong function of the chain length. Although bubble size measurements in bulk solution pointed towards similar gas dispersing abilities of fatty acids of different chain lengths, their foamabilities under the same conditions were remarkably enhanced by increasing chain length. Creation of large volumes of persistent foam was correlated with strong tendency to partition into the foam phase. Overall, the gas dispersing properties of fatty acids were comparable to those of a weak frother such as methyl isobutyl carbinol (MIBC), while only the foaming capabilities of hexanoate were similar to those of MIBC. Longer chain fatty acids were much stronger foaming agents than MIBC.

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A role of humic matter and ore oxidation in rheology of oil sand slurries and in bitumen extraction (2013)

Eight oil sands ores were tested in order to quantify the levels of humic acids in these samples through the alkali extraction test originally developed to determine the oxidation of bituminous metallurgical coals. The test gives a concentration of humic acids released from ores, which in combination with the measurement of the total organic carbon content in the alkali extracts provides a measure of ore/bitumen weathering. It was found that poor ores exhibited the highest tendency to leach large amounts of humic acids per gram of bitumen in the samples which was quantified using the absorbance at 520 nm obtained from the UV/visible spectra.The results of contact angle measurements of water on bitumen showed that bitumen became more hydrophilic as pH increased, and that the hydrophobicity of bitumen drastically decreased when the sample was artificially oxidized. Additionally, the results suggested that humic acids make bitumen hydrophilic only if they are part of the internal/surface bitumen structure. Slurries of good ores displayed higher yield stresses than slurries of poor ores. This result is explained by the higher bitumen concentration existing in slurries of good ores which leads to more aggregation. Additionally, it was shown that bitumen oxidation/hydrophobicity also affected the rheology of oil sands slurries which also explains that slurries of poor ores displayed lower cohesion/aggregation than slurries of good ores. Yield stress data agreed with data obtained from power draw measurements that showed that good processing ores required more power for mixing. Extraction data obtained from flotation experiments indicated that the role of humic acids naturally present in the ores was basically that of a depressant of bitumen since poor ores contained the highest proportion of humic acids per gram of bitumen. Overall, it is possible to assess the processability of oil sand ores by quantifying the occurrence of humic acids in the ores, and to correlate ore processability with the rheology of oil sands slurries. Although poor ores are characterized by lower viscosities and lower power requirements during mixing, the presence of humic acids in these ores and their depressing action also contribute to lower bitumen recoveries.

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The dispersing action of polysaccharides in oil sand slurries (2013)

Six carboxymethyl celluloses (CMC) of different degrees of substitution, molecular weights, and molecular weight distributions (MWDs) were researched as dispersants of oil sand slurries. The molecular weights and MWDs were determined by analytical ultracentrifugation. Viscometric studies on dilute solutions indicated semi-flexible, random coiling behavior of the polymers assuming an extended conformation in distilled water and coiled conformation in a dilute sodium chloride solution. It was found that the ionic strength, rather than pH or temperature, had the strongest effect on the intrinsic viscosity and conformation of CMC. Calculations of the persistence length and expansion factors of the polymers showed that the lowest molecular weight CMC was most flexible among the tested samples. As rheological and sedimentation tests showed, addition of CMC stabilized oil sand slurries towards aggregation and settling. All the polymers dispersed oil sand slurries by adsorbing on the solid particles and preventing mineral–mineral interactions. The molecular weight of the polymers was a more important factor than the degree of substitution in dispersing the slurries. The role of CMC was also to enhance the liberation of bitumen from solids. This role was analyzed through contact angle measurements in which it was demonstrated that all the CMC samples accelerated bitumen displacement and detachment from the illite surface. The CMC sample of the lowest molecular weight was found to be most effective in promoting bitumen displacement from the illite surface, and this action was attributed to the small effective size and high flexibility of the chain, which allowed the polymer to very closely approach the three-phase point of contact between the mineral, water, and bitumen. Wettability studies also revealed that CMC interacted very weakly with bitumen and did not permanently change the natural hydrophobicity of bitumen. Since a good rheological dispersant should not render bitumen hydrophilic and prevent bitumen extraction, the weak wetting action of CMC at the bitumen-solution interface is actually highly desirable. Overall, this dissertation demonstrated that CMC could play a significant role in improving the processability of low-grade oil sand ores, particularly since the polymer was also shown to be effective at neutral pH and low temperature.

