Marek Pawlik

Professor

Relevant Degree Programs

 

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
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 (2010 - 2018)
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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Molecular weight effects in guar gum adsorption and depression of talc (2013)

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.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.

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