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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Effect of radiation exposure on industrial flocculants and their performance (2021)

The effect of radiation exposure on four industrial flocculants under various physicochemical conditions, such as pH, ionic strength, flocculant concentration and number of CT exposures, was investigated by determining intrinsic viscosities from viscosity measurements on dilute flocculant solutions. Huggins equation was used for non-ionic flocculants and Fedors equation was used for anionic flocculants to evaluate the raw viscosity data through which intrinsic viscosity was calculated. The results indicated that the flocculants take a fully-extended conformation in distilled water at natural pH and 25°C and under no-exposure condition as seen from high intrinsic viscosity values. Exposing the dilute flocculant solution to x-rays resulted in decreases in the reduced and, in turn, the intrinsic viscosity. This effect can be attributed to the polymer degradation caused by the energy imparted by x-ray radiation. At a constant ionic strength of 0.01M NaCl, negatively charged carboxylate groups are shielded by the counterions from the salt, and the flocculant polymer assumes a coiled conformation, posing a smaller target for the x-rays. Similar intrinsic viscosities were observed under acidic conditions (pH ~3) as under dilute salt conditions, and thus the effects of x-rays were insignificant for a non-ionic flocculant and a marginal decrease in intrinsic viscosities was observed for anionic flocculants.Flocculation performance before and after exposure was also tested. These tests were conducted to validate the findings from intrinsic viscosity measurements and to assess if changes in intrinsic viscosity related to changes in flocculation performance. It was found that flocculation of model quartz suspension using a CT-exposed flocculant resulted in a lower settling rate of the flocs compared to flocculation using a fresh non-exposed polymer. This indicates the polymer breakage due to radiation exposure results in shorter polymer chain length and decreased flocculation performance.

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Floatability of jarosites in the presence of anionic surfactants (2019)

Five jarosite samples were synthesized and their surface properties relevant to froth flotation were examined. Sodium jarosite, low-silver sodium jarosite (3.47 % Ag), high-silver sodium jarosite (12.84% Ag), potassium jarosite, and high-silver potassium jarosite (5.56% Ag) were synthetized in an autoclave. No significant differences in zeta potential characteristics [pH 2-10] were observed between the samples, with a common isoelectric point at pH 5. Reagent adsorption and Hallimond tube (single mineral) flotation experiments were conducted with three anionic surfactants at pH 3.5 and at pH 10. The three reagents were: sodium laurate, sodium dodecyl sulfate, and octanohydroxamic acid. These surfactants represented different classes of flotation collectors: weak-electrolyte type (lauric acid and hydroxamic acid), strong-electrolyte type (dodecyl sulfate), highly soluble in water (dodecyl sulfate and hydroxamate) and poorly soluble in water (lauric acid). The experimental results were analyzed in terms of correlations between zeta potential, surfactant adsorption, and flotation results in order to enhance the fundamental understanding of surfactant-jarosite interactions. It was found from the adsorption and flotation results that the floatability of jarosites in the presence of the tested reagents followed two main trends. For several jarosite-reagent-pH combinations, the floatability of the mineral increased steadily with the increasing adsorption density of the reagent. In other cases, a minimum concentration of the reagent was required to initiate flotation even though the adsorption density of the surfactant continuously increased. It was postulated that in the latter case, the transition from poor to good flotation coincided with a change in the adsorption mechanism of the surfactant, while in the former case, one mechanism dominated the interaction. It was concluded that the adsorption of the anionic surfactants was driven by chemical interactions with iron sites on the jarosite surfaces regardless of the jarosite type. When analyzing the adsorption data, it was recognized that the jarosite surface at pH 10 was coated by a goethite (FeO(OH)) layer, while at pH 3.5 the surfactants adsorbed on a clean jarosite surface. No systematic trends were observed as a function of the silver content. Based on all the data, recommendations on the most promising flotation conditions were also made.

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Physicochemical characterization of a carbon containing phosphate ore (2019)

The current research project is aimed at investigating the occurrence of organic matter found in certain types of phosphate ores and the behavior of the ore under mechanical treatment. The presence of organic compounds, often collectively referred to as kerogen, complicates the froth flotation of such ores, and further advances in the processing of high-organics phosphate ores require a thorough understanding of the nature, occurrence, and distribution of organic compounds within phosphate ores.Among the most advanced methods, scanning electron microscopy (SEM) to generate maps of mineral components within grains of various sizes, and micro-Fourier transform infrared spectroscopy/microscopy (FTIR) to visualize the presence and distribution of various organic compounds on mineral particles were employed. These techniques provided information about associations of organics with different ore components. Finally, different mechanical treatment methods for pre-conditioning were tested in order to investigate the release of organics and other mineral phases as a possible alternative to indiscriminate crushing and grinding of the ore, and to selectively release clean phosphates of a higher grade.

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Collector Transfer between Bubble and Particle by Collision (2016)

The adsorption densities of dodecylamine hydrochloride at the quartz-liquid interface and at the bubble-liquid interface were measured in separate experiments using the solution depletion method. The amount of amine removed from solution by gas bubbles was measured by bubbling nitrogen through amine solutions of known concentrations and measuring the amount of amine remaining in solution. The obtained results were compared with the amount of dodecylamine depleted from solution under flotation conditions when three phases (solid, liquid, and gas) were present in the tested system. By analyzing the distribution of amine between the interfaces it was possible to identify the conditions (pH and amine concentration) leading to a transfer of amine between bubbles and quartz as a result of bubble-particle collisions. Two modes of interaction between amine and quartz were identified. In a true solution system (pH 6), it was found the surfactant could be transferred from gas bubbles to quartz particles only when the adsorption density of amine at the quartz-solution interface was relatively low, thus leaving space for additional amine adsorption, and the bubbles and the particles were oppositely charged in the presence of amine. Too high adsorption density, resulting in positively charged particles and bubbles largely prevented the amine transfer process. In a colloidal dispersion of amine (pH 11), the dynamic conditions of the flotation test actually seemed to lead to a lower amount of amine transferred to the froth zone than the theoretical amount calculated from adsorption on quartz and on bubbles. This result was attributed to the weak adhesion of the precipitate to the quartz particles and the detachment of the precipitate from both bubbles and quartz particles as bubbles coalesced and burst in the froth zone. Interaction with quartz and bubbles was further weakened by the lack of electrostatic attraction between the nearly uncharged colloidal precipitate and the negatively charged bubbles and particles. Experimental results supports the bubble transfer hypothesis (Digre and Sandvik, 1968) stating that under flotation conditions the adsorption of collector on solid surfaces is governed, to a large extent, by a transfer of collector from the gas-liquid interface to the solid surface.

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In situ mineral sediment characterization with light scattering and image analysis (2016)

In this study, optical backscattering (OBS) and in situ image analysis are used to measure sediment bed density and aggregate size. A method is described for the measurement and interpretation of OBS height scans to obtain a measurement of aggregate size and solid concentration profiles in sediment beds of flocculated minerals. It was found that when OBS height scans were measured during batch settling and from multiple angles at the end of batch settling, the resulting root-mean-square, ?rms, and mean, ?mean, signal values can be analysed to quantify the sediment bed solids concentration and aggregate size as a function of height in the sample. A size calibration method was applied which relates the ?rms values obtained from model solid ceramic spheres and silica particles to ?rms values measured from sediment beds of flocculated kaolin. An iterative fitting method is applied to obtain a calibration function which can be applied to obtain a quantitative description of solid volume as a function of height and time during the batch settling experiment, ?s(ℎ,?). Evaluation of the fitted solid volume versus height functions resulted in a reasonable relative error when compared with the measured solid volume in the sample. A brief analysis on a statistical interpretation of image data for various samples of flocculated mineral sediment beds is given. This study suggests that the evaluation of OBS signal values and high magnification image analysis can be applied on the lab scale for determination of aggregate size and sediment bed density and may form the basis of a measurement system that can be applied to larger scale batch settling or pilot thickening equipment to measure rheological properties and mass flux.

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Surface Properties of Crandallite in Relation to Froth Floatation (2012)

The surface properties of crandallite relevant to the anionic flotation of salt-type minerals were investigated through electrokinetic, turbidity, and wettability techniques. All the tests were performed on fine crandallite particles as a function of pH and reagent concentration. The selected reagents included starch and oleic acid.From the zeta potential measurements, the iso-electric point of crandallite was found to be at pH 5.5 and the mineral surface can be expected to be negatively charged under typical flotation conditions (pH 9-11). The value of the iso-electric point correlated well with the stability of crandallite particles towards aggregation. Suspensions of fine crandallite showed minimum turbidity at pH 5.5 suggesting that the aggregation of the mineral was most pronounced at the iso-electric point. Calcium ions behaved as potential determining ions by increasing the iso-electric point to pH 6.5. In addition, calcium ions also acted as specifically adsorbing ions at higher pH.In the presence of starch, crandallite particles were strongly flocculated producing supernatants with the clarity of tap water. At the same time, the effect of starch on the zeta potential of crandallite was rather weak, consistent with the non-ionic character of the polysaccharide. The stability of crandallite towards aggregation was not strongly affected by oleic acid suggesting that the surfactant did not interact with the mineral. Wettability measurements on crandallite particles showed that oleic acid did not render the mineral particles hydrophobic at pH 10.5 (under normal flotation conditions) or at pH 7, which was in strong contrast to the wettability response of apatite. Under these conditions, crandallite surface was negatively charged and the adsorption of the anionic surfactant seemed to involve physical electrostatic forces as opposed to chemical interactions known to occur between apatite and oleic acid.Overall, the experimental results strongly suggest that crandallite remains hydrophilic during apatite flotation at pH 10.5 and the main mechanism of contamination of apatite concentrates by crandallite is through mechanical entrainment in the froth rather than by true flotation. In this respect, the role of starch as a flocculant should be beneficial in reducing the amount of fine crandallite reporting to the apatite concentrate.

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